A prosthetic joint infection (PJI) is a serious complication following a total joint replacement. When PJI develops, a common and highly effective treatment is a two-stage revision process. The first stage focuses on eradicating the infection. During this initial surgery, the infected artificial joint is removed, and an antibiotic spacer is temporarily placed into the joint space. This specialized, antibiotic-loaded device manages the infection locally before a new, permanent joint is implanted in the second stage.
The Role of Antibiotic Spacers in Infection Treatment
The antibiotic spacer is an interim device serving a dual purpose: it acts as a highly effective drug delivery system and a temporary mechanical placeholder. Its primary function is to deliver extremely high concentrations of antibiotics directly into the infected joint space and surrounding tissue. These local drug levels far exceed what could be safely achieved through systemic administration. This high concentration is necessary to penetrate the protective biofilm created by bacteria on the original implant.
Spacers are typically made from bone cement, most commonly polymethylmethacrylate (PMMA). This cement is mixed with a customized, high-dose cocktail of antibiotics chosen to combat the specific infection. The cement matrix allows the antibiotics to slowly leach out over time, maintaining a therapeutic concentration at the site of infection. Mechanically, the spacer fills the void left by the removed prosthesis, preventing soft tissues from contracting or scarring down. Preserving the joint space and soft tissue tension makes the second-stage surgery less challenging.
Spacers are broadly classified into two types based on their mobility: static (non-articulating) and articulating (dynamic). Static spacers essentially fuse the joint temporarily, while articulating spacers allow some degree of movement. The chosen type influences the patient’s mobility during the interim period, but both deliver antibiotics and preserve the joint geometry.
Determining the Removal Timeline
The duration an antibiotic spacer stays in place is not fixed, as it depends entirely on the eradication of the infection. The typical interval between the first and second stage of surgery is generally between 6 and 12 weeks, though it can be longer in complex cases. The decision to proceed to the second stage is a complex medical determination. It requires sustained clinical and laboratory evidence that the infection has been cleared.
A primary measure of infection clearance is the normalization of specific blood tests that track inflammation. Physicians closely monitor the C-Reactive Protein (CRP) and the Erythrocyte Sedimentation Rate (ESR) levels. These inflammatory markers are typically elevated during an active infection and must return to normal or significantly reduced, stable levels. The decision for removal relies on a sustained trend of improvement, not a single reading.
In addition to laboratory markers, the patient’s clinical assessment is critical. Before the second stage, the patient must be symptom-free, meaning they have no fever and significantly reduced joint pain, and the surgical wound must be completely healed. Microbiological evidence is often sought just before the second surgery, usually involving a joint aspiration or tissue biopsy. This confirms the absence of residual infection, and this combination of clinical, serological, and microbiological clearance dictates the final timing for the removal of the spacer.
Living With the Spacer and Potential Complications
Living with an antibiotic spacer for several weeks or months requires significant adjustments to daily life, primarily concerning mobility. Depending on the type of spacer, a patient may be restricted to partial or non-weight bearing on the affected limb. Patients with static spacers are often immobilized or severely restricted in movement. Those with articulating spacers may have a limited, protected range of motion, which helps maintain muscle function.
Physical therapy is usually started cautiously to prevent severe stiffness and muscle atrophy, but the primary focus remains on protecting the temporary device. Despite being temporary, the spacer is a mechanical device that can fail. Potential complications include mechanical failure, such as a fracture or disintegration of the cement, or dislocation from the joint. These issues can cause pain and may require an unplanned, earlier return to the operating room.
Systemic complications, though less common, can occur due to the high-dose antibiotic elution. The body absorbs some of the antibiotics released by the cement, which can temporarily affect organ function, most notably the kidneys. Patients require close monitoring of their kidney function and antibiotic drug levels in the blood. Management during this interim period balances eradicating the infection with minimizing risks from the temporary device and high local antibiotic exposure.