Objective To demonstrate the greater accuracy of panoramic radiographs of the lower limbs (long) in relation to short radiographs of the knee in the measurement of the mechanical axis of the lower limb after total knee arthroplasty (TKA). Methods A retrospective study was conducted to evaluate the accuracy of long and short postoperative radiographic images of 70 patients submitted to TKA in our service. The images were analyzed at random, at different times, by three orthopedists. In all images, the mechanical axis of the limb, femur and tibia were traced and femorotibial angles (FTAs) were calculated. The intraclass correlation coefficient (ICC) was calculated to evaluate the agreement of the measurement of the inter- and intra-observer mechanical axis. Results It was observed that there was high intra and interobserver agreement when panoramic radiographs were used, with minimum intra and interobserver ICC of 0.89, equivalent to a very strong agreement. On short radiographs in the anteroposterior incidence (AP) of the knee, the ICC showed moderate agreement, obtaining a maximum value of 0.75. Conclusion There is a significant difference in accuracy for the measurement of the mechanical axis of the lower limb, comparing long and short radiographs of the lower limb. Thus, for the proper measurement of the mechanical axis of the lower limb, we suggest the performance of long radiography in the postoperative period of TKA.
Keywords: arthroplasty, replacement, knee; knee joint; radiography.
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