Prediction of three-dimensional femoral offset from AP pelvis radiographs in primary hip osteoarthritis

• Published in: European journal of radiology Vol. 82; no. 8; pp. 1278 - 1285
• Main Authors: Merle, C, Waldstein, W, Pegg, E.C, Streit, M.R, Gotterbarm, T, Aldinger, P.R, Murray, D.W, Gill, H.S
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier Ireland Ltd 01.08.2013
• Subjects: Adult; Aged; Arthroplasty; Cohort Studies; Female; Femur - diagnostic imaging; Hip; Hip Joint - diagnostic imaging; Humans; Imaging, Three-Dimensional - statistics & numerical data; Male; Middle Aged; Osteoarthritis; Osteoarthritis, Hip - diagnostic imaging; Osteoarthritis, Hip - epidemiology; Patient Positioning - methods; Pelvis - diagnostic imaging; Planning; Prevalence; Radiography; Radiology; Reproducibility of Results; Retrospective Studies; Sensitivity and Specificity; Tomography, X-Ray Computed - statistics & numerical data; United Kingdom - epidemiology; Radiography; CT; Arthroplasty; Planning; Osteoarthritis; Hip
• ISSN: 0720-048X; 1872-7727
• DOI: 10.1016/j.ejrad.2013.02.040

Abstract Background In pre-operative planning for total hip arthroplasty (THA), femoral offset (FO) is frequently underestimated on AP pelvis radiographs as a result of inaccurate patient positioning, imprecise magnification, and radiographic beam divergence. The aim of the present study was to evaluate the accuracy and reliability of predicting three-dimensional (3-D) FO from standardised AP pelvis radiographs. Methods In a retrospective cohort study, pre-operative AP pelvis radiographs, AP hip radiographs and CT scans of a consecutive series of 345 patients (345 hips, 146 males, 199 females, mean age 60 (range: 40–79) years, mean body-mass-index 27 (range: 19–57) kg/m2 ) with primary end-stage hip OA were reviewed. Patients were positioned according to a standardised protocol and all images were calibrated. Using validated custom programmes, FO was measured on corresponding radiographs and CT scans. Measurement reliability was evaluated using intra-class-correlation-coefficients. To predict 3-D FO from AP pelvis measurements and to assess the accuracy compared to CT, the entire cohort was randomly split into subgroups A and B. Gender specific regression equations were derived from group A (245 patients) and the accuracy of prediction was evaluated in group B (100 patients) using Bland–Altman plots. Results In the entire cohort, mean FO was 39.2 mm (95%CI: 38.5–40.0 mm) on AP pelvis radiographs, 44.1 mm (95%CI: 43.4–44.9 mm) on AP hip radiographs and 44.6 mm (95%CI: 44.0–45.2 mm) on CT scans. In group B, we observed no significant difference between gender specific predicted FO (males: 48.0 mm, 95%CI: 47.1–48.8 mm; females: 42.0 mm, 95%CI: 41.1–42.8 mm) and FO as measured on CT (males: 47.7 mm, 95%CI: 46.1–49.4 mm, p = 0.689; females: 41.6 mm, 95%CI: 40.3–43.0 mm, p = 0.607). Conclusions The present study suggests that FO can be accurately and reliably predicted from AP pelvis radiographs in patients with primary end-stage hip osteoarthritis. Our findings support the surgeon in pre-operative templating on AP-pelvis radiographs and may improve offset and limb length restoration in THA without the routine performance of additional radiographs or CT.