Metal to metal, metal - on - metalbearings, MoM) weight interface prosthesis was put forward as early as more than 40 years ago, early due to reasons such as compatibility of materials, production process, loose, high incidence of complications such as dislocation, metal ions pollution, thus being abandoned. With the improvement of new materials, design, manufacturing process and implantation technology, the friction coefficient between metal and metal bearing surface is significantly reduced. Due to its wear do not produce polyethylene wear particles at the same time, significantly reduce the incidence of bone dissolve, larger ball head and the use of metal to metal prosthesis can significantly reduce the dislocation rate, improve the patient's hip motion. These advantages make the metal to metal weight interface prosthesis has more than 10 years ago in the United States and other countries are all the rage, and some large hospitals in China gradually larger for young patients to carry out the surface displacement and larger ball head metal to metal THA surgery, good clinical results have been achieved.
However, with the extension of follow-up time, some problems of MoM prosthesis are gradually concerned. According to data from the Australian joint registration center for artificial joints, the five-year renovation rate of the total hip prosthesis of MoM's weight-bearing interface was 9.6%, and the renovation rate was 15.5% in 10 years. And from the UK registry data suggest that MoM weight interface total hip prosthesis for 5 years and nine years of renovation rate is 7.7% and 17.7%, respectively, to renovate rate as an index of clinical results significant difference from other interface combination weight. And artificial joint registration centre in New Zealand, according to the diameter of ball head 28 mm or less MoM prosthesis renovation rate was significantly lower than ceramic for ceramics, pottery and porcelain for polyethylene and metal for polyethylene composite prosthesis, and the diameter of ball head of 36 mm or MoM prosthesis clinical effect is not satisfactory. Also, for Australia's registry data further stratified analysis suggest that ball head diameter 28 mm or less MoM prosthesis for 5 years and 10 years renovation rate were 3.7% and 5.7% respectively, the result is superior to the traditional PE interface.
Therefore, the ball head diameter has a definite effect on the revision rate of MoM prosthesis. In addition to the diameter of ball head, MoM prosthesis design flaws (low profile of hemispherical mortar cup design, too big or too small tolerance zone), intraoperative prosthesis will increase the risk of renovated installation Angle is not perfect. In 2010, Johnson &johnson ASR metal to metal artificial hip joint prostheses from city to MoM interface caused great influence, the use of MoM there may be other risks include local soft tissue reaction, osteonecrosis around the prosthesis and the potential toxicity of metal ions. MoM cause local tissue reaction mechanism is not fully clear, some scholars put forward according to the analysis and research results of inflammatory pseudotumor hypothesis is put forward, that cause local tissue reaction is not metal ion itself, but a lot of nanoscale metal wear particles size, the wear particles after consumed by macrophages, in the acidic conditions of the phagosome, cobalt ions dissolved in great quantities, until, macrophage apoptosis cells release large amounts of cobalt ions to form cobalt ions (ion - wave), its local concentration far exceed cobalt ion concentration in serum and synovial fluid, causing huge necrosis of the surrounding fibroblasts, To form inflammatory pseudotumor and other soft tissue reactions.
