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 metal-metal femoral resurfacing technique originally developed by Amstutz, et al. (1986) has been proposed as an alternative to metal-on-metal total hip replacement. In femoral resurfacing, the femoral head is reshaped and capped with a metal ball, but the femoral head is not removed as in total hip replacement. The advantages of femoral resurfacing include a less invasive procedure; s reduced thigh pain since there is no stem in the femoral canal, and that it may allow patients to achieve higher range of motion thus theoretically reducing the risk of loosening and dislocations. Unfortunately, the early designs tried by Amstutz had high failure rates. There are also concerns that resurfacing may increase the risk of avascular necrosis and further collapse of the femoral head. But fortunately these concerns have been largely unfounded. In fact femoral resurfacing may become a procedure of choice (relative to total hip replacement) for patients with osteonecrosis of the femoral head, especially for the younger, more active patients.
Hip resurfacing can be categorized as partial hip resurfacing, in which a femoral shell is implanted over the femoral head, and total hip resurfacing, consisting of an acetabular and femoral shell. Partial hip resurfacing, also called hemi-resurfacing arthroplasty or Precision-fit hemisurface replacement of the femoral head, is considered a treatment option for avascular necrosis with collapse of the femoral head and preservation of the acetabulum.
Total hip resurfacing also known as Double Cup or Double Shell Arthroplasty is indicated for a wide variety of core and extended indications including osteoarthritis, rheumatoid arthritis, and advanced avascular necrosis, and may be considered an alternative to total hip replacement. This consideration is particularly applicable for the young active patients who would potentially outlive a total hip prosthesis.
Surface Replacement is in effect a procedure to stall or buy-time before the need for a total hip arthroplasty is imminent. Advantages of total hip resurfacing perceived or actual as compared to total hip replacement include improved stability and lower dislocation rates and preservation of the femoral neck thus making it easier to revise or convert to a total hip replacement, when required.
Indications for Surface Replacements
Surface Replacements are indicated in the following clinical situations:
- Non-inflammatory degenerative joint diseases such as osteoarthritis, avascular necrosis of the head of femur, ankylosing spondylitis
- Inflammatory joint diseases such as rheumatoid arthritis
- Current indications have been expanded to use in painful and Dysplastic hips
SR has been proposed as an alternative to THR for patients in whom THR is indicated and who are likely to outlive the 10 or more year's functional lifespan of a traditional prosthesis or essentially in patients at risk of requiring more than one hip joint replacement over their lifetimes. These mainly include the younger and the more active patient populations.
Advantages of Surface Replacements
The hip resurfacing operation has the following crucial advantages versus a conventional total hip replacement:
- Absence of Polyethylene is notable in the current generations of surface replacements. The anatomically similar sized metal on metal surfaces ensures that longevity is higher. The biomechanics simulate a normal hip joint which ensures more physiological range of motion and reduces loosening by eliminating wear debris by eliminating use of polyethylene.
- The bone stock is preserved. This helps in the event of needing a revision to a total joint arthroplasty or revision settings where substantial bone has been lost or osteolysis has occurred. Some studies mention that bone stock might actually improve after hip resurfacing although this is controversial.
- Another advantage is an unrestricted lifestyle and patients are actually encouraged to play sport and keep muscle tone. No activity is restricted including sitting on the floor, sitting cross legged or squatting in some patient populations in contrast to total hip replacement where a perennial danger of loosening or dislocation results.
- The patients with surface replacement almost always show speedy return to function. This has huge implications on hospital economics (microeconomics) and macroeconomics of the healthcare funding available. Most patients can resume normal activities at 4 weeks and can resume sporting activities after 12 weeks.
