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

Abstract 

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°, 4° and 8°, 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 4.90×10⁻⁶ 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° and 8° of rotation. The maximum values of von Mises stress at the contact surface at 0°, 4° and 8° 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.

Relevance

This new rotating hinge design of knee endoprosthesis can be used for joint reconstruction after wide resection of tumor around the knee. The new design with a congruous spherical contact surface provides a benefit of low contact stress that may minimize the wear process.

Keywords:  Rotating hinge, Spherical contact surface, Finite element analysis, Contact stress