Regenos spacers are not suitable for open-door laminoplasty because of serious adverse events caused by their insufficient mechanical strength.

•We used a newly developed, high-porosity unidirectional porous hydroxyapatite spacer with expectation of high bone conductive potential and biomechanical strength, both of which are essential for a lamina spacer for open-door type laminoplasty.•The aim of the present study was to elucidate the effectiveness of Regenos laminar spacers for open-door type laminoplasty.•Regenos spacers are not suitable for open-door laminoplasty because of adverse events.