Integrity of the Untorn Articular-Sided Tendon in Bursal-Sided Partial-Thickness Rotator Cuff Tear: A Comparative Study of Apoptotic Activity in Torn and Untorn Layers

Background: Conversion to full-thickness tear in partial-thickness rotator cuff tears (PTRCTs) is based on the quality and thickness of the normal-looking untorn rotator cuff layer. However, whether the untorn tendon is a healthy tissue remains to be elucidated. Purpose: To compare the apoptotic gene expression of the untorn articular layer with the torn bursal layer in PTRCTs. Study Design: Controlled laboratory study. Methods: Tendon tissues were harvested from 20 patients undergoing arthroscopic surgery for partial-thickness rotator cuff repair. As a control group, the tissues were harvested during intramedullary nail fixation in 10 proximal humeral fractures. In the experimental group, the samples were harvested from 2 sites: the torn bursal-sided tendon and the untorn articular-sided tendon. Hematoxylin and eosin (H&E) staining was conducted for basic histological evaluation, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining was used to detect apoptosis of tissue cells. The expression of caspase 3, 8, and 9 was confirmed immunohistochemically. Western blot analysis was used to assay the caspase activities. Results: In H&E staining, the direction of collagen bundles in untorn tendon was disoriented when compared with those of control tendon. However, the shape of the nuclei was not different, although the nuclei of the untorn tendon showed apoptosis in the TUNEL staining similar to those of the torn tendon. The immunohistochemical staining of caspase 3, 8, and 9 was increased concomitantly in untorn and torn tendons. All of the caspase activities in the untorn articular layer and torn bursal layer were significantly higher than in controls (P <.05). However, no significant differences were found between the two layers (P >.05). Conclusion: The study demonstrates that apoptotic gene expression is increased not only in the torn bursal layer but also in the untorn articular layer of PTRCTs. Clinical Relevance: The untorn articular layer of PTRCTs is abnormal, which triggers postoperative pain and further rotator cuff tears. Therefore, treatment of the abnormal untorn articular layer is essential in bursal-sided PTRCTs.