Dr. Kevin Yip

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

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Biomechanics

Few would dispute the critical role of the biceps brachii at the elbow joint and its function has been well documented at this position. It is with the LHB’s role at the shoulder where the arguments intensify. Many authors have suggested that the LHB has a role in humeral head depression—particularly with shoulder external rotation . Andrews et al.

It observed the biceps arthroscopically while electrically stimulating the biceps muscle and saw lifting of the labrum superiorly and compression of the glenohumeral joint. Likewise Kumar et al. It reported significant upward and anterior migration of the humeral head when the LHB was sectioned and then the biceps muscle was electrically stimulated. In another study, however, Lippmann saw no humeral head motion with active biceps contraction.

Electromyography (EMG) studies have also demonstrated varying findings. Basmajian  demonstrated that the LHB did have EMG activity during active shoulder flexion. The LHB was estimated to contribute 7% of the power of shoulder flexion. Jobe et al. showed peak biceps activity during follow-through and deceleration in the throwing motion. In separate studies, however, Yamaguchi et al.It modified the EMG experiment to control (limit) elbow flexion and both studies showed minimal to no EMG activity during isolated shoulder flexion.

Another intriguing EMG finding has been an increase in EMG activity of the LHB in patients with rotator cuff deficiency. This increased activity may result in the increased tendon diameter, which was observed by Rowe. Overall, although still somewhat controversial, there is some current literature supporting that the LHB has a depressing function in the shoulder and helps stabilize the humeral head in the glenoid. Even so, these effects are not dramatic.

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