Clinical Presentation and Diagnosis
Rupture most commonly occurs during forced extension of a flexed elbow which results in eccentric contraction of the biceps. Patients will often describe a sudden pain or “pop” on the anterior aspect of the elbow. This is usually associated with antecubital fossa and forearm bruising. Patients may also describe weakness and may have continued pain, especially in partial tears.
On inspection a “reverse pop-eye” sign may be seen, caused by retraction of the biceps muscle belly proximally. This may not always be apparent in case of a partial tear or if the lacertus fibrosus is still intact.
The “hook test” is the most sensitive and specific test (100% for each) and involves the examiner placing an index finger round the tendon from the lateral side during active flexion and supination of the elbow. The finger will usually hook underneath an in tact distal biceps. A common error is to mistake the lacertus fibrosus with distal biceps leading to delayed diagnosis.
The “bicipital aponeurosis flex test” can be undertaken to assess the integrity of the lacertus fibrosus. It is carried out by asking the patient to actively flex a supinated forearm whilst making a fist. At 75 degrees of flexion, the edge of the lacertus fibrosus can be felt medially in the cubital fossa (Sensitivity 100%, Specificity 90%).