Impact of Hypothyroidism on Short-Term and Long-Term Outcomes After Lumbar Fusion: A Nationwide Propensity-Matched Cohort Study

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Study Design Retrospective cohort study. Objectives Hypothyroidism is associated with increased perioperative risks across various surgical specialties and has recently been linked to hematologic and short-term complications following spinal fusion. However, its impact on long-term mechanical complications remains unclear. This study aims to evaluate short-term (45-day) and long-term (2-year) medical and mechanical complications in hypothyroid patients undergoing primary lumbar fusion. Methods A retrospective analysis was conducted using the TriNetX database to identify patients who underwent lumbar fusion between 2002 and 2022 with at least 2 years of follow-up. Patients with preoperative hypothyroidism (n = 3,348, identified via ICD-10-CM code E03.9) were propensity score–matched 1:1 to euthyroid controls based on demographic and clinical risk factors. Results After matching (n = 2850 per cohort), hypothyroid patients had higher rates of sepsis at 45 days (2.1% vs 1.3%; P = 0.019; RR: 1.62, 95% CI [1.08-2.44]). At 2 years, they had increased risks of chronic device-related infection (0.7% vs 0.3%; P = 0.019; RR: 2.27, 95% CI [1.12-4.61]), wound disruption (3.6% vs 2.7%; P = 0.031; OR: 1.35, 95% CI [1.03-1.75]), and proximal junctional kyphosis (3.2% vs 2.3%; P = 0.017; RR: 1.42, 95% CI [1.06-1.90]). No significant differences were observed in readmissions, revision surgery, or pseudoarthrosis rates. Conclusions Hypothyroidism is a risk factor for early and late postoperative complications in patients undergoing primary lumbar fusion. Appropriate preoperative optimization with thyroid hormone supplementation to achieve euthyroid status could potentially minimize the incidence of developing notable postoperative medical and mechanical complications.