Three-dimensional intervertebral kinematics in the healthy young adult cervical spine during dynamic functional loading

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If intervertebral disc degeneration can be identified early, preventative treatments may be initiated before symptoms become disabling and costly. Changes in disc mechanics, such as the decrease in the compressive modulus of the nucleus, are some of the earliest signs of degeneration. Therefore, in vivo changes in the disc response to compressive load may serve as a biomarker for pending or early disc degeneration. The aim of this study was to assess the potential for using in vivo dynamic disc deformation to identify pathologic structural degeneration of the intervertebral disc. A validated model‐based tracking technique determined vertebral motion from biplane radiographs collected during dynamic flexion/extension and axial rotation of the cervical spine. A computational model of the subaxial intervertebral discs was developed to identify the dynamic functional nucleus of each disc, that is, the disc region that underwent little to no additional compression during dynamic movements. The size and location of the dynamic functional nucleus was determined for 10 C5/C6 spondylosis patients, 10 C5/C6/C7 spondylosis patients, and 10 asymptomatic controls. The dynamic functional nucleus size was sensitive (significantly smaller than controls in 5 of 6 measurements at the diseased disc) and specific (no difference from controls in 9 of 10 measurements at non‐diseased discs) to pathologic disc degeneration. These results provide evidence to suggest that structural disc degeneration, manifested by changes in the disc response to functional loading, may be identified in vivo from dynamic imaging collected during functional movements. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1–7, 2019.

Section: Methodsmentioning

confidence: 99%

Dynamic functional nucleus is a potential biomarker for structural degeneration in cervical spine discs

LeVasseur

Wawrose

Pitcairn

et al. 2019

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“…These limitations were initially addressed individually, by using MRI images to track three‐dimensional spine kinematics in static supine positions, and by using single‐plane fluoroscopic imaging in combination with computer software to automatically track two‐dimensional dynamic vertebral body movement . More recently, imaging systems have been developed to collect synchronized biplane radiographs during functional three‐dimensional movements . Several groups have demonstrated that vertebral motion can be tracked with an accuracy of better than 1 mm and one degree during dynamic multi‐planar movements using this technology .…”

Section: Advances In Technologymentioning

confidence: 99%

“…). This novel imaging and tracking technology has recently been combined with custom computational algorithms to characterize cervical spine mechanics in young healthy adults, in middle‐aged asymptomatic adults and arthrodesis patients, and in arthrodesis and arthroplasty patients …”

Section: Advances In Technologymentioning

confidence: 99%

“…These studies have indicated that, progressing from the cranial to caudal motion segments, the center of rotation is located increasingly more superior and anterior relative to the inferior vertebra of each motion segment . Dynamic biplane radiography has revealed that intervertebral rotation does not occur about a fixed point during functional spine motion, and that the path of the center of rotation (i.e., the centrode), varies among motion segments during flexion/extension (Fig. ) and during multi‐planar movements (Fig.…”

Section: Cervical Spine Kinematicsmentioning

confidence: 99%

“…Dynamic biplane radiography has revealed that intervertebral rotation does not occur about a fixed point during functional spine motion, and that the path of the center of rotation (i.e., the centrode), varies among motion segments during flexion/extension (Fig. ) and during multi‐planar movements (Fig. ).…”

Section: Cervical Spine Kinematicsmentioning

confidence: 99%

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Narrative review of the in vivo mechanics of the cervical spine after anterior arthrodesis as revealed by dynamic biplane radiography

Anderst

2015

Arthrodesis is the standard of care for numerous pathologic conditions of the cervical spine and is performed over 150,000 times annually in the United States. The primary long-term concern after this surgery is adjacent segment disease (ASD), defined as new clinical symptoms adjacent to a previous fusion. The incidence of adjacent segment disease is approximately 3% per year, meaning that within 10 years of the initial surgery, approximately 25% of cervical arthrodesis patients require a second procedure to address symptomatic adjacent segment degeneration. Despite the high incidence of ASD, until recently, there was little data available to characterize in vivo adjacent segment mechanics during dynamic motion. This manuscript reviews recent advances in our knowledge of adjacent segment mechanics after cervical arthrodesis that have been facilitated by the use of dynamic biplane radiography. The primary observations from these studies are that current in vitro test paradigms often fail to replicate in vivo spine mechanics before and after arthrodesis, that intervertebral mechanics vary among cervical motion segments, and that joint arthrokinematics (i.e., the interactions between adjacent vertebrae) are superior to traditional kinematics measurements for identifying altered adjacent segment mechanics after arthrodesis. Future research challenges are identified, including improving the biofidelity of in vitro tests, determining the natural history of in vivo spine mechanics, conducting prospective longitudinal studies on adjacent segment kinematics and arthrokinematics after single and multiple-level arthrodesis, and creating subject-specific computational models to accurately estimate muscle forces and tissue loading in the spine during dynamic activities.

The effects of age, pathology, and fusion on cervical neural foramen area

LeVasseur

Pitcairn

Shaw

et al. 2020

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Cervical radiculopathy is a relatively common neurological disorder, often resulting from mechanical compression of the nerve root within the neural foramen. Anterior cervical discectomy and fusion (ACDF) is a common treatment for radicular symptoms that do not resolve after conservative treatment. One mechanism by which ACDF is believed to resolve symptoms is by replacing degenerated disc tissue with bone graft to increase the neural foramen area, however in vivo evidence demonstrating this is lacking. The aim of this study was to evaluate the effects of age, pathology, and fusion on bony neural foramen area. Participants included 30 young adult controls (<35 years old), 23 middle‐aged controls (36 to 60 years old), and 36 cervical arthrodesis patients tested before and after ACDF surgery. Participants’ cervical spines were imaged in the neutral, full flexion, and full extension positions while seated within a biplane radiography system. A validated model‐based tracking technique determined three‐dimensional vertebral position and orientation and automated software identified the neural foramen area in each head position. The neural foramen area decreased throughout the entire sub‐axial cervical spine with age and pathology, however, no changes in neural foramen area were observed due solely to replacing degenerated disc tissue with bone graft. The neural foramen area was not associated with disc height in young adult controls, but moderate to strong associations were observed in middle‐aged controls. The results provide evidence to inform the debate regarding localized versus systemic spinal degeneration and provide novel insight into the mechanism of pain relief after ACDF.