In a total knee replacement, there are two ways of attaching the components to the bone.
One of them is to use bone cement, which usually takes about 10 minutes to set. Bone cement are biomaterials obtained by mixing a powder phase and a liquid phase, which can be moulded and implanted as a paste and have the ability to set once implanted within the body. It is used to anchor artificial joints, as it adheres the prosthetic joint and the bone together, while remaining flexible enough to allow for movement and to absorb forces acting on the body. It’s also used to remodel lost bone and to fill gaps in bones.
The other is a cement-free approach, in which the components have a porous coating that allows the bone to grow onto it. While on the surface (no pun intended) this may seem like the natural choice, there are circumstances where cement may be better or vice-versa. The success of bone growth attaching implants is sensitive to a number of factors. When trying to induce bony growth onto the implants, there is a very low tolerance for error with the bone cuts. If a cut plane of bone is even half a degree off, it can be enough to inhibit bone growth due to micromotion at the interface between the bone and implant. A small amount of motion between the implant and cut bone surface promotes a fibrous tissue bonding rather than a secure bone bond, which inevitably leads to failure of the implant and likely revision surgery.
In some cases, a surgeon may use both techniques during the same operation. Ultimately, surgeons often determine the best option based on the individual patient circumstances.