Lumbar Spine Obliques

Even on a patient with normal anatomy, lumbar spine obliques can be quite a challenge no matter how many years of experience you have. If you've memorized the "scotty dog" anatomy, that's great and it will come into play during the critique of your images, but a basic understanding of how the anatomy is laid out in planes is good to know before you begin your positioning.

On most patients, the cervical spine is in the same plane as the lumbar spine, and this can prove to be a valuable positioning tool if utilized properly. In other words, if a patient is lying on their back and you had do take a tomo slice of the c-spine, the same exact tomo slice, centered over the lumbar spine would work as well. Additionally, if you look at a (normal) spine in the anatomical position, then rotate that spine 90 degrees, you could draw a straight line extending from the cervical spine down to the lumbar spine and it will be in the same plane.



So if you can go from AP to lateral with the C and L-spines in the same plane, then you should be able to go half-way (into an oblique position) and still have them in the same plane.



Of course, it's easy to demonstrate this with elaborate stick-man drawings, but it requires a bit of forethought when doing this on a patient. I like to use a radiolucent pad on the table for a couple of reasons... one, it's just mean not to when you have one available, and two, it is a valuable positioning tool when there is a sheet underneath it. It can easily be slid with a patient on it to better align or even help rotate the patient.

So, with the patient on a pad, position and shoot your AP film. I like to perform the RPO next, so I would inform the patient that I am going to roll them. If it is a small enough patient, it's easy to roll them instead of giving them instructions to roll. When they roll, they usually slide their hips over before rolling one way or the other. You can simply grab your 45 degree sponge and be ready to lift. Grab the pad by the patient's shoulders with one hand and hips with another. Slide them away from the center of the table if necessary so you don't roll them on the floor. Roll them up placing the sponge underneath the pad to the desired position. The sponge shouldn't slip if it's directly on the table.

If your patient is too heavy to do this with, some simple instructions will prevent them from shifting their hips, misaligning your C and L-spines. For RPO, have them bend their left knee. Then have them reach their left arm across their chest. Standing on their right side, place one hand on the left shoulder and the other on their left knee and just assist them while they roll. Wedge your sponge underneath and you're all set.

Once obliqued, align the L-spine and center your tube like you normally do. Now you have another way to check your positioning... go to the head of the table and see whether or not your central ray is in the same plane as your cervical spine. This only works when the patient does not slide their hips. Make minor adjustments as needed and check your results.

For conventional centering, it's always a good review to know the "finger-width" measurements that work for you. Look at an L-spine oblique film on an average sized patient that's centered well (print one out if you need to in order to get "actual size).



On the printed image, check to see how many fingers it takes you to place the horizontal crosshair at the center of L-3's vertebral body. Then see how many finger-widths it takes from the ASIS to the center of L-3. This should be a film that you performed, and it should be positioned exactly the same with each patient. If the patient is not obliqued the same amount, then the distance from the ASIS to L-3 will change. This is the most accurate way to know what works for you. You may have learned this in school, but I would bet that the person teaching you this had different sized fingers than you, and you have to measure this for yourself. The same thing goes with your spot film.

For laterals and spot films, you still need to keep the C and L-spine in the same plane, but the most common errors are in over/under-rotation - not the whole body, but in the shoulders and hips not being in the same plane. But that's another post...