Desktop Image processing System for Orthopaedic Surgery (1992 - 2000)
In the framework of this project a demonstrator for CT based operation planning andintraoperative guidance by individual templates has been established. Total kneeendoprothesis was selected as an exemplary clinical application.
To reduce the radiation dose, CT-slices are only generated in the area of the knee joint.The spatial position ofthe femoral head and ankle joint as well as the anatomical axis aremeasured by the use of two pilot scans (a.p. and lateral direction, see fig. 1).
With this results, the dislocation of the anatomical axis can be calculated and the systemcan generate a CT-based 3D model of the knee from the CT-dataset. This 3D reconstructionof the bone can be used to plan the reference cutplanes for the endoprothesis. To verifythe position and orientation of the cutplanes, the system simulates the osteotomies and ageometric 3D model of the endoprothesis can be placed on the bone structure. For this, thesystems database provides prothesis in different sizes and shapes. The computerautomatically generates all required osteotomies for the selected prothesis.
To transfer the results of the preoperative operation planning to the intraoperativeexecution the individual template approach is used.
The planning of the osteotomies under consideration of the prothesis geometry as well as the automatic correction of the anatomical axis is supported by the possibility tojudge the placement of the prothesis in different views. Especially the automaticallygenerated greycuts of the osteotomies are a useful additional information for the surgeonto find the best position for the prothesis.
To transfer the planning result into the operation theatre, a template design for thefemoral and tibial cutplane has been developed (see fig. 2). First lab trials with thisplanning system yielded an accuracy of better than 1mm in all directions and aninclination error smaller than 1degree. Initial clinical tests show that the templatedesigns also guarantee an unambiguous haptic positioning feedback. Therefore the templatesallow an exact intraoperative execution of the osteotomies planned preoperatively. Extra-and intramedullary rods are no longer required for this operation technique.