Osteomyelitis is a severe infection characterized by inflammation and destruction of the bone and bone marrow. When this condition arises in the presence of implanted hardware, such as joint replacements or internal fixation devices, it is classified as device-related osteomyelitis. These infections represent a serious complication following orthopedic surgery, leading to intense pain, joint failure, and significant patient morbidity. The presence of non-living foreign material fundamentally changes the nature of the infection, making it exceptionally difficult to treat and often necessitating complex surgical intervention.
Mechanisms of Device Colonization
Bacteria can reach the surface of an implanted device through two primary pathways, with the timing of the infection often indicating the source. The most frequent mechanism is intraoperative contamination, where microorganisms are introduced directly into the surgical site during the initial procedure. Early-onset infections, occurring within the first few weeks after surgery, often result from this contamination and are typically caused by virulent organisms like Staphylococcus aureus.
The alternative route is hematogenous spread, where bacteria travel through the bloodstream from a distant source of infection and settle on the implant surface. Hematogenous seeding can occur months or even years after the initial surgery, resulting in a late-onset infection often caused by less virulent organisms, such as coagulase-negative staphylococci. Once the bacteria adhere to the device surface, they transition from free-floating (planktonic) cells to a sessile, or attached, state.
Biofilm and Antibiotic Resistance
The transition to a sessile state initiates the formation of a complex structure called a biofilm, which is the defining feature of device-related osteomyelitis. A biofilm is a community of bacteria encased within a self-produced, protective extracellular matrix. This matrix, composed of exopolysaccharides, extracellular DNA, and proteins, solidifies the bacteria’s adhesion to the implant surface.
The formation of this structure makes these infections challenging to eradicate with conventional therapies. The biofilm acts as a physical barrier, shielding the bacteria from the body’s immune system cells, such as phagocytes, which cannot effectively penetrate the matrix. Furthermore, the matrix significantly impairs the penetration of systemic antibiotics. Bacteria within a biofilm can exhibit a 10-fold to 1,000-fold increase in antibiotic resistance compared to their planktonic counterparts.
The protective environment also leads to the formation of “persister cells,” which are metabolically dormant variants of the bacteria. These cells can evade antibiotic treatment entirely, as many antibiotics only target actively growing cells. They can reactivate once antibiotic therapy is withdrawn, leading to infection recurrence.
Identifying Device-Related Osteomyelitis
The initial suspicion for device-related osteomyelitis arises from patient symptoms, which often include persistent pain, swelling, and sometimes the formation of a draining tract from the skin to the implant. Laboratory tests are routinely used to detect systemic inflammation by measuring the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). While neither marker is definitive alone, elevated levels strongly suggest the presence of a deep infection.
Imaging studies provide visual evidence of the infection and its extent, starting with plain X-rays to check for signs of bone destruction or implant loosening. More advanced techniques like Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scans offer detailed views of soft tissue and bone, though metallic implants can sometimes create artifacts. Specialized nuclear medicine scans, such as a labeled leukocyte scan, can also be utilized to better localize the active infection. The definitive diagnosis relies on sampling the infected joint fluid or tissue through aspiration or biopsy to isolate the causative organism and determine its antibiotic sensitivities.
Comprehensive Treatment Strategies
The management of device-related osteomyelitis is complex and requires a multidisciplinary approach involving orthopedic surgeons, infectious disease specialists, and clinical microbiologists. Surgical intervention is almost always necessary because the biofilm renders non-surgical antibiotic treatment ineffective. The choice of surgical procedure depends heavily on the timing of the infection and the stability of the implant.
For very acute infections, typically occurring within a few weeks of surgery before the biofilm has fully matured, Debridement, Antibiotics, and Implant Retention (DAIR) may be considered. This involves surgically cleaning the infected area, exchanging modular components if possible, and administering an extended course of antibiotics, often with a success rate around 50%. Success with DAIR is significantly lower for chronic infections or when symptoms have been present for more than three to four weeks.
For most chronic or late-onset infections where the biofilm is well-established, the standard treatment involves complete Device Removal and Exchange, as the infected hardware cannot be sterilized in place. This is often performed as a two-stage exchange arthroplasty. In the first stage, the infected components are removed and a temporary antibiotic-loaded cement spacer is implanted. After a period of systemic antibiotic therapy, the second surgery implants a new, permanent prosthesis. Following any surgical procedure, patients must undergo a prolonged course of specialized antibiotic therapy to ensure the eradication of any remaining bacteria.