Intermediate biomechanical analysis of the effect of physiotherapy only compared with capsular shift and physiotherapy in multidirectional shoulder instability

Abstract

This study compared the kinematic parameters and activity pattern of muscles around the glenohumeral joint in multidirectional instability (MDI) treated by only physiotherapy and by capsular shift and physiotherapy, before and after treatment, to test the hypothesis that the surgery group would demonstrate better kinematic and muscle activity than the physiotherapy group. The study comprised 32 patients with MDI treated with only physiotherapy, 19 patients with MDI treated by capsular shift and physiotherapy, and 50 healthy shoulders as the control group. The investigated kinematic parameters were the range of humeral elevation in the scapular plane, the scapulothoracic and glenohumeral angle, the scapulothoracic and glenohumeral rhythms, and relative displacement between the rotational centers of the humerus and the scapula. The muscle activity was modeled by the on-off pattern of muscles around the shoulder. Before treatment, increased relative displacement between the rotational centers of the scapula and the humerus and different regression lines were observed in MDI patients. The physiotherapy strengthened the muscles, but regression lines remained monolinear. Capsular shift and physiotherapy resulted in bilinear regression lines and normal relative displacement between the rotation center of scapula and humerus was restored. After surgery and physiotherapy the activity pattern of muscles was almost normal. The significant alterations in kinematic parameters in MDI patients cannot be completely normalized by physiotherapy only. After the capsular shift and postoperative physiotherapy, the bilinear regression lines (angulation at 60 degrees ), the normal relative displacement between the rotational centers of scapula and humerus, and the normal muscular activity pattern were restored to normal ranges and maintained for at least 4 years.