Typically, hip replacement surgeries are considered when pain from osteoarthritis, caused by the normal aging process, drastically affects quality of life. Hip dysplasia can speed up this wear on the cartilage, making a total hip replacement (THR) necessary. A condition called avascular necrosis (AVN), caused by a loss of blood supply to the femoral head, often also necessitates a hip replacement because of the death of cartilage.
The materials used to make artificial hip joints have changed significantly since the 1920s. Originally, an artificial socket was made from plastic, and a femoral head and neck were made from cobalt-chrome. Today, titanium has become more common than cobalt-chrome. Regardless of the metal type, the plastic socket wears away at roughly 1 millimeter per year against the metal ball, thus limiting the life of the artificial hip to 10 to 15 years. New plastics are thought to wear out a lot slower, but at this point there is no long-term data to prove if they last longer. Newer developments include metal-on-metal joints and ceramic-on-ceramic joints.
The basic design of the prosthesis is similar regardless of the materials or the manufacturer, and the surgery itself is unchanged by the materials used. The surgeon removes the femoral head and neck through an incision over the hip joint. He or she then inserts an angled shaft with a smooth, balled implant into the bone. The next step is to smooth out the socket side of the joint and fit it with a cup. Depending on the type of artificial joint being used, the cup will either be cemented into place with bone cement or left uncemented. The cementless joint is made in such a way that the bone naturally grows into the surface to keep it in place.
For those with hip dysplasia, there needs to be roughly 70 percent contact of the cup to the socket bone. In some cases, hip dysplasia patients do not have enough of a "roof" in the hip for this surgery to be successful.
There are several possible complications of hip replacement:
- Dislocation is most likely to happen in the first 6 weeks after the surgery. However, as an artificial joint lacks the depth of the natural joint, it will always be easier to dislocate an artificial joint than a natural one. Your surgeon will give you a list of short-term and long-term precautions and range of motion limitations to help avoid dislocation.
- Infection is a rare but serious occurrence. Antibiotics are usually given before and after surgery to lessen this risk.
- As with the surgeries discussed previously, deep-vein thrombosis is a potential complication.
- Loosening of the joint over time is likely to result in the need for a revision surgery. The activity level of the patient and artificial hip materials used will help to determine the overall life of the joint.
Over the last 5 years, minimally invasive total hip replacement (THR) been used in hip replacements. Instead of a 6- to 8-inch (15- to 20-centimeter) incision, it uses two smaller incisions to attach a standard, cementless replacement. There are some advantages to minimally invasive THR:
- A shorter hospital stay with a faster rehabilitation (outpatient surgery has been achieved in both the U.S. and U.K.)
- Decrease in pain due to less muscle, tendon and ligament trauma
- Improved cosmetic appearance due to shorter scars
- Ability to use standard implants that have an established track record
Read on to learn about what happens when THRs start to wear out.