Periprosthetic joint infection (PJI)

Every year, millions of people throughout the world benefit from joint replacement surgery. A joint replacement that works well relieves pain, restores function and independence, and enhances the patient quality of life. While prosthetic implantation is already a common surgery, it is expected to become more common in the future. In 2010, 333,000 total hip and 720,000 total knee arthroplasties were performed in the United States alone. Hip and knee replacements are expected to reach 572,000 and 3.5 million by 2030, respectively. In Europe, primary hip arthroplasty is more common than primary knee arthroplasty. Shoulder, elbow, and ankle arthroplasties are now accessible in addition to hip and knee replacement. The number of patients who have had arthroplasties in the past is continuing to rise.

While most joint arthroplasties give pain-free function, a small percentage of patients will have device failure and require further surgery at some point during the device's lifetime. Loosening at the bone-cement interface, periprosthetic fracture, prosthetic material fracture, wear, implant malposition, dislocation-instability, or materials fatigue are all causes of aseptic failure. Periprosthetic joint infection (PJI), also known as periprosthetic infection, is an infection that affects the joint prosthesis and surrounding tissue. Over the last quarter-century, advances in the understanding of the epidemiology, diagnosis, therapy, and prevention of PJI have resulted in better results for this difficult infection.

Joint Infection

Septic arthritis is a severe and possibly destructive form of arthritis caused by a bacterial infection of a joint. Bacterial joint infections can be caused by a variety of bacteria, and they can affect both natural and artificial joints (e.g., after a knee replacement).

Neisseria gonorrhoeae, the sexually transmitted bacteria that causes gonorrhea, causes a common type of joint infection known as a gonococcal joint infection. Nongonococcal bacterial (septic) arthritis is caused by joint infection with bacteria other than Neisseria gonorrhoeae. A prosthetic joint infection is an infection of an artificial joint.

Periprosthetic Joint Infection Pathogenesis

The fact that prostheses are foreign bodies that can stimulate the production of biofilm by various noteworthy organisms is at the root of the pathophysiology of periprosthetic joint infection. On implant surfaces and necrotic tissues, these organisms form colonies in a hydrated polymeric matrix. The main cause of periprosthetic joint infection is bacterial aggregates, which have intrinsic resistance to antimicrobial treatments. Biofilm is a thin layer of microorganism-embedded glycocalyx (exopolysaccharides) that coats the prosthesis' surface and acts as an antibacterial barrier. Furthermore, certain strains of Staphylococcus aureus, a common cause of infections in prosthetic joints, can produce small colony variants that grow slowly and are linked to recurring and difficult-to-treat infections. The development of biofilms takes four weeks. The infection comes from the following sources:

Hematologic spread with the following are the most frequently reported foci for infection, as well as the species that are most commonly involved:

Infections affecting the skin and soft tissues (e.g., Staphylococcus aureus).
Infections of the respiratory tract (e.g., Streptococcus pneumonia).
Infections of the urinary tract (e.g., Klebsiella, Escherichia coli, Enterobacter spp.).
Infections of the gastrointestinal tract (e.g., Bacteroides, Salmonella, Streptococcus gallolyticus)
Dental procedures (e.g., Viridans streptococci).
Intravascular devices infection (e.g., Staphylococcus epidermidis).

Direct spread via a route connecting the prosthesis to the outside world, such as the sinus tract or an open periprosthetic fracture.

Local spread from an adjacent septic focus such as osteomyelitis or a soft tissue infection.

Periprosthetic Joint Infection Epidemiology

Physicians currently conduct roughly one million total hip and knee arthroplasties in the United States, but this rate is predicted to quadruple in the next one to two decades. It is predicted that as the number of procedures rises, so will the frequency of infections. Periprosthetic joint infection rates vary by center but typically range from 0.5 percent to 1.0 percent for hip and shoulder prostheses, and 0.5 percent to 2 percent for knee replacement surgery.

Infection rates are higher in the first two years after surgery than after two years. This is owing to the high vascularity of the periprosthetic tissue, which makes it vulnerable to hematogenous dissemination in the early years after the initial procedure.

