Clinical Significance of Lateral Pedicle Screw Malposition in Lumbar Spine Fusion

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

Our objective was to determine whether lateral pedicle screw breach affects fusion rates and patient-reported outcomes in lumbar fusion surgery.

SUMMARY OF BACKGROUND DATA

Although lateral pedicle screw malposition is considered relatively benign, few studies have focused specifically on clinical outcomes or fusion rates associated with lateral screw malposition.

METHODS

Twelve-month postoperative computed tomography scans were reviewed for lateral breach, severity of breach, and fusion status. Patients with lateral breach were compared with patients with no breach. Outcome measures included Numerical Pain Rating Scale for back and leg pain, Oswestry Disability Index, and SF-36 physical function (SF-36 PF). Multivariable linear and logistic regression and were adjusted for age, procedure, level, and/or baseline pain score.

RESULTS

Forty-five patients (31%) demonstrated 1 or more lateral breaches as compared with 99 patients without breach. After adjusting for baseline scores and fusion level, patients with 2 or more screw breaches experienced SF-36 PF score improvements that were 3.43 points less ( P =0.016) than patients with no lateral breach. After adjusting for baseline Numerical Pain Rating Scale, there was also a significant decrease in the odds of achieving minimally clinical important difference in back pain relief in these patients. There was no observed effect of lateral breach on the odds of successful fusion.

CONCLUSIONS

The current study did not observe an association between laterally malpositioned pedicle screws and nonunion. However, results are consistent with a negative effect on SF-36 PF scores and self-reported back pain at 12 months.

Early patellofemoral cartilage and bone pathology in a rat model of noninvasive anterior cruciate ligament rupture

OBJECTIVE

Anterior cruciate ligament rupture (ACLR) is a risk factor for the development of post-traumatic osteoarthritis (PTOA). While PTOA in the tibiofemoral joint compartment is well-characterized, very little is known about pathology in the patellofemoral compartment after ACL injury. Here, we evaluated the extent to which ACLR induces early patellofemoral joint damage in a rat model.

METHODS

Adult female Lewis rats were randomized to noninvasive ACLR or Sham. Two weeks post-injury, contrast-enhanced micro-computed tomography (µCT) of femoral and patellar cartilage was performed using 20% v/v ioxaglate. Morphometric parameters of femoral trochlear and patellar cartilage, subchondral bone, and trabecular bone were derived from µCT. Sagittal Safranin-O/Fast-Green-stained histologic sections were graded using the OARSI score in a blinded fashion.

RESULTS

Cartilage and bone remodelling consistent with an early PTOA phenotype were observed in both femoral trochleas and patellae. ACLR caused osteophyte formation of the patella and pathology in the superficial zone of articular cartilage, including surface fibrillation, fissures, increased cellularity, and abnormal chondrocyte clustering. There were significant increases in thickness of patellar and trochlear cartilage. Loss of subchondral bone thickness, bone volume fraction, and tissue mineral density, as well as changes to patellar and trochlear trabecular microarchitecture, were indicative of catabolic bone remodelling. Several injury-induced changes, including increased cartilage thickness and trabecular spacing and decreased trabecular number were more severe in the patella compared to the trochlea.

CONCLUSION

The patellofemoral joint develops mild but evident pathology in the early period following ACL rupture, extending the utility of this model to the study of patellofemoral PTOA.

Pedicle Screw-Associated Violation of the Adjacent Unfused Facet Joint: Clinical Outcomes and Fusion Rates

STUDY DESIGN

Retrospective review of a prospective randomized trial.

OBJECTIVES

To compare outcome scores and fusion rates in patients with and without pedicle screw-associated facet joint violation (FJV) after a single-level lumbar fusion.

METHODS

Clinical outcomes data and computed tomography (CT) imaging were reviewed for 157 patients participating in a multicenter prospective trial. Post-operative CT scans at 12-months follow-up were examined for fusion status and FJV. Patient-reported outcomes (PROs) included Oswestry Disability Index (ODI) and Visual Analog Scale (VAS) for leg and low back pain. Chi-square test of independence was used to compare proportions between groups on categorical measures. Two-sample t-test was used to identify differences in mean patient outcome scores. Logistic regression models were performed to determine association between FJV and fusion rates.

RESULTS

Of the 157 patients included, there were 18 (11.5%) with FJV (Group A) and 139 (88.5%) without FJV (Group B). Patients with FJV experienced less improvement in ODI (P = .004) and VAS back pain scores (P = .04) vs patients without FJV. There was no difference in mean VAS leg pain (P = .4997). The rate of fusion at 12-months for patients with FJV (27.8%) was lower compared to those without FJV (71.2%) (P = .0002). Patients with FJV were 76% less likely to have a successful fusion at 12-months.

CONCLUSION

Pedicle screw-associated violation of the adjacent unfused facet joint during single-level lumbar fusion is associated with less improvement in back pain, back pain-associated disability, and a lower fusion rate at 1-year after surgery.

Traumatic joint injury induces acute catabolic bone turnover concurrent with articular cartilage damage in a rat model of posttraumatic osteoarthritis

Assess acute alterations in bone turnover, microstructure, and histomorphometry following noninvasive anterior cruciate ligament rupture (ACLR). Twelve female Lewis rats were randomized to receive noninvasive ACLR or Sham loading (n = 6/group). In vivo μCT was performed at 3, 7, 10, and 14 days postinjury to quantify compartment-dependent subchondral (SCB) and epiphyseal trabecular bone remodeling. Near-infrared (NIR) molecular imaging was used to measure in vivo bone anabolism (800 CW BoneTag) and catabolism (Cat K 680 FAST). Metaphyseal bone remodeling and articular cartilage morphology was quantified using ex vivo μCT and contrast-enhanced µCT, respectively. Calcein-based dynamic histomorphometry was used to quantify bone formation. OARSI scoring was used to assess joint degeneration, and osteoclast number was quantified on TRAP stained-sections. ACLR induced acute catabolic bone remodeling in subchondral, epiphyseal, and metaphyseal compartments. Thinning of medial femoral condyle (MFC) SCB was observed as early as 7 days postinjury, while lateral femoral condyles (LFCs) exhibited SCB gains. Trabecular thinning was observed in MFC epiphyseal bone, with minimal changes to LFC. NIR imaging demonstrated immediate and sustained reduction of bone anabolism (~15%-20%), and a ~32% increase in bone catabolism at 14 days, compared to contralateral limbs. These findings were corroborated by reduced bone formation rate and increased osteoclast numbers, observed histologically. ACLR-injured femora had significantly elevated OARSI score, cartilage thickness, and cartilage surface deviation. ACL rupture induces immediate and sustained reduction of bone anabolism and overactivation of bone catabolism, with mild-to-moderate articular cartilage damage at 14 days postinjury.

Local and Systemic In Vivo Responses to Osseointegrative Titanium Nanotube Surfaces

Orthopedic implants requiring osseointegration are often surface modified; however, implants may shed these coatings and generate wear debris leading to complications. Titanium nanotubes (TiNT), a new surface treatment, may promote osseointegration. In this study, in vitro (rat marrow-derived bone marrow cell attachment and morphology) and in vivo (rat model of intramedullary fixation) experiments characterized local and systemic responses of two TiNT surface morphologies, aligned and trabecular, via animal and remote organ weight, metal ion, hematologic, and nondecalcified histologic analyses. In vitro experiments showed total adherent cells on trabecular and aligned TiNT surfaces were greater than control at 30 min and 4 h, and cells were smaller in diameter and more eccentric. Control animals gained more weight, on average; however, no animals met the institutional trigger for weight loss. No hematologic parameters (complete blood count with differential) were significantly different for TiNT groups vs. control. Inductively coupled plasma mass spectrometry (ICP-MS) showed greater aluminum levels in the lungs of the trabecular TiNT group than in those of the controls. Histologic analysis demonstrated no inflammatory infiltrate, cytotoxic, or necrotic conditions in proximity of K-wires. There were significantly fewer eosinophils/basophils and neutrophils in the distal region of trabecular TiNT-implanted femora; and, in the midshaft of aligned TiNT-implanted femora, there were significantly fewer foreign body giant/multinucleated cells and neutrophils, indicating a decreased immune response in aligned TiNT-implanted femora compared to controls.

Longitudinal characterization of intervertebral disc remodeling following acute annular injury in a rat model of degenerative disc disease

Objective: Characterize 3D remodeling of the rat intervertebral disc (IVD) following acute annular injury via in vivo micro-computed tomography (µCT), ex vivo contrast-enhanced (CE)-µCT, and histology. Design: Female Lewis rats (N = 4/group) underwent either sham surgery or anterior annular puncture to L3-L4 and L5-L6 (n = 8 IVDs/group) to induce IVD degeneration. Rats were allowed ad libidum cage activity before and after surgery and underwent in vivo µCT scanning at baseline and every 2 weeks post-op for 12 weeks to characterize longitudinal changes in IVD height. At 12 weeks, lumbar spines were dissected and underwent CE-µCT scanning to characterize endpoint glycosaminoglycan distribution and nucleus pulposus (NP) volume ratio. Spines were processed for safranin-O-stained sagittal histology, and IVD degeneration was graded via the Rutges scale. Results: Puncture IVDs exhibited loss of IVD height at all time points from 4 weeks onward compared to Sham-the most severe height loss occurred posteriorly, with significant changes also occurring in the NP and laterally. Puncture IVDs exhibited higher CE-µCT attenuation, indicative of lower glycosaminoglycan content, and reduced NP volume ratio compared to Sham. Histologically, Puncture IVDs had higher Rutges damage scores and exhibited reduced NP cellularity and hydration, disorganized annulus fibrosus (AF) lamellae with evidence of the stab tract, and indistinct AF-NP border compared to Sham. Conclusions: Characterization of the complex, 3D alterations involved in the onset and early progression of IVD degeneration can foster greater understanding of the pathoetiology of IVD degeneration and may inform future studies assessing more sensitive diagnostic techniques or novel therapies.

