We have been operating TKA for the deformity of OA and RA knee using OrthoPilot kinematic navigation system manufactured by Aesculap (Germany, Tutulingen) since 2005. It has the technology of ligament balance check capability, of which intra-operative registration is not so troublesome and also has the guidance system to achieve the correct bony cutting to the mechanical axis. Although we only have short-term results so far, we have evaluated our results and made some observations.

We have 151 cases at our institution composed of 114 OAs and 37 RAs, with 29 males and 122 females. Among them, 95 cases were able to follow-up over one year.

Limited only to three cases, we had to discontinue the usage of this system due to the loosening of the rigid body during surgery, which we had to change the maneuver to use manual instrument.

The average age at the time of surgery was 73.8 years (range, 38 to 90), and the average BMI was 24.5 (range, 15.6 to 37.7). The average femoral axis, which is the angle between the femoral mechanical axis and the femoral joint surface in the coronal plane, was 2.06 degrees (range, −9 to 10). The average pre-bone-cutting tibiofemoral axis was −8.04 degrees (range, −31 to 15), which after implantation became −0.18 degrees (range, −6 to 6). Tibial proximal cutting has to be perpendicular to the mechanical axis of the lower leg in the coronal plane. The average tibial medial cut was 1.61mm (range, 8 to −11) and tibial lateral cut was 6.78mm (range, 15 to −2). This difference of about 5mm indicates that the shape of tibia had varus deformity to the mechanical axis of the lower leg. On the femoral side, the average femoral medial cut was 9.72mm (range, 19 to 1) and femoral lateral cut was 8.23mm (range, 16 to 1). This almost identical cutting thickness indicates that there was almost no deformity to the mechanical axis on the femoral side. The final X-ray in the follow up period had not changed from the post-operative one. There was no change in VAS comparison three months post-operative.

The results of this study seem to indicate that the kinematic navigation system for TKA will lead to good results of patients’ satisfaction and long durability even for OA and RA knees.