Abstract
Introduction
Total knee arthroplasty (TKA) is a consolidated orthopaedic procedure and success of such operation depends on the prosthetic design [1]. Unfortunately, as there is a good survival rate of primary TKA, failures occur for factors concerning the polyethylene composition of the implants, secondary osteolysis, and ultimately loosening of the implants are the usual causes of failure after normal use [2]. Dynamic in vitro testing of the human knee continues to be an area of interest to the orthopaedic biomechanics community. The scope of this work was to assess pre-clinically the wear behaviour of polyethylene knee insert under a realistic stair climbing activity using a displacement knee simulator.
Materials & Methods
Four commercial posterior-stabilized fixed-bearing component prosthesis for TKA were tested in this study (Stryker®-Orthopaedics, Mahwah, NJ-USA). These were new and delivered in sterilized packages. Particularly, corresponding UHMWPE tibial inserts (size #7) were made of conventional surgical grade polyethylene resin (GURâ�¨1020), consolidated by compression moulding (accordingly to ISO 5834/1-2), and EtO sterilized. These were tested in conjunction with corresponding CoCrMo alloy femoral components.
For the implementation of realistic loading scenarios during in vitro wear testing for human joint prostheses, an in vitro protocol was designed to simulate the flexion/extension angle, intra/extra rotation angle, and antero/posterior translation. These movements were obtained in patients by three- dimensional video-fluoroscopy. Axial load data were collected by gait analysis [3].
Results
The components run under stair climbing simulation completed the planned two million cycles under bovine calf serum as lubricant. The volumetric wear trend is schematised in Figure 1. The wear patterns observed on the contact surfaces were similar over the three tested inserts. A few pitting phenomena were observed on the insert contact surfaces. In addition, unidirectional scratches were observed in both condyles along the AP direction.
Conclusion
The knee wear simulator executed the imposed physiological gait condition, under stair climbing waveforms. This new approach opens the way to more scenarios able to give comprehensive answers to the wear behaviour of knee components. Hence, further development will be the definition of a global protocol, with the implementation of various motor tasks (chair sitting and rising, squatting), using the same approach.
