A computer simulation of rotational acetabular osteotomy for dysplastic hip joint: does the optimal transposition of the acetabular fragment exist?

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.

The role of torsional stress in the development of subchondral insufficiency fracture of the femoral head: A finite element model analysis

BACKGROUND

Subchondral insufficiency fracture of the femoral head generally occurs without evidence of trauma or with a history of minor trauma. Insufficient bone quality is considered one cause; however, the detailed mechanism of fracture development at the subchondral area (SA) is not understood. The aim of this study was to clarify the directions of force that cause subchondral fracture using finite element model analysis.

METHODS

Two types of finite element models were generated from the CT data of femurs obtained from three individuals without osteoporosis (normal models) and another three with osteoporosis (osteoporosis models). Three directions of force, including compressive, shearing, and torsional, were applied to the femoral head. The distribution of von Mises stress (Mises stress) was evaluated at the SA, principal compressive trabeculae (PC), and principal tensile trabeculae.

RESULTS

Under compressive force, the mean Mises stress value was greatest at the PC in both the normal and osteoporosis models. Under shearing force, the mean Mises stress value tended to be greatest at the SA in the normal model and at the PC in the osteoporosis model. Under torsional force, the mean Mises stress value was greatest at the SA in both types of models.

CONCLUSIONS

The torsional force showed the greatest Mises stress at the SA in both the normal and osteoporosis models, suggesting the importance of torsion as a possible force responsible for subchondral insufficiency fracture development.

Finite Element Analysis of Various Osteotomies Used in the Treatment of Developmental Hip Dysplasia in Children

Late-discovered developmental hip dysplasia deformities often necessitate complex surgical treatments and meticulous preoperative planning. The selection of osteotomies is contingent upon the patient's age and the specific structural deformity of the hip. In our anatomical hip model, derived from the data of a 12-year-old patient, we performed virtual osteotomies that are commonly recommended for such cases. We precisely constructed geometric models for various osteotomies, including the Dega, Pemberton, Tönnis, Ganz, Chiari pelvic, and Pauwels femoral osteotomies. We employed Autodesk Inventor for the finite element analysis of the hip joint and the corrective osteotomies. In comparing one-stage osteotomies, we noted that the Dega and Ganz pelvic osteotomies, especially when combined with the Pauwels femoral osteotomy, yielded the most favorable outcomes. These combinations led to enhanced femoral head coverage and reduced intra-articular pressure. Furthermore, we calculated the femoral head-to-acetabulum volume ratio for both the Dega and Pauwels osteotomies. The encouraging results we obtained advocate for the integration of finite element analysis in virtual osteotomies of the pelvis and femur as a preoperative tool in the management of developmental hip dysplasia.

Visualization of acetabular coverage with radar chart before and after curved periacetabular osteotomy in dysplastic hips

BACKGROUND

Curved periacetabular osteotomy (CPO) is indicated for patients with developmental dysplasia of hip (DDH) to prevent progressive osteoarthritis. Patients with DDH have not only lateral acetabulum dysplasia but also anterior and posterior dysplasia. The full circumference acetabular coverage angle (ACA) of the femoral head should be evaluated preoperatively. This study aimed to determine the full circumference ACA in the patients with DDH before and after CPO compared with the coverage in normal patients.

METHODS

Twenty-three patients (a total of 24 hips) with DDH undergoing CPO between February 2006 and March 2014 were included in this study. The normal group was defined as the normal side in patients with unilateral osteonecrosis of the femoral head (ONFH) and the non-collapsed femoral head side in patients with bilateral ONFH. Pre- and postoperative hip functions were evaluated using the Japanese Orthopedic Association (JOA) hip score. ACA was measured using pre- and postoperative three-dimensional computed tomography (3DCT) and described as a clock using a radar chart. The ACA of the normal group was evaluated in the same manner as that for patients who underwent CPO. The ACA before CPO was compared with the ACA after CPO, the ACA before CPO was compared with that of the normal group and the ACA after CPO was compared with that of the normal group at each location.

RESULTS

The mean JOA hip scores improved significantly from 69 preoperatively to 88 postoperatively. The superior, posterior, and anterior ACA after CPO significantly increased and the inferior ACA decreased compared with ACA before CPO. The superior, posterior, and anterior ACA before CPO were significantly smaller than ACA in the normal group. The ACA after CPO were similar to the normal group.

CONCLUSIONS

CPO improved the anterosuperior coverage of the femoral head but reduced its inferior coverage. The radar chart could visualize acetabulum full circumference and was useful for three-dimensional pre-postoperative evaluation.

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.

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.

LibHip: An open-access hip joint model repository suitable for finite element method simulation

BACKGROUND AND OBJECTIVE

population-based finite element analysis of hip joints allows us to understand the effect of inter-subject variability on simulation results. Developing large subject-specific population models is challenging and requires extensive manual effort. Thus, the anatomical representations are often subjected to simplification. The discretized geometries do not guarantee conformity in shared interfaces, leading to complications in setting up simulations. Additionally, these models are not openly accessible, challenging reproducibility. Our work provides multiple subject-specific hip joint finite element models and a novel semi-automated modeling workflow.

