Long-term changes in bone mineral density following adolescent idiopathic scoliosis surgery: a minimum 34-year follow-up

Purpose To investigate longitudinal changes in bone mineral density (BMD) in middle-aged female patients who underwent spinal fusion for adolescent idiopathic scoliosis (AIS). Methods The study subjects were 229 female patients who were diagnosed with AIS and underwent spinal fusion between 1968 and 1988. A two-step survey study was conducted on 19 female AIS patients. BMD, Z-scores, T-scores, and the prevalence of osteoporosis and osteopenia were compared between the initial (2014–2016) and second (2022) surveys. Correlations between the annual changes in Z-scores and T-scores with radiographic parameters, body mass index (BMI), and the number of remaining mobile discs were analyzed. Results BMD decreased significantly from the initial (0.802 ± 0.120 g/cm 2 ) to the second survey (0.631 ± 0.101 g/cm 2 ; p < 0.001). Z-scores decreased from 0.12 ± 1.09 to − 0.14 ± 1.04, while T-scores decreased significantly from − 0.70 ± 1.07 to − 1.77 ± 1.11 ( p < 0.001). The prevalence of osteopenia and osteoporosis increased significantly from 36.8% to 89.5% ( p = 0.002), but the increase in osteoporosis alone was not statistically significant (5.3% to 26.3%; p = 0.180). Moderate negative correlations were found between annual changes in Z-scores and both main thoracic (MT) curve (r = − 0.539; p = 0.017) and lumbar curve (r = − 0.410; p = 0.081). The annual change in T-scores showed a moderate negative correlation with the MT curve (r = − 0.411; p = 0.081). Conclusion Significant reductions in BMD and an increased prevalence of osteopenia and osteoporosis were observed in middle-aged female AIS patients who had undergone spinal fusion. The decline in Z-scores in patients with AIS suggested that there was an accelerated loss of BMD compared with the general population. Larger residual curves could pose an added osteoporosis risk. Further research is needed to understand if the onset of osteoporosis in AIS patients is attributable to the condition itself or the surgical intervention.