Professor of Anatomy Belmont University Nashville, Tennessee, United States
Abstract Body : Introduction:
The Riche-Cannieu anastomosis (RCA) or connection between the ulnar and median nerves in the hand has a variable incidence and electrophysiologic verification is challenging. This study intends to characterize ulnar supply to the thenar eminence anatomically with gross dissection and functionally with nerve conduction in normal adults.
Methods:
38 (18 right and 21 left) limbs in 39 formalin fixed bodies were dissected. There were 27 male and 12 female donors with a mean age of 69.3 ± 10.5 years of age when deceased. Median to ulnar nerve communications were recorded as well as terminal ulnar branches in the thenar eminence. Any component of the flexor pollicis brevis lateral to the flexor pollicis longus tendon was designated as the superficial head of that muscle.
Nerve conduction testing in 76 limbs from 39 participants was completed. There were 15 males and 24 females with a mean age of 24.9 ± 4.4 years old participating in this portion of the study. The median and ulnar nerves were stimulated at the wrist and elbow with an active recording electrode over the APB.
An electrophysiological percent of ulnar contribution to the thenar eminence was calculated by dividing the sum of the ulnar and median wrist amplitudes from the ulnar wrist amplitude. Typical thenar innervation was defined as median supply to the APB, opponens pollicis and superficial head of the flexor pollicis brevis (FPB) with ulnar supply to the deep head of the FPB. Typical ulnar thenar supply was operationally defined as having 10-24% ulnar contribution.
Results:
Nine of 38 dissected hands presented with an RCA. There were an additional 5 limbs with expanded ulnar supply to the FPB (superficial head) and 3 of those had a branch to the APB.
A median response was recorded from the APB in all 76 limbs tested, and an ulnar response was recorded from the APB in 63 (83%) limbs. The electrophysiological ulnar percent contribution revealed a typical ulnar thenar supply in 29 limbs and expanded ulnar presence was identified in 29 limbs.
Discussion
We found an expanded ulnar supply in 37% of limbs dissected. We used formalin fixed cadavers without magnification so that delicate branches may have been damaged during dissection. It is likely that there were more ulnar branches and RCA connections than we were able to observe.
Clinical significance
Our findings of an expanded ulnar supply rate of 37% anatomically and 40% electrophysiologically may be enough to consider stimulating both median and ulnar nerves as a standard screen for expanded ulnar presence during an upper extremity nerve conduction.
