BACKGROUND: At present, the clinical short-term effect of Wallis non-fusion system is obvious.
OBJECTIVE: To establish the Wallis non-fusion system finite element model and to analyze the stress distribution under different physiological movement.
METHODS: Eight volunteers with mild degeneration of the lumbar intervertebral disc were subjected to compute tomography (CT) scanner. CT scanning images were imported into Materialise Mimics 10.01 software. Three-dimensional models of L4-5 disc and its intervertebral disc were reconstructed, and then the results were compared with literature results to verify the model validity. Wallis system were established by using the AutoCAD 2009 software, and then transformed into Materialise 3-Matic 4.3 software for re-meshing, the reconstructed Wallis system was fitted with lumbar spine model according to the standard operation mode, and then transformed into Abaqus 6.9 software to form finite element model, then the stress changes of lumbar flexion, extension, lateral bending and rotation of lumbar Wallis non-fusion system were analyzed.
RESULTS AND CONCLUSION: The three-dimensional finite element model of lumbar established in the experiment concluded 233 438 units and 48 174 nodes; the three-dimensional finite element model of Wallis system concluded 11 857 units and 3 398 nodes. After the two models were merged, it concluded 245 295 units and 51 572 nodes. The reconstructed three-dimensional model could accurately simulate the fixation of the Wallis non-fusion system. Then the stress changes of lumbar flexion, extension, lateral bending and rotation of lumbar Wallis non-fusion system were analyzed through stress contour. The stress contour showed that Wallis system was involved in the activities of lumbar spine in different directions and had a good match with the lumbar spine. Wallis system was conformed to the four movement conditions of lumbar spine, and the stress located between the upper and lower spinous part was more concentrated, and the stress contacted with the lower part of the vertebral spinous process was highest. Applications of sophisticated CT scanning technique and Mimics software could directly docking with Abaqus software which made the establishment of three-dimensional finite element model of Wallis non-fusion system more faster and accurate according to the direct assignment of the CT value. The implantation of the Wallis interspinous distraction device could share the stress of the disc and the small joints. The stresses of Wallis system and spinous processes were increased leading to the increasing possibility of spinous process fracture and implant fatigue rupture accordingly.