The cubital tunnel: anatomical study of its distal part.

Different levels of ulnar nerve compression have been reported (the medial intermuscular septum, the posterior compartment of the arm, soft tissue or bony abnormalities of the cubital tunnel). In some rare cases, compression can lie in a 10-cm long tunnel, distal to Osborne's ligament, between the humeral head of the ulnar flexor muscle of wrist (FCU) and the medial epicondylar muscles. Only few publications mention this fact as a factor of residual or recurrent symptoms after common surgical procedures. However, a distal pathology of the cubital tunnel has proved to be the only factor of nerve entrapment in our clinical practice. Specific anatomical dissection of this area was carried out to find and classify the anatomical structures that may play a role in ulnar nerve distal compression. Twenty-four embalmed limbs from 13 cadavers were dissected. The purpose of this study was to find anatomical fibrous structures at an average of 10 cm from the medial epicondyle. Anatomical structures were classified into five types: no aponeurosis between the FCU and the medial epicondylar muscles (54.2% of cases), a fibrous band taut between the FCU and the fourth- and fifth-finger ulnar insertions of the flexor digitorum superficialis (FDS) (8.3%), a thin (20.8%) or thick (4.2%) partial aponeurosis between the FCU and the medial epicondylar muscles, and total aponeurosis (12.5%). Anatomical variations of the distal cubital tunnel were divided in five types, but their clinical significance remains unclear.