Occipito-atlanto-axial Hypermobility:Clinical Features and Dynamic Analysis of Cranial Settling and Posterior Gliding of Occipital Condyle. Part 2:Findings in Patients with Post-traumatic Condition

Object:To examine that post-traumatic condition(PTC)can present with lower brain stem symptoms attributable to occipito-atlanto-axial hypermobility and cranial settling, and its relationship to Chiari malformation typeI(CMI). Methods:We defined the condition of continuous brain and neck symptoms after motor vehicle accidents or falling down with loss of consciousness as PTC and 56 patients met to the criteria. Osseous structures comprising the craniocervical junction were investigated morphometrically using reconstructed 2D-CT and plain x-ray images in 50 patients with PTC, and the results were compared to normal controls(n=55). Results:There were 28 cases(50%)in PTC of CMI. The diagnostic features of PTC with CMI had a greater incidence of lower brain stem symptoms and signs. We performed measurements of the basion-dens interval(BDI), basion-atlas interval(BAI), atlas-dens interval(ADI), dens-atlas interval(DAI), clivus-atlas angle(CAA), clivus-axis angle(CXA), and atlas-axis angle(AXA). They were the same in supine and upright positions in normal controls. In patients with PTC, there was reduction of the BDI (2.7 mm), enlargement of the BAI (2.8 mm), and reduction of the CXA(11.4°), CAA(6.6°, p<0.001), and AXA(11.0°)upon assumption of the upright position. These changes were reducible by cervical traction. Conclusions:Morphometric evidence in this cohort of cranial settling and posterior gliding of the occipital condyles in PTC suggests hypermobility of the atlanto-occipital and atlanto-axial joints. This hypermobility induces greater brain stem symptoms in patients associated with CMI. The patients with CMI have greater hypermobility of occipito-atlanto-axial joints. (Received:December 29, 2008;accepted:January 26, 2009)