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Load distribution on intervertebral cages with and without posterior instrumentation – Lumbar Fusion

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The article discusses a biomechanical cadaveric study that aimed to quantify the forces acting on intervertebral cages in the lumbar spine under axial compression force with and without posterior instrumentation. The study found that without posterior instrumentation, the cages absorbed more than 50% of the axial load, while with posterior instrumentation, the external load on the cages was significantly lower. The study also observed that the load sharing became dependent on the load amplitude, with a higher proportion of the load being transferred by the cages in high load situations. The article concludes that cage instrumentation allows for better distribution and reduction of the overall force on the pedicle screws and rods in the spinal construct

Summarised by Mr Mo Akmal – Lead Spinal Surgeon
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Published article

: Without posterior instrumentation, the intervertebral cages absorb more than 50% of the axial load and the load distribution is largely independent of the loading amplitude. With posterior instrumentation, the external load acting on the cages is significantly lower and the load sharing becomes dependent on the load amplitude, with a higher proportion of the load being transferred by the cages in high load situations. The bPLIF cages tend to absorb more force than the other two cage…

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Spine J. 2023 Nov 2:S1529-9430(23)03485-X. doi: 10.1016/j.spinee.2023.10.017. Online ahead of print.ABSTRACTBACKGROUND CONTEXT: Posterior and transforaminal lumbar interbody fusion (PLIF, TLIF) are well-established procedures for spinal fusion. However, little is known about load sharing between cage, dorsal construct, and biological tissue within the instrumented lumbar spine.PURPOSE: The aim of this study was to quantify the forces,

Spine J. 2023 Nov 2:S1529-9430(23)03485-X. doi: 10.1016/j.spinee.2023.10.017. Online ahead of print.

ABSTRACT

BACKGROUND CONTEXT: Posterior and transforaminal lumbar interbody fusion (PLIF, TLIF) are well-established procedures for spinal fusion. However, little is known about load sharing between cage, dorsal construct, and biological tissue within the instrumented lumbar spine.

PURPOSE: The aim of this study was to quantify the forces acting on cages under axial compression force with and without posterior instrumentation.

STUDY DESIGN: Biomechanical cadaveric study.

METHODS: Ten lumbar spinal segments were tested under uniaxial compression using load cell instrumented intervertebral cages. The force was increased in 100N increments to 1000N or a force greater than 500N on one load cell. Each specimen was tested after unilateral PLIF (uPLIF), bilateral PLIF (bPLIF) and TLIF each with/without posterior instrumentation. Dorsal instrumentation was performed with 55N of compression per side.

RESULTS: Cage insertion resulted in a median cage preload of 16N, 29N and 35N for uPLIF, bPLIF and TLIF. The addition of compressed dorsal instrumentation increased the median preload to 224N, 328N and 317N, respectively. With posterior instrumentation, the percentage of the external load acting on the intervertebral cage was less than 25% at 100N (uPLIF: 14.2%; bPLIF: 16%; TLIF: 11%), less than 45% at 500N (uPLIF: 31.8%; bPLIF: 41.1%; TLIF: 37.9%) and less than 50% at 1000N (uPLIF: 40.3%; bPLIF: 49.7%; TLIF: 43.4%). Without posterior instrumentation, the percentage of external load on the cages was significantly higher with values above 50% at 100N (uPLIF: 55.6%; bPLIF: 75.5%; TLIF: 66.8%), 500N (uPLIF: 71.7%; bPLIF: 79.2%; TLIF: 65.4%), and 1000N external load (uPLIF: 73%; bPLIF: 80.5%; TLIF: 66.1%). For absolute loads, preloads and external loads must be added together.

: Without posterior instrumentation, the intervertebral cages absorb more than 50% of the axial load and the load distribution is largely independent of the loading amplitude. With posterior instrumentation, the external load acting on the cages is significantly lower and the load sharing becomes dependent on the load amplitude, with a higher proportion of the load being transferred by the cages in high load situations. The bPLIF cages tend to absorb more force than the other two cage configurations.

CLINICAL SIGNIFICANCE: Cage instrumentation allows some of the compression force to be transmitted through the cage to the screws below, better distributing and reducing the overall force on the pedicle screws at the end of the construct and on the rods.

PMID:37924848 | DOI:10.1016/j.spinee.2023.10.017

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Load distribution on intervertebral cages with and without posterior instrumentation

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Spine J. 2023 Nov 2:S1529-9430(23)03485-X. doi: 10.1016/j.spinee.2023.10.017. Online ahead of print.ABSTRACTBACKGROUND CONTEXT: Posterior and transforaminal lumbar interbody fusion (PLIF, TLIF) are well-established procedures for spinal fusion. However, little is known about load sharing between cage, dorsal construct, and biological tissue within the instrumented lumbar spine.PURPOSE: The aim of this study was to quantify the forces

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