Three-Dimensional Analysis of the Radiological Risk Factors for Progression of the Thoracic Ossification of the Posterior Longitudinal Ligament After Posterior Decompression and Stabilization

Abstract

Although research shows that the ossified masses of ossification of the posterior longitudinal ligament (OPLL) continue to grow postoperatively, information regarding thoracic OPLL (T-OPLL) is lacking. To date, no study has investigated the progression of T-OPLL within each motion segment. The purpose of this study was to analyze the progression of T-OPLL in each motion segment using a 3-dimensional measurement and evaluate whether the type of T-OPLL and surgical methods affect its progression postoperatively. Clinical data from 20 patients (101 segments) with thoracic myelopathy secondary to OPLL were evaluated retrospectively. All patients underwent posterior decompression (laminectomy and stabilization or circumferential decompression [CD] and stabilization) at a single center. The 3-dimensional measurement of OPLL volume was performed using computed tomography scans. The ossified masses were classified into 2 types based on the fusion of each segment at the intervertebral space: type 1= complete bridging (fused); type 2= not fused. Statistical analyses were performed to determine the degree of T-OPLL progression according to the types and surgical methods. Mean OPLL progression was significantly higher in type 2. The mean annual growth rates of OPLL (AGRO) for groups 1 and 2 were 6.21% ± 6.11% per year and 23.50% ± 11.34% per year, respectively (P < 0.01). Further, no statistically significant differences were seen between the fixed and non-fixed groups (P= 0.23), and CD and non-CD segments (P= 0.56). The mean AGRO does not decrease even after stabilization and CD. Type 2 intervertebral space was a risk factor for T-OPLL progression. Cases of type 2 without CD need close follow-up.