Ranges of Cervical Intervertebral Disc Deformation During an In Vivo Dynamic Flexion–Extension of the Neck

Yu, Yan; Mao, Haoping; Li, Jingsheng; Tsai, Tsung‐Yuan; Cheng, Liming; Wood, Kirkham B.; Li, Guoan; Thomas, D.

doi:10.1115/1.4036311

Cited by 18 publications

(10 citation statements)

References 53 publications

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“…disc volume changes, disc height differences, etc. ), as well as hydration variation 51 (as a surrogate for mechanics), and to indirectly report IVD deformation in conjunction with 3D modeling 52 . Intratissue IVD strains have been reported indirectly with combinatorial methods (e.g.…”

Section: Discussionmentioning

confidence: 99%

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In vivo intervertebral disc deformation: intratissue strain patterns within adjacent discs during flexion–extension

Wilson

Bowen

Kim

et al. 2021

Sci Rep

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The biomechanical function of the intervertebral disc (IVD) is a critical indicator of tissue health and pathology. The mechanical responses (displacements, strain) of the IVD to physiologic movement can be spatially complex and depend on tissue architecture, consisting of distinct compositional regions and integrity; however, IVD biomechanics are predominately uncharacterized in vivo. Here, we measured voxel-level displacement and strain patterns in adjacent IVDs in vivo by coupling magnetic resonance imaging (MRI) with cyclic motion of the cervical spine. Across adjacent disc segments, cervical flexion–extension of 10° resulted in first principal and maximum shear strains approaching 10%. Intratissue spatial analysis of the cervical IVDs, not possible with conventional techniques, revealed elevated maximum shear strains located in the posterior disc (nucleus pulposus) regions. IVD structure, based on relaxometric patterns of T2 and T1ρ images, did not correlate spatially with functional metrics of strain. Our approach enables a comprehensive IVD biomechanical analysis of voxel-level, intratissue strain patterns in adjacent discs in vivo, which are largely independent of MRI relaxometry. The spatial mapping of IVD biomechanics in vivo provides a functional assessment of adjacent IVDs in subjects, and provides foundational biomarkers for elastography, differentiation of disease state, and evaluation of treatment efficacy.

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Section: Discussionmentioning

confidence: 99%

“…An MRI compatible 2-bar linkage loading plate system was constructed to achieve cyclic cervical spine flexion–extension of 10°, a limit of space constraints within the MRI scanner and well inside the cervical column range of motion 52 (Fig. 1 ).…”

Section: Methodsmentioning

confidence: 99%

In vivo intervertebral disc deformation: intratissue strain patterns within adjacent discs during flexion–extension

Wilson

Bowen

Kim

et al. 2021

Sci Rep

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“…This model was further utilized to predict the mechanical behavior of the implant with different placement and joint angle of the spine. We studied the different placements of the cage with respect to the anterior–posterior axis in 0.2 mm increments from 0 to 0.8 mm, and the angle of the superior vertebra in 2° increments for a total range of 14° of rotation to simulate the in vivo range of the cervical spine 44,45 . The original angle of the superior vertebra was visually predicted to be 6°.…”

Section: Methodsmentioning

confidence: 99%

Finite element modeling to predict the influence of anatomic variation and implant placement on performance of biological intervertebral disc implants

Koga,

Kim,

Lintz

et al. 2023

JOR Spine

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BackgroundTissue‐engineered intervertebral disc (TE‐IVD) constructs are an attractive therapy for treating degenerative disc disease and have previously been investigated in vivo in both large and small animal models. The mechanical environment of the spine is notably challenging, in part due to its complex anatomy, and implants may require additional mechanical support to avoid failure in the early stages of implantation. As such, the design of suitable support implants requires rigorous validation.MethodsWe created a FE model to simulate the behavior of the IVD cages under compression specific to the anatomy of the porcine cervical spine, validated the FE model using an animal model, and predicted the effects of implant location and vertebral angle of the motion segment on implant behavior. Specifically, we tested anatomical positioning of the superior vertebra and placement of the implant. We analyzed corresponding stress and strain distributions.ResultsResults demonstrated that the anatomical geometry of the porcine cervical spine led to concentrated stress and strain on the posterior side of the cage. This stress concentration was associated with the location of failure of the cages reported in vivo, despite superior mechanical properties of the implant. Furthermore, placement of the cage was found to have profound effects on migration, while the angle of the superior vertebra affected stress concentration of the cage.ConclusionsThis model can be utilized both to inform surgical procedures and provide insight on future cage designs and can be adopted to models without the use of in vivo animal models.

