Partial Infraspinatus Tendon Transection as a Means for the Development of a Translational Ovine Chronic Rotator Cuff Disease Model.

OBJECTIVE: Rotator cuff tendon tears are the most common soft tissue injuries in the shoulder joint. Various animal models have been described for this condition, but all current translational animal models have inherent weaknesses in their ability to generate chronically degenerated rotator cuff tendons. The objective of this study was to evaluate a partial infraspinatus tendon transection model as a means of creating a chronically degenerated rotator cuff tendon in an ovine model and compare the injury characteristics of this model to those observed in human patients with severe chronic rotator cuff tendon injuries. STUDY DESIGN: The infraspinatus tendons of six sheep were partially detached followed by capping of the detached medial section of the tendon with Gore-Tex. Human tissue samples of the supraspinatus tendon were harvested from patients undergoing primary reverse shoulder arthroplasty and served as positive controls of chronic rotator cuff tendinopathy. RESULTS: Transected sheep tendons were characterized predominantly by an acute reactive and reparative pathological process as compared with the chronic degenerative changes observed in the human tendons. In contrast, the non-transected portion of the ovine tendon showed histological changes, which were more chronic and degenerative in nature when compared with the transected tendon. CONCLUSION: Overall, histological features of the non-transected portion of ovine tendon were more similar to those observed in the chronic degenerated human tendon.

Biomechanical and Histological Assessment of a Polyethylene Terephthalate Screw Retention Technology in an Ovine Metatarsal Fracture Model.

OBJECTIVE: Screw loosening in fracture fixation poses a clinical risk which may lead to implant failure, particularly in poor bone quality. The objective of this study was to examine the effectiveness of a novel screw retention technology (SRT) for increased screw purchase in a large animal metatarsal fracture model. STUDY DESIGN: This was a biomechanical, radiographic, and histological study utilizing an ovine metatarsal fracture model. Twenty-four sheep metatarsi underwent 3-mm ostectomies and were repaired with a nine-hole plate and 3.5-mm screws placed in oversized 3.5-mm holes to simulate worst case revision surgeries (i.e. no initial screw thread bone contact). Sheep were sacrificed at 3, 6 or 12 weeks (n = 6 each) post-operation. Post-sacrifice, each surgically implanted screw underwent either destructive mechanical testing or histomorphometric analyses. RESULTS: Treated metatarsi showed improved screw retention and normal fracture healing. Significant improvement in breakout strength and pullout strength of screws treated with the SRT were found as a function of healing time. Histologically, bone ingrowth at the screw interface was also shown to significantly increase with healing time. Improvements in fracture healing, indicated by an increase in bone fraction and decrease in void space at the osteotomy, were also observed with healing time. CONCLUSION: The results demonstrate the effectiveness of the SRT as a method for improved screw retention in a rescue-screw type scenario.

A prospective study comparing tendon-to-bone interface healing using an interposition bioresorbable scaffold with a vented anchor for primary rotator cuff repair in sheep.

BACKGROUND: The purpose of this study was to evaluate the biomechanical and histologic properties of rotator cuff repairs using a vented anchor attached to a bioresorbable interpositional scaffold composed of aligned PLGA (poly(l-lactide-co-glycoside)) microfibers in an animal model compared to standard anchors in an ovine model. METHODS: Fifty-six (n = 56) skeletally mature sheep were randomly assigned to a repair of an acute infraspinatus tendon detachment using a innovative anchor-PLGA scaffold device (Treatment) or a similar anchor without the scaffold (Control). Animals were humanely euthanized at 7 and 12 weeks post repair. Histologic and biomechanical properties of the repairs were evaluated and compared. RESULTS: The Treatment group had a significantly higher fibroblast count at 7 weeks compared to the Control group. The tendon bone repair distance, percentage perpendicular fibers, new bone formation at the tendon-bone interface, and collagen type III deposition was significantly greater for the Treatment group compared with the Control group at 12 weeks (P ≤ .05). A positive correlation was identified in the Treatment group between increased failure loads at 12 weeks and the following parameters: tendon-bone integration, new bone formation, and collagen type III. No statistically significant differences in biomechanical properties were identified between Treatment and Control Groups (P > .05). CONCLUSIONS: Use of a vented anchor attached to a bioresorbable interpositional scaffold composed of aligned PLGA microfibers improves the histologic properties of rotator cuff repairs in a sheep model. Improved histology was correlated with improved final construct strength at the 12-week time point.