Disc prolapse: evidence of reversal with repeated extension.
Prolapse (Physiological aspects)
Intervertebral disk (Research)
Intervertebral disk (Physiological aspects)
Human mechanics (Research)
|Author:||Horton, Stuart J.|
|Publication:||Name: New Zealand Journal of Physiotherapy Publisher: New Zealand Society of Physiotherapists Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2010 New Zealand Society of Physiotherapists ISSN: 0303-7193|
|Issue:||Date: March, 2010 Source Volume: 38 Source Issue: 1|
|Topic:||Event Code: 310 Science & research|
Scannell JP and McGill SM (2009): Disc prolapse: Evidence of
reversal with repeated extension. Spine 34: 344-350. (Abstract prepared
by Stuart Horton)
Aim: To create in vitro disc prolapse and then investigate whether extension or combined extension and side flexion could reverse the position of the displaced nucleus.
Methods: The C3-C6 segments of 18 porcine cervical spines were prepared, with a radio-opaque mixture injected into the C3-C4 nucleus of the intervertebral disc of each segment. The segments were placed in a servo hydraulic dynamic testing machine and subjected to repeated axial compression and flexion, or combined flexion and side flexion to create a prolapse. Radiographs were taken at regular intervals to monitor the displacement of the nucleus. Specimens that prolapsed were immediately put through a reversal test, which consisted of axial compression and extension, or combined extension and side flexion.
Results: After failure testing, two specimens had endplate fractures, five did not fail, and 11 had prolapsed. Reversal of the position of the nucleus occurred in five of the 11 prolapsed discs, but did not occur in six specimens. Disc height loss was less in the specimens that showed reversal.
Conclusion: This study showed that in a number of porcine cervical spines, a displaced portion of nucleus could be repositioned back towards the centre of the disc in response to specific loading of repetitive movement.
This basic science experiment has demonstrated in vitro that the position of the nucleus pulposus of the intervertebral disc can be influenced by directional load. This has been demonstrated in previous in vitro studies (Gill et al 1987, Krag et al 1987, Seroussi et al 1989, Shah et al 1978), which have demonstrated posterior migration of the nucleus with flexion motion and anterior migration with extension. However, this is the first study to deliberately create a prolapse and then test for reversibility.
The rationale for this study is the clinical phenomenon of centralisation (McKenzie and May 2003), which describes the abolition of peripheral pain from a distal to proximal location in response to repeated end range movement testing of the spine. A conceptual model of internal disc displacement has been used to explain this clinical observation (McKenzie and May 2003) and a system of mechanical assessment has been designed around this. Clinically, many patients with suspected discogenic pain report worsening of systems with flexion biased postures, and a reduction of symptoms with extension movements, or a combination of extension and lateral movement (Donelson et al 1991, Donelson et al 1997). This animal study attempts to add plausibility to McKenzie's model.
The authors make two important observations from this study. The first is that not all the prolapsed discs could be reversed. This matches clinical observations that not all patients with suspected disc lesions are able to centralise their symptoms using repeated end range movements. Earlier work by Donelson et al (1997) has shown that the hydrostatic mechanism of the disc must be intact for this to occur, and indeed the integrity of the annulus can be predicted by this type of mechanical assessment.
The second observation is the significant loss of disc height in the discs that did not respond. The authors hypothesise that loss of disc height prevented enough range of extension to occur before the facets stopped the movement, with less compressive force able to be exerted. Once again a clinical observation is that complete end range movement is often necessary to achieve total centralisation of patient's symptoms. Furthermore, it is not uncommon for alternative loading (eg combined positions) or force progression strategies (eg mobilisation) to be required to facilitate end range to achieve centralisation.
Porcine cervical spines are anatomically and functionally similar to human lumbar spines so their use in this experiment is justified. It is also important to remember that previous studies looking at this disc model have limited or contradictory data to support this model in the symptomatic or degenerative disc, or cervical or thoracic discs (Kolber and Hanney 2009).
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Stuart J Horton, DipMPhty, DipMDT, MPhty
Professional Practice Fellow
School of Physiotherapy, University of Otago
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