Periprosthetic Joint Infection

What is Periprosthetic Joint Infection?

Periprosthetic joint infection (PJI) is a specific type of infection that occurs around joint replacements. Unlike infections that typically affect natural bones or joints, PJI is different and a bit more complicated. It primarily involves harmful organisms, like bacteria and sometimes fungi, interacting with the body’s immune system. An interesting thing about PJIs is that it only takes a small number of microbes to trigger one. These harmful organisms can stick to the surfaces of joint replacement parts and create biofilms – groups of microorganisms that stick together on a surface.

Biofilms make infections more difficult to treat because they are highly resistant to many anti-infectives and can evade the immune system successfully. Most PJI causing organisms come from the skin’s native microbial communities and may enter the body during the surgery to implant the joint replacement. Alternatively, these harmful organisms might reach the implanted joint after surgery by spreading through the bloodstream or coming directly from nearby infected tissues.

PJI is tricky to define, and its symptoms can vary between individuals. It can even strike without the usual infection symptoms such as fever, higher white blood cell count, or signs of sepsis. The presence of a joint replacement in the body alone increases the risk of infection. Importantly, the number of microbes it takes to cause infection in joint replacements is much lower compared to natural joints.

One of the most definitive ways to identify PJI is through a joint fluid sample or tissue around the implant that grows harmful organisms when cultivated in the lab. Other evidence of PJI may include a sinus tract linking with the joint space, wound splitting open, visible pus, loose joint replacement, higher white blood cells and neutrophils in joint fluid, and increased inflammatory markers levels in blood. However, it’s important to know that inability to identify a specific organism as the cause doesn’t necessarily rule out PJI.

PJIs are a significant health concern. They greatly increase illness and risk of death and have now become the leading reason for replacing joint implants. Understanding the causes, effects, diagnosis, and treatment of PJI is crucial. Prompt and effective care for patients with this joint replacement complication can significantly reduce their risk of further health problems.

What Causes Periprosthetic Joint Infection?

Periprosthetic joint infections (PJIs) refer to infections that occur around artificial joints. These infections can be caused by a variety of bacteria and fungi. A study revealed that a type of bacteria known as Staphylococcus epidermidis, along with other species of bacteria such as Staphylococcus aureus, Streptococcus, Enterococcus, Cutibacterium, and Enterobacterales, are often found in these joint infections.

The bacteria responsible for the infection can either be one type (monomicrobial) or various types (polymicrobial). In most PJIs, 70% were caused by one type of bacteria and 25% were caused by multiple types of bacteria. Other studies point out that a bacterium called C acnes is responsible for about 44% of shoulder joint infections.

PJIs can happen at different times after the artificial joint has been implanted, and each infection period tends to be caused by different types of bacteria. This differentiation helps doctors classify the infection as early, delayed, or late.

Early PJIs occur within the first four weeks after the artificial joint surgery. They are usually caused by strong bacteria such as Staphylococcus aureus, aerobic gram-negative bacilli, beta-hemolytic streptococci, and Enterococcus spp.

Delayed PJIs happen between 3 and 12 months post-surgery. These are typically caused by less virulent organisms including coagulase-negative staphylococci, C acnes, and enterococci. Staphylococcus aureus can cause a delay in the onset of the infection, but less frequently compared to early PJI.

Late joint infections occur 1 to 2 years after the initial surgery, and they typically spread through the bloodstream. Common causes include Staphylococcus aureus, coagulase-negative staphylococci, viridans streptococci, enterococci, and occasionally, gram-negative bacilli.

It is crucial to note that in some cases, the bacteria causing the PJI may not be identified from the patient’s samples (culture-negative PJIs). The percentage of these cases can vary greatly between studies due to differences in how the samples are tested and diagnosed. In some cases, the rate of culture-negative PJIs may reach 45%.

Risk Factors and Frequency for Periprosthetic Joint Infection

In the United States, around 1 million hip and knee replacements, also known as arthroplasties, are performed each year. This number is expected to quadruple in the next 10 to 20 years. Along with this increase, there’s also been a rise in hip and knee infections after surgery, also known as periprosthetic joint infections (PJI). The rate of PJI after a hip or knee replacement is between 1% to 2%, but the rate can vary due to different factors such as the patient’s health status, the definition of an infection, and follow-up times after surgery.