Intradiscal Delivery of Anabolic Growth Factors and a Metalloproteinase Inhibitor in a Rabbit Acute Lumbar Disc Injury Model

BACKGROUND

The purpose of our study was to examine the effect of controlled delivery of TGF-β₃, BMP-4, and TIMP-2 with a biocompatible biopolymer, chitosan, on an acutely injured intervertebral disc (IVD) in a rabbit model.

METHODS

After conducting an in vitro analysis of the chondrogenic capacity of the biomolecule cocktail use (ie, TGF-β₃, BMP-4, and TIMP-2) and confirming stem cell viability in chitosan hydrogel, 15 New Zealand white rabbits underwent a lateral approach of the L1 to L4 IVDs. In each rabbit, the L2 to L3 IVD was left pristine, whereas the L1 to L2 and the L3 to L4 IVDs in each rabbit underwent nucleotomy via a 25-G needle, and the animal was subsequently randomized to no further treatment (defect only), chitosan alone, Chitosan + TGF-β₃ + BMP-4, or chitosan + TGF-β₃ + BMP-4 + TIMP-2. At 6 weeks after injury and intervention, the rabbits were killed and spines harvested to undergo quantitative T2 magnetic resonance imaging (MRI) and subsequent histologic analysis.

RESULTS

In the in vitro analysis, cells treated with experimental media containing TGF-β₃, BMP-4, and TIMP-2 exhibited staining indicative of GAG production and began to exhibit a chondrocytic morphology. Quantitative T2 MRI mapping demonstrates that discs treated with chitosan, chitosan containing TGF-β₃ and BMP-4, or chitosan containing TGF-β₃, BMP-4, and TIMP-2 had consistently higher T2 relaxation times compared with defect-only discs. When the T2 relaxation times of each treatment group and defect-only discs were normalized to the healthy control disc, it was found that the T2 relaxation time of discs treated with chitosan containing TGF-β₃ and BMP-4 and discs treated with chitosan containing TGF-β₃, BMP-4, and TIMP-2 were significantly greater compared with defect-only discs (P = .048 and P = .013, respectively). Histologically, animals that received chitosan only, or chitosan with TGF-β₃ and BMP-4, showed a significantly higher intensity of Safranin-O staining (P = .016 and P = .02, respectively) compared with control discs, whereas the difference in staining intensity in animals that received chitosan loaded with TGF-β₃, BMP-4, and TIMP-2 failed to achieve significance (P = .161).

CONCLUSIONS

A combination of chitosan, TGF-β₃, and BMP-4 was effective at promoting regeneration in an acute disc injury rabbit model, whereas TIMP-2 did not have a significant effect.

0108 Brief Periods of Sleep and Quiet Rest Equivalently Benefit Memory Consolidation

Introduction

Past research has demonstrated that sleep benefits the consolidation of memories. However, more recent studies have suggested that quiet rest could have similar benefits for memory. Here, we examined the effect of a brief period of sleep, quiet rest, or active wakefulness on declarative and procedural memory. We hypothesized that sleep and quiet rest would equally benefit memory, compared to a period of active wakefulness.

Methods

After completing a declarative (Icelandic-English word pairs) and procedural memory task (the Motor Sequence Task (MST)), participants began a 30-min retention period with PSG monitoring, in which they either slept (n=24), quietly rested with their eyes closed (n=22), or completed a distractor task (n=28). Following the retention period, participants were tested on the same memory tasks they completed earlier.

Results

Percent improvement on the MST from the end of training to the end of the test session differed by condition, F(2, 73)=4.21, p=.019. Sleep and quiet rest led to nearly identical improvement (p=.95), with improvement in both of these conditions being significantly greater than in active wake (sleep vs. active wake: p=.01; quiet rest vs. active wake: p=.02). Similarly, retention of the Icelandic-English word pairs differed by condition (F(2, 73)=5.68, p=.005), with sleep and quiet rest demonstrating nearly identical memory change over time (p=.81), and retention in both of these conditions being significantly higher than in active wake (sleep vs. active wake: p=.007; quiet rest vs. active wake: p=.004).

Conclusion

These data suggest that sleep and quiet rest can exert an equivalent effect on memory consolidation for both declarative and procedural memory, at least across very brief retention durations. Therefore, neurobiology specific to sleep might not be necessary to induce offline improvement in memory across short intervals.

Support

This research was supported by National Institutes of Health Award R15MH107891.

Potential significance of facet joint fusion or posteromedial fusion observed on CT imaging following attempted posterolateral or posterior interbody fusion

BACKGROUND CONTEXT

Radiologic evidence of successful lumbar fusion has traditionally been based on bridging bone spanning the intertransverse processes (posterolateral fusion or PLF) or disc space (interbody fusion, or IBF). Often, postoperative computed tomography (CT) of unsuccessful PLF and IBF demonstrates bridging bone across the facet joints or connecting the medial transverse process to the ipsilateral superior articular facet of the caudal vertebra. The significance of this finding in terms of implant stability and clinical outcomes has not previously been reported.

PURPOSE

To determine rates of facet joint fusion (FJF)/posteromedial fusion (PMF) following single-level PLF surgery, with or without interbody. A secondary goal was to determine comparative outcomes associated with isolated FJF/PMF versus PLF and IBF.

STUDY DESIGN

Retrospective CT-based review.

PATIENT SAMPLE

Two hundred-three patients underwent single-level PLF surgery with local autograft bone or PLF+IBF with local autograft bone.

OUTCOME MEASURES

Fusion was assessed at 6-months and 12-months postoperatively using strict CT criteria. Patient reported outcome measures included visual analogue scale (VAS) scores for back pain and leg pain, Oswestry Disability Index (ODI), and SF-36.

METHODS

Thin-cut CTs were examined to determine whether successful fusion had occurred in seven different anatomic locations. One-way analysis of variance was used to determine significant differences in mean outcome scores and other continuous measures between groups at baseline and follow-up. Chi-square test of independence or Fisher's exact test was used to compare proportions between groups on categorical measures.

RESULTS

Two hundred-three patients and 157 patients completed 6- and 12 month follow-up, respectively. At 12 months, 35.1% of PLF patients demonstrated successful unilateral/bilateral PLF. Including unilateral or bilateral FJF/PMF, the fusion rate was 73.4%. Among PLF+IBF patients, 38.1% demonstrated successful IBF/PLF. Including unilateral or bilateral FJF/PMF, the fusion rate was 55.6%. All fusion groups demonstrated significant improvement in back pain and leg pain scores as well as ODI and SF-36 PF at 6- and 12 months compared with pre-op. No significant difference in any outcome measure, rates of implant loosening or reoperation was observed between successful PLF/IBF and FJF/PMF groups.

CONCLUSIONS

FJF/PMF is often observed on postoperative CT evaluation following surgery originally performed to achieve PLF or IBF. Short-term follow-up suggests no significant difference in implant loosening rates or patient reported outcomes when FJF/PMF is observed versus PLF or IBF in such patients. Long-term clinical outcomes of FJF/PMF versus PLF or IBF remain unknown. These findings apply solely to single-level instrumented spinal fusion surgery utilizing pedicle screws with or without IBF.

Effect of local retropharyngeal steroids on fusion rate after anterior cervical discectomy and fusion

BACKGROUND CONTEXT

Anterior cervical discectomy and fusion (ACDF) is considered the gold standard surgical intervention for cervical myelopathy and radiculopathy. Obtaining a solid fusion is an important goal of ACDF, and doing so has correlated with favorable clinical outcomes. A common complication after surgery is postoperative dysphagia. Multiple techniques have been utilized in attempt to prevent and treat dysphagia, including use of retropharygeal steroids.

PURPOSE

To examine the effects of retropharyngeal steroids on fusion rate in ACDF.

STUDY DESIGN

Case control METHODS: Forty-two patients who received local retropharyngeal steroids during ACDF surgery were the sample patient population. The control group consisted of matched cases based on number of spinal levels treated and age at approximately 1:2 case to control ratio. Data were collected on demographic variables, as well as operative and postoperative courses. Radiographic data were collected and fusion determined by <2 mm motion on flexion/extension views and bridging bone. Data were compared between case and control populations. Continuous variables were compared using Student's t test and nominal/ordinal values were compared using Z-test. Fusion status was assessed using Pearson chi-squared test.

RESULTS

A total of 121 patients were reviewed based on matching status and sufficient follow-up. The case and control groups were successfully matched based on age, spinal levels treated, and smoking status. The case group had an overall fusion rate of 64.7%, whereas the control group had a fusion rate of 91%. When analyzed at each level of attempted fusion, the case group had a fusion rate of 81% compared to 93% in the control group. There was a single patient in the case group that developed esophageal rupture and retropharygeal abscess requiring surgical intervention with irrigation, debridement and repair at 8 months after index operation.

CONCLUSIONS

The use of retropharyngeal steroids to mitigate postoperative dysphagia is associated with a decreased rate of radiographic fusion in ACDF surgery.

Biomechanical properties of the repaired and non-repaired rat supraspinatus tendon in the acute postoperative period

PURPOSE

The rat rotator cuff (RC) model is used to study RC pathology and potential treatment; however, native scar-mediated healing allows the rat RC to recover at 4-6 weeks but little is known about acute healing. This study characterized the properties of the repaired and non-repaired rat RC following surgical detachment.

