For people suffering from advanced, end-stage degenerative hip arthritis, total hip joint replacement surgery can be a life-changing procedure. Hip replacement surgery removes the offending arthritic surfaces of the hip joint, replacing them with high-tech metal and space-age plastic components. For all of the benefits derived from hip replacement surgery, it has its potential problems. But the incidence of problems is rather low.
Infection
Infection is, and has always been, one of the biggest risks and potential problems with artificial joint replacements. The major implant components of a hip replacement are typically made up of a high-tech metal and space-age plastic. These implants are placed into position in the femur, or thigh bone, and the acetabulum, or socket, by one of two methods: press-fit or the use of bone cement.
In either case, the metal, plastic and cement are constructed of materials that have no inherent blood supply to them, thus rendering the use of antibiotics useless for these components. If microorganisms happen to colonize in areas adjacent to these parts, the antibiotics cannot reach them without a blood supply to carry them there. This makes treating infections in artificial joint extremely difficult. Occasionally, infections become so severe and microorganisms so entrenched that the only meaningful treatment option is complete removal of the prosthetic parts and replacement with temporary components. These are frequently made of the same bone cement, only mixed with high doses of antibiotics that ooze into surrounding tissues over several weeks.
Prosthetic Loosening
Another potential problem with hip replacements is loosening of the components. When prosthetic implants are inserted by way of the press-fit method, the host bones are prepared in such a manner that accept them with extremely tight tolerances, frequently requiring the components to be pounded in with more than a little force. The tight press fit stimulates the host bone to literally heal itself to the implants. With the cemented method, the number of surface interfaces doubles. One interface is between the cement and the implant itself; the other interface is between the cement and the host bone. The potential for loosening exists between either, or both interfaces, and loosening of one or the other is enough to cause significant problems.
When implants become loose, the risk for further loosening is high. This also carries the potential for the formation of reactive bone--or calcification in soft tissues and spurs--or the possible resorption of surrounding bone secondary to the repetitive movement of the implant.
Dislocation
There is no perfect way to re-create a hip joint. The best attempts are made to reconstruct the normal muscle, tendon and ligament tension and angles of the implants to adequately reproduce the host joint components. Because the implants are made of metal and plastic, there is the risk of dislocation between the ball and socket interfaces if the parts are inserted improperly, or if activity and range of motion exceeds recommended limits.
Leg Length Discrepency
Advanced arthritis of the hip can ultimately cause the affected leg to become shorter than the unaffected one--mainly due to collapse of the femoral, or thigh bone, head as well as erosion and deepening of the acetabulum, or socket. A key goal in hip replacement surgery is to restore leg lengths to normal, or near normal, status. This can be very difficult, especially if both hips are bad and have some level of deformity to both. The potential risk is to have unequal leg lengths after surgery.