METHODS

we reconstruct 11 healthy subject-specific models, including the sacrum, the paired pelvic bones, the paired proximal femurs, the paired hip joints, the paired sacroiliac joints, and the pubic symphysis. The bones are derived from CT scans, and the cartilages are generated from the bone geometries. We generate the whole complex's volume mesh with conforming interfaces. Our models are evaluated using both mesh quality metrics and simulation experiments.

RESULTS

the geometry of all the models are inspected by our clinical expert and show high-quality discretization with accurate geometries. The simulations produce smooth stress patterns, and the variance among the subjects highlights the effect of inter-subject variability and asymmetry in the predicted results.

CONCLUSIONS

our work is one of the largest model repositories with respect to the number of subjects and regions of interest in the hip joint area. Our detailed research data, including the clinical images, the segmentation label maps, the finite element models, and software tools, are openly accessible on GitHub and the link is provided in Moshfeghifar et al.(2022)[1]. Our aim is to empower clinical researchers to have free access to verified and reproducible models. In future work, we aim to add additional structures to our models.

Systematic review of pre-operative planning modalities for correction of acetabular dysplasia

Acetabular dysplasia, related to developmental dysplasia of the hip, causes the abnormal distribution of hip joint forces. Surgical correction of acetabular dysplasia involves repositioning the acetabulum to achieve improved coverage of the femoral head. However, ideal placement of the acetabular fragment is challenging, and has led to an increased interest in pre-operative planning modalities. In this study, we used the PubMed and EBSCO host databases to systematically review all the modalities for pre-operative planning of acetabular dysplasia proposed in the current literature. We included all case-series, English, full-text manuscripts pertaining to pre-operative planning for congenital acetabular dysplasia. Exclusion criteria included: total hip arthroplasty (THA) planning, patient population mean age >35, and double/single case studies. A total of 12 manuscripts met our criteria for a total of 186 hips. Pre-operative planning modalities described were: Amira (Thermo Fischer Scientific; Waltham, MA, USA) 12.9%, OrthoMap (Stryker Orthopaedics; Mahwah, NJ, USA) 36.5%, Amira + Biomechanical Guidance System 5.9%, Mills et al. method 16.1%, Klaue et al. method 16.1%, Armand et al. method 6.5%, Tsumura et al. method 3.8% and Morrita et al. method 2.2%. As a whole, there was a notable lack of prospective studies demonstrating these modalities’ efficacy, with small sample sizes and lack of commercial availability diminishing their applicability. Future studies are needed to comprehensively compare computer-assisted planning with traditional radiographic assessment of ideal osteotomy orientation.

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°.

Biomechanical Guidance System for Periacetabular Osteotomy

This chapter presents a biomechanical guidance navigation system for performing periacetabular osteotomy (PAO) to treat developmental dysplasia of the hip. The main motivation of the biomechanical guidance system (BGS) is to plan and track the osteotomized fragment in real time during PAO while simplifying this challenging procedure. The BGS computes the three-dimensional position of the osteotomized fragment in terms of conventional anatomical angles and simulates biomechanical states of the joint. This chapter describes the BGS structure and its application using two different navigation approaches including optical tracking of the fragment and x-ray-based navigation. Both cadaver studies and preliminary clinical studies showed that the biomechanical planning is consistent with traditional PAO planning techniques and that the additional information provided by accurate 3D positioning of the fragment does not adversely impact the surgery.

Is There an Association Between Borderline-to-mild Dysplasia and Hip Osteoarthritis? Analysis of CT Osteoabsorptiometry

BACKGROUND

The definitive treatment of borderline-to-mild dysplasia remains controversial. A more comprehensive understanding of the etiology of osteoarthritis (OA) and clarification of any possible association between borderline-to-mild dysplasia and the pathogenesis of OA are essential.

QUESTIONS/PURPOSES

(1) Does the distribution of acetabular subchondral bone density increase according to dysplasia severity? (2) Is there an association between borderline-to-mild dysplasia and OA pathogenesis?

METHODS

We evaluated bilateral hips of patients with developmental dysplasia of the hip who underwent eccentric rotational acetabular osteotomy (ERAO) for inclusion in the dysplasia group and contralateral hips of patients with unilateral idiopathic osteonecrosis of the femoral head (ONFH) who underwent curved intertrochanteric varus osteotomy (CVO) for the control group. ERAO was performed in 46 patients and CVO was performed in 32 patients between January 2013 and August 2016 at our institution. All patients underwent bilateral hip CT. The study included 55 hips categorized according to dysplasia severity: (1) borderline-mild, 19 hips (15° ≤ lateral center-edge angle [LCEA] < 25°); (2) moderate, 20 hips (5° ≤ LCEA < 15°); (3) severe, 16 hips (LCEA < 5°); and (4) control, 15 hips. Thirty-seven dysplastic hips (age < 15 or > 50 years old, prior hip surgery, subluxation, aspherical femoral head, cam deformity, and radiographic OA) and 17 control hips (age < 15 or > 50 years old, bilateral ONFH, LCEA < 25° or ≥ 35°, cam deformity, and radiographic OA) were excluded. CT-osteoabsorptiometry (OAM) predicts physiologic biomechanical conditions in joints by evaluating subchondral bone density. We evaluated the distribution of subchondral bone densities in the acetabulum with CT-OAM, dividing the stress distribution map into six segments: anteromedial, anterolateral, centromedial, centrolateral, posteromedial, and posterolateral. We calculated the percentage of high-density area, which was defined as the upper 30% of Hounsfield units values in each region and compared least square means difference estimated by the random intercept model among the four groups.

