The effect of ex vivo flexion and extension on intervertebral foramina dimensions in the equine cervical spine

Abstract

Reasons for performing study: In dressage, the head and neck position has become an issue of concern as certain extreme positions may imply a welfare risk for the horse. In man, extension and flexion of the cervical spine cause a decrease and increase in intervertebral foramina dimensions, respectively. However, in horses, the influence of flexion and extension on foramina dimensions and its possible interference with peripheral nerve functioning remains unknown.Objectives: To determine the effect of ex vivo flexion and extension on intervertebral foramina dimensions in the equine cervical spine. Methods: Computed tomography was performed on 6 cadaver cervical spines from adult Warmblood horses subjected to euthanasia for reasons unrelated to cervical spine abnormalities, in a neutral position, in 20 and 40° extension, and in 20 and 40° flexion. Multiplanar reconstructions were made to obtain transverse images perpendicular to the long axis of each pair of intervertebral foramina from C2-T1. Intervertebral foramina dimensions were measured in the 5 positions. Results: Compared to the neutral position, 40° extension caused a decrease in foramina dimensions at segments C4-C5, C5-C6, C6-C7 (P<0.001) and C7-T1 (P<0.002); 20° extension caused a decrease in foramina dimensions at segments C5-C6 (P<0.02), C6-C7 (P<0.001) and C7-T1 (P<0.01); 20° flexion caused an increase in foramen length at segment C6-C7 (P<0.01).Conclusions: Ex vivo extension of the cervical spine causes a decrease in intervertebral foramina dimensions at segments C4-T1, similar to that found in man.Potential relevance: In vivo extension of the cervical spine could possibly interfere with peripheral nerve functioning at segments C4-T1. This effect may be even more profound in patients with a reduced intervertebral foramina space, for example in the presence of facet joint arthrosis. © 2010 EVJ Ltd.