Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Long Head of the Biceps

The long head of the biceps tendon has a variable origin, with 30% to 40% originating at the supraglenoid tubercle, 45% to 60% directly from the labrum, and 25% to 30% from both. It travels obliquely within the shoulder joint, then turns sharply to exit inferiorly beneath the transverse humeral ligament along the bicipital groove. It decreases in size and shape along its course.

The tendon becomes more flat as it progresses over the humeral head and more triangular in the bicipital groove. In abduction, the tendon deforms to follow the shape of the bicipital groove; in adduction, the proximal portion regains its original shape as it exits the groove.

The long head of the biceps tendon is covered by a reflection of the synovial sheath, which ends as a blind pouch at the distal part of the bicipital groove, thus making the tendon an intra-articular, but extrasynovial, structure. The tendon has an average length of 102 mm.

The role of the biceps in shoulder function continues to be a topic of debate. Neer and others have suggested that it functions as a humeral head depressor and, thus, that tenodesis should be avoided, especially in patients with an RTC tear.

Electromyographical (EMG) studies have shown that the biceps is extremely active in throwing athletes when the shoulder is placed in the vulnerable position of abduction and external rotation, as during the late cocking phase of pitching. These studies also have shown an even higher rate of activity of the biceps during this phase in pitchers with anterior instability.

In addition, biomechanical studies have shown that the long head of the biceps increased the torsional rigidity of the GH joint by 32%, thus providing greater anterior stability and also serving a protective role by decreasing the load required by the IGHL.

More recent EMG studies, however, have suggested that the biceps shows little action during shoulder motion, acts mainly to control the elbow, and is not active during simple shoulder abduction. This is an important concept, because it has been suggested that the biceps may prevent superior displacement of the humeral head in the case of a massive RTC tear. In contrast, Walch et al.

They have had success with tenodesis of the biceps tendon even in patients with RTC tears, and those authors have not observed instability in these patients. It also is possible that the long head of the biceps serves a proprioceptive function and that it may play a role in neuromuscular control and coordination of shoulder motion in relation to the elbow, because the muscle–tendon unit crosses both joints.

This theoretical role is supported by the interesting analogy to all the major proximal long bones, because two articulation muscles are a consistent finding in the human body (i.e., triceps in the upper arm and rectus femoris/hamstrings in the thigh). Research concerning—and the debate regarding—the function of the long head biceps tendon will surely continue.

Comments are closed.