The Crossing Motor Ulnar Nerve Branch at Elbow.

Background And Objectives: Cubital tunnel syndrome is the second most common nerve entrapment, and understanding the anatomy is crucial for the success of the nerve release. During ulnar nerve release for cubital tunnel syndrome, a motor branch is frequently encountered crossing anteriorly over the ulnar nerve from its medial/ulnar side proximally to the lateral/radial side distally. Little has been noted about this crossing branch in the literature. In this anatomic study, we sought to characterize this branch further and discuss its potential significance in cubital tunnel release.

Methods: We performed a cadaveric dissection of 48 elbow specimens as if performing a cubital tunnel release. We assessed for the presence of the crossing motor branch of the ulnar nerve and measured the distance from the medial epicondyle to the branch takeoff and to its target of innervation.

Results: Of our 48 specimens, 34 (71%) were noted to have a crossing motor branch at the area of compression by the deep flexor carpi ulnaris muscle fascia (common aponeurosis). On average, the distance from the medial epicondyle to the branch origin from the ulnar nerve was 18.2 mm and to the target muscle innervation was 28.4 mm.

Conclusion: Identifying this branch is important for performing a cubital tunnel release, and awareness of this anatomy during ulnar nerve decompression procedures may help avoid injury to this motor branch.