Determination of Load Transmission and Contact Force at Facet Joints of L2–l3 Motion Segment Using Fe Method

Abstract

In the human spine, it is well known that facet joints play a significant role in load transmission and providing stability. It has also been hypothesized to be one of most probable sources of low back pain. Experimental determination of the load-bearing role of lumbar intervertebral joints, such as the facets joints, under axial compression has not been a straightforward task. In this study, the role of the facets in load transmission through a L2–L3 motion segment under axial compression is investigated using a L2–L3 finite element (FE) model, incorporated with an accurate three-dimensional geometry of facet joints with the inclusion of surface-to-surface continuum contact representation. The effects of osteoarthritis on facet force and biomechanical behaviors are also investigated by assuming friction at the facet joints. The study shows that the facet joints resisted 8% more in load for joints with osteoarthritics as compared with the normal joints. High percentage increase in contact facet force was also predicted for joint with osteoarthritics deformity. The use of the analytical FE model provided yet another efficient alternative for predicting the load transmission and contact force for degenerative joints, so as to provide a better understanding of the biomechanics of the spine as well as the pathophysiology of the various spinal disorders and degenerative conditions.

A nonlinear contact algorithm predicting facet joint contribution in the lumbar spine of a specific person

“…The facet joints have been reported to transmit anywhere between 2% and 59% of the load through the spine in previous models and experiments (Yang and King 1984, Kim et al 1991, Teo et al 2003, Guo et al 2007). This large range indicates that load paths are not yet fully understood (Moore 1992).…”

“…The detailed geometry of the CT scans allows for extraction of radii of curvature at any point on the individual facets. According to the literature, cartilage thickness ranges from 0.2 (Sharma et al 1995, Teo et al 2003, Holzapfel and Stadler 2006 to 3.02 mm (Sokoloff 1966). Cartilage degenerates with time (E. Mendel, personal communication, 2008), so an estimate of 0.5 mm (on the lower end of the aforementioned range) was made for the thickness of the cartilage surrounding the facet joints (Natarajan et al 1999).…”

“…An iterative process was used to determine the force-displacement relationship. This procedure started with loading data from the literature (Yang and King 1984, Kim et al 1991, Teo et al 2003, Guo et al 2007) which were used as inputs into the modified Hertz formulas (Equation 1). Results show individual stiffness values and exponents for each of the facet contact regions in the lumbar spine.…”

“…Many linear elastic finite element method (FEM) solutions of the spine include posterior elements (Kim et al 1991, Goel et al 1993, 1994, Yoganandan et al 1996, Maurel et al 1997, Natarajan et al 1999, Teo et al 2003, Rohlmann et al 2006, Guo et al 2007, Schmidt et al 2007. The facet contact force has been chiefly represented by gap (contact) elements, which provide a restoring force when two deformable surfaces approach each other, and removes the contact force when the two surfaces separate.…”

“…Other models are static and usually do not include muscles or use a single equivalent muscle (Kim et al 1991, Kumaresan et al 1998, Calisse et al 1999. Also, many previous models do not include subject-specific motion or load data (Lorenz et al 1983, Yang and King 1984, Kim et al 1991, Teo et al 2003, Guo et al 2007.…”