A Finite Element Model Study Of Kyphoplasty For Osteoporotic Vertebral Compression Fractures Of Thoracolumbar Spine

Objectives: To estimate the biomechanical variations of the thoracolumbar (T11-T12-L1-L2), in normal conditions, osteoporosis ,after osteoporotic compression fracture of T12 and after kyphoplasty of T12 by using finite-element analysis.Methods: The CT images of thoracolumbar from a typical normal adult male were selected and three-diamensional finite-element models of thoracolumbar(T11-T12-L1-L2) including normal conditions ,osteoporotic conditions ,osteoporotic compression fracture of T12 and kyphoplasty of T12 were developed by using computer softwares as Mimics,Magic RP and MSC Patran.Then all finite element models were exerted constraints and loads by using a finite element analytic software Abaqus . A homogeneous and katadromous upper body weight (260N) was loaded on the supine surface of T11 vertebral body. TO simulate modes such as neutral position, compression, flexion, left bending and left rotation. Then the displacement ,load transfer ,stresses and strains of the thoracolumbar vertebral bodies could be analyzed.Results: The max principal strains(MPS) of osteoporotic thoracolumbar finite element models were increased compared with the normal models, it was 2.22 and 2.36 respectively when T11 was in anteflexion 10 degrees position and left-handed rotation 10 degrees position. while in normal finite element models it was only 1.50 and 1.45 respectively. As for T12, the greatest max principle strains appeared when models were in 10 degrees left bending positions. It was 8.44 in osteoporotic FEM and 7.44 in normal FEM respectively. the greatest MPS of L1 and L2 occurred when they were in 10 degrees left rotation positions, they were 31.82 and 4.70 respectively(osteoporotic FEM) and 22.70 and 3.39 respectively(normal FEM). For the osteoporotic vertebral compression fractures of the T11,the MPS of the T11 were increased 17 times after the fractures of T12 and the probability of refracture of T11 also increased greatly. The MPS of the T12 and L2 were increased too. But the MPS of the L1 were not changed obviously, even decreased when it was in left bending positions and left rotation positions. The MPS in the inferior articular processes and pedicles of the T11 and T12 were increased greatly after the OVCF of the T12. The MPS of the T12 would be recovered after the KP (the 1/3 of the vertebra were filled with PMMA ), but the MPS of the rest vertebra were still justo major.Conclusions: 1.The results of the study showed that KP could decrease the probability of the refractures after the occurrence of the OVCFs, and the risk of refractures were high on the vertebra which was next to the fractured vertebra,especially on the superior one. 2.Cataplasia of the facet joint would proceed after the OVCFs, especially from the fractured vertebra and superior ones. 3.The MPS of the vertebras that next to the fractured vertebra would not increased after the KP ,i.e KP would not add the chances of the refractures. 4. As KP was just a local therapy and only the osteoporotic compression fractured vertebra was filled with PMMA, the rest vertebra were still osteoporotic and which we should deal with. Or the refractures maybe occurred to the other vertebra in future.