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/semi replacement. Such joint replacement orthopaedic surgery is generally conducted to relieve arthritis pain or in some hip fractures. A total hip replacement 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. Patient satisfaction varies widely between different techniques and implants. 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 in the range of €7,117 to €11,091 in most European countries.
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.Outcomes
Hip replacement provides significantly better results than exercise training in terms of reducing pain 6 months afterwards. It is possible to play high-level sport after hip resurfacing, or even play professional tennis or baseball. People who have had hip replacements generally have reduced death rates than the matched population for 10 years after surgery, but rates then increase from 11 years onwards. For this reason it is sometimes argued that the age group 65-80 is the best time to consider having a hip replacement if activity is being severely curtailed by hip pain. Hip resurfacing is a less invasive type of hip replacement that may be more suitable for younger patients.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.Edema appears around the hip in the hours or days following the surgery. This swelling is typically at its maximum 7 days after the operation, then decreases and disappears over the course of weeks. Only 5% of patients still have swelling 6 months after the operation.
Dislocation
Dislocation is one of the most common complications. Hip prosthesis dislocation mostly occurs in the first three months after insertion, mainly because of incomplete scar formation and relaxed soft tissues. 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. Surgeons who perform more operations tend to have fewer dislocations. Important factors which are related to dislocation are: component positioning, preservation of the gluteal muscles and restoration of leg length and femoral offset. Keeping the leg out of certain positions during the first few months after surgery further reduces risk.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 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
Infection
In revision surgery, infected tissue surrounding the joint is removed, and the artificial joint replaced. This can be carried out in one- or two-stage surgery. In two-stage surgery the 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. In one-stage surgery infected tissue and implants are removed, and the new joint inserted, in a single procedure. Both kinds of surgery are equally effective but one-stage surgery results in faster recovery.
There is also an alternative called DAIR that is possible if the infection presents during the first month after primary surgery. In contrast to 1- or 2-stage revision surgery, DAIR involves replacing only the removable components while retaining the prosthesis itself. Also a thorough debridement of infected tissue is performed, antibiotics are administered and the treatment continuous for at least 6-12 weeks. The success rate of DAIR is approximately 75%, saving a lot of patients from more extensive surgery.
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 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 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
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 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 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 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.Wear and aseptic loosening
Abrasive wear of the polyethylene liner is a common cause of aseptic loosening after total hip arthroplasty. The erosion of the polyethylene liner generates debris, triggering an inflammatory response and subsequent osteolysis and loosening. There seems to be an association between a higher degree of wear and later revision due to loosening. There also seems to be an association between increased wear above 0.1 mm per year and development of osteolysis which could lead to loosening of the implant and a review by Dumbleton et al.suggested a practical threshold of 0.05 mm/year was proposed to minimize the risk of osteolysis due to particle-induced disease.Signs of loosening could either be radiological, clinical or both. Clinical symptoms include pain and loss of function, while radiological signs constitutes migration of the implant or development of radiolucent lines around the implant. The radiolucent lines can be describe using a seven-zone system of the femur described by Gruen et al. and a three-zone system of the acetabulum described by DeLee and Charnley. 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.
Migration pattern can be different depending on the implants and their fixation method. An early sign of implant failure seems to be if the acetabular cup migrates more than 1 mm within the first two years after surgery. For each additional millimeter of migration, the risk of revision within ten years increases by about 10%.