Contact stress analysis of the tibial component of prosthetic knee implants

EFFECT OF INTERFACE STRESSES ON ANISOTROPIC STRUCTURE OF THE ARTICULAR SURFACE

Fatigue failure of anisotropic structure of the artificial articular has been implicated in a number of clinical failure scenarios, especially the fatigue behaviour of the articular surface is poorly understood, At the same time, there is no established design and procedure, which is applicable to all load-bearing implants. However, materials degradation significantly may also be increased the life of sample by reducing the peak stresses and redistributing the load to the surrounding tissue. This paper presents the effect of the structural integrity of the shape and stresses distribution on the global material behaviour of articular cartilage. Then modulus degradation appears to be a result of trabecular fracture rather than as a result of tissue level material degradation. Furthermore, we found that Young's modulus normal to the contact surface increases from the superficial to the deep zone in articular cartilage.

Contact stress on polyethylene components of a new rotating hinge with a spherical contact surface

OBJECTIVE

To assess the nonlinear contact stress of a new rotating hinge of our knee prosthesis at various rotation angles.

DESIGN

The contact surface between the metal tibial bearing and the ultra-high-molecular weight polyethylene plate of a conventional rotating hinge is of cylindrical design. We have designed a new type of rotating hinge with a congruous spherical contact surface.

BACKGROUND

The endoprosthesis for reconstruction of limb after wide resection of malignant tumor around knee usually incorporates a rotating hinge. Our new rotating hinge with a spherical contact surface incorporates the benefits of an increased contact surface and potentially increased rotational stability during axial loading.

METHODS

We utilized the ABAQUS finite element program to assess the nonlinear contact stress of this new rotating hinge at rotation angles of 0 degrees, 4 degrees and 8 degrees, based on a contact force of about 2800 N.

RESULTS

The results show that von Mises stress for the finite element model of the polyethylene component of this rotating hinge ranges from 4.90 x 10(-6) to 8.22 MPa at the aforementioned rotational angles. The von Mises stress is about 1.31--1.82 MPa on the major parts of the ultra-high-molecular weight polyethylene plate, including both flanks. There is a mild stress concentration on the outer edge of polyethylene component, especially at 4 degrees and 8 degrees of rotation. The maximum values of von Mises stress at the contact surface at 0 degrees, 4 degrees and 8 degrees of rotation are 5.92, 7.49 and 8.22 MPa, respectively. These contact stresses are within the safety range of the ultra-high-molecular weight polyethylene (compressive yield strength, 14 MPa).

CONCLUSIONS

This new rotating hinge has an evenly distributed contact stress during axial load because of congruous contact design.

Wear of ultra-high molecular weight polyethylene (UHMWPE) in total knee prostheses: a review of key influences

The formation and development of wear is now widely accepted as one of the major concerns in the long-term survivorship of contemporary knee prostheses in vivo. This review examines the role of surface topography, third-body debris, load, contact mechanics and material quality in the wear process. Some of the kinematic and physiological issues that need to be modelled in the development of wear testing regimes for evaluation of material combinations and geometrical combinations in total knee implant designs are considered. Wear testing procedures and some of the results from wear tests are discussed and the need to consider the impact of rolling and sliding in the study of wear in total knee components is highlighted. The dominant wear mechanisms that occur in vivo are identified and the role of these mechanisms is currently being examined experimentally at the University of Limerick wear testing machine.