MATERIALS AND METHODS

Forty-eight rats underwent surgical RC detachment and received surgical repair (Repair) or left unrepaired (Defect) to either 12 or 19 days. Healthy controls were obtained from contralateral limbs. Biomechanical properties were assessed using stress relaxation and failure testing and mechanical modeling performed using quasilinear viscoelastic (QLV) and structurally based elastic models. Histology and micro-magnetic resonance imaging were used to qualitatively grade tendon-to-bone healing.

RESULTS

Repair and Defect exhibited significantly inferior mechanical properties compared to Healthy at both time points. Repair had significant increases in peak, equilibrium, and ultimate stress, modulus, and stiffness and significant decreases in cross-sectional area, % relaxation, and QLV constant "C" between 12 and 19 days, whereas Defect showed no change.

CONCLUSIONS

This study demonstrates acute differences in mechanical properties of the rat supraspinatus tendon in the presence and absence of surgical repair. Understanding the longitudinal recovery of mechanical properties can facilitate more accurate characterization of RC pathology or future treatments.

Analysis of Retrieved Unicompartmental Knee Implants and Tissue: Third-Body Wear as a Potential Contributor to Progression of Arthritis to Adjacent Compartments

Unicompartmental knee arthroplasty (UKA) for the treatment of single-compartment osteoarthritis has been associated with polyethylene wear and progression of osteoarthritis into adjacent compartments, leading to revision. In this study, damage and clinical failure modes of retrieved UKA implants were investigated and protein expression profiles between articular cartilage adjacent to UKA and primary osteoarthritic cartilage were compared. Fifty retrieved UKA implants were analyzed for various damage. Records review and radiographic analysis were performed to collect clinical data and implant characteristics. Cartilage harvested from revision UKA and primary total knee arthroplasty surgeries was characterized with a proteome profiling array detecting levels of 36 different cytokines, chemokines, and acute phase inflammatory proteins. Progression of osteoarthritis (n=18, 36%) and component loosening (n=17, 34%) were the most common reasons for revision. Liners exhibited the highest frequency of damage modes. Progression of arthritis positively correlated with radiographic presence of extruded bone cement and burnishing of liner components. A protein-level profile between revision UKA and primary total knee arthroplasty cartilage showed 12 differentially expressed cytokines. Failure of UKA may be secondary to the effects of wear debris particulate migration into the adjacent compartment, suggesting an additional pathway of cartilage damage manifesting as traditional clinical symptoms. [Orthopedics. 2019; 42(3):149-157.].

Nondestructive, indirect assessment of the biomechanical properties of the rat intervertebral disc using contrast-enhanced μCT

Mechanical characterization of the intervertebral disc involves labor-intensive and destructive experimental methodology. Contrast-enhanced micro-computed tomography is a nondestructive imaging modality for high-resolution visualization and glycosaminoglycan quantification of cartilaginous tissues. The purpose of this study was to determine whether anionic and cationic contrast-enhanced micro-computed tomography of the intervertebral disc can be used to indirectly assess disc mechanical properties in an ex vivo model of disc degeneration. L3/L4 motion segments were dissected from female Lewis rats. To deplete glycosaminoglycan, samples were treated with 0 U/ml (Control) or 5 U/ml papain. Contrast-enhanced micro-computed tomography was performed following incubation in 40% Hexabrix (anionic) or 30 mg I/ml CA⁴⁺ (cationic) for 24 h (n = 10/contrast agent/digestion group). Motion segments underwent cyclic mechanical testing to determine compressive and tensile modulus, stiffness, and hysteresis. Glycosaminoglycan content was determined using the dimethylmethylene blue assay. Correlations between glycosaminoglycan content, contrast-enhanced micro-computed tomography attenuation, and mechanical properties were assessed via the Pearson correlation. The predictive accuracy of attenuation on compressive properties was assessed via repeated random sub-sampling cross validation. Papain digestion produced significant decreases in glycosaminoglycan content and corresponding differences in attenuation and mechanical properties. Attenuation correlated significantly to glycosaminoglycan content and to all compressive mechanical properties using both Hexabrix and CA⁴⁺ . Predictive linear regression models demonstrated a predictive accuracy of attenuation on compressive modulus and stiffness of 79.8-86.0%. Contrast-enhanced micro-computed tomography was highly predictive of compressive mechanical properties in an ex vivo simulation of disc degeneration and may represent an effective modality for indirectly assessing disc compressive properties. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2030-2038, 2018.

Quantitative evaluation of retrieved reverse total shoulder arthroplasty liner surface deviation and volumetric wear

Polyethylene wear is a known complication in total joint arthroplasty, however, in vivo wear rates in reverse total shoulder arthroplasty (RTSA) remain largely unknown. This study aimed to quantify volumetric and surface deviation changes in retrieved RTSA humeral liners using a novel micro-computed tomography (μCT)-based technique. After IRB-approval, 32 humeral liners (single manufacturer and model) with term-of-service greater than 90 days were analyzed. Clinical demographics and surgical data were collected via chart review. Unworn liners were used as geometric controls. Retrieved and unworn liners underwent μCT scanning. Retrieved liner volumes were isolated, co-registered to controls of matching geometry, and surface deviations of the articulation surface and rim were computed. Differences in total volume loss (TVL), volumetric wear rate (VWR), and surface deviation were reported. Semi-quantitative grading evaluated rim damage presence and severity. Mean term-of-service for all liners was 2.07 ± 1.33 years (range: 0.30-4.73). Mean TVL and VWR were 181.3 ± 208.2 mm³ and 114.5 ± 160.3 mm³ /year, respectively. Mean articulation and rim surface deviations were 0.084 ± 0.065 and 0.177 ± 0.159 mm, respectively. Articulation surface deviation was positively correlated to term-of-service. Rim damage was present on 63% of liners and correlated significantly to rim surface deviation. This study reports in vivo wear rates of retrieved RTSA implants. Our results demonstrate volumetric and articulation surface wear in select RTSA liners that is correlated to term-of-service. Calculation of in vivo wear rates can help bridge the gap between clinical outcomes and experimental models such as wear simulations and computational models. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2007-2014, 2018.

Metabolomic serum profiling after ACL injury in rats: A pilot study implicating inflammation and immune dysregulation in post-traumatic osteoarthritis

ACL rupture is a major risk factor for post-traumatic osteoarthritis (PTOA) development. Little information exists on acute systemic metabolic indicators of disease development. Thirty-six female Lewis rats were randomized to Control or noninvasive anterior cruciate ligament rupture (ACLR) and to three post-injury time points: 72 h, 4 weeks, 10 weeks (n = 6). Serum was collected and analyzed by ¹ H nuclear magnetic resonance (NMR) spectroscopy and combined direct injection and liquid chromatography (LC)-mass spectrometry (MS)/MS (DI-MS). Univariate and multivariate statistics were used to analyze metabolomic data, and predictive biomarker models were analyzed by receiver operating characteristic (ROC) analysis. Topological pathway analysis was used to identify perturbed pathways. Two hundred twenty-two metabolites were identified by ¹ H NMR and DI-MS. Differences in the serum metabolome between ACLR and Control were dominated by medium- and long-chain acylcarnitine species. Further, decreases in several tryptophan metabolites were either found to be significantly different in univariate analysis or to play important contributory roles to multivariate model separation. In addition to acylcarnitines and tryptophan metabolites, glycine, carnosine, and D-mannose were found to differentiate ACLR from Control. Glycine, 9-hexadecenoylcarnitine, trans-2-Dodecenoylcarnitine, linoelaidyl carnitine, hydroxypropionylcarnitine, and D-Mannose were identified as biomarkers with high area under ROC curve values and high predictive accuracies. Our analysis provides new information regarding the potential contribution of inflammatory processes and immune dysregulation to the onset and progression of PTOA following ACL injury. As these processes have most commonly been associated with inflammatory arthropathies, larger-scale studies elucidating their involvement in PTOA development and progression are necessary. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1969-1979, 2018.

Effect of Bisphosphonate Pretreatment on Fresh Osteochondral Allografts: Analysis of In Vitro Graft Structure and In Vivo Osseous Incorporation

Fresh allograft transplantation of osteochondral defects restores functional articular cartilage and subchondral bone; however, rapid loss of chondrocyte viability during storage and osteoclast-mediated bone resorption at the graft-host interface after transplantation negatively impact outcomes. The authors present a pilot study evaluating the in vitro and in vivo impact of augmenting storage media with bisphosphonates. Forty cylindrical osteochondral cores were harvested from femoral condyles of human cadaveric specimens and immersed in either standard storage media or storage media supplemented with nitrogenated or non-nitrogenated bisphosphonates. Maintenance of graft structure and chondrocyte viability were assessed at 3 time points. A miniature swine trochlear defect model was used to evaluate the influence of bisphosphonate-augmented storage media on in vivo incorporation of fresh osteochondral tissue, which was quantified via μCT and decalcified histology. In the in vitro study, Safranin-O/Fast Green staining showed that both low- and high-dose nitrogenated-treated grafts retained chondrocyte viability and cartilage matrix for up to 43 days of storage. Allografts stored in nitrogenated-augmented storage media showed both μCT and histologic evidence of enhanced in vivo bony and cartilaginous incorporation in the miniature swine trochlear defect model. Several preclinical studies have shown the potential for enhanced storage of fresh osteochondral allografts via additions of relatively common drugs and biomolecules. This study showed that supplementing standard storage media with nitrogenated bisphosphonates may improve maintenance of chondrocyte viability and graft structure during cold storage as well as enhance in vivo osseous and cartilaginous incorporation of the graft. [Orthopedics: 2018; 41(3):e376-e382.].

Multidrug-Resistant Organisms in the Setting of Periprosthetic Joint Infection-Diagnosis, Prevention, and Treatment

BACKGROUND

Periprosthetic joint infection (PJI) is a rare yet challenging problem in total hip and knee arthroplasties. The management of PJI remains difficult primarily due to the evolution of resistance by the infecting organisms.

