Biomechanical study on the effect of five different lumbar reconstruction techniques on adjacent-level intradiscal pressure and lamina strain.
OBJECTIVE
The objectives of this study were to compare the biomechanical effects of five lumbar reconstruction models on the adjacent segment and to analyze the effects of three factors: construct stiffness, sagittal alignment, and the number of fused segments.


METHODS
Nondestructive flexion-extension tests were performed by applying pure moments to 10 calf spinal (L3-S1) specimens. One-segment (L5-6) or two-segment (L5-S1) posterior fusion methods were simulated: 1) one-segment posterolateral fusion (PLF); 2) one-segment PLF with interbody fusion cages (one-segment PLIF/PLF); 3) two-segment PLF; 4) two-segment PLIF/PLF; and 5) two-segment PLF in kyphosis (two-segment kyphotic PLF). The range of motion (ROM) of the reconstructed segments, intradiscal pressure (IDP), and lamina strain in the upper (L4-5) adjacent segment were analyzed. The ROM was significantly decreased in the PLIF/PLF models compared with that in the PLF alone models after both the one- and two-segment fusions. If the number of fused segments was increased, the pressure and strains were also increased in specimens subjected to the PLIF/PLF procedure, more so than the PLF-alone procedure. In the one-segment PLIF/PLF model the authors observed a reduced IDP and lamina strain compared with those in the kyphotic two-segment PLF model despite the latter's higher levels of initial stiffness.


CONCLUSIONS
If the number of fused levels can be reduced by using PLIF to correct local kyphosis, then this procedure may be valuable for reducing adjacent-segment degenerative changes.
Sudo
Hideki
H
Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, Sapporo, Japan. hidekisudo@yahoo.co.jp
Oda
Itaru
I
Abumi
Kuniyoshi
K
Ito
Manabu
M
Kotani
Yoshihisa
Y
Minami
Akio
A
D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D066298:In Vitro Techniques; D007403:Intervertebral Disc / Q000502:physiology*; D007593:Joint Instability / Q000601:surgery; D007738:Kyphosis / Q000601:surgery; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery*; D011312:Pressure; D016059:Range of Motion, Articular; D013123:Spinal Fusion; D013314:Stress, Mechanical