MORPHOLOGICAL 3-DIMENSIONAL ASSESSMENT, PREOPERATIVE SIMULATION AND RATIONALE OF INTRAOPERATIVE NAVIGATION IN ORTHOPEDIC-SURGERY - PRACTICAL APPLICATION FOR RE-ORIENTING OSTEOTOMIES OF THE HIP-JOINT

A few events represent progress in the development of orthopaedic surg ery imagery and especially imagery by Roentgen rays, brought up modern orthopaedic surgery about one hundred years ago. So-called convention al radiography also brought with it disadvantages and pitfalls and mis interpretations mostly due to the 'shadow' technique of imaging by pla nar projection of three-dimensional structures. Surgical handling of t he locomotor system is basically subject to the physical rules of stat ics and dynamics. Such handling may (and should today) be preceded by preoperative evaluation and planning using technology which operates w ithin three-dimensional space. Such technologies have been developed r ecently in the form of computerized radiographic tomography (CT) and c omputerized nuclear magnetic imaging (MRT). The path to the practical application of these techniques in orthopaedic surgery requires specia lized software, the use of which is described here. Such software intr oduces virtual reality in the interpretation of pathology and simulati on of corrective means by osteotomy. Surgical handling in orthopaedic surgery, similar to aircraft navigation, thus gains in reliability and precision and loses some of its adventurous aspect. Using virtual rea lity in simulating re-orientating osteotomies can also lead to misinte rpretation, for example, due to underestimating the role of the soft t issues. Soft tissues can be represented in static views but must be ex cluded when using intra-operative navigation. The rationale of using t hree-dimensional imagery has clear limits which have to be respected. Direct visualization of the hard tissue (bone) is mandatory in correct ion osteotomies even when using interactive image control because of t he unknown behaviour of soft tissue under strain. Endoscopic technique s are useful tools, complementing 3-D imaging and image interaction.