无症状青年人群股骨颈α角CT测量多个平面之间的比较

目的　比较无症状青年人群中多个平面CT测量股骨颈α角的差异，并对凸轮型股髋撞击综合征（FAI）形态改变的发生率进行评估。  方法　回顾性分析2009年5月至2013年11月120例无髋关节病症患者（20～40岁）的腹部或盆腔CT扫描资料。α角的测量采用平行于股骨颈长轴的斜轴位平面以及以股骨颈中心作为旋转轴的4个方向辐射状层面,两者差异的比较采用方差分析，α角大于55°提示凸轮型FAI形态异常。  结果　斜轴位平面α角均值为(39.5±6.51) º，共有12人（占10%，12/120）、14个关节α角大于55 º，10人为单侧、2人为双侧；在12点、1点、2点及3点方向各平面的α角均值分别为(42.8±7.3) º,(48.8±7.6)º,(47.3±7.2)º,(40.2±6.7)º，在所有辐射状平面中共有106个关节α角大于55 º，其中在1:00方向有54个关节α角增大，占受试者的35%（42 /120）（30人为单侧，12人为双侧）；斜轴位平面与12点、1点、2点方向平面测量的α角之间的差异有统计学意义（P<0.05）。  结论　在辐射状平面测量α角可能更准确；无症状青年人群中，其类似凸轮型FAI的形态改变有较高的发生率。

Comparison of CT alpha angle Measurement Planes in a Young Population without Symptoms

Objective　 To compare the alpha angle value measured on different planes and to determine the prevalence of cam-type femoroacetabular impingement(FAI) morphology in a young population without symptoms using computed tomography.　Methods　A retrospective review was performed on the data of 120 patients (age range, 20–40 years) with no current or previous hip disorder who underwent CT of the abdomen and pelvis from May 2009 to November 2013. Alpha angle were measured on both oblique axial plane images parallel to the long axis of the femoral neck and radial images in four planes obtained using the center of the femoral neck as the axis of rotation.Analysis of variance was used to evaluate differences between alpha angle values on the oblique axial plane and radial plane.Alpha angle greater than 55° was considered positive for cam-type FAI morphology.　Results　The mean alpha angle value on the oblique axial plane was (39.5±6.51)º，Alpha angles greater than 55° were found in 14 joints of 12 cases（10%，12/120） on the oblique axial plane image，10 cases were unilateral and 2 cases were bilateral. The mean alpha angle values at the 12,1,2,3 o’clock position were (42.8±7.3)º,(48.8±7.6 )º,(47.3±7.2)º,(40.2±6.7)º, respectively. 106 Alpha angles greater than 55° in total were found on the radial plane images. 54 abnormal alpha angles were measured at the 1:00 position, including 35% （42 /120）of the subjects.30 cases were unilateral and 12 cases were bilateral.The differences of the alpha angles between the oblique axial and the radial 12 o'clock, 1 o'clock, 2o'clock plane reached statistical significance（P<0.05）.　Conclusion　Alpha angle measurements on the radial plane images may be more accurate. The frequency of cam-type FAI morphology was high in a young population without symptoms.