METHODS

This review profiles acquired mechanisms of bacterial resistance and summarizes established and emerging techniques in PJI diagnosis, prevention, and treatment.

RESULTS

New techniques in PJI diagnosis and prevention continue to be explored. Antibiotics combined with 1 or 2-stage revision are associated with the higher success rates and remain the mainstay of treatment.

CONCLUSION

With higher prevalence of antibiotic-resistant organisms, novel antibiotic implant and wound care materials, improved methods for organism identification, and well-defined organism-specific treatment algorithms are needed to optimize outcomes of PJI.

Articular cartilage surface roughness as an imaging-based morphological indicator of osteoarthritis: A preliminary investigation of osteoarthritis initiative subjects

Current imaging-based morphometric indicators of osteoarthritis (OA) using whole-compartment mean cartilage thickness (MCT) and volume changes can be insensitive to mild degenerative changes of articular cartilage (AC) due to areas of adjacent thickening and thinning. The purpose of this preliminary study was to evaluate cartilage thickness-based surface roughness as a morphometric indicator of OA. 3D magnetic resonance imaging (MRI) datasets were collected from osteoarthritis initiative (OAI) subjects with Kellgren-Lawrence (KL) OA grades of 0, 2, and 4 (n = 10/group). Femoral and tibial AC volumes were converted to two-dimensional thickness maps, and MCT, arithmetic surface roughness (S_a ), and anatomically normalized S_a (normS_a ) were calculated. Thickness maps enabled visualization of degenerative changes with increasing KL grade, including adjacent thinning and thickening on the femoral condyles. No significant differences were observed in MCT between KL grades. S_a was significantly higher in KL4 compared to KL0 and KL2 in the whole femur (KL0: 0.55 ± 0.10 mm, KL2: 0.53 ± 0.09 mm, KL4: 0.79 ± 0.18 mm), medial femoral condyle (KL0: 0.42 ± 0.07 mm, KL2: 0.48 ± 0.07 mm, KL4: 0.76 ± 0.22 mm), and medial tibial plateau (KL0: 0.42 ± 0.07 mm, KL2: 0.43 ± 0.09 mm, KL4: 0.68 ± 0.27 mm). normS_a was significantly higher in KL4 compared to KL0 and KL2 in the whole femur (KL0: 0.22 ± 0.02, KL2: 0.22 ± 0.02, KL4: 0.30 ± 0.03), medial condyle (KL0: 0.17 ± 0.02, KL2: 0.20 ± 0.03, KL4: 0.29 ± 0.06), whole tibia (KL0: 0.34 ± 0.04, KL2: 0.33 ± 0.05, KL4: 0.48 ± 0.11) and medial plateau (KL0: 0.23 ± 0.03, KL2: 0.24 ± 0.04, KL4: 0.40 ± 0.10), and significantly higher in KL2 compared to KL0 in the medial femoral condyle. Surface roughness metrics were sensitive to degenerative morphologic changes, and may be useful in OA characterization and early diagnosis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2755-2764, 2017.

Neer Award 2017: wear rates of 32-mm and 40-mm glenospheres in a reverse total shoulder arthroplasty wear simulation model

BACKGROUND

Larger glenosphere diameters have been used recently to increase prosthesis stability and impingement-free range of motion in reverse total shoulder arthroplasty. The goal of this study was to evaluate the rate of polyethylene wear for 32-mm and 40-mm glenospheres.

METHODS

Glenospheres (32 mm and 40 mm, n = 6/group) and conventional polyethylene humeral liners underwent a 5-million cycle (MC) wear simulation protocol. Abduction-adduction and flexion-extension motion profiles were alternated every 250,000 cycles. At each interval, mass loss was determined and converted to volume loss and wear rate. At 0, 2.5 MC, and 5 MC, liners were imaged using micro-computed tomography to determine surface deviation. White light interferometry was performed on liners and glenospheres at 0 and 5 MC to quantify surface roughness. Wear particle morphology was characterized by environmental scanning electron microscopy.

RESULTS

Total volume loss was significantly higher in 40-mm liners from 1.5 MC onward (P < .05). Overall, volumetric wear rate was significantly higher in 40-mm liners compared with 32-mm glenospheres (81.7 ± 23.9 mm³/MC vs. 68.0 ± 18.9 mm³/MC; P < .001). However, micro-computed tomography surface deviation results demonstrated increased linear penetration on 32-mm glenospheres compared with 40-mm glenospheres (0.36 ± 0.03 µm vs. 0.28 ± 0.01 µm; P = .002). Surface roughness measurements showed no difference for liners; however, increased roughness was noted for 40-mm glenospheres at 5 MC compared with 32 mm (P < .05).

CONCLUSION

Larger glenospheres underwent significantly greater polyethylene volume loss and volumetric wear rates, whereas smaller glenospheres underwent greater polyethylene surface deviations. The enhanced stability provided by larger glenospheres must be weighed against the potential for increased polyethylene wear.

Acute mobilization and migration of bone marrow-derived stem cells following anterior cruciate ligament rupture

OBJECTIVE

Little is known regarding acute local and systemic processes following anterior cruciate ligament (ACL) rupture. No study has elucidated whether bone marrow-derived mesenchymal stem cells (MSCs) are mobilized into circulation and recruited to the injured joint.

METHODS

In Part 1, Lewis rats were randomized to noninvasive ACL rupture (Rupture) or non-injured (Control) (n = 6/group). After 72 h, whole blood MSC concentration was assessed using flow cytometry. Synovial fluid and serum were assayed for stromal cell-derived factor (SDF)-1α and cartilage degeneration biomarkers, respectively. In Part 2, 12 additional rats were randomized and intravenously-injected with fluorescently-labeled allogenic MSCs. Cell tracking was performed using longitudinal, in vivo and ex vivo near-infrared (NIR) imaging and histology. Synovium SDF-1α and interleukin (IL)-17A immunostaining was performed. Serum was assayed for SDF-1α and 29 other cytokines.

RESULTS

In Part 1, there was a significant increase in MSC concentration and synovial fluid SDF-1α in Rupture. No differences in cartilage biomarkers were observed. In Part 2, Rupture had significantly higher NIR signal at 24, 48, and 72 h, indicating active recruitment of MSCs to the injured joint. Ex vivo cell tracking demonstrated MSC localization in the synovium and myotendinous junction (MTJ) of the quadriceps. Injured synovia exhibited increased synovitis grade and higher degree of IL-17A and SDF-1α immunostaining.

CONCLUSION

ACL rupture induced peripheral blood mobilization of MSCs and migration of intravenously-injected allogenic MSCs to the injured joint, where they localized in the synovium and quadriceps MTJ.

Review of Mechanical, Processing, and Immunologic Factors Associated With Outcomes of Fresh Osteochondral Allograft Transplantation of the Talus

Osteochondral lesions of the talus (OLTs) are an increasingly implicated cause of ankle pain and instability. Several treatment methods exist with varying clinical outcomes. Due in part to successful osteochondral allografting (OCA) in other joints, such as the knee and shoulder, OCA has gained popularity as a treatment option, especially in the setting of large lesions. The clinical outcomes of talar OCA have been inconsistent relative to the positive results observed in other joints. Current literature regarding OCA failure focuses mainly on 3 factors: the effect of graft storage conditions on chondrocyte viability, graft/lesion size, and operative technique. Several preclinical studies have demonstrated the ability for bone and cartilage tissue to invoke an immune response, and a limited number of clinical studies have suggested that this response may have the potential to influence outcomes after transplantation. Further research is warranted to investigate the role of immunological mechanisms as an etiology of OCA failure.

LEVEL OF EVIDENCE

Level V, expert opinion.

Exposure of articular chondrocytes to wear particles induces phagocytosis, differential inflammatory gene expression, and reduced proliferation

The production of wear debris particulate remains a concern due to its association with implant failure through complex biologic interactions. In the setting of unicompartmental knee arthroplasty (UKA), damage and wear of the components may introduce debris particulate into the adjacent, otherwise, healthy compartment. The purpose of this study was to investigate the in vitro effect of polymeric and metallic wear debris particles on cell proliferation, extracellular matrix regulation, and phagocytosis index of normal human articular chondrocytes (nHACs). In culture, nHACs were exposed to both cobalt-chromium-molybdenum (CoCrMo) and polymethyl-methacrylate (PMMA) wear debris particulate for 3 and 10 days. At 3 days, no significant difference in cell proliferation was found between control cells and cells exposed to both CoCrMo or PMMA particles. However, cell proliferation was significantly decreased for CoCrMo exposed nHACs at both 6 (P < 0.001) and 10 days (P < 0.001) and PMMA at 10 days (P < 0.001). Target gene expression displayed both a time- and material-dependent response to CoCrMo and PMMA particles. Significant differences in COL10A1, ACAN, VCAN, IL-1β, TNF-α, MMP3, ADAMTS1, CASP3, and CASP9 regulation were found between CoCrMo and PMMA exposed nHACs at day 3 with gene regulation returning to near baseline at 10 days. Results from our study indicate a role of wear debris induced cartilage degeneration after exposure to polymeric and metallic wear debris particulate, suggesting an additional pathway of cartilage breakdown, potentially manifesting in traditional clinical symptoms.

