Navigation systems that increase alignment accuracies of the lower limbs have been applied widely in total knee arthroplasty and are currently being adopted for minimally invasive UKA (MIS UKA) with good alignment results. There is little debate that when compared with total knee arthroplasty (TKA), UKA is less invasive, causes less morbidity, better reproduces kinematics, and therefore offers quicker recovery, better range of movement and more physiologic function. However, despite improved alignment accuracies, advantages of use of navigation system in UKA in clinical outcomes and survivals are still debatable. To the best of our knowledge, no reports are available on the long-term results after UKA performing using a navigation system. The purpose of this prospective study was to compare the radiological, clinical, and survival outcomes of UKA that performed using the navigation system and using the conventional technique at average 8 years follows up.

Between January 2003 and December 2005, Total of 98 UKAs were enrolled for this study, 56 UKAs in the navigation group and 42 UKAs in conventional group were included in this study after a average 8 years follow-up. At the final follow up, the radiological measurements with regard to the mechanical axis, the inclination of the femoral and tibial components, and radiolucent line or loosening were evaluated and compared between two groups. The clinical evaluations were performed using range of motion, Western Ontario and McMaster Arthritis index (WOMAC) scores and Knee Society (KS) score.

Of the 98 patients (98 UNI knees), 2 (2.0%) had died at a mean 5.8years after surgery because of cardiovascular disease, 3 (3.1%) underwent revision surgery that 1 cases of periprosthetic stress fractures in medial tibial plateaus in the navigation group and a case of tibial component loosening and polyethylene wear in conventional groups were observed. At a final follow up, the mean of mechanical axis was statistically different between two groups (2.7 vs. 3.9 of varus). And there were significant difference between 2 groups in terms of the mean values (p=0.042) for the tibial component coronal alignment, mean coronal alignments of tibial components were 89.1 ± 2.4° in the NA-MIS and 87.6 ± 1.8° in the MIS group, however outlier result were similar in the 2 group (5 and 5 knees, respectively, p=0.673). Sagittal alignments of femoral and tibial component were similar in the two groups (p>0.05) Significant differences were found in WOMAC or HSS knee scores, in which, stiffness did not show any difference between two groups, but pain and function showed difference at the last follow-up. The mean knee flexion has improved from 135.0 ± 14.8° and 135.0 ± 14.1° preoperatively to 137.1 ± 6.5° and 136.5 ± 7.2° in the NA-MIS and MIS groups on the latest follow-up, which was not significant different (p=0.883). The navigation system in UKA can provide improved alignment accuracy. And better clinical outcomes in pain and HSS score compared with conventional technique after a average of 8 year follow-up.