Clinical Application of Anomalous Muscles for Tendon Transfer in the Upper Limb: A Systematic Review of the Literature.

Numerous anomalous muscles of the forearm and hand have been reported in the literature. The majority were encountered in cadaver dissections and some were incidentally detected during tendon transfer surgery. Because of the limited number of motors available for transfer, it may be advantageous if an anomalous muscle with favorable anatomy can function as a potential donor in a suitable clinical environment. Although several authors have illustrated various anomalies and their functional significance, the reports of actual utilization of such muscles as donors for tendon reconstructions are sparse. The aim of the study is to conduct a systematic review of the clinical applications of anomalous muscles in the upper extremity. After a thorough search of PubMed, Web of Science, Scopus, and Cochrane Library databases, only three out of 106 studies were found to be relevant. Two of them discussed the anomalous radial wrist extensor tendon transfer for thumb flexion. The third study described the usage of anomalous flexor carpi ulnaris (FCU) for thumb opposition and index finger flexion, and also proposed a classification. This is the first systematic review of the clinical application of anomalous muscles as donors in the upper extremity tendon transfer surgical procedures. Knowledge of the above classification helps in intraoperative evaluation of the type of the anomaly and the possible consideration of anomalous muscle as a source of transplant material in an appropriate clinical setting.