Contraindications for Surface Replacement Arthroplasty
- Individuals with a focus of infection e.g. Active urinary, gastro-intestinal or upper respiratory infection
- Individuals with poor bone stock inadequate to support the replacement
- In pregnancy or in females of child-bearing age due to unpredictable and potentially damaging effect of metal ion release on the fetus
- Individuals with known moderate to severe renal insufficiency
- Immunosuppressed status with uncontrolled diabetes, patients on steroids, IV drug users and with diseases such as AIDS
- Individuals who are overtly obese high BMI (Body Mass Index)
- Patients who have not yet attained skeletal maturity
- Individuals with known or suspected metal sensitivity
- Individuals with muscular dystrophies, neuromuscular disease or severe mental retardation unable to comprehend and follow the post-operative regime
Identification of suitable patient populations for SR
Several patient characteristics have been evaluated based on the longevity or the failure of the implants used especially in the younger age group of patients (particularly < 40 years) Several indices can be used to monitor outcomes.
Scoring Indices for Surface Replacement Arthroplasty
The Chandler Index has been used to identify patients at risk of failure following THR. The initial Chandler index included 6 factors: absence of collagen disease, avascular necrosis, unilateral hip disease, previous surgery, BMI and activity levels. One point was assigned to each factor.
Beaule and colleagues developed the surface arthroplasty risk index (SARI) for surface arthroplasty to optimize patient selection and to predict implant survivorship. With the SARI, higher scores indicate higher risk of failure. With the SARI, 2 points were given to femoral head cyst of greater than 1 cm; 2 points for a weight of less than 82 kg, 1 point for previous surgery, and 1 point for an activity level of greater than or equal to 7. Statistical analysis has confirmed that a score greater than 3 correlates with a 12-fold increased risk of early failure and/or adverse radiological changes. In another study involving 400 Surface replacement cases with a SARI greater than 3, joint survivorship was 89% at 4 years, compared with 97% among those who had a SARI of 3 or less (Amstutz et al. 2004).
Measuring Outcomes of Surface Replacement Arthroplasty
Postoperative clinical improvement is normally scored using the Harris Hip Score (Harris 1969), or the Oxford Hip Score (Dawson et al. 1996) and measuring the range of motion (ROM). Surface Replacement patients typically return to significant activity levels including impact sports. High activity levels enabling patients to take up sport (90 %) and employment (85 %) is the norm. (Treacy et al. 2005).
Resurfacing Arthroplasty can be variously differentiated by:
A) Use of cement
- Cemented femoral and Acetabular component
- Hybrid (Cemented femur and Uncemented acetabular shell)
- Uncemented femoral and acetabular shells
B) Components replaced
- Precision-fit hemi-surface arthroplasty ONLY replacing the surface of the femoral head. Also called hemi-resurfacing arthroplasty
- Total Surface Replacement of the femoral surface and the acetabulum. Also called double shell or double cup arthroplasty
C) Bearing surfaces
- Metal head against metal cup (MoM)
- Metal head against polyethylene cup (MoP)
- Ceramic on Ceramic (CoC)
D) Medical device manufacturing company
There are currently 5 main manufacturers of the Surface replacement arthroplasty in the world. These are:
- BHR (Birmingham Hip) from Smith and Nephew
- ASR (DuPuy)
- Cormet (Corin)
- Conserve Plus
- Durom (Zimmer)
Newer designs are being constantly evaluated yet need stringent FDA testing and approval before being introduced in the market.
Common complications after any major lower limb joint arthroplasty account for < 0.5 % of cases. Dislocation risk for Surface Replacement is as low as 1 in 500 (0.2%) as the hip is far more stable and hence the quick recovery.
The potential risk is approximately 0.7 % per year. The surface replacement typically wear less than conventional total hip replacement in younger people, however these results are only out to 10 years. A failed resurfacing can be easily converted to a THR if indicated.
Revision and Femoral Neck Fracture after HR
Several studies have been undertaken which show the risk of fracture needing revision to Total Hip Replacement to be from 2.7% in some series up to as high as 22% over 4 years. The risk of fractures is the highest for patients over 70 years of age. Revision is required for femoral neck fracture (FNF) or component loosening. Overall, FNF occurs an average of 15.4 weeks post surgery; women fracture at a mean of 18.5 weeks and men at 13.5 weeks. No evidence has convincingly shown linking the experience of the surgeon to the incidence or timing of the fracture. All fractures need revision to THR.
