Providing a computationally derived, mechanically optimised target correction during preoperative planning can improve joint contact mechanics of hip dysplasia treated with periacetabular osteotomy

AIM

Preoperative identification of acetabular corrections that optimally improve joint stability and reduce elevated contact stresses could further reduce osteoarthritis progression in patients with hip dysplasia who are treated with periacetabular osteotomy (PAO). The purpose of this study was to investigate how providing patient-specific, mechanically optimal acetabular reorientations to the surgeon during preoperative planning affected the surgically achieved correction.

METHODS

Preoperative CT scans were used to create patient-specific hip models for 6 patients scheduled for PAO. A simulated acetabular fragment was extracted from the preoperative pelvis model and computationally rotated to simulate candidate acetabular reorientations. For each candidate, discrete element analysis was used to compute contact stresses during walking, which were summed over the gait cycle and scaled by patient age to obtain chronic contact stress-time exposure. The ideal patient-specific reorientation was identified using a cost function that balances minimising chronic stress exposures and achieving surgically acceptable acetabular coverage angles. The optimal reorientation angles and associated contact mechanics were provided to the surgeon preoperatively. After PAO was performed, a model of the surgically achieved correction was created from a postoperative CT scan. Radiographic coverage and contact mechanics were compared between preoperative, optimal, and surgically achieved orientations.

RESULTS

While surgically achieved reorientations were not significantly different from optimal reorientations in radiographically measured lateral (p = 0.094) or anterior (p = 0.063) coverage, surgically achieved reorientations had significantly (p = 0.031) reduced total contact area compared to optimal reorientations. The difference in lateral coverage and peak chronic exposure between surgically achieved and optimal reorientations decreased with increasing surgeon experience using the models (R² = 0.758, R2 = 0.630, respectively).

CONCLUSIONS

Providing hip surgeons with a patient-specific, computationally optimal reorientation during preoperative planning may improve contact mechanics after PAO, which may help reduce osteoarthritis progression in patients with hip dysplasia.

A New Method for Creating Impact-Induced Intra-Articular Fractures in a Rabbit Model Induces Severe Post-Traumatic Osteoarthritis

OBJECTIVES

The objective of this work was to develop a model of intra-articular fracture (IAF) in a rabbit and document the speed and severity of degenerative joint changes after fracture fixation.

METHODS

With Institutional Animal Care & Use Committee approval, impact-induced IAFs were created in the distal tibia of 16 New Zealand White rabbits. Fractures were fixed with a plate and screws. Pain and function were monitored at regular postoperative intervals with limb loading analysis. Twelve or 26 weeks after fracture, animals were euthanized for histological assessment of cartilage degeneration and micro-computed tomography analysis of bone histomorphometry.

RESULTS

Eleven animals successfully completed the study. Maximum foot force in the fractured limb was 41% ± 21% lower than preoperative values ( P = 0.006) 12 weeks after fracture and remained 25% ± 13% lower ( P = 0.081) after 26 weeks. Cortical bone mineral density in micro-computed tomography images was 34% ± 13% lower 12 weeks after fracture ( P < 0.001) and remained (42% ± 8%) lower 26 weeks after fracture ( P < 0.001). Twelve weeks after fracture, Mankin scores of cartilage degeneration were significantly higher in the medial talus ( P = 0.007), lateral talus ( P < 0.001), medial tibia ( P = 0.017), and lateral tibia ( P = 0.002) of the fractured limb compared with the uninjured contralateral limb. Average Mankin scores in the talus increased from 12 to 26 weeks (5.9 ± 0.9 to 9.4 ± 0.4; P < 0.001 lateral; 5.4 ± 1.8 to 7.8 ± 2.0; P = 0.043 medial), indicating substantial and progressive joint degeneration.

CONCLUSIONS

The ankle joint of the New Zealand White rabbit provides the smallest available model of impact-induced IAF that can be treated with clinically relevant techniques and replicates key features of healing and degeneration found in human patients.

The Effects of Residual Femoral Deformity on Computed Contact Mechanics in Patients Treated With In Situ Fixation for Slipped Capital Femoral Epiphysis

OBJECTIVE

In situ fixation for treatment of slipped capital femoral epiphysis (SCFE) can stabilize the epiphysis and prevent further joint deformation but often leaves residual deformity that may adversely affect intra-articular contact mechanics. The purpose of this study was to investigate the relationship between residual deformity and contact mechanics in the post-SCFE hip.

METHODS

Patient-specific hip models were created for 19 patients with SCFE treated with in situ fixation. For each model, discrete element analysis was used to compute cumulative acetabular and femoral contact stress exposure during a walking gait cycle. Slip severity was evaluated for each patient using the two-dimensional Southwick angle and a novel three-dimensional (3D) assessment of multiplanar femoral deformity (3D slip angle).

RESULTS

Of the SCFE cases, 2/7 mild (Southwick angle ≤30 degrees) had peak cumulative femoral exposures equivalent to that of severe (Southwick angle ≥60 degrees) cases. Severe SCFE cases had higher peak ( P = 0.015) and mean ( P = 0.028) femoral contact stress exposure and lower cumulative femoral contact area ( P = 0.003) than mild (Southwick angle ≤30 degrees) SCFE cases. Mean femoral contact stress exposure was also higher in severe SCFE cases than in moderate SCFE cases ( P = 0.027). Acetabular and femoral contact mechanics metrics typically demonstrated stronger correlations with 3D slip angle than two-dimensional Southwick angle.

CONCLUSIONS

Increased slip severity adversely impacts intra-articular femoral contact mechanics. Contact mechanics metrics demonstrate higher correlations with 3D slip angle, indicating that this novel measurement may better describe global deformity and its relationship to intra-articular mechanics; however, the modest strength of these correlations may also imply that global impingement-generating deformity is not the primary factor driving contact mechanics in the post-SCFE hip.

CLINICAL RELEVANCE

Greater slip severity adversely impacts contact mechanics in the post-SCFE hip. However, focal regions of high contact stress were seen even in mild SCFE deformities, suggesting some type of deformity correction should be considered even for mild slips to alleviate secondary impingement, address focal incongruities, and reduce osteoarthritis development/progression.

Incorporating patient-specific hip orientation from weightbearing computed tomography affects discrete element analysis-computed regional joint contact mechanics in individuals treated with periacetabular osteotomy for hip dysplasia

Computational models of the hip often omit patient-specific functional orientation when placing imaging-derived bony geometry into anatomic landmark-based coordinate systems for application of joint loading schemes. The purpose of this study was to determine if this omission meaningfully alters computed contact mechanics. Discrete element analysis models were created from non-weightbearing (NWB) clinical CT scans of 10 hip dysplasia patients (11 hips) and oriented in the International Society of Biomechanics (ISB) coordinate system (NWB-ISB). Three additional models were generated for each hip by adding patient-specific stance information obtained via weightbearing CT (WBCT) to each ISB-oriented model: (1) patient-specific sagittal tilt added (WBCT-sagittal), (2) coronal and axial rotation from optical motion capture added to (1; WBCT-combo), and (3) WBCT-derived axial, sagittal, and coronal rotation added to (1; WBCT-original). Identical gait cycle loading was applied to all models for a given hip, and computed contact stress and contact area were compared between model initialization techniques. Addition of sagittal tilt did not significantly change whole-joint peak (p = 0.922) or mean (p = 0.871) contact stress or contact area (p = 0.638). Inclusion of motion-captured coronal and axial rotation (WBCT-combo) decreased peak contact stress (p = 0.014) and slightly increased average contact area (p = 0.071) from WBCT-sagittal models. Including all WBCT-derived rotations (WBCT-original) further reduced computed peak contact stress (p = 0.001) and significantly increased contact area (p = 0.001). Variably significant differences (p = 0.001-1.0) in patient-specific acetabular subregion mechanics indicate the importance of functional orientation incorporation for modeling applications in which local contact mechanics are of interest.

Mechanical Gains Associated With Virtual Prophylactic Intramedullary Nail Fixation in Femurs With Metastatic Disease

Background

Many patients with metastatic bone disease (MBD) of the femur undergo prophylactic surgical fixation for impending pathologic fractures; intramedullary nailing (IMN) being the most common fixation type. However, surgeons often question if IMN fixation provides sufficient improvements in mechanical strength for particular metastatic lesions. Our goal was to use patient-specific finite element (FE) modeling to computationally evaluate the effects of simulated IMN fixation on the mechanics of femurs affected with MBD.

Methods

Computed tomography (CT) scans were available retrospectively from 48 patients (54 femurs) with proximal femoral metastases. The CT scans were used to create patient-specific, non-linear, voxel-based FE models of the femur, simulating the instant of peak hip joint contact force during normal walking. FE analyses were repeated after incorporating virtual IMN fixation (Smith and Nephew, TRIGEN INTERTAN) into the same femurs. Femur strength and load-to-strength ratio (LSR; lower LSR indicates lower fracture risk) were compared between untreated and IMN conditions using statistical analyses.

Results

IMN fixation resulted in a very modest average 10% increase in mechanical strength (p<0.001), which was associated with a slight 7% reduction in fracture risk (p<0.001). However, there was considerable variation in fracture risk reduction between individual femurs (0.13-50%). In femurs with the largest reduction in fracture risk (>10%), IMN hardware directly passed through a considerable section of that femur's metastatic lesion. Femurs with lytic (10%) and diffuse (9%) metastases tended to have greater reductions in fracture risk compared to femurs with blastic (5%) and mixed (4%) metastases (p=0.073).

Conclusion

Given the mechanically strong baseline condition of most femurs in this cohort, evident by the low fracture risk at the time of CT scanning, the relative increase in stiffness with the addition of the IMN hardware may not make a substantial contribution to overall mechanical strength. The mechanical gains of IMN fixation in femurs with MBD appear most beneficial when the hardware traverses an adequate section of the lesion. Level of Evidence: III.

Altered Ulnar Variance With Full-Body Weight-bearing During Handstands With Upper Extremity Weight-bearing CT

PURPOSE

Ulnar variance (UV) is a radiographic measurement relating the articular surface heights of the distal radius and ulna. Abnormal UV increases the risk for wrist pathology; however, it only provides a static measurement of an inherently dynamic bony relationship that changes with wrist position and loading. The purpose of this study was to investigate how full-body weight-bearing affects UV using weight-bearing computed tomography (WBCT).

METHODS

Ten gymnasts completed two 45-second scans inside a WBCT machine while performing a handstand on a flat platform (H) and parallettes (P). A non-weight-bearing CT scan was collected to match clinical practice (N). Differences in UV between weight-bearing conditions were evaluated separately for dominant and nondominant sides, and then, UV was compared between weight-bearing conditions on pooled dominant/nondominant data.

RESULTS

Pooled analyses comparing weight-bearing conditions revealed a significant increase in UV for H versus N (0.58 mm) and P versus N (1.00 mm), but no significant change in UV for H versus P (0.43 mm). Significant differences in UV were detected for H versus N, P versus N, and H versus P for dominant and nondominant extremities. The change from N to H was significantly greater in the dominant versus nondominant side, but greater in the nondominant side from N to P.

CONCLUSIONS

Ulnar variance changed with the application of load and position of the wrist. Differences in UV were found between dominant and nondominant extremities.