RESULTS

In all regions, the percentage of high-density area did not differ between the borderline-mild group and the control (eg, anterolateral, 16.2 ± 5.6 [95% CI, 13.4 to 18.9] versus 15.5 ± 5.7 [95% CI, 12.4 to 18.5, p = 0.984]; centrolateral, 39.1 ± 5.7 [95% CI, 36.4 to 41.8] versus 39.5 ± 4.7 [95% CI, 36.6 to 42.5, p = 0.995]; posterolateral, 10.9 ± 5.2 [95% CI, 8.0 to 13.8] versus 15.1 ± 6.8 [95% CI, 11.7 to 18.5, p = 0.389]). In the anterolateral region, a smaller percentage of high-density area was observed in the borderline-mild group than in both the moderate group (16.2 ± 5.6 [95% CI, 13.4-18.9] versus 28.2 ± 5.1 [95% CI, 25.5-30.9], p < 0.001) and the severe group (16.2 ± 5.6 [95% CI, 13.4-18.9] versus 22.2 ± 6.8 [95% CI, 19.2-25.2, p = 0.026).

CONCLUSIONS

Our results suggest that the cumulative hip stress distribution in borderline-to-mild dysplasia was not concentrated on the lateral side of the acetabulum, unlike severe dysplasia.

CLINICAL RELEVANCE

Based on the stress distribution pattern, our results may suggest that there is no association between borderline-to-mild dysplasia and the pathogenesis of OA. Further studies are needed to evaluate the association between borderline-to-mild dysplasia and instability of the hip.

INFLUENCE OF MODELING METHODS FOR CARTILAGE LAYER ON SIMULATION OF PERIACETABULAR OSTEOTOMY USING FINITE ELEMENT CONTACT ANALYSIS

Finite element (FE) analysis has been used in the simulation of periacetabular osteotomy (PAO) to predict the improvement of contact pressure concentration in dysplastic hip joint. Since the cartilage layer is difficult to be segmented from CT or MRI images, most hip joint models were assumed to be a simple perfect ball and socket joint. However, the influence of different cartilage modeling methods on the reliability of the simulation has not been assessed. The objective of this study is to elucidate the influence of different cartilage modeling methods on predictions of cartilage layers’ contact pressure by FE contact analysis. In this study, the cartilage layer was generated by applying three typical kinds of modeling methods (spherical, uniform thickness, and midline-based). After comparisons with these cartilage modeling methods, the computational results demonstrate that the cartilage modeling methods have a dramatic influence on predictions of contact pressure in the PAO. The relatively continuous contact pressure distribution and lower peak contact pressure are observed in spherical cartilage modeling method. The discontinuous contact pressure distribution and higher peak contact pressure are obtained in uniform thickness and midline-based cartilage modeling methods. And the degree of discontinuous pressure distribution is even worse in the midline-based cartilage modeling method.

The mechanical effects of cup inclination and anteversion angle on the bearing surface

BACKGROUND

Regarding the cup setting in total hip arthroplasty, range of motion and prevention of dislocation are important. From past reports, the wear of the bearing surface may affect long-term results. This study evaluated the stress applied to the bearing surface by the combined use of the three-dimensional rigid spring model and the finite-element analysis.

METHODS

For contact pressure distribution of the bearing surface, interference analysis was performed using a three-dimensional rigid body spring model. Furthermore, stress was applied to the inner surface of the cup installed in the bone so that the same stress distribution obtained from the interference analysis was achieved. The finite-element analysis was then performed at each condition, which changed the inclination and anteversion angles of the cup to examine the relationship of maximum equivalent stress.

RESULTS AND DISCUSSION

The maximum equivalent stresses on the bearing surface under the condition with fixation of an anteversion angle of 0° were 0.78, 0.85, and 1.15 MPa at inclination angles of 25°, 40°, and 55°, respectively. The stress value at 55° was approximately 1.5 times greater than that at 25°. The maximum equivalent stresses on the bearing surface under the condition with fixation of an inclination angle of 40° were 0.85, 0.9, and 1.02 MPa at anteversion angles of 0°, 15°, and 30°, respectively. The stress value at 30° was approximately 1.2 times greater than that at 0°. This study suggests that large inclination and anteversion angles may enhance the stress on the bearing surface and affect long-term results.

