An X-Ray and Illustration Showing a Normal Hip Joint DISEASES OF THE HIP JOINT The term arthritis literally means inflammation of a joint, but is generally used to describe any condition in which there is damage to the cartilage. Inflammation, if present, is in the synovium. The proportion of cartilage damage and synovial inflammation varies with the type and stage of arthritis. Usually the pain early on is due to inflammation. In the later stages, when the cartilage is worn away, most of the pain comes from the mechanical friction of raw bones rubbing on each other.

      
An X-Ray and Illustration Showing an Arthritic Hip Joint There are two broad categories of arthritis OSTEOARTHRITIS AND RHEUMATOID ARTHRITIS Osteoarthritis mainly damages the joint cartilage, but there is often some inflammation as well. It usually affects only one or two major joints (usually in the legs). It does not affect the internal organs. The cause of hip osteoarthritis is not known. It is thought to be simply a process of wear and tear in most cases. Some conditions may predispose the hip to osteoarthritis, for example, a previous fracture that involved the joint. Growth abnormalities of the hip (such as a shallow socket) may lead to premature arthritis. Some childhood hip problems later cause hip arthritis (for example, a type of childhood hip fracture known as a Slipped Epiphysis; also Legg-Perthe’s Disease). In osteoarthritis of the hip the cartilage cushion is either thinner than normal (leaving bare spots on the bone), or completely absent. Bare bone on the head of the femur grinding against the bone of the pelvic socket causes mechanical pain. Fragments of cartilage floating in the joint may cause inflammation in the joint lining, and this is a second source of pain. X-rays show the “joint space” to be narrowed and irregular in outline. There is no blood test for osteoarthritis. Rheumatoid Arthritis (R.A.) starts in the synovium and is mainly inflammatory. The cause is not known. It eventually destroys the joint cartilage. Bone next to the cartilage is also damaged; it becomes very soft (frequently making the use of an uncemented implant impossible). R.A. affects multiple joints simultaneously. It also affects internal organs. Another form of hip arthritis that is mainly inflammatory is Lupus. There are other more rare forms of arthritis that are also mainly “inflammatory”. They are basically similar to R.A.. X-ray changes in R.A. are essentially similar to osteoarthritis plus a loss of bone density. Blood tests for rheumatoid arthritis are not very accurate. Rheumatoid Factor is present in the blood in about 80% of patients who have had rheumatoid arthritis for more than 18 months. Early on in the disease the percentage is much lower. Unfortunately, about 7% of people over the age of 70 test positive for rheumatoid factor, even though they do not have rheumatoid arthritis. The test, by itself, is therefore not very reliable. Anti-inflammatory medications are effective in treating the inflammatory aspect of either rheumatoid or osteoarthritis. Osteonecrosis is another serious cause of hip pain. It is not arthritis. It is a condition in which part of the femoral head dies. This dead bone can not stand up to the stresses of walking, the femoral head collapses, and becomes irregular in shape. The joint then becomes painful. The most common causes of osteonecrosis are excessive alcohol use and excessive use of cortisone-containing medications. TOTAL HIP REPLACEMENT SURGERY The modern total hip replacement was invented in 1962 by Sir John Charnley, an orthopedic surgeon working in a small country hospital in England. His work has been one of the great triumphs of Twentieth Century surgery. Two revolutionary features of the Charnley hip replacement were 1) the combination of metal gliding on plastic, and 2) the use of methacrylate cement to attach the artificial components to the bone. The arthritic femoral head is removed. It is replaced with a metal ball which is attached to a metal stem. The stem is cemented into the hollow marrow space of the femur. The worn out hip socket is lined with a plastic socket, which is also cemented in place. The painful parts of the arthritic hip are thereby completely replaced with metal and plastic surfaces. The plastic socket has a very low frictional resistance, and a very low wear rate against the metal ball. Sometimes the femoral ball component is made of ceramic (aluminum oxide or zirconium oxide) rather than metal. Plastic has an even lower wear rate against ceramic. Total hip replacement was first performed in the United States around 1969. Many hundred of thousands of replacements have been performed in the U.S. since then. The operation has become fairly routine and is successful around 96% of the time. One of the first three American surgeons to perform this type of surgery was Charles O. Bechtol. He started a total hip replacement program in 1969 while he was professor of orthopedic surgery at UCLA. Dr. Huddleston studied hip and knee surgery with him for one year in 1975. The two later became partners in a practice restricted to total joint replacement. Dr. Bechtol retired in 1984 and Dr. Huddleston took over the practice, and merged the practice with the Southern California Orthopedic Institute in 1988. NEWER DEVELOPMENTS IN HIP REPLACEMENT The major long-term problem with cemented hip replacements is loosening of the bond between the implant and the bone. There are two problems associated with the cement. Firstly, in time it cracks and becomes fragmented, resulting in loosening. Secondly, the body reacts to the smaller fragments, and attempts to remove them, but unfortunately in the process also removes bone adjacent to the cement particles, leaving the bone structurally weakened. If the implant loosens, a second surgery may become necessary to reattach it. Much research is being done to try and solve the loosening problem. It is widely believed that the solution is to eliminate the cement. This has led to the development of the Cementless Hip Replacement in which the surface of the metal parts is porous, and looks like coral. Bone can grow into the metal pores and lock the implant into place without the use of cement. There are several manufacturers of cementless hip replacements. The AML Total Hip Replacement is the most widely used cementless implant in the world, and has the longest track record (since 1978). Dr. Huddleston uses an AML type of non-cemented hip replacement. The long term results with the AML Hip have so far been extremely promising, especially in people with good bone quality. However, it will be at least ten years more before we will be certain that cementless hips are indeed superior to cemented hips. Initially, the cementless hips were used in patients of all ages, but it was soon found that in people with soft bones (osteoporosis) the femur bone does not always bond to the porous metal. For this reason it is generally agreed that cementing the femoral component is the best course in patients over 70. People in their 60's fall into an in-between category. For them the choice between a cemented and a cementless femoral component depends on the quality of their bones. This can usually be determined from their hip x-ray, but quite frequently a true assessment of bone quality can only be made at surgery. Dr. Huddleston’s final decision on the question of cement will be made in your best interest. Young patients (under 60) are usually advised to have cementless replacements in the belief that they will ultimately outlast cemented ones. On the other hand, uncemented socket components have been extremely successful, regardless of the patient’s age. Cement is rarely used on sockets nowadays. A combination of uncemented socket and cemented femoral component is known as a hybrid (mixed) hip. It is important for you to know that many other brands of cementless hip devices have not been as successful as the AML hip, and some designs have had a very poor track record indeed. OTHER SURGICAL CONSIDERATIONS DURING HIP REPLACEMENT Bone grafts are occasionally needed to restore bone defects. If so, the bone may be obtained from the discarded femoral head, or from the pelvis, through a small separate incision. Occasionally it may be necessary to cut tendons in the groin (Adductor Tenotomy) if these tendons restrict hip motion. This is done through one or two separate half inch incisions in the groin. It is possible to perform two hip replacements under the same anesthetic, but in general, Dr. Huddleston does not recommend it. If you need two hips replaced, a better course is to have the more painful hip replaced first, and to wait approximately 12 weeks before undergoing the second operation.