Biplanar Low-Dose Radiography is Accurate for Measuring Combined Anteversion after Total Hip Arthroplasty

Background Acetabular component position alone has not been predictive of stability after total hip arthroplasty (THA). Combined anteversion of the acetabulum and femur has the potential of being more predictive of stability. Unfortunately, femoral component position is difficult to measure on plain radiographs. Computed tomography (CT) is the gold standard for measuring implant position post-operatively, but CT exposes patients to a substantial amount of radiation. Questions/Purposes We sought to determine whether biplanar low-dose radiography can be used to accurately measure both acetabular and femoral implant position after THA. Methods Twenty patients underwent standing low-dose biplanar spine-to-ankle radiographs and supine CT scans 6 weeks after THA. Measurements of acetabular inclination, acetabular anteversion, and femoral anteversion were performed by two blinded observers and compared. Results The average absolute differences between biplanar radiographs and CT scans were 2 degrees +/- 2 degrees for acetabular inclination, 3 degrees +/- 2 degrees for acetabular anteversion, and 4 degrees +/- 4 degrees for femoral anteversion between EOS measurements and CT measurements. Interobserver agreement was good for acetabular inclination, acetabular anteversion, and femoral anteversion (Cronbach's alpha = 0.90) using biplanar low-dose imaging. Conclusion Biplanar radiography is a reliable low-radiation alternative for measuring acetabular inclination, acetabular anteversion, femoral version, and thus combined anteversion compared to CT. Femoral anteversion had the most variability but is still clinically relevant.