Joint Infection FAQ’s

What is a prosthetic joint infection?
Bacterial joint infection is a serious and a painful condition of the joint. It is also called septic arthritis. Bacteria can enter the joint and cause significant damage, especially when the joint is artificial joint. Most of the bacteria that travels to the artificial joint comes through the blood. It is important for any infection anywhere to be aggressively treated, especially skin or superficial infections. It is recommended to take antibiotics before dental cleaning because bacteria from the mouth can travel to the artificial joint through the blood and cause an infection.
How common is periprosthetic joint infection?
The possibility of getting a periprosthetic joint infection is from 0.5% to 7%. It is the number one reason for failure after a total knee replacement and number three reason for failure after a hip replacement.
How is infection of artificial joint diagnosed?
An infection is diagnosed based on history, physical examination, and on running the results of the blood and also by doing aspiration of the joint. There is a history of the patient to ensure significant pain, redness, swelling, and ability to bear weight. The physical findings will show a swollen joint, tenderness all over the joint, and significantly decreased range of motion and inability to bear weight on the joint. Usually it occurs in an acute manner within hours. Blood tests include running a CBC and ESR and CRP. There are also specialized tests available to diagnose joint infection. What is the most confirmatory test for diagnosing infection of artificial joint. Aspiration of the joint is a confirmatory test for diagnosing infection. We look for the total number of cells and inflammatory cells in the joint and also do a culture sensitivity of the fluid. A culture sensitivity allows us to look at the antibiotics that the infected joint will be susceptible to.
How is infection of artificial joint treated?
Artificial joint infection is treated in a variety of ways depending on the time the infection is diagnosed, whether the implants are still fixed or they’re loose, depending upon the life expectancy and the medical conditions of the patient. If the infection is diagnosed early and if the infection is inside the joint, irrigation of the debridement of the joint usually is sufficient. This is done to prevent it from becoming a chronic infection. The surgery involves cleaning the joint and usually changing the exchangeable pieces in the joint. The changeable pieces in the hip joint include the head of the stem that goes into the thigh bone and the plastic that goes inside the cup. The parts that are affixed to the bone are not removed or exchanged. If the implant is loose, the implant needs to be removed and needs to be replaced with an antibiotic spacer. Antibiotic spacer is cement loaded with extremely high dose of antibiotics. The first involves removing the implant, placing the antibiotic spacer, and treating the patient with additional IV antibiotics. After about four to six weeks the antibiotics are stopped, aspiration of the joint is done to confirm that the infection is eradicated, and then revision surgery is performed in which the antibiotic spacer is removed and the final prosthesis is placed into the joint. This procedure is called a staged reconstruction for treating artificial infected joints. The final scenario is a patient in which the medical conditions are significant, the life expectancy is very low, and chronic antibiotic suppression is used to treat these infections. Chronic antibiotic suppression means that the patient gets antibiotics for the rest of their lives.
What are the reasons for infection of total hip replacements?

Infection of total hip replacement can be immediately after the surgery, which what I call “acute” postoperative infections. There could be “delayed” deep infections which happen from three months to the next two years.

“Late” infections which typically happen after 2 years are called hematogenous (blood bourne) infections because these infections are most commonly because of bacteria seeding the joint and these bacteria have originated elsewhere from the hip joint.

Acute postoperative infections happen within the first three months of surgery and it’s important to distinguish whether these infections are superficial or deep. Superficial infections are outside the fascia and do not affect the inside of the joint. Deep infections are infections where the actual artificial joint is seeded with the bacteria.

The best way to differentiate a superficial from a deep infection is by doing aspiration of the hip joint and looking for cell count, culture sensitivity, Gram stain, etc. A cell count has to be differential- which means we look at individual white cells – lymphocytes etc. Aspirated cell count is an extremely useful test. The cell count for artificial joints that are infected are significantly lower than the counts associated with primary joint infection ie native joints getting infected.

Deep delayed infections occur after three months and could be from the surgery or could be from a hematogenous infection from elsewhere in the body including urinary tract infection or the nasal tract. Depending upon how the infection manifests, one option is to do irrigation and debridement (surgical cleaning) and exchanging of the head and the plastic and then treating the patient with IV antibiotics to achieve resolution of the infection.

Late hematogenous infection occur typically after two years and is from a source away from the hip joint. In these circumstances, the patient typically has to have a two stage reconstruction in which the joint has to be removed, antibiotic spacer has to be placed inside the hip joint, and after treatment with IV antibiotics, the antibiotic spacer is removed and the final hip revision is placed into position.

The advantage of the antibiotic spacers is that the antibiotic spacers eludes huge amount of antibiotics and kills the infection. Such high level of antibiotics is impossible to achieve through an IV dose because of possible toxicity to the body. The best way to treat late hematogenous infection is “staged reconstruction”. However, if the patient has significant medical problems with the extreme limitation of life expectancy, another option is to do removal of the implant which is called the “hanging hip” or “Girdlestone operation of the hip”.

There’s also been studies which show that a single-stage revision is an option for infected joint in which the infected joint is removed. Thorough debridement is done on the joint and a new hip joint is placed in position at the same time the infected joint is removed.

Studies looking at a single stage revision for infected joint arthroplasty are fairly limited.

What is an antibiotic spacer?
Antibiotic spacer is cement loaded with high-dose antibiotics. The antibiotics flow into the joint and the surrounding tissues and kill the infection. It is placed inside the joint and therefore high dose of antibiotics can be used. Usually this high of a dose cannot be used intravenously because it is a lethal dose. Antibiotic spacers are of two types. Static and articulating. I use articulating antibiotic spacers because the range of the hip joint is maintained after the articulating spacer. The amount of bone eroded from the infection is decreased because of the articulating joint spacer. Additionally, the revision surgery can be done in a less invasive manner.
What is a spacer in the hip joint?

A spacer in the hip joint is made from a cement mold. The measurement of the infected artificial hip joint that is to be removed is determined preoperatively and intraoperatively and there are molds of different sizes that can be used to create the antibiotic cement spacer.

My preferred method is to make the spacer even before making the incision so that the operative time is decreased. I do thorough planning preoperatively and I select the spacer preoperatively. I mix about 10 grams of tobramycin and 10 grams of vancomycin and make the cement spacer. I also peel off the plastic from the cement spacer before the incision is made.

After that, the incision is made, the infected prostheses is removed, and the cement antibiotic spacer is placed into position. Before placing the cement, the spacer, it’s very important to do a thorough debridement. I thoroughly clean out the femoral canal and remove the acetabulum so that the infected tissue is extracted as much as possible and then the cement spacer is placed into position.

After closure of the wound, IV antibiotics are given postoperatively for about four to six weeks and aspiration is performed after six weeks to ensure there’s no infection and then the patient is again scheduled for removal of the antibiotic spacer and placement of a revision hip surgery.

In these type of surgeries, the tourniquet has to be let down, and although hemostasis is achieved, there may be blood loss intraoperatively which may need a blood transfusion.

For patients who undergo a spacer, the spacer is not strongly adherent to the bone because it’s an antibiotic spacer, and the idea is not to cement it to the bone because removing the spacer in the second stage will lead to more bone loss.

Therefore, in patients who get a spacer, there is blood loss, not during the surgery but during the postoperative period. Patients who get a spacer after the removal of the knee joint do a transfusion on the second or the third day.

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