Nucleus Implant Parameters Significantly Change the Compressive Stiffness of the Human Lumbar Intervertebral Disc

Joshi, Abhijeet; Mehta, Samir; Vresilovic, Edward J.; Karduna, Andrew R.; Marcolongo, Michele

doi:10.1115/1.1894369

Cited by 31 publications

(24 citation statements)

References 8 publications

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“…Published axial compression data for disc replacements are few. One previous report of a hydrogel type nucleus prosthesis tested in human cadavers and implanted via an experimental annulus sparing technique had similar axial stiffness to that in the present study [42]. Another prosthetic (total) disc which is non-articulating and made of fiber reinforced polymers also had an axial compressive stiffness that was similar to the device described in the current study [39].…”

Section: Discussionsupporting

confidence: 80%

Biomechanical characterization of an annulus-sparing spinal disc prosthesis

Buttermann

Beaubien

2009

The Spine Journal

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Background Context Current spine arthroplasty devices, require disruption of the annulus fibrosus for implantation. Preliminary studies of a unique annulus sparing intervertebral prosthetic disc (IPD), found that preservation of the annulus resulted in load sharing of the annulus with the prosthesis. Purpose Determine flexibility of the IPD versus fusion constructs in normal and degenerated human spines. Study design/Setting Biomechanical comparison of motion segments in the intact, fusion and mechanical nucleus replacement states for normal and degenerated states. Patient setting Thirty lumbar motion segments. Outcomes Measures Intervertebral height; motion segment range-of-motion (ROM), neutral zone (NZ), stiffness. Methods Motion segments had multi-directional flexibility testing to 7.5 Nm for intact discs, discs reconstructed using the IPD (n=12), or after anterior/posterior fusions (n=18). Interbody height and axial compression stiffness changes were determined for the reconstructed discs by applying axial compression to 1500 N. Analysis included stratifying results to normal mobile vs. rigid degenerated intact motion segments. Results The mean interbody height increase was 1.5 mm for IPD reconstructed discs. vs 3.0 mm for fused segments. Axial compression stiffness was 3.0 ± 0.9 kN/mm for intact compared to 1.2 ± 0.4 kN/mm for IPD reconstructed segments. Reconstructed disc ROM was 9.0° ± 3.7° in flexion-extension, 10.6° ± 3.4° in lateral bending and 2.8° ± 1.4° in axial torsion which was similar to intact values and significantly greater than respective fusion values (p<0.001). Mobile intact segments exhibited significantly greater rotation after fusion vs. their more rigid counterparts (p<0.05), however, intact motion was not related to motion after IPD reconstruction. The NZ and rotational stiffness followed similar trends. Differences in NZ between mobile and rigid intact specimens tended to decrease in the IPD reconstructed state. Conclusion The annulus sparing IPD generally reproduced the intact segment biomechanics in terms of ROM, NZ, and stiffness. Furthermore, the IPD reconstructed discs imparted stability by maintaining a small neutral zone. The IPD reconstructed discs were significantly less rigid than the fusion constructs and may be an attractive alternative for the treatment of DDD.

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Section: Discussionsupporting

confidence: 80%

Biomechanical characterization of an annulus-sparing spinal disc prosthesis

Buttermann

Beaubien

2009

The Spine Journal

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“…Replacement of native NP with an implant, in the setting of healthy AF, may simultaneously reduce pain, slow progression of degeneration and restore non-degenerate spinal mobility. 8,9,10,11,12 Significant challenges to implant design include the need to match key NP mechanical behavior ex vivo and mimic the role of native non-degenerate NP in spinal motion. 8,11,13,14 Long term development and testing of nucleoplasty devices should include five assessments: 1) mechanical testing, 2) cell-materials interaction assimilation leading to material integration, 3) kinematic testing including ROM and resistance to expulsion, 4) biocompatibility and biodurability, and 5) safety testing.…”

Section: Introductionmentioning

confidence: 99%

“…8,9,10,11,12 Significant challenges to implant design include the need to match key NP mechanical behavior ex vivo and mimic the role of native non-degenerate NP in spinal motion. 8,11,13,14 Long term development and testing of nucleoplasty devices should include five assessments: 1) mechanical testing, 2) cell-materials interaction assimilation leading to material integration, 3) kinematic testing including ROM and resistance to expulsion, 4) biocompatibility and biodurability, and 5) safety testing. 15 Having previously completed mechanical testing 16,17 and cell-materials interaction assimilation leading to material integration 18 , this study will focus on step 3, ROM testing.…”

Section: Introductionmentioning

confidence: 99%

An Injectable Nucleus Pulposus Implant Restores Compressive Range of Motion in the Ovine Disc

