Evaluation of a Single Knee System: All-Polyethylene Tibia (APT) vs. Metal-Backed Tibia (MBT) in Primary Total Knee Arthroplasty

Background The all-polyethylene tibia (APT) in total knee arthroplasty (TKA) previously demonstrated similar survival and function compared to metal-backed tibia (MBT), without the associated risk of backside wear and at a lower cost. The LinkSymphoKnee (LSK) (Waldemar Link GmbH & Co. KG, Hamburg, Germany) and its corresponding APT received FDA 510(k) approval in 2021; however, clinical outcome data remain limited. The purpose of this study was to determine whether the LSK APT would have non-inferior pain outcomes compared to the LSK MBT within two years postoperatively and compile descriptive statistics on revision, repeat surgery, manipulation under anesthesia, and range of motion. Methods This retrospective cohort study analyzed data from patients who underwent primary TKA performed by a single surgeon at a single center between January 2021 and October 2024. Patient chart data were categorized based on tibial implant design(APT vs MBT). After applying exclusion criteria, propensity score matching incompletely but significantly reduced baseline differences between groups. A linear mixed-effects model was employed to analyze differences in pain with non-inferiority of APT for pain reduction, tested against a 10% delta. The study also compiled statistics on implant survival and adverse events. Results After best-case propensity score matching, 229 patients were included in each group (APT and MBT). The APT group was significantly older (mean 77.0 years vs. 71.0 years, p < 0.001), had a lower BMI (mean 28.9 vs. 30.9, p < 0.001), and contained more females (65 vs 92, p<0.008) compared to the MBT group. Numerical Rating Scale (NRS) pain scores decreased over time in both groups. The 95% confidence interval in NRS pain scores was (-0.51, 0.19), indicating no statistically significant difference in scores. Flexion range of motion was similar between groups, reaching approximately 120 degrees. The extension range of motion was also comparable, near zero degrees. Three patients with APT and one patient with MBT required manipulation under anesthesia within eight weeks. One revision of the femur occurred in the APT group, while two full revisions occurred in the MBT group. Additional adverse events included synovectomy, patella fracture, and polyethylene insert exchange. Conclusion This study suggests that APT in TKA demonstrates non-inferior pain outcomes compared to MBT when performed by a fellowship-trained surgeon using the LSK system. While descriptive analysis showed some differences in other outcomes like revision and manipulation under anesthesia, further research with larger, randomized controlled trials is needed to confirm these findings and assess long-term functional outcomes and patient satisfaction.