Dynamic Cervical "Distraction"
Dynamic imaging of the cervical spine may be warranted in order to evaluate the extension of a disc compression versus the presence of “Wobblers Disease” or facet hypertrophy. Similar to lumbo-sacral dynamic imaging, extending the neck can allow you to appreciate dynamic changes to the compression of the spinal cord. Dynamic imaging will be added as additional sequences after your normal imaging study. Typically this is accomplished with myelographic, T2 sagittal, and T2 axial dynamic images. It is usually ideal to perform pre and post imaging prior to dynamic changes in order for the pre and post images to match.
There are multiple ways to perform dynamic imaging of the cervical spine and they all come with certain risks. Any dynamic imaging should be performed under the direct supervision of a doctor. The first method is hyperextension with a bolster. In this method, with the patient in dorsal recumbency, place a foam bolster or rolled up towel under the middle of the patient’s neck. This method has several drawbacks as the amount of dynamic changes is inconsistent across the cervical spine with the most extreme pressure in the middle of the neck. The patient should be placed in this position very carefully to avoid additional injury to the neck. If there is any significant instability in the neck compromising the spinal cord this method should be strictly avoided.
The second and more widely accepted type of dynamic positioning is with the use of “traction” called a distraction imaging technique. Commonly, this is accomplished by suspending a weight off the end of the table which straightens and extends or “distracts” the vertebrae in the neck. With this method the pressure is uniform across the neck allowing for a dynamic evaluation of each disk space.
The weight used to achieve proper distraction is very specific and must be calculated for each patient. This methodology requires a weight equivalent to 20% of the patient’s body weight. The weight can consist of a number of IV fluid bags placed into a sack with the understanding that one 1000ml bag of saline weighs 1kg. For example: if the patient is 30kg then 20% of that is 6kg. Therefore 6 one liter saline bags can be used as the distraction weight. The weight is then secured to the patient’s head/canine teeth and suspended off of the end of the table.
* There are several very important things to note before attempting this procedure. 1) be very careful to secure the weight so that it doesn’t put uneven pressure on weak teeth or cut into the gums and that any connection should not compromise the jugular veins or carotid arteries. 2) This should be only performed under direct supervision of a doctor and the weight should be added slowly and gently. 3) the patient couch must not move and drag or drop the weight if it is not otherwise suspended by a fixed point.
The results of this study can also reveal if surgical fusion of the neck is necessary in order to resolve a dynamic compression in the cervical spine. The same traction technique can even be repeated in surgery to reproduce the exact amount of dynamic traction used for the imaging.