Postoperative Paralysis From Thoracic Ossification of Posterior Longitudinal Ligament Surgery Risk Factor of Neurologic Injury: Nationwide Multiinstitution Survey.

STUDY DESIGN Retrospective case-control study. OBJECTIVE The purpose of this study was to examine the factors of postoperative paralysis in patients who have undergone thoracic ossification of posterior longitudinal ligament (OPLL) surgery. SUMMARY OF BACKGROUND DATA A higher percentage of thoracic OPLL patients experience postoperative aggravation of paralysis than cervical OPLL patients, including patients that presented great difficulties in treatment. However, there were a few reports to prevent paralysis thoracic OPLL. METHODS The 156 patients who had received thoracic OPLL surgery were selected as the subjects of this study. The items for review were the duration of disease; the preoperative muscle strength (Muscle Manual Testing); OPLL levels (T1/2-4/5: high, T5/6-8/9: middle, and T9/10-11/12: low); the spinal canal occupancy ratio; the ratio of yellow ligament ossification as a complication; the ratio of transcranial-motor evoked potential (Tc-MEP) derivation; the preoperative/postoperative kyphotic angles in the thoracic vertebrae; the correction angle of kyphosis; the duration of surgery; and the amount of bleeding. The subjects were divided into two groups based on the absence or presence of postoperative paralysis to determine the factors of postoperative paralysis. RESULTS Twenty-three patients (14.7%) exhibited postoperative paralysis. Multivariate analysis identified factors associated with postoperative paralysis: the duration of disease (odds ratio, OR = 3.3); the correction angle of kyphosis (OR = 2.4); and the ratio of Tc-MEP derivation (OR = 2.2). CONCLUSION The risk factors of postoperative paralysis are a short duration of disease and a small correction angle of kyphosis. In addition, ratios of Tc-MEP derivation below 50% may anticipate paralysis. LEVEL OF EVIDENCE 4.