Cup and offset navigation with OrthoPilot system

Abstract

Optimal acetabular component orientation in total hip arthroplasty is a complex three dimensional problem with failure leading to increased wear and instability. Recent publications have demonstrated a connection between the positioning of the prosthesis and the frequency of dislocation [1-7]. Lewinnek et al. noted an increase of the hip dislocation rate from 1.5% to 6.1% if a safe range of 15° +/-10° radiographic anteversion or 40° +/-10° acetabular abduction were exceeded [8]. Recent computer simulations have studied range of motion and concluded that the greatest range of motion was noted with acetabular anteversion of 20 to 25°, acetabular abduction of 45°, and femoral stem anteversion of 15° [1, 9, 10]. The positioning of the acetabular component during surgery is dependent on the orientation of the bony acetabulum and position of the patient's pelvis on the operating table. McCollum et al. have stated that patient positioning is not always reproducible in the lateral decubitus position and often leads pelvic mal-alignment with resultant improper cup alignment. Pelvic flexion and adduction are virtually unavoidable in this position placing greater demands on the surgical technique for satisfactory outcome [11, 12]. Therefore, improvement in cup implantation will occur if either the pelvis position can be standardized or a method of correctly localizing the anatomical orientation of the acetabulum can be created. Computer-assisted orthpaedic surgery has been recently defined as the ability to utilize sophisticated computer algorithms to allow the surgeon to determine three dimensional placement of total hip implants in situ [13, 17]. A rapid ongoing evolution of technical advances have allowed the ability to move from cumbersome systems requiring a pre-operative computed tomography of the patient's hip joint to more elegant systems that utilize image- free registration or the simple use of fluoroscopy at the time of surgery [18-20]. In total hip replacement, several reports have cited the accuracy with which implants can be placed using computer-aided robotic devices or surgical navigation [16, 17, 21, 22]. The OrthoPilot-system has been found to be reliable, and the accuracy of cup placement has been proven by several authors (Kiefer 2002; Ottersbach 2005). Since 2005 there is the opportunity to control stem position as well. In this special chapter the procedure of cup computer controlled placement combined with a movement mapping of a mayo-like neck prosthesis called Metha-stem is described. © 2007 Springer Medizin Verlag Heidelberg.