reliability of diagnostic tests in rotator cuff muscle pathology

Background: Several tests to assist it in the diagnoses of rota- tor cuff impairment have been described in the literature but controversy still exists as to the accuracy of these tests. A study was therefore conducted to determine the reliability of the rotator cuff muscle tests (empty can, full can, lift off and external rotation) as a diagnostic tool. Methodology: Fifty three patients experiencing shoulder pain were assessedusing manual muscle tests (empty can; full can; lift off and external rotationtests). Both pain and weakness were recorded using numerical scales adapted from tests performed by Itoi et al, (1999). These results were compared to ultrasonic diagnoses made by a surgeon. Informed consent was obtained and anonymity was ensured for all participants. Results: A test was false positive when ultrasonic diagnosis indicated no tear in the muscle (although oedema or calcification may have been present), but the manual muscle test was positive regarding pain and weakness. A test on the other hand was false negative when the ultrasonic diagnosis indicated a muscle tear but the manual muscle tests indicated no pain or muscle weakness. Reliability was tested using sensitivity and specificity tests. The sensitivity of all four tests was high (80%), but the specificity was low (20% to 40%), implying that a large number of false positive diagnoses can be made. The major contributors to the false positive results were sub-acromial sub-deltoid bursitis and a decreased acromio-humeral space. When considering pain alone for a positive result the correlation increased a  little, however, taking both pain and muscle weakness into account, the correlation increased even more. Conclusion: The manual muscle tests were not as reliable as expected, but concurrent pathologies may be the main factor influencing the results of the tests. The combination of muscle strength and pain could be recommended as criteria for a positive test. The empty can and full can tests could both be recommended in predicting a torn supraspinatus tendon, as they were equally sensitive