BACKGROUND The association of laminar opening extent (LOE) with sagittal canal diameter (SCD) and the cross-sectional area (CSA) in unilateral door cervical laminoplasty (UDCL) was previously analyzed. However, the lamina abrasion has been neglected, which could lead to unreliable results. The present study aims to develop the concept of effective laminar opening extent (ELOE) with consideration of the lamina abrasion and to analyze the relationships between ELOE and SCD as well as the CSA of the spinal canal. MATERIAL AND METHODS A total of 138 patients treated by UDCL were included. Pre- and postoperative SCDs and CSAs and cervical Japanese Orthopaedic Association (JOA) scores were compared to verify the effectiveness of the surgery. Linear and curvilinear regression models were used to assess the association between postoperative SCD/CSA increases and ELOE. RESULTS All surgeries were successfully performed. A total of 602 mini-plates were used, and 12-mm mini-plates was the most often used (n=402, 66.78%), while 16-mm were used the least (n=25, 4.15%). The SCDs, CSAs, and JOA scores were increased significantly after surgery (P0.939, P0.938, P.