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Hip_resurfacing

Hip Resurfacing

Hip resurfacing has been developed as a surgical alternative to total hip replacement (THR). The procedure consists of placing a cobalt-chrome metal cap, which is hollow and shaped like a mushroom, over the head of the femur while a matching metal cup (similar to what is used with a THR) is placed in the acetabulum (pelvis socket), replacing the articulating surfaces of the patient’s hip joint and removing very little bone compared to a THR. When the patient moves the hip, the movement of the joint induces synovial fluid to flow between the hard metal bearing surfaces lubricating them when the components are placed in the correct position. The surgeon’s level of experience with hip resurfacing is most important; therefore, the selection of the right surgeon is crucial for a successful outcome.

The potential advantages of hip resurfacing compared to THR include less bone removal (bone preservation), a reduced chance of hip dislocation due to a relatively larger femoral head size (giving the patient has an anatomically correct femoral head size), and easier revision surgery for any subsequent revision to a THR device because a surgeon will have more original bone stock available. The potential disadvantages of hip resurfacing are femoral neck fractures (rate of 0–4%), aseptic loosening, and metal wear. Due to the retention of the patient’s complete femoral neck other advantages exist: Surgeon induced discrepancies in leg length (as could happen with THR) are now minimized. Also, the toe-in or toe-out faults that could occur interoperatively with THR are now over because the femoral neck that determines foot direction is left undisturbed with hip resurfacing.

Procedure:

The hip resurfacing devices are metal-on-metal articulating devices which differ from total hip replacement devices because they are more bone conserving and retain the natural geometry (so-called large ball THR devices share this trait). A THR requires that the upper portion of the femur bone be cut off to accept the stem portion of a THR device. The femur cap of the hip resurfacing devices does not require the femur bone be cut off; instead the top of the femoral head is shaped to closely fit the underside of the cap. Both hip resurfacing and hip replacement require that a cup is placed in the acetabulum of the hip socket. The main advantage of the hip resurfacing surgery is that when a revision is required, there is still an intact femur bone left for a THR stem. When a THR stem requires a revision, the metal stem in the femur has to be removed and often more bone is lost in the process of removal and replacement with a larger diameter stem. Having a hip resurfacing at a younger age means, that a revision will likely be easier to perform when required.

Recent studies have shown that the outcome of a hip resurfacing is dependent on surgeon experience and that proper positioning of hip resurfacing components is crucial. Therefore, in addition to ensuring that a proven device is used, patients should take care in selecting a surgeon with experience and a good track record.

Although formal labeling restrictions exist in some countries, including the United States, hip resurfacing may allow younger, active people to return to many activities they enjoyed prior to their hip problems, which is an advantage over a traditional hip arthroplasty. The large size cap and cup of the hip resurfacing devices are the same size as a person’s original ball and socket and thus are less prone to dislocation.

An often forgotten but very important advantage of hip resurfacing and thereby the retention of the femoral neck is the fact that hip resurfacing has the least measurable amount of “stress shielding” when compared to any type of THR. This means that with hip resurfacing the femur’s upper portion fully retains its natural mechanical characteristics under load, also ensuring less disturbance of the processes that place inside bone that is alive.

Is hip resurfacing a good alternative to hip replacement?

Hip resurfacing has lost favor with many surgeons because it can increase the amount of potentially harmful metal ions in the bloodstream. It also has a risk of bone fracture just below the metal cap placed on the top portion of the thighbone — particularly in women with poor bone quality.

Unlike traditional hip replacement, hip resurfacing doesn’t completely replace the “ball” of the hip with a metal or ceramic ball. Instead, the bone is reshaped and capped with a metal prosthesis. The hip socket is fitted with a metal cup. As these metal surfaces rub together, there is the potential for wear and release of metal ions. Low levels of metal ions usually don’t cause a problem, but higher levels may be problematic.

The socket prosthesis for a traditional hip replacement is usually lined with a thick layer of hard plastic, so there isn’t any metal-on-metal contact. While the components of an artificial hip will eventually wear out, most people can expect their joint replacements to last for at least 15 years.

Hip replacement is usually postponed until later in life, so the life span of the prosthesis more closely matches the remaining life span of the person. Subsequent hip replacement surgeries can be more difficult and typically have poorer results than initial hip replacements.

Hip resurfacing originally was seen as a stop-gap option for younger people with serious hip problems, because it would leave more bone available for a hip replacement in the future. Currently, however, hip resurfacing is generally recommended only in instances where there is severe deformity and few other options. The best candidates appear to be younger men with good quality bone.

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