Clinical reports of surgical intervention options, such as spacers or hemi-arthroplasties, particularly for treatment of young arthritic patients, have been poor [ Experiments were conducted in an anatomic pendulum friction simulator (SimSol, UK) using the medial femoral condyle of a bovine knee joint articulating against two conforming stainless steel (316L) tibial plates (R=50mm and 100mm). A simplified physiologic knee loading profile was applied represent both low loading and much higher physiological loading conditions, with peak load between 259N – 1.5kN). Tests were conducted in 25% bovine serum and run for 3600 and 300 cycles under the low and high loading conditions respectively. The motion was cycled at 1Hz with amplitude between −10°–13.1°. Cartilage wear was assessed qualitatively from surface roughness measurements using a surface profile using a surface profilometer (Taylor Hobson, UK). The friction and wear of cartilage articulating against the conforming tibial plates were compared to a positive control flat tibial plate model [
Metal-on-metal hip resurfacing arthroplasty is a conservative procedure that is becoming an increasingly popular option for young arthritic patients most likely to undergo a secondary procedure in their lifetime. The stability of the acetabular component is of particular concern in these patients who show an increased risk of failure of the cemented acetabular cups in conventional total hip replacements. The purpose of this study was to examine the initial stability of a cementless interference press-fit acetabular cup used in hip resurfacing arthroplasty and implanted into ‘normal’ versus poor quality bone. Also examined was the effect of the press-fit procedure on the contact mechanics at the cup-bone interface and between the cup and femoral head. A finite element (FE) model of the DUROM resurfacing (Zimmer GmbH) was created and implanted anatomically into the hip joint, which was loaded physiologically through muscle and subtrochanteric forces. The FE models included: a line-to-line, 1mm and 2mm interference press-fit cup. Also considered were two FE models based on the 1mm press-fit cups, in which the material properties of the cancellous and cortical bone tissues were reduced by 2 and 4 times, to represent a reduction in bone quality as seen with age or disease. Increasing the cup-bone interference resulted in a sig-nificant reduction in implant micromotion. All the pressfit models showed predicted cup-bone micromotion below 50 micrometers. This would ensure adequate initial stability and encourage secondary fixation through bone in-growth. The predicted acetabular stresses were found to increase with the amount of press-fit, however, there was no suggestion of a fracture. These stresses would further contribute to securing the cup. Reducing the bone quality showed an increase in the predicted micromotion and increased bone strain. Micromotion was below 50 micrometers, but the predicted compressive bone stresses, necessary for additional implant fixation, was reduced. This implied that poor quality bone would provide unsuitable support medium for the implant. The bearing surface contact mechanics were little affected by the amount of pressfitting.
It is possible in theory to optimise the geometry of the metallic bearing surfaces, based on the worn components, to minimise the running-in wear. However, such an improvement in lubrication cannot be readily achieved because of difficulties in surgical techniques and position of the components.
Viscosupplementation is the current treatment modality for early stage arthritis and in some cases for delaying joint replacement procedures. Rheological properties similar to that of synovial fluid and high molecular weight have been recognized as the determining factors in hyaluronic acids (HA) therapeutic and analgesic value (
Since 1977 we did implant all alumina (Al2O3) bearings total hip prostheses. A lot of data were documented concerning tissue reaction, in vivo wear behaviour, fractures, and clinical outcome. Ceramic materials retrieved at revision were analysed. In some cases, wear was as low as a few microns for a 15-year period in use. This is two thousand times less than a regular metal on polyethylene sliding couple. and 100 times less than a metal on metal prosthesis. Fracture mechanism is related to crack propagation into the material. During the first period, the fracture rate was in the range of 2%; it then dropped to less than 0.1 %. Few fractures could not be explained by technical or design mistakes. Clinical outcome: More than 4000 total hips in selected young and /or active patients were implanted. In a recently reported series of consecutive patients operated by P.Boutin during the year 1980, 118 hips in 106 patients were included. Mean age was 62 years. At the twenty-year follow-up evaluation, forty-five patients (fifty-one hips) were still alive and had not been revised, twenty-five patients (twenty-five hips) had undergone revision of either or both components, twenty-seven patients (thirty hips) had died from unrelated causes, and nine patients (twelve hips) were lost to follow-up. The mean Merle d’Aubigné hip score was 16.2 ± 1.8 at the latest follow-up. Survival of the cup at twenty years with revision for any reason as the end-point was 85.6 percent for cementless cups versus 61.2 % for cemented cups, respectively. Survival of the stem at twenty years with revision for any reason as the end-point was 84.9 % for cementless stems versus 87.3% for cemented stems. Wear of the prosthetic components was undetectable on plain radiographs. No fracture of the alumina socket or head was recorded. Another study concerned a more recent design of the socket which consisted in a metal back titanium alloy shell covered with a pure titanium mesh with an alumina liner. The nine year survival rate was 98.4% with revision for aseptic loosening as the end point. Conclusion This alumina on alumina bearing provides interesting results without any physical limitation specially in young and active patients.
Metal-on-metal (MOM) bearings for artificial hip joints have attracted significant attention recently as a way of reducing wear and consequently wear particle induced periprosthetic osteolysis, which is the major cause of failure. One of the most widely used MOM total hip implants is the Metasul system (Zimmer GmbH), in which a thick polyethylene backing is used underneath the metallic inlay. The purpose of this study was to investigate the effect of the polyethylene backing on the transient lubrication under dynamic loading and velocity conditions representative of walking. A 28mm diameter Metasul bearing was analysed, and the predicted lubricant film thickness was compared with that for an all metallic cup. The predicted transient lubricant film thickness in the Metasul system was found to be significantly greater than the corresponding prediction from the all metal cup. Therefore it was concluded that the polyethylene backing may play an important role in the lubrication and overall tribological performance of the Metasul bearing system with a diameter of 28mm.