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Hip replacement (total hip replacement), is a surgical procedure in which the hip joint is replaced by a prosthetic implant. Replacing the hip joint consists of replacing both the acetabulum and the femoral head. Such joint replacement orthopaedic surgery generally is conducted to relieve arthritis pain or fix severe physical joint damage as part of hip fracture treatment. Hip replacement is currently the most successful and reliable orthopaedic operation with 97% of patients reporting improved outcome. Rates of death for elective hip replacements are much less than 1%.
HistoryThe earliest recorded attempts at hip replacement (Gluck T, 1891), which were carried out in Germany, used ivory to replace the femoral head (the ball on the femur).
In 1940 at Johns Hopkins hospital, Dr.Austin T. Moore (1899-1963), an American surgeon, reported and performed the first metallic hip replacement surgery. The original prosthesis he designed was a proximal femoral replacement, with a large fixed head, made of the Cobalt-Chrome alloy Vitallium. It was about a foot in length and it bolted to the resected end of the femoral shaft (hemiarthroplasty). This was unlike later (and current) hip replacement prostheses which are inserted within the medullary canal of the femur. A later version of Dr. Moore's prosthesis, the so-called Austin Moore, introduced in 1952 is still in use today.
In 1960 a Burmese orthopaedic surgeon, Dr. San Baw (29 June 1922—7 December 1984), pioneered the use of ivory hip prostheses to replace ununited fractures of the neck of femur when he first used an ivory prosthesis to replace the fractured hip bone of an 83 year old Burmese Buddhist nun, Daw Punya. This was done while Dr. San Baw was the chief of orthopaedic surgery at Mandalay General Hospital in Mandalay, Burma. Dr. San Baw used over 300 ivory hip replacements from the 1960s to 1980s. He presented a paper entitled "Ivory hip replacements for ununited fractures of the neck of femur" at the conference of the British Orthopaedic Association held in London in September 1969. An 88% success rate was discerned in that Dr. San Baw's patients ranging from the ages of 24 to 87 were able to walk, squat, ride a bicycle and play football a few weeks after their fractured hip bones were replaced with ivory prostheses. Ivory may have been used because it was cheaper than metal at that time in Burma and also was thought to have good biomechanical properties including biological bonding of ivory with the human tissues nearby. An extract from Dr San Baw's paper, which he presented at the British Orthopaedic Association's Conference in 1969, is published in Journal of Bone and Joint Surgery (British edition), February 1970. With modern hip replacement surgery, one can expect to walk immediately post-op.
A titanium hip prosthesis, with a ceramic head and polyethylene acetabular cup.
The modern artificial joint owes much to the work of John Charnley at Wrightington Hospital; his work in the field of tribology resulted in a design that almost completely replaced the other designs by the 1970s. Charnley's design consisted of three parts—
1.a metal (originally stainless steel) femoral component,
2.a teflon acetabular component, the wear debris of which resulted in a condition called Osteolysis, and so it was replaced by Ultra High Molecular Weight Polyethylene or UHMWPE in 1962, both of which were fixed to the bone using
3.PMMA (acrylic) bone cement, and/or screws.
The replacement joint, which was known as the Low Friction Arthroplasty, was lubricated with synovial fluid. The small femoral head (7/8" (22.2 mm)) was chosen for its decreased wear rate; however, this has relatively poor stability (the larger the head of a replacement the less likely it is to dislocate, but the more wear debris produced due to the increased surface area). For over two decades, the Charnley Low Friction Arthroplasty, and subsequent similar designs were the most used systems in the world, far surpassing the other available options (like McKee and Ring). Recently the use of a polished tapered cemented hip replacement (like Exeter) and uncemented hip replacements have become more popular. Cemented stems are commonly used in older patients due to their lower cost, including the Austin Moore proximal femoral replacement for Medicaid patients, while more modern and longer lasting 'cementless' stems, often coated in Hydroxy-Apatite Ceramic, are used in 'younger' and more physically active patients. Other cementless materials included grit blasted titanium, titanium mesh, or the Trabecular Metal substrate made from tantalum from Zimmer, Inc.
One other innovation made in hip arthroplasty is the introduction of highly-crosslinked UHMWPE; these implants have a higher compressive wear resistance which reduces overall wear and once again allowed the use of larger diameter femoral heads (32 and 36mm), thereby increasing range of motion and lowering the risk of dislocation.
Once an uncommon operation, hip replacement is now common, even among active athletes including racecar drivers Bobby Labonte and Dale Jarrett.
CostsIn 2008, hip replacements in the U.S. cost about $45,000.
Dislocated artificial hip.
Hip prosthesis displaying aseptic loosening (arrows).
