ABSTRACT
Objective To study the influence of follower load on contact force of facet joints under various postures of lumbar spine. Methods A 3D nonlinear finite element model of lumbar spine (L1-S1) was developed, with consideration of the non-uniform thickness and nonlinear material properties of the cartilage layer in facet joints. The model was then applied with different follower preload (0, 0.5, 0.8, 1.2 kN), under pure moment of 7.5 N•m in different directions (flexion, extension, lateral bending, extension and torsion). The contact forces of facet joints on the two sides of each segment under different loading conditions were compared. The asymmetry influence of follower load on contact force of facet joints was also quantitatively studied. Results The follower preload increased the facet force under flexion-extension and bending (ipsilateral), while decreased the force on the contralateral facet under lateral bending. All the effects of follower load on facet force became weaker with the increase of preload. For torsion loading, the preload had almost no effect on facet force. The greatest asymmetry influence of follower load on facet force was under bending (the ipsilateral side), followed by flexion, bending (contralateral side), extension and torsion. Conclusions The follower load shows obviously different effects on contact force of facet joints with different postures. The asymmetry of facet joints should be fully considered in biomechanical studies of lumbar spine, especially in studies on post-structures of lumbar spine under physiological loads.
ABSTRACT
<p><b>OBJECTIVE</b>To study effects of different intraabdominal pressure of carbon dioxide (Cq2) pneumoperitoneum on hemorrheology and microcirculation in rabbits.</p><p><b>METHODS</b>Eighteen female healthy rabbits weighing 2.2 kg to 3.5 kg were randomly divided into three groups equally based on pneumoperitoneum pressure: 0 mmHg group (group I),10 mmHg group (group II) and 15 mmHg (group III). Each group received 1 h pneumoperitoneum under different pressure. Blood samples were taken at 5 min before CO2 pneumoperitoneum, at 30 and 60 min after pneumoperitoneum for the measurements of indexes of hemorrheology. Hemodynamics including heart rate (HR), mean arterial pressure (MAP) and the volume and velocity of the microcirculation of auricle were continuously monitored, such indexes were recorded at the related time.</p><p><b>RESULTS</b>Afer pneumoperitoneum at 30 and 60 min, compared with group I, HR, MAP, the whole blood viscosity, the aggregation and rigid indexes of RBC were significantly raised in group II (P < 0.05), the deformability indexes of RBC, the volume and velocity of the microcirculation were markedly decreased (P < 0.05). Even more significant changes were observed in group III (P < 0.01). The plasma viscosity and the hematocrit changed little.</p><p><b>CONCLUSION</b>After CO2 pneumoperitoneum, hemorrheology is decreased; Although HR, MAP are raised, the volume and velocity of the microcirculation are decreased.</p>