Comparison of Functional Outcomes and Implant Positioning between a CT-based, Semi-active Robotic System and a CT-free Passive Robotic System in Total Knee Arthroplasty.

Robotic Total Knee Arthroplasties (TKAs) have gained popularity over recent years, having been shown to achieve better component alignment than conventional TKAs. However, few studies have compared the different robotic systems. This study was conducted to compare the functional outcomes and implant positioning between a computed tomography (CT) based, semi-active robotic system and a CT-free, passive robotic system. A single-centre propensity score matched retrospective study was conducted comparing 181 CT-based and 113 CT-free cases. Patient reported outcome measures including Oxford Knee Score (OKS), Knee Society Score - Function (KSS-F), Visual Analogue Scale (VAS) pain score and Passive Range of Motion (ROM) were evaluated preoperatively and at 3 months, 1 year and 2 years postoperatively. Postoperative radiographs including lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), hip knee angle (HKA), femoral flexion and posterior tibial slope (PTS) were also measured. Postoperatively, the CT-based group had better KSS-F scores at 1 year (78.2 vs. 65.9) and 2 years (78 vs. 72), exceeding previously documented MCIDs. Better OKS scores were also demonstrated at 2 years (41.7 vs. 39.8) in the CT-based group. However this does not exceed previously documented MCIDs and is likely clinically insignificant. There was no significant observable difference in VAS pain score and passive ROM. The CT-based group also demonstrate better surgical accuracy, with MPTA (90.0° vs. 87.8°) and HKA (_0.22° vs. _2.52°) closer to planned targets of mechanical alignment. Femoral flexion (3.22° ± 0.37° vs 0.15° ± 0.47°, p = 0.001) was also closer to the target of 3° of flexion. There was no significant difference in posterior tibial slope. We conclude that a CT-based, semi-active robotic system resulted in better functional outcomes and implant positioning than a CT-free passive robotic system.