Unilateral Biportal Endoscopic Resection of the Posterior Arch of the Atlas for Crowned Dens Syndrome

BACKGROUND Crowned dens syndrome (CDS) is a rare disorder caused by calcium pyrophosphate deposition around the odontoid process. Although most patients respond favorably to conservative management, some develop refractory myelopathy requiring surgical intervention. We present a minimally invasive surgical technique for CDS complicated by spinal cord compression. CASE REPORT An 86-year-old woman with CDS exhibited progressive myelopathy, including thoracoabdominal girdle sensation, gait disturbance ("walking on cotton"), and impaired fine motor function in the upper extremities. Her symptoms were refractory to 9 months of conservative treatment. Computed tomography and magnetic resonance imaging demonstrated calcification of the transverse and alar ligaments at the craniovertebral junction with associated compression of the medulla oblongata. The patient underwent unilateral biportal endoscopic resection of the posterior arch of the atlas with spinal canal decompression. Intraoperatively, a midline bony defect was identified. Approximately 8 mm of the posterior arch was resected bilaterally using a high-speed drill; partial excision of the posterior atlanto-occipital membrane and posterior atlantoaxial ligament was performed. Postoperatively, neck pain and girdle sensation were greatly alleviated. At the 1-year follow-up, gait stability and fine motor function had substantially improved, the Japanese Orthopaedic Association score increased from 9 to 12, and no procedure-related complications were observed. CONCLUSIONS Unilateral biportal endoscopic posterior arch resection of the atlas with decompression represents a feasible and minimally invasive alternative to conventional open surgery for selected patients with CDS displaying myelopathy, particularly high-risk older individuals. This case underscores the importance of surgical intervention in patients with CDS and spinal cord compression.