Computer-assisted total hip navigation.

Accurate implant placement in total hip replacement is important in avoiding dislocation, impingement, and edge-loading throughout the patient's postoperative functional range of motion. Current implants and bearing surfaces now provide the potential for prolonged longevity of the reconstruction, which can be compromised by malposition of the components outside of designated "safe zones." Computer-assisted hip navigation offers the potential for more accurate placement of hip components and control of leg length and offset. Systems are now available that allow registration of the bony anatomy based on preoperative CT images, intraoperative fluoroscopic images, or imageless techniques based on palpation of the landmarks. In each of these approaches, cup position has been based on coordinate systems formed by identification of the anterior pelvic frontal plane. All systems have shown improved accuracy of acetabular cup placement compared with conventional manual techniques. Cup anteversion is less accurate than cup abduction with the imageless approach. Measurements made with the use of navigation systems also have shown a large variation in pelvic tilt or pelvic flexion-extension in series of cases, which can affect the appropriate cup position for each patient. The results of computer-assisted navigation in the future may be improved by incorporation of measurements of each patient's pelvic tilt, femoral stem position, and hip kinematics.