C2-fractures: part I. Quantitative morphology of the C2 vertebra is a prerequisite for the radiographic assessment of posttraumatic C2-alignment and the investigation of clinical outcomes

Abstract

Pertinent literature exists concerning indications, techniques, complications of treatment, and risk factors for nonunion in axis and odontoid fractures; however, there are scarce data regarding the incidence and definition of malunion in these fractures. As a prerequisite for the study of anatomical alignment following surgical and nonsurgical treatment of C2-fractures, an understanding of normal C2 anatomy is essential. Therefore, the authors intended to evaluate morphometrical dimensions of the C2 vertebra. The purpose was to provide normalized quantitative data to enable assessment of malalignment following the treatment of C2-fractures within a classification system. Using digitized cervical spine lateral and transoral odontoid radiographs of 100 consecutive patients without any evidence of traumatic or neoplastic disorders, the authors performed measurements on distinct anatomical structures and investigated morphometrical dimensions of the normal axis vertebra. The incidence of atlantoaxial arthritis was also evaluated. In addition, with the assessment of twenty arbitrarily chosen sets of radiographs by three different observers we calculated the interobserver reliability in terms of intraclass correlation coefficients for each parameter. With calculation of SD and 95% confidence limits, pathological cut-offs were reconstructed from measurements performed resembling non-physiological and pathological limits. Distinct parameters were selected to form a new classification system for radiographical follow-up that focuses on the quantitative C1-2 vertebral alignment. The measurement process resulted in 2,400 data points. Distinct morphometrical parameters, such as a quantitative characterization of the sagittal atlantoaxial congruency, the lateral mass inclination and the type of degenerative changes at the atlantoaxial joint could be demonstrated to be valuable and reliably used within a proposed classification for C2-malunions following C2-fractures. The current study offers a template including recommended radiological measurements for further research on the study of clinical outcome and posttraumatic alignment following C2-fractures.

Fig. 1

Artist’s drawings depict landmarks at anatomical structures of interest for making the measurements. Left AP-view of axis vertebra. Right Sagittally sectioned axis vertebra at the level of the right C2 pedicle

Fig. 2

AP and lateral radiographs with drawings depict measurements performed. See Table 1 and 2 for description of abbreviations used. Dashed lines mark the accessory lines resembling the endpoints for measurement on distinct anatomical landmarks

Fig. 3

The applied atlantoaxial osteoarthritis grading system according to Lakshamanan et al. [44] and the modified classification (in brackets). Left bilaterally Grade 0 (Type A); middle bilaterally Grade 1 (Type A); right left atlantoaxial joint shows Grade 3 (Type B), right joint shows Grade 2 (Type B)

Fig. 4

Scatterplot with regression lines depict age-related increase of sR1

Fig. 5

Age-related decrease of rAAJH (left) and lAAJH (right), respectively

Fig. 6

Illustrative case example for the application of the posttreatment C2-alignment, see text for explanation