Pennock AT, Pennington WW, Torry MR, Decker MJ, Vaishnav SB, Provencher MT, Millett PJ, Hackett TR. Am J Sports Med. 2011 Nov;39(11):2338-46. Epub 2011 Feb 7.
In the past, most rotator cuff tears involved the supraspinatus and infraspinatus muscles. Therefore, most diagnostic and rehabilitative data involved techniques and exercises to focus on these muscles. Increased awareness of subscapularis tears has lead to research that focuses on the causes, diagnosis, and treatments of subscapularis tears. The belly-press, lift-off and bear-hug tests are used to identify subscapularis muscle injuries. The belly-press and lift-off are the most commonly used tests with the belly-press being introduced most recently from Barth et al. With variability existing between clinicians in regard to arm position with each test and the influence that pain and decreased mobility may cause in test performance, this study attempted to determine the optimal arm and shoulder position for evaluating subscapularis muscle function with each test and compare the efficacy of each clinical test in the isolation of the subscapularis muscle. This study included 20 healthy males aged 18-45 years old with no prior history of neck, shoulder or scapular pain. Electromyography (EMG; muscle activity) of 7 muscles (upper and lower divisions of the subscapularis, supraspinatus, infraspinatus, latissimus dorsi, teres major, triceps, pectoralis major) was monitored for each special test at varying arm positions. The participants were instructed in proper test performance and given adequate time to practice each test with an emphasis on arm positioning. Muscle activity was recorded for each clinical test in the 3 positions for 3 trials, and lasting for 3 seconds each. The reported ideal positions for each clinical test were as follows: The bear-hug test was performed with the palm of the involved side on the AC joint of the contralateral shoulder, with the shoulder in 90° abduction. The belly-press was performed with the palm of the involved side against the abdomen just below the level of the xyphiod process with the elbow in line with the trunk in the sagittal plane. Finally, the lift-off test was performed with the arm of the involved shoulder behind the back with the dorsum of the hand just below the mid lumbar spine (L2-4). Results indicated that regardless of arm and shoulder positioning, the upper and lower scapularis muscle activity was significantly greater than all other muscles. Subscapularis muscle activity did not differ between tests. No difference was noted between each division of the subscapularis muscle across any of the 3 positions for each test. A difference in EMG activity was noted between the pectoralis major and triceps during the different clinical tests.
This study shows that all 3 clinical tests are effective in testing the integrity of subscapularis muscle function. It also demonstrates that patient arm position does not play a significant role in the activity of the subscapulris. This is of particular importance in the presence of pain and decreased joint mobility which will not allow for testing in certain arm positions in a subset of injured patients. It is common during a clinical examination of joint injury that pain and decreased mobility can limit the findings of special tests. Most times this causes the clinician to defer the tests till pain and mobility issues have resolved. This study shows that muscle integrity can still be determined despite these factors early in the examination process. This would aide the clinician in terms of early diagnosis and intervention with treatment techniques. Some limitations of this study include the limited amount of muscles chosen. There are several other muscles that are active during these tests that can compensate for the subscapularis and should be considered in the future. In addition, it would have also been interesting to see if differences would have been noted with a longer hold time for each trial. Future research should examine the variations of arm positioning for different special tests at the shoulder. Have any clinicians already started to occasionally deviate from ideal test positions with joint examinations?