Total hip replacements are devices that are considered highly successful in relieving pain and restoring movement. They are commonly made from ceramic, plastic or metal materials. However, the continuing problems with wear and particulate debris can eventually require further surgery, including totally replacing the prosthesis. Here, we will discuss the biological mechanisms of how wear debris can cause the condition 'aseptic loosening'. Different design strategies orthopedic researchers are focusing on to eliminate this problem will also be discussed.

             Biological Mechanism:.

             Wear debris from devices used in total hip replacements can cause a condition called aseptic loosening. Aseptic loosening is a loosening of the total joint that is not caused by bacteria.4 It is attributed to wear particles of the implant, tissue response dominated by macrophages and degrading enzymes.2 In a loose total joint, the joint lies in a cavity that forms around it that is padded with loose connective tissue. The total joint moves and changes position within this cavity and the shaft of the total hip sinks deeper into the femoral bone. Surfaces of an artificial hip joint produce many tiny particles when rubbed against. Movement of the total hip joint pressurizes the joint fluid, pushing it into niches around the total joint. There is usually some connective tissue left in these niches. Here are located the macrophages, 'garbage cells' whose job it is to clean dead cells from the tissues. However, when macrophages clean up the artificial particles, they get confused and begin to digest healthy bone tissue. As the soft connective tissue expands around the prosthesis, it dissolves even more healthy tissue. A vicious cycle develops that, in some patients, may completely destroy large parts of the skeleton.4 Further surgery is often required and sometimes complete replacement of the artificial total hip joint.