[Biomechanics of the shoulder and its surgical consequences: personal experience operating on 250 shoulders]

Functional anatomy induces functional surgery. According to the anatomy of the locomotor apparatus, biomechanics opens the way to a more logical surgery. Two main concepts rule the study of the shoulder: the articular complex; the muscular chain. The articular complex: the scapulo- humeral joint is the main of the motion. The 50% remaining are due to the movements of the scapula around the thorax. The muscular chain: sixteen muscles are concerned in shoulder motion. They are classified in two principal groups: long muscles, fixing the scapula upon the thorax short muscles are disposed in two plans: superficial (deltoïd) deep, called the rotator cuff (subs scapularis; supraspinatus; infra-spinatus; teres minor). They only produce motion of the humerus on the scapula. The lateral elevation of the arm relies on the harmonious contraction of all these muscles. The mechanical environment of the cuff, particularly of the supra spinatus is not a favorable one: poorly vascularised, overworking, it goes through a narrow osteo fibrous tunnel. This produces irritation or rupture of the muscle. The surgery is indicated only in case of medical treatment failure. It has two alternative purposes, either to suppress the anterior conflict between the acromial vault and the cuff, or to repair a rupture of the supra spinatus. The acromioplasty is a benign operation that gives excellent results: 65% recover a normal shoulder. We notice 10 to 15% failures (105 cases. Follow up one to ten years). The surgery of reinsertion of the supra spinatus is a little more difficult and the results are less convincing: 36% good and excellent results; 43% fair; 21% failures (82 cases. Follow up one to fifteen years).