Heinert G, Hendricks J, Loeffler M D
Department of Radiology, Colchester General Hospital, Turner Road, Colchester CO4 5JL, UK.
J Bone Joint Surg Br. 2009 Apr;91(4):459-62. doi: 10.1302/0301-620X.91B4.21730.
Digital templating in hip replacement is commonly performed with radiological markers to determine the magnification. The latter can also be determined by measuring the distance from the x-ray focal spot to the object and the distance from the x-ray focal spot to the radiological cassette or image receptor. We used post-operative radiographs of total hip replacements and hemiarthroplasties from 22 patients to calculate the magnification using both methods. The accuracy of each method was ascertained by measuring the size of the head of the implant projected on to the radiographs and comparing the result with the known size recorded in the medical records. The accuracy was found to be similar with a mean absolute measurement error of 2.6% (SD 1.4; 0.0% to 5.2%) for the radiological marker and 2.8% (sd 2.2; 0.4% to 10.1%) for the distance method (p = 0.75). The mean radiation dose for templating radiographs (pelvis and lateral of the hip) was similar when taken using a radiological marker (328 mSv SD 142) (n = 51) or using the distance measurement method (324 mSv SD 39) (n = 39) (p = 0.90). We conclude that the distance measuring method is as accurate as the radiological marker method, but may avoid some of the disadvantages such as misplacement of the marker or placement outside the radiological field. It may also be more acceptable to the patient and radiographer.
髋关节置换术中的数字模板通常借助放射标记来确定放大率。放大率也可通过测量X射线焦点到物体的距离以及X射线焦点到放射暗盒或图像接收器的距离来确定。我们使用了22例患者全髋关节置换术和半关节置换术的术后X线片，通过这两种方法来计算放大率。每种方法的准确性是通过测量植入物头部投影在X线片上的大小，并将结果与病历中记录的已知大小进行比较来确定的。结果发现，两种方法的准确性相似，放射标记法的平均绝对测量误差为2.6%（标准差1.4；0.0%至5.2%），距离法为2.8%（标准差2.2；0.4%至10.1%）（p = 0.75）。使用放射标记（328 mSv标准差142）（n = 51）或距离测量法（324 mSv标准差39）（n = 39）拍摄模板X线片（骨盆和髋关节侧位）时，平均辐射剂量相似（p = 0.90）。我们得出结论，距离测量法与放射标记法一样准确，但可能避免一些缺点，如标记放置不当或放置在放射野之外。它对患者和放射技师来说可能也更容易接受。
