We investigated the function of biceps in 18 patients (19 shoulders) with lesions of the rotator cuff. Their mean age was 59 years. Another series of 18 patients (19 shoulders) with normal rotator cuffs as seen on MRI acted as a control group. Their mean age was 55 years. A brace was used to maintain contraction of biceps during elevation. Anteroposterior radiographs were obtained with the arm elevated at 0°, 45° and 90° with and without contraction of biceps. The distance between the centre of the head of the humerus and the glenoid was compared in the two groups.

We found that in the group with tears there was significantly greater proximal migration of the head of the humerus at 0° and 45° of elevation without contraction of biceps but depression of the head of the humerus at 0°, 45° and 90° when biceps was functioning. We conclude that biceps is an active depressor of the head of the humerus in shoulders with lesions of the rotator cuff.