Experimental Study Of The Lumbar Minimally Invasive Interspinous Process System

Objective:1. To assess the influence of the lumbar minimally invasive interspinous process system on the biomechanical performance including the kinematics of the lumbar spine.2. To evaluate the safety, feasiblity and effectiveness of the lumbar minimally invasive interspinous process system.Methods:1. Finite element models of normal lumbar and lumbar minimally invasive interspinous process system in L4,5 were built with the Computed Tomography (CT) data from an adult healthy volunteer. The models were tested by applying a 400N axial load,followed by a 10N·m bending moment in four directions (lexion, extension, lateral bending and rotation). Compare the change of the range of motion (ROM) and the intervertebral disc maximum stress at L4,5 and adjacent segments. Observe the stress distribution on spinous process and the interspinous process system itself.2. The lumbar minimally invasive interspinous process system were applied to 4 fresh cadaver lumbar spine specimens (L2-S1), which were fixed in MotionAnalysis optical motion capture system and applied 8N·m bending moment in four directions (lexion,extension, lateral bending and rotation). The ROM was compared between the two groups at L4,5 and the adjacent segments.3. The lumbar minimally invasive interspinous process system was applied to L4 5 of 8 Guangxi Ba-Ma mini pigs (25-30kg). The intervertebral foramen diameter, transverse diameter, anterior height of intervertebral disc and posterior height of intervertebral disc in L4 5 were compared and the process of insertion, postoperative blood test results and nerve dysfunction were analysed.Results:1. The ROM and intervertebral disc maximum stress were reduced by 71.4% and 83.4%respectively in extension direction at L4,5 of finite element model implanted with the lumbar minimally invasive interspinous process system. No significant changes were observed in the ROM or intervertebral disc maximum stress in the other three directions (lexion, lateral bending and rotation) at L4,5or in all directions at adjacent segments. The maximum stress of L4 process, L5 process and the interspinous process system were 56.8 Mpa, 36.5 Mpa and 36.OMpa respectively.2. The ROM was reduced significantly (t=-3.444,P=0.009) in extension direction at L4,5 of the fresh cadaver lumbar spine specimens implanted with the lumbar minimally invasive interspinous process system. There was no significant difference (P>0.05) in the ROM in the other three directions (lexion, lateral bending and rotation) at L4,5 or in all directions at adjacent segments.3. The lumbar minimally invasive interspinous process system were implanted into 8 pigs successfully. Significant increases were found in intervertebral foramen diameter(t= - 2.214,P=0.044) , transverse diameter (t=-1.824,P=0.012) and posterior height of intervertebral disc (t=-2.441,P=0.029) in L4,5 postoperatively. No significant difference was observed in anterior height of intervertebral disc (t=-0.691,P=0.501).Postoperative blood test results were normal and no nerve dysfunction was observed.Conclusion: The application of lumbar minimally invasive interspinous process system,restricting the extension of lumbar, increasing the intervertebral foramen diameter,inteivertebral foramen transverse diameter and posterior height of intervertebral disc, is a safe, feasible and effective alternative to alleviate clinical symptoms of lumbar degenerative disease.