Clinical and radiographic outcomes following hinge fracture during open-door cervical laminoplasty

To investigate the clinical and radiographic fate of fractured hinges in open-door cervical laminoplasty, 135 segments of 36 patients who had undergone follow-up for more than two years after open-door cervical laminoplasty due to compressive cervical myelopathy were reviewed clinically and radiographically. Hinge fractures were identified by the intraoperative finding of obvious instability or click sounds (an obvious fracture), or by immediate postoperative computed tomography (CT) images showing a discontinuity of both the inner and outer cortex or a displacement of more than 1mm at the lamina hinge site (an occult fracture). At two years post-surgery, union and displacement of the fractured hinges were evaluated with CT and the clinical outcome was assessed by the Japanese Orthopedic Association (JOA) and Neck Disability Index (NDI) scores. Immediate postoperative CT scans revealed 28 hinge fractures in 16 patients. Only three fractures were identified during surgery, with most being identified on postoperative CT. Nineteen laminae showed non-displaced cortical discontinuity, five were anteriorly displaced by more than 1mm, and four were displaced posteriorly. Twenty-five laminae (89.3%) had achieved union according to the two-year postoperative CT scan. No de novo neurologic symptoms were found to be associated with hinge fracture. The two-year postoperative JOA and NDI scores did not differ significantly between patients with or without a hinge fracture. Most fractures at the hinge site occurred without intraoperative recognition, and usually re-unified without significant displacement or adverse clinical effects. When hinge fractures occur, careful observation without additional intervention is recommended.