ネジ型ケージと棘突起プレートによる後方進入腰椎椎体間固定術―X線学的検討

Postoperative Alignment Change and Cage Subsidence after Posterior Lumbar Interbody Fusion with Threaded Cages and a Spinous Process Plate

　Lumbar alligator plate（LA）は棘突起を挟んで固定する金属である．後方進入腰椎椎体間固定術84例を対象にLAで固定した群（n＝41）と椎弓根スクリューを使用したPS群（n＝43）に分けて術後1年の成績（骨癒合率，前弯，ケージ沈下）を比較した．両群全例で骨癒合を得，前弯維持に有意差はなかった．3mm以上ケージが沈下した症例数はLA群（26.8％）がPS群（2.3％）に比べ有意に多かったものの，沈下量に有意差はなかった．LAは椎弓根スクリューに比べ生体力学的固定力は劣るとされており今回の検討でも沈下症例は多かったが，誤刺入のリスクもなくより簡便で，骨癒合率も高く，今後の応用が期待される．

　The lumbar alligator plate (LA) is an original implant that we devised to hold spinous processes. In theory it should be safer than pedicle screws (PS), because there is no risk of displacement, although it provides less holding power weaker fixation for lumbar spinal segments. To determine whether solid fusion is achieved when the LA is used for posterior lumbar interbody fusion (PLIF), we prospectively compared two PLIF procedures：a procedure in which PS were used in combination with Brantigan I/F cages and a procedure in which the LA was used in combination with threaded cages (BAK Proximity Cages). During the 3―year study period of one surgeon performed all of the procedures in which PS were used (n＝43) and another surgeon performed all of the procedures in which the LA was used (n＝41), and the two groups were compable in regard to age at the time of surgery and the gender ratio. We evaluated the subsidence of the cage on lateral radiographs by measuring the anterior and posterior vertebral height of the implanted segment as well as the lordotic angle, before, immediately after, and one year after surgery. Bony fusion had been achieved in all patients in both groups when examined a year after surgery. There were no significant differences between the groups in the changes in lordotic angle or vertebral heights, but there was a significantly higher percentage of patients with postoperative cage subsidence gerater than 3mm in the LA group (26.8％ vs. 2.3％, p＝0.0014). However, there were no significant sequelae, associated with cage subsidence. LA combined with threaded cages proved to be useful alternative to PLIF with pedicle screws.