Spondylolisthesis and Stability

The technique:

Both views use the same technique as neutral lateral lumbars; 40" FFD, no tube tilt, central ray aimed at the top of the iliac crest (works for both L4 and L5 spondylos), 90 kVp, whatever mAs is calculated for patient thickness. You can use a smaller film (8" x 10") for this because you're only interested in the listhetic area. Be certain to collimate to less than film size. Specifics for positioning are given below.


You need to have some type of hanging bar support situated so that the patient can grab it and hang (remember monkey bars as a kid??). The toes can just touch the ground so that the patient doesn't sway. I have the patient perform this once quickly so that I can then determine the level of the film and tube and then get everything set up. When the patient assumes the position, produce the exposure as soon as possible.


We use a standard backpack with about 50 pounds of sand inside. It goes on both shoulders and we have the patient amble about the room for a couple of minutes (we tried for 5 but that was too long). Use common sense here, don't drop the pack on their shoulders. I don't think we've ever had someone that couldn't tolerate the pack because of pain and we've had some ptosed spondlyos. Position the patient and then produce the exposure.


The mensuration landmarks need to be visible on both traction and compression films. Place a dot on the posteroinferior corner of the listhetic vertebrae, another on the posterior edge of the vertebrae just inferior (prob the sacrum) and another on the anterior edge of the inferior vert (sacrum again). Connect the two lines on the inferior vertebrae then draw a perpendicular to that line that passes through the posteroinferior dot of the listhetic vertbrae. Three (3) mm change from traction to compression is defined as an unstable vertebrae.