FE Assessment of an Interspinous Implant (ISS)

The main objective of this work is the demonstration of a conceptual approach for efficient interspinous implant evaluation and design using finite element (FE) method. A novel dynamic stabilization system (Interspinous spacer (ISS), registered in France under FR05/003524 and FR05/11161) was developed, which has an important role in the treatment of the degenerative lumbar spine compared to conventional surgical treatment -spinal fusion for chronic low back pain due to degenerative disorders in the lumbar spine. Anatomically realistic FE models of healthy, nucleotomized and implanted models of lumbar L4-L5 motion segment were exercised the physiological loading configurations under flexion, extension, lateral bending and axial rotation to investigate the biomechanical effect of the ISS by comparison of the load-response curves of the three models. Under flexion and extension, the response curves show that the range of motion of the implanted model is greatly reduced in relation to the healthy and nucleotomized models. In lateral bending mode, the response curves show that the implanted segment relative less stiff compared to the nucleotomized segment. Under axial rotation, the response curves suggests that the interspinous relatively effective in the axial rotation mode without affecting the kinematics of the L4-L5 segment. Based on the implanted L4-L5 model, the interspinous spacer has the capability of restoring back the functionality of the dissected posterior ligaments, and the kinematics of the implanted model and nucleotomized model are of similar range. The much greater stiffness of the implanted segment under sagittal bending is an issue needed to be addressed, as the motion is greatly limited.