[Our experience with an image guided navigation system for accurate alignment in total hip replacement by minimally invasive posterolateral surgery].

PURPOSE OF THE STUDY The aim of the study was to compare a radiographic position of the acetabular component with a position guided by the navigation system in final acetabular cup alignment. MATERIAL Between May and October 2005, 15 patients underwent implantation of a cementless acetabular component from the posterolateral minimally invasive approach with the use of kinematic navigation. METHODS The final acetabular cup alignment was determined from the data saved in the navigation system. The radiographic measurement of acetabular cup inclination was made from an anteroposterior projection of both hips on one image, and anteversion was determined by the Ackland method. RESULTS The average values for inclination and anteversion shown on radiographs were 41.8 degrees (range, 35-51) and 19.8 degrees (range, 5-32), respectively. The average values of cup alignment recorded at implantation by the navigation system were 27.6 degrees (range, 22-35) for inclination and 24.3 degrees (range, 17-28) for anteversion. DISCUSSION The acetabular cup alignment is considered optimal when inclination is 45 degrees and anteversion 15 degrees. This is more difficult to achieve in minimally invasive surgery due to a limited view of the operating field. This disadvantage can be overcome by using various navigation systems the function of which depends on the accuracy of recorded data. CONCLUSIONS Because the data recorded by the system used in our study were not accurate, we do not consider the OrthoPilot navigation system to be an effective aid in minimally invasive posterolateral surgery.