CLINICAL RELEVANCE

Upper extremity loading patterns are affected by hand dominance as defined by a cartwheel and suggest skeletal consequences from repetitive load on a dominantly used wrist. Although statistically significant, subtle changes detected in this investigational study do not necessarily bear clinical significance. Future WBCT research can lead to improved diagnostic measures for wrist pathologies affected by active loading and rotational wrist behavior.

Radiographically successful periacetabular osteotomy does not achieve optimal contact mechanics in dysplastic hips

BACKGROUND

Optimal correction of hip dysplasia via periacetabular osteotomy may reduce osteoarthritis development by reducing damaging contact stress. The objective of this study was to computationally determine if patient-specific acetabular corrections that optimize contact mechanics can improve upon contact mechanics resulting from clinically successful, surgically achieved corrections.

METHODS

Preoperative and postoperative hip models were retrospectively created from CT scans of 20 dysplasia patients treated with periacetabular osteotomy. A digitally extracted acetabular fragment was computationally rotated in 2-degree increments around anteroposterior and oblique axes to simulate candidate acetabular reorientations. From discrete element analysis of each patient's set of candidate reorientation models, a mechanically optimal reorientation that minimized chronic contact stress exposure and a clinically optimal reorientation that balanced improving mechanics with surgically acceptable acetabular coverage angles was selected. Radiographic coverage, contact area, peak/mean contact stress, and peak/mean chronic exposure were compared between mechanically optimal, clinically optimal, and surgically achieved orientations.

FINDINGS

Compared to actual surgical corrections, computationally derived mechanically/clinically optimal reorientations had a median[IQR] 13[4-16]/8[3-12] degrees and 16[6-26]/10[3-16] degrees more lateral and anterior coverage, respectively. Mechanically/clinically optimal reorientations had 212[143-353]/217[111-280] mm2 more contact area and 8.2[5.8-11.1]/6.4[4.5-9.3] MPa lower peak contact stresses than surgical corrections. Chronic metrics demonstrated similar findings (p ≤ 0.003 for all comparisons).

INTERPRETATION

Computationally selected orientations achieved a greater mechanical improvement than surgically achieved corrections; however, many predicted corrections would be considered acetabular over-coverage. Identifying patient-specific corrections that balance optimizing mechanics with clinical constraints will be necessary to reduce the risk of osteoarthritis progression after periacetabular osteotomy.

Biomechanical guidance can improve accuracy of reduction for intra-articular tibia plafond fractures and reduce joint contact stress

Articular fracture malreduction increases posttraumatic osteoarthritis (PTOA) risk by elevating joint contact stress. A new biomechanical guidance system (BGS) that provides intraoperative assessment of articular fracture reduction and joint contact stress based solely on a preoperative computed tomography (CT) and intraoperative fluoroscopy may facilitate better fracture reduction. The objective of this proof-of-concept cadaveric study was to test this premise while characterizing BGS performance. Articular tibia plafond fractures were created in five cadaveric ankles. CT scans were obtained to provide digital models. Indirect reduction was performed in a simulated operating room once with and once without BGS guidance. CT scans after fixation provided models of the reduced ankles for assessing reduction accuracy, joint contact stresses, and BGS accuracy. BGS was utilized 4.8 ± 1.3 (mean ± SD) times per procedure, increasing operative time by 10 min (39%), and the number of fluoroscopy images by 31 (17%). Errors in BGS reduction assessment compared to CT-derived models were 0.45 ± 0.57 mm in translation and 2.0 ± 2.5° in rotation. For the four ankles that were successfully reduced and fixed, associated absolute errors in computed mean and maximum contact stress were 0.40 ± 0.40 and 0.96 ± 1.12 MPa, respectively. BGS reduced mean and maximum contact stress by 1.1 and 2.6 MPa, respectively. BGS thus improved the accuracy of articular fracture reduction and significantly reduced contact stress. Statement of Clinical Significance: Malreduction of articular fractures is known to lead to PTOA. The BGS described in this work has potential to improve quality of articular fracture reduction and clinical outcomes for patients with a tibia plafond fracture.

Joint contact stress improves in dysplastic hips after periacetabular osteotomy but remains higher than in normal hips

AIM

The purpose of this study was to use computational modeling to determine if surgical correction of hip dysplasia restores hip contact mechanics to those of asymptomatic, radiographically normal hips.

METHODS

Discrete element analysis (DEA) was used to compute joint contact stresses during the stance phase of normal walking gait for 10 individuals with radiographically normal, asymptomatic hips and 10 age- and weight-matched patients with acetabular dysplasia who underwent periacetabular osteotomy (PAO).

RESULTS

Mean and peak contact stresses were higher (p < 0.001 and p = 0.036, respectively) in the dysplastic hips than in the matched normal hips. PAO normalised standard radiographic measurements and medialised the location of computed contact stress within the joint. Mean contact stress computed in dysplastic hips throughout the stance phase of gait (median 5.5 MPa, [IQR 3.9-6.1 MPa]) did not significantly decrease after PAO (3.7 MPa, [IQR 3.2-4.8]; p = 0.109) and remained significantly (p < 0.001) elevated compared to radiographically normal hips (2.4 MPa, [IQR 2.2-2.8 MPa]). Peak contact stress demonstrated a similar trend. Joint contact area during the stance phase of gait in the dysplastic hips increased significantly (p = 0.036) after PAO from 395 mm2 (IQR 378-496 mm2) to 595 mm2 (IQR 474-660 mm2), but remained significantly smaller (p = 0.001) than that for radiographically normal hips (median 1120 mm2, IQR 853-1444 mm2).

CONCLUSIONS

While contact mechanics in dysplastic hips more closely resembled those of normal hips after PAO, the elevated contact stresses and smaller contact areas remaining after PAO indicate ongoing mechanical abnormalities should be expected even after radiographically successful surgical correction.

Effects of Radiotherapy Upon Bone Structure-Strength Relationships Vary With Sex and Fractionation of Dosing

Background

Radiotherapy for tumor treatment in or near bones often causes osteopenia and/or osteoporosis, and the resulting increased bone fragility can lead to pathologic fractures. Bone mineral density (BMD) is often used to screen for fracture risk, but no conclusive relationship has been established between BMD and the microstructural/ biomechanical changes in irradiated bone. Understanding the effects of radiation dosing regimen on the bone structure-strength relationship would improve the ability to reduce fracture-related complications resulting from cancer treatment.

Methods

Thirty-two C57B6J mice aged 10 - 12 weeks old were randomized to single dose (1 x 25 Gy) and fractionated dose (5 x 5 Gy) irradiation groups. Right hindlimbs were irradiated while the contralateral hindlimbs served as the non-irradiated control. Twelve weeks after irradiation, BMD and bone microstructure were assessed with micro-computed tomography, and mechanical strength/stiffness was assessed with a torsion test. The effects of radiation dosing regimen on bone microstructure and strength were assessed using ANOVA, and bone strength-structure relationships were investigated through correlation analysis of microstructural and mechanical parameters.

Results

Fractionated irradiation induced significantly greater losses in BMD in the femur (23% - male mice, p=0.016; 19% - female mice) and the tibia (18% - male mice; 6% - female mice) than the single-dose radiation. The associated reductions in trabecular bone volume (-38%) and trabecular number (-34% to -42%), and the increase in trabecular separation (23% to 29%) were only significant in the male mice with fractionated dosing. There was a significant reduction in fracture torque in the femurs of male (p=0.021) and female (p=0.0017) mice within the fractionated radiation group, but not in the single dose radiation groups. There was moderate correlation between bone microstructure and mechanical strength in the single-dose radiation group (r = 0.54 to 0.73), but no correlation in the fractionated dosing group (r=0.02 to 0.03).

Conclusion

Our data indicate more detrimental changes in bone microstructure and mechanical parameters in the fractionated irradiation group compared to the single dose group. This may suggest the potential for protecting bone if a needed therapeutic radiation dose can be delivered in a single session rather than administered in fractions.

Finite Element Model-Computed Mechanical Behavior of Femurs with Metastatic Disease Varies Between Physiologic and Idealized Loading Simulations

Background and objectives:

Femurs affected by metastatic bone disease (MBD) frequently undergo surgery to prevent impending pathologic fractures due to clinician-perceived increases in fracture risk. Finite element (FE) models can provide more objective assessments of fracture risk. However, FE models of femurs with MBD have implemented strain- and strength-based estimates of fracture risk under a wide variety of loading configurations, and “physiologic” loading models typically simulate a single abductor force. Due to these variations, it is currently difficult to interpret mechanical fracture risk results across studies of femoral MBD. Our aims were to evaluate (1) differences in mechanical behavior between idealized loading configurations and those incorporating physiologic muscle forces, and (2) differences in the rankings of mechanical behavior between different loading configurations, in FE simulations to predict fracture risk in femurs with MBD.

Methods:

We evaluated 9 different patient-specific FE loading simulations for a cohort of 54 MBD femurs: strain outcome simulations—physiologic (normal walking [NW], stair ascent [SA], stumbling), and joint contact only (NW contact force, excluding muscle forces); strength outcome simulations—physiologic (NW, SA), joint contact only, offset torsion, and sideways fall. Tensile principal strain and femur strength were compared between simulations using statistical analyses.

Results:

Tensile principal strain was 26% higher ( R2 = 0.719, P < .001) and femur strength was 4% lower ( R2 = 0.984, P < .001) in simulations excluding physiologic muscle forces. Rankings of the mechanical predictions were correlated between the strain outcome simulations (ρ = 0.723 to 0.990, P < .001), and between strength outcome simulations (ρ = 0.524 to 0.984, P < .001).

Conclusions:

Overall, simulations incorporating physiologic muscle forces affected local strain outcomes more than global strength outcomes. Absolute values of strain and strength computed using idealized (no muscle forces) and physiologic loading configurations should be used within the appropriate context when interpreting fracture risk in femurs with MBD.

Objective evaluation of chondrocyte density & cloning after joint injury using convolutional neural networks

Variations in chondrocyte density and organization in cartilage histology sections are associated with osteoarthritis progression. Rapid, accurate quantification of these two features can facilitate the evaluation of cartilage health and advance the understanding of their significance. The goal of this work was to adapt deep-learning-based methods to detect articular chondrocytes and chondrocyte clones from safranin-O-stained cartilage to evaluate chondrocyte cellularity and organization. The U-net and "you-only-look-once" (YOLO) models were trained and validated for identifying chondrocytes and chondrocyte clones, respectively. Validated models were then used to quantify chondrocyte and clone density in talar cartilage from Yucatan minipigs sacrificed 1 week, 3, 6, and 12 months after fixation of an intra-articular fracture of the hock joint. There was excellent/good agreement between expert researchers and the developed models in identifying chondrocytes/clones (U-net: R²  = 0.93, y = 0.90x-0.69; median F1 score: 0.87/YOLO: R²  = 0.79, y = 0.95x; median F1 score: 0.67). Average chondrocyte density increased 1 week after fracture (from 774 to 856 cells/mm² ), decreased substantially 3 months after fracture (610 cells/mm² ), and slowly increased 6 and 12 months after fracture (638 and 683 cells/mm² , respectively). Average detected clone density 3, 6, and 12 months after fracture (11, 11, 9 clones/mm² ) was higher than the 4-5 clones/mm² detected in normal tissue or 1 week after fracture and show local increases in clone density that varied across the joint surface with time. The accurate evaluation of cartilage cellularity and organization provided by this deep learning approach will increase objectivity of cartilage injury and regeneration assessments.