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“…Note that the strains at the anterior and posterior most aspects of the disc space were in accordance with previously reported disc space strains. (68)(69)(70) Reanalysis of imaging and data from Ghiselli et al (23) Although the sample size was small (10 patients), reanalysis of flexion-extension studies in which intraoperative assessments of fusion status were also available provided insights into the diagnostic performance of strain-and rotation-based diagnosis of pseudoarthrosis. At all 20 levels that were analyzed, there was at least 10% strain at one of the adjacent levels, providing some assurance that the spines were adequately stressed.…”

Section: Disc Strains In the Absence Of Fusionmentioning

confidence: 99%

Diagnosis of spine pseudoarthrosis based on the biomechanical properties of bone

Hipp,

Mikhael,

Reitman

et al. 2024

Preprint

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BackgroundCervical spine fusion, commonly performed with generally favorable outcomes, may result in postsurgical symptoms requiring further investigation and treatment. Anterior cervical discectomy and fusion (ACDF) aims to decompress neural structures, stabilize motion segments, eliminate intervertebral motion, and promote bridging bone formation. Failure to form bridging bone may result in persistent symptoms or symptomatic pseudoarthrosis. Traditional diagnosis involves computerized tomography to detect bridging bone and/or flexion-extension radiographs to assess whether segmental motion is above specific thresholds. This paper proposes a new biomechanically based diagnostic approach to address limitations in traditional diagnostic methods. The scientific basis of this approach is that bridging bone cannot occur if the strain is greater than the failure strain of the bone.MethodsFully automated methods were used to measure disc space strains. Errors in strain measurements were assessed from simulated radiographs. Measurement error combined with the reported failure strain of trabecular bone led to a proposed strain threshold for pseudoarthrosis diagnosis post-ACDF surgery. A reanalysis of previously reported flexion-extension radiographs for asymptomatic volunteers was used to assess whether flexion-extension radiographs, in the absence of fusion surgery, can be expected to provide sufficient stress on motion segments to allow for reliable strain-based fusion assessment. The sensitivity and specificity of strain- and rotation-based pseudoarthrosis diagnosis were assessed by reanalysis of previously reported post-ACDF flexion-extension radiographs, where intraoperative fusion assessments were also available. Finally, changes in strain over time were explored through the use of 9,869 flexion-extension radiographs obtained 6 weeks to 84 months post-ACDF surgery from 1,369 patients.ResultsThe estimated error in measuring disc space strain from radiographs was approximately 3%, and the reported failure strain of bridging bone was less than 2.5%. On that basis, a 5% strain threshold is proposed for pseudoarthrosis diagnosis. Good-quality flexion-extension radiographs can be expected to stress the spine sufficiently to facilitate strain-based diagnosis of pseudoarthrosis. Reanalysis of a study in which intraoperative fusion assessments were available revealed 67% sensitivity and 82% specificity for strain-based diagnosis of pseudoarthrosis, which is comparable to rotation-based diagnosis. Analysis of post-ACDF flexion-extension radiographs revealed rapid strain reduction for up to 24 months, followed by a slower decrease for up to 84 months. When rotation is less than 2 degrees, the strain-based diagnosis differs from the rotation-based diagnosis in approximately 14% of the cases.DiscussionSteps for standardizing strain-based diagnosis of pseudoarthrosis are proposed based on the failure strain of bone, measurement error, and retrospective data. These steps include obtaining high-quality flexion-extension studies, the application of proposed diagnostic thresholds, and the use of image stabilization for conclusive diagnosis, especially when motion is near thresholds. The necessity for an accurate diagnosis with minimal radiation exposure underscores the need for further optimization and standardization in diagnosing pseudoarthrosis following ACDF surgery.

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Ranges of Cervical Intervertebral Disc Deformation During an In Vivo Dynamic Flexion–Extension of the Neck

Cited by 18 publications

References 53 publications

In vivo intervertebral disc deformation: intratissue strain patterns within adjacent discs during flexion–extension

In vivo intervertebral disc deformation: intratissue strain patterns within adjacent discs during flexion–extension

Finite element modeling to predict the influence of anatomic variation and implant placement on performance of biological intervertebral disc implants

Diagnosis of spine pseudoarthrosis based on the biomechanical properties of bone

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