Bone replacement materials can be needed for a variety of reasons. They are sometimes required when a section of bone is missing and the gap needs to be filled in, for example following an accident or after the removal of a tumour.
There are several options for this type of bone replacement:
- Allografts involve using material from another patient. However, there are risks of infection and the implant being rejected, and the strength of the replacement bone may be reduced due to sterilisation.
- Autografts involve using material from the same patient, but from a different site (such as the pelvis). Although this reduces the chances of rejection, there is a limited amount of material available, and two surgical procedures are needed, leading to more pain and a higher risk of infection.
- Synthetic materials are gradually becoming more popular. Hydroxyapatite can be prepared easily in a laboratory, but since it is a ceramic, it is too brittle to be used on its own for large-scale applications. Composites of hydroxyapatite with degradable polymers can also be used, which resorb over time and allow bone to regrow and fill the space.
However, it is often not as simple a situation as needing to fill in a gap in an otherwise healthy bone, and other reasons for bone replacement materials being required are often age-related. Arthritis is a condition usually associated with old age in which the cartilage at joints wears away, meaning the bones at joints can rub against each other, causing pain and decreased mobility. Additionally, as people get older, their bones become more brittle, and they can experience extensive loss of bone mass (osteoporosis) that leaves them with an increased risk of a hip fracture. This is particularly true for female patients.
In these situations, it is impossible to repair the existing bone and joint replacements are often required. Hip replacement is one of the most common implant surgeries, and this example will be discussed throughout the remainder of this TLP.