THE NUMBER of hip and knee re-placements is set to soar, scientists from the University of Bristol have predicted.

The trend to operate earlier in life, and the fact that people are now living for longer, means that many more operations will be needed to revise or replace previous work. According to a report published this June, first time hip replacements are set to increase from 38,425 in 2000 to 46,772 in 2010, and first time knee re- placements from 32,942 to 53,712.

The researchers also found that, as well as first time hip operations doubling between 1991 and 2000, hip revision surgery as a result of natural wear and tear or complications had risen by 18 per cent. And, even more spectacularly, first time knee operations had doubled during the same period, with knee revision surgery rising by 300 per cent.

As well as the cost, the rise in knee and hip revision surgery also brings added complications.

Revision surgery typically requires a bone graft, which is usually harvested from the patient themselves. However, in the case of a large bone defect (in the case of the removal of a cancerous tumour, for instance), this frequently comes from a donated source. Bone grafting is also used to fix fractures, and correct spinal curvature such as scoliosis.

A shortage of bone required for this kind of surgery, and the risk of infection (such as MRSA), means that a bone graft is not an operation without its risks.

According to the US biotechnology information business website, BioPortfolio.com, the number of bone grafting procedures undertaken in Europe as a whole will rise from 287,300 in 2000, to 479,079 in 2005.

The harvesting of bone is a painful procedure – involving surgically chiselling out and then grinding down bone chips from one part of the body, and then implanting them into another – frequently leading to longer hospital inpatient stays and recovery time. Donated bone is screened for such diseases as HIV and hepatitis, but can cause complications if it is rejected by the recipient’s immune system.

However, the increasing demand for bone grafting material, and the shortage of supply, means that scientists have been searching for safer, synthetic options.

Among the options being investigated is sea coral, which has a porous structure similar to that of human bone and can be used as a three-dimensional “scaffold”. Stem cells derived from bone marrow are implanted into the coral scaffold, which biodegrades over time. Hoof lesions in sheep treated this way showed signs of bone remodelling and fusion. A similar technique has been successfully developed using the mineral hydroxyapatite, in which cells can be “bonded” in layers.

Another alternative is to use a more durable substance for joint replacement in the first instance. Until now metal has been a short to medium-term solution as it wears out after 10 to 15 years. But newer, stronger materials are being developed, such as oxinium (a substance that combines the best features of ceramics and cobalt chrome), which last much longer than conventional options and could drastically cut the number of revision operations needed in the future.