From the brachial plexus to the hand, multiple connections between the median and ulnar nerves may serve as bypass routes for nerve fibres

Abstract

Axons from the median and ulnar nerves can pass to each other through aberrant connections between them. Multiple interconnections between the nerves may provide a detour route for nerve fibres going to the hand. We investigated the incidence of variations and the associations between them in 90 cadaveric upper limbs. In 91% of upper limbs, one to five variations were found, with several statistically significant associations. The contribution of the C8 nerve to the lateral cord was positively associated with an accessory contribution of the lateral cord to the ulnar nerve. The latter variation showed positive association with the occurrence of any of the variations in the hand itself. Ulnar innervation of the superficial head of the flexor pollicis brevis was positively associated with the Riche-Cannieu communication. The co-existence of the variations and their associations may be the explanation for unusual clinical findings related to median and ulnar conduction, which appear contrary to anatomical knowledge.

A comprehensive review of motor innervation of the hand: variations and clinical significance

“…Some of this variation is thought to be due to connections between the Median and Ulnar nerves, such as the Riche -Cannieu anastomosis discussed below. In approximately 2% of hands the Ulnar nerve was found to innervate all the thenar muscles, and the Adductor Pollicis [2,56,70]. One author found that the median nerve solely innervated the thenar muscles in roughly one quarter of the population [22].…”

“…The MGA is formed in the forearm by an anastomosis between either the Anterior Interosseous Nerve or the main body of the Median nerve, to the Ulnar nerve [12,13,26,45,53,70]. The nerve axons start in the proximal Median nerve and cross the forearm to join the distal Ulnar nerve [70]. This anastomosis often carries motor fibers and has been shown to alter the innervation of the hand [12,20,42].…”

“…If the reader has no knowledge of aberrant connections, alternative innervation patterns or possible anastomosis, many peripheral nerve lesions will never be understood. Standard anatomical knowledge does not always explain the signs associated with nerve lesions [70], especially when anatomical variations are so common. For example, Rowntree found that the traditionally taught innervation pattern is found in only a third of the population, with one fifth of the population having significant variations of motor innervation [56] .…”

“…The Median and Ulnar nerves have a "normal" anatomical arrangement in only 8.9% of dissected limbs [70]. The remaining limbs displayed a wide array of variations that can have significant clinical implications, especially for hand surgery, trauma and compressive lesions.…”

Anastomosis Between the Deep Branch of Ulnar Nerve and a Branch of the Median Nerve (Cannieu-Riché Anastomosis) and Thenar Muscles Innervation. Anatomical Study and Clinical Implications

“…These authors emphasized that the incidence of CRA could potentially be higher if finer dissection techniques and fresh cadavers were used to avoid missing the smaller anastomotic fibers. According to Yang et al (2016), CRAs were observed in 45 of 90 cadaveric upper limbs (50 %).…”