Objective: Adjacent vertebral fractures (AVFs) are frequent in the early postoperative period following balloon kyphoplasty (BKP) for osteoporotic vertebral fractures (OVFs); however, the mechanism remains unclear. This study aimed to elucidate the mechanism of AVF by comparing early radiographic changes in patients with and without AVF. Methods: Sixty-three patients who underwent BKP within 60 days of OVF onset and were followed for at least 3 months postoperatively were included. Patients were divided into AVF and non-AVF groups. Comparative analyses were conducted for demographics, volume of bone cement injected, and radiological assessments presurgery, postsurgery, 1 and 2 weeks postoperatively, and at final follow-up. Key radiographic parameters, including vertebral kyphotic angle (VKA) and anteroposterior vertebral height ratio (A/P ratio), were evaluated between the groups. Results: AVF occurred in 8 out of 63 patients (12.7%). Demographics and bone cement volume showed no significant differences between groups. Radiographic analysis revealed earlier VKA deterioration in the non-AVF group, with significant differences at 2 weeks postoperatively. In the AVF group, VKA and the A/P ratio showed more pronounced changes from preoperative to postoperative measurements. The change in the A/P ratio was significantly greater in the AVF group than in the non-AVF group. Conclusions Vertebral correction deteriorated earlier in the non-AVF group, while BKP resulted in a more substantial correction of vertebral bodies in the AVF group. These findings suggest that the mechanical stability achieved by BKP may contribute to the differential progression of AVF, highlighting the need for tailored postoperative management.