Quantifying Strain on Posterior Shoulder Tissues During 5 Simulated Clinical Tests: A Cadaver Study
Borstad JD, Dashottar A. J Orthop Sports Phys Ther. 2011 Feb;41(2):90-9.
Clinically, the shoulder joint is one of the most difficult joints to evaluate due to its complex anatomy. Now, throw in overhead athletes and it adds an even deeper layer of complexity due to the structural adaptations that occur due to the stress of throwing. One such adaptation is an increase in shoulder external rotation and concurrent decrease in internal rotation. Several clinical tests have been developed to determine the internal rotation deficit; otherwise known as posterior shoulder tightness. However, the amount that each test is actually straining the posterior structures (capsule and rotator cuff) was previously unknown. To evaluate this question, five simulated clinical tests were compared using 8 cadaver shoulders: humerus cross-body adduction, and shoulder internal rotation with the humerus positioned in 4 combinations of plane and elevation angle. Strain gauges were attached to the posterior rotator cuff (infraspinatus and teres minor) and each clinical test was performed. The strain gauges were then attached to the middle and lower region of the posterior capsule and the process was repeated. Lastly, the posterior capsule was experimentally contracted with thermal energy to simulate a tight posterior capsule, which is thought to occur in overhead athletes, and each clinical test was then repeated. They found that in the experimentally contracted condition strain was greater when the humerus was in humeral flexion and internally rotated compared to when the humerus was in abduction and internally rotated. Also in the lower region of the capsule there was larger strain in the resting and abducted positions compared to cross-body adduction.
Their hypothesis was originally that the cross-body adduction position would produce the greatest strain based on previous research using this test to specifically evaluate posterior shoulder tightness. In fact they found that this test produced the lowest strains in the posterior capsule. They found the test that best strained the posterior capsule was humeral flexion in combination with internal rotation. This is a very clinically significant finding due to the prevalence of internal rotation deficits in overhead athletes. This helps us identify not only the positions we should be measuring capsular adaptations but also the positions that we should use to stretch the shoulder. Interestingly, the position that was found to produce the greatest strain was very similar to the “sleeper stretch” position which is very commonly used. Additional research is needed to determine the specific adaptations which are causing internal rotation deficits (bony and soft tissue) however recent preliminary research has demonstrated the capsule hypertrophies in throwers. The source of these adaptations and the techniques to address them is currently a topic of much debate. I would be interested in hearing everyone’s opinion on this topic and techniques that work clinically for increasing internal rotation.
Written by: Stephen Thomas
Reviewed by: Jeffrey Driban