Skeletal implants are biocompatible synthetic materials and structures utilised for the repair, augmentation or replacement of natural tissues and joints in orthopaedic and dental prostheses. In recent years the development of implants as artificial joints for the replacement of arthrotic hips has provided a major clinical advance in the treatment of arthritis, with nearly half a million patients on a world-wide basis (about half in Europe) benefiting annually from total hip arthroplasty. Parallel progress has been made with the treatment of other arthrotic joints, particularly of the knee, with approximately 400,000 patients treated per year by a joint replacement procedure. However all the current joint prostheses suffer from a finite lifetime before they need to be replaced, due to a basic mismatch between the implant and the adjacent tissue (bone) at regions of fixation (ranging from a mean of ~10 years for a 65+ year old patient to less than 5 years for a 45 year old patient), which leads to the need for a one or more revision operations. Based on the available statistics of prostheses lifetimes, the number of revisions required for existing joint replacements based on current technology will continue to escalate throughout Europe, with both a catastrophic effect on the total health care budget and a continuing absence of a suitable treatment for younger patients. The recognition of this major problem led to the formation of this concerted action in skeletal implants in 1989, with Professor Bonfield as project leader (co-ordinator). The following general achievements have resulted from the concerted action:

i) Methods have been developed for the standardisation and evaluation of retrieved skeletal implants on an European scale, as a basis for determining the mechanisms which result in significant prostheses failure.

ii) An European network has been established of laboratories involved in critical aspects of the underpinning science for the development of second generation skeletal implants, with an enhanced lifetime in the patient. Such optimised implants have application, not only in replacement joints, but in a wide range of procedures, such as the treatment of bone tumours, repair of cartilage lesions, ligament and tendon replacement, bone fracture fixation, maxillo facial reconstruction, spinal disc and vertebra replacement and dental implants.

The particular achievements are summarised as follows:

i) Implant retrieval

a) Appropriate analysis methods for implant retrieval were established.

b) A comparison with other protocols and standards was initiated.

c) A consensus as to critical parameters required for implant evaluation was consolidated.

d) A circuit was initated for evaluating the same retrieved specimen in different European laboratories utilising a range of expertise.

ii) Innovation of second generation implants

a) A European multi-disciplinary forum and laboratory network was established.

b) The conditions required at the tissue implant interface for long term stability were defined.

c) A consensus on the merits of novel bioactive materials, including hydroxyapatite ceramics and composites and modular systems, combined with an appropriate biomechanical environment, to provide optimised implants was approached.