The surgical operations of shoulder joint are guided by various principles: osteosynthesis in the case of fracture,
osteotomy in order to correct a deformation or to modify the functioning of the joint, or implementation of articular
prosthesis. At the end of the twentieth century, many innovations in the domains of biomechanics and orthopedic
surgery have been performed. Nevertheless, theoretical and practical problems may appear during the operation (visual
field of surgeon is very limited, quality and shape of the bone is variable depending on the patient). Biomechanical
criteria of success are defined for each intervention. For example, the installation with success of prosthetic implant will
be estimated according to the degree of mobility of the new articulation, the movements of this articulation being
function of the shape of the prosthesis and of its position on its osseous support. It is not always easy to optimize the
preparation of the surgical operation for every patient, and a preliminary computer simulation would allow helping the
surgeon in its choices and its preparation of the intervention. The techniques of virtual reality allow a high degree of
immersion and allow envisaging the development of a navigation device during the operating act.
The modelling of the shoulder joint is an important step to set a Computer-Aided Surgery System for shoulder prosthesis placement. Our approach mainly concerns the bones structures of the scapulo-humeral joint. Our goal is to develop a tool that allows the surgeon to extract morphological data from medical images in order to interpret the biomechanical behaviour of a prosthesised shoulder for preoperative and peroperative virtual surgery. To provide a light and easy-handling representation of the shoulder, a geometrical model composed of quadrics, planes and other simple forms is proposed.