Case 22 - FABS positioning on MRI: demonstration of distal biceps tear

Summary

Imaging description

The flexed abducted supinated (FABS) positioning of the elbow for MRI is the optimal positioning for best visualization of the distal biceps. This positioning nicely demonstrates the full length of the distal biceps brachii from the musculotendinous junction to the radial tuberosity on only one slice/image in the majority of patients (Figure 22.1). The patient can be positioned for these images by first abducting the shoulder to 180° with the arm by the patient’s head. Next, the elbow is flexed to 90° and the forearm is supinated to a thumb-up position with a coil placed around the elbow (Figure 22.2). In one study of 22 patients, this positioning demonstrated the full length of the distal biceps brachii on either one or two slices. This improves the visualization of both normal anatomy and pathology as this positioning moves the entire distal tendon and its attaching structures into a single plane instead of the tendon and its attaching structures being in multiple oblique planes.

Importance

Images obtained using the FABS positioning can aid the surgeon in their evaluation of the integrity (partial tear versus rupture) and the quality of the torn distal biceps tendon prior to surgical intervention (Figure 22.3).

Typical clinical scenario

The patient is usually a young to middle-aged adult male who sustained sudden, massive, eccentric contraction of the biceps (such as trying to catch a falling 250-pound rock) and felt sudden pain and a snap in the antecubital fossa region of the arm. MRI is typically ordered when the physical exam is equivocal for a complete rupture of the distal biceps or might be ordered for preoperative evaluation when the injury is subacute or chronic.

Teaching point

The FABS positioning is useful in demonstrating the full extent of the distal biceps brachii tendon from its musculotendinous junction to its insertion on only one or at most two sections. This improves the visualization of both normal anatomy and pathology.