Le Brian T N, Bourgeault-Gagnon Yoan, Lyons Matthew C, McCaffrey Samuel L, Salmon Lucy J, O'Sullivan Michael D
North Sydney Orthopaedic and Sports Medicine Centre, Suite 2 The Mater Clinic, 3 Gillies St, Wollstonecraft, Sydney, NSW, 2065, Australia.
School of Medicine, University of Notre Dame, Sydney, Australia.
Skeletal Radiol. 2025 Feb 19. doi: 10.1007/s00256-025-04895-5.
To compare the magnitude of post-arthroplasty leg length discrepancy (LLD) and incidence of clinically significant LLD measured on CT scanogram using a commonly used measurement method (from the acetabular apex to tibial plafond) to an alternative technique avoiding the use of the acetabular prosthesis as a landmark and to assess inter-observer and intra-rater reliability of the new technique.
In this retrospective study, post-arthroplasty LLD measurements were conducted in 100 hips by two interpreters on CT scanogram scout views from the acetabular apex to the tibial plafond (AA-TP) and the inter-teardrop line to the tibial plafond (IT-TP). Aggregate means and proportions of clinically relevant LLD (≥ 10 mm) were compared between methods. Inter-rater reliability was calculated, and both interpreters repeated measurements on ten randomly selected patients to calculate intra-rater reliability.
The commonly used AA-TP technique overestimated LLD by 3.7 mm compared to the IT-TP technique. The odds of LLD measurement exceeding the clinically significant threshold of 10 mm were 3.8 times higher when using the AA-TP technique. Excellent inter-rater (ICC 0.984, 0.958) and intra-rater reliability (ICC > 0.9) were found for both techniques.
CT scanogram measurements from the acetabular apex to the tibial plafond often overestimate operative limb length due to reference landmarks in different axial planes. Measurements from the inter-teardrop line to the tibial plafond yield significantly lower LLD values, possibly reflecting actual limb length better. The authors recommend using the inter-teardrop line and tibial plafond as reference landmarks to improve LLD assessment accuracy post-arthroplasty.
使用一种常用测量方法（从髋臼顶点至胫骨平台）在CT扫描图像上比较关节置换术后腿长差异（LLD）的大小以及临床显著LLD的发生率，并与一种避免将髋臼假体用作标志点的替代技术进行比较，同时评估新技术的观察者间和同一观察者内的可靠性。
在这项回顾性研究中，两名解读人员对100例髋关节的CT扫描图像定位像进行关节置换术后LLD测量，测量方法分别为从髋臼顶点至胫骨平台（AA-TP）以及从泪滴间线至胫骨平台（IT-TP）。比较两种方法之间临床相关LLD（≥10 mm）的总体均值和比例。计算观察者间可靠性，两名解读人员对10例随机选择的患者重复测量以计算同一观察者内可靠性。
与IT-TP技术相比，常用的AA-TP技术使LLD高估了3.7 mm。使用AA-TP技术时，LLD测量超过临床显著阈值10 mm的几率高出3.8倍。两种技术均具有出色的观察者间可靠性（ICC 0.984，0.958）和同一观察者内可靠性（ICC＞0.9）。
由于不同轴向平面中的参考标志点，从髋臼顶点至胫骨平台的CT扫描图像测量常常高估手术肢体长度。从泪滴间线至胫骨平台的测量得出的LLD值显著更低，可能能更好地反映实际肢体长度。作者建议使用泪滴间线和胫骨平台作为参考标志点，以提高关节置换术后LLD评估的准确性。
