Unusual coexistence of a variant abductor digiti minimi and reversed palmaris longus and their possible relation to median and ulnar nerves entrapment at the wrist

Abstract

During routine anatomical dissection of the left upper limb of a 73-year-old female cadaver, a unique coexistence of variant muscles was found. In the forearm region, a largely developed reversed palmaris longus was discovered. Its short distal tendon was in close relation to the median nerve. In the neighboring hypothenar region, an unusual abductor digiti minimi was also observed. Its muscular body was composed of two portions - medial and lateral one, arising from the reversed palmaris longus tendon. The lateral portion passed over the ulnar nerve and artery in the canal of Guyon. In the literature, there are descriptions of entrapment neuropathies caused by either reversed palmaris longus or variant abductor digiti minimi. Here, for the first time we describe a coexistence of these variant muscles and suggest it as a possible, even rare, cause of both the median and ulnar nerves entrapment and ulnar artery thrombosis.