胸椎後縦靱帯骨化症に対する後方除圧の適応と限界―MRI矢状断像による除圧範囲の骨化巣後弯角の有用性

Effectiveness of Posterior Decompression for Patients with Ossification of the Posterior Longitudinal Ligament in the Thoracic Spine. : Usefulness of the Ossification-Kyphosis Angle on MRI

　後方除圧を施行した胸椎後縦靱帯骨化症23例の術中超音波診断所見（echo free spaceの有無）から後方除圧の適応と限界について検討した．MRI矢状断像の除圧範囲の脊椎後弯角，除圧範囲の骨化巣後弯角，後方最大突出部骨化形態，CTによる後方最大突出部骨化の脊柱管内占拠率のうち，除圧範囲の骨化巣後弯角と後方最大突出部骨化の脊柱管内占拠率がecho free spaceの有無（除圧の成否）を反映していた．特に前者は後方除圧の適応と限界の目安として有用で，23°前後に後方除圧適否の臨界点があると考えられた．

　The indications or limits of posterior decompression for patients with ossification of the posterior longitudinal ligament in the thoracic spine were reviewed from the perspective of intraoperative ultrasonography findings and various preoperative imaging parameters in 23 patients. No significant differences in the kyphosis angle of the decompression site and the configuration of the maximal prominent OPLL were seen between the group with an echo-free space and the group without an echo-free space (p＝0.95, p＝0.43). The ossification-kyphosis angle of the decompression site was more than 23 degrees in all patients with no echo-free space. The occupation rate of the greatest prominence of the OPLL was significantly different between the groups (p＝0.033). The ossification-kyphosis angle on the sagittal view of MRI findings may be useful as an indicator of the effectiveness of posterior decompression in this disease. Angles close to 23 degrees may indicate a critical point of posterior decompression.