Subacromial impingement syndrome : Has evolution failed us?

Abstract

Evolution has endowed the human shoulder girdle with a unique range of movement, that when combined with elbow movement enables the hand to perform a myriad functions. Although the human shoulder girdle is capable of large ranges of movement, commonplace in many sporting and vocational pursuits, there are many features which suggest that the modern human arm is better adapted for use in a lowered position and is less well adapted for use in an elevated position. The human shoulder has evolved a relatively small suprascapular fossa, a laterally facing glenoid fossa and acromion, and a clavicle without a lateral upward flare. The insertional angle of the upward scapular stabilisers is similar to that of quadrupedal primates and less like our more immediate ancestors and the great apes. These changes may place a challenge on the shoulder, which makes it less suited to perform vocational and sporting pursuits in elevation and may be a contributing factor to the predisposition of subacromial pathology.