Morphometric Analysis of the Lateral Atlantoaxial Joints in Patients with an Old Type II Odontoid Fracture and Atlantoaxial Dislocation: A Study Based on CT Analysis.

Retrospective cohort study. We aimed to study and interpret the morphological features of the lateral atlantoaxial joints (LAJs) in patients with old type II odontoid fractures and atlantoaxial dislocation (AAD). The causes and consequences of the morphological changes of the LAJs in patients with old type II odontoid fractures and AAD have not been analyzed before. A retrospective study was performed on patients with old type II odontoid fracture and AAD. These patients were placed in group A (unstable or reducible dislocation) or group B (irreducible or bony dislocation) depending on the type of dislocation they had. We documented the morphological changes and measured the inclination angle of the articular surface of the LAJs in computerized tomographic images and compared the results collected for the two groups. The association between the history of injury and the inclination angle of the articular surface of the LAJs was assessed using the Pearson correlation coefficient. A total of 29 patients were enrolled (16 patients in group A, and 13 patients in group B). The inclination angle in group A was significantly greater than that in group B ( P  < 0.001). Patients in group B were more likely to have fish-lip-like changes, dome-like changes, or collapse of the LAJs. Age, history, atlantodental interval, and Japanese Orthopedic Association score were also significant differences between the two groups ( P  < 0.05). There was a negative correlation between the history of injury and the inclination angle of the articular surfaces of the LAJs (left: r = −0.726, P  < 0.001; right: r = −0.795, P  < 0.001). The morphological changes of the LAJs could progressively become more pronounced during the evolution of the disease. Level of Evidence: 4.