Relationship between the laminoplasty opening size and the laminoplasty opening angle, increased sagittal canal diameter and the prediction of spinal canal expansion following open-door cervical laminoplasty

OBJECTIVE: To clarify the relationship between the laminoplasty opening size (LOS), the laminoplasty opening angle (LOA) and the increase in sagittal canal diameter (SCD) and to predict the amount of canal enlargement during open-door cervical laminoplasty (ODCL). METHODS: Formula describing the relationship between LOS and LOA, the increase in SCD was deduced. The parameters of pre- and postoperative computed tomography scans of 36 patients who had undergone laminoplasty surgery were measured by picture archiving and communication system (PACS) software, and the amount of canal enlargement of these patients was predicted when the opening size of laminoplasty was 8, 10, 12, 14 and 16 mm according to the formula. RESULTS: For equivalent LOS, the amount of canal enlargement with each opening size differed throughout the cervical region. When the C3-C7 LOS was 10 mm the SCD increased >4.1 mm, and the canal area increased in C3-C6 >88 mm(2), and the canal area increased in C7 > 80 mm(2). When the C3-C7 LOS was 12 mm, the SCD increased >5.2 mm, and the canal area increased in C3-C6 >104 mm(2), and the canal area increased in C7 > 94 mm(2). CONCLUSION: Formula accurately showed the relationship between the LOS and the increase in SCD achieved by ODCL. The amount of canal enlargement following ODCL could be predicted by the formula. LOS of 10-12 mm at C3-C7 might be optimal during ODCL.