General Discussions

Sometimes it will be necessary to perform a dynamic imaging study on the lumbo-sacral junction in order to determine if a compressive L7-S1 disk requires surgical intervention and specifically a L/S fusion.

You should already be performing your routine MRI of the lumbar spine with the patient in a "hyperextended" position with their lower limb extended and secured away from their body. This position will force the L7-S1 disk into the most extreme amount of herniation and compression for the best visualization. As a result of this positioning the patient may experience some heightened discomfort and additional anesthetic intervention will like be necessary in order to keep the patient comfortable and asleep.

Once you've determined if the L/S disk is causing a significant compression we want to determine wether or not the disk is "dynamic" in nature. Meaning does it move in and out of the disk space with flexion and extension of the lumbo-sacral junction. This information will help determine what course of therapy or surgical intervention is required to address the issue.

If "FLEXION" imaging is requested for planning lumbo-sacral fusion surgery the patient must be repositioned in an "inverted sphynx" position as shown in the images below.

*NOTE: It is important to perform your entire routine study including post contrast imaging prior to repositioning because you will not get them back into the same position for post contrast comparison.

The idea of this is to position the patient in the same position they will be surgically fused in (though upside down in MRI) to determine the amount of decompression that a fusion will achieve. If performing this study in CT you can place the patient in ventral recumbency just as they would be on the surgical table. This also can allow the surgeons to pre plan their surgical approach, measurements, and procedure ahead of time. To take it a step further, we can 3D print a flexed model from a CT study at a 1:1 ratio an allow the doctors to physically plan their surgery, shape plates, and measure screw depths before the surgery even begins. This alone has significantly reduced surgical times for these kinds of procedures.

The sequences for flexion imaging are: Survey, Sagittal Myelo, T2 or Dual, and T2 axials in one large stack covering from the middle of L6 to S3.

Here are a few examples of the resulting images and the change that you will notice between the flexed and extended positions.

Notice how the dynamic positioning changes the amount of compression at the L7/S1 disk space.

- Kevin Stevens

Kevin's passion for supporting and educating veterinary imaging technologists was the driving factor in the creation of VIRA. He has been working in medical imaging since 2002 and began working in veterinary imaging in 2010. He is an ARRT registered technologist in radiography and magnetic resonance imaging. Aside from medicine, Kevin is a visual artist, recording artist, outdoor enthusiast, and coffee addict. He currently lives in Ottawa, Ontario, Canada.