Morphology of the injured posterior wall causing spinal canal encroachment in osteoporotic vertebral fractures

Abstract Background Context The relationship between fractured posterior vertebral wall patterns and the protrusion of bony fragments into the spinal canal is not clear. Purpose We sought to elucidate the effects of fracture patterns of the injured posterior wall on posterior wall instability and spinal canal encroachment using computed tomography myelography (CTM) in two different positions. Study Design/Setting Prospective analysis of CTM in both supine and semisitting positions. Patient Sample Thirty-six consecutive elderly patients with delayed neurological disorders due to insufficient bone union at the posterior vertebral wall after vertebral fracture. Outcome Measures Radiological parameters, including rates of dural compression and of occupation by bony fragments (OBFr) and the posterior vertebral body height ratio (PVBHr), were used. Methods All patients were examined using CTM in both the supine and semi-sitting positions. According to fracture patterns of the posterior vertebral wall, we classified injured posterior walls with one fragment as the simple type and those with two or more fragments as the comminuted type. Results The simple type was found in 19/36 cases, whereas the comminuted type was found in 17/36 cases. A significant correlation was identified between changes in OBFr and PVBHr in both the simple and comminuted types. The mean change of PVBHr between the two positions in the comminuted type was significantly larger (9.2%) than that in the simple type (4.8%). Likewise, the mean change in OBFr in the comminuted type (14.0%) was significantly larger than that in the simple type (8.2%), indicating that the injured posterior vertebral wall with the comminuted type would be more likely to collapse and protrude into the spinal canal. Conclusions Both simple and comminuted fracture types could cause protrusion of vertebral fragments into the spinal canal due to a collapsing nonunited posterior vertebral wall; however, the comminuted type showed more severe spinal canal encroachment, with axial loading. Morphology of the injured posterior wall is thus important for estimating instability.