Supraspinatus detachment causes musculotendinous degeneration and a reduction in bone mineral density at the enthesis in a rat model of chronic rotator cuff degeneration.

Abstract

To evaluate biological strategies that enhance tendon-bone healing in humans, it is imperative that suitable animal models accurately reproduce the pathological changes observed in the clinical setting following a tear. The purpose of the present study was to investigate rotator cuff degeneration in a rat, as well as assess the development of osteopenia at the enthesis following tendon detachment. Eighteen female Wistar rats underwent unilateral detachment of the supraspinatus tendon. Specimens were retrieved at 4 weeks (<i>n</i> = 6), 6 weeks (<i>n</i> = 6) and 9 weeks (<i>n</i> = 6) postoperatively for histological analysis and peripheral quantitative computer tomography. Three weeks following tendon detachment, there was a significant increase in the modified Movin score, characterized by a loss of muscle mass, fatty infiltration, an increase in musculotendinous cellularity, loss of normal collagen fibre structure/arrangement, rounded tenocyte nuclei and an increase in the number of vascular bundles. This was accompanied by a reduction in bone mineral density at the tendon insertion site. After 3 weeks however, these changes were less prominent. The rotator cuff tendon-muscle-bone unit in a rat model 3 weeks after detachment of supraspinatus represents a valid model for investigating rotator cuff degeneration.