Risk of Early Periprosthetic Tibial Fracture After Medial Unicompartmental Knee Arthroplasty with Cemented Versus Cementless Fixation: A Nationwide Cohort Study.

BACKGROUND The usage of medial unicompartmental knee arthroplasty (mUKA) is increasing, but concerns remain regarding the risk of early periprosthetic tibial fracture (PPTF), particularly following cementless mUKA. The aims of this study were to compare the risk of PPTF between cemented and cementless mUKAs and to analyze risk factors for early PPTF. METHODS Using data from the Danish Knee Arthroplasty Register and the Danish National Patient Registry, all mUKAs from 1997 to 2022 were identified and stratified as cemented or cementless mUKAs. Subsequent fractures were identified through the reason for revision, diagnosis codes, and fracture-specific procedure codes. RESULTS This study included 9,700 cemented mUKAs (mean follow-up of 9 years) and 12,380 cementless mUKAs (mean follow-up of 3 years). The 4-month cumulative proportions of PPTF were 0.2% (95% confidence interval [CI], 0.2% to 0.4%) after cemented mUKA and 0.7% (95% CI, 0.6% to 0.9%) after cementless mUKA. Risk factors for early PPTF (≤4 months) were cementless mUKA (hazard ratio [HR], 2.9; 95% CI, 1.6 to 5.5), female sex (HR, 2.6; 95% CI, 1.6 to 4.2), an age of ≥70 years (HR, 4.0; 2.5 to 6.4), body mass index (BMI) of ≥40 kg/m2 (HR, 2.4; 95% CI, 1.0 to 5.8), and a height of <160 cm (HR, 2.2; 95% CI, 1.3 to 3.6). Female patients ≥70 years of age with a BMI of ≥40 kg/m2 and/or a height of <160 cm represented 3% of all mUKAs. In this group, patients with cementless mUKA had a 4-month cumulative proportion of PPTF of 4.5% (95% CI, 2.9% to 6.9%). CONCLUSIONS The risk of early, surgery-related PPTF was higher after cementless mUKA compared with cemented mUKA. Risk factors for early PPTF include cementless mUKA, female sex, an age of ≥70 years, a BMI of ≥40 kg/m2, and a height of <160 cm. Our data highlight the need for careful, bone-conserving tibial preparation and consideration of cemented tibial fixation for female patients ≥70 years of age with a height of <160 cm and/or a BMI of ≥40 kg/m2. LEVEL OF EVIDENCE Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.