Muscular injuries after tendon rupture in the rotator cuff of animal models. Systematic review

This systematic review summarizes experimental evidence showing that chronic rotator cuff tendon rupture leads to progressive muscle degeneration characterized by atrophy, fibrosis, fatty infiltration, inflammation, and loss of regenerative capacity. Across sheep, rabbit, rat, and mouse models, tendon retraction consistently induces reduced muscle fiber diameter, a shift toward fast-twitch fibers, increased collagen deposition, lipid accumulation within and between fibers, and impaired satellite cell proliferation. Denervation further exacerbates these changes and alters the underlying mechanisms of atrophy. The review highlights fibro-adipogenic progenitors (FAPs) as a major cellular source of fibrosis and fatty infiltration and discusses pharmacological and cell-based interventions that partially attenuate degeneration but do not fully reverse it. The authors conclude that muscle degeneration after rotator cuff injury is multifactorial and remains a major unresolved barrier to successful surgical repair, emphasizing the need for targeted therapies addressing both fibrosis and fatty infiltration.