Accuracy of Reference Axes for Femoral Component Rotation in Total Knee Arthroplasty

Abstract

Background: Many reference axes are used to evaluate rotation of the femoral component during total knee arthroplasty, including the Whiteside line, surgical transepicondylar axis (sTEA), anatomical transepicondylar axis (aTEA), posterior condylar axis externally rotated 3° (PCA+3°ER), sulcus line, and femoral transverse axis (FTA). There is no consensus about which of these axes is most accurate. Methods: The Stryker Orthopaedic Modeling and Analytics (SOMA) database was used to identify 2,128 entire-femur computed tomography (CT) scans. The Whiteside line, aTEA, PCA+3°ER, sulcus line, and FTA were constructed according to published guidelines. Every axis was compared with the sTEA, which is widely regarded as the gold standard reference axis for rotation of the distal part of the femur but has low intraobserver and interobserver reliability intraoperatively. Results: The PCA+3°ER differed from the sTEA by a mean (and standard deviation) of 0.60° ± 1.64°; it was the most accurate but also had the highest degree of intersubject variability. The mean PCA-sTEA angle was 2.40°, close to the accepted “rule of thumb” of 3°. This value was significantly higher in women (2.64° ± 1.74°) than in men (2.18° ± 1.52°; p < 0.001). The Whiteside line differed from the sTEA by a mean of 1.90° ± 1.38°, and the sulcus line differed from the sTEA by a mean of 1.94° ± 1.49°; neither of these values varied significantly with sex or ethnicity. The FTA differed from the sTEA by a mean of 2.04° ± 1.50°. Least accurate was the aTEA, which differed from the sTEA by a mean of 2.05° ± 1.33°. The combination of 3 axes that are readily available intraoperatively (the Whiteside line, aTEA, and PCA+3°ER) differed from the sTEA by a mean of 1.80° ± 0.70°. Conclusions: In the largest study of its kind, analysis of CT scans of 2,128 femora revealed that no 1 axis could serve as a marker of femoral component rotation with both high accuracy and low variability. Utilizing a combination of 3 methods (PCA+3°ER, the Whiteside or sulcus line, and aTEA) to maximize accuracy and sex and ethnic generalizability when positioning the femoral component is recommended. Clinical Relevance: A large-scale study using a CT-based biomorphometric database demonstrated that use of a combination of 3 axes (PCA+3°ER, the Whiteside or sulcus line, and aTEA) was the optimal strategy for judging femoral component rotation.

A comparison of femoral component rotation after total knee arthroplasty in Kanekasu radiographs, axial CT slices and 3D reconstructed images

“…This significant difference was also found in comparison with 3D-CT measurements (− 4.92 ± 2.92 for Kanekasu; − 4.04 ± 1.95 for 2D-CT), which are based on the aTEA. These findings are in keeping with accepted principles [ 16 , 26 , 29 , 30 ]. A recent study of Jang et al [ 29 ] evaluated various reference axes of the femur based on 2128 CT scans.…”

“…These findings are in keeping with accepted principles [ 16 , 26 , 29 , 30 ]. A recent study of Jang et al [ 29 ] evaluated various reference axes of the femur based on 2128 CT scans. They found that the aTEA differed from the sTEA by a mean of 2.05° ± 1.33°.…”

Gender-Based Quantitative Analysis of the Grand Piano Sign in Mechanically Aligned Total Knee Arthroplasty in Asians

“…In our study, the MedL/LatL did not statistically differ between the sTEA and WSL in the entire study population and male subjects alone; nonetheless, there was a difference between the sTEA and WSL in female subjects. Jang et al reported an average difference of 1.9° between the WSL and sTEA, regardless of ethnicity or sex [ 34 ], and Reddy et al reported that there was no statistical difference between Indian men and women when using either the WSL or sTEA [ 35 ]. Koh et al reported no statistical difference in the groove angle of the proximal trochlea between men and women in a Korean study [ 22 ].…”

Morphological characteristics and clinical significance of the distal femur in patients with hemophilia-related knee arthritis

“…Rotational malalignment of the femoral component in TKA is associated with poor outcomes, including flexion instability, patellar maltracking, premature wear of the polyethylene, stiffness, anterior knee pain, and patient dissatisfaction. [ 13 , 14 ] During TKA, the rotation alignment and installation position of the femoral component are generally based on the anatomical signs of the distal femur. The most widely used anatomical signs are the APA, STEA, and PCL.…”