Periprosthetic joint infection (PJI) is a serious complication following total knee replacement. The standard treatment often involves a two-stage revision procedure to eliminate the infection before a new implant is placed. The first stage requires removing the infected knee components and contaminated tissue, creating a temporary gap in the joint. This gap is filled with an antibiotic knee spacer, a temporary device designed to manage the infection. The spacer acts as a placeholder while the patient receives systemic and localized antibiotics before the second, definitive surgery.
What is an Antibiotic Knee Spacer?
An antibiotic knee spacer is a temporary implant placed after removing an infected knee prosthesis. Its primary purpose is to deliver high concentrations of antibiotics directly into the joint space, which is more effective than systemic antibiotics alone. The spacer is typically composed of polymethylmethacrylate (PMMA), a cement mixed with specific antibiotics targeting the infection-causing bacteria.
The device also serves a crucial mechanical function by maintaining the proper joint space and soft tissue tension around the knee. Maintaining this space prevents surrounding muscles and ligaments from contracting and scarring, which simplifies the subsequent reimplantation surgery. Spacers are categorized as either static (non-moving) or articulating (mobile), with articulating spacers allowing for some knee motion during the interim period. The choice between static or articulating depends on the extent of bone loss and the condition of the surrounding soft tissues.
Weight-Bearing Guidelines and Mobility
Whether a patient can walk on an antibiotic knee spacer depends entirely on the type of spacer implanted and the surgeon’s specific instructions. The general goal is to allow protected mobility while preventing mechanical failure of the device. Surgeons typically prescribe one of three weight-bearing protocols: non-weight bearing (NWB), toe-touch weight bearing (TTWB), or partial weight bearing (PWB).
Static Spacers
When a static spacer is used, the protocol is usually non-weight bearing. Patients cannot put any weight on the affected leg to avoid damaging the device. Static spacers create a temporary joint fusion and are less structurally robust under full load.
Articulating Spacers
For patients with articulating (mobile) spacers, partial weight-bearing status is often permitted, sometimes allowing for full weight bearing in select cases. This mobile spacer type is designed to mimic a knee replacement, offering better stability and potentially an earlier return to some daily activities.
The surgeon determines the weight-bearing status based on the patient’s overall health, the quality of the surrounding bone, and the spacer’s specific design. Non-compliance with restrictions risks fracture or dislocation of the spacer, potentially requiring immediate additional surgery. Patients must use assistive devices, such as crutches or a walker, to manage mobility and protect the temporary implant. Strict adherence to the surgical team’s personalized instructions is essential, as protocols are customized to the individual’s case.
Living with the Temporary Spacer and Timeline
The spacer remains in place until the infection is fully eradicated, typically lasting between six and twelve weeks. During this interim period, patients are closely monitored using blood tests that track infection markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). Once these markers stabilize or return to normal levels, indicating the infection is clear, the patient is scheduled for the second surgery to implant the permanent knee replacement.
Living with the temporary spacer requires adjustments to daily life and mobility. Patients with static spacers may have their knee immobilized in a brace and are often advised not to bend the knee. Even with an articulating spacer, range of motion is limited to protect the implant and surrounding soft tissues from stress. Restrictions on activities like driving are common due to mobility limitations or the use of pain medication.
Managing swelling and pain is a major focus during this phase. The ultimate goal is to maintain the surrounding soft tissues and bone stock in good condition. This preparation ensures a smoother and more successful transition to the definitive knee replacement during the second stage.