Contrast-enhanced μCT of the intervertebral disc: A comparison of anionic and cationic contrast agents for biochemical and morphological characterization

The objective of this study was to quantify and compare the contrast-enhancing properties of the anionic contrast agent ioxaglate/Hexabrix, and cationic contrast agent CA⁴⁺ for biochemical and morphological characterization of the intervertebral disc (IVD) via μCT. Optimal contrast agent concentrations were determined by incubating rat lumbar IVDs in dilutions of Hexabrix-320 (20%, 30%, 40%, and 50%) and CA⁴⁺ (10, 20, 30, and 40 mg I/ml). μCT imaging was performed at 70 kVp, 114 μA, and 250 ms integration time, 12 μm voxel size. The kinetics of contrast enhancement were quantified with cumulative incubations for 0.5, 1, 2, 12, 16, 20, and 24 h using both agents. Agreement in morphological quantification was assessed via serial scans of the same IVDs. Correlation of attenuation to glycosaminoglycan (GAG) content was determined by enzymatic digestion of IVDs, subsequent μCT imaging, and GAG quantification via dimethylmethylene blue assay. Forty percent Hexabrix and 30 mg I/ml CA⁴⁺ were chosen as optimal concentrations. Hexabrix enabled greater delineation of the IVD from surrounding tissues, and CA⁴⁺ had the lowest uptake in surrounding soft tissue. Twenty-four hour incubation was sufficient for >99% equilibration of both agents. A high level of agreement was observed in the quantification of IVD volume (ICC = 0.951, r = 0.997) and height (ICC = 0.947, r = 0.991). Both agents exhibited strong linear correlations between μCT attenuation and GAG content (Hexabrix: r = -0.940; CA⁴⁺ : r = 0.887). Both agents enable biochemical and morphological quantification of the IVD via contrast-enhanced μCT and are effective tools for preclinical characterization. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1067-1075, 2017.

Lumbar pseudarthrosis: a review of current diagnosis and treatment

OBJECT Failed solid bony fusion, or pseudarthrosis, is a well-known complication of lumbar arthrodesis. Recent advances in radiographic technology, biologics, instrumentation, surgical technique, and understanding of the local biology have all aided in the prevention and treatment of pseudarthrosis. Here, the current literature on the diagnosis and management of lumbar pseudarthroses is reviewed. METHODS A systematic literature review was conducted using the MEDLINE and Embase databases in order to search for the current radiographie diagnosis and surgical treatment methods published in the literature (1985 to present). Inclusion criteria included: 1) published in English; 2) level of evidence I-III; 3) diagnosis of degenerative lumbar spine conditions and/or history of lumbar spine fusion surgery; and 4) comparative studies of 2 different surgical techniques or comparative studies of imaging modality versus surgical exploration. RESULTS Seven studies met the inclusion criteria for current radiographie imaging used to diagnose lumbar pseudarthrosis. Plain radiographs and thin-cut CT scans were the most common method for radiographie diagnosis. PET has been shown to be a valid imaging modality for monitoring in vivo active bone formation. Eight studies compared the surgical techniques for managing and preventing failed lumbar fusion. The success rates for the treatment of pseudarthrosis are enhanced with the use of rigid instrumentation. CONCLUSIONS Spinal fusion rates have improved secondary to advances in biologies, instrumentation, surgical techniques, and understanding of local biology. Treatment of lumbar pseudarthrosis includes a variety of surgical options such as replacing loose instrumentation, use of more potent biologies, and interbody fusion techniques. Prevention and recognition are important tenets in the algorithm for the management of spinal pseudarthrosis.

Biomechanical Evaluation of All-Polyethylene Pegged Bony Ingrowth Glenoid Fixation Techniques on Implant Micromotion

Newer glenoid components that allow for hybrid cement fixation via traditional cementation of peripheral pegs and bony ingrowth into an interference-fit central peg introduce the possibility of long-term biological fixation. However, little biomechanical work has been done on the initial stability of these components and the various fixation options. We conducted a study in which all-polyethylene glenoid components with a centrally fluted peg were implanted in polyurethane blocks with interference-fit, hybrid cement, and fully cemented fixation (5 per fixation group). Biomechanical evaluation of glenoid loosening, according to ASTM Standard F-2028-12, subjected the glenoids to 50,000 cycles of rim loading, and glenoid component motion was recorded with 2 differential variable reluctance transducers fixed to each glenoid prosthesis. Fully cemented fixation exhibited significantly less mean distraction in comparison with interference-fit fixation (P < .001) and hybrid cement fixation (P < .001). Hybrid cement fixation exhibited significantly less distraction (P < .001), more compression (P < .001), and no significant difference in glenoid translation (P = .793) in comparison with interference-fit fixation. Fully cemented fixation exhibited the most resistance to glenoid motion in comparison with hybrid cement fixation and interference-fit fixation. However, hybrid cement fixation and interference-fit fixation exhibited equivocal motion. Given these results, cementation of peripheral pegs may confer no additional initial stability over that provided by uncemented interference-fit fixation.

Surface roughness and thickness analysis of contrast-enhanced articular cartilage using mesh parameterization

OBJECTIVE

Articular cartilage (AC) morphology is an important metric for characterizing degeneration. We propose a novel morphologic analysis using mesh parameterization, enabling the use of surface roughness and thickness metrics to characterize degeneration in a rodent model of post-traumatic osteoarthritis.

METHODS

Six rats underwent anterior cruciate ligament transection (ACL-T) and six were controls (Control). At 4-weeks, femora and tibiae were harvested and imaged using contrast-enhanced micro-computed tomography (μCT). Cartilage surfaces were manually outlined, and 2-dimensional thickness maps were generated using mesh parameterization and analyzed by thickness and surface roughness (Sa). The parameterization technique was validated against the direct distance transform (DDT) and histologic AC thickness from sagittal Safranin-O/Fast-Green sections. Parameterization and DDT measurements were also validated using known, virtual shapes with zero, one, and two planes of curvature.

RESULTS

Parameterization had 0.00-6.26% error and DDT had 5.06-12.02% error in determining thicknesses of known shapes. Parameterization thickness correlated highly to DDT thickness (femur: r = 0.978, P < 0.001; tibia: r = 0.992, P < 0.001) and histologic thickness (femur: r = 0.952, P < 0.001; tibia: r = 0.959, P < 0.001). Thickness maps enabled visualization and quantification of AC degeneration. ACL-T samples displayed general thickening of cartilage, with adjacent regions of thickening and thinning on the medial femoral condyle. Compared to Control, ACL-T thickness was higher in the whole femur, whole tibia, and all compartments and sub-compartments. Sa was higher in the whole femur and medial and lateral condyle, and the whole tibia and medial and lateral plateau. The largest increases in Sa were observed on the medial femoral condyle.

CONCLUSIONS

Cartilage analysis using parameterization effectively characterized early degeneration in AC, including sub-compartmental thickening/thinning, and is a powerful tool for assessing degeneration in preclinical osteoarthritis.

Elucidating trends in revision reverse total shoulder arthroplasty procedures: a retrieval study evaluating clinical, radiographic, and functional outcomes data

BACKGROUND

The purpose of this study was to explore relationships between damage modes in explanted reverse total shoulder arthroplasty (RTSA) components, patient and radiographic risk factors, and functional data to elucidate trends in RTSA failure.

METHODS

Fifty RTSA systems, retrieved from 44 patients, with 50 polyethylene (PE) liners, 30 glenospheres, 21 glenoid baseplates, 13 modular humeral metaphases, and 17 humeral stems, were examined for damage modes, including abrasion, burnishing, dishing, embedding, scratching, and pitting. PE liners were also analyzed for delamination and edge deformation. Charts were reviewed for patient, surgical, and functional data. Pre-revision radiographs were analyzed for scapular notching and loosening.

RESULTS

Average term of implantation was 20 months (range, 0-81 months). Metallic components exhibited abrasion, burnishing, dishing, pitting, and scratching. PE liners displayed all damage modes. Damage was exhibited on 93% of glenospheres and 100% of PE liners. Of 29 aseptic shoulders, 13 showed evidence of scapular notching and 5 of humeral loosening. There was a moderate correlation between radiographically observed implant failure or dissociation and PE embedding (r = 0.496; P < .001). There were weak and moderate correlations between scapular notching severity and PE dishing (r = 0.496; P = .006), embedding (r = 0.468; P = .010), and delamination (r = 0.384; P = .040).

CONCLUSIONS

To date, this is the largest series of retrieved RTSA components and the first to relate damage modes to radiographic and clinical data. Most damage was observed on the PE liners, on both the articular surface and rim, and glenosphere components. Correlation of retrieval findings with radiographic and clinical data may help establish predictors of prostheses at risk for failure.

Wear rates of retentive versus nonretentive reverse total shoulder arthroplasty liners in an in vitro wear simulation

BACKGROUND

Although short-term outcomes of reverse total shoulder arthroplasty (rTSA) remain promising, the most commonly cited complication remains prosthetic instability. A retentive rTSA liner is commonly used to increase system constraint; however, no studies have evaluated the rate of polyethylene wear. Our hypothesis was that more constrained retentive liners would have higher wear rates than nonretentive liners.

METHODS

Six nonretentive and six retentive rTSA non-cross-linked polyethylene liners were subjected to 4.5 million cycles of alternating cycles of abduction-adduction and flexion-extension motion loading profiles. The rTSA liners were assessed for gravimetric wear loss, 3-dimensional volumetric loss by novel micro-computed tomography analysis, and particulate wear debris analysis.

RESULTS

Volumetric wear rates were significant at 7 specific time points (1.0, 2.0, 2.5, 3.25, 3.75, 4.0, and 4.5 million cycles) throughout testing between nonretentive and retentive liners; however, overall mean volumetric wear rate was not statistically significant (P = .076). Total volume loss between liner test groups was found to be significant starting after 3.5 million cycles of testing. Maximum and mean surface deviations were found to be larger for retentive liners vs. nonretentive liners by micro-computed tomography analysis across the entire articulation surface.

