Summary

We introduce the Swing test (ST), which is a new functional examination to evaluate change of the defensive thorax muscle tonus in response to anterior shoulder instability. Irrespective of sense of apprehension, in cases with the positive ST, when examiners tried to rock subjects’ shoulder back and forth, their shoulder was not swung at all due to defensively increased thorax muscle tonus.

Abstract

Purpose

Shoulder disorders, such as rotator cuff tear, throwing shoulder injury, and instability are greatly correlated with scapular dyskinesis and other disorders of thorax, spine, and hip which cause a malfunction of kinetic chain. However, improvement of kinetic chain by conditioning of these disorders has a good effect on keeping a good shoulder condition and preventing shoulder injuries. Proprioceptive function by the central nerve system plays an important role in preventing shoulder instability using the feedforward system which makes shoulder abductor muscles contracted beforehand. We introduce a new functional method, the Swing test (ST) based on this feedforward system to evaluate shoulder instability quantitatively.

Methods

We evaluated 25 shoulders with anterior shoulder instability using the ST (the mean of age with 25.3yrs). The ST evaluates change of thorax muscle tonus such as pectoralis major and latissimus dorsi during the anterior apprehension test which is a defensive reaction to avoid anterior shoulder instability. In cases with the positive ST, the thorax muscle tonus at instability side was clearly increased, irrespective of sense of apprehension. When examiners tried to rock subjects’ shoulder back and forth at the anterior apprehension test, their shoulder was not swung so well, while at healthy side, as the thorax muscle tonus was relaxed, their shoulder was swung well. At the time when they feel severe pain and apprehension around 90 degree’s abduction and external rotation, their shoulder was not swung at all owing to high muscle tonus of thorax and trunk. Increased trunk muscle tonus in cases with the positive ST could be improved as soon as either horizontal abduction or external rotation of the shoulder was slightly decreased, and their shoulder swung well like healthy shoulders.

Results

All of the 25 shoulders showed the positive ST result. Especially, at 80–100 degrees’ abducted position they showed thorax muscle tonus was even higher than that at the other abducted position, and their shoulders did not move at all.

Discussion

Our all 25 shoulders exhibited the ST positive and in order to prevent anterior instability, defensive thorax muscle tonus was clearly increased and their shoulder was not moved against passive swing, especially around 90 degrees’ abducted position. The ST was one of the most useful tests to evaluate anterior shoulder instability functionally and quantitatively by comparing thorax muscle tonus between injured and healthy side during anterior apprehension test. This test enabled not only examiners but also subjects to evaluate change of shoulder swing following defensive thorax muscle tonus together, and so subjects can notice what position makes their shoulder unstable, which plays an important role in prevention of their shoulder anterior dislocation and subluxation.