[Shoulder arthroplasty: biomechanics and design]

Shoulder arthroplasty is becoming increasingly important in orthopaedic surgery. Continuous development of the implants means that the modern endoprostheses make it possible to recreate the original anatomy with a high degree of accuracy. This is of decisive importance in the long-term restoration of physiological patterns of movement and achievement of pain relief. The modern shoulder arthroplasties allow adjustment of the important parameters: ante-/retroversion, inclination and offset to fit the individual anatomy of the proximal humerus. Fixation is the most important factor for the glenoid component; reduced bone stock can make this difficult. Cemented components are still the gold standard. For young patients surface replacement arthroplasty can be a good alternative treatment for early stages of osteoarthritis. In cuff tear arthropathy reverse prostheses can be used. Reversing the anatomical relationship between glenoid and humerus leads to medialisation and lowering of the center of rotation, which in turn leads to increased tension on the deltoid muscle. Because of the high complication rate this operation should be performed only by experienced shoulder surgeons.