Abstract: Objective To explore the risk factors for the formation of lower extremity deep vein thrombosis (DVT) after surgery for proximal humeral fractures of Neer type Ⅲ and Ⅳ in the elderly,and to analyze the correlation between BMI stratification and anticoagulation strategies.Methods The clinical data of 200 elderly patients after surgery for proximal humeral fractures of Neer type Ⅲ and Ⅳ admitted from June 2022 to June 2024 were retrospectively analyzed.According to BMI,the patients were divided into a low BMI group (BMI < 18.5kg/m²),a normal BMI group (18.5kg/m² ≤ BMI < 24.0kg/m²),an overweight BMI group (24.0kg/m² ≤ BMI < 28.0kg/m²),and an obese BMI group (BMI ≥ 28.0kg/m²).The general data,comorbidity status,surgery-related indicators,anticoagulation strategies,and DVT occurrence were compared among patients in different BMI groups.Multivariate Logistic regression analysis was used to screen for risk factors for DVT formation and analyze the correlation between BMI stratification and anticoagulation strategies.Results Among the 200 patients,32 cases of DVT occurred,with a total incidence of 16.0%.There were differences in age,comorbidities (hypertension,diabetes,cardiovascular diseases),operation time,and hospital stay among patients in different BMI groups (P<0.05).Multivariate Logistic regression analysis showed that obese BMI (OR=3.25,95%CI:1.56~6.77),hypertension (OR=2.18,95%CI:1.12~4.24),operation time ≥ 2 hours (OR=2.36,95%CI:1.21~4.60),and non-standard anticoagulation (OR=3.87,95%CI:1.95~7.69) were independent risk factors for the formation of DVT after surgery for proximal humeral fractures of Neer type Ⅲ and Ⅳ in the elderly（P＜0.05）.In terms of anticoagulation strategies,the proportion of standardized anticoagulation in the obese BMI group was the lowest,and the difference was statistically significant compared with other groups (P<0.05).Conclusion The formation of DVT after surgery for proximal humeral fractures of Neer type Ⅲ and Ⅳ in the elderly is affected by multiple factors,and obese BMI is one of the important risk factors.There is a correlation between BMI stratification and anticoagulation strategies.The proportion of standardized anticoagulation in obeseBMI patients is low.Clinically,individualized anticoagulation strategies should be developed according to the patient's BMI stratification to reduce the risk of DVT.

Key words: elderly, proximal humeral fractures of Neer type Ⅲ, proximal humeral fractures of Neer type Ⅳ, lower extremity deep vein thrombosis, BMI stratification, anticoagulation strategy