Periprosthetic Joint Infection Risk Factors

Previous revision arthroplasty or previous same-site periprosthetic joint infection, tobacco use, obesity, rheumatoid arthritis, cancer, immunosuppression, and diabetes mellitus are all patient-related risk factors for periprosthetic joint infection.

Wound healing complications (including superficial infection, hematoma, delayed wound healing, wound necrosis, or dehiscence), atrial fibrillation, heart attack, urinary tract infection, prolonged hospitalization, and Staphylococcus aureus bacteremia at any time after surgery are all postoperative risk factors. When determining the risk of postoperative PJI, all of these potential factors must be taken into account.

Periprosthetic Joint Infection Causes

Periprosthetic joint infection occurs 1-2% of the time in primary arthroplasties and 5% of the time in revision arthroplasties.

The bacteria associated with prosthetic joint infection can be divided into three groups based on how probable they are to be identified using culture materials over the duration of the implant.

Early infection. It is defined as occurring within the first four weeks following the initial operation. Highly aggressive organisms such as Staphylococcus aureus, aerobic gram-negative Bacilli, beta-hemolytic Streptococcus, and enterococci are commonly responsible.
Delayed infection. Low-virulent organisms such as coagulase-negative Staphylococcus, Propionibacterium acnes, and Enterococci are commonly responsible for the delayed infection, which can last anywhere from three months to a year. S. aureus may also be involved, but to a lesser extent.
Late infection. Staphylococcus aureus, coagulase-negative Staphylococcus, viridans streptococcus, Enterococci, and infrequently gram-negative bacilli induce late infection (over one year; some authors say over two years).

In conclusion, Staphylococci are responsible for more than half of all prosthetic joint infections. About 25% of cases are polymicrobial, 15% are caused by gram-negative bacteria, and 12% are culture-negative.

Periprosthetic Joint Infection Symptoms

As previously stated, the presentation can be early, delayed, or late. Early infections, most of which are contracted around the time of surgery and appear acutely with edema, redness, induration at the incision site, and wound discharge, are frequently caused by virulent bacteria. Delayed infections can occur around the time of surgery, but they are usually caused by low-virulent bacteria. Late infections, on the other hand, are generally hematogenous, with no fever, leaking wounds, or other visible signs of infection. Overall, symptoms are non-specific, with most patients experiencing joint swelling or chronic pain that worsens over time. Wound dehiscence, purulence around the prosthesis, sinus tract connecting with the joint cavity, joint instability, and ambulation problems are all common clinical manifestations.

Periprosthetic Joint Infection Diagnosis

Multiple variables, such as symptoms, signs, synovial fluid cell count, serum inflammatory markers, and culture, are commonly used to make an appropriate diagnosis of periprosthetic joint infection.

When compared to septic arthritis of a native joint, the baseline for diagnosing a periprosthetic joint infection using some of these markers is much lower. A synovial fluid white blood cell count (WBC) of more than 4200 cells/microliter represents hip periprosthetic joint infection, while a WBC count of more than 1700 cells/microliter endorses knee periprosthetic joint infection, unlike septic arthritis, where synovial fluid cell counts are generally in the tens of thousands. Neutrophil predominance is a common occurrence.

The use of culture in the identification of the periprosthetic joint infection is necessary.

Multiple sets of culture media should be sent with aspirated joint fluid culture. It is also recommended that several intraoperative culture samples be obtained. This is pretty important for the recovery and proper diagnosis of low-virulence organism-caused prosthetic joint infection because a single positive culture is insufficient to make a diagnosis. Because synovial fluid culture has a sensitivity of just 86%, a negative culture does not exclude the infection. Synovial fluid culture, on the other hand, has a 95% specificity, and positive cultures frequently indicate the presence of prosthetic joint infection.

Although imaging can help with diagnosis, it is generally used as a supplement.