Chronically elevated contact stress exposure correlates with intra-articular cartilage degeneration in patients with concurrent acetabular dysplasia and femoroacetabular impingement

Hip dysplasia is known to lead to premature osteoarthritis. Computational models of joint mechanics have documented elevated contact stresses in dysplastic hips, but elevated stress has not been directly associated with regional cartilage degeneration. The purpose of this study was to determine if a relationship exists between elevated contact stress and intra-articular cartilage damage in patients with symptomatic dysplasia and femoroacetabular impingement. Discrete element analysis was used to compute hip contact stresses during the stance phase of walking gait for 15 patients diagnosed with acetabular dysplasia and femoral head-neck offset deformity. Contact stresses were summed over the duration of the walking gait cycle and then scaled by patient age to obtain a measure of chronic cartilage contact stress exposure. Linear regression analysis was used to evaluate the relationship between contact stress exposure and cartilage damage in each of six acetabular subregions that had been evaluated arthroscopically for cartilage damage at the time of surgical intervention. A significant correlation (R2  = 0.423, p < 0.001) was identified between chondromalacia grade and chronic stress-time exposure above both a 1 MPa damage threshold and a 2 MPa-years accumulated damage threshold. Furthermore, an over-exposure threshold of 15% regional contact area exceeding the 1 and 2 MPa-years threshold values resulted in correct identification of cartilage damage in 83.3% (55/66) of the acetabular subregions loaded during gait. These results suggest corrective surgery to alleviate impingement and reduce chronic contact stress exposures below these damage-inducing thresholds could mitigate further cartilage damage in patients with hip dysplasia.

Finite element analysis potentially identifies nonessential prophylactic stabilization in femurs with metastatic disease

Metastatic bone disease (MBD) is often managed by non-specialized orthopedic surgeons who rely on Mirels’ criteria to predict pathologic fracture risk. However, low specificity of Mirels’ criteria implies many lesions are scored at high fracture risk when the actual mechanical fracture risk is minimal. Our goal was to retrospectively compare mechanical fracture risk in MBD patients to Mirels’ score and clinical treatment received. Using a CT-based finite element (FE) model of the proximal femur affected by MBD, femur strength and load-to-strength ratio (LSR) were determined for 52 femurs from 48 patients. Associations of femur strength with pain and Mirels’ scores (Pearson r/Spearman ρ correlations), and the decision to operate (percentile analysis), and associations of LSR with pain and Mirels’ scores (Spearman correlations) were determined. Nineteen of 52 femurs (37%) had a very low computed mechanical fracture risk (LSR < 0.4); 5 of those 19 underwent prophylactic stabilization, suggesting that clinical decision-making in MBD is substantially influenced by non-mechanical factors that likely overestimate pathologic fracture risk. Of the 30 femurs managed non-operatively, 24 had a low computed mechanical fracture risk (LSR ≤ 0.5), none of which (0%) experienced a fracture within 9 months. Patient-reported pain did not correlate with femur strength ( r = −0.05, p = 0.748) nor with LSR (ρ = 0.07, p = 0.632). Mirels’ score correlated weakly with femur strength (ρ = −0.32, p = 0.019) and with LSR (ρ = 0.29, p = 0.034). Computational mechanical tools like this FE model could be used as a clinical decision aid when considering non-surgical management in appropriate patients, potentially alleviating nonessential surgical treatment in some patients with femur MBD.

Extracellular biomolecular free radical formation during injury

Determine if oxidative damage increases in articular cartilage as a result of injury and matrix failure and whether modulation of the local redox environment influences this damage. Osteoarthritis is an age associated disease with no current disease modifying approaches available. Mechanisms of cartilage damage in vitro suggest tissue free radical production could be critical to early degeneration, but these mechanisms have not been described in intact tissue. To assess free radical production as a result of traumatic injury, we measured biomolecular free radical generation via immuno-spin trapping (IST) of protein/proteoglycan/lipid free radicals after a 2 J/cm² impact to swine articular cartilage explants. This technique allows visualization of free radical formation upon a wide variety of molecules using formalin-fixed, paraffin-embedded approaches. Scoring of extracellular staining by trained, blinded scorers demonstrated significant increases with impact injury, particularly at sites of cartilage cracking. Increases remain in the absence of live chondrocytes but are diminished; thus, they appear to be a cell-dependent and -independent feature of injury. We then modulated the extracellular environment with a pulse of heparin to demonstrate the responsiveness of the IST signal to changes in cartilage biology. Addition of heparin caused a distinct change in the distribution of protein/lipid free radicals at sites of failure alongside a variety of pertinent redox changes related to osteoarthritis. This study directly confirms the production of biomolecular free radicals from articular trauma, providing a rigorous characterization of their formation by injury.

Effect of modeling femoral version and head-neck offset correction on computed contact mechanics in dysplastic hips treated with periacetabular osteotomy

While correction of dysplastic acetabular deformity has been a focus of both clinical treatment and research, concurrent femoral deformities have only more recently received serious attention. The purpose of this study was to determine how including abnormalities in femoral head-neck offset and femoral version alter computationally derived contact stresses in patients with combined dysplasia and femoroacetabular impingement (FAI). Hip models with patient-specific bony anatomy were created from preoperative and postoperative CT scans of 20 hips treated with periacetabular osteotomy and femoral osteochondroplasty. To simulate performing only a PAO, a third model was created combining each patient's postoperative pelvis and preoperative femur geometry. These three models were initialized with the femur in two starting orientations: (1) standardized template orientation, and (2) using patient-specific anatomic landmarks. Hip contact stresses were computed in all 6 model sets during an average dysplastic gait cycle, an average FAI gait cycle, and an average stand-to-sit activity using discrete element analysis. No significant differences in peak contact stress (p = 0.190 to 1), mean contact stress (p = 0.273 to 1), or mean contact area (p = 0.050 to 1) were identified during any loading activity based on femoral alignment technique or inclusion of femoral osteochondroplasty. These findings suggest that presence of abnormal femoral version and/or head-neck offset deformities are not themselves predominant factors in intra-articular contact mechanics during gait and stand-to-sit activities. Inclusion of modified movement patterns caused by these femoral deformities may be necessary for models to adequately capture the mechanical effects of these clinically recognized risk factors for negative outcomes.

Automated quantification of live articular chondrocyte fluorescent staining using a custom image analysis framework

The goal of this study was to develop, validate, and implement an image analysis framework to automatically analyze chondrocytes in 3D image stacks of cartilage acquired using a fluorescent confocal microscope. Source specimens consist of viable osteochondral tissue co-stained with multiple live-cell dyes. Our framework utilizes a seeded watershed-based algorithm to automatically segment individual chondrocytes in each 2D slice of the confocal image stack. The resulting cell segmentations are colocalized in 3D to eliminate duplicate segmentation of the same cell resulting from the visibility of fluorescence signal in multiple imaging planes, and the 3D cell distribution is used to automatically define the cartilage tissue volume. The algorithm then provides chondrocyte density data, and the associated segmentation can be used as a mask to extract and quantify per cell intensity of a secondary, functional dye co-staining the chondrocytes. The accuracy of the automated chondrocyte segmentation was validated against manual segmentations (average IOU = 0.79). When applied to a cartilage surrogate, this analysis framework estimated chondrocyte density within 10% of the true density and demonstrated a good agreement between framework's counts and manual counts (R²  = 0.99). In a real application, the framework was able to detect the increased dye signal of monochlorobimane (MCB) in chondrocytes treated with N-acetylcysteine (NAC) after mechanical injury, quantifying intracellular biochemical changes in living cells. This new framework allows for fast and accurate quantification of intracellular activities of chondrocytes, and it can be adapted for broader application in many imaging and treatment modalities, including therapeutic OA research.

Do Relaxin Levels Impact Hip Injury Incidence in Women? A Scoping Review

PURPOSE

The aim of this review is to assess the current evidence regarding the impact of relaxin on incidence of soft tissue hip injuries in women.

METHODS

A trained research librarian assisted with searches of PubMed, Embase, CINAHL, and SPORTDiscus, with a preset English language filter. The review was completed per the Joanna Briggs Institute (JBI) Manual for Evidence Synthesis methodology. Included studies required assessment of relaxin effects on musculoskeletal health, pelvic girdle stability, or hip joint structures in human subjects. Letters, texts, and opinion papers were excluded.

RESULTS

Our screen yielded 82 studies. Molecularly, relaxin activates matrix metalloproteinases (MMPs) including collagenases MMP-1/-13 and gelatinases MMP-2/-9 to loosen pelvic ligaments for parturition. However, relaxin receptors have also been detected in female periarticular tissues, such as the anterior cruciate ligament, which tears significantly more often during the menstrual cycle peak of relaxin. Recently, high concentrations of relaxin-activated MMP-9 receptors have been found on the acetabular labrum; their expression upregulated by estrogen.

CONCLUSIONS

Menstrual cycle peaks of relaxin activate MMPs, which locally degrade collagen and gelatine. Women have relaxin receptors in multiple joints including the hip and knee, and increased relaxin correlates with increased musculoskeletal injuries. Relaxin has paracrine effects in the female pelvis on ligaments adjacent to hip structures, such as acetabular labral cells which express high levels of relaxin-targeted MMPs. Therefore, it is imperative to investigate the effect of relaxin on the hip to determine if increased levels of relaxin are associated with an increased risk of acetabular labral tears.

Changes in Muscle Volume and Composition After Treatment of Hip Dysplasia with Periacetabular Osteotomy

BACKGROUND

Periacetabular osteotomy (PAO) is a common treatment for pre-arthritic hip dysplasia in young adults. The purpose of this study was to better understand changes in muscle volume and composition after PAO visualized using magnetic resonance imaging (MRI).

METHODS

A prospectively collected series of individuals that underwent PAO for hip dysplasia were reviewed to identify subjects with pre- and postoperative MRI. In our practice, MRI was obtained preoperatively and greater than 6 months after PAO for persistent hip pain. MRI sequences were selected to optimize visualization of the muscle volume, fatty infiltration, and hip joint cartilage. MRI images were selected at predetermined bony landmarks and analyzed using 3D Slicer (©2021, www.slicer.org) software to measure muscle diameter and calculate muscle cross-sectional area (CSA) in 17 individual muscles surrounding the hip. Muscle atrophy was graded using the Goutallier classification for fatty infiltration and acetabular cartilage condition was graded using the Outerbridge classification. We compared pre- and postoperative muscle area and composition as well as cartilage for each case.

RESULTS

A series of six female patients met our inclusion criteria. Mean age was 26 years at time of surgery. All cases had MRI sequences adequate for muscle volume measurements. Fatty infiltration and cartilage changes were recorded in four subjects with appropriate MRI sequences. Separating muscle groups, external rotators underwent the largest volume increase. Hip flexors demonstrated mild volume decrease. CSA change among external rotators averaged +12%, hip flexors -9.3%, and hip abductors -9.2% after PAO. All muscles had either the same or increased fatty infiltration after surgery, with gluteus medius and iliacus undergoing the most average increase. Similarly, cartilage condition worsened by a small margin in this series.

