EXPANSIVE CERVICAL LAMINOPLASTIES - OBSERVATIONS ON COMPARATIVE CHANGES IN SPINOUS PROCESS LENGTHS FOLLOWING LONGITUDINAL LAMINAL DIVISIONSUSING AUTOGENOUS BONE OR HYDROXYAPATITE SPACERS

Expansive laminoplasty is devised to preserve the posterior structures , including the original length of the spinous process which anchors t he nucheal muscles, in order to prevent the postoperative development of instability and cervical kyphosis due to structural loss and poor t one of the nucheal muscles, which can result in late neurological regr ession after laminectomy for cervical myelopathy. We retrospectively c ompared the length of the spinous process at the time of follow-up wit h that within 3 months postoperatively using CT images. The shortening was observed in 80% of 60 spinous processes in 13 patients, where a h ydroxyapatite (HA) block was used as a spacer placed between the two s ides 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 sp acer, and the difference was significant (P<0.01, Chi-square test). Al though the usage of HA has the advantage of being less invasive than A BG, it may jeopardize the biomechanical function of nucheal muscles du e to reduction in the original length of the spinous process.