Comparison of enlargement of the spinal canal after cervical laminoplasty: open-door type and double-door type

The purpose of this study was to compare the degree of enlargement of the spinal canal between two methods of cervical laminoplasty (open-door laminoplasty and double-door laminoplasty) and to determine their appropriate surgical indications based on the results. Tension-band laminoplasty (TBL, one method of open-door type) was performed in 33 patients and double-door laminoplasty (DDL) in 20 patients. The operation level ranged from C2 to C7 in all patients. The width of the spinal canal and the inclination angle of the lamina at the C5 and C6 levels were measured using a computer software program (Image J) and pre- and postoperative CT films. Concerning the degree of enlargement of the spinal canal, the mean expansion ratio at the C5 level was 148.9% in TBL and 148.2% in DDL, and there was no significant difference between them. However, at the C6 level, it was 159.0% in TBL and 140.3% in DDL, which was significantly larger in TBL than DDL (p < 0.05). The increase of inclination angle of the lamina was 11.0° in TBL and 19.0° in DDL at the C5 level, and 9.2° in TBL and 19.3° in DDL at the C6 level. At both the C5 and C6 levels, it was significantly larger in DDL than TBL (p < 0.0001). In conclusion, the appropriate surgical indications of TBL were considered to be (1) cervical spondylotic myelopathy (CSM) combined with hemilateral radiculopathy, (2) severe prominence of ossification of the posterior longitudinal ligament (OPLL), and (3) patients with tiny spinous processes who cannot undergo DDL. Those of DDL were considered to be (1) usual CSM, (2) small and slight prominence of OPLL, (3) CSM combined with bilateral radiculopathy, and (4) cervical canal stenosis combined with instability necessitating posterior spinal instrumentation surgery.