Patients

This study was approved by the Institutional Review Board of Seoul National University Hospital (IRB No. H-1910-021-1067). A retrospective cohort study was designed with consecutive patients who underwent open-door laminoplasty in the subaxial cervical spine and dome-like laminectomy at C7 between March 2015 and December 2018. Patients whose follow-up was less than 6 months were excluded from the analysis. Among the patients who underwent C7 dome-like laminectomy, a total of 123 patients were ultimately evaluated. According to the presence of C7 fractures in the follow-up images, the patients were classified into two groups (C7 fracture group vs. no fracture group). The presence of C7 fracture was confirmed using computed tomography (CT) scan, which was taken at postoperative 6 or 12 months. If a disruption of cortical bone continuity or callus formation was seen, it was defined that there was a fracture (Fig. 1). The timing of the occurrence of C7 fracture was determined using postoperative X-ray images by observing fracture line at C7 isthmus or comparing the relative position of the C7 spinous tip to the adjacent spinous process tips.

Postoperative simple lateral X-ray and computed tomography (CT) scans of a 47-year-old patient who underwent C3–6 open-door laminoplasty and C7 dome-like laminectomy for cervical spondylotic myelopathy. A and B : A linear fracture line (white arrows) is seen in the lateral X-ray image taken at postoperative 3 months. This fracture, which developed along the isthmus, is also seen at a CT scan taken 6 months postoperatively. Callus formation was already visualized at the fracture sites. C and D : The fracture line is no longer visualized on postoperative 1-year images. A CT scan taken 1 year postoperatively shows complete healing of the fracture (blank arrows).