The depressor function of biceps on the head of the humerus in shoulders with tears of the rotator cuff

Abstract

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. Patients and MethodsBetween November 1996 and October 1997 we treated surgically 18 patients (19 shoulders) with tears of the rotator cuff which had been diagnosed by arthrography or MRI. There were 14 men and four women with a mean age of 59 years (44 to 77). Eleven shoulders had full-thickness tears, five of which were large (>3 cm), three medium (1 to 3 cm) and three small (<1 cm). Eight shoulders had partialthickness tears of which seven were medium and one small. The long head of biceps was intact in all of these patients. A control group of 19 shoulders was asymptomatic with normal rotator cuffs as seen on MRI. There were 15 men and four women with a mean age of 55 years (17 to 77). There was no significant difference in age (p = 0.38) and gender (p = 0.99) between the two groups. Anteroposterior radiographs were taken with the arm elevated at 0°, 45° and 90°, the elbow flexed and the forearm supinated, and a brace applied which allowed active contraction of biceps without the other muscles (Fig. 1). The resistant force produced by the band was approximately 1.5 kg. The distance between the centre of the head of the humerus and the glenoid was measured and processed using National Institute of Health software 11 (NIH Image; National Institute of Health, Bethesda, Maryland) (Fig. 2). In four volunteers with a mean age of 30 years (29 to 31) EMG was performed using the brace and activity in the anterior, middle and posterior deltoid, triceps, trapezius and pectoralis major recorded at 0°, 45° and 90° of elevation. We were able to confirm that when using the brace, only biceps was contracting significantly. These activities were measured as percentages of the maximum voluntary contraction (% MVC). 12,13Statistical analysis. The results in the two groups were compared using a one-way between-group analysis of variance (ANOVA), with statistical significance set at the 5% level.

Biceps Detachment Decreases Joint Damage in a Rotator Cuff Tear Rat Model

“…Specifically, a cadaveric study examined the role of the long head of the biceps in the presence of supraspinatus and infraspinatus tears [23] and found that loading of the long head of the biceps tendon decreased humeral head translations. Results from a clinical EMG study suggested that the long head of the biceps tendon assists the supraspinatus with humeral head depression during shoulder elevation [8]. However, due to confounding variables in clinical and cadaver studies, it is difficult to determine true cause and effect relationships.…”

“…The long head of the biceps tendon crosses the shoulder and may serve as an important joint stabilizer, particularly in the presence of cuff tears; however, its role in joint stability remains controversial. Specifically, some believe that it provides minimal stability at the shoulder [11,27], while others believe it serves mainly as a humeral head depressor, assisting the supraspinatus [7,8].…”

Cross-sectional area of the tendon and the muscle of the biceps brachii in shoulders with rotator cuff tears

“…Since the LHB tendon is an active stabilizer of the glenohumeral joint (Warner et al 1995) and an active depressor of the humeral head in cuff tear shoulders (Kido et al 2000), the widened LHB tendon may be due to hyperactivity of the biceps muscle in order to compensate for the functional deficit caused by rotator cuff tear. An EMG study by Kido et al (1998) demonstrated that only onethird of patients with rotator cuff tears showed increased activity of the biceps during arm elevation compared to that in subjects without rotator cuff tears.…”

“…Since the LHB is a stabilizer (Kumar et al 1989, Itoi et al 1994) and depressor (Warner et al 1995, Kido et al 2000 of the humeral head, the widened LHB tendon in cuff tear shoulders may be a hypertrophic change to compensate for the functional loss of the cuff (Matsen et al 1998). An et al (1991) reported that tendon cross-sectional area (CSA) correlated well with the physiological CSA (PCSA) of associated muscles.…”

Long Head of the Biceps Tendon Pain: Differential Diagnosis and Treatment

“…4,41,42,45,53,78 It is difficult to determine the extent to which biceps surgery will affect shoulder function, because the role of the biceps at the shoulder is not fully understood. Maintaining the biceps muscle length-tension relationship and the axis of the biceps muscle is thought to be important for preserving biceps function at the shoulder.…”