CONCLUSION

Our results provide preliminary indication that PAO may have noticeable effects on muscle characteristics and cartilage in the early postoperative period. This was a limited case series of subjects with adequate pre- and post-operative MRI imaging.Level of Evidence: IV.

Isolated changes in femoral version do not alter intra-articular contact mechanics in cadaveric hips

Abnormal femoral version is a deformity in the angle between the femoral neck and the transcondylar axis of the knee. Both femoral anteversion and retroversion alter passive and active rotation of the hip and are associated with intra-articular or extra-articular impingement. However, little is known about the effect of abnormal femoral version on intra-articular hip contact stresses. To quantify the effect of femoral version on hip contact stress, five cadaveric pelvis specimens were mechanically tested with a hip-specific Tekscan sensor inserted in the joint space. Specimens were oriented in a heel-strike position and loaded with 1000 N of compressive force. Pressure measurements were recorded by the Tekscan sensor with the femur oriented in 0°, 15°, and 30° of version. At the completion of testing, specimens were locked into place at 0° and post-test CT scans were obtained to register the pressure sensor measurements to the joint anatomy. There were minor changes in contact area (<7%) and translation of the peak contact stress location (8.8 ± 7.6 mm). There was no significant change in peak contact stress (p = 0.901) in either the retroverted (0°) or anteverted (30°) conditions relative to normal version (15°) under identical gait-related loading conditions. While abnormalities in patient gait and resultant joint loading caused by femoral version abnormalities may contribute to hip pain, the present findings would suggest that future joint degeneration in hips with version abnormalities are not simply the result of abnormal contact stress induced by joint incongruity due to femoral version abnormalities.

Simulated lesions representative of metastatic disease predict proximal femur failure strength more accurately than idealized lesions

Metastatic disease in bone is characterized by highly amorphous and variable lesion geometry, with increased fracture risk. Assumptions of idealized lesion geometry made in previous finite element (FE) studies of metastatic disease in the proximal femur may not sufficiently capture effects of local stress/strain concentrations on predicted failure strength. The goal of this study was to develop and validate a FE failure model of the proximal femur incorporating artificial defects representative of physiologic metastatic disease. Data from 11 cadaveric femur specimens were randomly divided into either a training set (n = 5) or a test set (n = 6). Clinically representative artificial defects were created, and the femurs were loaded to failure under offset torsion. Voxel-based FE models replicating the experimental setup were created from the training set pre-fracture computed tomography data. Failure loads from the linear model with maximum principal strain failure criterion correlated best with the experimental data (R² = 0.86, p = 0.024). The developed model was found to be reliable when applied to the test dataset with a relatively low RMSE of 46.9 N, mean absolute percent error of 12.7 ± 17.1%, and cross-validation R² = 0.88 (p < 0.001). Models simulating realistic lesion geometry explained an additional 26% of the variance in experimental failure load compared to idealized lesion models (R² = 0.62, p = 0.062). Our validated automated FE model representative of physiologic metastatic disease may improve clinical fracture risk prediction and facilitate research studies of fracture risk during functional activities and with treatment interventions.

Screw fixation of the syndesmosis alters joint contact characteristics in an axially loaded cadaveric model

BACKGROUND

The purpose of this study was to quantify the effects of rigid syndesmotic fixation on functional talar position and cartilage contact mechanics.

METHODS

Twelve below-knee cadaveric specimens with an intact distal syndesmosis were mechanically loaded in four flexion positions (20° plantar flexion, 10° plantar flexion, neutral, 10° dorsiflexion) with zero, one, or two 3.5-mm syndesmotic screws. Rigid clusters of reflective markers were used to track bony movement and ankle-specific pressure sensors were used to measure talar dome and medial/lateral gutter contact mechanics.

RESULTS

Screw fixation caused negligible anterior and inferior shifts of the talus within the mortise. Relative to no fixation, mean peak contact pressure decreased by 6%-32% on the talar dome and increased 2.4- to 6.6-fold in the medial and lateral gutters, respectively, depending on ankle position and number of screws.

CONCLUSIONS

Two-way ANOVA indicated syndesmotic screw fixation significantly increased contact pressure in the medial/lateral gutters and decreased talar dome contact pressure while minimally altering talar position.

Targeting mitochondrial responses to intra-articular fracture to prevent posttraumatic osteoarthritis

We tested whether inhibiting mechanically responsive articular chondrocyte mitochondria after severe traumatic injury and preventing oxidative damage represent a viable paradigm for posttraumatic osteoarthritis (PTOA) prevention. We used a porcine hock intra-articular fracture (IAF) model well suited to human-like surgical techniques and with excellent anatomic similarities to human ankles. After IAF, amobarbital or N-acetylcysteine (NAC) was injected to inhibit chondrocyte electron transport or downstream oxidative stress, respectively. Effects were confirmed via spectrophotometric enzyme assays or glutathione/glutathione disulfide assays and immunohistochemical measures of oxidative stress. Amobarbital or NAC delivered after IAF provided substantial protection against PTOA at 6 months, including maintenance of proteoglycan content, decreased histological disease scores, and normalized chondrocyte metabolic function. These data support the therapeutic potential of targeting chondrocyte metabolism after injury and suggest a strong role for mitochondria in mediating PTOA.

3D Talar Kinematics During External Rotation Stress Testing in Hindfoot Varus and Valgus Using a Model of Syndesmotic and Deep Deltoid Instability

BACKGROUND

External rotation stress (ERS) identifies ankle instability after fibular reduction of rotational ankle injuries. Combined hindfoot and ankle motions and an inconsistent starting position could mask differing degrees of instability resulting from syndesmotic and/or deltoid ligament disruption. The goal of this work was to use full 3D talar kinematics to evaluate the effects of hindfoot orientation and foot starting position during ERS on the ability to detect instability caused by ligament disruptions.

METHODS

Six cadaveric ankles with metallic fiducial markers were CT scanned in neutral and 3 stress positions: varus hindfoot internal rotation stress (IRS-var), valgus hindfoot ERS (ERS-val), and varus hindfoot ERS (ERS-var). Scans were obtained in stress positions after transecting the deep deltoid ligament (tDDL) and then the syndesmotic ligaments (tDDL+Syn). Talar rotations and translations were computed in the axial, coronal, and sagittal planes in each stress position. Changes in a fixed center of rotation (CoR) relative to the intact sequence were calculated.

RESULTS

Axial plane rotation beginning from IRS-var increased significantly for each level of ligamentous instability (P < .05 for all conditions) (10.9 degrees, intact; 14.1 degrees, tDDL; 22.7 degrees, tDDL+Syn during ERS-val; and 16.4 degrees, intact; 23.1 degrees, tDDL; 29.9 degrees, tDDL+Syn during ERS-var). With ERS-val, the talar CoR moved medially (3.6-5.4 mm) and posteriorly (0.5-5.2 mm); ERS-var moved anterior/laterally or posterior/medially depending on the specific ligamentous instability. With tDDL+Syn the ankle became grossly unstable and there were no clear trends in sagittal/coronal rotation or translation.

CONCLUSION

An ERS test from internal to external rotation consistently differentiates between normal, tDDL, and tDDL+Syn. Talar CoR moved outside the mortise with ligamentous instability.

CLINICAL RELEVANCE

Significant residual deep deltoid instability is likely underrecognized with current practice. The most discriminatory test for detecting such instability in our laboratory was an ERS test performed by internally rotating the foot to a hard, bony endpoint, positioning the hindfoot in varus, and then performing the entire external rotation maneuver while maintaining the varus hindfoot position.

Achilles Tension Mitigates Fibular Malalignment Measured in Cadaveric Studies of Syndesmotic Clamping

BACKGROUND:

Fibular malreduction is becoming a commonly recognized complication of surgical repair of the syndesmosis when a reduction clamp is used. The goal of this work was to determine the interdependent effects of transsyndesmotic reduction clamp position and applied compression force on fibular alignment in a realistic cadaveric preparation of complete syndesmotic injury.

METHODS:

Six through-the-knee cadaveric specimens were CT scanned intact, with the distal syndesmosis fully destabilized, and with 53, 102, and 160 N clamping forces each applied along an anteriorly, centrally, and posteriorly directed transsyndesmotic axis. Testing was repeated incorporating 178 N of Achilles tendon tension using all 3 clamping forces applied along the centrally directed axis. Fibular reduction was automatically quantified from CT scan-generated bony surfaces as rotation of the fibula around the tibia, rotation of the fibula within the incisura, medial/lateral fibular displacement, and anterior/posterior fibular displacement.

RESULTS:

Transsyndesmotic clamping along the anteriorly directed axis resulted in the best reduction quality by all 4 quantified measures. Along the centrally and posteriorly directed axes, progressively greater forces caused significantly greater sagittal plane fibular malreduction. Addition of Achilles tension reduced the magnitude of fibular malreduction and overcompression.

CONCLUSION:

Placing the medial tine of a transsyndesmotic reduction clamp on the anterior medial tibia resulted in the most accurate syndesmotic reduction and provided some protection against overcompression with large reduction clamp forces. Achilles tension appeared to contribute to reduction, decreasing the magnitude of measured malreduction from clamping.

CLINICAL RELEVANCE:

Previous studies estimating fibular malpositioning in cadaveric models that lacked passive muscle tension may have overestimated expected magnitudes of malalignment in patients treated with syndesmotic clamping. However, syndesmotic malreduction, particularly in the sagittal plane, was a real complication of syndesmotic clamping that was reduced by using an anterior position of the medial tine on the tibia.

The Influence of Different Rotator Cuff Deficiencies on Shoulder Stability Following Reverse Shoulder Arthroplasty

BACKGROUND

The primary indication for reverse shoulder arthroplasty (RSA) is rotator cuff arthropathy caused by a deficient rotator cuff. Cuff deficiency in patients is highly variable in its distribution and extent, with mechanical implications that may significantly affect post-operative recovery. This study investigated the effects of variable cuff deficiency on the propensity for impingement between the scapula and humeral component and resulting subluxation, the source of two common complications (scapular notching and instability).

METHODS

Five different finite element models of an RSA were analyzed with varying degrees of rotator cuff deficiency: (1) baseline, with intact subscapularis, infraspinatus and teres minor, (2) no subscapularis, (3) no subscapularis or infraspinatus, (4) no infraspinatus, and (5) no infraspinatus or teres minor. The supraspinatus was not included in any models, as it is absent in rotator cuff arthropathy. Each model was moved through a prescribed arc of 45° internal/ external rotation originating from neutral.

RESULTS

Greater rotator cuff deficiency was associated with more impingement and larger magnitudes of subluxation. The largest subluxation (7.5 mm) and highest impingement-related contact stress (479 MPa) was in the model lacking all rotator cuff muscle groups. Posterior subluxation was present in most models lacking the infraspinatus, while anterior subluxation was present in all models lacking the subscapularis.

