Biomechanical comparison of laminoplasty and in-site regrafting versus laminectomy with pedicle screw fixation for localized thoracic pathological ossification of the ligamentum flavum: a finite element analysis.

Abstract

Localized thoracic pathological ossification of the ligamentum flavum (TPOLF) is considered a significant factor in thoracic myelopathy, and surgery is the main treatment method. This study aimed to compare the biomechanical effects of two internal fixation techniques on spinal stability, range of motion (ROM), stress on internal fixation devices, and adjacent segment degeneration after localized TPOLF treatment using finite element analysis. CT data of a healthy male volunteer were imported into MIMICS software and further processed with Geomagic software to establish a three-dimensional model of T8-T12. First, the detailed surgical procedures of laminoplasty and in-site regrafting (LPIR) and laminectomy + spinal canal decompression + pedicle screw internal fixation technique (LSPT) were described. Then, two internal fixation schemes were established using SolidWorks software: laminoplasty and in-site regrafting (LPIR) and laminectomy + spinal canal decompression + pedicle screw internal fixation technique (LSPT). The overall ROM, ROM distribution of fixed segments, adjacent segment ROM, Von Mises stress on adjacent intervertebral discs and internal fixation devices were analyzed under physiological loading conditions. Among the two groups of internal fixation techniques, LPIR had the highest overall ROM, which was 1.58°, while the overall ROM of LSPT was only 0.40°. The LPIR group experienced greater stress on the adjacent intervertebral discs at the proximal and distal ends, which were 2.30 MPa and 1.79 MPa, respectively. In the LSPT group, the Von Mises stress on the adjacent intervertebral discs at the proximal and distal ends was 2.12 MPa and 0.87 MPa, respectively. In the LPIR group, the titanium plate and screws bore greater stress, which was 363.06 MPa. In all types of movements, the maximum stress on the plate-screw connection site near the laminectomy boundary of the plate was observed. In the LSPT group, the screws showed the maximum Von Mises stress during flexion, which was 60.51 MPa. These biomechanical results were consistent with our previous 2-year clinical follow-up data, which showed that LPIR preserved better spinal mobility with a lower adjacent segment degeneration rate (12.5%) compared with LSPT (25%-35%). Laminectomy and pedicle screw internal fixation provide better stability but reduce spinal flexibility. LPIR retains better spinal flexibility and is a feasible treatment strategy for TPOLF.