Cohort study (level 3).
To identify independent risk factors for residual low back pain (LBP) following osteoporotic vertebral fracture (OVF).
Non-union has been proposed as the primary cause of residual LBP following OVF. However, LBP can occur even when union is maintained. Other reported causes of LBP after OVF include vertebral deformities and spino-pelvic malalignment.
Sixty-seven patients with single-level thoracolumbar OVF who had not received previous osteoporotic treatment were enrolled. Conservative treatment was conducted using a soft lumbosacral orthosis plus osteoporosis drugs, either weekly alendronate (bisphosphonate) or daily teriparatide. Pain scores, kyphosis angle of fractured vertebra (VKA), and spino-pelvic alignment, including pelvic incidence minus lumbar lordosis (PI-LL), were assessed periodically during treatment. Radiographic union was evaluated independently by three specialists at 24 weeks post-admission. Patients were divided by pain scores >40% at 24 weeks into the LBP (n = 36) and non-LBP (n = 31) groups. Temporal changes and statistical associations were examined to identify risk factors for LBP at 24 weeks.
At 24 weeks, 25% of OVFs failed to achieve union. The LBP group consisted of 71% of non-union and 48% of union cases. Stepwise multinomial regression analysis showed VKA at 24 weeks over 25° was significant risk factor for the LBP group (odds ratio: 6.24, 95% confidence interval: 1.77 – 22.02, p = 0.004). Significant differences in VKA emerged during treatment in the LBP group, but PI-LL showed the tendency not to change throughout the treatment period. Non-union was correlated with VKA (area under the curve: 0.864).
Although spino-pelvic malalignment is considered as a pre-existing factor for LBP, VKA exacerbated by non-union predominantly led to LBP after a new OVF. Each incidence of OVF should be treated to limit further morphological changes to the fractured vertebra.