Medial mobile‐bearing unicompartmental knee arthroplasty following anterior cruciate ligament reconstruction is associated with an increased revision risk compared to controls

PURPOSE: Patients with prior anterior cruciate ligament reconstruction (ACLR) are at increased risk of early medial osteoarthritis. Medial mobile-bearing (MB) unicompartmental knee arthroplasty (UKA) offers a minimal-invasive and joint-preserving alternative to total knee arthroplasty (TKA), yet evidence in ACLR patients remains limited. This study compared survivorship, reoperation causes and functional outcomes of medial MB UKA in ACLR patients versus matched controls. METHODS: ; follow-up 5 ± 2 years) and 208 matched controls (n = 4 with only one match) with a minimum follow-up of 2 years. Kaplan-Meier analysis estimated 9-year survival for reoperation, implant revision (femur and/or tibia) and conversion to TKA. Reoperation causes and PROMs (Oxford Knee Score [OKS] and UCLA Activity Score) were compared. RESULTS: Cumulative 9-year reoperation-free survival was significantly lower (p = 0.026) in the ACLR group (81.2%; 95% confidence interval [CI]: 71.8-90.6) compared with matched controls (92.1%; 95% CI: 88.2-96.0). Cumulative 9-year implant revision-free survival was also significantly lower (p = 0.004) in the ACLR group (89.8%; 95% CI: 81.8-97.8) compared with matched controls (98.4%; 95% CI: 96.6-100.0). For conversion to TKA, survival rates were 92.7% (95% CI: 85.3-100.0) and 98.2% (95% CI: 96.2-100.0), respectively (p = 0.071). The risk for bearing dislocation was eightfold higher in the ACLR group compared with controls (3.8% vs. 0.5%; p = 0.046). The mean postoperative OKS in the ACLR group was 42.5 ± 6.2 and 42.3 ± 6.1 in controls; the UCLA Activity Score was 6.3 ± 1.2 and 6.1 ± 1.2, respectively. CONCLUSION: Despite excellent functional outcomes, ACLR patients undergoing MB UKA face a significantly higher risk for reoperation and inferior implant survival compared with matched controls. The increased risk for additional surgery in patients with prior ACLR, particularly for bearing dislocation, should be acknowledged when indicating medial UKA, and the usage of fixed-bearing implants reduces this risk. LEVEL OF EVIDENCE: Level III.