title: In vitro biomechanical effects of reconstruction on adjacent motion segment: comparison of aligned/kyphotic posterolateral fusion with aligned posterior lumbar interbody fusion/posterolateral fusion.
abstract: OBJECTIVE
  Posterior lumbar interbody fusion (PLIF) was developed to overcome the limitations of posterolateral fusion in correcting spinal deformity and maintaining lumbar lordosis. In this study the authors compare the biomechanical effects of three different posterior reconstructions on the adjacent motion segment.
  
  
  METHODS
  Ten calf spinal (L2-S1) specimens underwent nondestructive flexion-extension testing (+/- 6 Nm). The specimens were destabilized at the L5-S1 levels after intact testing. This was followed by pedicle screw fixation with and without interbody cages as follows: 1) with straight rods ("aligned" posterolateral fusion); 2) with kyphotically prebent rods ("kyphotic" posterolateral fusion); and 3) with interbody cages combined with straight rods ("aligned" PLIF/posterolateral fusion). The range of motion (ROM) of the operative segments, the intradiscal pressure (IDP), and longitudinal lamina strain in the superior adjacent segment (L4-5) were analyzed. The ROM associated with aligned PLIF/posterolateral fusion-treated specimens was significantly less than both the aligned and kyphotic posterolateral fusion-treated procedures in both flexion and extension loading (p < 0.05). The aligned PLIF/posterolateral fusion was associated with greater IDP and the lamina strain compared with the aligned and kyphotic posterolateral fusion groups in flexion loading. Under extension loading, greater IDP and lamina strain were present in the kyphotic posterolateral fusion group than in the aligned posterolateral fusion group. The highest IDP and lamina strain were shown in the aligned PLIF/posterolateral fusion group.
  
  
  CONCLUSIONS
  Compared with kyphotic posterolateral fusion, PLIF may lead to even higher load at the superior adjacent level because of the increased stiffness of the fixed segments even if local kyphosis is corrected by PLIF.
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, Japan. hidekisudo@yahoo.co.jp
authors.forename: Hideki
authors.initials: H
authors.lastname: Sudo
authors.forename: Itaru
authors.initials: I
authors.lastname: Oda
authors.forename: Kuniyoshi
authors.initials: K
authors.lastname: Abumi
authors.forename: Manabu
authors.initials: M
authors.lastname: Ito
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kotani
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Hojo
authors.forename: Akio
authors.initials: A
authors.lastname: Minami
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D066298:In Vitro Techniques; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery*; D023421:Models, Animal; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*