Finally, because the resurfacing relies on the bone of the femoral neck and head to support the metal cap, patients who have significantly abnormal bone anatomy are not good candidates. This may include those with previous fractures or surgeries, or patients who have such advanced degenerative disease that there is insufficient bone stock to support a resurfacing. These patients are better served with total hip replacements.
At a time when total hip replacements totally relied on polyethylene sockets (which are much less wear-resistant than metal) and when dislocation was much more common with athletic activities, this theory made some sense. However, total hips now utilize metal-metal and ceramic-ceramic articulations which provide tremendous longevity even in young, active patients, and cementless fixation provides for survival of the standard total hip replacement which may outlive even young, active patients. In contrast, the currently available resurfacing head is cemented into place, so there is technically even more reason to avoid impact loading activities – because these activities tend to crack the cement and lead to earlier loosening. Whether or not the various resurfacing devices will actually hold up to repetitive high-impact exercise is unknown because of a lack of long-term data. What is known is that all cemented implants eventually loosen, so it stands to reason that subjecting any cemented implant to high-impact loading stresses will lead to earlier loosening and need for revision surgery.
Evidence has now accumulated to demonstrate consistent and strong symptomatic and functional improvements with Surface replacement with follow-up times upto 5 years. Surface replacement outcomes are comparable to those obtained with current generation THR at similar time points in patients younger than 65 years of age. Surface Replacement preserves the patients bone stock and thus this is extremely useful at the point of conversion to THR or revision procedures. Although good long term data on the relative durability of Surface replacement compared to THR is presently being compiled current evidence is sufficient to conclude that Surface replacement is a safe, effective and superior surgical alternative in the younger, active and other properly indicated patient needing a hip replacement.
Surgeons should make sure that people considering having MoM hip resurfacing understand all the risks and benefits associated with it, and are aware that less is known about the safety and reliability of MoM devices than about conventional cup and ball THR devices
The data from the national joint registry will allow researchers to find out how long MoM hip resurfacing devices last before they need to be replaced. Until more long-term evidence is available, NICE recommends that surgeons should choose a device for MoM resurfacing for which there is at least 3 years' evidence. This evidence should show that the device is likely to meet a target of less than 1 in 10 devices needing replacing over 10 years.
The biggest disadvantage of hip resurfacings is that the early failure rate is much higher than that after total hip replacement. Although in the innovators’ hands, failures are less likely, the risk of a femoral neck fracture (the ball breaking off of the femur bone) in the first year is significant, as high as 3% or more. Fractures are often related to surgeon error, most commonly notching of the femoral neck or placing the artificial ball in a position which is too low (called “varus malpositioning.”). An additional factor may be disruption of the blood flow to the remaining femoral head, a condition known as avascular necrosis. A review of the published literature shows that the short term survival rates with resurfacing replacements vary from 75-100% while most well-designed total hip replacements have short and mid-term survival rates exceeding 95%, even in young, active patients.
Avascular necrosis is the loss of blood supply to the head of the hip bone. This can occur with any hip but is extremely rare, it maybe associated with some diseases and medications. If it occurs before surgery then it means a hip resurfacing is not possible and a total hip is required. If it occurs after surgery then it will cause the resurfacing to slowly loosen and it may need to be replaced with a stem (total hip conversion)
Patients treated in our hospital for degenerative arthritis of the hip with a Birmingham Hip Resurfacing (BHR) prosthesis were invited to return for follow-up evaluation.
Because there is no stem down the thigh bone with hip resurfacing there is a small risk of fracturing of the hip in the first 12 weeks after surgery. In one study this was less than 0.5% and is more common in people over the age of 70 or with brittle bones (osteoporosis). Most are breaks are associated with injury. If this occurs then a stem is placed down the thigh bone in a second operation. You should avoid activities that put you at risk of falling or injury for 12 weeks after surgery.
Dislocation of a hip prosthesis is in part related to the size of the ball and socket used. The larger the ball and socket, the less likely the hip will dislocate. Because a resurfacing prosthesis mimics the size of the natural ball and socket, it is less likely to dislocate than the ball and socket used with many total hip replacements, which may be only 1/2 – 2/3 the size of the natural hip ball. However, with newer instrumentation for standard total hip replacement allowing more accurate placement of components, use of larger balls and sockets, and better soft tissue repair techniques (), dislocation even after total hip replacements is becoming quite rare.
Just as disconcerting are failures occurring more than 5 years after implantation. The BHR femoral head prosthesis must be cemented in place while the socket is cementless. All cemented components will eventually loosen. So given enough time, all cemented resurfacings, just like cemented total hips, will loosen and fail, guaranteeing a second trip to the operating room for revision surgery at some point in young, active patients. In contrast, many cementless total hip replacements may remain intact indefinitely. Therefore, using the currently available cemented resurfacing prosthesis in a young, active patient, although conserving bone for a future revision, ironically almost guarantees that a revision surgery will be necessary at some point due to loosening of the cement. In contrast, using an entirely cementless total hip replacement could potentially last a lifetime, even in a young, active patient.
Background of Surface Replacement (SR)
In patients with debilitating degenerative joint disease of the hip for which conventional approaches (analgesics, assistive devices, and weight loss) are no longer effective, a total hip replacement procedure (arthroplasty) is indicated to relieve pain and restore patient function. THA is a reliable surgical intervention, with high success rates for joint survivorship and improved function at 5-10 years follow-up using current prostheses. Hip resurfacing has been promoted as an alternative to total hip replacement or for younger patients, to watchful waiting, and involves the removal and replacement of the surface of the femoral head with a hollow metal hemisphere. This hemisphere is usually used with a metal acetabular cup. The technique conserves femoral bone, maintains normal femoral loading and stresses. Because of bone conservation, it does not, theoretically compromise future total hip replacements. Revision of a resurfaced joint to a stemmed THR is typically easier and less complicated than revision of a primary THR. Thus, SR may be an advantageous option for younger and more active individuals likely to outlive the functional lifespan (10 years or more) of a traditional hip replacement device.
The advantage of Birmingham Hip resurfacing is the rate of wear and failure appears less than that of the more conventional total hip replacement in young people, however these results are only out to 10 years. When a resurfacing fails it can be converted to a total hip replacement with relative ease.