• 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° to -13° versus +20° to -11° with MRI. The mean difference between techniques was 2° (range 0-8°, SD ± 3°). 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° of the value on SFLA radiographs, 31/45 (69%) were within ±3° and 38/45 (84%) within ±5°. 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.