Contributions of Flexion–Extension Cyclic Loads to the Lumbar Spinal Segment Stability Following Different Discectomy Procedures

In Brief Study Design. An in vitro biomechanical cadaveric study. Objectives. To elucidate the effect of flexion–extension cyclic loads on the motion behavior of lumbar spine after different discectomies. Summary of Background Data. Biomechanical cadaveric studies to evaluate the effect of discectomy have been performed and have indicated the relevance between the volume of removed disc materials and increase of motion in affected intervertebral disc. However, there are no biomechanical studies to investigate the motion behavior of injured intervertebral disc after cyclic loads. Methods. Twenty-eight lumbar functional spinal units were randomized into fenestration, annulotomy, limited discectomy, and radical discectomy groups. Pure bending moments were applied to simulate various loading modes and determine the resulting displacements before and after surgery, and after cyclic loads of 1,000, 5,000, and 10,000 cycles at a frequency of 0.5 Hz and a force of ±3.0 Nm. Change of range of motion (ROM) was compared among each group. Results. Following surgery, in the radical discectomy group, the relative change of ROM mostly increased in all motion directions except right lateral bending. On the other hand, during cyclic loads up to 10,000 cycles, in the limited discectomy group, the relative change of ROM mostly increased in all motion directions except right lateral bending. Conclusions. These results demonstrate that the effect of cyclic loads after discectomy may increase ROM, leading to spinal instability even if the increase in ROM does not occur immediately after surgery for the minimum removal of nucleus pulposus case. Clinically, this may underscore the importance of postoperative lumbar support. The effects of flexion–extension cyclic loads on lumbar functional spinal unit motion behavior after different discectomies were investigated. The results demonstrate that the cyclic loads may increase range of motion even if the increase of range of motion does not occur immediately after surgery for the minimum removal of nucleus pulposus case.