Variable rotation of the femur does not affect outcome with patient specific alignment navigated balanced TKA

Excessive internal and external rotation of the femoral component has been associated with poor outcome with a measured-resection neutral mechanical alignment TKA. This technique assumes that every tibia is in 3° of varus so the femoral component is placed in 3° of external rotation relative to the posterior condylar axis to enable a balanced flexion gap. This is not the case as there is wide variability in the bony anatomy and soft tissue envelope of the knee so flexion imbalance may occur. A patient-specific alignment navigated balanced TKA technique was performed whereby the tibia is cut anatomically up to 3° of varus, then a ligament tensor is used to determine the optimal femoral component position for a balanced TKA. This results in variable femoral rotation. The hypothesis is that matching the femoral component rotation to the patient's anatomic tibial cut and soft tissue envelope will not affect clinical outcome METHODS: In a single surgeon series 287 consecutive varus aligned TKA's were performed using this technique with an Attune cruciate retaining fixed bearing TKA with an anatomic patella resurfacing. The angle between the posterior femoral cuts and the posterior condylar axis was collected using Brainlab software. Functional scores were collected prospectively preoperatively and at two years. The variable femoral component rotation was correlated with and compared with the functional outcome scores.

The femoral rotation varied from 7° of internal rotation to 8°of external rotation relative to the posterior condylar axis. The mean rotation was 1.1° of external rotation. There was no significant difference in the Oxford score, WOMAC score, Forgotten Knee Score, KOOS Joint Replacement score or Patient Satisfaction in respect to the variable femoral rotation relative to the posterior condylar axis.

When a more anatomic-balanced TKA technique is used variable femoral rotation will not affect clinical outcome at two years LEVEL OF EVIDENCE: II Prospective Cohort Study.