DISCUSSION AND CONCLUSION

Retentive liners undergo significantly greater volume loss and greater surface deviation compared with nonretentive liners, most notably at later time points representing extended implantation times. Additional stability afforded by retentive liners should be balanced against the potential for increased wear and potential for subsequent polyethylene wear-induced aseptic loosening.

The impact of rotator cuff deficiency on structure, mechanical properties, and gene expression profiles of the long head of the biceps tendon (LHBT): Implications for management of the LHBT during primary shoulder arthroplasty

The long head of the biceps tendon (LHBT) occupies a unique proximal intra-articular and distal extra-articular position within the human shoulder. In the presence of a rotator cuff (RC) tear, the LHBT is recruited into an accelerated role undergoing potential mechanical and biochemical degeneration. Intra-articular sections of the LHBT were harvested during primary shoulder arthroplasty from patients with an intact or deficient RC. LHBTs were stained (H&E, Alcian Blue) and subjected to histologic analysis using the semiquantitative Bonar scale and measurement of collagen orientation. LHBTs (n = 12 per group) were also subjected to gene-expression analyses via an RT(2) -PCR Profiler Array quantifying 84 genes associated with cell-cell and cell-matrix interactions. LHBTs (n = 18 per group) were biomechanically tested with both stress-relaxation and load-to-failure protocols and subsequently modeled with the Quasilinear Viscoelastic (QLV) and Structural-Based Elastic (SBE) models. While no histologic differences were observed, significant differences in mechanical testing, and viscoelastic modeling parameters were found. PCR arrays identified five genes that were differentially expressed between RC-intact and RC-deficient LHBT groups. LHBTs display signs of pathology regardless of RC status in the arthroplasty population, which may be secondary to both glenohumeral joint arthritis and the additional mechanical role of the LHBT in this population.

Predisposing factors for dural tear in patients undergoing lumbar spine surgery

OBJECT The purpose of this prospective cohort study was to identify risk factors for incidental durotomies in lumbar spine surgery. The authors hypothesized that the incidence of durotomy would be higher in cases involving multiple operations. METHODS The authors prospectively evaluated 523 patients who underwent lumbar and thoracolumbar spine surgery. They compared data on patients in whom a dural tear occurred and those in whom a dural tear did not occur. Data from patients in whom a dural tear occurred were compared with data from patients who did not experience durotomy. The data included basic demographic information, intraoperative data, and clinical information from a medical record review. RESULTS One hundred thirty-one patients underwent discectomy and 392 patients underwent laminectomy. Among the 131 patients who underwent discectomy 6 patients had a dural tear. Among the 392 patients who underwent discectomy 49 patients had dural tear. Patients with incidental durotomy were older (mean 65 ± 13 vs 60 ± 14 years of age; p = 0.044, t-test), and had longer surgery (146 ± 59 vs 110 ± 54 minutes; p = 0.025, t-test), compared with the patients without dural tear. The incidence of dural tear was more common in patients with a history of previous spine surgery (p < 0.001). CONCLUSIONS In patients who underwent lumbar and thoracolumbar spine surgery for degenerative problems, previous surgery and older age were found to be predisposing factors for dural tear.

Cement augmentation in vertebral burst fractures

As a result of axial compression, traumatic vertebral burst fractures disrupt the anterior column, leading to segmental instability and cord compression. In situations with diminished anterior column support, pedicle screw fixation alone may lead to delayed kyphosis, nonunion, and hardware failure. Vertebroplasty and kyphoplasty (balloon-assisted vertebroplasty) have been used in an effort to provide anterior column support in traumatic burst fractures. Cited advantages are providing immediate stability, improving pain, and reducing hardware malfunction. When used in isolation or in combination with posterior instrumentation, these techniques theoretically allow for improved fracture reduction and maintenance of spinal alignment while avoiding the complications and morbidity of anterior approaches. Complications associated with cement use (leakage, systemic effects) are similar to those seen in the treatment of osteoporotic compression fractures; however, extreme caution must be used in fractures with a disrupted posterior wall.

Hydatid Disease of the Femur Treated with a Total Femoral Replacement: A Case Report

CASE

A thirty-one-year-old woman presented with symptoms of worsening left knee and thigh pain. Radiographs and magnetic resonance imaging demonstrated extensive lytic and cystic changes throughout the femur. A biopsy demonstrated necrosis, chronic granulomatous inflammation, and laminations suggestive of an echinococcal cyst. Serology confirmed an Echinococcus granulosus infection. Treatment with anthelmintic agents was initiated, but reconstruction with a total femoral endoprosthesis was implemented as definitive management. The patient tolerated surgery well and returned for a one-year postoperative visit without evidence of recurrence of infection.

CONCLUSION

Osseous hydatidosis is a rare disease, but it should be included in the differential diagnosis of patients with extensive destructive bone processes.

Wear rates of highly cross-linked polyethylene humeral liners subjected to alternating cycles of glenohumeral flexion and abduction

BACKGROUND

Although short-term outcomes of reverse total shoulder arthroplasty have been promising, long-term success may be limited due to device-specific complications, including scapular notching. Scapular notching has been explained primarily as mechanical erosion; however, the generation of wear debris may lead to further biologic changes contributing to the severity of scapular notching.

METHODS

A 12-station hip simulator was converted to a reverse total shoulder arthroplasty wear simulator subjecting conventional and highly cross-linked ultra-high-molecular-weight polyethylene humeral liners to 5 million cycles of alternating abduction-adduction and flexion-extension loading profiles.

RESULTS

Highly cross-linked polyethylene liners (36.5 ± 10.0 mm(3)/million cycle) exhibited significantly lower volumetric wear rates compared with conventional polyethylene liners (83.6 ± 20.6 mm(3)/million cycle; P < .001). The flexion-extension loading profile exhibited significantly higher wear rates for conventional (P < .001) and highly cross-linked polyethylene (P < .001) compared with the abduction-adduction loading profile. Highly cross-linked wear particles had an equivalent circle diameter significantly smaller than wear particles from conventional polyethylene (P < .001).

CONCLUSIONS

Highly cross-linked polyethylene liners significantly reduced polyethylene wear and subsequent particle generation. More favorable wear properties with the use of highly cross-linked polyethylene may lead to increased device longevity and fewer complications but must be weighed against the effect of reduced mechanical properties.

Matrix metalloproteinase content and activity in low-platelet, low-leukocyte and high-platelet, high-leukocyte platelet rich plasma (PRP) and the biologic response to PRP by human ligament fibroblasts

BACKGROUND

Recent work has shown the presence of catabolic cytokines in platelet-rich plasma (PRP), but little is known about endogenous catabolic proteases such as matrix metalloproteinases (MMPs). Hypothesis/

PURPOSE

To quantify MMP content in 2 commercially available PRP preparation systems: Arthrex Double Syringe System autologous conditioned plasma (ACP) and Biomet GPS (GPS). The hypothesis was that MMPs are actively secreted from PRP immediately after preparation.

STUDY DESIGN

Controlled laboratory study.

METHODS

PRP was prepared using either ACP (low platelet, low leukocyte) or GPS (high platelet, high leukocyte). MMP-2, MMP-3, and MMP-9 concentrations were measured using multiplex enzyme-linked immunosorbent assays for up to 6 days in 2 donors, and MMP activity was measured in 3 donors using kinetic activity kits able to detect the enzymatic cleavage of a fluorogenic peptide. Human ligament fibroblasts were cultured and exposed to both ACP and GPS from 1 donor each. MMP-2, -3, and -9 concentrations were assayed in culture media at 24 and 48 hours after exposure.

RESULTS

GPS exhibited higher total MMP-2, -3, and -9 concentrations for up to 144 hours of release, while ACP had higher platelet-normalized MMP-2 and MMP-3 concentrations. GPS had significantly higher total and endogenous MMP-2 activity (P = .004 and .014, respectively), MMP-3 activity (P = .020 and .015, respectively), and MMP-9 activity (P = .004 and .002, respectively) compared with ACP. Once normalized to platelet count, differences in MMP activity were not significant between ACP and GPS. Compared with controls, cells stimulated with interleukin-1 beta (IL-1β) and treated with ACP showed significantly higher fold changes of MMP-2 (P = .001) and MMP-3 (P = .003) concentrations at 24 hours than did cells treated with GPS. Total MMP-9 content was higher in the media of GPS-treated, IL-1β-stimulated cells compared with ACP-treated cells (P = .001). At 48 hours, IL-1β-stimulated cells treated with GPS exhibited higher fold changes of MMP-2 concentration (P = .002) compared with controls, but no difference in MMP-3 concentration was found. At 48 hours, there was a significantly higher concentration of MMP-9 in the cell culture media of ACP-treated cells compared with GPS-treated cells (P = .003).

CONCLUSION

PRP prepared as both ACP and GPS contains MMP-2, -3, and -9, which is released over a period of at least 6 days. Furthermore, a large proportion of these MMPs are in their active form, and MMP activity is dependent on platelet count within the PRP preparation. Once exposed to ligament fibroblasts, both ACP and GPS cause the fibroblasts to release MMPs, most notably 24 hours after PRP exposure, and this release is dependent on prior IL-1β stimulation.

CLINICAL RELEVANCE

The results of this study demonstrate that PRP therapy delivers ng/mL-range concentrations of catabolic proteases, which could perpetuate inflammation and inhibit tissue healing.

Biomechanical testing of small versus large lesser tuberosity osteotomies: effect on gap formation and ultimate failure load

BACKGROUND

Subscapularis muscle dysfunction after total shoulder arthroplasty (TSA) can be a devastating complication. Recent biomechanical and clinical results suggest the superiority of lesser tuberosity osteotomy (LTO) over subscapularis tenotomy; however, disagreement over the best repair technique remains. This study aimed to characterize the strength of 2 novel repair techniques for LTO fixation compared with standard tenotomy and dual-row tuberosity osteotomies during TSA.

