Comparison of standard anteroposterior knee and hip-to-ankle radiographs in determining the lower limb and implant alignment after total knee arthroplasty

Background and Aims: the coronal alignment of the lower limb is important for planning and assessing outcome after total knee arthroplasty. this study compared postoperative estimation of alignment and measurement of angles using both hip-to-ankle radiographs and anteroposterior (ap) knee radiographs in standing position.

Patients and Methods: Consecutive standard ap knee and hip-to-ankle radiographs in 83 patients (103 knees) after total knee arthroplasty were analyzed.

Results: the tibiofemoral angle measured from both hip-to-ankle and knee radiographs correlated moderately with the mechanical axis (r = 0.646 and r=0.540, respectively). the correlation between tibiofemoral angles in the two radiographs was excellent (r = 0.860). furthermore, measurements of tibial and femoral component alignment between the two radiographs correlated highly (r = 0.718 and r = 0.773, respectively). intraand interobserver correlations were high in all analyses.

Conclusions: the standard ap knee radiograph appears to be a valid alternative to the hip-to-ankle radiograph for determining knee coronal plane alignment in routine followup after total knee arthroplasty. however, the hip-to-ankle radiograph alone provides accurate information on weight-bearing mechanical axis in patients with suspected lower limb malalignment.