Accessory Hand Muscles Over the Transverse Carpal Ligament: An Obstacle in Carpal

BACKGROUND: Carpal tunnel syndrome (CTS) is an entrapment neuropathy caused by compression of the me-dian nerve throughout the carpal tunnel. It is the most common entrapment neuropathy, with an estimated preva-lence of 4%-7%. Surgical management is more effective in moderate to severe and severe CTS. CTS recurs in approximately 20% of patients, and up to 12% of these patients require reoperation. Knowledge of normal anatomy and variations would improve the success rate of the index surgery. Atypical causes of CTS were reported, including ganglion cysts, synovial hypertrophy, lipomas, bone frac-ture, bone fragments, tumor of soft tissues or bones, neu-rofibromas, neuromas, vascular malformations, and accessory muscles. Accessory muscles are commonly detected in upper limbs. However, their concomitant pre-sentation with CTS has rarely been reported. We aimed to present different accessory muscles diagnosed during CTS surgery through a systematic review of the literature with our exemplary case. -METHODS: A systematic review/meta-analysis was performed concomitant with a case presentation. -RESULTS: Accessory muscles associated with CTS were as follows: palmaris longus, 28.6%; lumbrical muscles, 19.3%; palmaris profundus, 17.8%; flexor digitorum super-ficialis, 16.1%; transverse carpal muscle, 5%; flexor dig-itorum indicis, 4.2%; flexor superficialis indicis, 4.2%; flexor sublimis, 0.8%; accessory superficialis longus, 0.8%; flexor pollicis longus, 0.8%; abductor digiti minimi, 0.8%; abductor digiti quinti, 0.8%; and flexor digitorum super-ficialis brevis, 0.8%. Accessory muscles were mostly noticed during CTS surgery (88.2%). -CONCLUSIONS: Knowledge of possible variations within the carpal tunnel would improve the surgeon's capability during CTS surgery.