Anterior Arch Fracture of the Atlas on Postoperative Day 6 Following Unilateral C1 Laminectomy Requiring Occiput-to-C2 Fusion: A Case Report.

C1 laminectomy is a well-established posterior decompression procedure for craniovertebral junction stenosis. However, disruption of the ring structure of the atlas may alter load distribution across the anterior arch and lateral masses, occasionally resulting in atraumatic anterior arch fractures. Although several cases have been reported following bilateral C1 posterior arch resection or foramen magnum decompression, most developed weeks to months after surgery. In contrast, anterior arch fracture occurring during the acute postoperative period after unilateral C1 laminectomy has rarely been described. We report the case of an 82-year-old woman who developed an anterior arch fracture of the atlas on postoperative day 6 after left unilateral C1 laminectomy combined with C3-7 laminoplasty for cervical spinal canal stenosis. She presented with the sudden onset of severe headache. Initial head computed tomography (CT) showed no intracranial abnormalities. Because the headache persisted, cervical CT was obtained and demonstrated an anterior arch fracture of C1. Retrospective review revealed that the fracture had already been present on CT acquired on postoperative day 6. Conservative management with cervical immobilization was initiated; however, follow-up imaging demonstrated progressive fracture displacement and lateral mass subluxation, prompting surgical stabilization. Intraoperatively, marked instability of the C1 lateral masses precluded safe placement of C1 screws, and occiput-to-C2 fusion with autologous iliac crest bone grafting was performed. The patient's headache resolved promptly after surgery, and no neurological deterioration occurred. At the eight-month follow-up, progressive bony union was confirmed without recurrence of symptoms. This case represents one of the earliest reported anterior arch fractures following C1 laminectomy. The unusually early onset may have been related to a combination of asymmetric biomechanical loading after unilateral posterior arch resection, age-related impairment of bone quality, and additional biomechanical changes associated with multilevel laminoplasty, although a causal relationship cannot be established from a single case. Importantly, postoperative headache following C1 decompression should not be attributed solely to intracranial pathology or cerebrospinal fluid-related disorders. When new-onset headache or occipital pain develops after C1 laminectomy, early cervical CT should be considered to exclude structural complications. In patients with progressive fracture displacement or significant C1 instability, rigid internal fixation, including occiput-to-C2 fusion, may provide reliable stabilization.