Occipito-atlanto-axial Hypermobility : Clinical Features and Dynamic Analysis of Cranial Settling and Posterior Gliding of Occipital Condyle : Part 1 : Findings in Patients with Hereditary Disorders of Connective Tissue and Ehlers-Danlos Syndrome

Object:To investigate hereditary disorders of connective tissue(HDCT)and Ehlers-Danlos syndromes(EDS)that can present with lower brain stem symptoms attributable to occipito-atlanto-axial hypermobility and cranial settling, and relationship to Chiari malformation typeI(CMI). Methods:The diagnostic criteria for EDS and related HDCT were prospectively met by 155 patients. Osseous structures comprising the craniocervical junction were investigated morphometrically using reconstructed 2D-CT and plain x-ray images in 135 patients with HDCT・EDS and the results were compared to those in patients with normal controls(n=55). Results:There were 124 cases(80%) in HDCT・EDS of CMI. The diagnostic features of HDCT・EDS with CMI had a greater incidence of lower brain stem symptoms and signs. The measured distances 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)were the same in the supine and upright positions in normal controls. There was reduction of the BDI(3.3 mm), enlargement of the BAI(2.8 mm), and reduction of the CXA(10.8°), CAA (5.8°, p<0.001), and AXA(12.3°)upon assumption of the upright position. These changes were reducible by cervical traction. Conclusions:Morphometric evidence of cranial settling, posterior gliding of the occipital condyles in the HDCT・EDS cohort suggests hypermobility of the atlanto-occipital and atlanto-axial joints. This hypermobility induces more prominent 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)