The biceps muscle is attached to the bone at the elbow. The biceps muscle is inserted into the radial tuberosity by the distal biceps tendon. The biceps muscle is responsible for some elbow flexion and is the primary supinator of the forearm. Supination is the function used when turning a key or a door knob. The biceps muscle is responsible for over 50% of forearm supination. Rupture of the distal biceps tendon involves flexion of the elbow against resistance with eccentric loading and sudden tearing of the tendon. The muscle may retract into the upper arm causing a bump or “Popeye” sign. If the ruptured tendon is not repaired, the patient will lose the ability to supinate the forearm adequately. Injury to the lateral antebrachial cutaneous nerve may occur when treating a distal biceps tendon rupture. The lateral antebrachial cutaneous nerve lies between the brachialis and biceps muscles. The nerve can become injured from aggressive retraction. The lateral antebrachial cutaneous nerve originates cutaneous nerve originates from the musculocutaneous nerve. Injury to the nerve results in loss of sensation along the radial aspect of the forearm.
Treatment of a distal biceps tendon injury usually requires surgery due to the important supination function of the biceps muscle. Surgery may be done in the form of a single anterior incision or a two incision technique. Both of these techniques have their advantages and disadvantages. The anterior approach is easier with minimal risk of synostosis; however, there is a risk of injury to the posterior interosseous nerve. The two incision approach has less risk of injury to the posterior interosseous nerve, however there is a risk of synostosis. The lateral antebrachial nerve is the nerve most commonly injured during repair of a distal biceps tendon rupture regardless of the technique that is used. When treating the distal biceps tendon rupture, identify and protect the lateral antebrachial cutaneous nerve. Diffuse pain and paresthesia in the forearm after distal biceps tendon repair should be investigated for lateral antebrachial cutaneous nerve injury. In this situation, the nerve may need to be explored.