Review Question - QID 220075

With sharp pain and ecchymosis present in the proximal forearm after performing curls, a distal biceps tendon rupture is the likely diagnosis, despite a "normal" hook test, which can be falsely present if the examiner is performing it incorrectly. Based on the figures, the short head of the biceps tendon inserts distal and anterior on the radial tuberosity footprint (Answer 2).

Biceps tendon tears generally occur secondary to a sudden excessive eccentric contraction of the biceps brachii. These injuries are typically diagnosed clinically with significant ecchymosis directly over the distal biceps insertion and a mechanism of injury with a sudden eccentric contraction of the biceps brachii. This can be diagnosed with a hook test, which involves hooking your finger lateral to medial over the distal bicep insertion on the radial tuberosity. An abnormal hook test implies there is pathology, meaning your finger is not hooking any tendon over the distal bicep insertion and therefore, there is a complete tear/rupture of the distal biceps brachii. A common error can occur with hooking the lacertus fibrosis that may still be intact from medial to lateral instead of hooking the distal biceps tendon (that inserts more lateral) from lateral to medial, resulting in a falsely "normal" test. Treatment can be either non-operative or operative, depending on patient factors, including age, functionality, chronicity, and degree of tear.

A study by Jarrett et al. reviewed the anatomy and biomechanics of the short and long heads of the biceps brachii in 6 cadavers. They found the short head of the biceps brachii inserted distal and anterior to the long head on the radial tuberosity and typically included the apex of the radial tuberosity. They concluded that the long and short heads have separate insertional points on the radial tuberosity and the short head's insertion allows it to be more efficient with elbow flexion whereas the long head's insertion allows it to be more efficient with supination.

Kulshreshtha et al. reviewed the anatomy of the distal biceps insertion and its clinical relevance. They dissected 74 cadavers and found that the distal biceps insertion had a footprint measuring 19.3 mm (right) and 19.4 mm on the left. After dissection, they concluded that the anterior tendon receives fibers primarily from the short head, and the posterior tendon receives fibers from the long head.

Figure A is an axial MRI of the proximal forearm with a yellow highlight demonstrating the footprint of the distal biceps tendon on the radial tuberosity. The orange highlight shows the anterior portion of the footprint where the short head of the biceps tendon inserts. Figure B is a sagittal MRI of the proximal forearm demonstrating the distal bicep footprint (yellow highlight) and where the short head inserts on the radial tuberosity (orange highlight). Illustration 1 is an axial view of the proximal forearm showing that the more medial lacertus fibrosis (LF) envelops the flexor muscle bellies in the forearm and originates from the distal short head of the biceps tendon (BT).

Incorrect answer choices:
Answer 1: The annular ligament encompasses the anterior aspect of the radial head and provides stability to the proximal radioulnar joint. It does not attach to the radial tuberosity.
Answer 3: The long head of the biceps tendon inserts more proximal and posterior on the radial tuberosity footprint in relation to the short head.
Answer 4: The lacertus fibrosis is likely still intact with a falsely positive hook test. However, it lies more medial to the distal biceps tendon insertion, as shown in Illustration 1.
Answer 5: The brachialis is a more anterior structure and does not attach to the radial tuberosity. It inserts on the coronoid process and ulnar tuberosity.