By Mark F. Schinsky, M.D.
Basic Hip Anatomy. Your hip is essentially a ball-and socket joint that connects your leg (femur or thigh bone) to your trunk (pelvis). The head of your femur (the top, rounded, ball like part) fits into your acetabulum (the rounded socket part of your pelvis) and is allowed to move fairly freely while maintaining intimate contact and stability. Both the surface of the ball and the inside of the socket are covered in a quite resilient, smooth articular cartilage that cushions the bones and allows them to glide against each other. Your hip is also surrounded by a synovial membrane, which helps to provide nourishment to the joint and also produces a thin layer of fluid that lubricates the joint, decreasing the friction of the ball rubbing against the socket. There are also several strong, non-bony, soft-tissue structures around the hip joint that helps to provide stability so your hip does not dislocate (come out of socket). One of these is your labrum, which surrounds the rim of your acetabulum, and another is your hip capsule, which is a robust covering of your hip joint. The muscles around your hip also help to stabilize the joint and aid in function. When all of these structures are working normally, you are able to move your hip freely without pain or discomfort.
Hip Arthritis.
There are many different kinds of arthritis that can affect the hip. The most common is osteoarthritis. Other types of arthritis include post-traumatic arthritis and inflammatory arthritis. Other conditions such as developmental dyplasia of the hip or osteonecrosis/avascular necrosis can also affect the hip joint leading to degeneration and pain. Osteoarthritis usually occurs in
older individuals and is the type of arthritis generally referred to as "wear-and-tear" arthritis. There may or may not be a family history of osteoarthritis. In osteoarthritis, called OA for short, the articular cartilage wears away leaving exposed bony surfaces to rub together and grind. Bone spurs, known as osteophytes, are often formed. These changes lead to stiffness, pain, and in extreme cases, complete disability. Posttraumatic arthritis occurs after a significant injury to the hip, such as a dislocation or fracture, sometimes many years earlier. The trauma injures the articular cartilage in a variety of ways and over time results in its deterioration. In inflammatory arthritis, the most common type being rheumatoid arthritis, the synovial membrane becomes inflamed by an autoimmune process, which in and of itself can cause pain. In addition to pain, inflammatory arthritis can also lead to bone destruction/erosion, stiffness, and decreased function. All of this makes joint reconstruction more difficult.
Developmental/congenital dyplasia of the hip refers to the hip joint not forming properly from birth or early childhood. This condition causes the ball-and-socket joint to not be congruous which leads to early wear and degeneration. Osteonecrosis, sometimes also called avascular necrosis, is a term used to describe a condition where the blood supply to the bone is compromised and the bone dies in those certain areas. There are many causes of osteonecrosis and it can affect different areas
of the body such as the hips, knees, and shoulders.
History of Hip Resurfacing.
Hip resurfacing is not new. The original predecessors were cup arthroplasties (replacements) dating back to the 1940’s. Since that time, surface replacement has gone through many different changes over several decades. Some of the older implants were composed of all Teflon, metal-on-polyethylene (plastic), and different types of metal-on-metal designs. Also, the way the
components were fixed to the bones changed multiple times over the years. Nearly all of these implant designs failed. Some failed early, within a year or so; while others failed after a few years. Then, around the 1970’s, total hip arthroplasty became increasingly popular. The results with total hip replacement were excellent over both the short- and long-terms. For the most part,
surgeons stopped focusing on hip resurfacing, preferring the proven methods and implants associated with total hip replacement. Some surgeons, however, continued to work on hip resurfacing. The most recent design to be approved in the United States was first implemented in Europe in the mid-1990’s. It has a long and proven track record in Europe with excellent clinical results. The current hip resurfacing implants have only been approved by the FDA in the US since 2006. Many different types of hip resurfacing implants are available throughout the world. Other implant designs are currently under FDA review and are expected to be approved soon.
What is Hip Resurfacing and What are its Advantages/ Disadvantages?
