Review Question - QID 216308

Tardy ulnar nerve palsy in patients with cubitus varus deformity is commonly caused by anterior nerve subluxation followed by fibrous bands of the flexor carpi ulnaris (FCU) compressing the nerve.

Supracondylar humerus fractures with medial column comminution can lead to cubitus varus deformities. Rarely the deformity is the result of a growth disturbance. In some cases, tardy ulnar nerve palsy can result leading to pain and tingling sensation in the ring and small fingers with dorsoulnar hand involvement. Studies have demonstrated the most common mechanism of nerve irritation due to anterior nerve subluxation followed by nerve entrapment by scar tissue and fibrous bands of the FCU. Treatment typically involves anterior nerve transposition with or without a correcting osteotomy.

Fujioka et al. presented a series of four patients with tardy ulnar nerve palsy resulting from cubitus varus deformity after surgical treatment of supracondylar humerus fractures. They reported two patients had nerve entrapment of scar tissue that kinked the nerve with elbow flexion, one patient with anterior nerve instability with elbow flexion, and one entrapped in a fibrous band from the FCU. They concluded cubitus varus leads to abnormal anatomy of the elbow leading to nerve instability.

Jeon et al. presented seven cases of tardy ulnar nerve palsy from cubitus varus deformity. They reported a mean internal rotation angle of 30.7° and the most prominent feature being anterior nerve subluxation followed by fibrous bands of the FCU compressing the nerve. They concluded surgical treatment with anterior nerve transposition with or without varus correcting osteotomy can lead to clinical improvement.

Figure A is an AP radiograph of the right elbow depicting a cubitus varus deformity.

Incorrect answers
Answer 1: Compression by Osborne's ligament is one of the most common causes of cubital tunnel syndrome. However, in patients with abnormal anatomy from cubitus varus, anterior instability is the most common cause.
Answer 2: Cubitus valgus deformity can lead to traction irritation of the ulnar nerve.
Answer 4: Compression by the ligament of Struthers is one of the most common causes of median nerve entrapment.
Answer 5: Ulnar nerve compression in Guyon canal is unlikely in this scenario given the elbow deformity and symptom involvement of the dorsoulnar hand.