Archive for the 'Anti-Infectives' Category
Prosthetic joint infections are very common in the first 2 years after implantation of the prosthesis. Reported postoperative incidence is around 6.5 per 1000 within in the first year and 3.2 per 1000 in the second year. Risk factors for infection are the same as those previously mentioned for septic arthritis of a native joint but also include prior joint surgery and perioperative wound complications. Infectious organisms can be introduced directly into the wound or via airborne contamination during the procedure itself. Infection can also occur in the setting of postoperative bacteremia through hematogenous spread. Clinical presentation can vary from acute infectious arthritis to chronic pain due to prosthesis failure. Patients often complain of limited range of motion in the affected joint.
The most common organisms implicated in prosthetic joint infections are coagulase-negative staphylococci (25% of patients), followed by S. aureus, gram-negative bacilli, streptococci, anaerobes, and Enterococcus species. Polymicrobial infection is also commonly seen. These organisms can be isolated through culture of preoperative synovial fluid aspirate or intraoperative tissue. Additional diagnostic studies include erythrocyte sedimentation rate, complete blood cell count, C-reactive protein, and imaging through the use of plain radiographs, bone scan, MRI, or CT.
The choice of antibiotics is based on culture results. Vancomycin is the drug of choice for coagulase-negative staphylococcal infections, whereas nafcillin or cefazolin can be used to treat joint infections caused by S. aureus. Patients with gram-negative bacilli isolated on culture should be given a beta-lactam such as piperacillin, which can be combined with gentamicin.1
Eradication of infection can be achieved in the majority of patients through removal of the prosthesis combined with 4 to 6 weeks of intravenous antibiotic therapy directed at the appropriate pathogen. While re-implantation of a new prosthesis can be performed during the initial extraction, improved outcomes have been demonstrated with a two-stage procedure in which re-implantation follows the completion of a 6-week antibiotic course.
Chronic antibiotic suppression is used in select patients for whom prosthesis removal is not performed. Lifelong oral antibiotics can be given with some success to compliant patients in whom surgical removal is contraindicated. For these patients, one must demonstrate that the prosthesis is not loose and that the causative organism is of low virulence and is sensitive to oral antibiotics. This form of therapy may place patients at risk for developing antimicrobial resistance as well as extension of the infection beyond the joint space.
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