Expansive cervical laminoplasties - Observations on comparative changes in spinous process lengths following longitudinal laminal divisions using autogenous bone or hydroxyapatite spacers

Expansive laminoplasty is devised to preserve the posterior structures, including the original length of the spinous process which anchors the nucheal muscles, in order to prevent the postoperative development of instability and cervical kyphosis due to structural loss and poor tone of the nucheal muscles, which can result in late neurological regression after laminectomy for cervical myelopathy. We retrospectively compared the length of the spinous process at the time of follow-up with that within 3 months postoperatively using CT images. The shortening was observed in 80% of 60 spinous processes in 13 patients, where a hydroxyapatite (HA) block was used as a spacer placed between the two sides of the split spinous process. The incidence was 9% of 22 spinous processes in six patients where auto bone graft (ABG) was used as a spacer, and the difference was significant (P<0.01, Chi-square test). Although the usage of HA has the advantage of being less invasive than ABG, it may jeopardize the biomechanical function of nucheal muscles due to reduction in the original length of the spinous process.