hip replacement hip replacement hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant, that is, a hip prosthesis. hip replacement surgery can be performed as a total replacement or a hemi (half) replacement. such joint replacement orthopaedic surgery is generally conducted to relieve arthritis pain or in some hip fractures. a total hip replacement (total hip arthroplasty or tha) consists of replacing both the acetabulum and the femoral head while hemiarthroplasty generally only replaces the femoral head. hip replacement is one of the most common orthopaedic operations, though patient satisfaction varies widely. approximately 58% of total hip replacements are estimated to last 25 years. the average cost of a total hip replacement in 2012 was $40,364 in the united states, and about $7,700 to $12,000 in most european countries. hip replacementan x-ray showing a left hip (right of image) that has been replaced, with the ball of this ball-and-socket joint replaced by a metal head that is set in the femur and the socket replaced by a cupother nameship arthroplastyicd-9-cm81.51–81.53meshd019644medlineplus002975 medical uses total 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 after other therapies, such as physical therapy and pain medications, have failed. risks risks and complications in hip replacement are similar to those associated with all joint replacements. they can include infection, dislocation, limb length inequality, loosening, impingement, osteolysis, metal sensitivity, nerve palsy, chronic pain and death. weight loss surgery before a hip replacement does not appear to change outcomes. follow-up assessments are conducted to examine the need for revision surgery. however, a uk study showed that only 3-6% of hip replacements needed a revision. researchers recommended that routine follow-up may not be needed for up to 10 years. at this point, x-rays should be used to assess the joint, and there should be a clinical assessment of pain and mobility. dislocation dislocated artificial hip liner wear, particularly when over 2 mm, increases the risk of dislocation. liner creep, on the other hand, is normal remoulding. dislocation (the ball coming out of the socket) is the most common complication. the most common causes vary by the duration since the surgery. hip prosthesis dislocation mostly occurs in the first three months after insertion, mainly because of incomplete scar formation and relaxed soft tissues. it takes eight to twelve weeks for the soft tissues injured or cut during surgery to heal. the chance of this is diminished if less tissue is cut, if the cut tissue is repaired and if large diameter head balls are used. dislocations occurring between three months and five years after insertion usually occur due to malposition of the components, or dysfunction of nearby muscles. risk factors of late dislocation (after five years) mainly include: female sex younger age previous subluxation without complete dislocation previous trauma substantial weight loss recent onset or progression of dementia or a neurological disorder malposition of the cup liner wear, particularly when it allows head movement of more than 2 mm within the cup compared to its original position prosthesis loosening with migration surgeons who perform more operations tend to have fewer dislocations. an anterior approach seems to lower dislocation rates when small diameter heads are used, but that benefit has not been shown when compared to modern posterior incisions with the use of larger diameter heads. the use of larger diameter head size in itself decreases dislocation risk, even though this correlation is only found in head sizes up to 28 mm: larger heads do not result in a statistically significant decrease in dislocation rate. keeping the leg out of certain positions during the first few months after surgery further reduces risk. infection infection is one of the most common causes for revision of a total hip replacement. the incidence of infection in primary hip replacement is 1% or less in the united states. risk factors for infection include obesity, diabetes, smoking, immunosuppressive medications or diseases, and history of infection. in revision surgery, infected tissue surrounding the joint is removed, and the artificial joint replaced. typically, this is carried out in 2 stages: infected tissue and all joint replacement implants are removed in the first stage, and, after the infection is completely cleared, a new artificial joint is inserted in the second stage. one-stage surgery is also available whereby infected tissue and implants are removed, and the new joint inserted, in a single procedure. one-stage hip revisions were found to be as effective as two-stage procedures at relieving pain and improving hip stiffness and function. one-stage procedures were also better value for money. limb length inequality most adults have a limb length inequality of 0–2 cm which causes no deficits. it is common for people to sense a larger limb length inequality after total hip replacement. sometimes the leg seems long immediately after surgery when in fact both are equal length. an arthritic hip can develop contractures that make the leg behave as if it is short. when these are relieved with replacement surgery and normal motion and function are restored, the body feels that the limb is now longer than it was. this feeling usually subsides by six months after surgery as the body adjusts to the new hip joint. the cause of this feeling is variable, and usually related to abductor muscle weakness, pelvic obliquity, and minor lengthening of the hip during surgery (<1 cm) to achieve stability and restore the joint to pre-arthritic mechanics. if the limb length difference remains bothersome to the patient more than six months after surgery, a shoe lift can be used. only in extreme cases is surgery required for correction. the perceived difference in limb length for a patient after surgery is a common cause for lawsuits against the healthcare provider. fracture intraoperative acetabular fracture intraoperative fractures may occur. after surgery, bones with internal fixation devices in situ are at risk of periprosthetic fractures at the end of the implant, an area of relative mechanical stress. post-operative femoral fractures are graded by the vancouver classification. vein thrombosis venous thrombosis such as deep vein thrombosis and pulmonary embolism are relatively common following hip