[Relationship between the prediction of the opening angle and the increased value of cross-sectional area in single open-door laminoplasty].

Objective: To evolve the formula of relationship between opening angle of laminoplasty and the increased value of cross-sectional area, and to predict the opening angle according to the opening size of lanminoplasty.

Methods: From January 2013 to December 2015, 26 patients underwent single open-door laminoplasty in C₃-C₇. Among them, 10 patients with ossification of posterior longitudinal ligament, there were 6 males and 4 females, aged from 39 to 58 years old with an average of 49.2 years; and 16 patients with cervical spondylotic myelopathy, there were 10 males and 6 females, aged from 40 to 58 years old with an average of 50.2 years. Through the changes of spinal canal shape between preoperation and postoperation to set up the regular geometric model, and to deduce the formula of the relationship between the opening angle of laminoplasty and the increased value of cross-sectional area, and predict the formula of opening angle. According to the preoperative and postoperative CT scan, the needed parameters were measured, and were substituted in the above formula to get the change of cross-sectional area before and after operation, predicting the opening angle of laminoplasty. The differences between the change of cross-sectional area before and after operation, predictive the opening angle of laminoplasty and practical measured data were analyzed by statistical methods, thus to verify the feasibility of formula in practical application.

Results: All imaging data of 26 patients were obtained. There were significant differences in changes of cross-sectional areas in every patients (laminoplasty in C₃ to C₇) before and after operation in the same segment(<0.01). The increasing extent in cross-sectional areas was gradually diminished following the opening angle increasing. There was no significant difference between the opening angle attained by formula and the data measured by software in the same segment(>0.05).

Conclusions: Increment of cross-sectional areas following C₃-C₇ laminoplasty can be accurately attained and the opening angle can also be predicted by a certain formula, which can help surgeons to attain the accurate opening angle and reduce the postoperative complications.