title: Pre-operative analysis of lower limb coronal alignment - a comparison of supine MRI versus standing full-length alignment radiographs.
abstract: 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.
authors.affiliation: University Hospital Crosshouse, Kilmarnock Road, Kilmarnock KA2 0BE, United Kingdom. Electronic address: alison.winter@doctors.org.uk.
authors.forename: Alison
authors.initials: A
authors.lastname: Winter
authors.affiliation: University Hospital Crosshouse, Kilmarnock Road, Kilmarnock KA2 0BE, United Kingdom.
authors.forename: Kim
authors.initials: K
authors.lastname: Ferguson
authors.affiliation: University Hospital Crosshouse, Kilmarnock Road, Kilmarnock KA2 0BE, United Kingdom.
authors.forename: Brian
authors.initials: B
authors.lastname: Syme
authors.affiliation: University Hospital Crosshouse, Kilmarnock Road, Kilmarnock KA2 0BE, United Kingdom.
authors.forename: Jacquelyn
authors.initials: J
authors.lastname: McMillan
authors.affiliation: University Hospital Crosshouse, Kilmarnock Road, Kilmarnock KA2 0BE, United Kingdom.
authors.forename: Graeme
authors.initials: G
authors.lastname: Holt
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000473:pathology; D035002:Lower Extremity; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011300:Preoperative Care; D011859:Radiography; D012044:Regression Analysis; D012189:Retrospective Studies; D016683:Supine Position
keywords: Alignment; Arthoplasty; MRI