Prosthetic Joint Infection (Infected Joint Replacement)

How joint replacements become infected

Infection of a natural joint is called septic arthritis. With an implant, the problem is harder to clear.

Bacteria can reach the implant:

• during surgery, causing early or delayed infections. Skin bacteria such as Staphylococcus aureus and Staphylococcus epidermidis and Cutibacterium acnes are common
• through the bloodstream from an infection elsewhere, such as cellulitis, a urinary tract infection, pneumonia or a dental abscess, causing late infections
• through a wound complication after surgery (wound infection)

On the implant surface, bacteria form a biofilm, a protective layer that resists antibiotics and immune defenses. This is why surgery is usually needed.

Types by timing

Risk factors

• diabetes, especially poorly controlled
• obesity
• smoking
• rheumatoid arthritis and immunosuppressive medicines
• previous joint surgery or infection
• wound healing problems, hematoma or prolonged wound drainage
• skin conditions near the incision
• Staphylococcus aureus colonization in the nose or on the skin
• malnutrition and kidney disease

Symptoms

• pain that increases rather than improves after surgery, or new pain in a joint that was previously comfortable
• swelling, warmth and redness
• wound drainage or a sinus tract (a small opening draining fluid)
• fever and chills, though often absent in chronic infection
• stiffness and reduced movement
• a feeling of instability or loosening

Diagnosis

The diagnosis can be difficult, especially with low-grade infections. Doctors use:

• blood tests: CRP and ESR, which are usually raised, and D-dimer
• joint aspiration: fluid from the joint is tested for white cell count, neutrophil percentage, alpha-defensin and leukocyte esterase, and cultured
• cultures: multiple tissue samples during surgery
• X-rays: may show loosening or bone loss
• nuclear imaging in selected cases

Antibiotics should ideally be withheld until samples are taken, unless the person is very unwell, so that the bacteria can be identified. A sinus tract communicating with the implant confirms infection.

Treatment

Treatment is planned by orthopedic surgeons and infectious disease specialists.

Surgical options

• DAIR (debridement, antibiotics and implant retention): washing out the joint and exchanging removable parts while keeping the implant. Suitable for early infections (usually within about 4 weeks of surgery or of symptom onset) with a well-fixed implant
• One-stage revision: removing the infected implant and inserting a new one in the same operation, in selected cases
• Two-stage revision: removing the implant, placing an antibiotic-loaded cement spacer, treating with antibiotics for several weeks, then implanting a new joint. Traditionally the standard for chronic infections in the US
• Salvage procedures such as fusion, resection or, rarely, amputation for recurrent or untreatable infections

Antibiotics

• IV antibiotics initially, then often oral antibiotics, for a total of about 6 weeks to 3 months depending on the procedure
• rifampin is added for staphylococcal infections when the implant is retained, because it penetrates biofilm
• long-term suppressive antibiotics for people who cannot have further surgery

Complications

• recurrence of infection
• implant loosening and loss of function
• bone loss, fractures and instability
• sepsis
• the burden of multiple surgeries and prolonged recovery

Outlook

Success rates for eradicating infection are generally 70 to 90% depending on the organism, timing and procedure. Two-stage revision has high success for chronic infections. Recovery takes months, and function may be somewhat reduced compared with an uncomplicated joint replacement.

Prevention

• control blood sugar, stop smoking and optimize weight before surgery
• screening and decolonization for Staph aureus before surgery in some centers
• antibiotics given just before the incision
• prompt treatment of skin, urinary, dental and other infections after joint replacement
• antibiotic prophylaxis before dental work is not routinely recommended for most people with joint replacements, per AAOS and ADA guidance, but may be considered for people at high risk. Ask your surgeon

Frequently asked questions

What are the signs of an infected knee or hip replacement?

Signs include worsening or new pain, swelling, warmth, redness, drainage from the wound or a small draining hole, stiffness and sometimes fever. Infection can occur shortly after surgery or years later, often after an infection elsewhere in the body.

Can an infected joint replacement be treated with antibiotics alone?

Rarely. Bacteria form a biofilm on the implant that antibiotics cannot fully penetrate. Most infections need surgery, either a washout with exchange of parts or removal and replacement of the implant, combined with weeks of antibiotics.

How common is infection after joint replacement?

Infection occurs in about 1 to 2% of hip and knee replacements. The risk is higher in people with diabetes, obesity, rheumatoid arthritis, smoking or previous joint surgery.

How long does it take to recover from an infected joint replacement?

Recovery often takes several months. With two-stage revision, the gap between operations is usually 6 weeks to 3 months, followed by rehabilitation after the new implant. Many people regain good function, though it may be less than after the original replacement.

Do I need antibiotics before dental work with a joint replacement?

For most people with joint replacements, routine antibiotics before dental procedures are not recommended. Your surgeon or dentist may suggest them if you have a weakened immune system or other high-risk conditions.