Hypothyroidism increases risk of early medical and late mechanical complications after primary total knee arthroplasty: A propensity-matched cohort study.

Abstract

Level III retrospective matched cohort study. Total knee arthroplasty (TKA) is highly effective, yet identifying risk factors such as hypothyroidism is essential to optimizing outcomes. Hypothyroidism may impair healing and bone metabolism, but its impact on long-term mechanical complications remains unclear. This study evaluates the association between hypothyroidism and both 90-day medical and 2-year mechanical complications following primary TKA using a large, propensity-matched cohort. Utilizing the TriNetX database spanning 102 healthcare organizations, we conducted a retrospective cohort analysis. Patients undergoing primary TKA were stratified into those with preexisting hypothyroidism (n = 35,318) and controls (n = 35,318), matched 1:1 via propensity scores based on demographics (age, sex, race) and key comorbidities (diabetes, hypertension, obesity). Outcomes included 90-day medical (PJI/deep SSI, DVT, sepsis) and 2-year mechanical complications (revision TKA, aseptic loosening, PPF). Statistical analyses included risk ratios, risk differences, p-values, and Kaplan-Meier analysis. Baseline characteristics were well-balanced post-matching. At 90 days, the hypothyroidism cohort showed significantly higher risks of PJI/Deep SSI (1.7 % vs 1.2 %; p < 0.001), DVT (2.2 % vs 1.8 %; p < 0.001), and sepsis (0.6 % vs 0.4 %; p = 0.001). At 2 years, hypothyroidism was associated with significantly higher risks of revision TKA (2.0 % vs 1.4 %; p < 0.001), aseptic loosening (1.2 % vs 0.8 %; p < 0.001), periprosthetic fracture (0.7 % vs 0.5 %; p < 0.001), and PJI/Deep SSI (2.9 % vs 2.1 %; p < 0.001). Kaplan-Meier analysis confirmed lower implant survival for loosening and revision (p < 0.001) in the hypothyroidism group. Preexisting hypothyroidism is associated with increased early medical and longer-term mechanical complications following TKA. These findings support thyroid status as a relevant factor for preoperative risk stratification and patient counseling. Future prospective research is needed to evaluate whether biochemical optimization improves outcomes.