Comparative effects of bone marrow stimulation and shockwave therapy on rotator cuff healing in chronic massive rotator cuff tears: A rat model study.

Purpose: Surgical intervention for massive rotator cuff tear (MRCT) has been found to result in positive outcomes; however, a high retear rate has frequently been reported. The present study employed a chronic MRCT model to assess the impact of microdrilling, a bone marrow stimulation (BMS) technique and extracorporeal shockwave therapy (ESWT) on rotator cuff healing. We hypothesized that BMS would result in superior healing than ESWT, reflected by a more normal tendon-to-bone junction histomorphology. Methods: A chronic rotator cuff tear model was created in the supraspinatus and infraspinatus tendons of 30 Sprague-Dawley rats. Four weeks later, the tendons were repaired using the transosseous technique. The animals were randomly assigned to three groups. In Group I, the intervention consisted exclusively of tendon repair. In Group II, ESWT was administered at various time points in conjunction with the repair process. In Group III, microdrilling was performed prior to the initiation of repairs. The animals were euthanized at 4 and 8 weeks post-repair. Repaired tendons, specifically the tendon-to-bone junction, were evaluated histomorphologically using the Bonar score and immunohistochemically for CD34, bone morphogenetic protein-2 (BMP-2), bone morphogenetic protein-7 (BMP-7) and transforming growth factor-β1 (TGF-β1). Results: A lower Bonar scale score in Group III more closely resembled normal tissue with respect to tenocyte morphology, extracellular matrix composition and vascularity, although statistical significance was limited to vascularity and extracellular matrix composition. By contrast, Group II showed a significant time-dependent deterioration in tenocyte morphology. Group III exhibited elevated BMP-2 and BMP-7 expression levels, and an increase in CD34 at the tendon-to-bone junction was observed in Group II; however, these did not reach statistical significance. TGF-β1 expression remained comparable among all groups. Conclusions: Both biological augmentation with BMS and ESWT demonstrated beneficial effects on tendon-to-bone healing in a rat model of chronic MRCT; however, these effects were not statistically significant. Although increased BMP-2, BMP-7 and CD34 expressions were noted in Group III, significant improvements were noted in vascularity according to the Bonar scale score, along with early enhancements in ground substance and overall histological structure. The deterioration of tenocyte morphology in the ESWT group highlights the need for optimized energy parameters. Level of Evidence: N/A.