Stable 2-year migration on radiostereometric analysis and improved gait speed and function after bicruciate-retaining TKA: a prospective cohort of 25 patients

BACKGROUND AND PURPOSE: In bicruciate-retaining total knee arthroplasty (BCR TKA) the preservation of both cruciate ligaments necessitates a different tibial tray design with reduced bone-implant interface. These ligaments also influence knee joint force dynamics and may thereby affect component migration. The primary aim of our study was to assess the fixation of BCR TKA up to 2 years postoperatively. Secondary aims included the evaluation of clinical and functional outcomes. METHODS: This prospective study (https://osf.io/zqt8d) included 25 BCR TKA patients. Migration of both components was assessed at different follow-up time points by model-based radiostereometric analysis (RSA) using bone markers. Primary outcome was total translation (TT) and total rotation (TR) at the 2-year follow-up. Secondary outcomes included at-home gait parameters (gait speed, stride length, stride time) assessed with wearable sensors, patient-reported outcome measures (PROMs), and adverse events (AEs). RESULTS: At the 2-year follow-up, least-squares mean tibial TT was 0.22 mm (95% confidence interval [CI] 0.16-0.28) (tibia) and femoral TT 0.43 mm (CI 0.30-0.57). The least-squares mean tibial TR was 0.53° (CI 0.43-0.63) and femoral TR 0.64° (CI 0.46-0.82). PROMs improved significantly after surgery, with improvements exceeding the predefined minimal clinically important difference (MCID). Gait outcomes revealed a significant gait speed improvement, which remained below MCID, and no significant difference from healthy controls 1 year postoperatively. AEs included 2 intraoperative tibial eminence fractures, 4 cases of persistent postoperative pain, and 2 cases of postoperative oedema with temporary knee stiffness. CONCLUSION: RSA analysis of this BCR TKA demonstrated a stabilizing migration pattern that remained below established TKA benchmark values (for different designs), indicating good fixation at 2-year follow-up. The findings were accompanied by an improved PROM, whereas gait speed improvement was below MCID.