Although most PJI occur soon after the operation, it can happen at any time after the surgery as long as the artificial joint is in place. A significant number of PJI become noticeable after the first year of surgery. For instance, in some population studies, the rate of knee PJI rose from 0.8% at one year to 2.0% at 15 years. In the same vein, a Canadian study reported the rate of hip PJI to increase from 0.5% at one year to 1.4% at 15 years.

Factors that can increase the risk of developing a PJI include:

• Preoperative factors like previous surgery at the replacement site, current severe infection, and an ongoing infection at the surgery site.
• Modifiable risk factors like smoking, drinking alcohol excessively, drug use, poor hygiene, malnutrition, diabetes, and obesity.
• Nonmodifiable risk factors such as genetic factors, although the specific genes have not yet been identified.
• Surgery-related factors like a prolonged surgery time of more than 90 minutes and more complicated surgical procedures.

Taking proactive steps can help lessen the risk of PJI. For instance, patients undergoing surgery at smaller medical facilities by less experienced surgeons are more at risk of developing a PJI. On the other hand, preoperative screening for specific bacteria and patient advice on preoperative skin cleaning can reduce the risk of infection. Guidelines around surgical site preparation and shared best practices can also help.

Also, using the antibiotic cefazolin within the hour before the surgical cut and before using a special surgical tool called a tourniquet, can reduce the risk of PJI. Using other antibiotic treatments need more research to identify their effectiveness. It’s recommended to avoid aggressive treatment for blood clot prevention, and instead use aspirin.

Signs and Symptoms of Periprosthetic Joint Infection

Prosthetic Joint Infections (PJI) are medical conditions that mostly manifest as pain in the joint area. Some patients may also show signs of inflammation locally, such as redness, swelling, and warmness around the joint. However, it’s important to note that widespread symptoms like fever are often not present. Chronic PJIs may either show subtly, with pain being the only symptom, or conspicuously in cases where the prosthetic becomes loose or a sinus tract begins to drain. While a draining sinus is a clear signal of PJI, not having one doesn’t rule out the possibility of the condition.

PJIs can manifest at different times, and are referred to as early, delayed, or late infections. Early infections usually occur due to harmful organisms acquired during surgery and present with redness, swelling, hardness around the surgical wound, and drainage. Delayed infections can also originate during the surgical period, usually caused by less harmful organisms. Late PJIs typically originate from the bloodstream and often present without fever, draining wounds, or local infection signs.

In general, PJI symptoms are not unique. The majority of patients show swelling of the joint or continual and increasing pain. Incidents of joint instability and difficulty walking are not uncommon in PJIs affecting the lower body part.

• Pain in the affected joint
• Local inflammation signs (redness, swelling, warmth)
• Possible prosthetic loosening
• Draining sinus tract (in some cases)
• Joint swelling
• Persistent and progressively worsening pain
• Joint instability
• Difficulty walking (primarily for lower extremities)

Testing for Periprosthetic Joint Infection

Prosthetic joint infections (PJIs) can be challenging to diagnose. Doctors combine patient-reported symptoms, physical examinations, and lab tests such as synovial fluid cell counts, blood inflammation indicators, and culture results. Guidelines for diagnosing PJIs have been updated several times, most recently between 2018 and 2021.

For identifying a PJI, the requirements are lower than for septic arthritis of a native joint. In the case of septic arthritis, synovial fluid leukocyte counts (a type of white blood cells) are usually in the tens of thousands, while for a PJI, a count greater than 4200 cells/μL for a hip infection and over 1700 cells/μL for a knee infection suggests a PJI. If more than 80% of these cells are neutrophils (a type of leukocyte), it typically indicates both hip and knee PJIs.

Cultures, which are lab tests that grow bacteria or other microorganisms, of blood and synovial fluid are essential for diagnosing PJIs. The synovial fluid is tested under different conditions, considering the possibility of various types of bacteria and fungi. The analysis also includes looking for total leukocyte count and neutrophil percentage. If the lab is unsure about the relevance of the organism detected, doctors might conduct a second joint aspiration, or removal of fluid from the joint area.

In approximately 25% of PJIs, blood cultures can reveal the infecting organism, typically in early infections. However, the organism found through blood culture might not always be the same as through synovial fluid culture. Newer methods for identifying the causative agent of PJIs, such as genomic sequencing, show promise but are not yet widely used in clinical practices.