replacement surgery. standard treatment with anticoagulants is for 7–10 days; however, treatment for 21+ days may be superior. extended-duration anticoagulants (up to 35 days following surgery) may prevent vte in people undergoing hip replacement surgery. other research suggested that anticoagulants in otherwise healthy patients undergoing a so-called fast track protocol with hospital stays under five days, might only be necessary while in the hospital. emerging evidence supports the use of aspirin for venous thromboembolism prophylaxis. large randomised control trials suggested that aspirin is not inferior to low-molecular weight heparins and rivaroxaban. however, aspirin may not be appropriate in all cases, especially for patients who have additional risk factors for venous thromboembolisms or may have an inadequate response to aspirin. some physicians and patients may consider having an ultrasonography for deep vein thrombosis after hip replacement. however, this kind of screening should only be done when indicated because to perform it routinely would be unnecessary health care. intermittent pneumatic compression (ipc) devices are sometimes used for prevention of blood clots following total hip replacement. osteolysis many long-term problems with hip replacements are the result of osteolysis. this is the loss of bone caused by the body's reaction to polyethylene wear debris, fine bits of plastic that wear off the cup liner over time. an inflammatory process causes bone resorption that may lead to subsequent loosening of the hip implants and even fractures in the bone around the implants. ceramic bearing surfaces may eliminate the generation of wear particles. metal cup liners joined with metal heads (metal-on-metal hip arthroplasty) were developed for similar reasons. in the lab these show excellent wear characteristics and benefit from a different mode of lubrication. highly cross-linked polyethylene plastic liners experience significantly reduced plastic wear debris. the newer ceramic and metal prostheses may not have long-term performance records. ceramic piece breakage can lead to catastrophic failure. this occurs in about 2% of implants. they may also cause an audible, high pitched squeaking noise with activity. metal-on-metal arthroplasty can release metal debris into the body. highly cross linked polyethylene is not as strong as regular polyethylene. these plastic liners can crack or break free of the metal shell that holds them. loosening hip prosthesis displaying aseptic loosening (arrows) hip prosthesis zones according to delee and charnley, and gruen. these are used to describe the location of for example areas of loosening. on radiography, it is normal to see thin radiolucent areas of less than 2 mm around hip prosthesis components, or between a cement mantle and bone. these may indicate loosening of the prosthesis if they are new or changing, while areas greater than 2 mm may be harmless if they are stable. the most important prognostic factors of cemented cups are absence of radiolucent lines in delee and charnley zone i, as well as adequate cement mantle thickness. in the first year after insertion of uncemented femoral stems, it is normal to have mild subsidence (less than 10 mm). the direct anterior approach has been shown to itself be a risk factor for early femoral component loosening. metal sensitivity concerns were raised in the early 2000s regarding metal sensitivity and the potential dangers of metal particulate debris from hip prostheses, including the development of pseudotumors, soft tissue masses containing necrotic tissue, around the hip joint. it appears these masses were more common in women, and these patients showed a higher level of iron in the blood. the cause was then unknown, and was probably multifactorial. there may have been a toxic reaction to an excess of particulate metal wear debris or a hypersensitivity reaction to a "normal" amount of metal debris. metal hypersensitivity is a well-established phenomenon and is not uncommon, affecting about 10–15% of the population. skin contact with certain metals can cause immune reactions such as hives, eczema, redness and itching. although little is known about the short- and long-term pharmacodynamics and bioavailability of circulating metal degradation products in vivo, there have been many reports of immunologic-type responses temporally associated with implantation of metal components. individual case reports link immune hypersensitivity reactions with adverse performance of metallic cardiovascular, orthopedic and plastic surgical and dental implants. metal toxicity most hip replacements consist of cobalt and chromium alloys, or titanium. stainless steel is no longer used. any metal implant releases its constituent ions into the blood. typically, these are excreted in the urine, but in certain individuals the ions can accumulate in the body. in implants which involve metal-on-metal contact, microscopic fragments of cobalt and chromium can be absorbed into the person's bloodstream. there are reports of cobalt toxicity with hip replacement, particularly metal-on-metal hip replacements, which are no longer in use. use of metal-on-metal hip replacements from the 1970s was discontinued in the 1980s and 1990s, particularly after the discovery of aseptic lymphocyte-dominant vasculitis-associated lesions (alval). however, the fda's 510k approval process allowed companies to have new and "improved" metal-on-metal hips approved without much clinical testing. some people with these prostheses experienced similar reactions to the metal debris as occurred in the 20th century; some devices were recalled. nerve palsy post operative sciatic nerve palsy is another possible complication. the frequency of this complication is low. femoral nerve palsy is another, but much rarer, complication. both of these will typically resolve over time, but the healing process is slow. patients with pre-existing nerve injury are at greater risk of experiencing this complication and are also slower to recover. chronic pain a few patients who have had a hip replacement suffer chronic pain after the surgery. groin pain can develop if the muscle that raises the hip (iliopsoas) rubs against the edge of the acetabular cup. bursitis can develop at the trochanter where a surgical scar crosses the bone, or if the femoral component used pushes the leg out to the side too far. also some patients can experience pain in cold or damp