Rotational malalignment of the femoral component during total knee arthroplasty (TKA) is associated with poor outcomes, but how best to assess femoral component rotation intraoperatively remains an unanswered question for arthroplasty surgeons. Now, in the largest study of its kind, Jang et al. conclude in the December 4, 2019 issue of JBJS that combining 3 reference axes is the optimal strategy for ensuring accurate femoral component positioning, sex/ethnic generalizability, and intraoperative efficiency.
The authors compared 5 reference axes commonly used for intraoperative assessment of femoral component rotation by mapping them to >2,100 entire-femur CT scans from patients with nonarthritic knees. Using the surgical transepicondylar axis (sTEA) as the gold-standard reference, Jang et al. found that no single other axis was both highly accurate and relatively immune to ethnic and sex variability. Based on their findings, they instead recommend using a combination of 3 axes—posterior condylar axis externally rotated 3° (PCA + 3° ER), the Whiteside or sulcus line, and the anatomical transepicondylar axis (aTEA)—to ensure rotational alignment.
The authors also suggest a straightforward intraoperative process for using these 3 axes:
- Start with the PCA + 3° ER, which most accurately approximates the gold-standard sTEA.
- Then use the Whiteside or sulcus line, neither of which is significantly affected by sex or ethnicity.
- Finally, palpate for the aTEA to narrow the margin of error.
Citing a limitation to this CT-based study of nonarthritic knees, the authors note that “we could not account for the effects of cartilage wear or other changes caused by degenerative arthritis.”