Loose shoulder shows abnormal instability and various symptoms, but it's mechanism is not analyzed clearly.
In this study, we measured the ball roll(B) and gliding(G) in loose shoulders and compared them with those in healthy subjects. Using an image analyzing system, B and G values during active elevation on the scapular plane were measured, and the B+G values and | G | /B ratios were calculated in 28 loose shoulders (LS) and 60 normal subjects (N). In addition, evaluation was made in 4 phases of motion, setting phase, hanging joint phase, transitional zone phase and phase of joint needing support.
The results were as follows:
1) As the arm was elevated, in group LS, the B values gradually decreased, but the G values varied widely.
2) Glenohumeral movement in group N could be divided into 3 phases according to the B+G values and the | G | /B ratios, but in group LS no regularity was observed.
3) The slipping phenomenon in group LS was found at the transitional zone phase and the phase of joint needing support.
4) Motion range of the center of the humeral heatl was 8% of the long axis of the glenoid in group N, but in group LS it was 16%.
5) In group LS, glenohumeral movement, especially gliding mechanism was failed.
