Injection Technique for Anconeus Epitrochlearis

Indications and Clinical Considerations

Anconeus epitrochlearis is an uncommon cause of lateral forearm pain and weakness that can be quite distressing to the patient. It is caused by entrapment and compression of the ulnar nerve at the elbow by an accessory anconeus muscle ( Figs. 57.1 and 57.2 ). This entrapment neuropathy manifests as pain and associated paresthesias in the lateral forearm that radiates to the wrist and ring and little fingers in a manner analogous to tardy ulnar palsy. The symptoms are often aggravated by prolonged flexion of the elbow. The pain of anconeus epitrochlearis has been characterized as unpleasant and dysesthetic. The onset of symptoms is usually after repetitive elbow motions or from repeated pressure on the elbow, such as occurs from using the elbows to arise from bed. Anconeus epitrochlearis is also seen in throwing athletes, such as baseball pitchers and quarterbacks. Direct trauma to the ulnar nerve as it enters the cubital tunnel may also result in a similar clinical presentation, as can compression of the ulnar nerve as it passes through the cubital tunnel by osteophytes, lipomas, ganglia, and aponeurotic bands. If the condition is untreated, progressive motor deficit and ultimately flexion contracture of the affected fingers can result.

Physical findings include tenderness over the ulnar nerve at the elbow. A positive Tinel sign over the ulnar nerve as it passes beneath the aponeuroses is usually present. Weakness of the intrinsic muscles of the forearm and hand that are innervated by the ulnar nerve may be identified with careful manual muscle testing, although early in the course of the evolution of anconeus epitrochlearis, the only physical finding other than tenderness over the nerve may be the loss of sensation on the ulnar side of the little finger. As the syndrome progresses, the affected hand may take on a clawlike appearance. A positive Wartenberg sign indicative of weakness of the adduction of the fifth digit is often present. A positive Froment sign may also be present.

Electromyography helps to distinguish cervical radiculopathy and anconeus epitrochlearis from “golfer’s elbow.” Plain radiographs are indicated for all patients with anconeus epitrochlearis to rule out occult bony disease, such as osteophytes impinging on the ulnar nerve. On the basis of the patient’s clinical presentation, additional testing, including complete blood cell count, uric acid, sedimentation rate, and antinuclear antibody testing, may be indicated. Magnetic resonance imaging and/or ultrasound imaging of the elbow is indicated if joint instability is suspected and will clearly identify if the compression of the ulnar nerve is caused by an accessory anconeus muscle. Injection of the ulnar nerve will serve as both a diagnostic and a therapeutic maneuver ( Fig. 57.3 ).

Anconeus epitrochlearis is often misdiagnosed as golfer’s elbow, which accounts for the many patients whose golfer’s elbow fails to respond to conservative measures. Anconeus epitrochlearis can be distinguished from golfer’s elbow, in which the maximal tenderness to palpation is over the ulnar nerve 1 inch below the medial epicondyle, whereas in golfer’s elbow, the maximal tenderness to palpation is directly over the medial epicondyle. Anconeus epitrochlearis should also be differentiated from cervical radiculopathy involving the C7 or C8 roots and golfer’s elbow. Furthermore, it should be remembered that cervical radiculopathy and ulnar nerve entrapment may coexist as the “double crush” syndrome, which is seen most often with median nerve entrapment at the wrist or carpal tunnel syndrome.

Clinically Relevant Anatomy

Working with the other muscles of the posterior elbow, the anconeus muscle helps stabilize the elbow by stabilizing the proximal ulna during pronation of the forearm to prevent ulnar subluxation as well as by adducting and medially rotating the humerus. Situated posterior to the elbow joint, the anconeus muscle is a triangular muscle that arises from the lateral epicondyle of the humerus and finds its insertion into the lateral margin of the olecranon and posterior ulna ( Fig. 57.4 ). The muscle is innervated by the radial nerve. The anconeus muscle is susceptible to trauma and to wear and tear from overuse and misuse and may develop myofascial pain syndrome as well as epicondylitis at its origin on the lateral epicondyle of the humerus.