A comparison of radiological and computer navigation measurements of lower limb coronal alignment before and after total knee replacement

We compared lower limb coronal alignment measurements obtained pre- and post-operatively with long-leg radiographs and computer navigation in patients undergoing primary total knee replacement (TKR). A series of 185 patients had their pre- and post-implant radiological and computer-navigation system measurements of coronal alignment compared using the Bland-Altman method. The study included 81 men and 104 women with a mean age of 68.5 years (32 to 87) and a mean body mass index of 31.7 kg/m(2) (19 to 49). Pre-implant Bland-Altman limits of agreement were -9.4 degrees to 8.6 degrees with a repeatability coefficient of 9.0 degrees. The Bland-Altman plot showed a tendency for the radiological measurement to indicate a higher level of pre-operative deformity than the corresponding navigation measurement. Post-implant limits of agreement were -5.0 degrees to 5.4 degrees with a repeatability coefficient of 5.2 degrees. The tendency for valgus knees to have greater deformity on the radiograph was still seen, but was weaker for varus knees. The alignment seen or measured intra-operatively during TKR is not necessarily the same as the deformity seen on a standing long-leg radiograph either pre- or post-operatively. Further investigation into the effect of weight-bearing and surgical exposure of the joint on the mechanical femorotibial angle is required to enable the most appropriate intra-operative alignment to be selected.