Finite element analysis of mechanical behavior of human dysplastic hip joints: a systematic review

Developmental dysplasia of the hip (DDH) is a common condition predisposing to osteoarthritis (OA). Especially since DDH is best identified and treated in infancy before bones ossify, there is surprisingly a near-complete absence of literature examining mechanical behavior of infant dysplastic hips. We sought to identify current practice in finite element modeling (FEM) of DDH, to inform future modeling of infant dysplastic hips. We performed multi-database systematic review using PRISMA criteria. Abstracts (n = 126) fulfilling inclusion criteria were screened for methodological quality, and results were analyzed and summarized for eligible articles (n = 12). The majority of the studies modeled human adult dysplastic hips. Two studies focused on etiology of DDH through simulating mechanobiological growth of prenatal hips; we found no FEM-based studies in infants or children. Finite element models used either patient-specific geometry or idealized average geometry. Diversities in choice of material properties, boundary conditions, and loading scenarios were found in the finite-element models. FEM of adult dysplastic hips demonstrated generally smaller cartilage contact area in dysplastic hips than in normal joints. Contact pressure (CP) may be higher or lower in dysplastic hips depending on joint geometry and mechanical contribution of labrum (Lb). FEM of mechanobiological growth of prenatal hip joints revealed evidence for effects of the joint mechanical environment on formation of coxa valga, asymmetrically shallow acetabulum and malformed femoral head associated with DDH. Future modeling informed by the results of this review may yield valuable insights into optimal treatment of DDH, and into how and why OA develops early in DDH.

Application of a 3-dimensional printed navigation template in Bernese periacetabular osteotomies: A cadaveric study

The aim of the present study was to describe the application of 3D printed templates for intraoperative navigation and simulation of periacetabular osteotomies (PAOs) in a cadaveric model.Five cadaveric specimens (10 sides) underwent thin-slice computed tomographic scans of the ala of ilium downwards to the proximal end of femoral shaft. Bernese PAO was performed. Using Mimics v10.1 software (Materialise, Leuven, Belgium), 3D computed tomographic reconstructions were created and the 4 standard PAO bone cuts-ischial, pubic, anterior, and posterior aspects of the ilium-as well as rotation of the dislocated acetabular bone blocks were simulated for each specimen. Using these data, custom 3D printed bone-drilling templates of the pelvis were manufactured, to guide surgical placement of the PAO bone cuts. An angle fix wedge was designed and printed, to help accurately achieve the predetermined rotation angle of the acetabular bone block. Each specimen underwent a conventional PAO. Preoperative, postsimulation, and postoperative lateral center-edge angles, acetabular indices, extrusion indices, and femoral head coverage were measured and compared; P and t values were calculated for above-mentioned measurements while comparing preoperative and postoperative data, and also in postsimulation and postoperative data comparison.All 10 PAO osteotomies were successfully completed using the 3D printed bone-drilling template and angle fix wedge. No osteotomy entered the hip joint and a single posterior column fracture was observed. Comparison of preoperative and postoperative measurements of the 10 sides showed statistically significant changes, whereas no statistically significant differences between postsimulation and postoperative values were noted, demonstrating the accuracy and utility of the 3D printed templates.The application of patient-specific 3D printed bone-drilling and rotation templates in PAO is feasible and may facilitate improved clinical outcomes, through the use of precise presurgical planning and reduced surgical complications with the precisely guided bone drilling.

Mid-term radiological and clinical results of incomplete triple pelvic osteotomy

OBJECTIVE

The aim of this study was to assess clinical and radiological results of incomplete triple pelvic osteotomy in acetabular dysplasia.

PATIENTS AND METHODS

Twenty-six hips of 24 patients (5 males, 19 females) treated with incomplete triple pelvic osteotomy by a single surgeon from February 1995 to October 2001 were retrospectively reviewed at an average follow-up time of 12 years. The mean age at the time of surgery was 21.6 years (range: 14-41). Radiological evaluation was based on the central edge angle, acetabular angle, acetabular index, acetabular head index and lateralisation. Clinical and radiological scoring was performed using the Harris scoring system, Ömeroğlu scoring system and the Tönnis criteria for osteoarthritis.

RESULTS

There was significant improvements in all of the radiological parameters with 88.5% good radiological results, 96.2% excellent clinical results, no significant progression to osteoarthritis and no need for conversion to total hip arthroplasty. The rate of major complication was 11%. Retroversion was seen in 15.4% of the hips.

CONCLUSION

Our results support the use of incomplete triple pelvic osteotomy as a safe choice in the treatment of acetabular dysplasia as it offers clinical and radiological benefits and contributes to the prevention of osteoarthritis.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Does the optimal position of the acetabular fragment should be within the radiological normal range for all developmental dysplasia of the hip? A patient-specific finite element analysis

Background

The success of Bernese periacetabular osteotomy depends significantly on how extent the acetabular fragment can be corrected to its optimal position. This study was undertaken to investigate whether correcting the acetabular fragment into the so-called radiological “normal” range is the best choice for all developmental dysplasia of the hip with different severities of dysplasia from the biomechanical view? If not, is there any correlation between the biomechanically optimal position of the acetabular fragment and the severity of dysplasia?

Methods

Four finite element models with different severities of dysplasia were developed. The virtual periacetabular osteotomy was performed with the acetabular fragment rotated anterolaterally to incremental center-edge angles; then, the contact area and pressure and von Mises stress in the cartilage were calculated at different correction angles.

