Posterior fixation combined with vertebroplasty for osteoporotic vertebral fractures has shown favorable clinical outcomes. However, limited evidence exists regarding postoperative bone union. This study investigated the bone union rate at one year after surgery and analyzed factors associated with union in patients with osteoporotic thoracolumbar vertebral fractures.

This case control study included 67 patients who underwent posterior fixation combined with vertebroplasty and were followed for at least one year. The mean age was 79.1 years. 41 patients were female and 26 were male. Bone union at one year was defined as bridging formation between adjacent vertebrae on both cranial and caudal sides of the fractured vertebra on plain radiographs, or a change of less than 1 degree in the vertebral wedge angle on dynamic radiographs. Evaluated variables included time from injury to surgery, preoperative Hounsfield unit value, preoperative and postoperative osteoporosis medication, preoperative vertebral instability angle defined as the difference in wedge angle between standing and supine positions, changes in vertebral wedge angle, and activities of daily living.

Bone union was achieved in 48 patients (72 percent). No significant differences were observed in age, sex, or body mass index. The mean interval from injury to surgery was significantly shorter in the union group than in the nonunion group (1.9 months versus

3.9 months, p < 0.01). The preoperative vertebral instability angle was significantly smaller in the union group (9.6 degrees versus 15.3 degrees, p < 0.01). Other variables showed no significant differences. Receiver operating characteristic analysis identified cutoff values of 3 months for time to surgery and

12 degrees for instability angle. Approximately 70 percent of patients achieved bone union at one year. Early surgery within 3 months and lower preoperative instability angle of 12 degrees or less were associated with successful union.