Same patient, same total knee arthroplasty, different outcomes? A pilot study comparing conventional vs. OMNIBotics...

Total knee arthroplasty (TKA) is a well-established treatment for end-stage knee osteoarthritis. Robotic-assisted TKA (RA-TKA) has emerged over the past decade, enabling patient-specific implantation, precise bone cuts, and intraoperative control of gap balance and alignment. The HLS Kneetec^TM is a third condyle posterior stabilized TKA, initially designed for implantation using conventional manual instrumentation (C-TKA), and intended for use with an adjusted mechanical alignment. It can now also be implanted with robotic assistance. This pilot study aimed to evaluate the association between RA-TKA versus C-TKA and clinical outcomes in patients with bilateral knee osteoarthritis.

This was a retrospective cohort of patients operated on by primary RA-TKA in a second osteoarthritic knee after contralateral C-TKA. Twenty-two patients constituted their own control group (44 knees). Mean age was 71.9 ± 7.4 years. The mean time between the two procedures was 22 ± 19 months. Primary outcomes measured were limb alignment (hip-knee-ankle (HKA)), range of motion (ROM), and Forgotten Joint Score (FJS) at one year postoperatively. Secondary outcomes included operating time, hospital stay, incision length, blood loss, and radiographic evaluation (femoral mechanical angle (FMA), tibial mechanical angle (TMA), tibial component slope angle (TSA), patellar tilt angle (PTA), and femoral axial rotation angle (FARA)).

RA-TKA was associated with an HKA angle significantly closer to the target (177.9° vs. 175.3°, p = 0.012), with higher flexion (+7°, p = 0.032) and a higher FJS (+13.9 points, p < 0.001). Operating time was longer in the RA-TKA group (+19.5 min, p = 0.004), while hospital stay, blood loss, and incision length did not differ significantly between groups. Radiographically, RA-TKA was associated with reduced femoral valgus (FMA -1.3°, p = 0.001), with no significant differences in TMA or TSA. Patellar tilt was similar, whereas femoral external rotation was increased with RA-TKA (+1.1°, p = 0.0006).

In this pilot study, RA-TKA was associated with superior frontal alignment and better patient-reported functional outcomes compared to C-TKA. However, given the inherent temporal confounding of the bilateral sequential design and the small sample size, these findings should be interpreted with caution. Further prospective, adequately powered studies are warranted to confirm these results.