Humeral Impingement on the Acromion in a Scottish Island Population of c. 1600 AD

Abstract

Apparently-articular facets on the undersurface of the anterior third of the acromion have been known in skeletal material since 1922 but without full discussion of the mechanism responsible. Twelve instances are described here, selected because an impingement area could be demonstrated on the greater tubercle of the humerus or on osteophytes that had replaced it. Both sides were affected but, with two exceptions, the right more severely; the less affected side could be regarded as an earlier stage. All were affected by osteoarthrosis. One was complicated by coraco-humeral impingement. The anatomical mechanism that normally prevents the humerus from rising against the coraco-acromial arch is described as well as the causes of the breakdown in the mechanism that leads to the impingement, derived largely from the clinical field, where the disorder is well-known. The complexity of the relation of the disorder to degenerative arthrosis is discussed because the degeneration is an age change in which wear and tear plays a localized part and the changes as they affect the shoulder joint differ fundamentally from those in the weight-bearing hip-joint. The mean estimated age of the group of twelve was 59 years but the occurrence of the acromion impingement disorder in young athletes illustrates the part played by mechanical joint abuse. Women predominated in this small group, partly because, through their longer life-spans, their joints were exposed longer to the susceptible period of age-related degeneration and also because their less robust musculo-skeletal systems were less adapted than men's to the equally shared labour. Two traditional women's tasks, corn-grinding and tweed-shrinking, are shoulder stressful.