Background <p>The aim of this study was to evaluate clinical and treatment-related factors associated with advanced-stage femoral head avascular necrosis (AVN) (Ficat stage III–IV) in patients who developed osteonecrosis following COVID-19 infection, based on long-term follow-up data.</p> Methods <p>This single-center retrospective cohort study included patients diagnosed with femoral head AVN after confirmed COVID-19 infection who had at least five years of clinical and radiological follow-up. Demographic characteristics, comorbidities, clinical severity of COVID-19, duration of hospitalization, intensive care unit (ICU) requirement, type and duration of systemic corticosteroid therapy, and duration of antiviral treatment were recorded. AVN was staged according to the Ficat and Arlet classification. Patients were divided into early-stage (stage I–II) and advanced-stage (stage III–IV) groups. Independent predictors of advanced-stage AVN were evaluated using logistic regression analysis. Receiver operating characteristic (ROC) analysis was performed to determine the discriminatory ability of antiviral treatment duration for advanced-stage disease. Time to osteonecrosis was defined as the interval between confirmed RT-PCR diagnosis of COVID-19 and first MRI confirmation of femoral head AVN.</p> Results <p>A total of 40 patients were included. Advanced-stage AVN was significantly associated with longer hospitalization duration, prolonged corticosteroid use, extended antiviral treatment, and the presence of hypertension. Multivariable logistic regression analysis identified hypertension, hospitalization duration, steroid treatment duration, and antiviral treatment duration as independent risk factors for advanced-stage AVN. ROC analysis demonstrated that an antiviral treatment duration ≥ 9.5 days showed excellent discriminatory performance for advanced-stage AVN (AUC = 0.950). These results reflect associations within a selected cohort of patients with post-COVID AVN and do not imply a direct causal relationship. However, this finding should be interpreted with caution due to the limited sample size and should be considered exploratory rather than definitive.</p> Conclusions <p>In patients who develop femoral head AVN following COVID-19 infection, disease progression appears closely related to the clinical severity of COVID-19 and overall treatment burden. Patients with severe COVID-19 requiring prolonged hospitalization and extended treatment exposure should be carefully monitored for progression to advanced-stage AVN. The identified cut-off value should be considered hypothesis-generating rather than definitive.</p>