Hip resurfacing is a bone conserving surgical procedure that is used as an alternative to conventional total hip replacement in patients who have advanced hip arthritis. As opposed to conventional hip replacement, hip resurfacing does not remove and replace the entire femoral head and neck. The arthritic acetabulum is still replaced, as would be done in a conventional hip replacement, but only the arthritic portion of the femoral head is removed using precise instruments. The femoral head is then reshaped to accommodate the metal prosthetic shell (cap). This saves more of the natural bone to be used in the future should a revision be required. This is of particular importance for younger patients. The current hip resurfacing technique uses a metal-on-metal bearing surface, which has been shown in some studies to have high wear resistance and reduced bone loss. Compared to a conventional hip replacement, the resurfaced hip is both biomechanically and anatomically closer to a normal hip, allowing the patient to return to more normal activities. The size of the resurfaced head is very similar to a normal femoral head, which makes it more stable and decreases the risk of dislocation. Disadvantages relating to hip resurfacing include the potential for complications that can occur during any major surgical procedure including infection, bleeding, nerve injury, blood clots, and those that occur with anesthetic use. Due to the design of the hip resurfacing implants, there is an increased release of metal ions into the body, though the long term systemic problems relating to this, if any, have yet to be determined. Also, since hip resurfacing maintains your femoral neck, there is a higher chance of femur fracture following hip resurfacing than with traditional total hip replacement.
Who is a Candidate for Hip Resurfacing?
Only an orthopaedic surgeon experienced with hip resurfacing can determine if you are a candidate for this surgery. Occasionally, additional tests such as a CT scan or bone density scan are required to facilitate the surgeon in making a determination. In general, individuals who suffer from advanced joint disease but who desire to return to a robust life are excellent candidates for hip resurfacing if they are under age 65, active, and have good bone quality. Because resurfacing preserves more bone than does conventional total hip replacement, it is frequently an appropriate course of action for younger candidates, who may require additional hip surgeries in the future. Hip resurfacing is not appropriate for people with certain types of hip problems and/or deformities, people with poor bone quality, or for the inactive and/or elderly. There is also a difference in length of incision, surgical dissection, and post-operative recovery as compared to a standard or minimally-invasive hip replacement. Your surgeon can discuss these differences with you at length.
How Long Will a Resurfaced Hip Last?
At this time, we simply cannot predict the durability of hip resurfacing. This is largely due to the fact that how long an implant lasts is related to how it is used. Factors influencing the implant’s performance include the patient’s activity level, the quality of the patient’s bone at the time of implantation and over the subsequent years, the design and material properties of the implants, and the surgeon’s ability to properly implant the devices. Other patient factors, such as not complying with the
post-operative therapy regime, may hasten the failure of hip resurfacing. One study shows that European patients receiving the same resurfacing implants as those currently approved in the U.S. had a 98.4% implant survivorship five years after resurfacing. This success is comparable to conventional total hip replacement at that time period in the under 60 age group. However, several other studies have also shown that the complication rate with hip resurfacing is greater than with traditional total hip replacement, particularly for femoral bone fracture. Since the current hip resurfacing devices have only been
used for less than a decade, no long term clinical results are available. Additional studies are underway and should help us to predict long-term implant survivorship.
Summary. Hip resurfacing is a bone conserving surgical procedure used to treat advanced hip arthritis. Although similar, it is commonly used as an alternative to total hip replacement in younger active patients. While there are potential complications associated with hip resurfacing, the benefits include preservation of more of your natural bone (so that if a revision is needed in subsequent years, it can be more easily accomplished), reduction in the risk of significant leg length inequality, and a lower rate of dislocation after surgery when compared to conventional total hip replacement. Although only your surgeon can determine if you are a candidate, hip resurfacing is a consideration in patients under 65 years of age who are
active and have good bone quality without significant deformity. Castle Orthopaedics & Sports Medicine, S.C. is now pleased to be the first in the Aurora area to offer this advanced procedure for our patients. Please call for more information or to schedule a consultation.
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