Accuracy and clinical outcomes in total knee arthroplasty using an image-free navigation system

The purpose of this study was to investigate the accuracy of an image-free navigation system and to investigate the effect of the postoperative coronal lower limb alignment and implant alignment on clinical outcomes following mechanically aligned (MA)-total knee arthroplasty (TKA).

In this retrospective study, 180 primary cemented posterior-stabilized TKAs were performed using an image-free navigation system. Patients were divided into groups based on their postoperative hip-knee-ankle angle (HKA; a neutral HKA group [0 ± 3°] and an outlier group [<-3° or > 3°]), lateral distal femoral angle (LDFA; a neutral LDFA group [90 ± 3°] and an outlier group [< 87° or > 93°]), and medial proximal tibial angle (MPTA; a neutral MPTA group [90 ± 3°] and an outlier group [< 87° or > 93°]). The range-of-motion, 2011 Knee Society score (2011 KSS), and Forgotten Joint Score-12 (FJS-12) were compared between the neutral and outlier groups at 1 and 2 years postoperatively.

The percentage of knees with a neutral HKA was 91.1% and clinical outcomes significantly improved postoperatively. No significant differences were detected between the neutral HKA (n = 164) and outlier groups (n = 16, all varus) for any clinical outcome. Considering LDFA, the outlier group was too small (n = 3, all varus) for statistical analysis. The overall 2011 KSS and symptoms at 2 years postoperatively and FJS-12 at 1 and 2 years postoperatively were significantly higher in the neutral MPTA group (n = 174) than in the outlier group (n = 6, all varus).

The accuracy of an image-free navigation system was satisfactory in MA-TKA and led to good clinical outcomes. No significant differences in clinical outcome were detected between postoperative patients with an HKA within 3° of the neutral position and postoperative patients with an HKA <-3°. Patients with a postoperative MPTA within 90 ± 3° achieved better clinical outcomes than those of patients with an MPTA < 87°.