Velocity drop in anconeus epitrochlearis-associated cubital tunnel syndrome

The anconeus epitrochlearis (AE) muscle is a common anatomical variation in the cubital tunnel retinaculum of the elbow with an incidence of up to 28%; it is one cause of compressive ulnar neuropathy. In this study, we report the significance of preoperative recognition of AE-associated cubital tunnel syndrome, based on the grade of velocity drop of the compressed ulnar nerve in electrophysiological studies. Twenty-two cases with idiopathic cubital tunnel compression (CTC) were retrospectively analyzed; AE was present in 6 cases. Velocity drop of the ulnar nerve was calculated by dividing the difference in velocity (m/s) by distance (cm); the results were classified into the following grades: + (0-2.99 m/s per cm) and ++ (< 3.00 m/s per cm). Categorical data were compared using Fisher's exact test; the Mann-Whitney U test was used to determine statistical significance of ordinal data. In patients with AE-associated CTC, 3 of the 6 (50%) cases had grade ++ velocity drop. In comparison, only 1 patient of the 16 non-AE cases (6%) had grade ++ velocity drop (P = .046). Preoperative nerve velocity conduction studies that show grade ++ velocity drop (< 3.00 m/s per cm) in ulnar nerve are highly suggestive of the presence of AE.