Prior anterior cruciate ligament reconstruction: Comparable outcomes but reduced knee flexion after robotic functionally aligned total knee arthroplasty

PURPOSE: Total knee arthroplasty (TKA) after anterior cruciate ligament reconstruction (ACLR) is technically demanding and has been associated with higher complication rates. This study aimed to evaluate whether patients with prior ACLR undergoing image-based robotic-assisted TKA performed under functional alignment (FA) principles achieve comparable clinical outcomes and early implant survivorship to patients undergoing primary TKA without previous ligament surgery. METHODS: This retrospective comparative study (between March 2021 and December 2023) included consecutive patients who underwent image-based robotic-assisted TKA under FA principles with a minimum 24-month follow-up. Patients were divided into those with prior ACLR (study group) and those without previous ligament surgery (control group). Demographics, radiographic alignment, robotic implant positioning, knee society scores (KSS), forgotten joint score (FJS), active knee flexion, complications and all-cause revision rates were analysed. Kaplan-Meier survival analysis was performed. RESULTS: A total of 383 TKAs were included (45 ACLR, 338 controls). Patients with prior ACLR were younger (62 vs. 70 years, p < 0.0001) and had lower BMI (25.34 vs. 28.32 kg/m², p < 0.0001). Postoperatively, KSS-knee (95 [interquartile range, IQR] 88-100) vs. 94 [90-100], p = 0.79], KSS-function (90 [89.5-100] vs. 90 [90-100], p = 0.82) and FJS (83 [63-94] vs. 86 [67-94], p = 0.80) were comparable between groups. Active knee flexion was lower in the ACLR group (120° [112.5-130] vs. 130° [120-130], p = 0.048). Overall complication rates were 15.6% versus 9.2% (p = 0.18). All-cause revision rates were 2.2% versus 1.5% (p = 0.70). Kaplan-Meier analysis demonstrated no difference in implant survivorship (HR = 1.62, 95% CI 0.13-19.57, p = 0.70). CONCLUSION: Robotic-assisted TKA performed under FA principles provides comparable patient-reported outcomes and early implant survivorship in patients with prior ACLR and those undergoing standard primary TKA, although a modest reduction in postoperative knee flexion persists in the ACLR subgroup. LEVEL OF EVIDENCE: Level III.