Comparison of Femoral Offset Measurement Accuracy between Three-Dimensional-CT and X-ray in Developmental Dysplasia of the Hip Patients and Normal People

Background: Femoral offset (FO) is essential for the guidance of prosthesis choice in the Total Hip Arthroplasty (THA). In current clinical practice, X-ray is the primary method to measure FO. However, the X-ray measurement of FO has low accuracy, especially for DDH. In this study, three-dimensional (3D)-CT was conducted to provide more accurate measurements. Methods: 3D-CT and X-ray measurements of FO from 55 DDH patients and 60 normal volunteers were conducted twice by two osteoarticular surgeons. The inter- and intra-observer reproducibility was analyzed by intraclass correlation coefficient (ICC). The FO values measured by 3D-CT and X-ray were compared and the absolute value of the difference was recorded as the error value of X-ray. These values were analyzed by paired-sample t-test, independent-sample t-test and Dunnett's t-tests, p < 0.05 was considered to be significant. Results: Significant differences were founded between 3D-CT and X-ray in the FO measurements, the absolute values of these differences were 5.42 ± 4.66 mm in DDH patients and 3.74 ± 2.80 mm in normal people, which was regarded as the X-ray error values. According to 3D-CT measurement, the FO value of DDH patients (including Hartofilakidis-I, II, III) was lower than that of normal people. The FO value of Hartofilakidis-II DDH patients was lower than that of Hartofilakidis-I patients. Conclusion: 3D-CT is more precise than X-ray in the measurement of FO in DDH patients and normal people. The 3D-CT method should be recommended to measure FO for the choice of prosthesis in DDH patients before THA.