Effects of Cervical Extension on Deformation of Intervertebral Disk and Migration of Nucleus Pulposus

Characterizing baseline fixed charge density in human cervical intervertebral discs

This study provides quantification of fixed charge density in human cervical intervertebral discs. Fixed charge density, which occurs due to negatively charged proteoglycans in the extracellular matrix, is a key determinant of the intervertebral disc osmotic environment and swelling properties. While regional fixed charge density patterns have been characterized in lumbar discs, they remain unexplored in cervical discs. Using fresh-frozen cadaveric cervical discs from five donors, fixed charge density was measured using a two-point electrical conductivity method. Glycosaminoglycan content and porosity were also assessed. Fixed charge density (0.18 ± 0.1 mEq/g wet tissue) was highest in the cartilage endplate region and significantly greater than in that in the annulus fibrosus (p = 0.006). No significant difference in fixed charge density was observed between the nucleus pulposus and annulus fibrosus. Glycosaminoglycan content (40.3 ± 14.4 µg/mg wet tissue) showed a strong positive correlation with fixed charge density across regions (r = 0.65, p = 0.0047). Unlike lumbar discs, fixed charge density was found to be more homogeneous between the nucleus pulposus and annulus fibrosus regions. This result likely reflects adaptations for reduced tissue swelling in cervical discs to accommodate lower weight-bearing demands and increased flexibility. The elevated fixed charge density in the cervical endplates may protect the intervertebral disc-vertebral bone interface, potentially to avoid mechanical damage in a kinematically more mobile environment. These findings establish key benchmarks for understanding cervical disc electro-biomechanics and may inform other cervical disc tissue-characterization efforts.

Disc measurement and nucleus calibration in a smoothened lumbar model increases the accuracy and efficiency of in-silico study

Backgrounds

Finite element analysis (FEA) is an important tool during the spinal biomechanical study. Irregular surfaces in FEA models directly reconstructed based on imaging data may increase the computational burden and decrease the computational credibility. Definitions of the relative nucleus position and its cross-sectional area ratio do not conform to a uniform standard in FEA.

Methods

To increase the accuracy and efficiency of FEA, nucleus position and cross-sectional area ratio were measured from imaging data. A FEA model with smoothened surfaces was constructed using measured values. Nucleus position was calibrated by estimating the differences in the range of motion (RoM) between the FEA model and that of an in-vitro study. Then, the differences were re-estimated by comparing the RoM, the intradiscal pressure, the facet contact force, and the disc compression to validate the measured and calibrated indicators. The computational time in different models was also recorded to evaluate the efficiency.

Results

Computational results indicated that 99% of accuracy was attained when measured and calibrated indicators were set in the FEA model, with a model validation of greater than 90% attained under almost all of the loading conditions. Computational time decreased by around 70% in the fitted model with smoothened surfaces compared with that of the reconstructed model.

Conclusions

The computational accuracy and efficiency of in-silico study can be improved in the lumbar FEA model constructed using smoothened surfaces with measured and calibrated relative nucleus position and its cross-sectional area ratio.

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

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 T_1ρ 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.

Classification by pain pattern for patients with cervical spine radiculopathy

OBJECTIVES

A prospective observational cohort study was conducted to (1) report the prevalence of Mechanical Diagnosis and Therapy (MDT) classifications, Centralization (CEN), and Non-CEN among patients with Cervical Spine Radiculopathy (CSR), and (2) describe the association between classification via CEN and Non-CEN and clinical outcomes at follow-up.

METHODS

Data were collected from 680 consecutive patients who presented to outpatient, orthopedic physical therapy clinics with primary complaints of neck pain with and without radiculopathy; thirty-nine patients (6%) met the physical examination inclusion criteria for CSR. First examination and follow-up data were completed by 19 patients.

