3-dimensional computer tomography is more accurate than traditional long-leg radiographs in the planning and evaluation of coronal alignment in total knee arthroplasty: a prospective study on 121 knees

Background and purpose - Accurate measuring tools are essential in preoperative planning and for the study of the association between postoperative alignment and clinical outcome in total knee arthroplasty (TKA). We aimed to describe a simple method to measure preoperative hip- knee-femoral shaft (HKFS) angle and postoperative coronal alignment in TKA with the use of standard 3D CT and to compare preoperative HKFS angles and postoperative coronal alignment measured with the 3D CT technique and with standing long-leg hip-knee-ankle (HKA) radiographs.Patients and methods - HKA radiographs and 3D CT were taken preoperatively and 3 months after the operation in 121 knees. The interrater reliability for the 3D CT method was calculated with intra-class correlation coefficient (ICC). The preoperative HKFS angles and the postoperative deformity measured with the 2 methods were compared and illustrated on Bland-Altman plots, frequency tables, and by Cohen's kappa coefficients (K).Results - The 3D CT method was feasible in all knees and the ICC was excellent. Mean (SD, range) difference in HKFS angle measured on HKA radiographs and on 3D CT was -0.3 degrees (0.9 degrees, -4.1 degrees to 2.4 degrees). Mean (SD, range) difference in postoperative deformity was 0.1 degrees (1.6 degrees, -5 degrees to 6 degrees). The 95% limits of agreement were 1.4 degrees and -2 degrees for HKFS and +/- 3 degrees for postoperative alignment. The agreement in outlier (>= 3 degrees) identification was moderate with a K (95% confidence interval) of 0.48 (0.32-0.64).Conclusion - 3-dimensional computer tomography was feasible and was shown to be more accurate than traditional long-leg radiographs