Biomechanical characteristics of a novel interspinous distraction fusion device in the treatment of lumbar degenerative diseases: a finite element analysis

Abstract

Background: A novel interspinous distraction fusion (ISDF) device has been used to treat lumbar degenerative diseases. As a minimally invasive technique, ISDF differs from the traditional interspinous process distraction devices. Currently, biomechanical studies on ISDF are rare.

Objective: To investigate the biomechanical properties of the ISDF device (BacFuse) which is used to treat lumbar degenerative diseases.

Methods: Three-dimensional L3-L5 models were created. The models were divided into four groups: intact (M1), local decompression alone (M2), internal fixation alone (M3) and local decompression combined with internal fixation (M4), based on different surgical procedures. Local laminectomy was performed to resect the lower part of the L4 lamina and the upper part of the L5 lamina at the right lamina of L4/5 in the M2 and M4 groups. After meshing the models elements, Abaqus were used to perform the finite element (FE) analysis. The intervertebral range of motion (ROM) was measured during flexion, extension, left lateral bending, right lateral bending, left rotation and right rotation under a follower load of 400 N with a 7.5Nm moment. The distributions of disc and facet joint stresses were observed and recorded. Spinal vertebral stress was compared, and internal fixation device stress was observed.

Results: The ROM of L4/5 in M2 increased in flexion, extension, left lateral bending, right lateral bending, left rotation and right rotation compared with that in M1. In all motion directions, the ROM at L4/5 decreased, and the ROM at L3/4 increased after implantation of the ISDF device in M3 and M4 groups. The disc stress and facet joint stresses in the instrumented segment decreased after implantation of the ISDF device. The spinous process loaded a certain amount of stress in M3 and M4 groups. The spikes of the internal fixation device were loaded with the maximum stress.

Conclusion: BacFuse exhibited a reduction in intervertebral ROM, as well as decreased stress on the intervertebral disc and facet joint, while also demonstrating a discernible impact on the upper adjacent segment.

Keywords: Biomechanical properties; Finite element analysis; Interspinous distraction fusion device; Lumbar degenerative diseases.

Fig. 1

(a) The finite analysis model included three vertebrae (L3, L4 and L5), two IVDs (L3/4 and L4/5), four facet joints, and seven ligaments. (b) Four kinds of 3D lumbar models (L3-L5). (A) Intact model. (B) Unilateral decompression model. (C) Internal fixation alone model. (D) Unilateral decompression combined with internal fixation model

Fig. 2

Comparison of intervertebral ROM between current intact model and previous literature. ROM, range of motion

Fig. 3

Changes in intervertebral ROM comparing the three intervention models to the intact model at the surgical and proximal level in the three models. ROM, range of motion

Fig. 4

Changes in intervertebral stress comparing the three intervention models to the intact model at the surgical and proximal levels

Fig. 5

Intervertebral disc stress comparison between the intact model and the internal fixation alone model in different motions. FF, front flexion; BE, back extension; LB, left bending; RB, right bending; LR, left rotation; RR, right rotation

Fig. 6

Facet joint stress distribution at L4/5 segment in M2 and M4. FF, front flexion; BE, back extension; LB, left bending; LR, left rotation

Fig. 7

Lumbar vertebral stress distribution in flexion motion

Fig. 8

Internal fixation stress distributions in different motion directions. (A) Flexion. (B) Extension. (C) Lateral bending. (D) Rotation