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Three-Dimensional View of Pedicle Screws after Neck Fusion

Posted on: 11/30/1999
Fusion surgery for the neck comes with complications. For example, there is the possibility that a screw will loosen, move, or break. Doctors need an accurate way to assess screw placement and results.

X-rays have been used and studied for this purpose. This is the first study to look at CT scans as a way to check on screws in the neck (cervical spine). CT scans are three-dimensional (3-D) and give the best detail of the bone. Screws are inserted to hold the bones together while fusion occurs. Putting screws through the part of the vertebra called the pedicle is the method used in this study.

The authors report concern over the use of pedicle screws in the cervical spine. The vertebrae are small in this part of the spine, and the pedicles are narrow. There isn't much room for error. Arteries and nerves can easily be damaged. A screw in the wrong place can result in permanent paralysis or disability. On the other hand, pedicle screws are less likely to loosen and give greater strength than other screw placements.

Researchers used cadavers in a pilot study. (Cadavers are human bodies preserved after death for study.) A pilot study means it's the first time something has been tried. Usually a small number of test subjects are used to see if it is going to work. If it is successful, a larger study is done after the pilot study.

In a previous study, screws were inserted into the cervical spine. For this study, each spine segment was scanned after the screws were in place. The CT scan gives a 3-D image in slices of various thicknesses. The researchers scanned each cadaver five times with different-sized slices. Radiologists read the CT scans as a success or failure for correct pedicle screw placement.

Then the specimens were opened up and the screws were looked at directly. A comparison was made between the results according to a CT scan and the actual results. Those reading the scans were correct between 50 and 74 percent of the time. Seeing the actual results compared to the CT scan gave the readers training.

In the second step of this study, a new set of cadaver cervical spines was used. Pedicle screws were inserted and CT scans taken. The readers improved to almost 90 percent accuracy. The authors report that slices of less than three millimeters give the best reading.

The authors conclude that CT scans can help show if pedicle screws are in good alignment. But it may be too soon to rely on CT images. The accuracy isn't high enough yet. More studies and better training are needed. CT scans are only as good as the reader.

Hak-Sun Kim, MD, et al. The Accuracy of Computed Tomography in Assessing Cervical Pedicle Screw Placement. In Spine. November 1, 2003. Vol. 28. No. 21. Pp. 2441-2446.

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