Dual-Energy Computed Tomography Collagen Density Mapping of the Cranio-Cervical Ligaments-A Retrospective Feasibility Study

Abstract

The objectives of this study were to investigate the mean collagen content of the atlanto-axial joint (AAJ) ligaments in a cohort without inflammatory disease and to analyze clinical confounders such as age, sex, and presence of ligamentous calcifications. A total of 153 patients who underwent dual-energy computed tomography (DECT) due to various reasons (e.g., suspected cancer or infection) were included in this retrospective study. Reconstruction of collagen density maps from the DECT dataset was performed. Region of interest (ROI) analysis was performed to assess densities in the following regions: ligamentum transversum atlantis (LTA), ligamenta alaria, fasciculi longitudinales, ligamentum nuchae, and retro-odontoid soft tissue (RDS). Osteoarthritis (OA) and the presence of calcifications were assessed by two experienced readers blinded to clinical data. Subgroup comparisons were performed using unpaired t-tests. The correlation of collagen density and clinical factors was investigated using Pearson's correlation coefficient. Mean LTA collagen density was 141.7 (SD 35.7). Ligamentous calcifications were rare (14.4 %). OA of the AAJ was common (91.5 %). LTA collagen density was not associated with age (Pearson's r of 0.109; p = 0.180) and was not significantly higher in patients with OA (p = 0.070). No correlations between RDS thickness, collagen density or calcifications were found. Our results show collagen density mapping of the cranio-cervical joint ligaments to be feasible; collagen densities are not significantly associated with age, sex, AAJ degeneration, or asymptomatic ligamentous calcification.

Keywords: atlanto-axial joint; chondrocalcinosis; collagen; dual-energy CT; ligaments.

Figure 1

Measurement of collagen density and retro-odontoid soft tissue. CT = computed tomography, DECT = dual-energy CT, LTA = ligamentum transversum atlantis, FL = fasciculi longitudinalis, LA = ligamenta alaria, LN = ligamentum nuchae, and RDS = retro-odontoid soft tissue thickness. Upper row indicates CT with 135 kVp reconstructions. Lower row refers to DECT-based collagen maps. Region of interest (ROI) measurements were performed with predefined size of 9.5 mm² for all measurements using the collagen density maps. In total, twelve ROI measurements were performed (six in 135 kVp images, six in collagen maps) as follows: LTA (two ROIs per reconstruction in axial orientation (left and right orientation, yellow ROIs); FL (one ROI per reconstruction in coronal orientation, blue ROI); LA (two ROIs per reconstruction in coronal orientation, yellow ROIs); and LN (one ROI per reconstruction in sagittal orientation, yellow ROI). Thickness of the retro-odontoid soft tissue (indicated by the yellow arrow) was measured using the 135 kVp CT reconstruction in axial orientation.

Figure 2

Imaging examples of osteoarthritis of the atlanto-axial joint. Imaging examples of five different patients according to the Kellgren and Lawrence [18] grading of osteoarthrosis (OA). Upper row (A) with axial orientation of 135 kVp images, and lower row (B) with sagittal orientation of 135 kVp images, respectively. From left to right (both rows) an increase in OA grading with no OA (0), beginning OA (1), minimal OA (2), moderate OA (3), and severe OA (4) of the atlanto-axial joint is shown (yellow arrowheads).

Figure 3

Imaging examples of ligament calcification grading. Imaging examples of three different patients according to the assessment of ligament calcifications of the ligamentum transversum atlantis based on axial-orientated 135 kVp image reconstructions. Grading was performed as follows: absence of calcifications (0), punctuate calcifications (1), and confluent calcifications (2) (yellow arrowheads).

Figure 4

Flowchart of the study inclusion and results of the scoring. LTA = ligamentum transversum atlantis, AAJ = atlantoaxial joint, KL = Kellgren and Lawrence grading.