Hip–Knee–Ankle Radiographs Are More Appropriate for Assessment of Post-Operative Mechanical Alignment of Total Knee Arthroplasties than Standard AP Knee Radiographs

Weight-bearing hip–knee–ankle (HKA) radiographs are the gold standard for measuring lower limb alignment after total knee arthroplasty (TKA), however the majority of UK units use standardised anteroposterior (AP) knee radiographs. This study aimed to determine whether standardised AP knee radiographs adequately assess lower limb alignment after TKA. HKA radiographs from 50 post-operative TKAs were cropped to the size of a standardised AP knee radiograph allowing comparison of mechanical and anatomical alignment measurements between the two views. Repeatability of alignment measurements was significantly better for HKA radiographs, however, there was poor agreement of the mechanical alignment measured between the two views. Standardised AP knee radiographs are insufficient to assess the mechanical alignment of post-operative TKA and we recommend routinely using HKA radiographs.