Total hip replacement is an operation designed to replace the damaged hip joint. Various prosthetic designs and types of procedures are available to the surgeon. Our surgeons carefully evaluate the patient to: 1) determine if surgery is indicated; 2) determine the most appropriate type of procedure; and 3) develop a plan of treatment. The types of replacement, methods of fixation and new alternate bearing materials are discussed below.
Unlike conventional total hip replacement (THR), hip resurfacing is conservative in that the femoral head and neck of the hip joint are not removed nor is bone removed from the femur. In the case of surface replacement, less bone is also removed from the acetabulum as compared to conventional THR since no polyethylene liner is used.
Minimally Invasive Hip Resurfacing
JRI Research
The staff of JRI is engaged in various research studies, including: improving long term joint replacement durability by selective use of new replacement bearing technology, histological characterization of implant fixation, relationship between wear debris and aseptic loosening.
Hip Replacement
Ceramic-on-Ceramic Bearings
All alumina-ceramic bearings have been utilized in Europe since the early 1970s. A problem with the early ceramic materials was its large grain structure which led to fractures. Manufacturing of ceramics is now much improved with small grain size creating a much stronger material. These bearings also produce low wear similar to that of metal-on-metal bearings with substantial reductions over plastic bearings. Because of concerns related to the strength of the material, the shells must be made thicker in order to minimize fracture and, therefore, surface replacements are not feasible. The new generation components are much improved for stem-type devices. The all-alumina bearings are another option in the effort to minimize wear and tissue reaction and to provide longer term durability. However, the components must be optimally manufactured to minimize the risk of fracture and inserted precisely to minimize wear.
Hemi-Surface Replacement for Osteonecrosis
One option to minimize wear debris and tissue reaction is to eliminate the bearing by replacing only the diseased part of the joint. A hemi-surface replacement is often recommended for patients who have osteonecrosis of the femoral head (also referred to as avascular necrosis) and have some remaining articular cartilage on the acetabulum or pelvic side (Figure 5). The hemi-surface replacement preserves and maintains bone by providing physiological stress transfer to the femoral neck and proximal femur. It avoids inflammatory reaction and loosening due to polyethylene wear debris.
Beginning in 1981, custom hemi-surface devices were inserted utilizing a titanium alloy which is a relatively soft metal and scratches easily. These devices have been surprisingly successful with many still functioning over 16 years even in young patients whose average age was 32 years.
In 1996, newly designed components and instruments became available and are now being used in many centers in the United States and internationally. Although the durability depends on the quality of the cartilage at the time of surgery, it is possible that even longer durability may be achieved with the new, harder surface cobalt chrome components which do not scratch easily. The technique is exacting and does require precision fitting of the hemi-arthroplasty to the articular cartilage of the pelvis. Patients who have had fractures of the neck of the femur require a stemmed hemi-arthroplasty. Surface hemi-arthroplasty has definite advantages over stem-type hemi-arthroplasty for patients with osteonecrosis because of its conservative nature.
Surface Replacement of the Hip
In surface replacement, the femoral neck is preserved rather than amputated as is done in conventional stem-type total hip replacement. The femoral head is reshaped and resurfaced with a prosthetic shell. As a result, the femoral bone is loaded more like a normal hip and the bone is preserved. Since the resurfaced head is very similar in size to the normal hip (about 40-50 mm), it is more stable and dislocation risk is minimal. An example of a surface replacement is shown in Figures 6A and 6B.
Figure 5
Figure 6A
Figure 6B
Several different hip resurfacing systems were introduced in five countries in the early 1970s. They were implanted in young patients who were expected to require more than one replacement in their lifetime because they were thought to be more conservative devices than the conventional replacements. Some surface replacements with polyethylene have had long-term durability of up to 18 years thus far. However, because of the large diameter ball size of the surface replacement, there was more polyethylene bearing wear (the debris accumulation which undermines the fixation) which results in loosening of the prosthesis. Most surgeons abandoned surface replacements with polyethylene in the 1980s and early 1990s. Despite the fact that the durability was often less than desired, the femoral bone preserved by these systems was especially valuable for these young patients when revision surgery was required making that second surgery comparable to primary replacement.
The conservative and more physiologically compatible nature of the surface replacement has always been appealing to both surgeons and patients. There is renewed interest which has been fostered by the reintroduction of all-metal bearings which could dramatically increase the durability. The first of these metal/metal surface replacements was introduced in Germany and subsequently in England and at the JRI in the early 1990s. The instruments and design have been improved using modern techniques to further reduce wear and to facilitate the procedure. The major advantage of the surface replacement is in the preservation of the femoral head and neck. Further, unlike the acetabular reconstruction with the earlier designs which contained polyethylene bearings, very little bone is removed and the procedure is now conservative on the acetabular pelvic side of the joint as well. In short, no "bridges are burned" with the surface replacement procedure.
Surface replacement may also permit higher levels of post- surgery activity with fewer downside risks than does a stem-type device. The increased stability is particularly conducive for sports and work activities where a more normal range of motion of the hip is required.
The lessons that we have learned regarding design and technique issues during the past 25 years combined with the modern precision manufacturing of metal/metal bearing surfaces have led to a very much improved device. Although it is impossible to predict how much increased durability will be achieved, the volumetric wear reduction is substantial, and it is unlikely that these devices will "wear out". We also believe that the metallic wear debris, based on our histological observations to date, appears to be well tolerated in the tissues. Potential long term undesirable consequences of these devices are unknown. However, they have been successfully implanted for over thirty years so we believe the risk is minimal.
- Treatment of Hip Arthritis
- Types of Hip Replacement and Methods of Fixation
- Benefits, Risks and Potential Complications
- Revision Hip Surgery
- Alternatives to Hip Replacement
- Special Studies
- Planning for Your Surgery
- The Operation
- Postoperative Course
- After You Go Home
- Long-term Precautions and Advice
Copyright 2005 Joint Replacement Institute Los Angeles, CA · (213) 484-7600 · JRIinfo@dochs.org
