No neurological involvement for more than 40 years in Klippel-Feil syndrome with severe hypermobility of the upper cervical spine.

We report the case of a 42-year-old woman with Klippel-Feil syndrome, who showed severe hypermobility of the upper cervical spine without neurological involvement for more than 40 years. Radiographs revealed the presence of the odontoid bone and fusion of the atlas, odontoid bone, and occiput. Congenital fusion was present from the axis to C5 as a block vertebra. Lateral flexion-extension radiographs revealed severe hypermobility at the junction between the odontoid bone and the axis. Prophylactic surgical stabilization has been recommended in patients with severe hypermobility, but adjacent disc problems may possibly occur at the unfused levels in the future. We believe that early prophylactic stabilization should not be indicated for Klippel-Feil syndrome without neurological involvement only because of hypermobility.