Effect of highly purified capsaicin on articular cartilage and rotator cuff tendon healing: An in vivo rabbit study.

Highly purified capsaicin has emerged as a promising injectable compound capable of providing sustained pain relief following a single localized treatment during orthopedic surgical procedures. To further assess its reliability for clinical use, the potential effect of highly purified capsaicin on articular cartilage metabolism as well as tendon structure and function warrants clarification. In the current study, rabbits received unilateral supraspinatus transection and repair with a single 1 ml injection of capsaicin (R+C), PEG-only placebo (R+P), or saline (R+S) into the glenohumeral joint (GHJ). An additional group received 1 ml capsaicin onto an intact rotator cuff (I+C). At 18 weeks post-op, cartilage proteoglycan (PG) synthesis and content as well as cell viability were similar (p>0.05) across treatment groups. Biomechanical testing revealed no differences (p>0.05) among tendon repair treatment groups. Similarly, histologic features of both cartilage and repaired tendons showed minimal differences across groups. Hence, in this rabbit model, a single injection of highly purified capsaicin into the GHJ does not induce a deleterious response with regard to cartilage matrix metabolism and cell viability, or rotator cuff healing. These data provide further evidence supporting the use of injectable, highly purified capsaicin as a safe alternative for management of postoperative pain following GHJ surgery.

Rotator cuff healing after continuous subacromial bupivacaine infusion: an in vivo rabbit study.

BACKGROUND: The objective of this study was to evaluate the effects of continuous subacromial bupivacaine infusion on supraspinatus muscle and rotator cuff tendon healing using gross, biomechanical, and histologic analyses. MATERIALS AND METHODS: Thirty-three New Zealand White rabbits underwent unilateral supraspinatus transection and rotator cuff repair (RCR). Rabbits were assigned to 1 of 3 groups: (1) RCR only, (2) RCR with continuous saline infusion for 48 hours, or (3) RCR with continuous 0.25% bupivacaine with epinephrine (1:200,000) infusion for 48 hours. Rabbits were euthanized postoperatively at 2 weeks (for histologic assessment) or 8 weeks (for biomechanical and histologic assessment). RESULTS: Tensile testing showed a significantly higher load to failure in intact tendons compared with repaired tendons (P < .01); however, no statistical differences were detected among RCR only, RCR saline, and RCR bupivacaine groups. Histologically, the enthesis of repaired tendons showed increased cellularity and disorganized collagen fibers compared with intact tendons, with no differences between treatment groups. Muscle histology demonstrated scattered degenerative muscle fibers at 2 weeks in RCR saline and RCR bupivacaine groups, but no degeneration was noted at 8 weeks. CONCLUSIONS: The healing supraspinatus tendons exposed to bupivacaine infusion showed similar histologic and biomechanical characteristics compared with untreated and saline-infused RCR groups. Muscle histology showed fiber damage at 2 weeks for the saline and bupivacaine-treated groups, with no apparent disruption at 8 weeks, suggesting a recovery process. Therefore, subacromial bupivacaine infusion in this rabbit rotator cuff model does not appear to impair muscle or tendon after acute injury and repair.

Biomechanical similarities among subscapularis repairs after shoulder arthroplasty.

HYPOTHESIS: Many authors suggest that subscapularis deficiency after shoulder arthroplasty has a negative effect on long-term outcomes. Thus, increasing emphasis has been placed on the technique for repair of the tendon. This study evaluated the biomechanical strength of 3 different repairs: osteotomy, tendon to bone, and a combined method. MATERIALS AND METHODS: Twenty-four paired shoulders from deceased donors were prepared for shoulder arthroplasty. The subscapularis tendon was removed/repaired with the lesser tuberosity in the osteotomy group, was removed periosteally in the bone-to-tendon group, and was tenotomized in the combined group. The tendon-to-bone repair used bone tunnels, and the combined construct added tendon-to-tendon fixation. A materials testing system machine was used for cycling. A digital motion analysis system with spatial markers was used for analysis. RESULTS: There were no significant differences (P > .05) in age, bone mineral density, or construct thickness. No statistically significant differences (P > .05) in elongation amplitude (P = .67) or cyclic elongation (P = .58) were detected within the constructs or between repair techniques. Failure testing revealed no differences in maximum load, stiffness, or mode of failure. DISCUSSION: There remains no consensus about the optimal method of repairing the subscapularis tendon during shoulder arthroplasty. Furthermore, the results of the current study do not support one technique over another with regard to initial fixation properties. All constructs investigated exhibited comparably robust biomechanical performance. Durability may, therefore, be more a result of healing potential than the specific construct chosen.