Insight on the Mechanical and Tribological Characteristics of Ball-on-Socket Artificial Disc under Alternate Motion of Flexion Extension–Axial Rotation and Lateral Bending–Axial Rotation

Abstract

Ball-on-socket articulation is the major structural type of artificial joints. The insight on the mechanical and bio-tribological characteristics of this structure is important for designing both the device itself and its wear assessment regime. Two kinds of ball-on-socket structures were studied including a simplified general model and a real artificial cervical disc. The bio-tribological behaviors were evaluated by in vitro wear simulation method using four kinds of pairs with different combinations of structure, frictional material and testing duration under alternate motion of FE-AR (flexion extension and axial rotation) and LB-AR (lateral bending and axial rotation). In order to analyze the formation mechanism of representative wear characteristics, the mechanical behaviors were also studied by finite element analysis method. The results indicated that there were similar mechanical and bio-tribological characteristics for these two structures after about 9 MC (Million Cycles) tests. Under the axial load, it revealed more serious wear severity in the edge region than that in the central region for both convex polymer component and concave metal component, which may be due to much higher values of equivalent stress and equivalent elastic strain in the edge region than that in the central region. Under FE (flexion extension) or LB (lateral bending) motion, it showed common wide and curved wear grooves with ring distribution in the edge region for both ball component and nucleus pulposus component, which may be attributed to the higher equivalent stress and equivalent elastic strain at the limit position. It just indicated several sliding scratches for TC4 (Ti6Al4V alloy) metal component with an abrasive wear mechanism, while it revealed plastic deformation, surface cracks, sliding scratches and wear grooves for XPE (crosslinking polyethylene) polymer component with a mix of abrasive wear and adhesive wear mechanism. Hence, there was a strong correlation between structural design and bio-tribological characteristics for ball-on-socket prostheses.