Is the preoperative leg axis similar in radiographic and computer measurements in frontal deformities?

Introduction: A prerequisite for ensuring a good clinical and functional outcome in total knee arthroplasty is knowing the preoperative leg alignment. This alignment is obtained using a long radiograph including the hip and knee, or a computer algorithm derived from palpation of landmarks and mapping of bone structures. It has been recommended to omit the preoperative radiograph if technology-assisted systems are to be used, but doubts exist regarding the similarity between both measurements, especially in frontal varus or valgus deformities. Material and methods: The preoperative leg alignment was analyzed in 123 patients scheduled for total knee arthroplasty. Thirty-eight had a preoperative valgus axis radiographically, and 85 had a varus axis. A computer program was used to perform the radiographic measurement of the mechanical axis of the leg, and at the start of the procedure, this same measurement was verified with a technology-assisted navigation system (TAS). Results: In the valgus group, the mean preoperative radiographic axis was 169.1º (SD 5.06), while the axis measured using the TAS was 171.9º (SD 3.96) (p=0.009). In the varus group, the mean radiographic axis was 191.9º (SD 5.86), and the axis measured using the TAS was 189.7º (SD 4.84) (p=0.008). The Pearson correlation coefficient comparing both measurements was 0.650 in the varus group and 0.237 in the valgus group (p=0.151). Conclusions: The discrepancy between limb axis measurements obtained radiographically and those obtained with technological aids does not preclude the use of radiography in the preoperative evaluation of total knee arthroplasties.