Metal Ion Levels in Surface Replacements
Metal on plastic as used in conventional THRs produce polyethylene wear debris that can irritate the hip over years and cause osteolysis and loosening. There are far lower levels of particulate debris generated in Surface Replacements and thus osteolysis is rare. In a significant study by Hart et al (JBJS 2006) Cobalt and chromium levels were significantly elevated in the patients with metal-on-metal hip resurfacings, compared with the patients with standard metal-on-polyethylene designs. There was a statistically significant decrease in the level of CD8+ cells (T-cytotoxic/suppressor) in the metal-on-metal hip resurfacing group. A threshold level of blood cobalt and chromium ions was associated with reduced CD8+ T-cell counts. They found no evidence that any patients suffered as a result of this reduced level of CD8+ T-cells. In spite of evidence to contrary there is speculation that this may cause allergy or even malignancy over decades of exposure. This has not been substantiated.
CLINICAL EFFECTIVENESS AND COST-EFFECTIVENESS FOR SURFACE REPLACEMENTS
The National Institute for Health and Clinical Excellence or NICE is a special health authority of the National Health Service (NHS) in England and Wales. It was set up as the National Institute for Clinical Excellence in 1999 and in April 2005 joined with the Health Development Agency to become the new National Institute for Health and Clinical Excellence. NICE publishes clinical appraisals of whether particular treatments should be considered worthwhile by the NHS. http://en.wikipedia.org/wiki/National_Institute_for_Health_and_Clinical_Excellence – cite_note-3
NICE has made the following recommendations about the use of metal on metal (MoM) hip resurfacing:
MoM hip resurfacing is recommended as an option for people with advanced hip disease who would otherwise receive a conventional primary total hip replacement (THR) and are likely to live longer than the device is likely to last.
When considering MoM hip resurfacing surgeons should bear in mind:
A) The activity level of the individual patient
B) That the evidence available at the moment for the clinical effectiveness and cost effectiveness of MoM hip resurfacing comes mainly from studies that have involved people less than 65 years of age
Information on MoM resurfacing operations carried out should be collected as part of a UK national joint registry. The information collected will help the NHS to gather evidence on both the clinical effectiveness and cost effectiveness of MoM hip resurfacing.
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.
MoM hip resurfacing should be performed only by surgeons who have received training in the technique.
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
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.
The relative indications for femoral surface replacement alone versus total surface replacement can be summarized as follows:
Surface replacement (Double cup or Double shell)
Recent Articles on Surface Replacements
The Birmingham Hip Resurfacing Prosthesis An Independent Single Surgeon's Experience at 7-Year Follow-Up. Madhu TS, Akula MR, Raman RN, Sharma HK, Johnson VG. J Arthroplasty. 2010 Jan 5
The influence of head size and sex on the outcome of Birmingham hip resurfacing. McBryde CW, Theivendran K, Thomas AM, Treacy RB, Pynsent PB. J Bone Joint Surg Am. 2010 Jan;92(1):105-12.
Metal ion release from bearing wear and corrosion with 28 mm and large-diameter metal-on-metal bearing articulations: a follow-up study. Vendittoli PA, Roy A, Mottard S, Girard J, Lusignan D, Lavigne M. J Bone Joint Surg Br. 2010 Jan;92(1):12-9.
Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: A consequence of excess wear. Langton DJ, Jameson SS, Joyce TJ, Hallab NJ, Natu S, Nargol AV. J Bone Joint Surg Br. 2010 Jan;92(1):38-46.
Risk factors for inflammatory pseudotumour formation following hip resurfacing. Glyn-Jones S, Pandit H, Kwon YM, Doll H, Gill HS, Murray DW. JBJS Br.2009. Dec;91(12):1566-74.
- BlueCross and BlueShield Association Medical Policy Reference Manual; Policy No. 7.01.80
- Amstutz HC, Beaul