In vitro biomechanical evaluation of a monocoque plate-spacer construct for cervical open-door laminoplasty

Purpose To evaluate biomechanical differences between two surgical procedures for cervical open-door laminoplasty using human cadaveric spines. Methods Twenty-four cervical vertebrae (C4-C6) from eight fresh-frozen human cervical spines were subjected to mechanical testing after being instrumented for open-door laminoplasty using a newly designed plate-spacer device with a monocoque structure (plate-spacer group; n = 12) or by conventional miniplate-alone fixation (miniplate group; n = 12). Cantilever bending testing was performed by applying a compressive load in the cranio-caudal direction to the base of the spinous process of the reconstructed laminar arch constructs until failure and strength and stiffness of the laminar arch were determined. The results are presented as mean +/- standard deviation. Results The plate-spacer group was approximately twice as strong as the miniplate group (27.6 +/- 16.5 N vs. 13.5 +/- 7.3 N, p < 0.05). Stiffness in the plate-spacer group exhibited the same trend (19.6 +/- 9.3 N/mm vs. miniplate group: 11.4 +/- 6.9 N/mm, p < 0.05). Conclusion The fixation with the monocoque plate-spacer construct for open-door laminoplasty provided higher structural properties when compared against the plate-alone fixation. The spacer in the plate-spacer construct appears to contribute by preventing large deformations of the laminar arch caused by bending in cranio-caudal direction. Future studies will be required to investigate stress/strain distribution in the laminar arch constructs.