Abstract
Limitations in the material properties of arthroplasty bearings have been a major impediment to increasing the longevity and durability of total joint replacement. These limitations most often manifest as wear debris related osteolysis and bearing failure. While these problems cause serious complications in THR and TKR, as arthroplasty is applied to the spine, such problems could become catastrophic. An ideal bearing material and design would be biocompatible, provide for restoration of normal range of motion, and be durable enough to sustain long term unrestricted high demand activities without mechanical failure, significant wear, or contribution to particulate related osteolysis. A new material, Polycrystalline Diamond Compact (PDC), appears to closely approximate the ideal bearing material for applications from large joints to intervertebral discs.
PDC is a diamond structure formed at ultra high pressure and temperature and bonded to a metal substrate. Bond strength to substrate approximates substrate tensile strength. PDC has unprecedented impact toughness and hardness, and has the lowest unlubricated coefficient of friction of any manmade contact bearing. A screening study was used to evaluate wear properties with ceramic and CoCr controls. Full prototypes were tested in a PMED hip simulator for 10 million cycles and on a spinal disc simulator for 30 million cycles.
In the screening study, PDC specimens demonstrated a significant advantage in wear over controls, whose wear rates were consistent with earlier studies. In simulator studies, the PDC specimens experienced extremely low wear at 10 million cycles (~1.0 mg per bearing surface) under austere conditions of no lubrication. In the spinal disc simulator, wear was approximately 0.3 mg at 20 million cycles under similar austere condition.
PDC’s unique material properties lend themselves to designs with thin (5 mm) acetabular bearings that provide for improved ROM and decreased dislocation risk, as well as to spinal applications where space is at a premium. Its properties of extraordinary impact toughness and high wear resistance lend themselves to arthroplasty applications which may require no undue activity restrictions, and may make prostheses available in which bearing wear and mechanical failure are no longer a factor affecting longevity.
The abstracts were prepared by Nico Verdoschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, Universitair Medisch Centrum, Orthopaedie / CSS1, Huispost 800, Postbus 9101, 6500 HB Nijmegen, Th. Craanenlaan 7, 6525 GH Nijmegen, The Netherlands.
