Stress and strain analysis of a new design of cervical intervertebral disc under daily activity

Abstract

Neck pain one of the most common diseases, with intervertebral disc degeneration being one of the main reasons for such pain. As part of developing of a surgical procedure for intervertebral disc replacement (artificial intervertebral disc), a new design of intervertebral disc (cervical vertebra) was created using biomedical steel L 316, for the part fixed on the intervertebral disc, and polyethylene as the intermediate part between the two metals, which also biomedical material. This is designed to absorb and redistribute heavy loads from the vertebrae in a more equal way to reduce pressure; the symmetrical design offers many benefits where the intervertebral replacement is installed in an appropriate manner. Taking into account the different circumstances of surgery, three types of load were considered: the first was compressive, the condition when the neck is at rest and load is completely vertical without any moment; the second was extension, as the head moves upward and force and moment is applied; and the third was flexion, when the head moves downward and opposing force and moment is applied. By using Ansys 18.2, both stress and strain on the artificial intervertebral components were assessed, which showed that, under movement, the stress was much larger than when at rest due to the inflecting of moment on the artificial intervertebral disc. The soft polyethylene section suffered some degeneration and damage; however, the rounded shape of the parts allowed the load to be distributed more regularly, and the maximum value of the stress was seen at flexion at 256 mpa, as compared to 42 and 152 mpa for compression and extension, respectively. The maximum value of the strain at flexion was 0.076 as compared to 0.0689 and 0.00619 for compression and extension, respectively. Comparison between the new design and the currently used ProDisc implant showed that the strain on the former was lower, but that the stress in extension and flexion was higher.