The most important study is plain radiographs. Plain imaging may provide valuable clues about joint effusion, joint alignment, bone-cement or metal-bone interface lucency, periosteal reactions, and patchy osteopenia, despite its low overall sensitivity and specificity. It may also reveal bone loss around the implant as well as transcortical sinus tracts.

CT and MRI scans are rarely ordered by doctors, but when they are, they may reveal bone erosion, abscesses, sinus tract, or slippage of the prosthesis.

There are several modalities of technetium bone scans that are used when an infection is suspected medically but cannot be confirmed by arthrocentesis or lab testing. It has a poor specificity of 30-40 percent but is extremely sensitive to up to 99 percent. Tc-99m (technetium) can be used to detect inflammation, while In-111 (indium) can be used to detect leukocytes. A triple scan can also distinguish infection from fractures or bone remodeling.

FDG-PET scan (using fluorinated glucose to detect areas of high metabolic activity) is a very sensitive and precise technique.

Periprosthetic Joint Infection Diagnostic Criteria

The Musculoskeletal Infection Society (MSIS) recently reviewed the literature and established a set of criteria for defining periprosthetic joint infection.

A definite PJI exists when the following criteria are met:

A sinus tract connecting the prosthesis.
A pathogen is identified from two or more different tissue or fluid samples collected from the infected prosthetic joint by culture.

Or when four of the six criteria are met:

Increased erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels in the blood
Synovial white blood cell count is high
Increased polymorphonuclear proportion in synovial fluid
Purulent discharge from the involved joint
Isolation of a bacteria from periprosthetic tissue or fluid in a single culture
Histologic study of periprosthetic tissue at 400x magnification revealed more than 5 neutrophils per high-power field.

PJI may be present if less than four of these criteria are not met, and several of these criteria may not be met despite the presence of PJI in certain infections caused by low-virulent organisms like Propionibacterium acnes.

Periprosthetic Joint Infection Treatment

An interdisciplinary team strategy is required to manage periprosthetic joint infections. Medical treatment (long-term antibiotics) and repeated surgeries are frequently used.

The following are some of the treatment principles:

Cure (treatment of infection, restoration of joint function, and alleviation of symptoms)
Palliative treatment (may include antibiotics, joint fusion, and symptom control).

Antimicrobial treatment is frequently required; however, it should be postponed until culture samples (at least joint aspiration culture) have been collected. The only exception is in the case of sepsis or life-threatening infection. Antibiotic treatment should be tailored to the timing of infection using empirical evidence. Antibiotics should, as a general rule, give appropriate coverage against Staphylococcus aureus (including methicillin-resistant Staphylococcus aureus (MRSA)), coagulase-negative staphylococci, and aerobic gram-negative bacilli. Rifampin and fluoroquinolones, which have good antibiofilm activity, are frequently used in treatment. Minocycline, linezolid, and trimethoprim-sulfamethoxazole are some other oral antibiotic options for periprosthetic joint infection.

Surgical options are further divided into five categories, as follows:

