In-hospital outcomes of fibromyalgia patients undergoing primary total hip arthroplasty: a seven-year United States National Inpatient Sample propensity-matched analysis

Fibromyalgia (FM) is a chronic nociplastic pain syndrome characterized by widespread pain, fatigue, and sensory amplification. While FM is linked to increased perioperative resource use and poorer patient-reported outcomes, its influence on in-hospital complications after total hip arthroplasty (THA) remains unclear. We analyzed the National Inpatient Sample (2016-2022) for adults undergoing elective primary THA for osteoarthritis. FM was defined as ICD-10-CM code M79.7. Exclusions included fracture, revision arthroplasty, infection, malignancy, inflammatory arthritis, COVID-19, and non-elective admissions. A 1:1 nearest-neighbor propensity score match without replacement (caliper 0.2 SD of logit) balanced demographics, comorbidities, and hospital characteristics. Primary outcomes were length of stay (LOS), total hospital charges, and routine discharge. Secondary outcomes included acute kidney injury (AKI), venous thromboembolism (VTE), pneumonia, postoperative pain, blood-loss anemia, transfusion, intraoperative fracture, and dislocation. From 1,957,284 THA patients, 40,825 (2.1%) had FM. Post-match (n = 81,650), groups were well balanced (all standardized differences < 0.10). FM patients had shorter LOS (2.2 vs. 2.6 days, P < 0.01), higher charges (USD 65,893 vs. 61,510, P < 0.01), but similar routine discharge rates. No significant differences in AKI, VTE, pneumonia, or postoperative pain were observed. FM was associated with lower blood-loss anemia (21.7% vs. 27.0%, P < 0.01), lower transfusion (3.8% vs. 4.9%, P < 0.01), lower intraoperative fracture (1.2% vs. 1.6%, P = 0.03), but higher dislocation (0.3% vs. 0.0%, P < 0.01). FM was not associated with increased in-hospital complications post-THA. Despite shorter LOS and lower anemia/transfusion rates, FM patients incurred higher charges and a small increase in dislocation risk. FM should not preclude THA, although implant stability and cost-management strategies are advised.