Cervical laminoplasty: evaluation of bone bonding of a high porosity hydroxyapatite spacer

Object. The purpose of this study was to evaluate the usefulness of a high-porosity hydroxyapatite (HA) spacer in cervical laminoplasty. Bone-spacer bonding rates, complications associated with the implant, and factors related to bone bonding were examined. Methods. The authors evaluated 33 consecutive patients with cervical myelopathy who underwent high-porosity HA spacer-assisted laminoplasty and were followed for at least 1 year (mean 30 months). The results of bone-spacer bonding of the 147 implants were evaluated using computerized tomography (CT) scanning. The symptoms significantly improved in 30 patients. No difference in results was detected between patients with cervical spondylosis and those with ossification of posterior longitudinal ligament. Breakage of seven spacers occurred in four patients without causing neck pain or neurological deficits. There were no other HA spacer-related complications. The spacers became rigidly bound to bone in 61% of the cases, and bone regrowth developed around the spacer in 91%. The rate of bone-spacer bonding increased over time, and the CT-documented attenuation value (Hounsfield unit) of the spacer adjacent to the bone-spacer junction in the group in which union occurred was significantly higher than in the nonunion group. Conclusions. High-porosity HA spacer-augmented laminoplasty produced good bonding-related results. Bone bonding continued to progress 1 year after surgery, indicating the good osteoconductive capability of high-porosity HA. To avoid breakage of a spacer, a minimum 7-mm distance between spacers is necessary.