FACTORS RELATED TO THE SEVERITY OF MYELOPATHY IN ATLANTOAXIAL INSTABILITY

Study Design. This study retrospectively reviewed the factors seemingl y associated with neurologic symptoms in 46 patients with atlantoaxial instability. Objectives. This study revealed the most significant fac tors related to the severity of myelopathy and surgical prognosis of a tlantoaxial instability. Summary of Background Data. Spinal morphometr y has been reported to provide a useful means of predicting the progno sis of cervical spondylotic myelopathy after surgery. However, no quan titative and statistical evaluation of this method has been reported i n atlantoaxial instability. Furthermore, there is a poor correlation b etween neurologic deficit and plain radiographic findings of atlantoax ial instability. Methods. Four items of clinical information were inve stigated, six parameters were measured on radiographs, and two morphom etric parameters of the spinal cord were measured. These parameters we re used as predictor variables. Three multiple regression analyses wer e carried out, using pre- and post-treatment Japanese Orthopaedic Asso ciation scores as criteria variables. Results. Pretreatment Japanese O rthopaedic Association scores were found to correlate with the spinal compression ratio, history of trauma, and the C1-C2 ratio. Postoperati ve Japanese Orthopaedic Association scores correlated with preoperativ e Japanese Orthopaedic Association scores, the C1-C2 ratio, and the co mpression ratio, The multiple coefficient of determination was 93.2%. The recovery rate correlated with the C1-C2 ratio and age. Conclusions . Neurologic symptoms were found to be closely related to the morpholo gy of the spinal cord. Compression ratio and the C1-C2 ratio were foun d to be useful in understanding neurologic symptoms. The C1-C2 ratio s eems to serve as an important predictor of the prognosis of atlantoaxi al instability.