Using Low-Dose, Biplanar Imaging to Reduce Screw Misplacement

With pedicle shapes and sizes varying wildly in the scoliotic spine, misplacement of a screw—as well as and under- or oversizing—are real possibilities in spine surgery. A team from The Netherlands banded together to determine if preoperative EOS images for pedicle size measurements in idiopathic scoliosis patients could reliably minimize screw misplacement.

Their work, “Assessment of pedicle size in patients with scoliosis using EOS 2D imaging: a validity and reliability study,” was published in the April 25, 2021 edition of the European Spine Journal.

Co-author Carlo Peeters, a physician in training with the Department of Orthopaedics at the University of Groningen explained to OTW how pedicle screw misplacement remains one of the key concerns for spine surgeons. “Posterior spinal instrumentation and fusion with pedicle screws is regarded as a safe and effective procedure in the majority of the patients but appropriate placement of well-sized pedicle screws can be challenging in scoliosis due to the different morphometric characteristics of the pedicle dimensions and vertebral rotation.”

“There is a wide variation in pedicle shapes and sizes in a scoliotic spine. Consequently, screw misplacements and under- or oversizing are risks. This subsequently increases the risk of neurologic or vascular injury, pedicle fracture, and screw loosening.”

Before the advent of advanced, intelligent imaging and navigation tools, free-hand pedicle screw insertion methods was standard of care. These new “smart” imaging and navigation tools gives surgeons valuable preoperative information to minimize screw misplacement. Specifically, said Peeters, “Preoperative knowledge about the pedicle size helps to maximize screw containment and minimize the risk of pedicle breach.”

Can a Low-Dose, Biplanar X-Ray Device Consistently Reduce Screw Misplacement?

“To accurately measure the pedicle sizes, a preoperative computed tomography (CT) scan is needed. However, this is not done routinely in clinical practice due to the exposure of this young population to high levels of radiation. Plane radiographs as alternative have the disadvantage that there is divergence in both the horizontal and vertical planes.”

“Radiographs taken by a biplanar low-dose X-ray device (EOS) have no divergence in the vertical plane. Therefore, the criterion validity and reliability of preoperative EOS images for pedicle size measurements in patients with idiopathic scoliosis was investigated in this study.”

The investigators prospectively studied 16 patients with idiopathic scoliosis who underwent surgery. Specifically, they looked at intra- and extracortical pedicle height and width measurements on EOS images as compared with reconstructed intra-operative 3D images of the isthmus of included pedicles. In addition, the researchers examined intra- and interobserver reliability of pedicle size measurements on EOS images.

According to Peeters, “The results of this study indicate a good validity and reliability for pedicle size measurements on EOS radiographs. For pedicles classified as Nash–Moe 0, no significant differences in intra- and extracortical pedicle width were observed, but when measuring pedicles with a Nash–Moe score > 0 surgeons should be aware of a significant systematic small underestimation of the pedicle width measurements on EOS images. As a result, EOS radiographs may be used for a preoperative estimation of pedicle size and subsequent screw diameter in patients with idiopathic scoliosis.”