Analysing ‘lift-off’ events during knee wear testing

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Description/Abstract

The lower conformity and bi-condylar nature of the knee makes condylar ‘lift-off’ (LO) an issue; fluoroscopy studies show condylar LO in many cases[1]. Distinct from this effect, a moving contact causes intermittent exposure at different points on the polymer surface: this discontinuous contact may be termed a ‘local’ LO event. This can occur without condylar LO, and both may contribute to increased wear in different ways. Point-LO has been studied in pin-on-disc (POD) tests and has been shown to have the potential to increase wear[2,3]; condylar LO has also been re-created for knee wear tests, again increasing wear[4]. However, it is difficult to determine in-vitro whether an increase in wear is due directly to condylar LO, or a resulting increase in local LO. Condylar LO will modify the kinematics of the knee, allowing greater mobility for the contra-lateral condyle, and increasing contact pressure; however an increased level of local LO may also occur, which could increase wear potential in other ways. In-silico models provide a means to explore this interaction and visualise LO