The internal mechanical properties of cervical intervertebral discs as revealed by stress profilometry

Abstract

Extensive anatomical differences suggest that cervical and lumbar discs may have functional differences also. We investigated human cervical discs using ''stress profilometry''. Forty-six cadaveric cervical motion segments aged 48-90 years were subjected to a compressive load of 200 N for 20 s, while compressive 'stress' was recorded along the posterior-anterior midline of the disc using a pressure transducer, side-mounted in a 0.9 mm diameter needle. Stress profiles were repeated with the transducer orientated horizontally and vertically, and with the specimen in neutral, flexed and extended postures. Profiles were repeated again following creep loading (150 N, 2 h) which simulated diurnal water loss in vivo. Stress profiles were reproducible, and measured ''stress'' at each location was proportional to applied load. Stress profiles usually showed a hydrostatic nucleus with regions of higher compressive stress concentrated anteriorly in flexion, and posteriorly in extension. Stress concentrations increased in degenerated discs and following creep. Some features were unique to cervical discs: many showed a stress gradient across their central regions, even though vertical and horizontal stresses were equal to each other, and stress concentrations in the posterior annulus were generally small. Central regions of many cervical discs show the characteristics of a ''tethered fluid'' which can equalise stress over small distances, but not large. This may be attributable to their fibrous texture. The small radial diameter of the cervical posterior annulus may facilitate buckling and thereby prevent it from sustaining high compressive stresses.

Non-invasive biomechanical characterization of intervertebral discs by shear wave ultrasound elastography: a feasibility study

“…It is likely that a significant portion of the annulus thickness, in the radial direction, was included in the ROI: Skrzypiec et al (Skrzypiec et al, 2007) reported an average frontal thickness of about 7 mm for the annulus, which is similar to the thicknesses observed in b-mode image (Figure 1).…”

Disc herniations in astronauts: What causes them, and what does it tell us about herniation on earth?

“…Data from studies on Earth show that some degree of cervical spine lengthening occurs with recumbency [26,27]. There are a number of differences between cervical and lumbar discs: in composition [28], anatomy [29] and biomechanical characteristics [30]. However, these data do not help us understand why the risk of IVD herniation is much more elevated at the cervical spine than at the lumbar spine in astronauts.…”

Biodegradable Xylitol‐Based Polymers

“…[18,19] In addition, the mechanical properties of xylitolbased elastomers correspond to biologically relevant values that fall close to or are equal to those of various tissues, such as acellular peripheral nerves, [20] small diameter arteries, [21] cornea [22] and intervertebral discs. [23] In this report, we have shown only three examples of possible polymers based on this monomer. Potential combinations for the chemical composition of xylitol-based polymers are numerous and therefore it provides a platform to tune mechanical properties, degradation profiles and cell attachment.…”