Results

The optimal position of the acetabular fragment for patients 1, 2, and 3 was when the acetabular fragment rotated 17° laterally (with the lateral center-edge angle of 36° and anterior center-edge angle of 58°; both were slightly larger than the “normal” range), 25° laterally following further 5° anterior rotation (with the lateral center-edge angle of 31° and anterior center-edge angle of 51°; both were within the “normal” range), and 30° laterally following further 10° anterior rotation (with the lateral center-edge angle of 25° and anterior center-edge angle of 40°; both were less than the “normal” range), respectively.

Conclusions

The optimal corrective position of the acetabular fragment is severity dependent rather than within the radiological “normal” range for developmental dysplasia of the hip. We prudently proposed that the optimal correction center-edge angle of mild, moderate, and severe developmental dysplasia of the hip is slightly larger than the “normal” range, within the “normal” range, and less than the lower limit of the “normal” range, respectively.

Electronic supplementary material

The online version of this article (doi:10.1186/s13018-016-0445-3) contains supplementary material, which is available to authorized users.

Computer-Assisted Rotational Acetabular Osteotomy for Patients with Acetabular Dysplasia

Rotational acetabular osteotomy (RAO) is a well-established surgical procedure for patients with acetabular dysplasia, and excellent long-term results have been reported. However, RAO is technically demanding and precise execution of this procedure requires experience with this surgery. The usefulness of computer navigation in RAO includes its ability to perform three-dimensional (3D) preoperative planning, enable safe osteotomy even with a poor visual field, reduce exposure to radiation from intraoperative fluoroscopy, and display the tip position of the chisel in real time, which is educationally useful as it allows staff other than the operator to follow the progress of the surgery. In our results comparing 23 hips that underwent RAO with navigation and 23 hips operated on without navigation, no significant difference in radiological assessment was observed. However, no perioperative complications were observed in the navigation group whereas one case of transient femoral nerve palsy was observed in non-navigation group. A more accurate and safer RAO can be performed using 3D preoperative planning and intraoperative assistance with a computed tomography-based navigation system.

Current Concepts in Hip Preservation Surgery: Part I

Context:

An evolution in conceptual understanding, coupled with technical innovations, has enabled hip preservation surgeons to address complex pathomorphologies about the hip joint to reduce pain, optimize function, and potentially increase the longevity of the native hip joint. Technical aspects of hip preservation surgeries are diverse and range from isolated arthroscopic or open procedures to hybrid procedures that combine the advantages of arthroscopy with open surgical dislocation, pelvic and/or proximal femoral osteotomy, and biologic treatments for cartilage restoration.

Evidence Acquisition:

PubMed and CINAHL databases were searched to identify relevant scientific and review articles from January 1920 to January 2015 using the search terms hip preservation, labrum, surgical dislocation, femoroacetabular impingement, peri-acetabular osteotomy, and rotational osteotomy. Reference lists of included articles were reviewed to locate additional references of interest.

Study Design:

Clinical review.

Level of Evidence:

Level 4.

Results:

Thoughtful individualized surgical procedures are available to optimize the femoroacetabular joint in the presence of hip dysfunction.

Conclusion:

A comprehensive understanding of the relationship between femoral and pelvic orientation, morphology, and the development of intra-articular abnormalities is necessary to formulate a patient-specific approach to treatment with potential for a successful long-term result.

Effects of rotational acetabular osteotomy on the mechanical stress within the hip joint in patients with developmental dysplasia of the hip

In this study we used subject-specific finite element analysis to investigate the mechanical effects of rotational acetabular osteotomy (RAO) on the hip joint and analysed the correlation between various radiological measurements and mechanical stress in the hip joint.

We evaluated 13 hips in 12 patients (two men and ten women, mean age at surgery 32.0 years; 19 to 46) with developmental dysplasia of the hip (DDH) who were treated by RAO.

Subject-specific finite element models were constructed from CT data. The centre–edge (CE) angle, acetabular head index (AHI), acetabular angle and acetabular roof angle (ARA) were measured on anteroposterior pelvic radiographs taken before and after RAO. The relationship between equivalent stress in the hip joint and radiological measurements was analysed.

The equivalent stress in the acetabulum decreased from 4.1 MPa (2.7 to 6.5) pre-operatively to 2.8 MPa (1.8 to 3.6) post-operatively (p < 0.01). There was a moderate correlation between equivalent stress in the acetabulum and the radiological measurements: CE angle (R = –0.645, p < 0.01); AHI (R = –0.603, p < 0.01); acetabular angle (R = 0.484, p = 0.02); and ARA (R = 0.572, p < 0.01).

The equivalent stress in the acetabulum of patients with DDH decreased after RAO. Correction of the CE angle, AHI and ARA was considered to be important in reducing the mechanical stress in the hip joint.

Cite this article: Bone Joint J 2015;97-B:492–7.

