Clinical significance of articulating facet displacement of lateral atlantoaxial joint 3D CT in diagnosing atlantoaxial subluxaion

Background/Purpose: To improve the recognition of articulating facet displacement of lateral atlantoaxial joint (AFDLAJ), and to evaluate the significance of AFDLAJ in diagnosing atlantoaxial subluxation. Methods: The three-dimensional computed tomography (3D CT) imaging findings of 54 patients with atlantoaxial subluxation were retrospectively analyzed, and the imaging features of AFDLAJ were discussed. All the patients were examined in neutral position, and 25 in an additional rotary position. 3D images of the atlantoaxial joints were obtained by surface shade display and volume rendering. The diagnostic results of 3D CT, routine CT and X-ray were compared. Results: All the 54 patients with atlantoaxial subluxation were correctly diagnosed by 3D CT with no suspicious or missed diagnoses, including 38 cases of rotatory subluxation, 11 of anterior subluxation and five of posterior subluxation. AFDLAJ was found in all the 54 patients in neutral position, with the extent of subluxation between 2.0 mm and 9.0 mm. Among the 25 cases in rotary position, rotational fixation was found in 10 cases and rotational asymmetry in 15. The diagnostic accuracy of 3D CT was higher than that of X-ray or routine CT. Conclusion: Once AFDLAJ appears in neutral position and rotational fixation or asymmetry in rotary position, atlantoaxial subluxation can be ascertained, as well as the type and extent of subluxation, and fake subluxation due to the head's rotation or normal lateralized odontoid can be excluded. AFDLAJ is a vital direct sign in diagnosing atlantoaxial subluxation.