Biomechanics and design of shoulder arthroplasty

Since the introduction by Neer in 1973 of the metal-on-plastic unconstrained total shoulder replacement, unfortunately there have been no long-term clinical follow-up reports. Short- to mid-term information (less than ten years) indicates good to excellent clinical results in approximately 90 per cent of cases. While this early experience is encouraging, much attention has been focused on lucencies of the glenoid component, which although they may not predispose to failure, have led to considerable design activity. The humeral component has also advanced in design, with modularity of the head in particular providing greater intra-operative flexibility. State-of-the-art instrumentation, borrowing key features found beneficial to hip and knee joint replacement, is an important advancement in contemporary systems. The aim of this paper is to position shoulder arthroplasty in relation to biomechanical considerations and recommendations from clinical experience.