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Biomechanical analysis of the lumbar spine on facet joint force and intradiscal pressure--a finite element study.

Kuo CS, Hu HT, Lin RM, Huang KY, Lin PC, Zhong ZC, Hseih ML - BMC Musculoskelet Disord (2010)

Bottom Line: The results revealed that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger loadings.Although the effect of the preloads on facet joint forces was not apparent, intradiscal pressure did increase with preload, and its magnitude increased more markedly in flexion than in extension and axial rotation.Compared with the applied preloads, the postures played a more important role, especially in axial rotation; the facet joint forces were increased in the contralateral facet joints as compared to the ipsilateral ones at the same level of the lumbar spine.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Civil Engineering, National Cheng Kung University, Tainan, Taiwan. kcs60417@ms17.hinet.net

ABSTRACT

Background: Finite element analysis results will show significant differences if the model used is performed under various material properties, geometries, loading modes or other conditions. This study adopted an FE model, taking into account the possible asymmetry inherently existing in the spine with respect to the sagittal plane, with a more geometrically realistic outline to analyze and compare the biomechanical behaviour of the lumbar spine with regard to the facet force and intradiscal pressure, which are associated with low back pain symptoms and other spinal disorders. Dealing carefully with the contact surfaces of the facet joints at various levels of the lumbar spine can potentially help us further ascertain physiological behaviour concerning the frictional effects of facet joints under separate loadings or the responses to the compressive loads in the discs.

Methods: A lumbar spine model was constructed from processes including smoothing the bony outline of each scan image, stacking the boundary lines into a smooth surface model, and subsequent further processing in order to conform with the purpose of effective finite element analysis performance. For simplicity, most spinal components were modelled as isotropic and linear materials with the exception of spinal ligaments (bilinear). The contact behaviour of the facet joints and changes of the intradiscal pressure with different postures were analyzed.

Results: The results revealed that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger loadings. In axial rotation, the facet joint forces were relatively larger in the contralateral facet joints than in the ipsilateral ones at the same level. Although the effect of the preloads on facet joint forces was not apparent, intradiscal pressure did increase with preload, and its magnitude increased more markedly in flexion than in extension and axial rotation.

Conclusions: Disc pressures showed a significant increase with preload and changed more noticeably in flexion than in extension or in axial rotation. Compared with the applied preloads, the postures played a more important role, especially in axial rotation; the facet joint forces were increased in the contralateral facet joints as compared to the ipsilateral ones at the same level of the lumbar spine.

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Intradiscal pressures at (a) levels L1/L2 and L4/L5, and (b) levels L2/L3 and L3/L4 under a preload of 460 N.
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Figure 10: Intradiscal pressures at (a) levels L1/L2 and L4/L5, and (b) levels L2/L3 and L3/L4 under a preload of 460 N.

Mentions: In order to validate the constructed model, we rearranged the results shown in Figure 9(b) by separating levels L1/L2 to L4/L5 for the intradiscal pressures of the lumbar spine under a preload of 460 N and different loadings into two parts: levels L1/L2 and L4/L5 in Figure 10(a), and levels L2/L3 and L3/L4 in Figure 10(b). The calculated data shown in Figures 10(a) and 10(b) appear to exhibit a trend similar to that for the intact lumbar spine reported in the literature [9,18], in which a total load of 460 N resulting from an applied load of 260 N representing the weight of upper body was adopted, together with a compressive follower load of 200 N representing the stabilizing effect of the local muscle forces. In addition to the above loadings, Rohlmann et al. [9] employed the following physiological loadings: (1) standing, 30° flexion (forward bending), 15° extension of the lumbar spine, and 6° torsion (axial rotation); and (2) standing, 30° flexion, 20° extension, and 10° torsion [18]. In the case of standing, the intradiscal pressures at levels L1/L2 and L4/L5 calculated in the present study were 0.351 MPa and 0.349 MPa, respectively. However, Rohlmann et al. obtained higher values of approximately 0.61 MPa and 0.58 MPa at the corresponding levels. This disparity can be attributed to an additional force in the erector spinae or the rectus abdominis, and/or the different manner of applying loads used in the previous studies, as well as the stronger homogeneous annulus fiber elements that were used in our study. An additional sensitivity analysis was conducted to validate our assumption, as shown in Figure 3. In the cases of other postures, intradiscal pressures had larger values in flexion rather than in extension and left/right rotations, particularly at level L1/L2. There was a similar trend of changes with loading in flexion, extension, and left/right rotations between the present analysis and that reported in the literature [9,18]. A further trend can be observed in Figure 10(b); namely, that the pressures at levels L2/L3 and L3/L4 were clearly reduced in the case of extension under moments of 5 Nm to 10 Nm or 15 Nm. This phenomenon might be interpreted as a variation in the curvature of the lumbar spine at different levels. The magnitude of the moments appeared to slightly alter the curvature of the spine at level L2/L3 or L3/L4 during the period of extension, whereas the pressure had a large value at level L1/L2. The latter observation could be related to the backward bending moment that was applied over the superior surface of the L1 vertebral body nearing the disc most closely at level L1/L2. In addition, the intradiscal pressures in the nuclei pulposi increased with increasing magnitude of preloads (Figures 9(a), (b) and 9(c)), and this appeared to be a reasonable outcome for the general physiological loading cases.


