髓核固定/滑动型人工颈椎间盘应力特征对比及关节面摩擦学优化设计

Comparison of Stress Characteristics and Tribological Optimization of Articular Surface Design for Artificial Cervical Disc with Fixed or Sliding Nucleus Pulposus

对比了髓核固定型和滑动型人工颈椎间盘应力和变形特征,根据应力和λ值(最小膜厚与等效粗糙度之比),采用正交试验法进行关节面摩擦学优化设计.结果表明:两款球窝假体应力集中均发生在相对运动关节面和组件连接处,且髓核上表面应力最大值呈环形分布特征.滑动型相对固定型,优势是运动模式更丰富、应力传递更均匀,劣势是复杂运动会加大髓核应力(从1.36 MPa到2.43 MPa).固定型的髓核变形量仅是滑动型的22.5%,但总变形均集中在前后两端.关节面参数对应力影响权重是球缺高度>球头半径>球窝间隙,且高度和半径越大、间隙越小越好;对润滑状态影响权重是球窝间隙>球头半径,且间隙越小、半径越大,润滑状态越佳.半径、间隙和高度的最佳组合为16.00 mm、10.0μm和1.2 mm,在此组合下滑动型假体最大应力数值最小(2.79 MPa),且润滑状态最佳(λ值0.573).

Two kinds of artificial cervical discs were designed with fixed or sliding nucleus pulposus, based on the database of physiological parameters of Chinese cervical spine. The stress and deformation characteristics of the two products were compared by the finite element analysis method. Three key parameters of ball-on-socket structure were selected including ball radius, radial clearance and hemispherical height. The orthogonal test method was used to optimize the tribological design on the articular surface, according to the maximum contact stress and the λ value(Ratio of minimum film thickness to equivalent roughness). The results showed that the stress concentration of the ball-onsocket prosthesis occurred on the articular surface and the connection location between different components. The maximum stress on the upper surface of nucleus pulposus presented a circular distribution. Compared with the prosthesis with fixed nucleus pulposus, the prosthesis with sliding nucleus pulposus showed the advantages of richer movement mode, more uniform stress transmission, while the disadvantages of increasing stress from 1.36 MPa to 2.43 MPa due to complex movement of nucleus pulposus. The total deformation of fixed type was much smaller than that of sliding type.Taking nucleus pulposus component as an example, the former was only 22.5% of the latter. However, both types showed the phenomenon of bigger total deformation on the front and back end of the prosthesis. The order of the influence weight on contact stress was hemispherical height > ball radius > radial clearance for articular surface parameters. It revealed lower stress with bigger values of hemispherical height and ball radius as well as smaller value of radial clearance. The order of the influence weight on lubrication state was radial clearance > ball radius. It revealed better lubrication state under smaller value of radial clearance and bigger value of ball radius. The best parameter combination was 16.00 mm, 10.0 μm and 1.2 mm for ball radius, radial clearance and hemispherical height, respectively.Under this combination, the maximum contact stress of the prosthesis with sliding nucleus pulposus was the smallest with a value of 2.79 MPa, and the lubrication state was the best with a λ value of 0.573.