PLF単独およびPLIF併用の脊柱再建術が隣接椎間に与える生体力学的影響

Biomechanical Effects of PLF Alone and PLIF/PLF on the Adjacent Segment

　抄録：腰椎後側方固定（PLF）と後方進入椎体間固定（PLIF）併用による固定脊柱の剛性は極めて高く，脊椎配列の保持に優れるといわれる．一方，その高い剛性が，固定隣接椎間の早期変性を招く可能性が指摘されているが，現在までPLFとPLIFの隣接椎間への力学的影響を比較した報告はない．本研究の目的は，PLF単独およびPLIF併用の腰椎再建が隣接椎間に及ぼす影響を明らかにすることである．仔牛屍体の腰仙椎を使用し生体力学試験を行った．前後屈の純粋モーメントを負荷した（最大±6N）．固定椎間数は1ないし2とし，上位隣接椎間板内圧と椎弓の歪み量を測定した．2椎間以上の固定の場合，隣接椎間への影響はPLF単独よりPLIF併用のほうが大きいことが示唆された．椎体間固定を行う場合，固定椎の剛性の高いPLFとPLIFの併用は隣接椎間に対する力学的影響を高め早期変性を招く危険性がある．

　Combinding posterolateral fusion (PLF) with posterior lumbar interbody fusion (PLIF) has been reported to increase construct stiffness and maintain the lumbar lordosis better than PLF alone, but few studies have compared PLF and PLIF combined with PLF in terms of their effect on adjacent motion segments. The aim of this study was to investigate the biomechanical effects of posterior reconstructions on the adjacent motion segment and to assess the indications for PLF and PLIF. The lumbosacral spine of calves were subjected to non-destructive flexion-extension testing (±6 Nm). Single-or two-segment posterior reconstruction was performed by pedicle screw fixation with and without interbody cages, and intradiscal pressure and longitudinal lamina strain in the upper adjacent segment were analyzed. When two segments were fixed by a combination of PLIF and PLF, intradiscal pressure and lamina strain were greater than after PLF alone. The Addition of PLIF may produce greater adjacent level load transmission and lead to early degenerative changes on adjacent segments.