Biomechanical analysis of the lumbar spine on facet joint force and intradiscal pressure--a finite element study.

Kuo CS, Hu HT, Lin RM, Huang KY, Lin PC, Zhong ZC, Hseih ML - BMC Musculoskelet Disord (2010)

Intradiscal pressures at (a) levels L1/L2 and L4/L5, and (b) levels L2/L3 and L3/L4 under a preload of 460 N.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2913991&req=5

Figure 10: Intradiscal pressures at (a) levels L1/L2 and L4/L5, and (b) levels L2/L3 and L3/L4 under a preload of 460 N.
Mentions: In order to validate the constructed model, we rearranged the results shown in Figure 9(b) by separating levels L1/L2 to L4/L5 for the intradiscal pressures of the lumbar spine under a preload of 460 N and different loadings into two parts: levels L1/L2 and L4/L5 in Figure 10(a), and levels L2/L3 and L3/L4 in Figure 10(b). The calculated data shown in Figures 10(a) and 10(b) appear to exhibit a trend similar to that for the intact lumbar spine reported in the literature [9,18], in which a total load of 460 N resulting from an applied load of 260 N representing the weight of upper body was adopted, together with a compressive follower load of 200 N representing the stabilizing effect of the local muscle forces. In addition to the above loadings, Rohlmann et al. [9] employed the following physiological loadings: (1) standing, 30° flexion (forward bending), 15° extension of the lumbar spine, and 6° torsion (axial rotation); and (2) standing, 30° flexion, 20° extension, and 10° torsion [18]. In the case of standing, the intradiscal pressures at levels L1/L2 and L4/L5 calculated in the present study were 0.351 MPa and 0.349 MPa, respectively. However, Rohlmann et al. obtained higher values of approximately 0.61 MPa and 0.58 MPa at the corresponding levels. This disparity can be attributed to an additional force in the erector spinae or the rectus abdominis, and/or the different manner of applying loads used in the previous studies, as well as the stronger homogeneous annulus fiber elements that were used in our study. An additional sensitivity analysis was conducted to validate our assumption, as shown in Figure 3. In the cases of other postures, intradiscal pressures had larger values in flexion rather than in extension and left/right rotations, particularly at level L1/L2. There was a similar trend of changes with loading in flexion, extension, and left/right rotations between the present analysis and that reported in the literature [9,18]. A further trend can be observed in Figure 10(b); namely, that the pressures at levels L2/L3 and L3/L4 were clearly reduced in the case of extension under moments of 5 Nm to 10 Nm or 15 Nm. This phenomenon might be interpreted as a variation in the curvature of the lumbar spine at different levels. The magnitude of the moments appeared to slightly alter the curvature of the spine at level L2/L3 or L3/L4 during the period of extension, whereas the pressure had a large value at level L1/L2. The latter observation could be related to the backward bending moment that was applied over the superior surface of the L1 vertebral body nearing the disc most closely at level L1/L2. In addition, the intradiscal pressures in the nuclei pulposi increased with increasing magnitude of preloads (Figures 9(a), (b) and 9(c)), and this appeared to be a reasonable outcome for the general physiological loading cases.

Bottom Line: The results revealed that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger loadings.Although the effect of the preloads on facet joint forces was not apparent, intradiscal pressure did increase with preload, and its magnitude increased more markedly in flexion than in extension and axial rotation.Compared with the applied preloads, the postures played a more important role, especially in axial rotation; the facet joint forces were increased in the contralateral facet joints as compared to the ipsilateral ones at the same level of the lumbar spine.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Civil Engineering, National Cheng Kung University, Tainan, Taiwan. kcs60417@ms17.hinet.net

ABSTRACT

Background: Finite element analysis results will show significant differences if the model used is performed under various material properties, geometries, loading modes or other conditions. This study adopted an FE model, taking into account the possible asymmetry inherently existing in the spine with respect to the sagittal plane, with a more geometrically realistic outline to analyze and compare the biomechanical behaviour of the lumbar spine with regard to the facet force and intradiscal pressure, which are associated with low back pain symptoms and other spinal disorders. Dealing carefully with the contact surfaces of the facet joints at various levels of the lumbar spine can potentially help us further ascertain physiological behaviour concerning the frictional effects of facet joints under separate loadings or the responses to the compressive loads in the discs.

Methods: A lumbar spine model was constructed from processes including smoothing the bony outline of each scan image, stacking the boundary lines into a smooth surface model, and subsequent further processing in order to conform with the purpose of effective finite element analysis performance. For simplicity, most spinal components were modelled as isotropic and linear materials with the exception of spinal ligaments (bilinear). The contact behaviour of the facet joints and changes of the intradiscal pressure with different postures were analyzed.

Results: The results revealed that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger loadings. In axial rotation, the facet joint forces were relatively larger in the contralateral facet joints than in the ipsilateral ones at the same level. Although the effect of the preloads on facet joint forces was not apparent, intradiscal pressure did increase with preload, and its magnitude increased more markedly in flexion than in extension and axial rotation.

Conclusions: Disc pressures showed a significant increase with preload and changed more noticeably in flexion than in extension or in axial rotation. Compared with the applied preloads, the postures played a more important role, especially in axial rotation; the facet joint forces were increased in the contralateral facet joints as compared to the ipsilateral ones at the same level of the lumbar spine.

Show MeSH
Related in: MedlinePlus