CONCLUSIONS

This study helps clarify how different rotator cuff deficiencies influence shoulder stability following RSA and can ultimately help predict which patients may be at greater risk for impingement-related scapular notching and subluxation.

CLINICAL RELEVANCE

Surgeons should carefully consider the nature of the rotator cuff deficiency and its influence on impingement and instability when planning for RSA.Level of Evidence: V.

Deep Learning for Chondrocyte Identification in Automated Histological Analysis of Articular Cartilage

BACKGROUND

Histology-based methods are commonly used in osteoarthritis (OA) research because they provide detailed information about cartilage health at the cellular and tissue level. Computer-based cartilage scoring systems have previously been developed using standard image analysis techniques to give more objective and reliable evaluations of OA severity. The goal of this work was to develop a deep learning-based method to segment chondrocytes from histological images of cartilage and validate the resulting method via comparison with human segmentation.

METHODS

The U-Net approach was adapted for the task of chondrocyte segmentation. A training dataset consisting of 235 images and a validation set consisting of 25 images in which individual chondrocytes had been manually segmented, were used for training the U-Net. Chondrocyte count, detection accuracy, and boundary segmentation of the trained U-Net was evaluated by comparing its results with those of human observers.

RESULTS

The U-Net chondrocyte counts were not significantly different (p = 0.361 in a paired t-test) than the algorithm trainer counts (Pearson correlation coefficient = 0.92). The five expert observers had good agreement on chondrocyte counts (intraclass correlation coefficient = 0.868), however the resulting U-Net counted a significantly fewer chondrocytes than the average of those expert observers (p < 0.001 in a paired t-test). Chondrocytes were accurately detected by the U-Net (F1 scores = 0.86, 0.90, with respect to the selected expert observer and algorithm trainer). Segmentation accuracy was also high (IOU = 0.828) relative to the algorithm trainer.

CONCLUSIONS

This work developed a method for chondrocyte segmentation from histological images of arthritic cartilage using a deep learning approach. The resulting method detected chondrocytes and delineated them with high accuracy. The method will continue to be improved through expansion to detect more complex cellular features representative of OA such as cell cloning.

CLINICAL RELEVANCE

The imaging tool developed in this work can be integrated into an automated cartilage health scoring system and helps provide a robust, objective and reliable assessment of OA severity in cartilage.

Biomechanical Comparison of Syndesmotic Repair Techniques During External Rotation Stress

BACKGROUND

The purpose of this study was to compare mechanical behavior of conventional syndesmosis fixation devices with new anatomic repair techniques incorporating various repair augmentations to determine which approach would return rotational ankle mechanics closer to those of an intact ankle.

METHODS

Ten pairs of fresh-frozen through-the-knee cadaveric lower limbs were subjected to 7.5 Nm of external rotation torque while under 750 N of axial compression. After testing specimens intact and with the deltoid and syndesmotic ligament complexes completely destabilized, specimens underwent syndesmotic fixation using a screw, a suture button construct, a prototype structurally augmented flexible trans-syndesmotic fixation device, or the prototype device plus suture repairs of the anterior-inferior tibiofibular ligament and deep deltoid ligament. Syndesmotic repair devices were exchanged between tests so that each specimen was tested with 2 different fixation techniques. Whole-foot rotation angles at 7.5 Nm of applied torque were measured for comparison of the different repair strategies, and reflective markers mounted on the tibia, fibula, and talus were used to track translations and rotations of the talus and the fibula relative to the tibia during testing.

RESULTS

Syndesmotic destabilization significantly ( P < .001) increased whole-foot, talus, and fibula rotation in an axial plane and posterior fibula translation under 7.5 Nm of torque. Neither the suture button nor the augmented flexible trans-syndesmotic fixation device reduced those increases. Screw fixation or addition of anatomic ligament repairs to the augmented flexible fixation device successfully reduced axial plane rotations and sagittal plane translations to near intact levels.

CONCLUSION

Flexible trans-syndesmotic fixation alone was found to be insufficient for restoring rotational stability to the ankle/talus or preventing sagittal plane displacement of the fibula.

CLINICAL RELEVANCE

Repairs to simulate anatomic structures disrupted during a syndesmosis injury were required to restore rotational stability to the foot when using flexible trans-syndesmotic fixation that may have clinical applicability.

Unaddressed Cam Deformity Is Associated with Elevated Joint Contact Stress After Periacetabular Osteotomy

BACKGROUND

Femoral cam deformity is frequently present in patients with acetabular dysplasia. Computational modeling can be used to identify how this deformity affects joint mechanics. Our purpose was to identify the relationship between cam deformity and joint contact stress after periacetabular osteotomy (PAO). We hypothesized that cam deformity is associated with an increase in peak joint contact stress after PAO.

METHODS

This was a retrospective review of patients treated for hip dysplasia with PAO without femoral osteochondroplasty. Patient-specific hip models created from preoperative and postoperative computed tomography (CT) scans were evaluated using discrete element analysis to determine maximum joint contact stress after PAO. Twenty hips with a postoperative increase in maximum contact stress were compared with 20 that demonstrated decreased maximum contact stress. Hips were assessed for cam deformity on cross-sectional imaging. Radiographic measures of acetabular dysplasia before and after PAO were assessed and compared with the change in maximum contact stress after PAO.

RESULTS

There was a moderate relationship between the change in maximum contact stress and the α angle (r = 0.31; p = 0.04), and the average α angle in the hips with increased maximum contact stress was significantly different from that in the hips with decreased joint contact stress (51° ± 11.4° versus 42° ± 5.1°; p = 0.04). All 6 hips with an α angle of >60° demonstrated increased joint contact stress.

CONCLUSIONS

Cam deformity is common in patients with hip dysplasia. In our study, α angles of >60° were associated with increased postoperative joint contact stress. The α angle should be assessed preoperatively, and deformity should be addressed for optimal joint mechanics after PAO.

CLINICAL RELEVANCE

A reduction in joint contact stress is a proposed mechanism for the increased joint longevity following periacetabular osteotomy for hip dysplasia. Impingement from abnormal femoral offset negatively impacts clinical outcome, but this finding has not been evaluated from a biomechanical perspective previously and a threshold for performing femoral osteochondroplasty has not been established previously. This study provides biomechanical evidence supporting surgical management of femoral cam deformity for an α angle of >60°.

Joint contact stresses calculated for acetabular dysplasia patients using discrete element analysis are significantly influenced by the applied gait pattern

Gait modifications in acetabular dysplasia patients may influence cartilage contact stress patterns within the hip joint, with serious implications for clinical outcomes and the risk of developing osteoarthritis. The objective of this study was to understand how the gait pattern used to load computational models of dysplastic hips influences computed joint mechanics. Three-dimensional pre- and post-operative hip models of thirty patients previously treated for hip dysplasia with periacetabular osteotomy (PAO) were developed for performing discrete element analysis (DEA). Using DEA, contact stress patterns were calculated for each pre- and post-operative hip model when loaded with an instrumented total hip, a dysplastic, a matched control, and a normal gait pattern. DEA models loaded with the dysplastic and matched control gait patterns had significantly higher (p = 0.012 and p < 0.001) average pre-operative maximum contact stress than models loaded with the normal gait. Models loaded with the dysplastic and matched control gait patterns had nearly significantly higher (p = 0.051) and significantly higher (p = 0.008) average pre-operative contact stress, respectively, than models loaded with the instrumented hip gait. Following PAO, the average maximum contact stress for DEA models loaded with the dysplastic and matched control patterns decreased, which was significantly different (p < 0.001) from observed increases in maximum contact stress calculated when utilizing the instrumented hip and normal gait patterns. The correlation between change in DEA-computed maximum contact stress and the change in radiographic measurements of lateral center-edge angle were greatest (R2 = 0.330) when utilizing the dysplastic gait pattern. These results indicate that utilizing a dysplastic gait pattern to load DEA models may be a crucial element to capturing contact stress patterns most representative of this patient population.

Effects of knockout of the receptor for advanced glycation end-products on bone mineral density and synovitis in mice with intra-articular fractures

Our group employed the mouse closed intra-articular fracture (IAF) model to test the hypothesis that the innate immune system plays a role in initiating synovitis and post-traumatic osteoarthritis (PTOA) in fractured joints. A transgenic strategy featuring knockout of the receptor for advanced glycation end-products (RAGE ^-/- ) was pursued. The 42 and 84 mJ impacts used to create fractures were in the range previously reported to cause PTOA at 60 days post-fracture. MicroCT (μCT) was used to assess fracture patterns and epiphyseal and metaphyseal bone loss at 30 and 60 days post-fracture. Cartilage degeneration, synovitis, and matrix metalloproteinase (MMP-3, -13) expression were evaluated by histologic analyses. In wild-type mice, μCT imaging showed that 84 mJ impacts led to significant bone loss at 30 days (p < 0.05), but recovered to normal at 60 days. Bone losses did not occur in RAGE^-/- mice. Synovitis was significantly elevated in 84 mJ impact wild-type mice at both endpoints (30 day, p = 0.001; 60 day, p = 0.05), whereas in RAGE^-/- mice synovitis was elevated only at 30 days (p = 0.02). Mankin scores were slightly elevated in both mouse strains at 30 days, but not at 60 days. Immunohistochemistry revealed significant fracture-related increases in MMP-3 and -13 expression at 30 days (p < 0.05), with no significant difference between genotypes. These findings indicated that while RAGE ^-/- accelerated recovery from fracture and diminished synovitis, arthritic changes were temporary and too modest to detect an effect on the pathogenesis of PTOA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2439-2449, 2018.

Effect of Posterior Malleolus Fracture on Syndesmotic Reduction: A Cadaveric Study

BACKGROUND

Syndesmotic malreduction and fractures of the posterior malleolus negatively influence outcomes of rotational ankle fractures. Recent data have shown that posterior malleolus fixation contributes to the stability of the syndesmosis. The purpose of this study was to analyze syndesmotic reduction within the context of different sizes of posterior malleolus fracture fragments and different qualities of reduction.

METHODS

A model of stage-IV supination-external rotation injury was created in 9 through-the-knee cadaveric specimens. The specimens were randomized to receive either a small (one-third of the incisura, n = 4) or a large (two-thirds of the incisura, n = 5) posterior malleolus fracture. High-resolution computed tomography (CT) scans were obtained of each intact specimen and then with clamp reduction of the syndesmosis along with a fracture fragment that was (1) unreduced, (2) anatomically reduced, or (3) fixed with a 4.8-mm-gap malreduction. Syndesmotic reduction in both the anterior-posterior and the medial-lateral direction was assessed relative to the intact specimen.

RESULTS

Clamp reduction of the syndesmosis increased medial translation of the distal part of the fibula in the specimens with an unfixed or an anatomically fixed posterior malleolus fracture fragment and caused lateral displacement of the distal part of the fibula in the specimens with gap malreduction of the posterior malleolus fracture. Clamp reduction of the syndesmosis caused a slight anterior shift of the fibula in the specimens with a small unfixed or anatomically fixed posterior malleolus fracture fragment and caused a posterior shift of the fibula in the specimens with gap malreduction of a large fragment.

