The scapula: principles of construction and stress.

According to current generally accepted theories, analysis of the shape of a bone provides clues to the stresses acting upon it. Although many investigations have ensured that understanding of the lower limb is relatively advance, knowledge relating to the upper limb, and particularly to the scapula, is still far from complete. We have therefore endeavoured to interpret the shape of this bone morphometrically. To this end various scapular parameters have been standardised and statistically analysed, and the results examined both from the functional and the clinical points of view. Our investigation has established that, as in the case of the long bones, the form of the scapula is dependent upon both height and sex. Assessment of the architecture of the subacromial space and its possible parameters of influence have also demonstrated that the size of this space is essentially dependent upon the height of the subject and the size of the acromial and scapulospinal angles. A short distance between the acromion and the upper edge of the glenoid cavity and a small glenoid-spinal angle can be regarded from a functional point of view as factors predisposing to the development of the impingement syndrome. We have also been able to show that certain constant structural features produce an optimal distribution of the forces acting upon the scapula. In particular, the relationship of the supporting pillars (the lateral border and the spine) of this bone to one another appears to represent the expression of an ideal adaptation to the action of those forces.