Risks and complications in hip replacement are similar to those associated with all joint replacements. They can include dislocation, loosening, impingement, infection, osteolysis, metal sensitivity, nerve palsy, pain and death.
Dislocation is the most common complication of hip replacement surgery. At surgery the femoral head is taken out of the socket, hip implants are placed and the hip put back into proper position. It takes eight to twelve weeks for the soft tissues injured or cut during surgery to heal. During this period, the hip ball can come out of the socket.
The chance of this is diminished if less tissue is cut, if the tissue cut is repaired and if large diameter head balls are used. Surgeons who perform more of the operations each year tend to have fewer patients dislocate.
Doing the surgery from an anterior aproach seems to lower dislocation rates when small diameter heads are used, but the benefit has not been shown when compared to modern posterior incisions with the use of larger diameter heads.
Patient can decrease the risk further by keeping the leg out of certain positions during the first few months after surgery.
Use of alcohol by patients during this early period is also associated with an increased rate of dislocation.
In the long term, many problems relate to osteolysis from polyethylene wear debris, fine bits of plastic that come 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.
In an attempt to eliminate the generation of wear particles, ceramic bearing surfaces are being used in the hope that they will have less wear and less osteolysis with better long term results.
Metal cup liners joined with metal heads (metal-on-metal hip arthroplasty) were also developed for similar reasons. In the lab these show excellent wear characteristics and benefit from a different mode of lubrication.
At the same time these two bearing surfaces were being developed, highly cross linked polyethylene plastic liners were also developed.
The greater cross linking significantly reduces the amount of plastic wear debris given off over time. These new prostheses do not always have the long term track record of established metal on poly bearings.
Ceramic pieces can break leading to catastrophic failure. This occurs in about 2% of the time. They may also cause an audible, high pitched squeaking noise with activity.
Metal-on-metal arthroplasty releases metal particulate debris into the body raising concerns about the potential dangers of these accumulating in the body over time. 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.
Concerns are being raised about the metal sensitivity and 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.
Metal hypersensitivity is a well-established phenomenon and is common, affecting about 10-15% of the population. Contact with metals can cause immune reactions such as skin 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 hypersensitivity immune reactions with adverse performance of metallic clinical cardiovascular, orthopedic and plastic surgical and dental 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).
In the United Kingdom the Medicines and Healthcare products Regulatory Agency commenced an annual monitoring regime for metal-on-metal hip replacement patients from May 2010.
Data which is shown in The Australian Orthopaedic Association's 2008 National Joint Replacement Registry, a record of nearly every hip implanted in that country over the previous 10 years, tracked 6,773 BHR (Birmingham Hip Resurfacing) Hips and found that less than one-third of one percent may have been revised due to the patient's reaction to the metal component.
Other similar metal-on-metal designs have not fared as well, where some reports show 76% to 100% of the people with these metal-on-metal implants and have aseptic implant failures requiring revision also have evidence of histological inflammation accompanied by extensive lymphocyte infiltrates, characteristic of delayed type hypersensitivity responses.
It is not clear to what extent this phenomenon negatively affect orthopedic patients. However for patients presenting with signs of an allergic reactions, evaluation for sensitivity should be conducted. Removal of the device that is not needed should be considered, since removal may alleviate the symptoms.
Patients who have allergic reactions to cheap jewelry are more likely to have a reactions to orthopedic implants. It is important to note that there is increasing awareness of the phenomenon of metal sensitivity and many surgeons now take this into account when planning which implant is optimal for each patient.
Post operative sciatic nerve palsy is another possible complication. The incidence of this complication is low. Femoral nerve palsy is another but much more rare 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.
A few patients who have had a hip replacement suffer chronic pain after the surgery. Groin pain can develop if the tendon 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 weather. Incision made in the front of the hip (anterior approach) can cut a nerve running down the thigh leading to numbness in the thigh and occasionally chronic pain where the nerve was cut.
Rates of death for elective hip replacements are much less than 1%.
Most hip replacements consist of cobalt and chromium alloys. They release these ions into the blood. There have been reports of cobalt toxicity with hip replacement patients.
Leg Length Inequality
The leg can be lengthened or shortened during surgery. Unequal legs are the most common complaint by patients after surgery with over lengthening the most common problem. 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 like 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 then it was. If the legs are truly equal, the sense of this resolves within a month or two of surgery. If the leg is unequal, it will not. A shoe lift for the short leg, or in extreme cases, a corrective operation may be needed.
True leg length inequality is caused by improper implant selection. The femoral component may be too large and stick out of the femur further then needed. The head ball selected may sit too proud on the stem. Stiffness in the lower back from arthritis or previous fusion surgery seems to magnify the perception of leg length inequality.
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