The aim of this retrospective cohort study was to identify any difference in femoral offset as measured on pre-operative anteroposterior (AP) radiographs of the pelvis, AP radiographs of the hip and corresponding CT scans in a consecutive series of 100 patients with primary end-stage osteoarthritis of the hip (43 men and 57 women with a mean age of 61 years (45 to 74) and a mean body mass index of 28 kg/m2 (20 to 45)).
Patients were positioned according to a standardised protocol to achieve reproducible projection and all images were calibrated. Inter- and intra-observer reliability was evaluated and agreement between methods was assessed using Bland-Altman plots.
In the entire cohort, the mean femoral offset was 39.0 mm (95% confidence interval (CI) 37.4 to 40.6) on radiographs of the pelvis, 44.0 mm (95% CI 42.4 to 45.6) on radiographs of the hip and 44.7 mm (95% CI 43.5 to 45.9) on CT scans. AP radiographs of the pelvis underestimated femoral offset by 13% when compared with CT (p < 0.001). No difference in mean femoral offset was seen between AP radiographs of the hip and CT (p = 0.191).
Our results suggest that femoral offset is significantly underestimated on AP radiographs of the pelvis but can be reliably and accurately assessed on AP radiographs of the hip in patients with primary end-stage hip osteoarthritis.
We, therefore, recommend that additional AP radiographs of the hip are obtained routinely for the pre-operative assessment of femoral offset when templating before total hip replacement.
The authors would like to thank Professor G. Aldinger and Priv.-Doz. Dr. R. Moll for clinical advice and for support in data collection.The authors thank the non-profit foundation ENDO-Stiftung, Hamburg, Germany, and the NIHR Biomedical Research Unit of Musculoskeletal Disease, Nuffield Orthopaedic Centre & University of Oxford, UK for supporting this study.
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
Supplementary material. Three tables, detailing i) the demographic data of the cohort, ii) the mean values for the measurements of femoral offset, diameter of the head and femoral anteversion for the entire cohort and by gender, and iii) the mean differences in femoral offset between the measurements performed on pelvis and hip anteroposterior radiographs and CT, for the entire cohort and by gender, are available with the electronic version of this article on our website www.jbjs.boneandjoint.org.uk
- Received July 29, 2011.
- Accepted December 15, 2011.
- ©2012 British Editorial Society of Bone and Joint Surgery