Lubrication Modelling of Knee Implants

simplifying the research I did during my PhD - for every knowledge level

Middle School:

People get knee implants when their knees stop working. Putting a knee implant in your body requires surgery, and surgery hurts, so you probably want to get it right the first time. My work was about making sure that the knee implant doesn't break and lasts as long as it can, so you don't need to replace it with another one.

High School:

The knee implant is made of two parts; the femoral component and the tibial insert (see image). It is a hinge joint. Imagine how painful it would be if the two parts scraped against each other while moving. That is why lubrication is necessary between them to reduce friction. My work involves making sure that the lubrication is sufficient, and to make sure the two parts don't scrape each other and wear out. Because then you'd need another implant, and another surgery. We don't want that.

Knee Implant

A knee implant consists of a femoral component and a tibial insert, with a lubricating fluid in between. The red surfaces are the ones that are usually in contact with each other, and must be lubricated to ensure proper movement.

Engineering Undergraduate:

When a person moves, load is applied to the components. This load is transferred to the lubricating film, and so this becomes a fluid-structure interaction problem. The thickness of the lubricating film varies throughout motion (this is what we are solving for), and we optimise the shape and material of the implant to ensure that sufficient lubrication is always present. Otherwise, wear will occur and it will shorten the lifespan of the implant. The following physics need to be modelled:

The lubricating film is non-Newtonian and has pressure-dependant viscosity.
The fluid pressure is governed by the Reynolds thin-film lubrication equation.
The implants can be deformed by the fluid pressure. This deformation is on a very small scale, but enough to vastly affect the results.
The implants are not smooth, and surface roughness must be considered. This affects the flow of the fluid and contact mechanics.
The applied load must be balanced either by the pressure in the lubricating film, or direct surface-surface contact.
The complex geometry of the implant must be considered (and not approximated to e.g. a sphere on a plane).

Previous studies approximate the above physics, and so the novelty is in the detail.

Page updated

Google Sites

Report abuse