Adjacent segment range of motion after different insertion depth of lumbar interspinous dynamic stabilization device(Coflex): a biomechanical study

English Keywords:Lumbar vertebrae  Adjacent segment  Internal fixators  Prosthesis implantation  Biomechanics

English Abstract:

  【Abstract】 Objectives: To evaluate the lumbar adjacent segment range of motion after different insertion depth of lumbar interspinous dynamic stabilization device(Coflex). Methods: Six fresh adult human cadaveric lumbar spine specimens(L1-L5) were fixed in a material testing system(MTS) by embedding to clamps with L1 and L5 vertebrae. L3/4 of each specimen was operated. The L2, L3, L4, L5 vertebra was inserted one spacer respectively which was used to record the range of motion(ROM) of the adjacent segments(L2/3, L4/5). Each lumbar spine specimen was tested according to the loading sequence at 3 groups: intact(keeping lumbar ligament and facet joint intact) group, 5mm insertion(distance between apex of U-shaped Coflex and dural sac was 5mm) group and 0mm insertion(distance was 0mm) group. Each lumbar spine specimen was loaded with pure moments of 8N·m according to a loading sequence consisting of flexion, extension, left/right lateral bend?鄄ing, left/right axial rotation and the ROM of adjacent segment was recorded. Adjacent segments(L2/3, L4/5) ROM of 3 groups in 6 directions was analyzed respectively with one-way ANOVA test and multiple comparisons were based on LSD method. Results: In L2/3 segment： the mean ROM of 3 groups was equal in flexion, extension, left/right lateral bending, left/right axial rotation(intact group: 4.23°±0.25°, 3.56°±0.14°, 3.07°±0.12°, 3.34°±0.08°, 2.53°±0.16°, 2.44°±0.11°; 5mm insertion group: 4.40°±0.21°, 3.64°±0.14°, 3.09°±0.11°, 3.35°±0.07°, 2.54°±0.16°, 2.46°±0.10°; 0mm insertion group: 4.47°±0.20°, 3.72°±0.16°, 3.14°±0.10°, 3.38°±0.08°, 2.58°±0.15°, 2.49°±0.12°), and there were no significant differences among 3 groups(all P>0.05). In L4/5 segment： the mean ROM of 3 groups was equal in flexion, extension, left/right lateral bending, left/right axial rotation (intact group: 3.80°±0.28°, 3.45°±0.11°, 3.25°±0.11°, 3.28°±0.13°, 2.44°±0.11°, 2.42°±0.11°; 5mm insertion group: 3.86°±0.28°, 3.52°±0.11°, 3.28°±0.09°, 3.31°±0.05°, 2.50°±0.07°, 2.46°±0.09°; 0mm insertion group: 4.47°±0.20°, 3.72°±0.16°, 3.14°±0.10°, 3.38°±0.08°, 2.58°±0.15°, 2.49°±0.12°), and there were no significant differences among 3 groups(all P>0.05). Conclusions: The adjacent segments after different insertion depth(when distance between apex of U-shaped Coflex and dural sac was or less than 5mm) of lumbar interspinous dynamic stabilization device(Coflex) allow no significantly more motion than the intact specimen in flexion, extension, left/right lateral bending, left/right axial rotation.