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

Abstract

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 postrepair histological and cellular responses at the tendon-bone attachment site (enthesis) is needed. We examined operated shoulders from 42 New Zealand female white rabbits. 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 nonchondrocytes were quantified at 0, 1, 2, and 4weeks postrepair. 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 2weeks of enthesis formation. Between 2 and 4weeks, fibrocartilage staining plateaued while chondrocyte number decreased. The presence of nonchondrocytes remained similar between 0- and 1-week postrepair but then decreased abruptly at 2weeks. There was a linear correlation between fibrocartilage staining area and load to failure as well as stiffness. Nonchondrocyte number negatively correlated with stiffness. Early plateau of fibrocartilage staining and decrease in chondrocytes between 2 and 4weeks postrepair suggest a blunted enthesis formation response in our animal model.