Distal Biceps Rupture

Incidence: Distal biceps injuries at the elbow joint account for less than 5% of biceps tendon ruptures overall (the great majority are at the shoulder). They occur at a rate of 2.5 per 100,000 patient-years. Risk factors include smoking as well as increased body mass index. The average age of patients is 47 and more than 90% are male.

Injury Mechanism: Ruptures of the distal tendon near the elbow usually occur when an unexpected force is applied to a bent arm. This is most commonly an activity such as lifting a very heavy object or doing weights at the gym. It can also happen during sports such as a rugby tackle or a snowboarder using the arm to try to break a fall.

Injury Types: The tendon usually tears off the bone but ruptures can occur at the musculotendinous junction (usually with glenohumeral elevation, elbow extension, and forearm supination). It is possible for a patient to tear the short head of biceps only and this is usually incorrectly described or reported as a partial tear of the distal biceps tendon. Unfortunately, it is actually a complete tear of the short head with the long head intact. While the patient seems to recover well initially, they never restore full function to the elbow and most patients will eventually come to surgery with a short head tear.

Functional Outcomes: Without surgical repair, patients who have a complete rupture of the distal biceps will notice loss of strength at the elbow.  The strength loss will affect both the ability to flex the elbow and supinate against resistance.  Typically, patients get fatiguing and cramping in the muscle belly with repetitive use. Some people find speaking on the telephone difficult due to spasm of the muscle. Most people will find a functionally significant loss of supination and flexion strength, as well as decreased resistance to fatigue.

Diagnosis: The patient usually experiences sudden pain over the front of the elbow after a forceful effort against a flexed elbow (eccentric load). There may be a snap or pop and the muscle may curl up into the arm. Swelling and bruising around the elbow are common, usually in the forearm. Movement usually returns over a few days and the abnormal muscle shape becomes more obvious (reverse Popeye sign).  The hook test will be positive, which can be both sensitive and specific for complete distal tears. (O’Driscoll SW, Goncalves LB, Dietz P. The hook test for
distal biceps tendon avulsion. Am J Sports Med. 2007;351(11):1865e1869).

Isolated short head tear can be more difficult to diagnose because the muscle does not retract up the arm but does look abnormal. The hook test will also be ‘different’ but not actually positive because the long head is still intact.

Musculotendinous junction tears are rare and often present with antecubital pain, bruising, swelling but a negative hook test.

Imaging: The diagnosis of a distal biceps rupture is made on history and clinical examination.  Plain xrays of the elbow should be obtained to ensure that there is nothing unusual with the bone such as a cyst or tumour before drilling a hole in the bone. The only reason to order an MRI is to look for an isolated short head tear. A full tear will be obvious clinically. In my experience the report of a musculotendinous tear is often wrong with the patient having a complete bone avulsion of the tendon most of the time. Ultrasound rarely adds anything to the clinical findings. If an MRI is ordered then a special view with the arm flexed,
abducted and supinated should be performed.