Significance of segmental instability in cervical ossification of the posterior longitudinal ligament and treated by a posterior hybrid technique

Retrospective cohort case study. To evaluate significance of segmental instability (SI) in cervical ossification of the posterior longitudinal ligament (OPLL) myelopathy and effectiveness of a posterior hybrid technique in the treatment of OPLL associated with SI. Some studies suggested both static and dynamic compression factors accounted for the pathogenesis of myelopathy in the OPLL patients. Between May 2005 and August 2007, 15 patients with multilevel cervical OPLL, diagnosed to be associated with SI, were treated by a posterior hybrid technique including laminoplasty and fusion at instable levels with lateral mass screw fixation. Another 15 cohort patients without SI treated by laminoplasty in the same period were included in the control group. Radiological and clinical data were compared between two groups. There were no significant differences in Preop. lordotic angle, extent of OPLL, type of OPLL and occupying rate, but more patients tended to present high-intensity zone (HIZ) on MRI in the group with SI. In 15 patients with SI, 17 intervertebral levels had SI, which were distributed at the noncontinuous levels of mixed-type OPLL or the adjacent levels of continuous-type OPLL. They were also consistent with the presence of HIZ levels in the major of patients. After operation, the lordotic angle was maintained well by the posterior hybrid technique in the OPLL with SI group, and was significantly greater than that in the OPLL without SI at the 3- and 4-year follow-up point. Postoperative kyphotic change of the cervical spine and postoperative progression of the ossified lesion were not observed in the OPLL with SI group, but they were respectively observed in four cases (26.7 %) and two cases (13.3 %) in the OPLL without SI group at the 4-year follow-up point. The preoperative C-JOA score in the OPLL with SI group was lower than that in the OPLL without SI group. The average C-JOA score and improvement rate were comparable in the first 2 years after operation between two groups, but there was a decrease in C-JOA score and improvement rate in the following 2 years in the OPLL without SI group. At the 3- and 4-year follow-up points, both postoperative C-JOA score improvement rate in the OPLL with SI group were superior to those in the OPLL without SI group. Each group had one case developing C5 palsy, but three cases in the OPLL without SI group developed late neurological deterioration due to postoperative kyphotic change or progression of the ossified lesion. Segmental instability, a degenerative dynamic factor, is important to the OPLL myelopathy. The posterior hybrid technique seemed to be effective and safe in the treatment of selective OPLL patients associated with SI. The benefits may include providing stabilization environment for spinal cord recovery, and preventing progressive kyphotic change and progression of OPLL.