Glenohumeral Muscle Activation During Provocative Tests Designed to Diagnose Superior Labrum Anterior-Posterior Lesions
Wood VJ, Sabick MB, Pfeiffer RP, Kuhlman SM, Christensen JH, Curtin MJ. Am J Sports Med. 2011 Aug 29. [Epub ahead of print]
Superior labrum anterior to posterior (SLAP) lesions have become a very common injury in sports medicine, especially among baseball players. The most common mechanism of injury occurs during the late cocking phase of the overhead throw which is described as the “peel back mechanism.” Although the mechanism of injury is well understood, clinical diagnosis is still very challenging. Countless clinical special tests have been created to facilitate the diagnosis of SLAP lesions; however, no “gold-standard” special test has been identified. Therefore, Wood et al examined the muscle activity (with electromyography [EMG]) of several shoulder muscles (long and short heads of the biceps brachii, anterior deltoid, pectoralis major, latissimus dorsi, infraspinatus, and supraspinatus) during several SLAP lesion special tests (active compression, Speed’s, pronated load, biceps load I, biceps load II, resisted supination external rotation, and Yergason’s; descriptions of the tests are located in the full length manuscript) to determine the best test for creating tension at the insertion site of the long head of the biceps (LHB). This was based on the assumption that increased muscle activity equates to increased tension of the tendon. Twenty-one healthy volunteers were recruited for this study. Muscle activity was recorded and participants performed the special tests in a standardized method. For six of the seven tests, a Biodex System was used for resistance to minimize variability across participants. Muscle activity was characterized as a peak % of maximum voluntary isometric contraction (MVIC) and proportion of total muscle activity (activity of the muscle of interest divided by the sum of all muscle activity). They found that Speed’s, active compression palm-up, biceps load I, and biceps load II produced higher peak values of LHB activity. Based on the LHB selectivity (LHB proportion of total muscle activity) resisted supination external rotation, biceps load I, biceps load II, and Yergason’s tests were highest.
This is an interesting study attempting to selectively identify the best special tests for SLAP lesions with use of muscle activity. They found that overall the biceps load I and biceps load II were the best tests based on peak activity and LHB selectivity. In addition, the Speed’s and active compression with the palm up had the highest peak muscle activity; while, resisted supination and Yergason’s were the most selective. The authors propose that higher muscle activity or selectivity will create higher tension on the LHB insertion site and therefore elicit pain. This is very true but it is only one piece of the puzzle. Numerous other factors may influence the performance of these tests: 1) arm position, 2) presence of scapular dyskinesis, 3) presence of tight and thick posterior capsule, as well as 4) if the patient has a large amount of external rotation. These are all things that we need to consider when performing these special tests. By keeping all of these things in mind we will be better at determining the proper special test for each athlete with a shoulder injury. There have been several studies examining the sensitivity and specificity of these special tests (or combination of tests). One recent study suggested that the combination of special tests is the optimal way to successful diagnose SLAP lesions. This may be an effective way of increasing the accuracy of your clinical exam. Finally, it is important to keep in mind that clinical tests (or combination of tests) are rarely perfect. Therefore, we need to recognize how the tests influence various anatomical structures in a region (e.g., LHB tendon tension) so that we can understand why one test performs well with one patient but not another. What is your experience with special tests for SLAP lesions? Which do you find the most affective? Does combining tests work?
Written by: Stephen Thomas
Reviewed by: Jeffrey Driban