CONCLUSIONS

The overall anterior-posterior reduction of the syndesmosis was generally unaffected by a posterior malleolus fracture except when there was malreduction of a large fragment. Medial-lateral syndesmotic reduction was affected by the conditions of the posterior malleolus fixation, with malreduction of the posterior malleolus leading to syndesmotic malreduction.

CLINICAL RELEVANCE

When posterior malleolus fractures occur with syndesmotic injury, anatomic fracture reduction and fixation are paramount as they can affect syndesmotic reduction, especially with larger fragments.

Cadaveric Evaluation of Dorsal Intermetatarsal Approach for Plantar Plate and Lateral Collateral Ligament Repair of the Lesser Metatarsophalangeal Joints

BACKGROUND

Access to the plantar plate has been described using either a plantar approach or an extensive dorsal approach that required complete joint destabilization and often a metatarsal osteotomy. Clinical scenarios related to plantar plate tear vary and the pathologies in early stages are frequently limited to unilateral soft tissue structures; a less invasive operative approach may be possible. A novel approach requiring a release of only the lateral collateral ligament and the lateral half of the plantar plate is presented in this cadaver model; the extent of joint exposure possible is described. The ability to place a secure suture through the lateral collateral ligament and the plantar plate was analyzed.

METHODS

Nine fresh-frozen cadaveric specimens were dissected in a randomized fashion across the second to fourth metatarsophalangeal joints through the intermetatarsal space dorsally. Under distraction, soft tissue was sequentially released, including dorsal capsule, lateral collateral ligament, and the lateral half of the plantar plate. Integrity of the extensor tendons, deep transverse intermetatarsal ligament, proximal attachment of the plantar plate, and osseous structures was carefully preserved. The joint exposure was quantified after each step with sizing rods. Using a suture passer, 2-0 nonabsorbable braided sutures were passed into the lateral collateral ligament and the plantar plate, and the construct strength was measured using a tensiometer.

RESULTS

Progressive increase in mean joint exposure was noted after each step of soft tissue release with the final exposure of 6 mm after release of the lateral half of the plantar plate. Joint exposures after a capsulotomy and a lateral collateral release were 3 mm and 4 mm, respectively. Under distraction, the unilateral release of soft tissue created a lateral opening of the joint while the proximal phalangeal base adducted and medially deviated. Successful suture passage was noted in all specimens that could sustain a minimum tension of 25 N without a catastrophic failure. There was no statistically significant correlation with age, sex, foot length, and rays of the specimens when joint exposure was considered.

CONCLUSION

The dorsal intermetatarsal approach appeared to be feasible for access to the lateral collateral ligament and the lateral half of the plantar plate. The average joint exposure of 6 mm allowed a quality suture passage by a suture passer in both structures in all specimens without the need of a metatarsal osteotomy.

CLINICAL RELEVANCE

This operative approach may be appropriate for early stages plantar plate tear when only lateral soft tissue repair is needed. This technique should not preclude conversion to a more extensile operative approach or an additional metatarsal osteotomy if needed. Applicability of this operative approach in cases with more advanced pathologies or involving only medial soft tissue structures requires further studies.

Changes in Joint Contact Mechanics in a Large Quadrupedal Animal Model After Partial Meniscectomy and a Focal Cartilage Injury

Acute mechanical damage and the resulting joint contact abnormalities are central to the initiation and progression of post-traumatic osteoarthritis (PTOA). Study of PTOA is typically performed in vivo with replicate animals using artificially induced injury features. The goal of this work was to measure changes in a joint contact stress in the knee of a large quadruped after creation of a clinically realistic overload injury and a focal cartilage defect. Whole-joint overload was achieved by excising a 5-mm wedge of the anterior medial meniscus. Focal cartilage defects were created using a custom pneumatic impact gun specifically developed and mechanically characterized for this work. To evaluate the effect of these injuries on joint contact mechanics, Tekscan (Tekscan, Inc., South Boston, MA) measurements were obtained pre-operatively, postmeniscectomy, and postimpact (1.2-J) in a nonrandomized group of axially loaded cadaveric sheep knees. Postmeniscectomy, peak contact stress in the medial compartment is increased by 71% (p = 0.03) and contact area is decreased by 35% (p = 0.001); the center of pressure (CoP) shifted toward the cruciate ligaments in both the medial (p = 0.004) and lateral (p = 0.03) compartments. The creation of a cartilage defect did not significantly change any aspect of contact mechanics measured in the meniscectomized knee. This work characterizes the mechanical environment present in a quadrupedal animal knee joint after two methods to reproducibly induce joint injury features that lead to PTOA.

Complementary models reveal cellular responses to contact stresses that contribute to post-traumatic osteoarthritis

Two categories of joint overloading cause post-traumatic osteoarthritis (PTOA): single acute traumatic loads/impactions and repetitive overloading due to incongruity/instability. We developed and refined three classes of complementary models to define relationships between joint overloading and progressive cartilage loss across the spectrum of acute injuries and chronic joint abnormalities: explant and whole joint models that allow probing of cellular responses to mechanical injury and contact stresses, animal models that enable study of PTOA pathways in living joints and pre-clinical testing of treatments, and patient-specific computational models that define the overloading that causes OA in humans. We coordinated methodologies across models so that results from each informed the others, maximizing the benefit of this complementary approach. We are incorporating results from these investigations into biomathematical models to provide predictions of PTOA risk and guide treatment. Each approach has limitations, but each provides opportunities to elucidate PTOA pathogenesis. Taken together, they help define levels of joint overloading that cause cartilage destruction, show that both forms of overloading can act through the same biologic pathways, and create a framework for initiating clinical interventions that decrease PTOA risk. Considered collectively, studies extending from explants to humans show that thresholds of joint overloading that cause cartilage loss can be defined, that to at least some extent both forms of joint overloading act through the same biologic pathways, and interventions that interrupt these pathways prevent cartilage damage. These observations suggest that treatments that decrease the risk of all forms of OA progression can be discovered. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:515-523, 2017.

Time-dependent loss of mitochondrial function precedes progressive histologic cartilage degeneration in a rabbit meniscal destabilization model

The goals of this work were to characterize progression of osteoarthritic cartilage degeneration in a rabbit medial meniscus destabilization (MMD) model and then to use the model to identify pre-histologic disruptions in chondrocyte metabolism under chronically elevated joint contact stresses in vivo. To characterize PTOA progression, 24 rabbits received either MMD or sham surgery. Limb loading was analyzed preoperatively and at regular postoperative intervals using a Tekscan pressure-sensitive walkway. Animals were euthanized 8 (n = 8 MMD; n = 8 sham) or 26 weeks (n = 8 MMD) postoperatively for histological cartilage evaluation by an objective, semi-automated Mankin scoring routine. To examine pre-histologic pathology, MMD was performed on an additional 20 rabbits, euthanized 1 (n = 9) or 4 weeks (n = 10) postoperatively. Chondrocytes were harvested fresh for measurement of mitochondrial function, an intracellular indicator of pathology after mechanical injury. Both MMD and sham surgery caused slight decreases in limb loading which returned to preoperative levels after 2 weeks. Histologically apparent cartilage damage progressed from 8 to 26 weeks after MMD. Changes in chondrocyte respiration were variable at 1 week, but by 4 weeks postoperatively chondrocyte mitochondrial function was significantly reduced. Many human injuries that lead to PTOA are relatively mild, and the cell-level mechanisms leading to disease remain unclear. We have documented PTOA progression in an animal model of subtle joint injury under continued use, and demonstrated that this model provides a realistic environment for investigation of multi-stage cellular pathology that develops prior to overt tissue degeneration and which could be targeted for disease modifying treatments. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:590-599, 2017.

Effect of Posterior Malleolus Fracture on Syndesmosis Reduction

Category:

Trauma

Introduction/Purpose:

Syndesmotic malreduction and the presence of posterior malleolus fractures negatively influence outcomes in rotational ankle fractures. While there are no universally accepted criteria for posterior malleolar fixation, it has recently been shown that posterior malleolar fixation contributed to the stability of the syndesmosis. However, little is known if and how anatomic or non-anatomic fixation of the posterior malleolus affects syndesmotic reduction. A study analyzing syndesmotic reduction in specimens with varying in size and quality of reduction of the posterior malleolus was conducted.

Methods:

Nine through-knee cadaveric specimens were randomized into two groups with small (a third of the fibular notch, n=4) and large (two-third of the fibular notch, n=5) posterior malleolar fragments. A model of stage IV supination external rotation injury after fibular repair was created by sharply releasing anterior inferior tibiofibular ligament, superficial and deep deltoid ligaments, and interosseous membrane. Posterior malleolar fracture with predefined sizing was created with preservation of posterior inferior tibiofibular ligament. High resolution CT scan was obtained in each specimen at the four stages; intact, neutral- axis syndesmotic clamping only, with anatomic fixation of the posterior malleolus, and with non-anatomic fixation of the posterior malleolus using a 4.8 mm interposed spacer. Measurement of syndesmotic reduction in both anteroposterior and mediolateral planes was made automatically using a validated technique assisted by custom-developed software at 1 cm proximal to the ankle joint.

Results:

The presence of either a neutral-axis clamping alone or with an anatomically reduced fracture fragment caused a slight anterior shift of the fibula that was more pronounced in the smaller fragment group. Two-way ANOVA indicated no significant effects of fragment size (p=0.73) or reduction (p=0.09) on AP fibular movement. However, presence of non-anatomical fixation caused the fibula to move significantly posteriorly in the presence of a large posterior malleolar fragment (p=0.03 and p=0.01 relative to the intact and clamping only states). In the mediolateral direction, a neutral-axis clamping alone and clamping with an anatomically reduced fracture fragment both increased medial translation of the distal fibula. The non-anatomic reduction model of the posterior malleolus associated with corresponding lateral displacement of the distal fibula.

Conclusion:

The overall anteroposterior reduction of the syndesmosis using neutral-axis clamping was generally not affected by posterior malleolar fracture except in a non-anatomic fixation of large fragments. Mediolateral syndesmotic reduction was affected by the conditions of posterior malleolar fixation with best results in anatomic fixation but the intact state was still not replicated. Malreduction of the posterior malleolus led to a corresponding syndesmotic malreduction. When a posterior malleolar fixation is indicated in cases with syndesmotic injury, anatomic fracture fixation is paramount as it can affect syndesmotic reduction especially with larger fragments.

Rigid Syndesmotic Fixation Alters Joint Contact Mechanics and Talar Kinematics

Category:

Trauma

Introduction/Purpose:

The variety of methods available for performing syndesmotic fixation have led to significant controversy about the optimal method of surgical fixation, and the effects of syndesmotic fixation on the biomechanics of the ankle remain poorly understood. The purpose of the present study was to use a cadaveric model to evaluate the effects of progressively increasing syndesmotic fixation on talar motion and contact stress on the talar dome and in the medial and lateral gutters.

