Internal Intervertebral Disc Mechanics as Revealed by Stress Profilometry

McNally, Donal; Adams, Michael A.

doi:10.1097/00007632-199201000-00011

Cited by 321 publications

(191 citation statements)

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“…This was not surprising since the calf specimens all had healthy, not degenerated discs, which was not the case for the human specimens [2,10]. Small interindividual differences are advantageous since implant-related trends such as the suppression of the pressure increase in extension with the Coflex implant can more clearly be depicted.…”

Section: Discussionmentioning

confidence: 95%

Are the spines of calf, pig and sheep suitable models for pre-clinical implant tests?

et al. 2007

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Pre-clinical in vitro tests are needed to evaluate the biomechanical performance of new spinal implants. For such experiments large animal models are frequently used. Whether these models allow any conclusions concerning the implant's performance in humans is difficult to answer. The aim of the present study was to investigate whether calf, pig or sheep spine specimens may be used to replace human specimens in in vitro flexibility and cyclic loading tests with two different implant types. First, a dynamic and a rigid fixator were tested using six human, six calf, six pig and six sheep thoracolumbar spine specimens. Standard flexibility tests were carried out in a spine tester in flexion/ extension, lateral bending and axial rotation in the intact state, after nucleotomy and after implantation. Then, the Coflex interspinous implant was tested for flexibility and intradiscal pressure using another six human and six calf lumbar spine segments. Loading was carried out as described above in the intact condition, after creation of a defect and after implantation. The fixators were most easily implantable into the calf. Qualitatively, they had similar effects on ROM in all species, however, the degree of stability achieved differed. Especially in axial rotation, the ROM of sheep, pig and calf was partially less than half the human ROM. Similarly, implantation of the Coflex interspinous implant caused the ROM to either increase in both species or to decrease in both of them, however, quantitatively, differences were observed. This was also the case for the intradiscal pressure. In conclusion, animal species, especially the calf, may be used to get a first idea of how a new pedicle screw system or an interspinous implant behaves in in vitro flexibility tests. However, the effects on ROM and intradiscal pressure have to be expected to differ in magnitude between animal and human. Therefore, the last step in pre-clinical implant testing should always be an experiment with human specimens.

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Section: Discussionmentioning

confidence: 95%

Are the spines of calf, pig and sheep suitable models for pre-clinical implant tests?

et al. 2007

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“…The stresses in the outer disc differ from those found in the central disc. Here compressive stresses are predominant, whereas in the outer annulus there is only a small compressive but large tensile component [14].…”

Section: Discussionmentioning

confidence: 99%

Does the thickness of the vertebral subchondral bone reflect the composition of the intervertebral disc?

et al. 1997

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Degeneration of the intervertebral disc, seen radiologically as loss of disc height, is often associated with apparent remodelling in the adjacent vertebral body. In contrast, maintenance or apparent increase in disc height is a common finding in osteoporosis, suggesting the properties of the intervertebral disc may be dependent on those of the vertebral body or vice versa. We have investigated this relationship by measuring the radiological thickness of the subchondral bone and comparing it to the chemical composition of the adjacent disc. Sagittal slabs were sampled from lumbar spines obtained at autopsy and X-rayed microfocally. The thickness of the subchondral bone was measured and correlated with the composition of the adjacent intervertebral disc. Eighty-three cadaveric endplates were studied from individuals aged 17-85 years. There was regional variation in thickness of the subchondral bone, being greater adjacent to the annulus than the nucleus, and the endplates cranial to the disc were thicker than those caudal. There was a positive correlation between the thickness of the subchondral bone and the proteoglycan content of the adjacent disc, particularly in the region of the nucleus. A weaker correlation was seen here between water content and thickness, whilst there was no significant correlation at the annulus or between the bone thickness and collagen content. The positive relationship between the radiographic thickness of vertebral subchondral bone and the proteoglycan content of the adjacent disc seen in human cadaveric material could be due to the bone responding to a greater hydrostatic pressure being exerted by discs with higher proteoglycan content than by those with less proteoglycan present. It is suggested that while this is true in "normal" specimens, the relationship becomes altered in disease states, possibly because of changes to the nutritional pathway of the disc, with resultant endplate-bone remodelling affecting the flow of solutes to and from the intervertebral disc.

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“…The normal disc is isotropic that is to say that it behaves liked a fluid filled bag, and transmits load uniformly across the surface of the disc and to the endplate [27]. This has a number of important biomechanical consequences.…”

Section: The Intervertebral Discmentioning

confidence: 99%

“…Another important consequence of the uniformity of distribution of load transmission across the surface of the disc is that it transmits load to the annulus, producing a tension in the annulus, and converting it into a loadbearing structure. It is established that disc degeneration alters the isotropic nature of the disc [19,27] and, as a consequence, load transmission over the endplate becomes irregular, leading to high spot-loading, particularly associated with certain positions. It will be appreciated that the degree of disc degeneration itself will not affect to the loading pattern, as the anatomy of the degenerate disc is so varied.…”

Section: The Intervertebral Discmentioning

confidence: 99%

“…Using the technique developed by McNally [27], it was therefore possible for us to carry out a profilometry immediately before the discography at each level examined. Discs which demonstrated that the nucleus was taking no load, that is, it was all annular load, or discs that had very focal areas of high load were the painful discs.…”

Section: Biomechanics Of the Disc And Relation To Load Bearingmentioning

confidence: 99%

See 1 more Smart Citation

The myth of lumbar instability: the importance of abnormal loading as a cause of low back pain

Mulholland¹

2008

Eur Spine J

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Internal Intervertebral Disc Mechanics as Revealed by Stress Profilometry

Cited by 321 publications

References 0 publications

Are the spines of calf, pig and sheep suitable models for pre-clinical implant tests?

Are the spines of calf, pig and sheep suitable models for pre-clinical implant tests?

Does the thickness of the vertebral subchondral bone reflect the composition of the intervertebral disc?

The myth of lumbar instability: the importance of abnormal loading as a cause of low back pain

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