Dynamic study is important to evaluate the condition of loose shoulder. We reported at the 14th Japan Shoulder Society meeting that the muscle contraction curve produced a different pattern in those with instability, and we thought this muscular imbalance might cause functional disorder of the loose shoulder. This time we have analyzed more materials and post medical treatment cases, using a Cybex II isokinetic dynamometer. Twenty-nine patients, with forty-nine shoulder joints were investigated. Their shoulders were significantly unstable, and this was checked by arthrography. The control group consisted of forty-one normal individuals, with eighty-one shoulder joints.
Results.
It was found that muscle contraction power was lower in abduction, adduction, extension and flexion in the patients group compared with the control group. The correlation between these four directions could be seen in the control group, but in the patients group, the correlation between abducition and adduction, and also between flexion and extension could not. The muscle contraction curve showed a different pattern, with an abnormal wave in twentyseven patients (89%). But this abnormal wave improved after surgical or conservative treatment.
Discussion
Our results show that the lower and ill-balanced muscle strength and dynamic instability might cause a functional disorder of the loose shoulder. The isokinetic study was useful in evaluating the dynamic instability of loose shoulder and the effects of its treatment.