Development of a biomechanical guidance system for periacetabular osteotomy

PURPOSE

This paper presents and validates a computer-navigated system for performing periacetabular osteotomy (PAO) to treat developmental dysplasia of the hip. The main motivation of the biomechanical guidance system (BGS) is to plan and track the osteotomy fragment in real time during PAO while simplifying the procedure for less-experienced surgeons. The BGS aims at developing a platform for comparing biomechanical states of the joint with the current gold standard geometric assessment of anatomical angles. The purpose of this study was to (1) determine the accuracy with which the BGS tracks the hip joint through repositioning and (2) identify improvements to the workflow.

METHODS

Nineteen cadaveric validation studies quantified system accuracy, verified system application, and helped to refine surgical protocol. In two surgeries, navigation and registration accuracy were computed by affixing fiducials to two cadavers prior to surgery. All scenarios compared anatomical angle measurements and joint positioning as measured intraoperatively to postoperatively.

RESULTS

In the two cases with fiducials, computed fragment transformations deviated from measured fiducial transformations by 1.4 and 1.8 mm in translation and 1.0° and 2.2° in rotation, respectively. The additional seventeen surgeries showed strong agreement between intraoperative and postoperative anatomical angles, helped to refine the surgical protocol, and demonstrated system robustness.

CONCLUSION

Estimated accuracy with BGS appeared acceptable for future surgical applications. Several major system requirements were identified and addressed, improving the BGS and making it feasible for clinical studies.

A new discrete element analysis method for predicting hip joint contact stresses

Quantifying cartilage contact stress is paramount to understanding hip osteoarthritis. Discrete element analysis (DEA) is a computationally efficient method to estimate cartilage contact stresses. Previous applications of DEA have underestimated cartilage stresses and yielded unrealistic contact patterns because they assumed constant cartilage thickness and/or concentric joint geometry. The study objectives were to: (1) develop a DEA model of the hip joint with subject-specific bone and cartilage geometry, (2) validate the DEA model by comparing DEA predictions to those of a validated finite element analysis (FEA) model, and (3) verify both the DEA and FEA models with a linear-elastic boundary value problem. Springs representing cartilage in the DEA model were given lengths equivalent to the sum of acetabular and femoral cartilage thickness and gap distance in the FEA model. Material properties and boundary/loading conditions were equivalent. Walking, descending, and ascending stairs were simulated. Solution times for DEA and FEA models were ~7 s and ~65 min, respectively. Irregular, complex contact patterns predicted by DEA were in excellent agreement with FEA. DEA contact areas were 7.5%, 9.7% and 3.7% less than FEA for walking, descending stairs, and ascending stairs, respectively. DEA models predicted higher peak contact stresses (9.8-13.6 MPa) and average contact stresses (3.0-3.7 MPa) than FEA (6.2-9.8 and 2.0-2.5 MPa, respectively). DEA overestimated stresses due to the absence of the Poisson's effect and a direct contact interface between cartilage layers. Nevertheless, DEA predicted realistic contact patterns when subject-specific bone geometry and cartilage thickness were used. This DEA method may have application as an alternative to FEA for pre-operative planning of joint-preserving surgery such as acetabular reorientation during peri-acetabular osteotomy.

Subject-specific analysis of joint contact mechanics: application to the study of osteoarthritis and surgical planning

Advances in computational mechanics, constitutive modeling, and techniques for subject-specific modeling have opened the door to patient-specific simulation of the relationships between joint mechanics and osteoarthritis (OA), as well as patient-specific preoperative planning. This article reviews the application of computational biomechanics to the simulation of joint contact mechanics as relevant to the study of OA. This review begins with background regarding OA and the mechanical causes of OA in the context of simulations of joint mechanics. The broad range of technical considerations in creating validated subject-specific whole joint models is discussed. The types of computational models available for the study of joint mechanics are reviewed. The types of constitutive models that are available for articular cartilage are reviewed, with special attention to choosing an appropriate constitutive model for the application at hand. Issues related to model generation are discussed, including acquisition of model geometry from volumetric image data and specific considerations for acquisition of computed tomography and magnetic resonance imaging data. Approaches to model validation are reviewed. The areas of parametric analysis, factorial design, and probabilistic analysis are reviewed in the context of simulations of joint contact mechanics. Following the review of technical considerations, the article details insights that have been obtained from computational models of joint mechanics for normal joints; patient populations; the study of specific aspects of joint mechanics relevant to OA, such as congruency and instability; and preoperative planning. Finally, future directions for research and application are summarized.

Effect of intra-articular lesions on the outcome of periacetabular osteotomy in patients with symptomatic hip dysplasia

In order to clarify how intra-articular lesions influence the survival of a periacetabular osteotomy in patients with dysplasia of the hip, we performed an observational study of 121 patients (121 hips) who underwent a transposition osteotomy of the acetabulum combined with an arthroscopy. Their mean age was 40.2 years (13 to 64) and the mean follow-up was 9.9 years (2 to 18). Labral and cartilage degeneration tended to originate from the anterosuperior part of the acetabulum, followed by the femoral side. In all, eight hips (6.6%) had post-operative progression to Kellgren–Lawrence grade 4 changes, and these hips were associated with the following factors: moderate osteoarthritis, decreased width of the joint space, joint incongruity, and advanced intra-articular lesions (subchondral bone exposure in the cartilage and a full-thickness labral tear). Multivariate analysis indicated subchondral bone exposure on the femoral head as an independent risk factor for progression of osteoarthritis (p = 0.003). In hips with early stage osteoarthritis, femoral subchondral bone exposure was a risk factor for progression of the grade of osteoarthritis.

