Tsukada Sachiyuki, Wakui Motohiro
Department of Orthopaedic Surgery, Niigata Central Hospital, 1-18 Shinko-chou, Chuo-ku, Niigata 950-8556, Japan.
J Orthop Sci. 2010 Nov;15(6):758-63. doi: 10.1007/s00776-010-1546-1. Epub 2010 Nov 30.
Optimal acetabular cup position is an important determinant of the success of total hip arthroplasty (THA), and navigation systems have been developed and applied to improve placement precision. However, the registration method touching bony landmarks through soft tissues may decrease the accuracy in obese cases and in patients with acetabular dysplasia.
Placement accuracy in 69 joints in which THA was performed with imageless navigation was calculated by comparing the placement angle in the anterior pelvic plane and the placement angle in the x-ray table plane with the patient in the supine position. We defined the difference between the placement angle in the anterior pelvic plane and the angle displayed on the navigation screen as the error and the difference between the placement angle in the plane of the x-ray table and the target angle of acetabular component position as the difference in target angle. Patients were divided into obese (BMI ≥ 25) and nonobese (BMI < 25) groups and into acetabular dysplasia and nondysplasia groups.
The mean ± SD navigation errors for all cases were 2.4° ± 2.0° for inclination and 3.7° ± 2.3° for anteversion. The mean difference in target angle for all cases was 2.8° ± 2.5° for inclination and 4.2° ± 3.0° for anteversion. The error in anteversion was significantly higher in the obese group (4.8° ± 2.5°) than in the nonobese group (3.2° ± 2.6°) (P = 0.01). No significant difference was observed between the acetabular dysplasia and nondysplasia groups.
Imageless navigation can be performed with an error of approximately 3° at the anterior pelvic plane. However, accuracy was found to decrease in obese cases.
髋臼杯的最佳位置是全髋关节置换术（THA）成功的重要决定因素，并且已经开发并应用了导航系统以提高放置精度。然而，通过软组织触摸骨性标志的注册方法在肥胖病例和髋臼发育不良患者中可能会降低准确性。
通过比较仰卧位患者在前骨盆平面的放置角度和X线检查台平面的放置角度，计算69例采用无图像导航进行THA的关节的放置精度。我们将前骨盆平面的放置角度与导航屏幕上显示的角度之间的差异定义为误差，将X线检查台平面的放置角度与髋臼组件位置的目标角度之间的差异定义为目标角度差异。患者分为肥胖（BMI≥25）组和非肥胖（BMI<25）组，以及髋臼发育不良组和非发育不良组。
所有病例的平均±标准差导航误差为倾斜度2.4°±2.0°，前倾角3.7°±2.3°。所有病例的目标角度平均差异为倾斜度2.8°±2.5°，前倾角4.2°±3.0°。肥胖组的前倾角误差（4.8°±2.5°）明显高于非肥胖组（3.2°±2.6°）（P = 0.01）。髋臼发育不良组和非发育不良组之间未观察到显著差异。
在前骨盆平面，无图像导航的误差约为3°。然而，发现在肥胖病例中准确性会降低。
