Preoperative Thrombocytopenia and Risk of Periprosthetic Joint Infection After Total Knee Arthroplasty: A Propensity-Matched Cohort Study.

Abstract

Periprosthetic joint infection (PJI) remains one of the most devastating complications following total joint arthroplasty (TJA). While platelets are recognized for their role in hemostasis, growing evidence suggests they also serve as immune effectors. Experimental data support a link between platelet depletion and infection risk, yet clinical evidence is limited. We performed a retrospective cohort study using a large national database to identify patients undergoing primary total knee arthroplasty (TKA) between 2015 and 2023. Patients were stratified by preoperative platelet count: ≤ 50,000/μL, 50,000 to 99,000/μL, 100,000 to 149,000/μL, and ≥ 150,000/μL. The primary endpoint was PJI within one year, and the secondary endpoint was superficial surgical site infection (SSI). Multivariable logistic regressions and propensity score matching were used to adjust for demographics and comorbidities. Of 182,043 patients included in the study, 8,380 (4.6%) had platelet counts < 150,000/μL. In adjusted models, risk of PJI increased stepwise with lower platelet counts: odds ratio (OR) 1.42 (95% confidence interval (CI): 1.15 to 1.73) for 100,000 to 149,000/μL, OR 3.67 (95% CI: 2.57 to 5.10) for 50,000 to 99,000/μL, and OR 5.12 (95% CI: 1.73 to 12.19) for ≤ 50,000/μL compared with ≥150,000/μL (P-value trend < 0.001). Platelet count was not significantly associated with SSI at any threshold in all models. Preoperative thrombocytopenia is strongly and progressively associated with increased risk of PJI, but not SSI, after TKA. These results highlight the role of platelets as immune effectors in the periprosthetic space and suggest platelet count and function as underrecognized, potentially modifiable risk factors for arthroplasty infection. Prospective studies are needed to determine whether optimization of platelet levels can reduce PJI risk.