• Xiao-Jiang Yang, Hong-Xun Sang, Chen-Xin Liu, Zhen-Sheng Ma, Bing Meng, Tian-Qing Li, Ming-Chun Jiang, Xiao-Zhong Liu, Wei Lei, and Yang Zhang.
• Department of Orthopaedic Surgery, Xijing Hospital, The Air Force Medical University, No. 127 Changlexi Road, Xincheng District, Xi'an, 710032, Shaanxi, China.
• Eur Spine J. 2019 Oct 1; 28 (10): 2302-2310.

PurposeTo 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.MethodsThe 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.ResultsThe 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.ConclusionApplying 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.

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