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

Background ContextThe relationship between fractured posterior vertebral wall patterns and the protrusion of bony fragments into the spinal canal is not clear.PurposeWe 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/SettingThis is a prospective analysis of CTM in both supine and semi-sitting positions.Patient SampleThe sample includes 36 consecutive elderly patients with delayed neurologic disorders due to insufficient bone union at the posterior vertebral wall after vertebral fracture.Outcome MeasuresRadiological parameters, including the rates of dural compression and of occupation by bony fragments (OBFr) and the posterior vertebral body height ratio (PVBHr), were used.MethodsAll patients were examined using CTM in both 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.ResultsThe simple type was found in 19 of 36 cases, whereas the comminuted type was found in 17 of 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.ConclusionsBoth simple and comminuted fracture types could cause protrusion of vertebral fragments into the spinal canal because of a collapsing non-united posterior vertebral wall; however, the comminuted type showed more severe spinal canal encroachment, with axial loading. The morphology of the injured posterior wall is thus important for estimating instability.