Significance of asymmetrical posteromedial and posterolateral femoral condylar chamfer cuts in total knee arthroplasty.

Abstract

Orthopedic surgeons remove more bone from the posteromedial femoral condyle than the posterolateral condyle to achieve the desired femoral component rotation. Here, the correlation between the asymmetry of chamfer cuts and femoral component rotation in total knee arthroplasty was determined. A model was built to simulate anterior chamfer cuts performed during total knee arthroplasty to measure posterior condylar offset. Right knee axial magnetic resonance imaging slices were examined from 280 consecutive patients (142 men, 138 women; mean age 31.4±6.6years). The anatomic and surgical transepicondylar axes, as well as the posterior condylar joint line, were drawn. Differences in the posteromedial and posterolateral offsets and the femoral rotation angles relative to the posterior joint line were measured. The mean surgical femoral rotation angle was 4.8°±1.2°, and the mean posterior condylar offset difference was 4.4±1mm, with a strong correlation (p<0.0001; r=0.803). There was no statistically significant difference between genders. Linear regression analyses revealed that a 0.8-mm difference between the anteroposterior dimensions of the medial and lateral posterior condylar offsets corresponded to 1° of femoral external rotation (p<0.0001, R (2)=0.645). The accuracy of the applied technique intra-operatively can be verified by correlating the asymmetry of posterior chamfer cuts with the achieved femoral component rotation, as determined by measuring the thicknesses of posterior chamfer cuts with a caliper. Technical errors can also be minimized by confirming the association between the femoral component rotation-as predicted by the posterior condylar offset difference-and the preoperatively measured femoral rotation angle. II.