Quantification of cord deformation and dynamics during flexion and extension of the cervical spine using MR imaging

The magnetic resonance (MR) cine display of flexion and extension (F/E) manoeuvres in the cervical spine has proved useful in the evaluation of cord compression due to bone and joint instability, spondylosis, and multiple tumours. It has advantages over X-ray F/E and CT myelography in that it is noninvasive and produces images with high soft tissue contrast. The MR F/E technique does have its limitations, however, in that each structure in the images has a degree of independent movement and rotation that can make visual interpretation difficult. It also does not address the problem of assessing the relative significance of each lesion where numerous lesions may be present, for example, in compression due to spondylosis, rheumatoid arthritis, or neurofibromatosis. In this paper a novel technique is described that produces quantitative indices of cord deformation and dynamics during MR F/E. A computer program automatically calculates a series of contiguous profiles perpendicular to the cord throughout its length and for each image in the manoeuvre. Orthogonal polynomial curve fitting techniques are used to fit these profiles and extract statistical parameters that are quantitative indices of deformation and dynamics. The four main parameters calculated are kurtosis as an index of bilateral cord compression, skewness as an index of unilateral or asymmetric contact pressure, angulation as a measure of cord deformation about a lesion, and anteroposterior cord width as a direct measure of indentation and attenuation. Illustrative examples of results from normal volunteers and patients suffering from cervical myelopathy are presented. The technique may prove particularly useful to the spinal surgeon in assessing the relative significance of individual lesions and may also be a powerful research tool in the study of cord biomechanics in the living body.