Implant Analysis on the Lumbar-Sacrum Vertebrae Using Finite Element Method

Abstract

Disc degeneration is a common phenomena occurring due to ageing and is observed as changes occurring in the anatomical and physiological functioning of the disc. Degenerative Disc Disease (DDD) occurs when the inner core leaks out through the outer portion of the disc which places pressure on nearby nerves or the spinal cord. Intervertebral discs deteriorate and grow thinner as age progresses, which cause lower back pain. In many cases this is treated with medication and in severe cases surgery is preferred. In surgical procedures, for the fusion of bone in degenerated regions, pedicle screw implant has gained more importance. But in post-operative condition, loosening of screw occurs in the lower lumbar spine L5-S1 region. This is due to the high stress developing on the screws post surgery. The objective of this work is to compare the stress developed in the normal and abnormal subjects for various loads using finite element analysis. The data was acquired from two subjects (Normal −1, aged 43 and the other abnormal −1 diagnosed with DDD aged 61). A 3D model was generated from CT images by identifying the regions of interest. In addition to it volume and surface rendering techniques were employed in obtaining a 3D model. Intervertebral disc for L5-S1region was generated and pedicle screw implant was designed. The screw along with the vertebrae was subjected to stress analysis using Finite element method . Analysis was carried out for various loads applied on the L5-S1 region. It was observed that the stress values varied from 1.979e+02 to 1.371e+04 without screws and from 5.831e+04 to 6.936e+05 with the screws for normal subject. For the abnormal subject, it has been observed that the stress values varied from 1.337e+02 to 6.269e+03 for mild degeneration and from 1.029e+02 to 5.051e+03 for severe degeneration without the screws. Further, it has been noted that the stress values varied from 1.792e+04 to 2.130e+05 for mild degeneration and from 5.831e+04 to 6.936e+05 for severe degeneration with the implant placed. This study proves to be clinically highly relevant in addressing post-surgery issues due to placement of implants and in analysing the subjective appropriateness of the implant being used.