Discovering an Anatomic Variant of the Palmaris Profundus during Open Carpal Tunnel Release

A 46-year-old female presented after 3 years of steadily increasing numbness in her hands bilaterally with worse symptoms in her right hand. She reported nighttime paresthesia and exacerbation of her symptoms while writing, typing, and driving. Tinel's and carpal tunnel compression test were positive bilaterally. During the right hand carpal tunnel release, a layer of synovium was present deep to the carpal ligament with a tendinous portion running midline longitudinally along the median nerve. This layer was an anomalous palmaris profundus (PP) tendon within the carpal tunnel, which inserted distally in the palmar fascia. The PP tendon was freed and released. The PP is a rare muscle variation of the forearm and wrist, and although it has no function, it has been reported as a cause of median nerve compression at the wrist. More commonly, it is an incidental finding during carpal tunnel surgery. Because of its close association with the median nerve, it can cause confusion when encountered during carpal tunnel surgery. Clinicians should be aware of this rare finding, which may be present during carpal tunnel surgery. We present a case, with intraoperative photographs, of a PP tendon that was encountered during a carpal tunnel release.