The biomechanical effect of clavicular shortening on shoulder muscle function, a simulation study.

ABSTRACT

BACKGROUND: Malunion of the clavicle with shortening after mid shaft fractures can give rise to long-term residual complaints. The cause of these complaints is as yet unclear. METHODS: In this study we analysed data of an earlier experimental cadaveric study on changes of shoulder biomechanics with progressive shortening of the clavicle. The data was used in a musculoskeletal computer model to examine the effect of clavicle shortening on muscle function, expressed as maximal muscle moments for abduction and internal rotation. FINDINGS: Clavicle shortening results in changes of maximal muscle moments around the shoulder girdle. The mean values at 3.6cm of shortening of maximal muscle moment changes are 16% decreased around the sterno-clavicular joint decreased for both ab- and adduction, 37% increased around the acromion-clavicular joint for adduction and 32% decrease for internal rotation around the gleno-humeral joint in resting position. INTERPRETATION: Shortening of the clavicle affects muscle function in the shoulder in a computer model. This may explain for the residual complaints after short malunion with shortening. LEVEL OF EVIDENCE Basic Science Study. Biomechanics. Cadaveric data and computer model.