METHODS

Twenty fresh frozen cadaveric shoulders were dissected of all soft tissues except the humeri and attached subscapularis myotendinous unit. Humeri and subscapularis muscle belly were secured to a materials testing frame and subjected to cyclic loading, followed by load to failure for characterization of gap formation, ultimate failure load, and mechanism of failure. Repair techniques investigated were traditional subscapularis tenotomy and dual-row fleck LTO compared with novel techniques of single-cable and 2-suture large LTO repairs.

RESULTS

No significant difference in ultimate failure load was noted among the repair techniques (P = .565). The tenotomy repair (6.0 ± 3.9 mm) displayed significantly greater gapping in response to increasing load than LTO repair techniques (P < .05). No significant difference was noted between any LTO repairs at specific loads during cyclic testing (P > .05).

CONCLUSION

Our study displayed superior repair integrity of LTO vs tenotomy repairs. The advantages of the 2-suture large LTO technique over other LTO techniques include its simple technique, with a minimum amount of suture, avoidance of metallic hardware, and greater access to the glenoid, while providing comparable repair stability. Further research is warranted to fully evaluate these new techniques.

Radiographic predisposing factors for degenerative spondylolisthesis

This study was a retrospective radiographic study involving analysis of computed tomography scans obtained for patients with degenerative spondylolisthesis of the L4-L5 segment and a control group. The purpose of the study was to identify radiological predisposing factors for degenerative spondylolisthesis of the L4-L5 segment. The authors reviewed all computed tomography scans (N=3370) performed at their institution between January 2005 and December 2008. Eighty-four patients with degenerative spondylolisthesis were identified and compared with a control group regarding facet joint orientation, the presence of sacralization of the L5 vertebra, the presence of major degenerative changes in the L5-S1 disk space, and the location of the intercrestal line. There was a statistically significant difference between the 2 groups regarding facet joint orientation, with more sagittal facet joints in the degenerative spondylolisthesis group (56° and 54° in the right and left facets, respectively, in the study group, and 46° and 42° in the right and left facets, respectively, in the control group) (P<.001). There was no statistically significant difference between the 2 groups regarding the presence of sacralization of the L5 vertebra, the presence of major degenerative changes in the L5-S1 disk space, and the location of the intercrestal line relative to the lumbar spine. There is an association between sagittal orientation of the facet joints at the L4-L5 segment and degenerative spondylolisthesis at the same level.

The GraftLink ulnar collateral ligament reconstruction: biomechanical comparison with the docking technique in both kinematics and failure tests

BACKGROUND

Ulnar collateral ligament (UCL) reconstruction aims to restore valgus stability, and numerous techniques have been described in the literature. HYPOTHESIS/ PURPOSE: To biomechanically compare the GraftLink (GL) technique with traditional bone tunnels used in the docking (DO) technique. It is hypothesized that the GL method will offer a stiffer, less lax construct compared with the DO.

STUDY DESIGN

Controlled laboratory study.

METHODS

Native and reconstructed states were tested in 7 matched pairs of cadaveric arms. To test kinematics, a 1.5-N·m valgus torque was applied and the resultant displacement at 15° to 90° of flexion was measured. Dissipated energy and the torque at the peak of the 10th cycle of preconditioning were analyzed during kinematic tests. Failure testing was performed by internal rotation of the humerus at 4.5 deg/s in 70° of flexion. Ulnotrochlear joint (UTJ) gapping was quantified during failure tests by use of video tracking.

RESULTS

Kinematics testing revealed no differences between the native state and the reconstructed state in either the DO or the GL group at any flexion angle. Stiffness was lower in the reconstructed specimens in both the DO (39.92 N·m/rad) and GL (50.74 N·m/rad) groups compared with their matched native states (DO Native, 71.41 N·m/rad, P = .005; GL Native, 86.36 N·m/rad, P = .002). There was no difference in stiffness between DO and GL. Reconstructed specimens in the GL group had lower torque at failure compared with native specimens (17.404 N·m vs 24.63 N·m, P = .038), but there was no difference in the DO group at failure. There was no difference in torque at failure between DO and GL. The DO exhibited higher angular displacement at failure compared with the native state (34.21° vs 21.79°, P = .010) and compared with the GL when normalized (1.58-fold vs 1.19-fold, P = .039). Compared with their native states, both DO and GL had significantly higher UTJ gapping at 3 N·m and at failure. The DO had significantly higher normalized UTJ gapping than the GL at 3 N·m (P = .037) and at failure (P = .043).

CONCLUSION

The DO and GL both restored joint kinematics under low loading conditions. Although less stiff, the GL exhibited lower joint gapping and laxity than did the DO.

CLINICAL RELEVANCE

Understanding the biomechanics of UCL reconstruction has significant implications for postoperative management as it relates to early rehabilitation. Biomechanically inferior constructs could risk graft failure or early loosening during rehabilitation, and comparing the biomechanics of new techniques to established, widely used procedures such as the docking technique can provide important information about the immediate postoperative performance.

Hidden blood loss during posterior spine fusion surgery

BACKGROUND CONTEXT

Posterior spine fusion is associated with significant intra- and postoperative blood losses. When referring to the total blood loss during spine surgery, the standard is to measure the intraoperative bleeding plus the postoperative drainage. This ignores the "hidden" blood loss that was found to be significant in other fields of surgery.

PURPOSE

The purpose of this study was to examine whether posterior spine fusion carries a substantial hidden blood loss.

STUDY DESIGN/SETTING

A prospective study.

PATIENT SAMPLE

We prospectively studied 114 patients undergoing instrumented posterior spinal fusion at one center between January 2011 and April 2011.

OUTCOME MEASURES

Total blood loss, visible blood loss, and hidden blood loss.

METHODS

For each patient, the hidden blood loss was calculated by deducting the observed perioperative blood loss from the calculated total blood loss based on the hematocrit changes. We compared the percentage of the hidden blood loss out of the total blood loss for primary versus revision posterior spine fusion.

RESULTS

Primary decompression and posterior fusion patients had a mean total true loss of 1,439 mL. Their calculated hidden loss was 600 mL, 42% of the total loss. After revision posterior spinal fusion surgery, the mean total blood loss was 1,606 mL. The mean visible loss was 975 mL, and the mean hidden loss was 631 mL, 39% of the total loss. Thus, there was no statistical difference in the hidden blood loss between primary and revision posterior spinal fusion surgeries (p>.05). We did not find a significant difference in the percentage of the hidden blood loss between patients who underwent one, two, or three or more levels of surgery.

CONCLUSIONS

After posterior spinal fusion, there may be a large amount of the hidden blood loss.

Biomechanical evaluation of the TightRope versus traditional docking ulnar collateral ligament reconstruction technique: kinematic and failure testing

BACKGROUND

Numerous variations of ulnar collateral ligament (UCL) reconstruction have been described since the original technique by Jobe et al. Purpose/

HYPOTHESIS

To biomechanically compare the new TightRope technique and the traditional ulnar bone tunnels as used in the docking technique. The hypothesis was that the TightRope technique would exhibit improved kinematics and comparable failure properties.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven matched pairs of cadaveric arms (mean age, 44.71 years) were tested in both the native state and reconstructed state. Kinematics were assessed at 15° to 90° of flexion by applying a 1.5-N·m valgus torque and measuring the resultant angular displacement. Failure testing was performed by loading to failure at 4.5 deg/s in 70° of flexion. Sides of a matched pair were randomized to the TightRope (TR) and docking (DO) techniques after testing the native state.

RESULTS

There was no significant difference in kinematic results between the native state and reconstructed state in either the TR or DO group at 15° to 75° of flexion. At 90°, the TR group had significantly higher angular displacement (2.23° ± 1.0°) compared with the native state (1.31° ± 0.7°) (P = .020). The TR-reconstructed specimens had significantly lower initial stiffness (49.34 ± 19.3 N·m/rad vs 82.47 ± 36.0 N·m/rad, respectively; P = .007) and total stiffness (53.81 ± 27.8 N·m/rad vs 101.06 ± 34.4 N·m/rad, respectively; P < .001) than did the paired native specimens. In addition, the TR-reconstructed specimens had significantly lower torsional torque at 5° of valgus rotation (mean, 4.61 ± 2.2 N·m vs 7.62 ± 3.7 N·m, respectively; P = .010), at 15° of valgus rotation (12.24 ± 4.4 N·m vs 20.65 ± 6.8 N·m, respectively; P = .002), and at ultimate failure (19.18 ± 7.5 N·m vs 25.42 ± 7.1 N·m, respectively; P = .025) than did the paired native specimens. There was no significant difference in torsional torque between the TR and DO groups at 5° of valgus rotation (4.61 ± 2.2 N·m vs 4.09 ± 1.7 N·m, respectively; P = .644), at 15° of valgus rotation (12.24 ± 4.4 N·m vs 17.94 ± 7.23 N·m, respectively; P = .178), or at failure (19.18 ± 7.5 N·m vs 23.19 ± 10.6 N·m, respectively; P = .444). The DO group exhibited significantly higher angular displacement at failure than did the native state (28.12° ± 8.5° vs 18.04° ± 4.8°, respectively; P = .009), but there was no difference at 3 N·m of loading. There was no significant difference in angular displacement either at 3 N·m or at failure between the native state and reconstructed state in the TR group.

CONCLUSION

Both the TR and DO techniques restored native joint kinematics from 15° to 75° of flexion under low loading conditions. While the TR technique exhibited inferior failure torque compared with the native state, the DO technique did not differ from the native state. No differences were found between the TR and DO groups when compared directly. The DO technique restored valgus stability under high loading to a greater extent than did the TR technique but also failed at higher angular displacement.