Methods:

Twelve fresh-frozen cadaveric specimens were dissected to expose the ankle joint while leaving ligaments, syndesmosis, and interosseus membrane intact, simulating a best-case fibular reduction. Rigid clusters of reflective markers were attached to the tibia, the distal fibula, and the talus for tracking with a motion capture system. A Tekscan pressure sensor was inserted into the tibiotalar joint (n=6) or into both gutters (n=6) for measuring contact stress. A 600N axial load was applied in a custom-built ankle simulator which permitted free internal/external rotation and inversion/eversion while holding either 20°plantar flexion, 10° plantar flexion, neutral, or 10° dorsiflexion. Specimens were tested without fixation, with one 3.5mm screw, and with two 3.5mm screws. Motion data were rotated into an anatomic reference frame and a fixed center of rotation (CoR) of the talus was calculated in the sagittal plane. Tekscan data were analyzed for changes in peak contact stress and changes in contact area.

Results:

Antero-posterior translation of the talus was variable with increasing fixation and specimen dependent. A single 3.5mm screw shifted the average CoR posteriorly 0.4 mm, and two 3.5mm screws shifted the average talar CoR anteriorly 1.6mm. Five specimens shifted posteriorly with fixation, while the other specimens moved anteriorly, resulting in extremely large standard deviations of AP movement. Peak contact stress on the talar dome decreased 10%-20% with the addition of syndesmotic fixation. Contact area on the talar dome decreased with increased syndesmotic fixation. Conversely, peak contact stress in the medial and lateral gutters increased with the addition of syndesmotic screws, although the magnitude was substantially lower than peak stresses in the talar dome. Contact areas in both gutters tended to increase with each syndesmotic screw.

Conclusion:

Fixation of the distal tibiofibular syndesmosis altered the biomechanical behavior of the ankle, generally shifting the talus slightly anteriorly, decreasing the load on the tibiotalar articulation, and increasing medial and lateral gutter contact stress. The specimen-to-specimen variability was noteworthy. While the variability lead to large standard deviations and prevented some mechanical trends from achieving statistical significance, it became very apparent that there are certain individuals who would suffer grossly abnormal ankle mechanics after rigid syndesmotic fixation, and a more aggressive fixation would amplify the mechanical abnormalities.

The Dorsal Intermetatarsal Approach for Plantar Plate and Lateral Collateral Ligament Repair of the Lesser Metatarsophalangeal Joints

Category:

Lesser Toes

Introduction/Purpose:

Access to the plantar plate has been described using either a plantar approach or an extensile dorsal approach that required complete joint destabilization and often a metatarsal osteotomy. Clinical scenarios related to plantar plate tear vary and the pathologies in early stages are frequently limited to unilateral soft tissue structures, a more focused surgical approach deemed appropriate. A novel approach requiring a release of only the lateral collateral ligament and the lateral half of the plantar plate was described and the adequacy of joint exposure was evaluated in a cadaver model. The ability to place a suture through the lateral collateral ligament and the plantar plate were analyzed and validated with pull-out strength.

Methods:

Nine fresh frozen cadaveric specimens were dissected in a randomized fashion across the 2nd to 4th MTP joints through the intermetatarsal space dorsally. Under distraction, soft tissue was sequentially released including dorsal capsule, lateral collateral ligament, and the lateral half of the plantar plate. Integrity of the extensor tendons, deep transverse intermetatarsal ligament, proximal attachment of the plantar plate, and osseous structures was carefully preserved. The joint exposure was quantified after each step with sizing rods. 2/o non-absorbable sutures were passed into the lateral collateral ligament and the plantar plate using a suture passer; and their pullout strength was measured using a tensiometer.

Results:

Progressive increase in mean of joint exposure was noted after each step of soft tissue release with the final exposure of 6mm after release of the lateral half of the plantar plate. Joint exposures after a capsulotomy and a lateral collateral release were 3mm and 4mm, respectively. Under distraction, the unilateral release of soft tissue created a lateral opening of the joint while the proximal phalangeal base adducted and medially deviated. Successful suture passage was noted in all specimens with mean pullout strength of 76 N for the lateral collateral ligament and 67 N for the plantar plate. There was a statistically significant (p < 0.01) higher suture pullout strength for the lateral collateral ligament in males when compared to female specimens

Conclusion:

The dorsal intermetatarsal approached appeared to be feasible for the access to the lateral collateral ligament and the lateral half of the plantar plate. The average joint exposure of 6 mm allowed a quality suture passage by a suture passer in both structures in all specimens without the need of a metatarsal osteotomy.

Delayed administration of recombinant human parathyroid hormone improves early biomechanical strength in a rat rotator cuff repair model

BACKGROUND

Despite advances in intraoperative techniques, rotator cuff repairs frequently do not heal. Recombinant human parathyroid hormone (rhPTH) has been shown to improve healing at the tendon-to-bone interface in an established acute rat rotator cuff repair model. We hypothesized that administration of rhPTH beginning on postoperative day 7 would result in improved early load to failure after acute rotator cuff repair in an established rat model.

METHODS

Acute rotator cuff repairs were performed in 108 male Sprague-Dawley rats. Fifty-four rats received daily injections of rhPTH beginning on postoperative day 7 until euthanasia or a maximum of 12 weeks postoperatively. The remaining 54 rats received no injections and served as the control group. Animals were euthanized at 2 and 16 weeks postoperatively and evaluated by gross inspection, biomechanical testing, and histologic analysis.

RESULTS

At 2 weeks postoperatively, rats treated with rhPTH demonstrated significantly higher load to failure than controls (10.9 vs. 5.2 N; P = .003). No difference in load to failure was found between the 2 groups at 16 weeks postoperatively, although control repairs more frequently failed at the tendon-to-bone interface (45.5% vs. 22.7%; P = .111). Blood vessel density appeared equivalent between the 2 groups at both time points, but increased intracellular and extracellular vascular endothelial growth factor expression was noted in the rhPTH-treated group at 2 weeks.

CONCLUSIONS

Delayed daily administration of rhPTH resulted in increased early load to failure and equivalent blood vessel density in an acute rotator cuff repair model.

Variable Volumes of Resected Bone Resulting From Different Total Ankle Arthroplasty Systems

BACKGROUND

The increased popularity and success of total ankle arthroplasty (TAA) has resulted in the development of varying TAA hardware designs, many of which include specific bone-sparing or bone-sacrificing features. The goal of this work was to determine differences in the volume of bone removed for implantation of different total ankle arthroplasty hardware systems.

METHODS

Sixteen cadaveric specimens were computed tomography-scanned preoperatively and after total ankle arthroplasty using either an INBONE II, Salto Talaris, STAR, or Zimmer TMTA implant. Geometries of the talus and the distal tibia were manually segmented and converted to 3D bony surface models. The volume of bone removed for each implant was calculated as the difference in volume between the preoperative and postoperative bone models. To account for differences in specimen size, volume was expressed as a percentage of the intact bone.

RESULTS

There was a significant difference (P = .049) in the average percent of talar bone removed, with the STAR and INBONE II systems requiring removal of greater volumes of bone. The INBONE II system required significantly (P < .004) more tibial bone resection than the other 3 implants when evaluating a long span of the distal tibia. However, most of this increased bone resection was medullary bone. Close to the articular surface, bone volumes removed for the various tibial components were not significantly different (P = .056).

CONCLUSION

Volume and location of bone removed for different implant systems varied with implant design.

CLINICAL RELEVANCE

Primary bone resection associated with different implant hardware systems varied more on the talar side of the articulation, and the stemmed prosthesis did not result in dramatic increases in periarticular bone resection. Clinicians should weigh the effects of greater or lesser bone resection associated with various implant designs against other factors used for hardware selection.

A clinically realistic large animal model of intra-articular fracture that progresses to post-traumatic osteoarthritis

OBJECTIVE

Translation of promising treatments for post-traumatic osteoarthritis (PTOA) to patients with intra-articular fracture (IAF) has been limited by the lack of a realistic large animal model. To address this issue we developed a large animal model of IAF in the distal tibia of Yucatan minipigs and documented the natural progression of this injury.

DESIGN

Twenty-two fractures were treated using open reduction and internal fixation with either an anatomic reduction or an intentional 2-mm step-off. Pre-operatively, and 3 days, 1, 2, 4, 8, and 12 weeks post-operatively, animals were sedated for synovial fluid draws and radiographs. Limb loading was monitored at the same time points using a Tekscan Walkway. Animals were sacrificed at 12 weeks and the limbs were harvested for histological evaluation.

RESULTS

All animals achieved bony union by 12 weeks, facilitating nearly complete recovery of the initial 60% decrease in limb loading. TNFα, IL1β, IL6, and IL8 concentrations in the fractured limbs were elevated (P < 0.05) at specific times during the 2 weeks after fracture. Histological cartilage degeneration was more severe in the step-off group (0.0001 < P < 0.27 compared to normal) than in the anatomic reconstruction group (0.27 < P < 0.99 compared to normal).

CONCLUSIONS

This model replicated key features of a human IAF, including surgical stabilization, inflammatory responses, and progression to osteoarthritic cartilage degeneration, thereby providing a potentially useful model for translating promising treatment options to clinical practice.

Injury risk to extraosseous knee vasculature during osteotomies: a cadaveric study with CT and dissection analysis

BACKGROUND

Realignment osteotomies about the knee may be performed as distal femoral or proximal tibial osteotomies; both may be performed either on the medial or lateral sides of the knee, in closing- or opening-wedge fashion. Although rare, injury to neurovascular structures may occur, and the proximity of the vascular structures to the osteotomy saw cuts has been incompletely characterized.

QUESTIONS/PURPOSES

We performed a cadaver study to assess the risk of vascular injury in patients undergoing realignment osteotomies by (1) quantifying the distances between osteotomy saw cuts and blood vessels using three-dimensional CT reconstruction after distal femoral and proximal tibial osteotomies; and (2) qualitatively describing the small- and medium-sized vasculature around the knee, to provide the link between the CT analysis and wedge incision measures, and better show the potential extraosseous supply to the regions investigated.

METHODS

Twelve human cadaveric knees were injected with a latex and barium sulfate suspension into the superficial femoral artery. Each specimen underwent CT to evaluate vascular perfusion and was randomized to either a lateral opening-wedge distal femoral osteotomy and medial opening-wedge proximal tibial osteotomy group, or a medial closing-wedge distal femoral osteotomy and lateral closing-wedge proximal tibial osteotomy group. Postoperatively, knees underwent CT in extension to measure the shortest distance between the osteotomies and the popliteal artery, anterior and posterior tibial arteries, and genicular arteries. Vessels between 5 mm and 10 mm from the osteotomy cut were considered in a zone of moderate risk for damage, while vessels less than 5 mm from the cut were considered in a zone of high risk for damage. Vessels more than 10 mm from the cut were not considered to be at risk. Subsequently, knees underwent dissection and chemical débridement to qualitatively describe the smaller vessels. This part of the study added visual information and gave a comprehensive overview of the vessels at risk.

