Laminar closure after classic Hirabayashi open-door laminoplasty.

STUDY DESIGN: Prospective analysis of preoperative and postoperative radiological data. OBJECTIVE: To assess the incidence and extent of laminar closure after Hirabayashi open-door laminoplasty, as determined by multi-detector computed tomography (CT), and to investigate the influence of this phenomenon on spinal cord compression, as shown by magnetic resonance imaging (MRI). SUMMARY OF BACKGROUND DATA: Although laminar closure occurs after laminoplasty, little is known about its progression or its effect on restenosis of the spinal canal. METHODS: Thirty-five patients (132 laminae) underwent classic Hirabayashi laminoplasty and were followed for at least 12 months. Multi-detector CT was performed preoperatively, at 1 week, or less, and 6 months after surgery. At each level, the anteroposterior (AP) diameter of the spinal canal and the angle of the opened lamina were measured. MRI was performed preoperatively and 1 year after surgery to evaluate the severity of cord compression based on a six-grade classification system. RESULTS: The mean AP diameter and the mean opening angle increased immediately after surgery (P <0.05 each) and decreased 6 months after surgery (P < 0.0001 each), with the AP diameter and opening angle decreasing by 9.4% and 10.2%, respectively. CT at 6 months showed fusion of the hinge in 91% of opened laminae. Segments with high-grade cord compression (grade ≥3) at 1 year showed greater decreases in AP diameter and opening angle (P < 0.05). CONCLUSION: After classic Hirabayashi open-door laminoplasty, opened laminae showed reclosure at 6 months, with approximately 10% decrease in AP diameter and opening angle. Postoperative lamina closure was associated with recurrent spinal cord compression, suggesting the need for other augmenting techniques that keep the laminae opened.