Effect of Shortening Deformity of the Clavicle on Scapular Kinematics

Abstract

Background In some short malunion cases, midshaft clavicular fractures are reported to result in unsatisfactory clinical outcomes. Shortening deformity of the clavicle could change the anatomical alignment of the shoulder girdle and is surmised to affect shoulder kinematics on arm movements. Nevertheless, no report has ever referred to documented changes. Hypothesis Scapular motion will change with clavicular shortening in cadaveric models. Study Design Controlled laboratory study. Methods Twelve cadaveric shoulders were used, and sequential clavicular shortening by 0%, 5%, 10%, 15%, and 20% from the original length was simulated in this study. The scapulothoracic motion during passive arm elevation in 3 planes was monitored using an electromagnetic tracking device. Differences in kinematics of the scapula between the 0% shortening models and the other 4 experimental groups were analyzed. Results During arm elevation, posterior tilting and external rotation of the scapula significantly decreased with ≥10% shortening of the clavicle. Decreased posterior tilting was found with a shorter clavicle and at higher positions of arm elevation in all planes and became obvious during coronal plane elevation. Upward rotation of the scapula did not change with shortening at any elevated arm positions. Conclusion The findings of this study clearly indicated that shortening of the clavicle affects the kinematics in the shoulder girdle. Clinical Relevance The results of this cadaveric study suggest that clavicular shortening of ≥10% affects scapular kinematics and might produce clinical symptoms.