Is the Superior Articular Process a Reliable Landmark for Determining the Transverse Plane Angulation of Thoracic Pedicles in Patients With Adolescent Idiopathic Scoliosis?

Purpose: To analyze the usefulness of the superior articular process (SAP) as an external landmark for determining the transverse plane angulation of thoracic pedicles in scoliotic spines.

Methods: Two investigators reviewed thoracic spine CT scans of 60 patients with adolescent idiopathic scoliosis. The gantry was adjusted to obtain axial images parallel to the superior endplate. Each investigator measured the Cobb angle of the thoracic curve and identified the apical vertebra. This vertebra as well as the vertebrae bordering it superiorly and inferiorly was examined. A line was subtended at a 90° angle to the surface of the SAP, with a starting point at the midpoint of the lateral half of the SAP. It was documented whether the line was contained within the pedicle or breeched it medially or laterally. Breeches were corrected to an ideal projection, and the degree and direction of correction was recorded. Curves of 50°-60° were then compared to curves ≥70°.

Results: Four subjects in our cohort were excluded as a result of inadequate imaging. Of 336 measurements, 89.3% were contained in bone, resulting in a breech rate of 10.7%. A majority of wall violations were on the lateral side (94.4%), with the average degree of correction being 6.1°. Interobserver agreement was calculated to be 95%, 87.5%, and 89.3% for superior, apical, and inferior vertebral measurements, respectively. On further stratification of the patients based on a Cobb angle of 50°-60° and ≥70°, we found that patients with curves ≥70° have a greater incidence of wall breech at the apical vertebra (10% vs. 5.6%) (p = .02).

Conclusion: The SAP can serve as a reliable external landmark for determining the transverse plane angulation of thoracic pedicles in scoliotic spines.

Level Of Evidence: Level 3.