BACKGROUND: Hip preservation surgery with vascularized iliac bone flap transplantation is currently an important method for treating patients with early-stage femoral head necrosis and collapse. However, if hip preservation fails, total hip arthroplasty (THA) is the only treatment option. This study aimed to compare the clinical efficacy and complications of direct anterior (DAA) and posterior (PA) approaches for subsequent THA in patients with failed hip preservation. METHODS: The data of patients who initially underwent vascularized iliac crest bone grafting for hip preservation, and subsequently progressed to end-stage hip osteonecrosis which required THA from January 2013 to March 2020 were retrospectively analysed. These patients were divided into two groups (group DAA; group PA). Baseline information of the included patients was collected. Surgical time, blood loss, and perioperative complications were compared between the two groups. Visual analog scale (VAS) results were recorded for all patients at 1, 3,and 6 months postoperatively to assess the severity of pain. Harris hip scores (HHS) were evaluated at 3, 6, and 12 months postoperatively to assess hip joint function recovery. Radiographic measurements were used to evaluate prosthesis placement. RESULTS: The study included 62 patients (62 hips), with 28 patients (28 hips) in the DAA group and 34 patients (34 hips) in the PA group. The two groups were well-balanced in terms of basic characteristics (p > 0.05). Perioperative outcomes comparison revealed that in subsequent THA surgeries, PA was associated with significantly longer surgical time and greater intraoperative blood loss than DAA (p < 0.05). Patients who received THA in the direct anterior approach experienced less pain The direct anterior approach demonstrated superior pain relief within the first month and third month postoperatively compared to the posterior approach (p < 0.05). Furthermore, at the 3-month follow-up, patients receiving DAA had significantly higher HHS scores than those undergoing PA, suggesting enhanced joint function recovery benefits from DAA (79.54 ± 7.91 vs. 76.62 ± 7.76, p = 0.000). CONCLUSION: In cases where vascularized iliac crest bone grafting for hip preservation fails, subsequent THA performed via DAA appears to result in shorter surgical time and less intraoperative blood loss compared to PA. However, compared with PA, DAA seems to have a higher risk of complications, so surgeons need to be extra cautious during surgery.