Biology of Rotator Cuff Injury and Repair

The glenohumeral joint is a complex anatomical structure commonly affected by injury such as tendinopathy and rotator cuff tears. Despite advances in surgical reconstruction of chronic rotator cuff tears, failure rates are still quite high. Significant research efforts have been focused on a better understanding of normal tendon biology, its pathological changes, the healing process and environment, and the whole shoulder stability and function. Rotator cuff injury has indeed a multifactorial pathogenesis, which includes anatomical, mechanical, and biological factors. Many theories have been postulated to explain this pathogenesis, trying to unify intrinsic and extrinsic theories. The precise role of each factor is not fully understood yet, although recent evidence strongly suggests that most of the tendinopathies and tendon ruptures are caused by primary failed healing response. The goals of tendon repair are to restore its force transmission function and recreate the relationships with the surrounding tissues, which allow the tendon to move smoothly. The success of tendon healing depends on the activation of cellular elements able to synthesize a new extracellular matrix and to remodel it with structural properties suitable for sustaining tensile loads. This chapter intends to give an overview on tendon histology and structure, shoulder joint motion and stability, causes of injury and mechanisms of tendon healing, including the possible pitfalls in this process.