Transepicondylar line and condylar line as parameters for axial alignment in knee arthroplasty

In order to investigate the reliability of the transepicondylar line and the condylar line as indicators for lower limb alignment in knee arthroplasty, the femorotibial angle (FTA), and the angle between the transepicondylar line and the tangential line of tibial plateau (angle epsilon) and condylar-plateau angle (CPA) were measured in 107 (78 patients) full-length standing X-ray films of lower limbs. The mean FTA was measured to be 178.0+/-9.3 degrees, the CPA 1.5+/-8.5 degrees and angle epsilon -0.8+/-8.5 degrees. The correlation between FTA and the CPA was analyzed to be significant with a correlation coefficient of 0.63, while another correlation between FTA and angle epsilon was calculated to be significant with a correlation coefficient of 0.81 at the same time. As a result, the correlation of the latter one was highly significant, having a R2 value of 0.648 (P<0.001), while the R2 of the former was only 0.397 (P<0.001). In conclusion, the transepicondylar line could be considered as a more reliable indicator for lower limb alignment, which may play an important role in ligament balancing and improvement of the guiding system in knee arthroplasty.