Biomechanics of the shoulder and therapeutic applications

Abstract

The influence of biomechanics in surgery of the locomotor apparatus has been constantly increasing over the last few decades. The purpose of this study was to determine wether biomechanical studies can significantly influence therapy and treatment of shoulder injuries, especially shoulder instability. The investigation was performed on 23 fresh human specimens with intact capsular ligaments of the glenohumeral joint. A Bankart lesion from 3 o'clock to 6 o'clock was repaired, and a Bankart repair and anterior inferior capsular shift, as described by Neer, were performed. The measurement was done on six clinically relevant positions of instability: superior, anterior, anterior-inferior, inferior, posterior-inferior, posterior. Measurement was done using a specially developed strain-gauge system. It was demonstrated that both instability and too much stability of the shoulder joint lead to a significant change in shoulder biomechanics. The anatomical O-position of the glenohumeral joint in 110 degrees of abduction is a position of about 60 degrees of external rotation compared to the O-position for clinical measurement. From the therapy point of view, one has to ask for anatomical reconstruction instead of tight repair in soft-tissue repair in the glenohumeral joint. Immediate post-operative rehabilitation in a 60 degrees range of motion is possible.