Abstract: Objective 　To investigate the effects of 20° sharp rongeur or high-speed-micro- drill on the open angle to make hinges in cervical posterior open-door expansive laminoplasty.　Methods 　Patients who received cervical posterior open-door expansive laminoplasty were collected in our hospital and were followed up prospectively. They were divided into 2 following groups according to the instrument of making hinges, which are a 20°sharp rongeur group and a high speed micro-drill group. Cervical vertebra computed tomography (CT) was performed before operation and within 1 week after operation in all patients. The angles between the lamina and the coronal vertebral body on the CT cross-section were measured before and after surgery. Then these data were statistically analyzed.    Results    40 patients were collected in and were followed up, including 23 cases in the rongeur group and 17 cases in the drill group. In the rongeur group, the mean angle between the open segment lamina and the coronal plane before operation was (37.58±4.09)°, while the angle in the drill group was (36.19±3.92)°, which showed no statistical difference between them (P=0.286). And the open angle of the rongeur group after operation was (62.27±3.99)°, while (67.17±3.48)° in drill group, which were significantly different (P<0.001). In addition, there were statistical difference in the lamina expansion angle, preoperative and postoperative open angle ratio, and expansion rate of open angle between these two groups (P<0.01).    Conclusions    Using 20° sharp rongeur to make hinges can control the open angle more precisely and closer to the ideal open angle than using high speed micro-drill.

Key words: Cervical vertebra expansive laminoplasty;　Open angle, Sharp rongeur;　High- speed-micro-drill