We analyzed affecting factors associated with the tibiofemoral alignment after minimally invasive unicompartmental knee arthroplasty (UKA) used to treat medial compartmental osteoarthritis of the knee.

From January 2003 to December 2003, 128 UKA were performed in 114 patients with minimally invasive surgery. The revealed tibiofemoral angle, tibial translation, posterior slope and the coronary orientation of the tibial and femoral component were measured using the preoperative and postoperative weight-bearing radiographs. The possible factors associated with the corrective tibiofemoral angle were analyzed statistically.

The average corrective angle of the tibiofemoral axis was 5.8 ° from varus 0.6 ° preoperatively to valgus 5.2 ° postoperatively. The average corrective angle of the tibiofemoral axis was 6.1 ° in the mobile bearing group and 3.6 ° in the fixed bearing group. There was significantly more corrective tibiofemoral angle postoperatively with a larger varus deformity of the knee preoperatively (p<0.0001). The corrective tibiofemoral angle had an increasing tendency with increasing bearing size but this was not statistically significant. Surgeons, the age of the patients, tibial translation, posterior slope of the tibial component, and coronary orientation of the tibial component and femoral component did not affect the degree of the corrective tibiofemoral angle.

The average corrective angle of the tibiofemoral axis after minimally invasive UKA was 5.8 °. The preoperative tibiofemoral angle and the types of implants affected the postoperative tibiofemoral axis after minimally invasive UKA.