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The purpose of this study was to determine the clinical usefulness of the full can and empty can tests for determining the presence of a torn supraspinatus tendon. The two tests were performed in 143 shoulders of 136 consecutive patients. In each test, the muscle strength was determined by manual muscle testing, and the presence of pain during the maneuver was recorded. We interpreted the tests as positive when there was 1) pain, 2) muscle weakness, or 3) pain or muscle weakness or both. Shoulders were examined by high-resolution magnetic resonance imaging with 95% accuracy for full-thickness rotator cuff tears. There were 35 shoulders with full-thickness tears of the supraspinatus tendon. The accuracy of the tests was the greatest when muscle weakness was interpreted as indicating a torn supraspinatus tendon in both the full can test (75% accurate) and the empty can test (70% accurate). However, there was no significant difference between the accuracy of the tests when this criterion was used. Pain was observed in 62 shoulders (43%) during the full can test and in 71 shoulders (50%) during the empty can test, but the difference was not statistically significant. Muscle weakness should be interpreted as indicative of supraspinatus tendon tear. Using this indicator, both tests are equivalent in terms of accuracy, but considering pain provocation, the full can test may be more beneficial in the clinical setting.

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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.

We investigated electromyographic activities of the biceps in 40 shoulders with full-thickness tears of the rotator cuff and 40 asymptomatic shoulders, with a normal rotator cuff on MRI, to determine the role of the biceps in cuff-deficient shoulders. Using surface electrodes, biceps activities were recorded during arm elevation in the scapular plane with and without a 1-kg load. The percentages of integrated electromyograms to the maximum voluntary contraction (%MVC) were obtained at 30 degrees, 60 degrees, 90 degrees, and 120 degrees of elevation. In the normal shoulders, %MVC of the biceps was always less than 10% through the arc of elevation both with and without load. Among 40 shoulders with rotator cuff tears, 14 showed increased activities of the biceps more than 10% in %MVC (p < 0.0001), whereas the remaining 26 shoulders had activities similar to the normal shoulders. The biceps activities in these 14 shoulders increased with load application and at higher angles of elevation. The muscle strength tended to be weaker in shoulders with increased biceps activities than in those without. Our findings suggest a potential supplemental function of the biceps in shoulders with rotator cuff tears.