RESULTS

Seventy-nine percent of patients' conditions were classified as Reducible Derangement at first examination and 21% were classified as either Irreducible Derangement, Entrapment, or Mechanically Inconclusive. The prevalence of CEN and Non-CEN was 36.8% and 47.4%, respectively. All patients treated via MDT methods made clinically significant improvements in disability, but not pain intensity, at follow-up. The magnitude of change in clinical outcomes was greatest for patients who exhibited CEN; however, the changes in disability and pain intensity at follow-up were not statistically significant compared to patients who exhibited Non-CEN at first examination. Patients who exhibited CEN were discharged, on average, ten days earlier and had one less treatment visit compared to patients who exhibited Non-CEN.

DISCUSSION

The findings of this study show that patients with CSR can be classified and treated via MDT methods and experienced clinically significant improvements in disability, but not pain intensity, at follow-up. Providers should consider MDT classification and treatment to improve clinical outcomes for their patients affected by CSR.

The acute response of the nucleus pulposus of the cervical intervertebral disc to three supine postures in an asymptomatic population

BACKGROUND

The dynamic disc model refers to the ability of a spinal disc's position to be manipulated by body postures and movements. Research on lumbar discs has indicated movement of the anterior and posterior disc that correlates with posture of the spine. The aim of this study was to assess whether, despite its structural differences, the cervical disc responds to flexed and extended postures in a similar fashion to the lumbar disc.

METHOD

A repeated measures study. Twenty five asymptomatic participants (age: 33.7 ± 9.1 years) volunteered. Scans were performed in supine using an Esaote 0.2T magnetic resonance imaging scanner. Participants lay with their cervical spine initially placed in neutral, followed by flexion and finally extension. The position of the posterior disc nucleus pulposus at C5-6 and C6-7 was measured against a vertical line connecting the posterior vertebral bodies above and below each disc.

RESULTS

Changes in cervical spine position were associated with significant changes in posterior disc nucleus pulposus position at both C5-6 and C6-7 (p < 0.01 for both). Post hoc testing showed a significant difference in posterior disc nucleus pulposus position at C5-6 between flexion and extension (p = 0.02). There was similarly a significant change at C6-7 between neutral and flexion (p = 0.001), and between flexion and extension (p = 0.02).

CONCLUSIONS

These results indicate that the cervical posterior nucleus pulposus is affected by spinal loading, consistent with the concept of the dynamic disc model.

A Dynamic Magnetic Resonance Imaging Study of Changes in Severity of Cervical Spinal Stenosis in Flexion and Extension

Objective

To evaluate changes in the severity of cervical spinal stenosis (CSS) in flexion and extension and determine whether the rate of change with motion varied with severity.

Methods

The study included 92 symptomatic patients with a mean age of 57.80±10.41, who underwent cervical spine dynamic magnetic resonance imaging. The severity of stenosis was evaluated using a semi-quantitative CSS score, ranging from 0 (no spinal stenosis) to 18 (severe stenosis). Radiological evaluation included flexion, neutral, and extension measurements, as determined by the C2–C7 Cobb angle. The severity of stenosis was represented by the total CSS score. The total CSS score in flexion, neutral, and extension positions was compared using repeated measures one-way analysis of variance. The change rate of stenosis per angle motion (CRSPAM) was defined as change in total CSS score divided by change in Cobb angle. The correlation of CRSPAM with severity of stenosis, represented by total CSS score in neutral position, was evaluated using Pearson correlation analysis.

Results

The total CSS score was significantly higher in extension (6.04±2.68) than in neutral position (5.25±2.47) (p<0.001), and significantly higher in neutral than in flexion position (4.40±2.45) (p<0.001). The CRSPAM was significantly and positively correlated with total CSS score in neutral position in the flexion-extension range (r=0.22, p=0.04) and flexion-neutral range (r=0.27, p=0.01).

Conclusion

In symptomatic CSS patients, the radiological severity of stenosis increases with extension and decreases with flexion. In patients with CSS, the rate of variation in spinal stenosis increases with increased severity.