A new method for determining the effect of follower load on the range of motions in the lumbar spine

In this study, a new method of applying follower load in finite element (FE) model of lumbar spine was presented. The effect of follower load on the range of motions (ROM) in lumbar spine was also investigated. A three-dimensional nonlinear FE model of lumbar spine (L1-S1) has been developed and validated. Connector elements between each pair of endplates were created to apply follower load. The endpoints of each connector were close to the center of endplate. The follower load of 0N, 500N, 800N, 1200N were respectively applied to explore their influence on the motion response of lumbar spine to the moment of 7.5NM in three principle planes (extension, flexion, right bending, left bending, right torsion, left torsion). The results showed that the direction of follower load was almost along with the curvature of spine and induced very small segmental motion. The follower load made the ROM of lumbar spine slightly increase in extension, while produced the decrease in ROM in other five moments. This stiffening effect became more obvious with an increase in the follower load. The largest percent decrease in motion of lumbar spine due to pre-load was in left torsion (47%), and then right torsion(42%), right lateral bending (21%), left lateral bending(20%), flexion(11%).