Abstract:

BACKGROUND: The degeneration of the intervertebral disc and zygapophyseal joints (facet joint) is the main cause of degenerative lumbar stenosis with the clinical outcomes including chronic low back pain and neurogenic intermittent claudication. Dynamic stabilization devices, especially non-fusion interspinous process stabilization devices (IPD), are noteworthy in saving segmental movement, showing faster recovery and rehabilitation without increasing the degeneration of adjacent segments.
OBJECTIVE: To compare and quantify the disc pressure to understand the likelihood of accelerated disc degeneration in the implanted level to optimize the usage of the implant.
METHODS: Six cadaver lumbar specimens (L_2–5) were loaded in flexion, neutral, and extension. A pressure measuring film measured the disc load during each of the three positions at each L_3-4 disc level. The implant with different spacer height including 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm was placed at L₃-L₄ by turns, and the pressure measurements were repeated.
RESULTS AND CONCLUSION: The IPD with 10 mm spacer height could not significantly share the disc load. The 12 mm implant significant shared posterior annulus load only in extension. The 14 mm implant decreased the stress in posterior annulus and nucleus in extension and neutral but slightly increased the anterior annulus load. Though the 16 mm-20 mm implants decreased the posterior annulus’ stress significantly, the anterior annulus load was increased about 400% in aforementioned three positions. Different distraction degrees of interspinous process may lead to different disc load distribution, the implant would be not appropriate to those serious spinal stenosis because of the contradictions that though the over distraction can decrease the posterior annulus load and distract the intervertebral foramina, it will lead to an acceleration of disc degeneration by the excessive load increasing in anterior annulus.