Radiographic Assessment of Segmental Motion at the Atlantoaxial Junction in the Klippel-Feil Patient

In Brief Study Design. A retrospective review of 33 consecutive Klippel-Feil syndrome (KFS) patients at a single institution. Objectives. To assess in KFS patients the presence and degree of radiographic segmental motion at the atlantoaxial junction, factors contributing to such motion, and associated clinical manifestations. Summary of Background Data. Studies suggest that abnormal segmentation in KFS patients may result in cervical hypermobility, increasing the risk of developing neurologic compromise and the need for surgical intervention. The use of the anterior and posterior atlantodens interval (AADI/PADI) has gained interest as a method for assessing atlantoaxial instability and for space available for the cord. Although helpful for identifying instability after trauma, these measurements are not understood in KFS patients. In addition, the effects of the fusion process associated with KFS on atlantoaxial motion and associated clinical findings have not been properly addressed. Methods. Radiographs were analyzed for the presence of occipitalization, number/location of congenitally fused segments, and the AADI and PADI. Results. There were 15 males and 18 females (mean age, 13.9 years). Occipitalization occurred in 48.5% of patients. A fused C2–C3 segment was noted in 72.7% of cases. More motion with respect to AADI was evident on O–C1 and C2–C3 fusion only patients, which were all asymptomatic. Overall, 24.2% of patients were symptomatic. Mean AADI and PADI difference was 2.0 mm (symptomatic: mean, 1.5 mm; asymptomatic: mean, 2.1 mm) and −1.7 mm (symptomatic: mean, −1.0 mm; asymptomatic: mean, −2.0 mm), respectively (P > 0.05). Conclusions. Hypermobility of the atlantoaxial junction, as indicated by increased AADI on flexion-extension radiographs, is not necessarily associated with an increased risk for the development of symptoms or neurologic signs in the KFS patient. Occipitalization plays an integral role in the degree of motion at the atlantoaxial region. Greatest AADI values were in patients with occipitalization and a fused C2–C3 segment. The presence of symptoms was not related to the degree of AADI change. Evaluation of the PADI provides additional information for identifying patients at risk for developing symptoms. Nonetheless, KFS patients remain largely asymptomatic. The purpose of this study was to assess segmental motion at the atlantoaxial junction in 33 patients with Klippel-Feil syndrome (KFS) using the anterior and posterior atlantodens interval flexion-extension radiographic measurements, and to evaluate the role of various fused cervical patterns on atlantoaxial mobility and symptoms. The study found that a large majority of KFS patients are asymptomatic and that hypermobility at the atlantoaxial junction is not synonymous with atlantoaxial instability. The posterior atlantodens interval may prove as a useful marker to determine patients at risk to developing symptoms.