Can We Reduce the Rate of Rotator Cuff Repair Failure with the Local Supplementation of an Amino Acid?

Commentary Rotator cuff repair surgery is one of the most common shoulder surgical procedures performed in the United States, yet, despite advances in surgical techniques over the past few decades, structural failure after repair remains a persistent finding in the literature1. As a result, consistent efforts are made in innovating new techniques and investigating patches, grafts, and biologics to improve healing, particularly in patients considered at high risk for retear. Older age2 and low bone mineral density3 represent 2 of the many known risk factors for repair failure. In their current study, Wang et al. investigated supplementation with the most abundant amino acid in the body, glutamine, as a means of enhancing healing of rotator cuff repair in patients with age-related osteoporosis. Using a well-established rat model and a fibrin gel as a delivery vehicle for glutamine, the investigators found better bone quality at the proximal humerus, a thicker trabecular bone structure, a more organized tendon-bone interface, and higher osteoblast counts with local glutamine supplementation. In concept, glutamine supplementation has potential theoretical advantages. Given its ubiquitous presence in the body, it is likely that the adverse-effect profile would be benign compared with that of many newer interventions for rotator cuff repair healing. Furthermore, given the wide availability of glutamine supplementation through enteral routes, local supplementation would presumably not be costly, placing it favorably in terms of the value equation. Methodologically, there are limitations to consider. First, the authors surgically created a tear that was immediately repaired. This creates a healing environment more in line with an acute traumatic tear rather than a degenerative tear more commonly encountered in patients with age-related osteoporosis. Second, the authors’ premise for this study is that osteoporosis undermines the secure fixation of surgical anchors, yet the model utilizes a single bone tunnel and a single suture for surgical repair. This does not replicate the clinical scenario in humans. Failure of modern surgical anchors is not a common occurrence, given that intraoperative findings of poor bone quality usually would be addressed by altering the type, size, and location of suture anchors. Lastly, it should be considered that older patients with osteoporosis and degenerative rotator cuff tears are often considered excellent candidates for conservative treatment rather than surgical repair, and so this intervention may be applicable to only a small proportion of patients indicated for rotator cuff repair. The study of glutamine supplementation to optimize the healing of the tendon enthesis in repairs performed in patients without osteoporosis could be of interest. However, if glutamine really does ameliorate the effects of osteoporosis, enhancing rotator cuff healing in elderly patients would represent a very small fraction of the overall benefit that it could provide to the musculoskeletal health of our patients.