Topographic Anatomy on the Supinator Muscle and the Deep Radial Nerve in Relation with its Entrapment Syndrome

Won, Hyung Sun; Hur, Mi Sun; Oh, Chang Seok; Chung, In Hyuk

Abstract

The deep radial nerve could be compressed by the medial border of the extensor carpi radialis brevis muscle, superior or inferior border of the superficial layer of the supinator muscle and pathologic structures between two layers of the supinator muscle. The aim of this study was to clarify the topographic relationships between the deep radial nerve and the supinator muscle in the place where the entrapment syndrome of the nerve could be occurred. Sixty-six Korean adult cadavers (124 arms) were used. The angles of the deep radial nerve with the radius were measured on the anteroposterior and lateral radiographs. The average distance between a line through the tips of both epicondyles of the humerus, and the division sites of the radial nerve into superficial and deep branches, was 16.8+/-12.8 mm in the cases where the division sites were proximal to the line, and 7.8+/-5.0 mm in the cases where the division sites were distal to the line. The arcade of Frohse was 32.2+/-6.6 mm apart from the line connecting both tips of humeral epicondyles. The average length of the deep radial nerve covered by the superficial layer of the supinator muscle was 35.1+/-8.0 mm. The arcade of Frohse was classified into two types; semi-circular type in 68.6% and dull curved line type in 31.4%. The lateral border of the arcade of Frohse was composed of muscle, tendon, and both muscle and tendon in 12.1%, 26.6%, and 61.3%, respectively. The muscle fibers of two layers of the supinator muscle were fused with each other, at the area where the deep radial nerve came out between two layers of the muscle. The average angles of the deep radial nerve with the radius, were 23.4+/-4.6 degrees and 13.7+/-5.3 degrees, on the anteroposterior and lateral radiographs, respectively. The inferior border of the superficial layer of the supinator muscle was composed of tendon, muscle, and both muscle and tendon in 61.5%, 12.5%, and 17.3%, respectively. We discussed about the morphologic variations which could cause the entrapment syndrome of the deep radial nerve in the proximal and distal portions of the supinator muscle, and between the superficial and deep layers of the muscle.