BACKGROUND: Porous tantalum rod implantation combined with core decompression in the treatment of early non-traumatic necrosis of the femoral head has a good effect, but there are still reports of femoral head collapse after treatment with an incidence of 2%-56%. OBJECTIVE: To explore the collapse status and influencing factors of porous tantalum rod after treatment of association research circulation osseous (ARCO) stage I-II non-traumatic osteonecrosis of the femoral head. METHODS: The medical record data of 77 patients with non-traumatic necrosis of the femoral head in ARCO stage I-II, who were enrolled in First Hospital of Shijiazhuang City from May 2014 to April 2018 and treated with porous tantalum rod, were retrospectively analyzed. There were 58 males and 19 females, aged 22-58 years. The collapse of femoral head was observed during follow-up after operation. The clinical and surgical data of the patients were recorded, such as sex, age, etiology, side, location and scale of necrosis area, ARCO stage, implantation position of tantalum rod (the distance between the top of tantalum rod and the center of necrosis, the distance ratio between tantalum rod and the cortex on both sides of the border area of femoral head and neck). The clinical and surgical data were analyzed by univariate analysis. Binary multivariate logistic regression analysis was used to screen out the independent influencing factors of the collapse after the treatment of ARCO stage I-II non-traumatic necrosis of the femoral head with porous tantalum rod. This study was approved by the Ethics Committee of First Hospital of Shijiazhuang City (approval No. 201403011). RESULTS AND CONCLUSION: (1) Seventy-seven patients were followed up for 3-60 months, including 23 cases of femoral head collapse and 54 cases of no collapse. (2) The results of univariate analysis showed that there was no significant difference in sex, age, lesion side, ARCO stage, and the distance ratio between tantalum rod and the cortex on both sides of the border area of femoral head and neck between collapse group and non-collapse group (P > 0.05). There were significant differences in etiology, location and scale of necrosis area, and the distance between the top of tantalum rod and the center of necrosis between the two groups (P < 0.05). (3) The results of binary multivariate logistic regression analysis showed that steroid induced necrosis of femoral head, necrosis area located in the load-bearing area, C1 type of necrosis area location and the distance between the top of tantalum rod and necrotic center were the independent factors of collapse after treatment of ARCO I-II non-traumatic necrosis of femoral head with porous tantalum rod [OR=7.977, 95%CI(1.031, 61.708), P=0.047; OR=7.248, 95%CI(1.563, 34.548), P=0.012; OR=16.028, 95%CI(1.074, 239.267), P=0.044; OR=2.310, 95%CI(1.388, 3.845), P=0.001]. (4) Reuslts suggest that the short-term clinical effect of porous tantalum rod was good in the treatment of non-taumatic necrosis of femoral head in ARCO I-II stage. Steroid induced necrosis of femoral head, necrosis area, location of necrosis and the distance from the top of tantalum rod to the necrosis center were the influencing factors of collapse after the treatment of non-traumatic necrosis of femoral head in ARCO I-II stage. [ABSTRACT FROM AUTHOR]