Malhotra

Han²,

Beckstein³

et al. 2012

Spine

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Study Design Investigation of injectable nucleus pulposus (NP) implant. Objective To assess the ability of a recently developed injectable hydrogel implant to restore non-degenerative disc mechanics through support of NP functional mechanics. Summary of Background Data While surgical intervention for low back pain is effective for some patients, treated discs undergo altered biomechanics and adjacent levels are at increased risk for accelerated degeneration. One potential treatment as an alternative to surgery for degenerated disc includes the percutaneous delivery of agents to support NP functional mechanics. The implants are delivered in a minimally invasive fashion, potentially on an outpatient basis, and do not preclude later surgical options. One of the challenges in designing such implants include the need to match key NP mechanical behavior and mimic the role of native non-degenerate NP in spinal motion. Methods The oxidized hyaluronic acid gelatin implant material was prepared. In vitro mechanical testing was performed in mature ovine bone-disc-bone units in three stages: intact, discectomy, and implantation vs. sham. Tested samples were cut axially for qualitative structural observations. Results Discectomy increased axial range of motion (ROM) significantly compared to intact. Hydrogel implantation reduced ROM 17% (p < 0.05) compared to discectomy and returned ROM to intact levels (ROM intact 0.71 mm, discectomy 0.87 mm, post-implantation 0.72 mm). While ROM for the hydrogel implant group was statistically unchanged compared to the intact disc, ROM for sham discs, which received a discectomy and no implant, was significant increase compared to intact. The compression and tension stiffness were decreased with discectomy and remained unchanged for both implant and sham groups, as expected because the annulus fibrosus was not repaired. Gross morphology images confirmed no ejection of NP implant. Conclusion An injectable implant that mimics non-degenerate NP has the potential to return motion segment ROM to normal subsequent to injury.

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“…A significant change is the loss of proteoglycans in the central region, the nucleus. Proteoglycans attract and bind fluid, working to resist mechanical stresses in the solid matrix of the nucleus and, through hydration of the molecules, provide a hydrostatic pressure to the outer layers of the disc, the annulus, whose fibers function in tension to support these additional stresses 5. In a dehydrated disc, the function of the nucleus to transfer load to the annulus through creation of intradiscal pressure no longer occurs at a normal level.…”

mentioning

confidence: 99%

Effects of aging and degeneration on the human intervertebral disc during the diurnal cycle: A finite element study

Massey

Donkelaar

Vresilovic

et al. 2011

Journal Orthopaedic Research

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A significant biochemical change that takes place in intervertebral disc degeneration is the loss of proteoglycans in the nucleus pulposus. Proteoglycans attract fluid, which works to reduce mechanical stresses in the solid matrix of the nucleus and provide a hydrostatic pressure to the annulus fibrosus, whose fibrous nature accommodates this stress. Our goals are to develop an osmoporoelastic finite element model to study the relationship between proteoglycan content and the stress distribution within the disc and to analyze the effects of degeneration on the disc's diurnal mechanical response. Stress in the annulus increased with degeneration from $0.2 to 0.4 MPa, and an increase occurred in the center of the nucleus from 1.2 to 1.6 MPa. The osmotic pressure in the central nucleus region decreased the most with degeneration, from $0.42 to $0.1 MPa in a severely dehydrated disc. A 3% decrease in diurnal fluid lost with degeneration equated to $21% decrease in fluid exchange, and hence a decrease in nutrients that require convection to enter the disc. We quantified the increases in internal stresses in the nucleus and annulus throughout the various stages of degeneration, suggesting that these changes lead to further remodeling of the tissue. Keywords: intervertebral disc; degeneration; osmotic pressure; diurnal cycle; finite element During a diurnal cycle, the intervertebral disc experiences $16 h of functional loading (e.g., standing and sitting), followed by 8 h of recovery (lying prone). As the disc is compressed and fluid is exuded, the density of the fixed charges within the nucleus is increased, creating an osmotic gradient with the interstitial fluids surrounding the disc; this osmotic potential aids in drawing fluid back into the disc. 1The intervertebral disc changes with age and degeneration.2-4 Alterations in its major biochemical constituents coincide with aging and disc degeneration, and can subsequently alter its ability to support load. A significant change is the loss of proteoglycans in the central region, the nucleus. Proteoglycans attract and bind fluid, working to resist mechanical stresses in the solid matrix of the nucleus and, through hydration of the molecules, provide a hydrostatic pressure to the outer layers of the disc, the annulus, whose fibers function in tension to support these additional stresses.5 In a dehydrated disc, the function of the nucleus to transfer load to the annulus through creation of intradiscal pressure no longer occurs at a normal level. However, the effects of these changes on the internal stresses and strains are not well understood. Also, since proteoglycans govern fluid content in the disc, their loss with degeneration affects fluid flow into and out of the disc throughout a diurnal cycle.Poroelastic theory does not account for the effects of swelling due to osmotic pressure on the mechanical behavior of the disc. Fixed negative charges from the proteoglycans help draw fluid back into the disc after loading (and work to retain the fluid during load...

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Nucleus Implant Parameters Significantly Change the Compressive Stiffness of the Human Lumbar Intervertebral Disc

Cited by 31 publications

References 8 publications

Biomechanical characterization of an annulus-sparing spinal disc prosthesis

Biomechanical characterization of an annulus-sparing spinal disc prosthesis

An Injectable Nucleus Pulposus Implant Restores Compressive Range of Motion in the Ovine Disc

Effects of aging and degeneration on the human intervertebral disc during the diurnal cycle: A finite element study

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