Plain radiographs, or x-rays, offer limited help in diagnosing PJIs. These images might show joint misalignment, interface lucencies, periosteal reactions, loose bone pieces, bone absorption near the prosthesis, or transchannel sinus tracts, any of which might be signs of a PJI. Other advanced imaging techniques have limited diagnostic usefulness but might reveal bone erosion, an abscess or sinus tract formation, or a loose prosthesis.

Even if preoperative synovial fluid culture identifies the infecting organism, tissue cultures are still crucial as many PJIs are caused by multiple organisms. To confirm a PJI, it’s necessary to find the same microorganism in two or more samples. Doctors usually avoid prescribing antibiotics for at least two weeks before tissue culture because it might give more accurate results.

The Musculoskeletal Infection Society proposed a scoring-based system of diagnostic criteria for PJIs in 2018. The system uses major and minor criteria to determine the likelihood of infection. If the scoring still doesn’t confirm the infection, doctors will need to proceed with an intraoperative diagnosis. If results still remain inconclusive, next-generation sequencing is recommended for further diagnostic testing.

Treatment Options for Periprosthetic Joint Infection

Treating a prosthetic joint infection often involves a team of medical specialists working together, and it typically involves a combination of surgical procedures and intravenous (antibiotics that are injected into the blood) antibiotics for a six-week duration or longer. The goal can either be curing the infection and returning joint function and comfort to the patient, or it may be to simply control the symptoms. This could mean suppressing the infection, performing surgery to fuse the joint, and focusing on controlling symptoms.

Antibiotic therapy is almost always a part of the treatment plan, but it’s generally delayed until after blood samples and synovial fluid (the clear, sticky fluid that’s found in joints) have been obtained for a more accurate diagnosis. The only time this might not be the case is if you’re suffering from sepsis, a severe infection that can spread throughout your body. Your doctor will decide on the best course of antibiotics based on when the infection occurred and make sure they cover germs like S. aureus, which includes MRSA, a type of bacteria that’s resistant to some antibiotics.

There are a few different surgical options for prosthetic joint infections and the right one depends on your unique situation. If the infection is detected early, the existing metallic implants are left in place and the joint cavity is cleared of infection. This is a common approach if the disease’s symptoms have been present for less than three weeks, the implant is stable, and no sinus tracts (abnormal passageways in the body) are present. This procedure is often followed by a lengthy course of intravenous antibiotics.

Other surgical procedures include a one-stage exchange and a two-stage exchange. A one-stage exchange involves removing the entire infected prosthesis and replacing it in the same procedure. This is more commonly done in Europe and not typically done in the United States. The patient must have a healthy immune system, minimal other health issues, and healthy soft tissues. The bacteria causing the infection must be of low virulence and treatable with known antibiotics. An alternative is the two-stage exchange, which is the standard approach in the US. This involves removing the infected prosthesis, placing an antibiotic-infused joint spacer, giving IV antibiotics for 2 to 8 weeks, and then installing a new prosthesis. Patients need to be able to tolerate multiple procedures and have adequate bone health.

Finally, there are salvage options for patients who can’t undergo a two-stage exchange or for whom the other surgical options weren’t successful. Long term antibiotic treatment may be used for patients who aren’t good candidates for surgery due to being bedridden, weakened, or having multiple severe health issues.

Sometimes, the prosthesis may be removed without replacement, a procedure known as resection arthroplasty. This is usually only done in elderly patients with high surgical risks or when replacing the prosthesis wouldn’t significantly improve the patient’s mobility. However, it could be necessary in patients with inadequate bone health, compromised soft tissues, recurrent infections, a history of multiple unsuccessful revision surgeries, or when all other options have failed. In the most extreme cases, an above-knee amputation may be necessary.

What else can Periprosthetic Joint Infection be?

Diagnosing a joint infection, also known as PJI, can be tricky because it is often confused with non infectious complications. These non infectious complications can present similar symptoms like pain, swelling around the joint, reddened skin and reduced motion in the joint. While signs like increased wear, loss of bone, or issues with the bonding of cement can hint towards non infectious joint issues, it’s important to rule out PJI before performing any repair surgery. This is because around 12% of non-infectious cases might actually have an underlying joint infection.

