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 4 weeks 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 2 weeks of enthesis formation. Between 2 and 4 weeks, fibrocartilage staining plateaued while chondrocyte number decreased. The presence of nonchondrocytes remained similar between 0-and 1-week postrepair but then decreased abruptly at 2 weeks. 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 4 weeks postrepair suggest a blunted enthesis formation response in our animal model. K E Y W O R D S arthroplasty, histology, rotator cuff, tendons 1 | INTRODUCTION Rotator cuff (RC) tears are the most common cause of upper limb pain in humans and frequently impair function (Mitchell et al., 2005; Williams et al., 2004). Full-thickness tears have been detected in at least one-fifth of the general population and this proportion increases with age, reaching up to 50% in individuals in their eighties

Effects of hindlimb unloading and subsequent reloading on the structure and mechanical properties of Achilles tendon‐to‐bone attachment

“…Very recently, Abraham et al (2022) 18 reported increased stiffness of the mouse supraspinatus tendon enthesis as well as increased PG content after downhill treadmill training. In addition, in a rabbit model of rotator cuff anchor repair, PG content was positively correlated with tendon supraspinatus stiffness, 4 weeks of post‐repair 65 . Further support is provided by the reported reduction in transverse compressive and axial tensile strains during ankle dorsiflexion, indicating a more rigid Achilles tendon enthesis, in patients with insertional Achilles tendinopathy 66 with, at the histological level, an increase in PG content 67 .…”

“…In addition, in a rabbit model of rotator cuff anchor repair, PG content was positively correlated with tendon supraspinatus stiffness, 4 weeks of post-repair. 65 Further support is provided by the reported reduction in transverse compressive and axial tensile strains during ankle dorsiflexion, indicating a more rigid Achilles tendon enthesis, in patients with insertional Achilles tendinopathy 66 with, at the histological level, an increase in PG content. 67 The impact of PG on Achilles tendon stiffness is probably mediated by interactions of some of these macromolecules with collagens.…”