• Tetsuo Hayashi, Takeshi Maeda, Takayoshi Ueta, Keiichiro Shiba, and Yukihide Iwamoto.
• Department of Orthopedic Surgery, Japan Labour Health and Welfare Organization, Spinal Injuries Center, Fukuoka, Japan. tetsuo884hayashi@yahoo.co.jp
• Spine. 2012 Sep 1;37(19):E1203-8.

Study DesignA prospective radiographical trial.ObjectiveTo elucidate effects of loading associated with spinal canal encroachment (SCE) in patients with insufficient bone union after vertebral fractures in the elderly, using computed tomography-myelography in 2 different positions.Summary Of Background DataIn elderly patients with vertebral fractures, influence of loading would be involved in SCE, but the details are not well understood.MethodsSeventeen patients (mean age, 77.4 ± 8 yr; range, 62-91 yr) with various degrees of neurological deficit due to insufficient bone union at both vertebral body and posterior vertebral wall were included in this study. Computed tomography-myelography was performed in both semisitting and supine positions. Kyphotic angle, rate of dural compression, ratio of occupation by bony fragments, and posterior vertebral body height ratio were measured and compared between positions.ResultsMean ratio of occupation by bony fragments was significantly higher in the semisitting position (47.9 ± 9.2%) than in the supine position (33.9 ± 10.0%, P, 0.001). Similarly, mean posterior vertebral body height ratio was significantly lower in the semisitting position (67.8 ± 10.8%) than in the supine position (76.3 ± 13.3%), indicating a significant loss of vertebral height in the semisitting position (P, 0.001). Mean rate of dural compression was likewise significantly higher in the semisitting position (48.6 ± 13.3%) than in the supine position (33.3 ± 16.5%; P, 0.001). Mean change in ratio of occupation by bony fragments, change in posterior vertebral body height ratio, and angular instability between positions were 13.9 ± 8.6%, 8.5 ± 6.7%, and 13° ± 5.7°, respectively. A significant correlation was identified between change in ratio of occupation by bony fragments and change in posterior vertebral body height ratio (P = 0.001).ConclusionOur study demonstrated that collapse of the nonunited posterior vertebral wall and intracanal protrusion of vertebral fragments would occur simultaneously with axial loading, causing SCE. Computed tomographic scan obtained in semisitting position seems quite useful to evaluate the amount of SCE by an unstable posterior wall.

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