J Korean Orthop Assoc.  2007 Dec;42(6):789-794. 10.4055/jkoa.2007.42.6.789.

A Biomechanical Analysis on Disc Pressure Distribution Changes with Interspinous Spinal Spacer Insertion for Lumbar Spinal Stenosis

• Kwon SY
• Jun SC
• Moon SJ
• Tack GR
• Lee SJ
• Shin KC

• KMID: 1947786
• DOI: http://doi.org/10.4055/jkoa.2007.42.6.789

Abstract

PURPOSE: To assess the biomechanical effects and effectiveness of an interspinous spinal spacer (ISS) on the intradiscal pressure using in vitro biomechanical tests.
MATERIALS AND METHODS
Six calf spine specimens (less than 2 weeks of age, L1-L5) were divided to two groups the intact and the surgery groups (n=3 each). For the surgery group, an ISS made from PMMA (Greek pi=12-mm) were inserted into the space between the spinous processes of L3-L4. The intradiscal pressures at the various regions of the annulus (anterior, posterior, and posterolateral locations) and the nucleus pulposus were measured using the four pressure transducers under pure compression (700 N) and extension loads (700 N+7.5 Nm).
RESULTS
An increase in pressure was observed from neutral to extension at the posterior and posterolateral annulus. After inserting the ISS, the changes in pressure at the adjacent disc levels (L2-L3, L4-L5) were negligible regardless of the loading conditions (p>0.05). However, at the implanted level (L3-L4) statistically significant changes in the pressure were found under extension loading at the nucleus pulposus, posterior and posterolateral regions of the annulus with a pressure drop from 1.48 MPa, 1.42 MPa, 1.71 MPa to 1.11 MPa, 0.961 MPa, 1.08 MPa, at the respective locations (p<0.05). The relative percentage decrease were 25%, 31.7%, and 36.8%.
CONCLUSION
On the implanted level, these results showed that the insertion of the ISS with PMMA can effectively reduce the intradiscal pressures by at least 25% quite uniformly over the intravertebral disc during extension. More effective reduction was observed at the posterolateral location. The pressure changes at the adjacent levels were negligible in contrast to the abnormal pressure changes that are frequently reported after conventional rigid fusion. This suggests that the likelihood of adjacent level degeneration after surgery can be minimized using the ISS insertion.

Keyword

Biomechanical test; ISS (interspinous spinal spacer); Intradiscal pressure

MeSH Terms

Polymethyl Methacrylate
Spinal Stenosis*
Spine
Transducers, Pressure
Polymethyl Methacrylate

Figure

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  Fig. 1 Pressure transducers (A) the size and attachment of the pressure transducers. (B) Insertion location of the pressure transducers in a disc.

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  Fig. 2 Biomechanical tests under compression and the extension loads. (A) Schematic diagram of the set-up, (B) specimen under pure compression loading condition (C) under extension.

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  Fig. 3 Pressures of the internal disc between L3-L4 under pure compression (700 N) Antero-central annulus, Nucleus pulposus, Postero-central annulus, Postero-lateral annulus Pressure (MPa) in Intact spine and Surgical spine.

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  Fig. 4 Pressures of the internal disc between L3-L4 under extension loading (700 N+7.5 Nm) Antero-central annulus, Nucleus pulposus, Postero-central annulus, Postero-lateral annulus Pressure (MPa) in Intact spine and Surgical spine.

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