Introduction

Infection is normally acquired at the time of surgery/instrumentation although only a small proportion of patients will present with infection as an early complication. Many pathogens are low virulence organisms from the skin flora and a greater proportion of these patients will present within a month of surgery.

Infection rates have come down steadily due to ultra-clean air theatres and antibiotic prophylaxis.

Aetiology of orthopaedic device infections

There are some differences in the aetiology of infections, which present early after surgery (early presentation) and those that present some time after surgery (late presentation).

Early presentation

Common pathogens include:

• Coagulase-negative Staphylococcus spp.
• Staphylococcus aureus (including strains of MRSA ).

Less common pathogens include:

• Propionibacterium spp.  (These may be more common than previously thought as the organism is incorporated in a biofilm on the surface of the implant, and is slow-growing and difficult to culture.)
• Corynebacterium spp.
• Enterococcus spp. and Streptococcus spp.
• Pseudomonas aeruginosa
• Enterobacteriaceae
• Other anaerobes
• Candida spp.
• Mycobacterium tuberculosis.

Late presentation

Infections presenting some time after surgery have two possible sources:

• Organisms introduced during surgery, which have remained dormant, often for long periods.  Coagulase-negative Staphylococcus spp. are common
Haematogenous spread from another focus of infection within the body. The pathogens reflect the primary infection source and are commonly
Gram-negative.

Diagnosis of orthopaedic device infection

Clinical

Diagnosis of infection in a prosthetic joint can be difficult. Signs and symptoms vary depending on whether infection presents early or late after joint replacement surgery.  In one series of revision hip surgery, 22% of implants were found to be infected but infection was suspected in only one-third of these.

Signs and symptoms of early and late presenting orthopaedic device infections

Microbiology

• Blood culture.
• Joint aspiration and microbiological examination of fluid/pus.  However, as many pathogens are skin flora, two consecutive positive cultures are required for identification.  Prolonged incubation may also be required to get a positive culture.
• Tissue samples from biopsy can also be examined.
• Culture from draining sinuses is not often useful.
• White blood cell count may not be elevated in all cases.
• ESR and CRP may be elevated during infection.

Imaging

Management of orthopaedic device infection

Antibiotic therapy alone will not normally cure prosthetic implant infections.

There are two factors that offer serious challenges to effective antibiotic therapy:

• A biofilm can form at the implant or cement/bone interface
• Many of the pathogens can be sequestered within macrophages.

However, there are data to suggest that a conservative approach may be worth an attempt for patients who are unsuitable for or unwilling to undergo surgery.

A combination of oral rifampicin plus either IV flucloxacillin or vancomycin for two weeks followed by oral rifampicin and ciprofloxacin for 3–6 months, together with initial debridement, has been shown to resolve staphylococcal infections of less than 21 days’ standing in stable implants without the need for device removal.

Further, in one series, 15/18 patients had a good response and retained their prosthesis after IV antibiotic therapy for 6–8 weeks and debridement, followed by prolonged oral antibiotics. 

Early surgical debridement may help to conserve the device, but in established infection surgical removal of all prosthetic material, bone and soft tissue is required. Removal of the infected joint followed by at least four weeks of parenteral antibiotic therapy before reimplantation has been shown to be successful and can be repeated for subsequent infection.  The alternative is a one-step procedure where the infected joint is removed and new one implanted in a single operation; this is cheaper but is believed to be less effective in removing the infection.

In spinal instrumentation, removal of the device and debridement may be required, but some infections can be managed with antibiotics alone.  This might include irrigation with antibiotics or placement of antibiotic-releasing beads.

In chronic/late infection it is less likely that an organism will be found and in these infections where intracellular eradication is important, the chosen regimen should include an agent with good intracellular penetration.

If Gram-positive cocci are seen in culture, and particularly if there are risk factors for MRSA (such as known local incidence, diabetes, or referral from a nursing home), suitable antibiotic therapy should be discussed with a microbiologist.

• The choice of antibiotic should be tailored according to the bacteriological diagnosis in consultation with your microbiologist.
• High-dose parenteral agents should be used, at least initially.  Treatment should be continued for weeks or months.

Empirical therapy

The range of possible pathogens includes MRSA , coagulase-negative Staphylococcus spp. (many strains of which are antibiotic-resistant) and diptheroids.

Consult your microbiologist to ensure the treatment reflects local resistance patterns and antibiotic policies.

Typical treatment will consist of combinations of antibiotics such as:

• Vancomycin plus rifampicin with or without a quinolone such as ciprofloxacin.

Rifampicin should NEVER be used as monotherapy because of the high risk of promoting resistance within 24 h.

Prevention of orthopaedic device infection

The British Orthopaedic Association recommends that joint replacement be performed with a high level of aseptic precautions.

Antibiotic prophylaxis

There is clear evidence of a benefit of antimicrobial prophylaxis during prosthetic device surgery. The duration of antibiotic prophylaxis is usually longer in surgery with a prosthetic device than other surgical procedures. However, there is no evidence to suggest that antibiotic coverage for longer than 24 h after hip or knee replacement is beneficial.

The timing of antibiotic administration should be such that maximum concentrations are achieved during surgery, and Gram-positive organisms should be targeted.  The British Orthopaedic Association recommends IV broad-spectrum antibiotics at introduction of anaesthesia and for the first 24–36 h for hip replacement.

• In penicillin-allergic patients, clindamycin can be used instead of cefuroxime
• In those patients at risk of MRSA: IV vancomycin can be added to the above regimens at induction with a second dose 12 h later.
In those patients at risk of MRSA: IV vancomycin can be added to the above regimens at induction with a second dose 12 h later.

The role of antibiotic-impregnated cement in primary prevention of infection is not clear, although it is valuable in re-operation for previous infection.  The cement is usually impregnated with gentamicin, so it is important to ensure that the organism is susceptible.  The British Orthopaedic Association notes that this technique further reduces the risk of infection.

Other issues

There is still some debate about the requirement for antibiotic prophylaxis during dental procedures in patients with major arthroplasties.  However, a British Society of Antimicrobial Chemotherapy (BSAC) working party reported that there was no evidence to support the use of antibiotic prophylaxis in these patients.  There may still be a need for caution in other invasive procedures, such as endoscopy.