Relevant shoulder biomechanics

Abstract

The glenohumeral joint has a vast three-dimensional mobility that is balanced by the need to maintain joint stability. Motion with stability is made possible by the intricate interactions of the articular, capsuloligamentous, and musculotendinous stabilizers. Because the articular architecture has been found to contribute little native joint stability, the joint must depend on capsuloligamentous and musculotendinous structures for stability. Knowledge of the location and orientation of the glenohumeral ligaments is essential to understanding the biomechanics of the joint. In addition, two principal muscle layers, the outer deltoid complex and the inner rotator cuff musculature, have particularly essential functions in glenohumeral joint stability. These dynamic stabilizers impart stability through several mechanisms: passive muscle forces, joint-compressive forces, positioning allowing secondary ligamentous tightening, and bulk-effect forces. The inferior glenohumeral ligament complex with its anterior and posterior portions is probably the most essential capsulogigamentous contributor to stability. It should be emphasized that stability depends on contributions from all components to appropriately distribute applied loads. This concept of load sharing illustrates that a small deficiency in any single component may lead to significant cumulative damage. Clinical interest in glenohumeral biomechanics will continue to take on greater significance as the general population continues to become more active. Current knowledge of biomechanics has shown that both the rotator cuff and the capsuloligamentous complex are essential to shoulder stability. Further study with dynamic glenohumeral models should allow better definition of the important interaction between the static and dynamic stabilizers. © 1991 W. B. Saunders Company.