New type of artificial hip - ceramic-on-metal

A new type of artificial hip, more robust and longer lasting than conventional artificial joints, is to undergo clinical trials and could be available for patients within five years.

These ‘ceramic-on-metal’ joints cause less damage to the surrounding bone than conventional artificial hips, therefore many recipients will avoid the need for further surgery. They could also lower the age at which it is practical for patients to undergo hip replacement, helping them to continue to lead active lives. The limitations of conventional artificial hips mean that many patients are advised to wait as long as possible, often in considerable discomfort, before having an artificial hip put in place.

The research is being carried out by engineers, medical researchers and biologists at the University of Leeds, underpinned by funding from the Engineering and Physical Sciences Research Council (EPSRC).

This research is a further improvement on work carried out by the same team to develop ‘metal–on-metal’ joints, which have been in use for a number of years. The ceramic part of the new artificial joint is the knuckle head and the cup of the hip is made out of the metal.

‘Metal-on-metal’ joints improve on the traditional ‘metal-head-in-polyethylene-cup’ implants, being longer lasting and more robust. This latest ‘ceramic-on-metal’ joint further improves on ‘metal-on-metal’ as it generates ten times less metal wear. The ceramic head remains smooth and undamaged throughout the lifetime of the joint and this improves the joint lubrication process, reducing friction and wear. The research team use a unique ‘Hip Simulator’ to carry out their work

Professor John Fisher of the School of Mechanical Engineering is leading the research. He says: “An increasing number of younger and active patients now need hip replacements, and are demanding better-performing artificial joints. These recent developments will lead to a ten-fold improvement in wear performance.”

Local bone damage occurs because, as the head of an artificial hip rubs against the cup that holds it, tiny wear particles are produced. These accumulate over time and cause an adverse reaction in the living cells around the implant, leading to the death and eventual loss of bone tissue. ‘Metal-on-metal’ and ‘ceramic-on-metal’ joints generate a lower volume of wear particles than traditional ‘metal-head-in-polyethylene-cup’ implants. The metal particles are also much smaller and so disperse more readily around the body. In contrast the polyethylene wear particles are larger, being micron or sub-micron in size, these are retained in tissues around the artificial joint and stimulate inflammation and bone loss, which leads to loosening and failure.

The EPSRC funding is also being used to analyse the wear particles generated in the body by artificial hips on a much smaller scale than has been previously possible (ie down to the nanoscale) and to determine how the body responds to them. Nanoscale particles are widely transported around the body, hence substantially diluting their local concentrations and effects. They do, however, have the potential to interact more widely with a range of other organs and tissues in the body. Current work has not only quantified particles down to five nanometres in size, but it is also investigating any potential influences of very low concentrations of nanoparticles with different organs and tissues. This research will underpin further developments in surface engineering and materials. It has also enabled the research team to develop pioneering techniques for simulating and testing artificial hip joint performance, and to invest in a unique laboratory infrastructure that includes the world’s largest wear simulation facility of its kind.

Currently over 10% of hip replacement patients need follow-up operations to address problems caused by damaged bone tissue. The new hips could cut this figure significantly, reducing the risk of dislocations and other long-term problems.

This research is one of the areas of work at the University of Leeds currently receiving EPSRC support under a Portfolio Partnership Award. This Portfolio Partnership is consolidating existing projects and incorporating new projects into a 5-year programme on Tissue Replacement and Regeneration, and providing grant support of over £2.2 million over the period 2003-2008.