A BSTRACT Background: Riche–Cannieu anastomosis (RCA) is an anatomic variation in which the thenar muscles are innervated partially or totally by the ulnar nerve. Its detection plays a crucial role in grading carpal tunnel syndrome (CTS). Objective: To determine the effects of RCA, as detected in nerve conduction studies (NCS) used in clinical practice, on patients with severe CTS. Methods: Fifty-one hands with severe CTS belonging to 35 patients, who had needle electromyography (EMG) recordings from the abductor pollicis brevis (APB) muscle together with both ulnar and median nerve compound motor action potentials (CMAP) from APB muscles were involved in this retrospective study. All statistics were performed using the R Studio program. Results: Hands were grouped into two categories according to electrophysiologic signs of ulnar innervation of the APB muscle: 16 hands having an ulnar nerve CMAP with initial negative deflection, and the remaining 35 hands, 32 of them having an ulnar nerve CMAP with initial positive deflection and three without an ulnar nerve CMAP from APB. Hands with an ulnar nerve CMAP with initial negative deflection had significantly less thenar atrophy ( P = 0.01) and were more likely to have the reinnervation signs in the needle EMG examination ( P = 0.02). Conclusion: RCA could mask the physical examination findings of severe CTS. Contrarily, it may compensate for the functional loss. A detailed electrodiagnostic assessment could elucidate the hallmarks of the condition.
Isil Tatlidil (Wed,) studied this question.