Biologics in rotator cuff repair

Introduction

Rotator cuff pathology is a common source of shoulder pain, dysfunction, and disability in the general population. The incidence of rotator cuff tears is known to increase with age. With an increasingly active aging population, improved surgical techniques and implants, more refined rehabilitation protocols, and greater surgeon comfort in evaluating and treating rotator cuff pathology, rotator cuff repair is currently a widely performed surgery. Nonetheless, there is a high rate of failed healing following repair, with failure rates reported as high as 30% to 70% in certain populations.

The native rotator cuff insertion consists of a fibrocartilage transition zone that bridges the tendon to bone; however, in the setting of repair, healing occurs through fibrovascular scar formation ( Fig. 29.1 ). From a basic science perspective, rotator cuff healing relies on several key factors: tissue quality, biomechanical properties, and the biological environment. Tissue quality is dependent on numerous factors, including the patient’s genetics, overall health (comorbidities and habits), and history of prior injury. The biomechanical properties of a tendon are directly determined by the underlying microstructure and composition of the tendon, as well as tear morphology and chronicity. Factors under the surgeon’s control that affect the biomechanical environment include tendon fixation technique (sutures, knots, type of anchor, number of rows) and the postoperative rehabilitation protocol. The biological healing milieu consists of the cells, signaling molecules, and tissue architecture of the healing environment immediately following repair, and is largely dependent on innate biological pathways. Biological augmentation has the ability to impact all three components of rotator cuff healing. This chapter explores a number of biologic approaches used to treat rotator cuff tears, such as growth factor-based, cellular, and scaffold therapies, as well as mechanical modulation of the healing environment. Systemic treatments that are known to impact tendon and bone healing are considered as well.

Direct biological augmentation

The tendon-bone healing process consists of the initial inflammatory response followed by healing through fibrovascular scar formation and subsequent tissue remodeling. Manipulation of the biologic environment can favorably tip the delicate balance of tendon healing and tissue breakdown in the setting of injury. While extra-articular tissues such as the medial collateral ligament of the knee and the Achilles tendon are known to have good innate healing potential, it is thought that a fundamental reason for poor healing of intra-articular tendons is the failure of a fibrin clot to form and serve as a provisional scaffold for healing. The presence of fibrinolysates in the injured joint prevents formation of a stable fibrin clot, which is necessary as a provisional scaffold to support healing. The presence of inflammatory cytokines in the postsurgical environment has a profound effect on the initiation and regulation of the healing process. These inflammatory mediators are associated with increased levels of matrix-degrading enzymes (matrix metalloproteinases [MMPs]), and the altered homeostasis between these enzymes and their endogenous inhibitors has an adverse effect on new tissue formation at the healing tendon-bone interface. This decreased innate healing ability is the rationale for biological augmentation. Direct augmentation of the biological milieu can be achieved through several techniques, including factor-specific augmentation, combined augmentation with multiple factors simultaneously, and augmentation with progenitor cells.