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Assessment of the dynamic disc model in the cervical spine: the role of McKenzie’s conceptual model of disc displacement

Elmaazi, Areej (2016) Assessment of the dynamic disc model in the cervical spine: the role of McKenzie’s conceptual model of disc displacement. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The effects of lumbar spine posture on position of the lumbar disc has been extensively researched in the literature, with findings supporting early assertions that flexed postures, through vertebral loading of the anterior disc, cause posterior disc displacement with extended postures causing anterior displacement. This loading is thought to occur through anterior and posterior approximation of the vertebral segments in flexed and extended postures respectively. The late Robin McKenzie, a world renowned and accredited physiotherapist, promoted this concept of disc displacement through spinal loading. With this biomechanical reasoning, he created a series of spinal exercises, now taught worldwide, aimed at repositioning herniated disc material for those presenting with what he termed to be a ‘derangement syndrome’. To date, there have been no published studies that have assessed whether cervical flexion and extension cause an alteration in position of the cervical disc in the same pattern of movement that has been shown to occur in the lumbar spine. There have also been no direct measurements of cervical disc position following performance of one of McKenzie’s extension based exercises. Therefore, the aim of this programme of studies was to assess the effects of three cervical postures on position of the posterior NP at the C5-6 and C6-7 disc levels in an asymptomatic population. It also aimed to assess whether McKenzie’s ‘retraction-extension exercise in sitting’ produced anterior displacement of the posterior NP at the C5-6 and C6-7 disc levels in a symptomatic population. Measurements were also taken of vertebral segment angles in three cervical postures to assess whether approximation of the vertebral segments occurred in a similar pattern as has been shown to occur in the lumbar spine. Cervical MR images were obtained from asymptomatic participants positioned in supine with their cervical spines in a neutral, followed by a flexed and finally an extended position. These images were used to assess the effects of posture on anterior and posterior C5-C6 to C7-T1 vertebral position, as well as on position of the posterior C5-6 and C6-7 posterior NP. The second group of symptomatic participants were scanned before and after performance of McKenzie’s retraction-extension exercise in sitting. Findings support the assertion that vertebral position and position of the posterior cervical disc can be manipulated by posture. Results showed significant changes in both anterior and posterior vertebral position in flexion compared to neutral, as well as significant changes in the posterior nucleus pulposus at both disc levels in flexion compared to neutral and extension. McKenzie’s retraction-extension exercise in sitting was found to cause anterior displacement of the posterior NP at the C5-6 disc level. These findings support the assertion that, compared to a neutral head posture, a flexed head posture causes a significant degree of posterior disc nucleus displacement. Therefore, avoiding a flexed head posture, and maintaining a neutral head position, may help to reduce the potential for developing pain provocative posterior disc herniations. These findings also help support the reasoning behind McKenzie’s extension-based retraction-extension exercise in sitting for those presenting with spinal pain classified as a ‘derangement syndrome’. Further research assessing various cervical postures in sitting will provide further information regarding the effect of a common occupational posture on cervical disc and vertebral angle position.

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