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To investigate the effects of inclined axial compressive force and flexion moment on the anterior and posterior shear stiffness of the lumbosacral segment.
Six fresh-frozen human cadaveric L5-S1 segments were tested under intact and two progressively impaired structural conditions: intact, a 4-mm bilateral facet joint gap, and anterior discectomy with nucleus pulposus removal plus circumferential release of the inner annular fibers (disc injury). A 300 N axial compressive force was applied either vertically downward or with a 10° or 20° anterior inclination through the disc's shear center. Anterior (0 N to 250 N) and posterior (-50 N to 0 N) shear tests were conducted using a material testing machine. These tests were repeated under a 5 N·m flexion moment. The relative motion between L5 and S1 was measured using a three-dimensional motion capture system.
In the intact state, the inclination of the axial compressive force did not significantly alter anterior or posterior shear stiffness. However, the application of a flexion moment increased anterior shear stiffness by 49.3%. Progressive structural damage resulted in incremental increases in anteroposterior shear translation and corresponding reductions in stiffness. Notably, under combined loading with axial compression and flexion moment, anterior stiffness decreased from 939 N/mm (intact) to 224 N/mm (disc injury), while posterior stiffness decreased from 572 N/mm to 217 N/mm. Within the low-load range, no significant differences in shear stiffness were observed across any structural conditions, regardless of axial force inclination or combined with a flexion moment.
This study supports the clinical view that retro-inclination of the pelvis serves as a compensatory mechanism to enhance segmental shear stability. However, this compensatory capacity gradually diminishes and ultimately fails as spinal degeneration progresses.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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