An anomalous flexor digitorum superficialis muscle-tendon unit associated with ulnar neuropathy. A case report.

A previously undescribed accessory flexor digitorum superficialis muscle-tendon unit was discovered on surgical exploration of the wrist in an 18-year-old girl with symptoms of distal ulnar neuropathy and a volar soft-tissue mass. Excision of the muscle-tendon unit resulted in complete resolution of symptoms. The preoperative diagnosis of an accessory muscle is difficult, being commonly mistaken for synovitis, ganglia, or tumor.