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 investigate the changes between pressure of trochlea of talus surface and distribution of area after anterior lower tibiofibular ligament rupture, and provide basis for treating anterior lower tibiofibular ligament rupture.</p><p><b>METHODS</b>Six fresh adult ankle joint specimens (4 males and 2 females, ranging age from 25 to 60 years, with an average of 44.6 years) were adopted. The specimens were removed from skin and muscles, remained ankle joint capsule, medial and lateral ligaments and anteroinferior tibiofibular ligament. The ankle joint was fixed with a special fixture in neutral position. Pressure sensitive film (700 N axial load ) was respectively used to measure mean pressure, peak pressure and stress distribution area of the upper articular facet of talar trochlea of the normal ankle joint and the ankle joint with anterioinferior tibiofibular ligament rupture.</p><p><b>RESULTS</b>The stress distribution areas of the control group and the ruptured group were respectively (367.8 +/- 54.0) mm2 and (386.0 +/- 53.7) mm2; the mean pressures were respectively (1.40 +/- 0.12) MPa and (1.70 +/- 0.35) MPa; the peak pressures were respectively (2.60 +/- 0.33) MPa and (3.20 +/- 0.32) MPa. The experimental results showed that the change in stress distribution area after anterioinferior tibiofibular ligament rupture was not significant (t = 0.021, P = -0.983). When stress distribution changed, the region of stress concentration transferred to poster lateral,and mean pressure (t = 4.140, P = 0.020) and peak pressure (t = 3.169, P = 0.010) increased significantly.</p><p><b>CONCLUSION</b>When anterior lower tibiofibular ligament rupture occurs, mean pressure,peak pressure and stress distribution of pressure of trochlea of talus surface is changed, which may cause traumatic arthritis, and surgical treatment is considerably used to restore normal anatomy.</p>