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Objectives and questions: Cementless total knee arthroplasty (TKA) has regained interest, yet comparative outcomes versus cemented fixation and potential age-dependent effects remain debated. This study compared patient-reported outcomes (PROMs) and revision risk after cemented versus cementless primary TKA and evaluated whether age modifies the association between fixation and outcomes.

Material and methods: A retrospective cohort study of 5,512 primary TKAs from an institutional arthroplasty database was performed. Femoral fixation was classified as cemented (n=3,863) or cementless (n=1,649). PROMs were assessed using the Knee Society Clinical Rating System (KSCRS) Total Score preoperatively, at 1 year, and at latest follow-up. Multivariable linear regression (ANCOVA framework) compared KSCRS at 1 year (primary PROM endpoint) and latest follow-up, adjusting for preoperative KSCRS, age, sex, body mass index (BMI), surgery year, implant design (CR vs PS), and surgical technique (conventional, navigation, robotic). Revision risk was assessed using multivariable Cox proportional hazards regression with the same covariates. Effect modification by age was evaluated using pre-specified strata (<65, 65–74, ≥75 years) and fixation-by-age interaction terms for PROMs, and penalized logistic regression (Firth) for early revision within 1 year.

Results: Cementless patients were younger (66.5±9.1 vs 68.8±9.5 years) and more frequently male (49.6% vs 35.1%). In adjusted analyses, fixation type was not associated with KSCRS at 1 year (β=-0.26; 95% CI -3.98 to 3.46; p=0.893). At latest follow-up, cementless fixation demonstrated a modest adjusted improvement in KSCRS (β=4.52; 95% CI 0.99 to 8.05; p=0.012). In survivorship analysis (complete-case n=3,581; 158 revisions), cementless fixation was not associated with a significant difference in revision risk compared with cemented fixation (HR=1.32; 95% CI 0.84 to 2.09; p=0.229). Effect modification by age was not observed for KSCRS at 1 year (interaction p=0.325), but was present at latest follow-up (interaction p=0.046), with a greater cementless-associated KSCRS improvement in patients aged ≥75 years (β=9.14; 95% CI 1.56 to 16.73; p=0.018). Cementless fixation was not associated with early revision within 1 year in any age stratum.

Discussion and conclusions: Cementless fixation demonstrated comparable 1-year PROMs and revision risk versus cemented fixation in this large cohort. A small improvement in latest PROMs was observed with cementless fixation, with a potentially greater benefit in patients aged ≥75 years. Longer follow-up is required to confirm whether age-dependent differences persist over time.