The Relationship Between Prone Range of Motion and Measured Femoral Version on Advanced Imaging in Adolescent Patients

Background: Femoral version (FV) is often assessed clinically on physical examination using prone hip range of motion (ROM) and quantified anatomically with advanced imaging measurements. Uncertainty exists over the relationship between the two, as well as which modality represents the benchmark. The purpose of this study is to assess the association between prone ROM and measured FV in pediatric and adolescent patients. Methods: This was a retrospective cohort study identifying all patients ≤18 years of age presenting to the study institution with hip pain. Patients were included if they had both documented prone ROM and hip magnetic resonance imaging (MRI) and/or CT scan with axial cuts through the distal femoral condyles done within 6 months of their clinical examination. Total hip arc of motion was calculated by adding prone internal (IR) and external (ER) rotation. Patients lacking advanced imaging studies or with neuromuscular disorders, altered femoral head anatomy, or history of surgical procedures to the hip before imaging were excluded. Pearson correlation coefficient was calculated to assess the strength of the relationship between prone hip ROM and FV as measured on CT and MRI. Results: One hundred forty-six patients (259 hips) were included. Mean age at the time of evaluation was 15.2 ± 2.8 years; 122 patients (83.0%) were female. Mean total arc of motion was 91.5° ± 16.5°. Prone IR and prone ER moderately correlated with FV as measured on both CT (IR r = 0.63; P < 0.001; ER r = −0.63; P < 0.001) and MRI (IR r = 0.60; P < 0.001; ER r = −0.62; P < 0.001). Measurements of FV on CT strongly correlated with those on MRI (r = 0.95; P < 0.001). Discussion: We demonstrate a moderate correlation between prone motion and advanced imaging measurements of FV in the largest adolescent cohort to date. Future studies should seek to limit variability in physical examination and advanced imaging measurements with more standardized techniques for both. Level of Evidence: III (Retrospective cohort study)