Pre-operative analysis of lower limb coronal alignment - A comparison of supine MRI versus standing full-length alignment radiographs

Background: In this study we compare the results of pre-operative standing full-length alignment (SFLA) radiographs with supine MRI assessment of the lower limb alignment prior to MRI based patient specific total knee arthroplasty (TKA). Methods: Imaging was performed in 45 knees (45 patients). Assessment of SFLA radiographs was performed by three independent assessors. Inter-observer correlation was high and so the mean values were calculated. This data was then compared to MRI alignment data used to create the patient specific cutting jigs. Results: The range of alignment on SFLA radiographs ranged from + 25 degrees to - 13 degrees versus + 20 to -11 degrees with MRI. The mean difference between techniques was 2 degrees (range 0-8 degrees, SD +/- 3 degrees). Supine MRI under-estimated the degree of deformity in 31/45 (69%) cases. In 25/45 (56%) cases the supine MRI result was within +/- 2 degrees of the value on SFLA radiographs, 31/45 (69%) were within +/- 3 degrees and 38/45 (84%) within +/- 5 degrees. There was no correlation between the degree of varus/valgus deformity and the magnitude of the difference between imaging modalities (Spearman's r(2) = 0.02, p = 0.41). Conclusions: The findings from this study would indicate that supine MRI underestimates the degree of deformity at the knee joint, a conclusion which may be important for pre-operative planning or follow-up of corrective osteotomy or TKA. (C) 2014 Published by Elsevier B.V.