Study Design: Case report.
Summary of Background Data: Cervical myelopathy caused by osteophyte formation appearing at the pseudoarthrosis between the posterior arch of the atlas and the lamina of the axis is extremely rare. To our knowledge, only 2 cases in non-Klippel-Feil syndrome have been reported so far.
Methods: A 61-year-old man, who was diagnosed as Klippel-Feil syndrome with assimilation between C2 and C3 vertebrae, which were fused in hyperlordosis, suffered cervical myelopathy. Complete bipartition of the atlas was also demonstrated. Massive osteophytes, which severely compressed the spinal cord at the pseudoarthrosis between the posterior arch of the atlas and the lamina of the axis, were seen. Surgical resection of the osteophytes was performed.
Results: The patient had significant clinical improvement after posterior resection of the osteophytes.
Conclusions: Coincidence of several bony anomalies such as assimilation of C2 and C3, which were fused in hyperlordosis, and the bipartition of the atlas may biomechanically influence the formation of pseudoarthrosis between the posterior arch of the atlas and the lamina of the axis. Because symptoms appeared in the patient's 60s despite congenital bony anomaly, degeneration might contribute to the formation of massive osteophytes. Posterior decompression was effective in this case.