The posterior branch of the medial antebrachial cutaneous nerve (MACN) is at risk to be damaged during cubital tunnel surgery. The purpose of this study was to identify the location of the posterior branch of the MACN (PBMACN) in relation to surgical landmarks pertinent in cubital tunnel surgery.

We performed an anatomical study on 20 limbs from 13 fresh cadavers. The nerve was dissected from 10cm proximal to 10cm distal of the medial epicondyle. We measured the distance between the nerve and the medial epicondyle, and also the distance separating the PBMACN from the ulnar nerve passage between the two heads of the flexor carpi ulnaris. Measurements were performed with the elbow at 45° and 90° of flexion, as well as in full pronation and supination.

After its emergence from the main trunk of the MACN, the posterior branch ran anteriorly to the medial epicondyle, taking an oblique direction toward the ulnar shaft. The PBMACN was in average 2.53cm under the medial epicondyle when the elbow was flexed at 45°, and 2.96cm when the elbow was flexed at 90°. Average distance between the PBMACN and the penetrating point of the ulnar nerve within the flexor carpi ulnaris was 1.54cm when the elbow was flexed at 45°, and 1.62cm when the elbow was flexed at 90°. Pronation and supination positions of the forearm did not significantly modify our measurements.

Understanding the position of MACN posterior branch during ulnar nerve release surgery at the elbow may help in preventing iatrogenic injury. According to our measurements, incision and superficial dissection anterior to the medial epicondyle or distal to the ulnar nerve penetrating point between the two heads of the flexor carpi ulnaris should be avoided or done with an elbow flexed at 90°.