Medial Patellofemoral Ligament Reconstruction: Fixation Technique Biomechanics.

Introduction The medial patellofemoral ligament (MPFL) is the primary soft-tissue stabilizer of the patella and it is often reconstructed in patients with recurrent patella instability. This biomechanical analysis evaluates the integrity of four methods of MPFL reconstruction subjected to cyclic loading using a porcine model. Methods Four techniques of MPFL reconstruction were analyzed using a 4 mm flexor tendon graft, all with two points of patellar fixation to best recreate the native MPFL anatomy. The four techniques were: (1) interference screw technique, (2) suture anchor technique, (3) converging tunnel technique, and (4) two bone tunnel technique. Maximum load, yield load, and stiffness of the graft fixation/bone complex were analyzed, and statistics were performed with SPSS and significance set at a p-value of < 0.05. Results The converging tunnel technique demonstrated the highest maximum load and yield load, significantly higher than the interference screw or suture anchor groups (p = 0.007). In addition, the converging tunnel technique demonstrated the greatest stiffness with significantly greater stiffness than the two bone tunnel techniques (p = 0.016). Conclusion The combination of strength and stiffness, the avoidance of patella implants, and the creation of a single transosseous tunnel make the converging tunnel technique a desirable technique for MPFL reconstructions.

Use of platelet-rich plasma to enhance tendon function and cellularity.

Clinical studies have shown inconsistent healing with subjective improvement after use of platelet-rich plasma (PRP) for tendinosis and partial tendon tears. We conducted a study to assess changes after injecting PRP into an intact rabbit patellar tendon (PT) model. In the study group (n = 10), an incision was made over the PT and PRP was injected into multiple sites on the PT. The control group (n = 8) was injected with saline. PTs were harvested 7 and 28 days after injection. Hematoxylin-eosin staining showed hypercellularity in the PRP group at 7 days, but the effect was not as marked at 28 days. At 7 days, polarized microscopy showed increased crimp density of collagen in the PRP group, compared with the control group, demonstrating up-regulation in collagen matrix. Cellular proliferation measured by tritiated thymidine was also significantly increased (P = .02) in the PRP group, compared with the control group, but the difference was not as significant at 28 days. At 7 and 28 days, there were no significant changes in basic fibroblast growth factor, insulin-like growth factor, vascular endothelial growth factor, or platelet-derived growth factor with 2B chains. Injection of PRP into rabbit PT enhances collagen remodeling and hypercellularity with increased metabolic activity, which could have a positive effect on healing.

Treatment of articular cartilage defects in the goat with frozen versus fresh osteochondral allografts: effects on cartilage stiffness, zonal composition, and structure at six months.

BACKGROUND: Understanding the effectiveness of frozen as compared with fresh osteochondral allografts at six months after surgery and the resultant consequences of traditional freezing may facilitate in vivo maintenance of cartilage integrity. Our hypothesis was that the state of the allograft at implantation affects its performance after six months in vivo. METHODS: The effect of frozen as compared with fresh storage on in vivo allograft performance was determined for osteochondral allografts that were transplanted into seven recipient goats and analyzed at six months. Allograft performance was assessed by examining osteochondral structure (cartilage thickness, fill, surface location, surface degeneration, and bone-cartilage interface location), zonal cartilage composition (cellularity, matrix content), and cartilage biomechanical function (stiffness). Relationships between cartilage stiffness or cartilage composition and surface degeneration were assessed with use of linear regression. RESULTS: Fresh allografts maintained cartilage load-bearing function, while also maintaining zonal organization of cartilage cellularity and matrix content, compared with frozen allografts. Overall, allograft performance was similar between fresh allografts and nonoperative controls. However, cartilage stiffness was approximately 80% lower (95% confidence interval [CI], 73% to 87%) in the frozen allografts than in the nonoperative controls or fresh allografts. Concomitantly, in frozen allografts, matrix content and cellularity were approximately 55% (95% CI, 22% to 92%) and approximately 96% (95% CI, 94% to 99%) lower, respectively, than those in the nonoperative controls and fresh allografts. Cartilage stiffness correlated positively with cartilage cellularity and matrix content, and negatively with surface degeneration. CONCLUSIONS: Maintenance of cartilage load-bearing function in allografts is associated with zonal maintenance of cartilage cellularity and matrix content. In this animal model, frozen allografts displayed signs of failure at six months, with cartilage softening, loss of cells and matrix, and/or graft subsidence, supporting the importance of maintaining cell viability during allograft storage and suggesting that outcomes at six months may be indicative of long-term (dys)function. CLINICAL RELEVANCE: Fresh versus frozen allografts represent the "best versus worst" conditions with respect to chondrocyte viability, but "difficult versus simple" with respect to acquisition and distribution. The outcomes described from these two conditions expand the current understanding of in vivo cartilage remodeling and describe structural properties (initial graft subsidence), which may have implications for impending graft failure.

