Disc herniations occur in a biomechanical environment consistent with forward bending, i.e. compression and flexion of the spine. During forward bending, athletic trainers and physical therapists encourage activation of the posterior spinal extensor muscles known as the erector spinae muscles. Activation of these muscles may encourage facet contact, which could effectively offset compressive and shear loading from the disc to the facets and protect the disc during forward bending activities.
Computer simulation programs provide researchers with cost-effective methodologies for studying internal stresses and loads on biological specimens. Previous research conducted by Explico’s engineers have involved developing a validated three-dimensional finite element model of the lumbar spine capable of predicting disc herniation mechanics. The current study utilized the previously developed finite element model to evaluate the association between the posterior spinal muscles and facet contact in reducing disc herniation risk during forward bending. We hypothesized that the presence of intact and properly engaged facets and increased posterior muscle activation would result in decreased stresses and loads experienced by the disc.
Results of our study confirmed our hypothesis and demonstrated that the disc was at lowest risk for herniation when the facets were properly engaged and when the posterior muscle activation was the highest. Activation of the posterior spinal muscles contributed to greater facet engagement and allowed the facet to act as a fulcrum and offset the loads experienced by the disc. This study demonstrated the importance of posterior muscle strength and facet engagement in maintaining a healthy disc environment.