Graf制動術の生体力学的研究―除圧モデルにおける制動効果

A Biomechanical Study on the Stabilizing Effect of Graf Ligamentoplasty in a Graded Destabilization Model of Porcine Lumbar Spine

　抄録：除圧術による不安定化モデルを作成し，除圧術後のGraf手術の制動効果について検討した．成豚より摘出した腰椎機能的脊柱単位（FSU）を計11個使用し，①intact（Int）群，②両側内側椎間関節切除術（MF）群，③左椎間関節全切除（TF）群，の3つの除圧段階に，それぞれ①インプラントなし，②Graf制動術（Graf），③pedicle screw固定術（PS）を連続的に行い，屈伸，側屈，回旋の6方向運動を負荷して，剛性およびneutral zone（NZ）を計測した．Graf制動術によって，剛性は顕著に向上し，MFであればintactのFSUに比べて2倍以上に達した．しかし，TFになると剛性は低下し，回旋ではintactのFSU以下にまで低下した．一方，NZは各除圧段階とも顕著に減少し，MFであれば，回旋以外の加重モードではPS固定術と同程度のNZを示した．しかし，TFになった場合，回旋モードではintactのFSUよりもNZは大きくなった．Graf制動術は内側椎間関節切除後には良好な制動力を発揮するが，一側でも椎間関節全切除となった場合は適応外である．

　A biomechanical study was carried out to clarify the stabilizing effects of Graf ligamentoplasty in a graded destabilization model of porcine lumbar spine. Eleven functional spinal units (FSUs) taken from fresh porcine spines were used. Three stages of graded decompression were modeled as follows：stage Ⅰ, intact：stage Ⅱ, bilateral medial facetectomy (MF)：and stage Ⅲ, Ⅱplus left total facetectomy (TF). No instrumentation, Graf ligamentoplasty, and pedicle screw fixation were sequentially performed in each stage. Flexion, extension, bending, and torsion to the FSUs were performed in all stages and stiffness and neutral zone (NZ) were measured. In a stage of MF, Graf ligamentoplasty significantly increased stiffness more than twice compared to intact FSUs in all loading modes. In a stage of TF, however, stiffness after Graf ligamentoplasty decreased especially in torsion. Although NZ after Graf ligamentoplasty significantly decreased even in a stage of MF, NZ increased in torsion to the same level of intact FSU in a stage of TF. These results suggest that Graf ligamentoplasty effectively stabilizes the destabilized segment by medical facetectomy, but if the ipsilateral facet has been damaged, a stabilization effect can not be expected.