Regional Differences in Autofusion and Segmental Deformity in the Natural History of Pyogenic Vertebral Osteomyelitis: Our Institution’s 18-year Experience

Introduction: Pyogenic vertebral osteomyelitis (PVO) is a devastating complication with poor outcomes associated with hematogenous spread or direct inoculation of the spine with microorganisms. It is known, given that antibiotic treatment rates are high, that autofusion and segmental deformities may occur such as kyphosis as part of the natural history of disease but whether there is a structural underpinning by region is poorly understood.Our aim in this study was to evaluate the rates of autofusion and segmental deformity, including kyphosis, over the course of the natural history of PVO.

Methods: An institutional consecutive series of adult patients with PVO and radiographic follow-up of at least three months yielded 307 patients, of which 202 were non-surgical. Non-surgical patients’ MRI radiographs were evaluated for autofusion and deformity of the segment over time. We defined the rigid group as T3-T10, and the non-rigid group as any subaxial segment. Exclusion criteria included radiographic follow-up of less than three months.

Results: Demographics and comorbidities were similar between groups (p > 0.05). Cervical (72.0%) and thoracic (78.8%) rates of autofusion were significantly greater than lumbar (42.4%) rates of autofusion (p < 0.0001). On follow-up, although patients with cervical (12.8°) and thoracic (16.0°) PVO were more kyphosed than lumbar (-5.9°) PVO, the change in kyphosis on follow-up was similar between groups (p = 0.6768). When using the SINS criteria, rates of autofusion were greater in the rigid (84.3%) than the non-rigid (50.0%) group (p = 0.0004).

Conclusion : When considering whether to surgically treat, let alone fuse, patients with PVO, the threshold for intervention may not be as low as first thought, notwithstanding severe neurologic complication. Rates of autofusion are relatively high in the cervicothoracic spine without surgery, although there are similar changes in degrees of kyphotic change on follow-up throughout the spine.