Abstract: BACKGROUND: Osteonecrosis of the femoral head is a common complication in patients with systemic lupus erythematosus. The prediction and validation of the risk in advance will help to avoid or delay the progression of osteonecrosis of the femoral head.
OBJECTIVE: To analyze risk factors for the occurrence of osteonecrosis of the femoral head in systemic lupus erythematosus patients and to construct and validate a nomogram prediction model of systemic lupus erythematosus patients with osteonecrosis of the femoral head. 
METHODS: A retrospective study was conducted to analyze the medical records of 914 systemic lupus erythematosus patients who first visited First Affiliated Hospital of Henan University of Chinese Medicine between January 2013 and December 2022. All patients were divided into osteonecrosis of the femoral head (n=100) and non-osteonecrosis of the femoral head (n=814) groups according to whether they had suffered from osteonecrosis of the femoral head or not. Univariate, LASSO regression, and multifactorial logistic regression analyses were used to screen and identify the risk factors for systemic lupus erythematosus complicating osteonecrosis of the femoral head. The dataset was also randomly divided into training and test sets in a ratio of 7:3. A nomogram prediction model of the risk of systemic lupus erythematosus complicating osteonecrosis of the femoral head was constructed based on the results of the multifactorial logistic regression analysis. The performance of the nomogram was evaluated using the receiver operating characteristic curve, Hosmer-Lemeshow calibration curve, and decision curve analysis.
RESULTS AND CONCLUSION: (1) There were significant differences in disease duration of systemic lupus erythematosus, systemic lupus erythematosus disease activity, lupus nephritis, respiratory involvement, gastrointestinal involvement, Sjögren's syndrome, osteoporosis, anti-ribonucleoprotein, complement C3 decrease, cyclophosphamide, mycophenolate mofetil, biologics, maximum daily dose of glucocorticosteroids, and pulses of intravenous methylprednisolone between the osteonecrosis of the femoral head and non-osteonecrosis of the femoral head groups (P < 0.05). (2) Ten predictor variables related to the risk of osteonecrosis of the femoral head in patients with systemic lupus erythematosus were screened using LASSO regression analysis. Multivariate logistic regression analysis further confirmed disease duration of systemic lupus erythematosus, respiratory involvement, Sjögren's syndrome, osteoporosis, anti-ribonucleoprotein, cyclophosphamide, mycophenolate mofetil, biologics, and maximum daily dose of glucocorticosteroids were independent risk factors for osteonecrosis of the femoral head in systemic lupus erythematosus patients (P < 0.05). (3) The area under the receiver operating characteristic curve for predicting the risk of occurrence of osteonecrosis of the femoral head in systemic lupus erythematosus patients was 0.802 (95%CI=0.742-0.862) in the training set and 0.811 (95%CI=0.745-0.876) in the testing set. The Hosmer-Lemeshow calibration curve fit was well (P=0.447 in raining set; P=0.870 in testing set). Decision curve analysis showed that it was beneficial in predicting the risk of osteonecrosis of the femoral head in systemic lupus erythematosus patients using the nomogram prediction model. (4) Menstrual abnormalities were one of the risk factors for osteonecrosis of the femoral head in female systemic lupus erythematosus patients. (5) The results suggest that the risk factors for systemic lupus erythematosus complicating osteonecrosis of the femoral head are multi-factorial, and a nomogram prediction model containing nine risk factors was also developed, which could be used to predict the risk of osteonecrosis of the femoral head in systemic lupus erythematosus patients. In addition, we reported for the first time that menstrual abnormalities were one of the risk factors for systemic lupus erythematosus complicating osteonecrosis of the femoral head in female.

Key words: systemic lupus erythematosus, osteonecrosis of the femoral head, risk factor, nomogram, prediction model, menstrual abnormality, LASSO regression, multivariate logistic regression