The biomechanics of abduction in the humeroscapular joint and the 'impingement syndrome'

Abstract

According to Cyriax, intra-articular lesions are characterised by what he called the 'capsular pattern'. This implies movement restriction in all directions in which the joint can move, and the restriction follows a characteristic pattern. If, however, restriction affects only one direction, this must be due to an obstacle outside the joint. In the case of the shoulder joint, this concerns abduction restricted by an obstacle situated beneath the coraco-acromial ligament. This obstacle is caused by changes of the bursa subdelto-acromialis and/or by changes in the rotator cuff which interferes with the mechanism of abduction. Changes of these soft-tissue or bony structures have been shown by magnetic resonance imaging and ultrasonography: on further scrutiny, however, they are also found in asymptomatic subjects. According to biomechanics, the head of the humerus is situated in the uppermost part of the fossa glenoidalis and must descend during abduction. In cases of restricted abduction, resistance against this caudal movement is met. We have found that mobilisation of the joint promptly restores mobility and relieves pain, and we report on 10 consecutive such cases.

Keywords:

• IMPINGEMENT
• CORACO-ACROMIAL LIGAMENT
• ROTATOR CUFF
• JOINT PLAY
• BIOMECHANICS
• MOBILISATION