## EPIDEMIOLOGY

Key Clinical Questions

• How is prosthetic joint infection (PJI) diagnosed, and distinguished from aseptic failure of the joint?

• How and why does the diagnosis and treatment of PJI differ from native joint septic arthritis?

• What are the medical and surgical treatment options for infected prosthetic joints?

• Can an infected prosthetic joint be effectively treated with retention of the prosthesis?

• How should patients with PJIs on long-term antibiotics be monitored and followed up?

Joint replacement surgery (arthroplasty) is a cost-effective intervention for alleviating pain and improving mobility and quality of life in patients with debilitating joint disease. Over a million prosthetic joints are implanted each year in the United States. It is projected that more than 4 million primary arthroplasties will be performed annually by 2030. Hips and knees are the most commonly replaced joints, but shoulder, elbow, ankle and other small joint arthroplasties are not uncommon. Most prosthetic joints last 10 to 15 years, but 1 in 10 may need revision sooner. Of those that need revision, the majority are due to mechanical problems, such as loosening, fracture, or dislocation. Overall, the incidence of prosthetic joint infection (PJI) is about 1% to 2%. Total knee arthroplasties (TKAs) have a higher incidence of infection compared with total hip arthroplasties (THAs) (2.5% vs 1.5%). The incidence of infection in revised prosthetic joints is higher, compared to primary arthroplasties. About two-thirds of PJIs occur within the first 2 years of implantation or index arthroplasty.

Despite the relatively lower proportion of joint failure attributable to infection, the rising number of joints replaced every year and the exponential increase in existing arthroplasties have caused an upsurge in the cumulative numbers of PJI. Infection remains the most devastating and costly complication of arthroplasty. Potential dire consequences of PJI may include multiple surgeries on the index joint (with the attendant risks of anesthesia and surgery), permanent removal of the prosthesis, large skeletal defects after surgery, prolonged courses and associated adverse effects of antimicrobial therapy. Patients may be left with severe functional impairment and persistent joint pain. Rarely, PJIs result in loss of limb or life. The cost of treatment of PJIs is in excess of $50,000 per episode, with an estimated total expenditure of over$566 million per year in the United States, in 2009. This is projected to reach \$1.62 billion by 2020.

## RISK STRATIFICATION

Factors that predispose a prosthetic joint to infection can be classified as host factors, arthroplasty factors, perioperative factors, and postoperative factors. Host characteristics include advanced age, morbid obesity (BMI > 35), diabetes mellitus (and perioperative hyperglycemia), immunosuppression (malignancy, HIV seropositivity), and the use of immunomodulating agents such as systemic corticosteroids. Arthroplasties in patients with rheumatoid arthritis are four times more likely to be infected compared to those performed for degenerative osteoarthritis. Prior PJI is an independent risk factor for infection.

The incidence of infection following joint revision, ...

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