Konan S, Rayan F, Haddad F S
University College London Hospital, UK.
J Bone Joint Surg Br. 2010 Jan;92(1):47-50. doi: 10.1302/0301-620X.92B1.22359.
The radiological evaluation of the anterolateral femoral head is an essential tool for the assessment of the cam type of femoroacetabular impingement. CT, MRI and frog lateral plain radiographs have all been suggested as imaging options for this type of lesion. The alpha angle is accepted as a reliable indicator of the cam type of impingement and may also be used as an assessment for the successful operative correction of the cam lesion. We studied the alpha angles of 32 consecutive patients with femoroacetabular impingement. The angle measured on frog lateral radiographs using templating tools was compared with that measured on CT scans in order to assess the reliability of the frog lateral view in analysing the alpha angle in cam impingement. A high interobserver reliability was noted for the assessment of the alpha angle on the frog lateral view with an intraclass correlation coefficient of 0.83. The mean alpha angle measured on the frog lateral view was 58.71 degrees (32 degrees to 83.3 degrees ) and that by CT was 65.11 degrees (30 degrees to 102 degrees ). A poor intraclass correlation coefficient (0.08) was noted between the measurements using the two systems. The frog lateral plain radiograph is not reliable for measuring the alpha angle. Various factors may be responsible for this such as the projection of the radiograph, the positioning of the patient and the quality of the image. CT may be necessary for accurate measurement of the alpha angle.
股骨头前外侧的放射学评估是评估凸轮型股骨髋臼撞击症的重要工具。CT、MRI和蛙式侧位X线平片均被建议作为此类病变的成像选择。α角被公认为凸轮型撞击症的可靠指标，也可用于评估凸轮病变手术矫正的成功率。我们研究了32例连续的股骨髋臼撞击症患者的α角。使用模板工具在蛙式侧位X线片上测量的角度与在CT扫描上测量的角度进行比较，以评估蛙式侧位在分析凸轮撞击症α角时的可靠性。在蛙式侧位上评估α角时，观察者间的可靠性较高，组内相关系数为0.83。蛙式侧位X线片上测量的平均α角为58.71度（32度至83.3度），CT测量的平均α角为65.11度（30度至102度）。两种测量系统之间的组内相关系数较差（0.08）。蛙式侧位X线平片测量α角不可靠。多种因素可能导致这种情况，如X线片的投影、患者的体位和图像质量。准确测量α角可能需要CT检查。
