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

<bold>Purpose: </bold>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.<bold>Methods: </bold>The model was based on geometric analysis on deformation of spinal canal; the formula was derived and characterized as: y (mm) = 2 [Formula: see text] × sin(β/2) = c - d (y is the size of LOS, [Formula: see text] 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.<bold>Results: </bold>The effects of surgery SDCL were very significant; for each patient, the SCD was enlarged dramatically after the surgery (P < 0.01). The differences between the data obtained by PACS and Lei's ruler were no statistically significant (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.<bold>Conclusion: </bold>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. [ABSTRACT FROM AUTHOR]