Lateral Antebrachial Cutaneous Nerve Block

Indications and Clinical Considerations

Lateral antebrachial cutaneous nerve entrapment syndrome is caused by entrapment of the lateral antebrachial cutaneous nerve by the biceps tendon, the brachialis muscle, or the antebrachial superficial fascia. This entrapment syndrome is occasionally seen following rupture of the proximal biceps tendon and subsequent migration of the biceps muscle distally, resulting in compression of the lateral antebrachial cutaneous nerve as it passes beneath the distal biceps musculotendinous unit ( Figs. 75.1 and 75.2 ). Clinically, the patient with lateral antebrachial cutaneous nerve entrapment syndrome reports pain and paresthesias radiating from the elbow to the base of the thumb. Dull aching of the radial aspect of the forearm is also a common symptom. The pain of lateral antebrachial cutaneous nerve entrapment syndrome may develop after an acute twisting injury to the elbow, hematoma formation in the antecubital fossa and forearm after venous or arterial puncture, or direct trauma to the soft tissues overlying the lateral antebrachial cutaneous nerve. The onset of pain may be more insidious, without an obvious inciting factor. The pain is constant and is made worse with use of the elbow. Patients with lateral antebrachial cutaneous nerve entrapment syndrome often note increasing pain while keyboarding or playing the piano. Sleep disturbance is common. On physical examination, there is tenderness to palpation of the lateral antebrachial cutaneous nerve at the elbow at a point just lateral to the biceps tendon. Elbow range of motion is normal. Patients with lateral antebrachial cutaneous nerve entrapment syndrome exhibit pain on active resisted flexion or rotation of the forearm.

Cervical radiculopathy and tennis elbow can mimic lateral antebrachial cutaneous nerve entrapment syndrome. Lateral antebrachial cutaneous nerve entrapment syndrome can be distinguished from tennis elbow in that in lateral antebrachial cutaneous nerve entrapment syndrome the maximal tenderness to palpation is at the level of the biceps tendon, whereas in tennis elbow the maximal tenderness to palpation is over the lateral epicondyle (see Chapter 61 ). Electromyography helps distinguish cervical radiculopathy and lateral antebrachial cutaneous nerve entrapment syndrome from tennis elbow, and plain radiographs are indicated to rule out occult bony disease. On the basis of the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, uric acid level, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging and/or ultrasound imaging of the elbow is indicated if joint instability is suspected. The injection technique described later serves as both a diagnostic and a therapeutic maneuver.