[Biomechanical considerations on shoulder joint prosthesis implantation]

The biomechanical goals of prosthetic reconstruction of the shoulder are to restore the normal anatomy and range of motion, and to recreate the normal soft tissue balance of the static and dynamic stabilizers of the glenohumeral joint. An unconstrained prosthesis design best reproduces the physiological articulation and original anatomy of the shoulder. Humeral head components have been recently developed, which are adaptable to the variable anatomy of the proximal humerus (third generation design). A precise reconstruction of the three dimensional structure of the proximal humerus may lead to an improved functional outcome. However, there is still a lack of biomechanical data to support this concept. The optimal design of the glenoid component remains a challenge for future research. Specific issues including the choice of biomaterials, the optimum shape, radius of curvature, surface area of the articulation, component height and stem design remain under investigation. Although the prosthetic design represents an important factor in the success of glenohumeral arthroplasty, the surgical reconstruction of the soft tissues to recreate the normal soft tissue balance as well as postoperative rehabilitation determine the functional outcome.