Femoral Version Measurements Vary Significantly Between Commonly Used Methods: Implications for Defining Diagnostic Thresholds

An accurate measurement of femoral version is essential for diagnosing version abnormalities, determining the need for a surgical intervention, and establishing the extent of correction required. However, in the literature, numerous measurement techniques have been described. To (1) evaluate the differences among 4 different 2- and 3-dimensional (2D and 3D, respectively) techniques for measuring femoral version, (2) assess the effect of femoral version on differences between measurement techniques, and (3) examine the accuracy of an automated method in determining femoral version using commonly employed techniques. Cohort study; Level of evidence, 3. A total of 100 patients who underwent hip preservation surgery at a single academic center were analyzed (measured and segmented). Pelvic computed tomography was used to measure femoral version using 4 established methods: 2 were 2D axial techniques (Murphy and Reikeras), and 2 were 3D reconstructions (Sugano and Lee). Overall, 4 assessors performed the axial measurements. Measurements were performed relative to the posterior condylar axis (PCA) and transepicondylar axis (TEA). Discrepancies in femoral version between different techniques and interobserver correlations were determined. Linear regression equations to convert femoral version values between methods were established. Using these equations, we calculated the range for each method to be 10&#xb0; to 25&#xb0; as per the Murphy method, described as "normative" in the literature. All 2D measurements demonstrated excellent interobserver reliability (interclass correlation coefficients = 0.93-0.97). The mean femoral version according to the 4 methods varied from 3.4&#xb0;&#xb1; 9.6&#xb0; (Lee; lowest) to 23.2&#xb0;&#xb1; 11.2&#xb0; (Murphy; highest). Distally, the TEA exhibited an external rotation of 5.2&#xb0;&#xb1; 1.6&#xb0; relative to the PCA. Linear regression equations showed a strong correlation (> 0.8) for converting femoral version values between methods. The normative range, derived from these equations, varied from 10&#xb0; to 25&#xb0; (Murphy) to -7&#xb0; to 5&#xb0; (Lee). Excellent correlations were identified between the manual 2D and automatic 3D methods for both distal (TEA: &#x3c1; = 0.942,< .001; PCA: &#x3c1; = 0.984,< .001) and proximal (Reikeras: &#x3c1; = 0.924,< .001; Murphy: &#x3c1; = 0.965,< .001) femoral measurements. Femoral version measurements varied significantly between methods, with more proximal reference axes yielding lower values. Despite high reproducibility, the methods differed in mean values, emphasizing the importance of method-specific normal ranges. While 2D methods are common, 3D imaging, supported by quick and user-friendly software, serves as a more detailed and practical assessment.