A Comparison of Plain Radiography with Computer Tomography in Determining Coronal and Sagittal Alignments following Total Knee Arthroplasty

Abstract

Introduction: Optimal coronal and sagittal component positioning is important in achieving a successful outcome following total knee arthroplasty (TKA). Modalities to determine post-operative alignment include plain radiography and computer tomography (CT) imaging. This study aims to determine the accuracy and reliability of plain radiographs in measuring coronal and sagittal alignment following TKA. Materials and Methods: A prospective, consecutive study of 58 patients undergoing TKA was performed comparing alignment data from plain radiographs and CT imaging. Hip-knee-angle (HKA), sagittal femoral angle (SFA) and sagittal tibial angle (STA) measurements were taken by two observers from plain radiographs and compared with CT alignment. Intra- and inter-observer correlation was calculated for each measurement. Results: Intra-observer correlation was excellent for HKA (r>0.89) with a mean difference of <1.9°. The least intra-observer correlation was for SFA (mean r=0.58) with a mean difference of 8°. Inter-observer correlation was better for HKA (r>0.95) and STA (r>0.8) compared to SFA (r=0.5). When comparing modalities (radiographs vs CT), HKA estimations for both observers showed the least maximum and mean differences while SFA observations were the least accurate. Conclusion: Radiographic estimation of HKA showed excellent intra- and inter-observer correlation and corresponds well with CT imaging. However, radiographic estimation of sagittal plane alignment was less reliably measured and correlated less with CT imaging. Plain radiography was found to be inferior to CT for estimation of biplanar prosthetic alignment following TKA.

Keywords: computer tomography; coronal alignment; radiographs; sagittal alignment; total knee arthroplasty.

Fig. 1:

(a) Post-operative measurements of Hip-Knee Angle on 4-foot standing films and (b) Sagittal Femoral Angle and Sagittal Tibial Angle on 18-inch long lateral radiographs.

Fig. 2:

Post-operative measurements of (a) Hip-Knee Angle, (b) Sagittal Femoral Angle and (c) Sagittal Tibial Angle on CT radiographs using the CT Perth Protocol.

Fig. 3:

Relationship between the difference and mean of inter-observer radiographic measurements for (a) Hip-Knee Angle, (b) Sagittal Femoral Angle and (c) Sagittal Tibial Angle.

Fig. 4:

Relationship between difference and mean values of alignment as measured via radiographs and CT by the first observer for (a) Hip-Knee Angle, (b) Sagittal Femoral Angle and (c) Sagittal Tibial Angle.

Fig. 5:

Relationship between difference and mean values of alignment as measured via radiographs and CT by the second observer for (a) Hip-Knee Angle, (b) Sagittal Femoral Angle and (c) Sagittal Tibial Angle.