The other medical conditions that need to be considered when trying to diagnose joint infection include:

• Hemarthrosis (bleeding into the joint space)
• Crystalline deposition disease (excess crystals in the joint fluid)
• Referred pain (pain felt in a joint but arising from another area such as the spine or hip)
• Vascular, inflammatory or nerve-related diseases (systemic neuropathic, vascular, or inflammatory conditions)

Additionally, complications from metal on metal joint replacements that cause signs similar to a joint infection can also appear. These include conditions such as aseptic lymphocyte-dominant vasculitis-associated lesions and adverse tissue reactions. Special lab tests involving white blood cells may provide useful info in these cases.

What to expect with Periprosthetic Joint Infection

If prosthetic joint infections (PJIs) are not treated correctly or are overlooked, they can continue to cause problems. These issues can lead to detrimental effects, such as disability and lower quality of life. Handling PJIs often involves a significant financial cost, a lot of time, and extensive use of healthcare resources.

Compared to individuals with hip replacements that aren’t infected, those suffering from a PJI often encounter a reduced quality of life, problems with their replacement joint, and are more likely to need help with moving around and daily care.

Possible Complications When Diagnosed with Periprosthetic Joint Infection

Having a joint infection, also known as PJI, can result in longer hospital stays, unsuccessful treatments, increased disability, poorer quality of life, and a higher likelihood of death than non-infected joint replacements.

Patients with PJI often stay in the hospital longer than those who have a regular joint replacement. For hip replacements, the average stay is 7.6 days compared to 3.3 days. For knee replacements, it’s 5.3 days versus 3.0 days. The information about the results of having a PJI comes from smaller studies and individual reports as there haven’t been any large, thoroughly controlled trials.

The success of surgeries to treat PJIs depends on multiple factors, such as how serious and long-lasting the infection is, when treatment begins, and other existing conditions the patient has. The average success rate for clearing the infection through one-stage and two-stage knee replacement revisions is around 87% and 83% respectively. But this might be an overestimate because many patients don’t go through the second stage of a two-stage revision. The actual success rates change depending on how long after surgery the PJI starts: 74% for early on, 49% for delayed, and 44% for chronic PJI.

For the two-stage revisions, the one-year death rates after removing the implant are 13% for hip replacements and 9% for knee replacements. The 5-year death rate for hip-related PJI is 21%, which is four times higher than the expected rates for people of the same age without a PJI. The 10-year death rates are 45%.

Surgery Risks and Success Rates:

• Longer hospital stays
• Possible unsuccessful treatment
• Possible increased disability
• Possible poorer quality of life
• Possible higher likelihood of death
• One-stage knee replacement revisions success rate: 87%
• Two-stage knee replacement revisions success rate: 83%
• Early-stage PJI success rate: 74%
• Delayed PJI success rate: 49%
• Chronic PJI success rate: 44%
• One-year death rate (hip replacements): 13%
• One-year death rate (knee replacements): 9%
• Five-year death rate (hip-related PJI): 21%
• Ten-year death rate for PJI: 45%

Preventing Periprosthetic Joint Infection

Periprosthetic joint infection, or PJI, has a significant impact on a person’s physical, social, and emotional well-being. This comes as a result of having to go back to the hospital multiple times, having to go through several costly surgeries, spending extended periods of time in the hospital, needing to use outpatient services more frequently, and needing long-term antibiotic treatments. PJI can lead to a decrease in physical abilities, being confined to a bed, needing long-term antibiotics, a loss of independence, and increased fear of the disease getting worse or even fear of death. These issues can lead to mental health problems such as distress, feeling isolated, and increased depression and anxiety, similar to patients with cancer. Even when patients successfully recover, the long recovery period can cause significant mental strain. For doctors, particularly surgeons, PJI can lead to feelings of guilt and mental strain, which may even lead to burnout in their profession.

The cost of treating a single PJI instance is estimated to be about $89,000 for hip infections and $116,000 for knee infections. It’s projected that by 2030, the total annual cost for treating hip and knee PJI in the United States will increase to an estimated $1.85 billion. Current Medicare coverage rates for treating PJI are widely considered not to be enough and need revision to keep up with these rising costs while still ensuring patients get the high-quality care they need. This concern is especially relevant considering the possibility that this problem may affect underprivileged groups more due to the existing gaps in Medicare coverage.