A Matched Comparison of Implant and Functional Outcomes of Cemented and Cementless Unicompartmental Knee Replacements

Background: Unicompartmental knee replacement (UKR) is an effective treatment for end-stage medial compartment osteoarthritis, but there can be problems with fixation. The cementless UKR was introduced to address this issue. It is unknown how its functional outcomes compare with those of the cemented version on a national scale. We performed a matched comparison of the clinical and functional outcomes of cementless and cemented UKRs. Methods: Using the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR), 14,764 Oxford UKRs with linked data regarding patient-reported outcomes were identified. A total of 6,906 UKRs (3,453 cemented and 3,453 cementless) were propensity score matched on the basis of patient, surgical, and implant factors. Results: The 10-year cumulative implant survival rate was 93.0% (95% confidence interval [CI], 90.0% to 95.1%) for cementless UKRs and 91.3% (95% CI, 89.0% to 93.0%) for cemented UKRs. The cementless UKR group had a significantly lower revision risk (hazard ratio [HR], 0.74; p = 0.02). Subgroup analyses showed a stronger effect size (HR, 0.66) among UKRs performed by high-caseload surgeons (i.e., surgeons performing ≥30 UKRs/year). In the overall cohort, the postoperative Oxford Knee Score (OKS) in the cementless group (mean and standard deviation, 39.1 ± 8.7) was significantly higher (p = 0.001) than that in the cemented group (38.5 ± 8.6). The cementless group gained a mean of 17.6 ± 9.3 points in the OKS postoperatively and the cemented group gained 16.5 ± 9.6 points, with a difference of 1.1 points between the groups (p < 0.001). The difference in OKS points gained postoperatively was highest among UKRs performed by high-caseload surgeons, with the cementless group gaining 1.8 points more (p < 0.001) than the cemented group. Conclusions: The cementless UKR demonstrated better 10-year implant survival and postoperative functional outcomes than the cemented UKR. The difference was largest among UKRs performed by high-caseload surgeons, with the cementless fixation group having an HR for revision of 0.66 and an approximately 2-point greater improvement in the OKS compared with the cemented fixation group. Level of Evidence: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.