RESULTS

All variations of the osteotomies put at least one artery at risk. The popliteal artery was found in a risk zone for injury in two specimens during closing-wedge distal femoral osteotomy (median distance, 11.6 mm; range, 5.2-14.6 mm). The superior lateral genicular artery was in a risk zone in all the specimens during opening-wedge distal femoral osteotomy (median distance, 3.0 mm; range, 0.7-6.5 mm), and in five specimens during closing-wedge distal femoral osteotomy (median distance, 4.5 mm; range, 1.3-11.2 mm). A concomitant risk for superior medial genicular artery injury was observed in five specimens during opening-wedge distal femoral osteotomy (median distance, 8.7 mm; range, 0.8-13.9 mm) and in four specimens during closing-wedge distal femoral osteotomy (median distance, 4.1; range, 0.5-41.7 mm). The popliteal artery was in a risk zone in four specimens during opening-wedge proximal tibial osteotomy (median distance, 9.6 mm; range, 6.6-12.9 mm), and in three specimens during closing wedge proximal tibial osteotomy (median distance, 9.6 mm; range, 4.4-11 mm). The inferior medial genicular artery could be classified at risk in five specimens during opening-wedge proximal tibial osteotomy (median distance, 2.1 mm; range, 0.3-32 mm) and in five specimens during closing-wedge proximal tibial osteotomy (median distance, 5.8 mm; range, 1.4-13 mm). Furthermore, the inferior lateral genicular artery was found in a risk zone in two specimens of closing-wedge proximal tibial osteotomies (median distance, 17.4 mm; range, 8-23.3 mm). There were no differences between opening-wedge and closing-wedge distal femoral osteotomies and proximal tibial osteotomies in the vessels at risk during the procedure. After chemical débridement, knees showed abundant vascularization of the distal femur and lateral tibia, whereas the medial tibia contained few arteries.

CONCLUSIONS

With the numbers available, we found that none of the osteotomy techniques performed was safer than any other in terms of the proximity of the major arterial structures and some vessels appear to be at relatively high risk during these procedures.

CLINICAL RELEVANCE

This study clarifies that the genicular arteries on the opposite side of the surgical field, which cannot be seen and protected during the procedure, can be at risk of injury, particularly when the cortical hinge is compromised. Additional studies are necessary to address the potential risk of the dissection needed for plate placement and injuries related to drilling and screw placement during osteotomies around the knee.

Validation and reproducibility of a biplanar imaging system versus conventional radiography of foot and ankle radiographic parameters

BACKGROUND

Diagnosis of foot deformities is frequently supported by objective measures of bony alignment made on AP and lateral weight-bearing radiographs. The EOS biplanar imaging system has the capability of simultaneously capturing orthogonal AP and lateral images of the foot during weight-bearing with reduced radiation exposure. The purpose of this study was to evaluate the validity and reproducibility of common foot and ankle radiographic measurements made on images acquired with the EOS biplanar imaging system.

METHODS

Fifty consecutive patients indicated for foot and ankle realignment surgeries were enrolled. Radiographic studies included conventional AP and lateral ankle weight-bearing radiographs and long-leg AP and lateral weight-bearing images acquired using the EOS system with both a staggered feet and a nonstaggered feet position. Sixteen radiographic parameters of foot, ankle, and lower limb alignment were measured by 2 blinded observers, with 1 observer repeating all measurements 6 weeks later. Inter- and intraobserver reliability was assessed using intraclass correlation coefficients. Between-group comparison was assessed using Pearson correlation coefficients, ANOVA, and paired t-tests.

RESULTS

There was no statistically significant difference in any commonly used foot and ankle radiographic parameters measured on conventional radiographs or EOS images acquired with staggered and nonstaggered feet (ANOVA P = .792 to .997 and paired t tests P = .067 to .977). However, the staggered foot position resulted in significantly different limb length measurements in the rear leg (P = .000 to .049). Intra- and interrater reliabilities of limb alignment measurements from EOS system images were excellent in both foot positions (ICC = .938 to 1.000).

CONCLUSION

Images acquired using EOS biplanar imaging system allowed for valid and reliable measurement of commonly used foot and ankle radiographic parameters; however, the staggered foot position required for simultaneous imaging of both feet in the lateral view affected limb length measurements in the rear leg.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

The effect of suture-button fixation on simulated syndesmotic malreduction: a cadaveric study

BACKGROUND

The accuracy of reduction of distal tibiofibular syndesmosis disruptions has been associated with the clinical outcome. Suture-button fixation of the syndesmosis is a dynamic alternative mode of fixation. We hypothesized that with deliberate clamp-induced malreduction, suture-button fixation of the syndesmosis would allow a more anatomic post-fixation position compared with screw fixation.

METHODS

Forty-eight syndesmotic fixations were performed on twelve through-knee cadaveric specimens. The syndesmosis was destabilized and off-axis clamping was used to produce both anterior and posterior malreduction patterns. In twelve scenarios (six anterior and six posterior malreductions), syndesmotic screw fixation was used, followed by computed tomography. With tenacula holding the malreduction, the syndesmosis screws were exchanged for a suture-button construct and the specimens underwent a subsequent computed tomography scan. In the other twelve scenarios, the suture-button fixation was achieved first, followed by screw fixation. Standardized measurements of anterior-posterior and medial-lateral fibular displacement were performed by two observers blinded to the method of fixation.

RESULTS

With anterior off-axis clamping, the mean sagittal malreduction was 2.7 ± 2.0 mm with screw fixation and 1.0 ± 1.0 mm with suture-button fixation (p = 0.02). With posterior off-axis clamping, the sagittal malreduction was 7.2 ± 2.3 mm with screw fixation and 0.5 ± 1.4 mm with suture-button fixation (p < 0.01). No differences were observed between fixation types in the coronal plane (p = 0.20 for anterior malreductions and p = 0.06 for posterior malreductions).

CONCLUSIONS

With deliberate malreduction in a cadaver model, suture-button fixation of the syndesmosis results in less post-fixation displacement compared with screw fixation. The suture button's ability to allow for natural correction of deliberate malreduction was greatest with posterior off-axis clamping.

CLINICAL RELEVANCE

Although the clinical relevance is unknown, dynamic syndesmotic fixation may mitigate clamp-induced malreduction.

Replication of chronic abnormal cartilage loading by medial meniscus destabilization for modeling osteoarthritis in the rabbit knee in vivo

Medial meniscus destabilization (MMD) is a surgical insult technique for modeling osteoarthritis (OA) by replicating chronic abnormal cartilage loading in animal joints in vivo. The present study aimed to characterize the immediate biomechanical effects (ex vivo) and short-term histological consequences (in vivo) of MMD in the rabbit knee. In a compressive loading test, contact stress distribution in the medial compartment was measured in eight cadaver rabbit knees, initially with all major joint structures uninjured (Baseline), after MMD, and finally after total medial meniscectomy (TMM). Similarly, the effects on sagittal joint stability were determined in an anterior-posterior drawer test. These biomechanical (ex vivo) data indicated that both MMD and TMM caused significant (p < 0.001), distinct (>1.5-fold) elevation of peak local contact stress in the medial compartment, while leaving whole-joint stability nearly unchanged. Histological consequences in vivo were assessed in a short-term (8-week) survival series of MMD or TMM (five animals for each group), and both caused moderate cartilage degeneration in the medial compartment. The MMD insult, which is feasible through posterior arthrotomy alone, is as effective as TMM for modeling injurious-level chronic abnormal cartilage loading in the rabbit knee medial compartment in vivo, while minimizing potential confounding effects from whole-joint instability.

Tripod index: a new radiographic parameter assessing foot alignment

BACKGROUND

No single radiographic measurement takes into account complete foot alignment. We have created the Tripod Index (TI) to allow assessment of complex foot deformities using a standing anteroposterior (AP) radiograph of the foot. We hypothesized that TI would demonstrate good intraobserver and interobserver reliability and correlate with currently accepted radiographic parameters, in both flatfoot and cavovarus foot deformities.

METHODS

Three groups of patients were studied: 26 patients (30 feet) with flatfoot, 29 patients (30 feet) with cavovarus foot, and 51 patients (60 feet) without foot deformity as controls. Weight-bearing radiographs were obtained: foot AP with a hemispherical marker around the heel plus standard lateral and hindfoot alignment views. Radiographic measurements were made by 2 blinded investigators. Statistical analysis included intraclass correlation coefficients (ICCs), correlation of the TI with existing radiographic measurements using Pearson coefficients, and comparison between patient groups using analysis of variance.

RESULTS

Intraobserver and interobserver ICCs of TI (0.99 and 0.98, respectively) were excellent. In the flatfoot group, TI significantly correlated with AP talonavicular coverage angle (r = 0.43), medial cuneiform-fifth metatarsal height (r = -0.59), coronal plane hindfoot alignment (r = 0.53), and clinical hindfoot alignment (r = 0.39). In the cavovarus foot group, TI correlated significantly with AP talonavicular coverage angle (r = 0.77), calcaneal pitch angle (r = 0.39), medial cuneiform-fifth metatarsal height (r = -0.65), coronal plane hindfoot alignment (r = 0.55), and clinical hindfoot alignment (r = 0.61). Statistically significant differences between flatfoot-control and cavovarus foot-control were found in TI, AP talonavicular coverage angle, lateral talo-first metatarsal angle, calcaneal pitch angle, medial cuneiform-fifth metatarsal height, coronal plane hindfoot alignment, and clinical assessment of hindfoot alignment (all with P < .001).

CONCLUSION

The TI was demonstrated to be a valid and reliable radiographic measurement to quantify the magnitude of complex foot deformities when evaluating flatfoot and cavovarus foot.

CLINICAL RELEVANCE

The TI may be helpful as an integrated assessment of complex foot deformities. Further clinical studies are recommended.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Maximizing safety in screw placement for posterior facet fixation in calcaneus fractures: a cadaveric radio-anatomical study

BACKGROUND

Successful screw fixation of reduced posterior facet fragments to the unexposed, nondisplaced sustentaculum tali avoids breaching the subtalar joint or disrupting surrounding soft tissue structures. Safe passage for screw fixation through this narrow bony corridor has not been rigorously defined.

METHODS

Computed tomography scans of 8 cadaveric feet were digitally reconstructed in 3-D; 3.5-mm-diameter screws were simulated, aiming at the center of the sustentaculum tali from 5 locations (0%, 25%, 50%, 75%, and 100%) along the posterolateral facet joint. The range of entry points, screw paths trajectories, and screw lengths that did not breach the subtalar joint or the medial calcaneal cortex were evaluated.

RESULTS

To prevent violation of the subtalar joint or the medial calcaneal cortex while reaching the center of the sustentaculum tali, screws must be inserted at least 5 mm below the joint line. Screw placement 15 ± 1 mm below the posterior facet measured perpendicular to the joint line provided the widest safe corridor with the trajectory of the ranges from 6 to 36 degrees parallel to the joint depending on the location along the posterior facet and 20 ± 2 degrees perpendicular to the joint at all locations. The average maximal length of screws placed at the ideal entry points ranged from 44 to 46 mm, longest at the 100% location and shortest at the 25% location.

CONCLUSIONS

Operative guidelines facilitating instrumentation into the sustentaculum tali have been defined applying to most calcanei, assuming the fractures are well reduced: screws, approximately 40 mm in length, should be started 15 mm below the posterior facet measured perpendicular to the joint line and aimed 20 degrees perpendicular to the joint line toward the joint and 6 to 36 degrees anteversion parallel to the joint line increasing at each position from anterior to posterior.

CLINICAL RELEVANCE

The operative guidelines described in this study may assist surgeons in the placement of screws for the fixation of posterior facet fragments to the sustentaculum tali.