Kinematic aligned femoral rotation leads to greater patella tilt but similar clinical outcomes when compared to traditional femoral component rotation in total knee arthroplasty. A propensity score matched study

Purpose

External rotation of femoral component in total knee arthroplasty (TKA) with reference to the posterior condyles is recommended in mechanical alignment (MA) to ensure optimum patella tracking. In kinematic knee alignment (KA) technique, femoral component is more internally rotated as the femoral resection is based on flexion–extension axis. This study aims to investigate the clinical and radiological outcomes of the patellofemoral joint in patients who underwent TKA using KA versus mechanical alignment.

Methods

A review of prospectively collected registry data of 378 consecutive cruciate retaining primary TKAs (P.F.C.^® Total Knee System, DePuy Synthes, Massachusetts, United States) was performed. Propensity scoring was performed matching patients who received KA TKA (n = 93) to MA TKA (n = 93). Oxford Knee Score (OKS), Knee Society Score (KSS), Short-Form 36 (SF-36), range of motion as well as radiographs assessing patella tilt were compared at 6 months and 2 years after surgery. All patients received the same implant and had their patella resurfaced.

Results

OKS, KSS, physical component of SF-36 and satisfaction rates were comparable at both 6 months and 2 years after surgery. There was moderate association between preoperative and postoperative patella tilt in KA TKA (Cramer’s V = 0.260, p < 0.05). Postoperatively, KA group had a greater number of patients with lateral patella tilt compared to the mechanical group (12 [12.9%] vs 1 [1.1%], p < 0.001). Patella tilts, however, resolved two years after surgery.

Conclusion

The relative internal rotation of the femoral component in KA TKA results in greater incidence of lateral patella tilt postoperatively. Nevertheless, patella tilt resolution was noted at 2 years.

Level of evidence

Level III Evidence—Retrospective Cohort Study.