A CT-based method (''HipMotion'') for the noninvasive three-dimensional assessment of femoroacetabular impingement (FAI) was developed, validated, and applied in a clinical pilot study. The method allows for the anatomically based calculation of hip range of motion (ROM), the exact location of the impingement zone, and the simulation of quantified surgical maneuvers for FAI. The accuracy of HipMotion was 0.7 AE 3.18 in a plastic bone setup and À5.0 AE 5.68 in a cadaver setup. Reliability and reproducibility were excellent [intraclass correlation coefficient (ICC) > 0.87] for all measures except external rotation (ICC ¼ 0.48). The normal ROM was determined from a cohort of 150 patients and was compared to 31 consecutive hips with FAI. Patients with FAI had a significantly decreased flexion, internal rotation, and abduction in comparison to normal hips ( p < 0.001). Normal hip flexion and internal rotation are generally overestimated in a number of orthopedic textbooks. HipMotion is a useful tool for further assessment of impinging hips and for appropriate planning of the necessary amount of surgical intervention, which represents the basis for future computerassisted treatment of FAI with less invasive surgical approaches, such as hip arthroscopy. ß

The range of motion of normal hips and hips with femoroacetabular impingement relative to some specific anatomic reference landmarks is unknown. We therefore described: (1) the range of motion pattern relative to landmarks; (2) the location of the impingement zones in normal and impinging hips; and (3) the influence of surgical débridement on the range of motion. We used a previously developed and validated noninvasive 3-D CT-based method for kinematic hip analysis to compare the range of motion pattern, the location of impingement, and the effect of virtual surgical reconstruction in 28 hips with anterior femoroacetabular impingement and a control group of 33 normal hips. Hips with femoroacetabular impingement had decreased flexion, internal rotation, and abduction. Internal rotation decreased with increasing flexion and adduction. The calculated impingement zones were localized in the anterosuperior quadrant of the acetabulum and were similar in the two groups and in impingement subgroups. The average improvement of internal rotation was 5.4 degrees for pincer hips, 8.5 degrees for cam hips, and 15.7 degrees for mixed impingement. This method helps the surgeon quantify the severity of impingement and choose the appropriate treatment option; it provides a basis for future image-guided surgical reconstruction in femoroacetabular impingement with less invasive techniques.

Using a total of 30 cadaveric hips, the accuracy of a fluoroscopy-based computer navigation system for cup placement in total hip arthroplasty (THA) was investigated and an error analysis was carried out. The accuracy of placing the acetabular component within a predefined safe zone using computer guidance was compared to the precision that could be achieved with a freehand approach. Accurate control measurements of the implanted cup were obtained using fiducial-based matching to a pre-operative CT scan with respect to the anterior pelvic plane. A significantly higher number of cups were placed in the safe zone with the help of the navigation system. The variability of cup placement could be reduced for cup abduction but not substantially for cup version. An error analysis of inaccurate landmark reconstruction revealed that the registration of the mid-pubic point with fluoroscopy was a potential source of error. Keeping this pitfall in mind, fluoroscopy-based navigation in THA is a useful tool for registration of the pelvic coordinate system, particularly those points that cannot be reached by direct pointer digitization with the patient in the lateral decubitus position.

Using a total of 30 cadaveric hips, the accuracy of a fluoroscopy-based computer navigation system for cup placement in total hip arthroplasty (THA) was investigated and an error analysis was carried out. The accuracy of placing the acetabular component within a predefined safe zone using computer guidance was compared to the precision that could be achieved with a freehand approach. Accurate control measurements of the implanted cup were obtained using fiducial-based matching to a pre-operative CT scan with respect to the anterior pelvic plane. A significantly higher number of cups were placed in the safe zone with the help of the navigation system. The variability of cup placement could be reduced for cup abduction but not substantially for cup version. An error analysis of inaccurate landmark reconstruction revealed that the registration of the mid-pubic point with fluoroscopy was a potential source of error. Keeping this pitfall in mind, fluoroscopy-based navigation in THA is a useful tool for registration of the pelvic coordinate system, particularly those points that cannot be reached by direct pointer digitization with the patient in the lateral decubitus position.

No abstract