The optimal coronal alignment after total knee arthroplasty (TKA) has become an area of increased debate. Sources of variability among investigations include the radiographic technique used for both preoperative surgical planning and postoperative alignment assessments. This study’s purpose was to assess the impact of the imaging modality used on the measurement of coronal plane alignment after TKA.
A consecutive series of patients undergoing TKA using the same cruciate-retaining prosthesis were included for analysis. Postoperatively, all patients received both a rotationally controlled, scout computed tomography scan and a hip–knee–ankle (HKA) image using the EOS Imaging system (EOS Inc., Paris, France). Two, independent observers measured the HKA angle, and femoral and tibial component alignment from each image.
After classifying overall and component alignment as neutral, varus, or valgus, 40.6% (65 of 160) of knees had a discordant alignment classification for HKA, 28.1% (45 of 160) for femoral component alignment, and 26.9% (43 of 160) for tibial component alignment between their computed tomography and EOS images. Overall, 24.4% (39 of 160) of patients had a HKA difference of ≥3° between the 2 images, whereas 18.8% (30 of 160) and 20.0% (32 of 160) of patients had a femoral and tibial component alignment difference of ≥2°, respectively.
Significant differences are present when comparing 2 measurement techniques of mechanical alignment after TKA. The impact of imaging modality on postoperative assessments must be accounted for and be consistent when comparing the results of different investigations.