The Investigation Of The Lateral Atlanto-Dental Space Of Atlanto-dental Joint By Multi-slice CT

Objective: A clinical investigation was conducted in both healthy volunteers and patientsto study the image features of the lateral atlanto-dental space (LADS) of atlanto-axialjoint in neutral and functional rotation positions to differentiate the normal physiologicalvariance and pathological conditions. Methods: 240 healthy volunteers/patients withoutatlanto-axial joint dysfunction including 4 groups (aged＜15, 15～30, 30～50,≥50 years;30 male and 30 female were included in each group) and 28 patients with torticollis andfunctional impairment were recruited to participate in this study. Subjects were examinedin both neutral and max rotation positions to the left/right with Multi-slice CT. Clinicalendpoints including VBLADS,variance range of the LADS and asymmetric conditionswere evaluated. Results:①In the normal contral group: Asymmetry of bilateral LADSwere observed in 85.00% of 240 healthy volunteers who had continuous lateral edge ofatlanto-axial lateral mass.The average and 95% normal ranges of VBLADS were 1.210±0.930mm,0～2.736mm in the young (＜15 years) and 0.806±0.718mm,0～1.983mm inthe adult(≥15 years). Therefore, 3.0mm,2.0mm were considered as the upper normallimits for the young and adult respectively. There was no correlation between VBLADSand rotatory angle of atlas on dentata (RAAD) in normal people (r=-0.139,-0.116,0.264,p＞0.05).②In the study with patients,15 of 28 had Atlanto-axial lateralsubdislocation(AALSD), and all of them had a shift of atlas on dentata and andiscontinuous lateral edge of adlanto-axials lateral mass. The average of the VBLADSwas 3.407 mm in 14 youths(＜15 years). There was a statistically significant difference ofthe VBLADS between the normal control group and 14 youths with AALSD (t=7.761,p=0.001). and 1 adult patient≥15 years had VBLADS≥20mm; 7 of 28 patients hadatlanto-axial rotatory dislocation(AARD) including 4 youths VBLADS＜3.0mm,3 adultsVBLADS＜2.0mm. No statistical significance was found comparing the VBLADSaverage(1.125mm) of 4 youths with AARD to the normal (t=0.180, p=0.858), all of the7 patients with AARD had unilateral parasol LADS in neutral position; 6 of 28 patientshad atlanto-axial complicated dislocation(AACD) including 5 youths VBLADS≥3.0mm,1 adult VBLADS≥2.0mm. A statistically significant increase of the VBLADSwith average of 4.800mm in the 5 youths(＜15 years) with AACD was observed(t=8.136, p=0.001). Conclusins:①Based on our study in the healthy volunteers,3.0mm in the young(＜15 years),2.0mm in the adult(≥15years) was consided as the upper limits of VBLADS; Asymmetry of bilateral LADS and VBLADS within the upperlimits in the normal was very common and didn't infect the rotatory function ofatlanto-axial joint. Therefore, this image finding might be a physiological variation ratherthan a pathological condition and no further treatment needed to be applied.②There weretwo kinds of pathologic asymmetry of bilateral LADS. Firstly,the increased VBLADS,exceeding the upper limits of normal range, could be used as a reference for the diagnosisof AALSD. In general, the bigger the VBLADS were, the higher the diagnosticsignificance might had. Secondly,for the patients with AARD, unilateral parasol LADS inneutral position was more meaningful than the increased VBLADS. In addition, adynamic CT should be applied to confirm the diagnosis.③There might be someoverlapping for the VBLADS between the normal and pathological conditions, Therefore,coronal planar reconstruction of atlanto-axial joint should be adopted before making thediagnosis of dislocation/subdislocation of atlanto-axial joint.