S. M. Putnam, J. C. Clohisy, J. J. Nepple, Washington University Department of Orthopedic Surgery, St. Louis, MO, USA.
Clin Orthop Relat Res. 2019 May;477(5):1066-1072. doi: 10.1097/CORR.0000000000000636.
The false profile radiograph assesses acetabular coverage in prearthritic hip conditions. Precise rotation of this radiograph is difficult to obtain, so the clinician must interpret radiographs with nonstandard pelvic rotation or tilt, despite limited evidence of how this may affect the anterior center edge angle measurement.
QUESTIONS/PURPOSES: (1) Does pelvic rotation alter the measurement of the anterior center edge angle on false profile views? (2) Does pelvic tilt alter the measurement of the anterior center edge angle on false profile views? (3) Is there an objective way to assess appropriate pelvic rotation for the false profile view?
Eight cadaver hips (four female, four male; one hip randomly selected per pelvis) were included in the study. Hips with degenerative changes, evidence of previous fracture or trauma, or previous surgical intervention were excluded. Specimens were between 68 to 92 years of age (median, 76 years). The specimens were fixed to a custom jig, and radiographs were taken at 5° intervals of rotation (45-85°) and 5° intervals of pelvic tilt (+10° to -10°). The primary outcome variable, anterior center edge angle, was measured for each rotation and tilt.
Every degree increase in pelvic rotation toward a true lateral resulted in 0.18° increase in the anterior center edge angle (95% confidence interval [CI], 0.07-0.29; p = 0.002). For every degree increase in pelvic tilt, the anterior center edge angle increased 0.65° (95% CI, 0.5-0.8; p < 0.001). We verified that standard pelvic rotation of 65° for a false profile radiograph was present when the space between the femoral heads is 66% to 100% of the diameter of the femoral head being imaged.
This study shows that the anterior center edge angle increases as pelvic tilt increases, with a 6° increase in anterior center edge angle for each 10° increase in pelvic tilt. Since the false profile radiograph is obtained standing, the patient should be counseled to avoid adopting a forced posture, ensuring the radiograph remains an accurate functional representation of the patient's anatomy. In contrast, pelvic rotation did not influence the anterior center edge angle by an important margin, and while we recommend that radiographs continue to be obtained with standardized pelvic rotation, aberrant pelvic rotation will likely not result in a clinically meaningful difference in anterior center edge angle measurements. In the future, studies to identify the specific regions of acetabular anatomy that constitute the radiographic measurement of the anterior center edge angle would enhance current understanding of the associated radiographic anatomy, and consequently improve the ability of the surgeon to treat the specific area of pathology.
In practice, the clinician should pay close attention to pelvic tilt, as a 10° change in tilt may cause 6° of change in the anterior center edge angle. However, false profile radiographs obtained within ± 20° of the targeted 65° of rotation will result in less than 4° change in the anterior center edge angle.
假关节位 X 线片评估髋关节关节炎前的髋臼覆盖情况。由于很难准确地获得该 X 线片的旋转，因此临床医生必须在骨盆旋转或倾斜的非标准情况下解读 X 线片，尽管目前还没有充分的证据表明这会如何影响前中心边缘角的测量。
问题/目的：（1）骨盆旋转是否会改变假关节位 X 线片上前中心边缘角的测量值？（2）骨盆倾斜是否会改变假关节位 X 线片上前中心边缘角的测量值？（3）是否有一种客观的方法来评估假关节位 X 线片的适当骨盆旋转？
本研究纳入了 8 具尸体髋（4 具女性，4 具男性；每具骨盆随机选择 1 髋）。排除了有退行性改变、有先前骨折或外伤史或先前手术干预的髋关节。标本的年龄在 68 至 92 岁之间（中位数，76 岁）。将标本固定在定制夹具上，以 5°的旋转间隔（45-85°）和 5°的骨盆倾斜间隔（+10°至-10°）拍摄 X 线片。每个旋转和倾斜角度都测量了主要观察变量，即前中心边缘角。
骨盆向真正的侧方每旋转 1 度，前中心边缘角就会增加 0.18°（95%置信区间，0.07-0.29；p = 0.002）。骨盆每倾斜 1 度，前中心边缘角就会增加 0.65°（95%置信区间，0.5-0.8；p < 0.001）。我们验证了，当股骨头之间的空间为成像股骨头直径的 66%至 100%时，假关节位 X 线片的标准骨盆旋转为 65°。
本研究表明，前中心边缘角随骨盆倾斜度的增加而增加，骨盆倾斜每增加 10°，前中心边缘角增加 6°。由于假关节位 X 线片是在站立位拍摄的，因此应告知患者避免采取强制姿势，以确保 X 线片仍然准确地反映患者的解剖结构。相比之下，骨盆旋转对前中心边缘角的影响并不重要，虽然我们建议继续使用标准化的骨盆旋转来获取 X 线片，但异常的骨盆旋转不太可能导致前中心边缘角测量值出现有临床意义的差异。未来，对确定构成前中心边缘角影像学测量的髋臼解剖特定区域的研究将增强对相关影像学解剖的理解，从而提高外科医生治疗特定部位病变的能力。
在实践中，临床医生应密切关注骨盆倾斜度，因为倾斜度的 10°变化可能导致前中心边缘角的 6°变化。但是，在目标 65°旋转的±20°范围内获得的假关节位 X 线片，前中心边缘角的变化将小于 4°。
