FP2.7 Femoral Version Measurements Vary Significantly Between Commonly Used Methods – Implications for diagnosis and management

Background: Accurate measurement of femoral version is essential for diagnosing rotational deformities, determining the need for surgical intervention, or establishing the extent of correction required. However, in the literature numerous measurement techniques have been described. This study aims to 1) Evaluate the differences among different 2- and 3- dimensional (2D/3D) techniques for measuring femoral version; 2) Investigate intra- and inter-observer reliability of measurements amongst orthopaedic surgeons and radiologists; and 3) Assess effect of version on differences between measurement techniques.

Methods: This is a retrospective, single-, academic- center, study. One-hundred patients/femora that underwent hip preservation surgery were analyzed (measured and segmented). Pelvic CT scans, which included the distal femur, were utilized to measure femoral version, employing different sets of landmarks as per different definitions Four well-described and commonly used measurements were determined. Those were from femoral version measurements from axial slices (2D) of the hip and knee (Murphy and Reikeras methods), or from 3D reconstructions of segmented femurs (Sugano and Lee methods) were performed. Four assessors performed the axial measurements (1 hip preservation fellow; 2 young adult hip staff surgeon and 1 MSK radiologist). Measurements were performed relative to the posterior- and inter-epicondylar- axes. Discrepancies between the different techniques and the inter-observer correlations were determined.

Results: The mean anteversion according to the 4 methods varied between 8.9°±11.6 (Reikeras; lowest) to 16.3°±12.2 (Murphy; highest). Referencing off the epicondylar axis reduced version measurements by 5.2°±2.6, compared to the posterior condylar axis.

Significant inter-observer correlations were observed, but the agreement was higher for Murphy’s method (ICC:0.80; 95%CI: 0.72-0.86), compared to Reikeras (ICC:0.74; 95%CI: 0.63-0.82). While the Sugano and Lee methods (3D methods) showed strong correlations with both Murphy (ρ=0.937 and ρ=0.941, respectively) and Reikeras (ρ=0.936 and ρ=0.922, respectively), they demonstrated smaller discrepancies in absolute values with Reikeras (7.1°±3.6 and -3.0°±4.9 respectively) than with Murphy (9.3°±4.0 and 19.4°±4.1 respectively).

Femoral version correlated positively with difference in measurements between Murphy/Reikeras (ρ=0.291), Lee/Murphy (ρ=0.402), Sugano/Lee (ρ=0.616), and negatively between Sugano/Murphy (ρ=-0.246) and Sugano/Rekeiras (ρ=-0.423).

Discussion: Amongst the four observers, Murphy’s method demonstrated greatest agreement but illustrated greatest version compared to rest, which needs to be considered as neglecting these differences can lead to errors in surgical decision making and planning degree of correction. As higher femoral version correlates with increased disparities between certain measurement techniques, it is important to consider these differences in patients with instability presenting with persistent femoral anteversion, when considering derotational osteotomy.