The cubital tunnel in ulnar entrapment neuropathy.

Anteroposterior radiographs of the fully flexed and slightly externally rotated elbow were obtained in 122 cases of cubital tunnel syndrome (CUTS) and in 33 normal elbows. Medial trochlear lip osteophytes were not found in the studies of normal elbows but were noted in 20% of ulnar nerve entrapment cases. Medial incongruity between the trochlea and the olecranon greater than or equal to 5 mm was found in 29% of CUTS cases and in 6% of normal elbows. The presence of posttraumatic elbow-joint deformities seen on radiographs correlated significantly with the degree of clinical involvement. Depth and area measurements of ulnar nerve compression, performed using a line-art representation of the radiographs, showed a significant (P less than .0001) correlation between decrease in the area of the cubital tunnel and ulnar innervated muscle atrophy. These findings confirm the importance in this syndrome of both osteoarthritis and incongruity of the medial structures of the elbow joint.