A biomechanical assessment of tendon repair after radiofrequency treatment.

After acute tendon injury, rapid mobilization prevents adhesions and improves the ultimate strength of the repair. Radiofrequency (RF) ablation is proposed to enhance angiogenesis in the early stages of healing. The mechanism and effect of RF have not yet been described in an animal model of tendon injury. To investigate the biomechanical effect of bipolar RF on acute injury in a rabbit model of partial Achilles tendon transection and suture repair, RF-treated tendon repairs were compared to untreated tendons. Cross-sectional area, Young's modulus, and ultimate tensile strength were determined. At 6 and 12 weeks after repair, RF-treated tendons had significant increases in cross-sectional area (P<.001; P< .0001) and ultimate tensile strength (P<.0001; P<.01). Young modulus of RF-treated tendons was increased at 6 weeks but not at 12 weeks (P<.01) Compared with untreated tendons, RF-treated tendons showed faster return to mechanical integrity. This may allow earlier rehabilitation.

Etanercept enhances preservation of osteochondral allograft viability.

BACKGROUND: Osteochondral allografts are an increasingly popular treatment for the repair of articular cartilage lesions. Current tissue bank protocols require bacteriological testing that takes from 21 to 28 days to process. During this time, tumor necrosis factor-alpha (TNF-α, a proapoptotic cytokine) is upregulated, resulting in loss of chondrocyte viability. To date, etanercept (a cytokine inhibitor) has not been studied in the current storage paradigm with the intention of preserving cell viability. PURPOSE: This study was undertaken to assess whether the addition of etanercept can improve the chondrocyte viability ofosteochondral allograft during storage. STUDY DESIGN: Controlled laboratory study. METHODS: Osteochondral allografts were harvested from 8 Boer goat femurs and placed into storage media and stored at 4°C for 28 days. The experimental group was supplemented with 10 µg/mL of etanercept. After storage, cell viability was assessed by live/dead staining and confocal microscopy. Specimens were also analyzed histologically and underwent histomorphologic analysis. TNF-α expression was measured with semiquantitative polymerase chain reaction. RESULTS: At 28 days, the percentage viability of the superficial zone in etanercept-treated allografts was maintained at significantly higher levels than those measured in the untreated group (69.3 ± 9.4 compared with 47.8 ± 19.1, P = .01). No difference was found histologically between the etanercept and the untreated group (ie, safranin O staining for glycosaminoglycan expression). Histomorphologic assessment showed no difference in indentation stiffness or roughness between groups. TNF-α expression was significantly decreased in the etanercept group compared to the untreated group. CONCLUSION: Etanercept was able to maintain cell viability of osteochondral allografts significantly better than the current storage paradigm after 28 days of storage. CLINICAL RELEVANCE: Maintaining the viability of the superficial zone will benefit outcomes by facilitating joint articulation via improved lubrication. Additionally, maintaining the cellular viability for increased periods of time may allow a greater window of time in which a suitable recipient may be found.

Epidemiology and risk factors of humerus fractures among skiers and snowboarders.

BACKGROUND: The incidence of humerus fractures while participating in snowboarding and skiing is undefined. Very little is known about the risk factors associated with these fractures. HYPOTHESIS: Snowboarders are at increased risk for sustaining humerus fractures when compared with skiers. In addition, the types of fractures, laterality, and risk factors differ between the 2 groups. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: At a major ski area clinic, 318 humerus fractures were evaluated over 34 seasons. Radiographs were classified according to the AO and Neer systems. Patient data were analyzed and compared with that of a control population of uninjured skiers and snowboarders to determine incidence and risk factors. RESULTS: The incidence of humerus fractures among snowboarders (0.062 per 1000 snowboarder days) was significantly higher than that of skiers (0.041 per 1000, P < .05). Skiers were more likely to sustain proximal fractures, and snowboarders were relatively more likely to sustain diaphyseal and distal fractures (P < .05). Of glenohumeral dislocations, 6.56% were associated with proximal humerus fractures among skiers (1.7% among snowboarders). Snowboarders who lead with their left foot were more likely to fracture their left humerus (P = .023). Helmet use and gender were not risk factors for humerus fractures among either skiers or snowboarders. Jumping was involved in 28.3% of humerus fractures among snowboarders and in 5.4% among skiers. Skiers with humerus fractures were more skilled, older, and fell less frequently than controls. Snowboarders were less skilled, younger, and fell at a similar rate compared with controls. CONCLUSION: Snowboarders are at significantly higher risk of sustaining humerus fractures than skiers. In skiers, humerus fractures show no laterality and most often involve the proximal humerus. In contrast, snowboarders more often fracture the left humerus at the diaphysis.