Distal biceps tendon ruptures have been reported with increasing frequency, occurring 1.2 times per 100,000 patients per year, representing 3% of tendinous avulsions involving this muscle.1,2 This injury occurs most commonly in men between the ages of 40 and 60 years, and more often in the dominant extremity after an unexpected or violent eccentric contraction.2,3 Generally, the patient is performing a task that is more strenuous than usual and only performed occasionally; usually, it is a flexion task. The biceps muscle is the most superficial muscle in the anterior compartment of the arm with the distal tendon passing deep in the antecubital fossa to insert at the radial tuberosity (Figure 1). Pronation of the forearm rotates the radial tuberosity medially and posteriorly, drawing the biceps tendon distally with it (Figures 1-3). The biceps muscle is primarily responsible for supination of the forearm, although it is also important in elbow flexion.4,5 The bicipital aponeurosis (lacertus fibrosus) arises from the medial aspect of the muscle belly at the junction of the musculotendinous unit and the distal biceps tendon. This passes distally and medially across the antecubital fossa, blending with the fascia overlying the proximal flexor mass of the forearm, and inserts on the subcutaneous border of the ulna.3 A complete rupture of the distal biceps insertion can produce a 40% loss of supination strength, a 47% loss of supination endurance, and a 21% to 30% loss of flexion strength at the elbow when compared with the contralateral intact extremity.1,2,4
Prompt diagnosis of a distal biceps tendon complete rupture increases the ability to perform a primary repair, and to restore motion and strength.3 Patients with acute ruptures of the distal biceps typically present with a history of experiencing a painful “pop” after a violent eccentric load force at the time of injury. Clinical examination of a patient with a distal biceps tendon rupture shows a loss of the normal upper arm contour, pain with flexion and supination of the forearm, ecchymosis, and an inability to palpate the distal biceps tendon in the antecubital fossa.5 It is important to note that a false-negative test can be elicited when examining the integrity of the muscle contour if the lacertus fibrosus remains intact when there is a complete rupture of the distal biceps tendon.6 This false negative also can occur with examination of the upper arm contour as the elbow flexes. Radiographic studies to evaluate the distal biceps tendon can aid in the diagnosis of ruptures but are not a substitute for a thorough history taking and physical examination.3 Plain radiographs may show hypertrophic bone formation at the radial tuberosity, although they are generally unrevealing.3,6 After a complete clinical examination of the distal biceps tendon, magnetic resonance imaging (MRI) can be an important tool for evaluation of the distal biceps tendon.3 This article introduces a special test used as a diagnostic tool during the physical examination to isolate the distal biceps tendon from the lacertus fibrosus and to evaluate the integrity of the distal biceps brachii tendon.
To perform the supination-pronation test, the patient is positioned with both shoulders abducted to 90º and the elbows flexed to approximately 60º to 70º (Figures 4, 5). The examiner stands in front of the patient and observes the contour of the biceps muscle; the unaffected arm is used as a comparison. The examiner may either visually observe the contour of the muscle or may place a hand on the muscle belly throughout the test to feel for movement. The patient is asked to actively supinate and pronate the forearms by turning the hands. Through trial and error, we have found that the change in contour is most pronounced when placing the elbow in 60º to 70º of flexion. Additionally, through clinical experience, we have found testing the patient with both shoulders abducted to 90º provides the examiner with a reproducible examination that is easy to demonstrate to the patient; however, this shoulder position is not mandatory and can be modified if the patient struggles to get into testing position. Forearm position will maximize the size of the biceps, so the result is visually easier to appreciate. If the distal biceps tendon is intact, there is a substantial change in the shape of the biceps as the arm is supinated (the biceps moves proximally), then pronated (the biceps moves distally). Lack of migration of the biceps muscle during supination and pronation is considered a positive test, indicating rupture of the distal biceps tendon from its insertion on the radial tuberosity (Figure 6). We have found the anatomic correlations to a distal biceps injury may be clearly observed through the maneuver of the supination-pronation test and, therefore, provide a reliable clinical method to diagnose a complete distal biceps tendon rupture.