Inter- and intraobserver reliability assessment of computed tomographic 3D measurement of pedicles in scoliosis and size matching with pedicle screws

Abstract

Background In patients with scoliosis, the morphology of the pedicles differs from those in normal spines. Preoperative three-dimensional information of these complex anatomic situations means a great advantage for the surgeon in order to assess which pedicles can be instrumented safely avoiding screw misplacement and for the decisions in choosing the appropriate screw size. The objective of this study was to measure pedicle dimensions in scoliotic spines on three-dimensional computed tomographic (CT) scans and to determine the intra-and interobserver reliability of the method. Additionally, the pedicles that cannot be instrumented safely by available screws were identified. Methods All pedicles from T1 to L5 in 30 patients with scoliosis were measured by two independent observers. The pedicle width, height and length were assessed for two times with a 3-week interval. Intraclass correlation coefficients were used to determine the intra-and interobserver reliabilities. The diameters of the pedicles were matched with the dimensions of the smallest available pedicle screws of scoliosis implant systems. Results The intrarater reliability was strong in 60% of the parameters and moderate in 40%. The interrater reliability was strong in all parameters but in pedicle length. The concave-sided pedicles in the curve revealed to be smaller compared to the convex-sided ones. The highest percentage of size mismatch was found in levels T7 (31%) and T8 (33%). Conclusions Measurement of pedicle dimensions on three-dimensional CT scans is a reliable but time-consuming procedure to assess pedicle dimensions. CT measuring should be reserved for special cases, where the anatomic situation remains unclear despite X-ray. In scoliotic spines, one-third of the mid-thoracic pedicles cannot be instrumented safely with pedicle screws.

What is the Difference in Morphologic Features of the Thoracic Pedicle Between Patients With Adolescent Idiopathic Scoliosis and Healthy Subjects? A CT-based Case-control Study

“…Krag et al [14] and Misenhimer et al [24] reported good correlation between CT-based and true morphometric measurements of pedicles in cadavers. Gstoettner et al [7] found substantial intra-and interobserver reliability of CT scans. However, to the best of our knowledge, numerous studies investigating morphologic features of the pedicle only focused on comparison between the concave and convex sides of scoliosis, which provides limited information regarding the deformed spine [2-4, 11, 15, 31, 35].…”

Currently Adopted Criteria for Pedicle Screw Diameter Selection

“…It should be noted that screw sizes available from the major manufacturers are limited, typically in 0.5 mm increments. Two studies in the current review specifically noted the inadequacy of current pedicle screw systems for instrumenting the midthoracic levels, with Liau et al 34 commenting that current systems are not suitable for the majority of the Malay population, and Gstoettner et al 36 concluding that one-third of midthoracic pedicles of scoliosis patients cannot be instrumented safely.…”

“…Furthermore, when these studies are grouped by the age of their relevant patient population, only those dealing at least in part with a pediatric population offered recommendations for SD wider than the pedicle. 24,36,37 These studies, based on both insertion techniques, define the upper limits for pediatric SD/PW between 1.15 and 1.25.…”

“…Of the qualitative studies found, 3 made SD/PW recommendations relevant for pediatric populations and averaged 1.18. 24,36,37 These high SD/PW values can be explained by the relative plasticity of the pedicle cortex in the pediatric spine, which has been suggested to be capable of expanding 25% upon screw insertion. 24,37…”

Assessing Foraminal Stenosis in the Cervical Spine: A Comparison of Three-Dimensional Computed Tomographic Surface Reconstruction to Two-Dimensional Modalities

“…New protocols have allowed for postacquisition generation of 3D surface reconstructions, which provide virtual 3D anatomic structures. Studies utilizing 3D reconstruction of 2D CT imaging data are promising, and the utility of this imaging technology has been demonstrated in the diagnosis of rotational and shear vertebral fractures, 6 assessment of congenitally abnormal pedicles, 7 and also establishment of safe entry points for pedicle screws in corrective scoliosis surgeries. 8 …”