Debridement and retention. The implant is left in place, but the joint space is debrided, either with or without the synovial polyethylene lining removed. If the implant is stable, the disease duration is shorter than 3 weeks, there are no sinus tracts, and the isolated pathogen is responsive to active biofilm antibiotics, this is usually the surgical method for early prosthetic joint infection. Acute hematogenous infection with symptoms lasting less than 72 hours is another indication. Antibiotics for 3 to 6 months are frequently required (three months for retained hip and 6 months for retained knee joint).
One-stage exchange. It is a surgical procedure that is routinely used in Europe but is not considered a standard of care in the United States. It entails removing the infected prosthesis and replacing it with a new one at the same time. When the patient is not immunocompromised, has few medical comorbidities, and has healthy soft tissues, this is appropriate. Antibiotics should not be used for an extended period of time, and no bone grafts should be inserted. Preoperatively, the organism must be of low virulence and antibiotic sensitivity. Two weeks of intravenous antibiotics are usually followed by three to six months of oral antibiotics. This method offers the advantages of being less expensive, having a shorter hospital stay, and immobilizing the patient. However, this comes at the cost of a significant chance of infection recurrence.
Two-stage exchange. This is the gold standard of care in the United States, and it provides the best chance of cure, particularly for delayed and late periprosthetic joint infections. In its most basic form, it entails the complete extraction of the infected prosthesis, the implantation of an antibiotic-impregnated joint spacer, antibiotic treatment for two to eight weeks, and the insertion of a new prosthesis. Patients must be fit and healthy enough to undergo many procedures and have sufficient bone stock. Reimplantation must be confirmed by physical exam, normal lab testing, and negative cultures two weeks after the antibiotic course is completed.
Resection arthroplasty (Implant removal without replacement). This is a reasonable option for elderly, non-ambulatory patients with high operative risks or when prosthesis exchange is unlikely to provide a functional advantage. Inadequate bone stock and soft tissue, repeated infections, and several past failed revision surgeries are all possible causes. It is frequently accompanied by arthrodesis.
Above-knee amputation. This is recommended when a prosthetic knee joint infection has resisted all conservative and surgical treatment methods and the patient is still in significant pain. Also used to treat severe bone and soft tissue loss, as well as vascular problems.
Chronic antibiotic therapy. When surgery is not a possibility, such as in severely disabled individuals or those with several severe comorbidities, chronic suppressive antibiotic treatment is used.

Periprosthetic Joint Infection Prognosis

On prosthetic joint infections, there are no big randomized clinical studies, and the outcomes are limited to small retrospective case studies and case reports. The success of various procedures ranges from 0% to 100%, depending on the severity of the infection, duration of treatment, patient comorbidity, and infection length. When dealing with periprosthetic joint infections, the problem is whether to withdraw all of the hardware, which leaves the patient disabled. Although the use of spacers has proven beneficial, it is not a cure-all for all types of prosthetic joint infections. Overall, delayed exchange arthroplasty has shown positive results, with success rates ranging from 40 to 80 percent. Unfortunately, after an infection, the majority of patients have discomfort, joint instability, and limited joint function.

Periprosthetic Joint Infection Prevention

Correction of malnutrition, overweight, good blood glucose regulation, lower immunosuppressive drug dosages, remote site infection treatment, and pre-operative dental and urinary tract assessment are all part of the host's pre-operative enhancement. The use of an antiseptic shower before surgery and the application of mupirocin to the nares have been shown to reduce postoperative Staphylococcus aureus infection. Antibiotic prophylaxis should be started before surgery and given within two hours of the incision. The risk of postoperative wound infection is reduced by a good incision, a suitable prosthesis size, wound hemostasis, a shorter operative time, ultra-clean air, and minimal OR traffic.

Antibiotic prophylaxis is recommended in patients with prosthetic joints who are having dental procedures, according to the American Dental Association and the American Academy of Orthopedic Surgeons:

Patients taking immunosuppressive medications.
Patients with insulin-dependent diabetes, hemophilia, systemic lupus erythematosus (SLE), and rheumatoid arthritis.
Patients who have had a prosthetic joint infection before.
Patients who have had a joint replacement in the last two years.

Conclusion

Millions of people benefit from joint replacement. Diagnosing and treating infections caused by these devices necessitates a unique approach. Several organizations have suggested PJI classification schemes, which are expected to be modified over time as more data becomes available. There have been significant breakthroughs in determining the best technique to diagnosing PJI, and there are now PJI-specific diagnostic tests. In the coming years, newer diagnostics for PJI are expected, as well as a better understanding of the etiology of what is now known as culture-negative PJI. Although large, high-quality, multi-institutional studies utilizing a common language are essential to more precisely identifying the best treatment techniques, today's treatment algorithms give satisfactory overall success rates. Laboratorians and physicians can expect an increase in PJIs in the coming years, given the growing number of people who will have joint replacement surgery. The epidemiology of PJI is now well understood, and future research should use this information to identify people at high risk of infection and prevent infection. Finally, breakthroughs in PJI prevention will be required to address the expected increase in PJI cases in the coming years.