Biomechanical effects of laminoplasty versus laminectomy: Stenosis and stability

Study Design. In vitro human cadaveric study simultaneously quantifying sagittal plane flexibility and spinal canal stenosis. Objective. To compare biomechanical stability and the change in cross-sectional area during flexion and extension after laminectomy and open-door laminoplasty. Summary of Background Data. Spinal canal stenosis has been quantified in vitro but has not been quantified in studies of laminectomy or laminoplasty. Methods. Cadaveric specimens were loaded in physiologic-range flexion and extension using nonconstraining pure moments while recording segmental angles optoelectronically. Custom flexible tubing was placed within the spinal canal, and water was continuously pumped through the tubing while measuring upstream pressure. Spinal canal cross-sectional area correlated to water pressure, allowing continuous monitoring of the smallest cross-sectional area of the canal. Specimens were tested (1) normal, (2) after modeling stenosis by inserting hemispherical wooden beads in the spinal canal at 3 levels, (3) after open-door laminoplasty at 5 levels, and (4) after expanding laminoplasty to laminectomy. Results. Range of motion (ROM) in the normal, stenotic, and laminoplasty conditions did not differ significantly. However, laminectomy increased ROM significantly more than other conditions. ROM after laminectomy was 13% greater than after laminoplasty. After modeling stenosis, the cross-sectional area decreased to 52% ± 12% of normal. Laminoplasty restored the cross-sectional area to 70% ± 12% of normal whereas laminectomy restored cross-sectional area to 101% ± 4% of normal. Among all conditions, areas differed significantly except normal versus laminectomy. Conclusion. Laminoplasty leaves the spine in a significantly more stable condition than laminectomy. However, laminoplasty failed to relieve stenosis completely. In this study, stenosis was modeled as about 50% occlusion of the spinal canal. The degree of stenosis should be considered in clinical decisions of whether laminectomy or laminoplasty is more appropriate.