Anconeus epitrochlearis is an uncommon cause of lateral forearm pain and weakness that can be quite distressing to the patient. Anconeus epitrochlearis is caused by entrapment and compression of the ulnar nerve at the elbow by an accessory anconeus muscle.
This entrapment neuropathy manifests as pain and associated paresthesias in the lateral forearm that radiate to the wrist and ring and little fingers in a manner analogous to tardy ulnar palsy. The symptoms often are 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 using the elbows to arise from bed. Anconeus epitrochlearis also is seen in throwing athletes such as baseball pitchers and quarterbacks.
Direct trauma to the ulnar nerve as it enters the cubital tunnel may result in a similar clinical presentation, as can compression of the ulnar nerve as it passes through the cubital tunnel by osteophytes, lipomas, ganglions, and aponeurotic bands. Untreated, progressive motor deficit and ultimately flexion contracture of the affected fingers can result.
What are the Symptoms
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 have a claw-like appearance.
A positive Wartenberg sign indicative of weakness of voluntary adduction results in involuntary abduction of the little finger. A positive Froment sign also may be present.
How is Anconeus Epitrochlearis diagnosed?
Electromyography helps distinguish cervical radiculopathy and anconeus epitrochlearis from golfer’s elbow. Plain radiographs are indicated in all patients who present with anconeus epitrochlearis to rule out occult bony pathology, such as osteophytes impinging on the ulnar nerve.
Based on the patient’s clinical presentation, additional testing, including complete blood cell count, uric acid level, erythrocyte sedimentation rate, and antinuclear antibody testing, may be indicated.
Magnetic resonance imaging (MRI) of the elbow is indicated if joint instability is suspected and clearly identifies whether the compression of the ulnar nerve is caused by an accessory anconeus muscle. Ultrasound imaging will help assess the status of the ulnar nerve at the elbow. Injection of the ulnar nerve serves as a diagnostic and therapeutic maneuver.
Anconeus epitrochlearis is often misdiagnosed as golfer’s elbow, and this fact accounts for the many patients with golfer’s elbow who fail to respond to conservative measures. In anconeus epitrochlearis, 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 also should be differentiated from cervical radiculopathy involving the C7 or C8 roots and golfer’s elbow.
Cervical radiculopathy and ulnar nerve entrapment may coexist as the “double crush” syndrome. The double crush syndrome is seen most commonly with median nerve entrapment at the wrist or carpal tunnel syndrome.
Initial treatment of the pain and functional disability associated with anconeus epitrochlearis should include a combination of nonsteroidal antiinflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors and physical therapy. Local application of heat and cold also may be beneficial. The repetitive movements that incite the syndrome should be avoided.
For patients who do not respond to these treatment modalities, injection of the ulnar nerve at the elbow with a local anesthetic and steroid may be a reasonable next step. If the symptoms of anconeus epitrochlearis persist, surgical exploration, resection of the accessory anconeus muscle, and decompression of the ulnar nerve are indicated.
The major complications associated with anconeus epitrochlearis fall into two categories: (1) iatrogenically induced complications resulting from persistent and overaggressive treatment of “resistant golfer’s elbow” and (2) the potential for permanent neurological deficits resulting from prolonged untreated entrapment of the ulnar nerve.
Failure of the clinician to recognize an acute inflammatory or infectious arthritis of the elbow may result in permanent damage to the joint and chronic pain and functional disability.
An accessory anconeus muscle is present in approximately 11% of the adult population. Anconeus epitrochlearis is a distinct clinical entity that is often misdiagnosed as golfer’s elbow, and this fact accounts for the many patients with “golfer’s elbow” who fail to respond to conservative measures.
With anconeus epitrochlearis, the maximal tenderness to palpation is over the ulnar nerve and a positive Tinel sign is present, whereas with golfer’s elbow, the maximal tenderness to palpation is over the medial epicondyle.
If anconeus epitrochlearis is suspected, injection of the radial nerve at the elbow with a local anesthetic and steroid gives almost instantaneous relief.
Careful examination to identify preexisting neurological deficits that may later be attributed to the nerve block should be performed on all patients before beginning ulnar nerve block at the elbow.