Unexpected Neurological Deterioration Following Occipitocervical Fusion Surgery: A Case Report.

Occipitocervical posterior decompression and fusion (O-C fusion) surgery is occasionally required for treating high cervical myelopathy due to atlantoaxial subluxation. The advance of the instrumentation systems has led to favorable clinical outcomes following O-C fusion surgery. However, the rate of perioperative complications in O-C fusion surgery is relatively high, including instrumentation failure, respiratory complications, and dysphagia. Here we report a rare case involving an unexpected deterioration of myelopathy following O-C fusion surgery. A 49-year-old male was transported to our hospital by ambulance with left-sided upper and lower limb paralysis. At the initial visit, a neurological examination revealed left upper limb weakness (manual muscle testing (MMT) grade 2). X-ray and CT revealed severe atlantoaxial subluxation due to os odontoideum, while MRI revealed significant spinal cord compression at the C2 level. On the diagnosis of acute exacerbation of high cervical myelopathy, an O-C2 posterior decompression and fusion surgery, including C1 laminectomy, was performed. Postoperatively, the patient exhibited a deterioration in right-sided upper limb paralysis (MMT grade 2), despite proper implant placement confirmed by CT. During two weeks postoperatively, there was no improvement in the right-sided upper limb paralysis, and bilateral deep sensory impairment worsened. Follow-up X-rays revealed a progressive decrease in the O-C2 angle, and dynamic X-ray imaging demonstrated a recurrence of instability at the O-C2 level. On the diagnosis of the instrumentation failure, a revision surgery was performed three weeks after the primary surgery. Intraoperative findings revealed instability at the C2 screw head and loosening of the set screw on the C2 screw head. To achieve a more secure fixation, we extended the fusion to C4 with a triple rod connection. Following the revision surgery, his myelopathy and paralysis gradually improved. At the final follow-up, six months after surgery, X-rays showed that O-C2 was firmly stabilized. In conclusion, screw head fixation close to the O-C rod bending site may result in unexpected instrumentation failure in O-C fusion surgery.