Rotator cuff anchor repair: Histological changes associated with the recovering mechanical properties in a rabbit model.

Rotator cuff anchor repair is an increasingly common surgical procedure but the failure rate remains high. In order to improve surgical outcomes, a better understanding of post-repair histological and cellular responses at the tendon-bone attachment site (enthesis) is needed. We examined operated shoulders from 42 New Zealand female white rabbit. The animals underwent unilateral supraspinatus detachment followed by anchor repair a week later. To assess enthesis reformation, fibrocartilage staining area and the number of chondrocytes or non-chondrocytes were quantified at 0, 1, 2, and 4 weeks post-repair. Using linear regression, we correlated these results with the load to failure and stiffness recorded during mechanical testing of the tendons. Fibrocartilage staining and chondrocyte number increased during the first 2 weeks of enthesis formation. Between 2-4 weeks, fibrocartilage staining plateaued while chondrocyte number decreased. The presence of non-chondrocytes remained similar between 0- and 1-week post-repair but then decreased abruptly at 2 weeks. There was a linear correlation between fibrocartilage staining area and load to failure as well as stiffness. Non-chondrocyte number negatively correlated with stiffness. Early plateau of fibrocartilage staining and decrease in chondrocytes between 2-4 weeks post-repair suggest a blunted enthesis formation response in our animal model. This article is protected by copyright. All rights reserved.