Biomechanics changes of lumbar spine caused by foraminotomy via percutaneous transforaminal endoscopic lumbar discectomy

Abstract

Objective: To analyze the biomechanics changes of lumbar spine caused by foraminotomy via percutaneous transforaminal endoscopic lumbar discectomy using the finite element method. Methods: Three healthy adult males (aged 35.6 to 42.3 years) without spinal diseases were enrolled in this study and 3D-CT scans were carried out to obtain the parameters of lumbar spine. Mimics software was applied to build a 3D finite element model of lumbar spine. Graded resections (1/4, 2/4, 3/4 and 4/4) of the left superior articular process of L(5) were done via percutaneous transforaminal endoscopic lumbar discectomy. Then, the pressure of the L(4/5) right facets, the pressure of the L(4/5) intervertebral disc and the motion of lumbar spine were recorded after simulating the normal flexion and extension, lateral flexion and rotation of the lumbar spine model during different resections. The data were compared among groups with analysis of variance. Results: Comparing with the normal group, after 1/4 resection of the left superior articular process of L(5), the pressure of the L(4/5) right facets showed significant differences during left lateral flexion and rotation of lumbar spine (q=8.823, 8.248, both P<0.05); and the pressure of L(4/5) intervertebral disc also changed significantly during extension and right rotation of lumbar spine (q=6.918, 6.438, both P<0.05); the motion of lumbar spine showed obvious differences during right lateral flexion and rotation (q=6.845, 7.772, 13.58, all P<0.05). Comparing with the normal group, after 2/4 resection of the left superior articular process of L(5), the pressure of the L(4/5) right facets presented significant differences during all conditions (q=5.670-17.830, all P<0.05); the pressure of L(4/5) intervertebral disc changed significantly during flexion, extension, lateral flexion and right rotation (q=5.260, 17.150, 5.727, 8.890, 15.660, all P<0.05); the motion of lumbar spine also existed differences during extension, lateral flexion and rotation (q=9.106, 5.431, 12.060, 11.160, 17.260, all P<0.05). However, after 3/4 resections, the pressure of the L(4/5) right facets, the pressure of the L(4/5) intervertebral disc and the motion of lumbar spine presented differences during all conditions when compared with those in normal group (q=6.303-25.48, all P<0.05). After 4/4 resections, the pressure of the L(4/5) right facets and the pressure of the L(4/5) intervertebral disc and the motion of lumbar spine showed significant differences during all conditions when compared with those in normal group (q=8.065-45.70, all P<0.05). Conclusions: The biomechanics and the stability of lumbar spine changed partly after 1/4 resection of the superior articular process and obviously after more than 2/4 is resected. The superior articular process should be paid more attention during foraminotomy via percutaneous transforaminal endoscopic lumbar discectomy.