Although the outcome of transposition osteotomy of the acetabulum was satisfactory, post-operative progression of osteoarthritis occurred at a high rate in hips with advanced intra-articular lesions, particularly in those where the degenerative process had reached the point of femoral subchondral bone exposure.

Pelvic positioning creates error in CT acetabular measurements

BACKGROUND

CT allows for accurate measurement of acetabular orientation and shape, but malpositioning of the pelvis may lead to measurement variance.

PURPOSE

We therefore sought to determine: (1) whether acetabular anteversion measurements using the femoral head centers differed from those using the posterior ischia, and (2) the extent to which changing obliquity, rotation, and tilt of a pelvis in a CT scanner affected the measurement of acetabular variables.

METHODS

A radiopaque human pelvis model with articulated hips was suspended from a plastic sheet as part of an adjustable frame. Changes in the transverse and sagittal planes created rotation and tilt, while rotating the frame in the coronal plane created obliquity. CT scans were obtained, varying the combinations of obliquity, rotation, and tilt by intervals of 5°, up to 20°. Acetabular anteversion (AA), anterior acetabular sector angle (AASA), posterior acetabular sector angle (PASA), and horizontal acetabular sector angle (HASA) were measured.

RESULTS

The two methods for measuring AA yielded values differing by 1° to 4° but correlated (r = 0.981) across the spectrum of pelvis positioning. Pelvic obliquity and tilt were linearly associated with changes in the measurements. For each 1°-increase in pelvic obliquity, AA changed -0.4°, and AASA, PASA, and HASA changed 1.93°, 0.99°, and 2.80°, respectively. For each 1°-increase in pelvic tilt, AA changed 0.8°, and AASA, PASA, and HASA changed -1.07°, 0.52°, and -0.51°, respectively. Rotation had no affect on the variables.

CONCLUSIONS

Small changes in pelvic obliquity and tilt were associated with variances in acetabular measurements. The measured changes were directly proportional to the changes in obliquity and tilt, and were additive. Pelvic rotation created no changes in measurement.

Subchondral insufficiency fracture of the femoral head may be associated with hip dysplasia: a pilot study

BACKGROUND

Subchondral insufficiency fracture of the femoral head occurs mainly in elderly patients with osteoporosis. Spontaneous resolution is observed after nonoperative treatment in some patients whereas other show progressive joint destruction requiring THA. Several studies report the occurrence of subchondral insufficiency fracture of the femoral head in dysplastic hips.

QUESTIONS/PURPOSES

We asked whether the extent of hip dysplasia or osteoporosis was greater in patients with subchondral insufficiency fracture of the femoral head than in normal control subjects.

PATIENTS AND METHODS

We compared the clinical and imaging findings of 13 patients with subchondral insufficiency fractures of the femoral head and 12 patients scheduled for TKA with asymptomatic hips. Age, gender, and body mass index were comparable in the two groups.

RESULTS

Higher mean Sharp angles, lower acetabular head indices, lower center-edge angles, and higher acetabular roof angles in patients with subchondral insufficiency fracture of the femoral head than in those with asymptomatic hips suggested a greater degree of hip dysplasia. Bone mineral density and serum levels of Type I collagen cross-linked N-telopeptide and bone alkaline phosphatase were similar in the two groups.

CONCLUSIONS

We speculate an excessive amount of stress on the acetabular edge from dysplasia may be associated with the occurrence of subchondral insufficiency fracture of the femoral head.

Periacetabular osteotomy reduces the dynamic instability of dysplastic hips

We compared the dynamic instability of 25 dysplastic hips in 25 patients using triaxial accelerometry before and one year after periacetabular osteotomy. We also evaluated the hips clinically using the Harris hip score and assessed acetabular orientation by radiography before surgery and after one year. The mean overall magnitude of acceleration was significantly reduced from 2.30 m/s(2) (sd 0.57) before operation to 1.55 m/s(2) (sd 0.31) afterwards. The mean Harris hip score improved from 78.08 (47 to 96) to 95.36 points (88 to 100). The radiographic parameters all showed significant improvements. This study suggests that periacetabular osteotomy provides pain relief, improves acetabular cover and reduces the dynamic instability in patients with dysplastic hips.

Three-dimensional mechanical evaluation of joint contact pressure in 12 periacetabular osteotomy patients with 10-year follow-up

BACKGROUND AND PURPOSE

Because of the varying structure of dysplastic hips, the optimal realignment of the joint during periacetabular osteotomy (PAO) may differ between patients. Three-dimensional (3D) mechanical and radiological analysis possibly accounts better for patient-specific morphology, and may improve and automate optimal joint realignment.

