A new method for calculating the desired laminoplasty opening size based on the target sagittal canal diameter before single-door cervical laminoplasty

[摘要] To build a mathematical model which could calculate the desired laminoplasty opening size (LOS) based on the target sagittal canal diameter (SCD) before single-door cervical laminoplasty (SDCL) when taking the effects of surgery drill into consideration. The model was based on geometric analysis on deformation of spinal canal; the formula was derived and characterized as: y (mm) = 2 $$ \overline{\text{CD}} $$  × sin(β/2) = c − d (y is the size of LOS, $$ \overline{\text{CD}} $$ the size of transverse canal diameter, β the size of laminoplasty opening size, c the size of mini-plate and d the diameter of the drill bit used during the surgery operation). The parameters of pre- and postoperative computed tomography scans of 20 patients who had undergone SDCL were measured by the picture archiving and communication system (PACS) software and a new instrument named as Lei’s ruler, respectively. The effects of surgery SDCL were very significant; for each patient, the SCD was enlarged dramatically after the surgery (P  0.05). According to the derived formula, the 95% confidence intervals of SCD after the surgery were within the range of 14 mm and 14.5 mm. Applying the mathematical model and derived formula, the desired LOS could be calculated according to the target SCD which could help the surgeon select an optimum mini-plate before SDCL. At the same time, a new measuring device named Lei’s ruler is designed for the convenience of the derived formula. These slides can be retrieved under Electronic Supplementary Material.

[关键词] Cervical spine;Single-door cervical laminoplasty;Laminoplasty opening size;Sagittal canal diameter