Hip replacement breakthrough

The new product is the Birmingham Hip Resurfacing 'BHR' implant, about to be launched commercially worldwide. An all-metal artificial hip joint, it represents a major advance in both design and materials technology.

The implant resurfaces the head of the femur with a metal dome which fits into a metal cup attached to the pelvis. Conventional hip replacement operations are much more radical, cutting off the head and neck of the femur altogether and replacing them with a ball - mounted on a spike driven down the centre of the bone - which fits into a polyethylene cup fixed in the pelvis.

Major advantages of the BHR include:

 A surface wear rate so slow that it is expected to easily last for the patient's lifetime, whereas a conventional joint can last less than 10 years in an active patient
 which means that younger patients can be operated on in the knowledge that even if the bearing should eventually fail, it can then be replaced with a conventional joint.
 Full mobility is restored because BHR resurfacing is much less traumatic than conventional total hip replacement and does not damage muscles to the same extent - remarkably, two patients have already resumed international sporting careers.
 Recovery and rehabilitation times are far quicker, and post-operative pain is rare.
 A new method of creating an integral (Porocast) surface texture on the outside of the cup component, into which pelvic bone quickly grows and locks, spells the end of conventional sintered-on or plasma sprayed surfacing particles which tend to come off and damage the joint.

The detective story began in 1990 when Birmingham-based surgeon Derek McMinn noticed that some 25 year old recovered metal-on-metal traditional hip joints were in almost perfect condition. This was astonishing, because such joints had long been
abandoned in favour of metal-on-plastic ones on account of their poor record for wearing excessively or even seizing up.

But metal-on-plastic joints have serious disadvantages - not apparent when they were introduced in the 1960s but brought to light by increasing patient expectations and longevity. The metal ball wears the plastic cup, causing Osteolysis which leads to implant loosening and damage to the remaining bone. This problem limits joint life to five to 10 years in active patients.

Derek McMinn realised that the exceptionally good condition of the recovered all-metal joints must be due to manufacturing tolerances or surface properties, or both.

So he approached Midland Medical Technologies and their Sheffield-based specialist casters Doncasters Centaur Precision Castings, and Centaur in turn approached Sheffield Hallam University's Materials Research Institute. Together these partners developed a specification which mimicked the profiles and surface microstructures of the recovered joints, then created new casting and finishing technologies to turn the specification into a successful product.

The secret lies in even distribution of hard-wearing carbides in the surface of the metal and in precise manufacturing tolerances that were simply not possible 30 years ago.

Every year there are some 50,000 hip replacement operations in the UK and half a million worldwide, so the new product's potential is huge. To date more than 1,400 BHRs have been implanted in young patients in Birmingham, with a complication rate of less than 1 per cent in five years.

For further information: contact Jon Pyle (head of media and corporate affairs) on 0114 225 4187.

Sheffield Hallam University

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