CLINICAL RELEVANCE

Strong postoperative UCL reconstruction fixation is important to restore ulnotrochlear joint stability. Our study demonstrates that the new TR technique has comparable kinematic and failure properties to the traditional DO technique.

A biomechanical analysis of initial fixation options for porous-tantalum-backed glenoid components

BACKGROUND

Porous-tantalum (PT)-backed glenoid components have recently been developed to improve fixation and minimize the incidence of glenoid component loosening, which remains a key limiting factor in long-term survival in total shoulder arthroplasty. PT-backed glenoids promote bony ingrowth as a method of preventing glenoid loosening at the prosthesis-glenoid interface. The use of polymethyl-methacrylate (PMMA) cement for initial fixation may prevent osteointegration due to mechanical occlusion of the porous surface and the nonosteoconductive properties of PMMA. This study aims to investigate alternative fixation methods of PT-backed glenoids in a biomechanical investigation.

MATERIALS AND METHODS

Nine PT-backed monoblock glenoid components were implanted in a polyurethane bone substitute using either press-fit, PMMA cement, or calcium phosphate cement techniques. A control group of 3 all-polyethylene pegged glenoid components was implanted with PMMA. Glenoid and humeral head components were fixed to a biomechanical testing machine for testing according to ASTM Standard F-2028. The humeral head was translated ±1.5 mm along the superior-inferior axis for 50,000 cycles for characterization of glenoid rocking and inferior-superior translation.

RESULTS

Glenoid compression and glenoid distraction followed similar patterns for PT-backed glenoids. Overall, the all-polyethylene cemented glenoid demonstrated superior fixation compared to all PT-backed groups throughout the test. Glenoids fixed with PMMA cement displayed more favorable initial fixation and resistance to glenoid motion throughout cyclic testing.

CONCLUSION

This study showed that among PT-backed glenoids, PMMA fixation provided an increase in stability during initial and final cycles compared to press-fit and calcium-phosphate fixation techniques. This improved stability may enhance the osteointegration of the implant.

Strength of ulnar fixation in ulnar collateral ligament reconstruction: a biomechanical comparison of traditional bone tunnels to the tension-slide technique

BACKGROUND

Surgical reconstruction of the ulnar collateral ligament after rupture has evolved substantially since the original description. Reconstruction techniques vary significantly at the ulnar and humeral interface. The purpose of this study was to develop a model to isolate, test, and compare the ulnar fixation of the traditional bone tunnel technique and a new technique, the tension slide.

MATERIALS AND METHODS

Six matched pairs of cadaveric arms were dissected to isolate the ulna. Pairs were randomized to the bone tunnel or tension-slide ulnar fixation technique, and consistent tendon grafts were used for each reconstruction. A specialized tendon clamp was used to grip the grafts. Specimens were preloaded with a valgus force to 1 N x m and tested to failure in torsion at 4.5°/s. Statistical analysis was performed with 1-way analysis of variance with the Tukey post hoc test (α = .05).

RESULTS

The bone tunnel technique exhibited higher initial and total stiffness, as well as higher torsional torque at 10° and 30° of valgus angulation and at ultimate failure. The tension-slide technique exhibited significantly higher angular displacement at 3 N x m but not at ultimate failure. The bone tunnel technique exhibited higher work at 10° and 30° of valgus angulation.

CONCLUSION

In this model, traditional bone tunnels performed superior to the tension-slide construction in terms of both strength and stiffness. Whether there is a kinematic benefit to the tension slide, which moves the ulnar fixation to within the native ulnar collateral ligament footprint, is yet to be determined. Further study is needed to assess the clinical benefit of a stronger ulnar fixation.

Wear simulation of reverse total shoulder arthroplasty systems: effect of glenosphere design

BACKGROUND

Although early results with reverse total shoulder arthroplasty (rTSA) have been promising, concern exists about the high reported rates of scapular notching and the potential for catastrophic failure of glenoid component fixation. Generation of polyethylene wear debris may also contribute to notching and osteolysis of the scapula. A testing model for polyethylene wear is currently unavailable for reverse shoulder prostheses. The goal of this study was to develop a testing protocol using a commercially available hip simulator. Component design may also influence the generation of polyethylene debris. It is hypothesized that increased polyethylene wear occurs in glenospheres with holes in the articulating surface.

MATERIALS AND METHODS

Custom fixtures were fabricated to simulate both glenohumeral abduction and flexion on a 12-station hip wear simulator. Loading profiles for both abduction and flexion were alternated every 250,000 cycles for a total of 5 million cycles. Gravimetric analysis of humeral cups throughout the test was used to characterize wear. Lubricant fluid was collected throughout the test and digested for polyethylene particle analysis.

RESULTS

Comparisons of volumetric wear rates and total volume loss between glenospheres with and without holes and between flexion and abduction loading profiles showed similar results. Particle analysis displayed fibrillar particles with an equivalent circle diameter of 0.3 ± .1 μm and an aspect ratio of 2.5 ± 1.4.

CONCLUSIONS

This study represents the first wear simulation and particle characterization of reverse shoulder systems. No significant difference in wear was reported between glenospheres with and without holes.

Suture capsulorrhaphy versus capsulolabral advancement for shoulder instability

PURPOSE

The purpose of this study was to test the strength of a suture capsulorrhaphy repair versus a capsulolabral repair with knotless suture anchors in a cadaveric model with anteroinferior shoulder instability.

METHODS

Fourteen cadaveric shoulders were tested with either a suture capsulorrhaphy to the intact labrum or a capsulolabral advancement using a knotless suture anchor into the glenoid. Specimens were translated with the shoulder in an abducted, externally rotated position to failure.

RESULTS

The capsulolabral advancement showed a significantly higher load to failure than did the suture capsulorrhaphy group (P = .030).

CONCLUSIONS

Capsulolabral advancement with suture anchors may offer greater initial strength when compared with a suture capsulorrhaphy. In the setting of shoulder instability without evidence of a labral tear, the capsulolabral advancement technique may be considered biomechanically superior.

CLINICAL RELEVANCE

In the setting of shoulder instability due to capsular insufficiency, the capsulolabral advancement may be considered biomechanically superior to a traditional suture capsulorrhaphy.

The acute effect of bipolar radiofrequency energy thermal chondroplasty on intrinsic biomechanical properties and thickness of chondromalacic human articular cartilage

Radio frequency energy (RFE) thermal chondroplasty has been a widely-utilized method of cartilage debridement in the past. Little is known regarding its effect on tissue mechanics. This study investigated the acute biomechanical effects of bipolar RFE treatment on human chondromalacic cartilage. Articular cartilage specimens were extracted (n = 50) from femoral condyle samples of patients undergoing total knee arthroplasty. Chondromalacia was graded with the Outerbridge classification system. Tissue thicknesses were measured using a needle punch test. Specimens underwent pretreatment load-relaxation testing using a spherical indenter. Bipolar RFE treatment was applied for 45 s and the indentation protocol was repeated. Structural properties were derived from the force-time data. Mechanical properties were derived using a fibril-reinforced biphasic cartilage model. Statistics were performed using repeated measures ANOVA. Cartilage thickness decreased after RFE treatment from a mean of 2.61 mm to 2.20 mm in Grade II, II-III, and III specimens (P < 0.001 each). Peak force increased after RFE treatment from a mean of 3.91 N to 4.91 N in Grade II and III specimens (P = 0.002 and P = 0.003, respectively). Equilibrium force increased after RFE treatment from a mean of 0.236 N to 0.457 N (P < 0.001 each grade). Time constant decreased after RFE treatment from a mean of 0.392 to 0.234 (P < 0.001 for each grade). Matrix modulus increased in all specimens following RFE treatment from a mean 259.12 kPa to 523.36 kPa (P < 0.001 each grade). Collagen fibril modulus decreased in Grade II and II-III specimens from 60.50 MPa to 42.04 MPa (P < 0.001 and P = 0.005, respectively). Tissue permeability decreased in Grade II and III specimens from 2.04 ∗10(-15) m(4)/Ns to 0.91 ∗10(-15) m(4)/Ns (P < 0.001 and P = 0.009, respectively). RFE treatment decreased thickness, time constant, fibril modulus, permeability, but increased peak force, equilibrium force, and matrix modulus. While resistance to shear and tension could be compromised due to removal of the superficial layer and decreased fibril modulus, RFE treatment increases matrix modulus and decreases tissue permeability which may restore the load- bearing capacity of the cartilage.

Characterization of daptomycin-loaded antibiotic cement

Antibiotics are commonly mixed with polymethylmethacrylate (PMMA) cement to suppress severe periprosthetic infections associated with total joint arthroplasty. The relationship between antibiotic concentration and the resulting elution kinetics remains unclear. The purpose of this study was to characterize the release of daptomycin from PMMA cement and the subsequent effects on mechanical properties.Varying concentrations of daptomycin and tobramycin were vacuum mixed in commercially available PMMA and subjected to an in vitro elution period. High-performance liquid chromatography was used to quantify the concentration of the amount of daptomycin eluted at predetermined time points. Samples were subjected to compressive loading to analyze the effect of antibiotic concentration on cement mechanical properties. Daptomycin elution increased when initial tobramycin concentration was increased. Furthermore, the addition of antibiotics increased the compressive strength of the cement in the postelution period. The binary addition of tobramycin with daptomycin antibiotics modifies the elution and mechanical properties of PMMA bone cement. Based on the findings of our study, 2 g of daptomycin and 3.6 g of tobramycin per 40-g packet of cement should be used to promote daptomycin elution without sacrificing PMMA mechanical properties.