In the long term, many problems relate to osteolysis from acrylic bone cement debris, and/or wear debris. An inflammatory process causes bone resorption and subsequent loosening or fracture often requiring revision surgery. Very hard ceramic bearing surfaces are being used in the hope that they will have less wear and less osteolysis with better long term results. Large metal heads (metal-on-metal hip arthroplasty) are also used for similar reasons as these also have excellent wear characteristics and benefit from a different mode of lubrication. However large fixed metal heads,such as the Austin Moore devices, can result in protrusio acetabuli. A greater head neck ratio also contributes to stability. These new prostheses do not always have the long term track record of established metal on poly bearings. As metal-on-metal arthroplasty becomes more widespread, concerns are being raised about the potential dangers of metal particulate debris. There are new publications  that have demonstrated development of pseudotumors, soft tissue masses containing necrotic tissue, around the hip joint. It appears these masses are more common in women and these patients show a higher level of iron in the blood. The cause is unknown and is probably multifactorial. There may be a toxic reaction to an excess of particulate metal wear debris or a hypersensitivity reaction to a normal amount of metal debris.
Post operative sciatic nerve palsy is another possible complication.
A few patients who have had a hip replacement suffer chronic pain after the surgery despite normal imaging.
IndicationsTotal hip replacement is most commonly used to treat joint failure caused by osteoarthritis. Other indications include rheumatoid arthritis, avascular necrosis, traumatic arthritis, protrusio acetabuli, certain hip fractures, benign and malignant bone tumors, arthritis associated with Paget's disease, ankylosing spondylitis and juvenile rheumatoid arthritis. The aims of the procedure are pain relief and improvement in hip function. Hip replacement is usually considered only once other therapies, such as physical therapy and pain medications, have failed.
There are several different incisions, defined by their relation to the gluteus medius. The approaches are posterior (Moore), lateral (Hardinge or Liverpool), antero-lateral (Watson-Jones), anterior (Smith-Petersen) and greater trochanter osteotomy. There is no compelling evidence in the literature for any particular approach, but consensus of professional opinion favours either modified anterio-lateral (Hardinge) or posterior approach.
- The posterior (Moore) approach accesses the joint through the back, taking piriformis muscle and the short external rotators off the femur. This approach gives excellent access to the acetabulum and preserves the hip abductors. Critics cite a higher dislocation rate, although repair of the capsule and the short external rotators negates this risk.
- The lateral approach is also commonly used for hip replacement. The approach requires elevation of the hip abductors (gluteus medius and gluteus minimus) in order to access the joint. The abductors may be lifted up by osteotomy of the greater trochanter and reapplying it afterwards using wires (as per Charnley), or may be divided at their tendinous portion, or through the functional tendon (as per Hardinge) and repaired using sutures.
- The anterolateral approach develops the interval between the tensor fasciae latae and the gluteus medius.
- The anterior approach utilises an interval between the sartorius muscle and tensor fascia latae.
The double incision surgery and minimally invasive surgery seeks to reduce soft tissue damage through reducing the size of the incision. However component positioning accuracy is impaired and surgeons using these approaches are advised to use computer guidance systems.
Computer Assisted Surgery techniques are also available to guide the surgeon to provide enhanced accuracy and visualization. Several commercial CAS systems are available for use worldwide. HipNav was the first system developed specifically for total hip replacement, and included navigation and preoperative planning based on a preoperative CT scan of the patient.
Alternatives to Hip Replacement
The first line approach as an alternative to hip replacement is conservative management which involves a multimodal approach of medication, activity modification and physical therapy. Conservative management can prevent or delay the need for hip replacement.
Hip resurfacingThe method is an alternative to hip replacement surgery. It is a bone conserving procedure that places a metal cap on the femoral head instead of amputating it. There is no long stem placed down the femur so it is more like a natural hip and may allow patients a return to many activities, including marathons and triathlons, some patients have even completed Ironman and Ultraman competitions (citation needed) following hip resurfacing surgery although patients must have good bone quality to qualify for it. It has been used in Europe for over 17 years and become a common procedure. The first device, the BHR or Birmingham Hip Resurfacing device was approved by the FDA on May 9, 2006. doi:10.2106/JBJS.H.00603
Complications of Metal-on-Metal Implants
By 2010 reports in the orthopaedic literature have increasingly cited the problem of early failure of metal on metal prostheses in a small percentage of patients. Failures may relate to release of minute metallic particles or metal ions from wear of the implants, causing pain and disability severe enough to require revision surgery in 1-3% of patients. . Design deficits of some prothesis models, especially with heat-treated alloys and a lack of special surgical experience accounts for most of the failures. Surgeons at leading medical centers such as the Mayo Clinic have reported reducing by 80 percent their use of metal-on-metal implants over the last year in favor of those made from other materials, like combinations of metal and plastic.  The cause of these failures remain controversial, and may include both design factors, technique factors, and factors related to patient immune responses (allergy type reactions)..
Current alternatives also include viscosupplementation, or the injection of artificial lubricants into the joint. Some believe the future of osteoarthritis treatment is bioengineering, targeting the growth and/or repair of the damaged, arthritic joint. Centeno et al. have reported on the partial regeneration of an arthritic human hip joint using mesenchymal stem cells in one patient. It is yet to be shown that this result will apply to a larger group of patients and result in significant benefits.
The FDA has stated that this procedure is being practiced without conforming to regulations, but Centeno claims it is exempt from FDA regulation. It has not been shown in controlled clinical trials to be effective...