The Effect of Cyclic Loadings Simulating Oscillatory Joint Mobilization on the Posterior Capsule in the Glenohumeral Joint: A Cadaveric Study.

Muraki T, Yamamoto N, Berglund LJ, Sperling JW, Steinmann SP, Cofield RH, An KN. J Orthop Sports Phys Ther. 2011 Feb 2. [Epub ahead of print]

Among overhead athletes the posterior capsule may contract and recently has been shown to hypertrophy due to the repetitive stress during the deceleration phase of the throwing. This contracted and hypertrophied capsule has also been associated with a decrease in internal rotation and an increased risk for injury; a familiar finding among overhead athletes. Clinically joint mobilizations are commonly used to reduce capsular restrictions at the shoulder and other joints. However, there is currently no evidence to demonstrate the effectiveness of joint mobilizations to increase mobility of movements limited by an altered posterior capsule. This study used twenty-one fresh-frozen cadaver shoulders to test the effect of joint mobilization on posterior capsule mobility and stiffness. The shoulders were dissected of all soft tissue except for a 30-mm wide sample of the posterior capsule. The humerus was potted in an acrylic tube and the scapula was mounted in an aluminum box and secured to a servohydraulic testing machine. The specimens were then positioned in 40° of abduction and internal rotation. In this position the humerus was subjected to a posterior cyclic load (simulating our manual mobilizations). There were 3 loading groups (5N, 20N, and 40N) which represented the toe region (tissue slack), transition region (initial tissue stretch), and linear region (extensive tissue stretch) of the load-displacement curve respectively. Displacement during 5N of loading were measured at the 1st, 100th, 200th, 300th, 400th, 500th, and 600th cycles. Stiffness was also calculated after the 1st, 600th cycle, and 1 hour post testing. They found that displacement was significantly greater at the 100th through the 600th cycle compared to the 1st cycle for all loading groups. Stiffness was increased after the 1st cycle and 1 hour after completion of the testing for both the 20N and 40N loading groups.

This was an interesting study that examined the effect of joint mobilization on the posterior capsule. Clinically, this suggests that small load mobilizations increase displacements of the posterior capsule; however they do not have long lasting effects. Low level mobilizations have been shown to decrease pain and may play a therapeutic effect in symptomatic patients; however improved motion will not occur due to structurally altering the posterior capsule. Larger load mobilization is required to increase posterior capsule mobility permanently and increase range of motion. In addition, with the increased tissue mobility there were no decreases in tissue stiffness, which indicate there was no tissue damage. The increased displacement may have occurred from breaking of collagen crosslinking and not necessarily due to collagen fiber damage. One limitation that was not mentioned in the study was that a normal capsule was used for testing. A hypertrophied or contracted capsule may require increased forces to cause similar results that were found in this study. Performing joint mobilizations in vivo might also result in physiologic responses that can’t be tested in a cadaver model but may cause additional structural or biochemical changes to the tissue or the joint. Clinical studies on overhead athletes are required to observe if joint mobilizations can increase range of motion overtime and also decrease shoulder and elbow injuries. What are other people’s experiences with posterior mobilizations in this population?
Written by: Stephen Thomas
Reviewed by: Jeffrey Driban