PATIENTS AND METHODS

We evaluated the 10-year outcomes of 12 patients following PAO. We compared 3D mechanical analysis results to both radiological and clinical measurements. A 3D discrete-element analysis algorithm was used to calculate the pre- and postoperative contact pressure profile within the hip. Radiological angles describing the coverage of the joint were measured using a computerized approach at actual and theoretical orientations of the acetabular cup. Quantitative results were compared using postoperative clinical evaluation scores (Harris score), and patient-completed outcome surveys (q-score) done at 2 and 10 years.

RESULTS

The 3D mechanical analysis indicated that peak joint contact pressure was reduced by an average factor of 1.7 subsequent to PAO. Lateral coverage of the femoral head increased in all patients; however, it did not proportionally reduce the maximum contact pressure and, in 1 case, the pressure increased. This patient had the lowest 10-year q-score (70 out of 100) of the cohort. Another hip was converted to hip arthroplasty after 3 years because of increasing osteoarthritis.

INTERPRETATION

The 3D analysis showed that a reduction in contact pressure was theoretically possible for all patients in this cohort, but this could not be achieved in every case during surgery. While intraoperative factors may affect the actual surgical outcome, the results show that 3D contact pressure analysis is consistent with traditional PAO planning techniques (more so than 2D analysis) and may be a valuable addition to preoperative planning and intraoperative assessment of joint realignment.

Evaluation of a computerized measurement technique for joint alignment before and during periacetabular osteotomy

Periacetabular osteotomy (PAO) is intended to treat a painful dysplastic hip. Manual radiological angle measurements are used to diagnose dysplasia and to define regions of insufficient femoral head coverage for planning PAO. No method has yet been described that recalculates radiological angles as the acetabular bone fragment is reoriented. In this study, we propose a technique for computationally measuring the radiological angles from a joint contact surface model segmented from CT-scan data. Using oblique image slices, we selected the lateral and medial edge of the acetabulum lunate to form a closed, continuous, 3D curve. The joint surface is generated by interpolating the curve, and the radiological angles are measured directly using the 3D surface. This technique was evaluated using CT data for both normal and dysplastic hips. Manual measurements made by three independent observers showed minor discrepancies between the manual observations and the computerized technique. Inter-observer error (mean difference +/- standard deviation) was 0.04 +/- 3.53 degrees for Observer 1; -0.46 +/- 3.13 degrees for Observer 2; and 0.42 +/- 2.73 degrees for Observer 3. The measurement error for the proposed computer method was -1.30 +/- 3.30 degrees . The computerized technique demonstrates sufficient accuracy compared to manual techniques, making it suitable for planning and intraoperative evaluation of radiological metrics for periacetabular osteotomy.

Safe fixation with two acetabular screws after Ganz periacetabular osteotomy

BACKGROUND AND PURPOSE

With Ganz periacetabular osteotomy, the osteotomized acetabular fragment is reoriented in an adducted, extended, and rotated position. The acetabular fragment is fixated with 2 screws and the patients are allowed 30 kg of weight bearing immediately after surgery. We were interested in examining the stability of the reoriented acetabulum after Ganz osteotomy; thus, the migration of the acetabular fragment was assessed by radiostereometry.

PATIENTS AND METHODS

32 dysplastic patients (27 females; 32 hips) were included in the study. Median age was 39 (20-57) years. Radiostereometric examinations were done at 1 week, 4 weeks, 8 weeks and 6 months. Data are presented as mean (SD).

RESULTS

6 months postoperatively, the acetabular fragment had migrated 0.7 (0.8) mm medially, and 0.7 (0.5) mm proximally. Mean rotation in adduction was 0.5 degrees (1.3). In other directions, mean migration was below 0.5 mm/degrees. There were no statistically significant differences in migration at 8 weeks and 24 weeks postoperatively regarding translation and rotation.

INTERPRETATION

Due to the limited amount of migration, we find our postoperative partial weight-bearing regime safe.

Preoperative planning in pelvic and acetabular surgery: the value of advanced computerised planning modules

An experimental computer program for virtual operation of fractured pelvis and acetabulum based on real data of the fracture is presented. The program consists of two closely integrated tools, the 3D viewing tools and the surgeon simulation tools. Using 3D viewing tools the virtual model of a fractured pelvis is built. This procedure is performed by computer engineers. Data from CT of a real injury in DICOM format are used. With segmentation process each fracture segment becomes a separate object and is assigned a different colour. The virtual object is then transferred to the personal computer of the surgeon. Bone fragments can be moved and rotated in all three planes and reduction is performed. After reduction, fixation can be undertaken. The appropriate ostheosynthetic material can be chosen. Contouring of the plate is performed automatically to the reduced pelvis. The screws can be inserted into the plate or across the fracture. The direction and length of the screws is controlled by turning the pelvis or by making bones more transparent. The modeling of the plate in all three axes can be recorded as the exact length of the screws. There is also a simulation tool for intraoperative C-arm imaging in all directions. All the steps of the procedure are recorded and printed out. Postoperative matching of real operation and virtual procedure is also possible. We operated on 10 cases using virtual preoperative planning and found it very useful. The international study is still in progress. One case is presented demonstrating all the possibilities of the virtual planning and surgery. The presented computer program is an easily usable application which brings significant value and new opportunities in clinical practice (preoperative planning), teaching and research.