An antibiotic spacer is a temporary implant placed inside a joint after an infected artificial joint (like a hip or knee replacement) has been removed. It serves two purposes at once: it holds the joint space open so surrounding muscles and tissues don’t collapse inward, and it delivers high concentrations of antibiotics directly to the infected area to kill remaining bacteria. The spacer stays in place for weeks to months while the infection clears, then it’s removed and replaced with a new permanent joint.
What the Spacer Is Made Of
Antibiotic spacers are made from polymethylmethacrylate, a type of medical-grade bone cement commonly called PMMA. During manufacturing or in the operating room, antibiotics are mixed directly into this cement. Gentamicin and vancomycin are the most commonly used antibiotics, chosen because they target the bacteria most likely to infect joint replacements. Many spacers also contain a stainless steel core that acts as an internal skeleton, giving the device enough structural strength to support the joint.
Why High Local Antibiotic Doses Matter
The key advantage of a spacer over IV antibiotics alone is the concentration of drug it delivers right where the infection lives. On the first day after placement, local antibiotic levels in the joint fluid can reach hundreds or even over a thousand micrograms per milliliter. For context, these levels far exceed what’s needed to kill the bacteria causing the infection, and they’re dramatically higher than what IV antibiotics can safely achieve through the bloodstream. The cement slowly releases antibiotics over days to weeks, with the highest burst in the first few days and a gradual taper afterward.
When a Spacer Is Needed
Spacers are used to treat periprosthetic joint infection, meaning an infection that develops around an existing joint replacement. These infections are diagnosed based on a combination of findings: visible drainage tracts connecting to the implant, bacteria identified in tissue or fluid samples, elevated inflammatory markers in the joint fluid, or pus within the joint itself.
Infections that have been present for more than about four weeks are classified as chronic, and these are the cases where a spacer is most commonly used. For chronic infections, the standard approach is a two-stage revision, which is considered the gold standard. A single surgery to clean around the existing implant usually isn’t enough to eliminate a well-established infection in bone and tissue.
How the Two-Stage Process Works
The first surgery involves removing the infected joint replacement entirely, along with any damaged or dead bone and tissue. The surgical team collects tissue samples to identify exactly which bacteria are involved, then thoroughly irrigates the area. The antibiotic spacer is then placed into the joint space.
Between stages, you’ll typically receive IV or oral antibiotics alongside the local delivery from the spacer. Your surgical team monitors bloodwork and infection markers to determine when the infection has cleared. This interval usually lasts somewhere between 6 and 12 weeks, though some patients with favorable conditions can move to the second stage in as little as 2 to 4 weeks, and others may need longer than 18 weeks. One study found the optimal retention time was under 12 weeks.
The second surgery removes the spacer and any remaining cement, collects new tissue samples to confirm the infection is gone, and implants a new permanent joint replacement.
Static vs. Articulating Spacers
There are two basic designs. Static spacers lock the joint in place, preventing any movement. They’re typically built around a metal rod that passes through the bones above and below the joint, with antibiotic cement molded around it. The idea is that immobilizing the soft tissues may help with infection control.
Articulating spacers, by contrast, are shaped to mimic the joint surface and allow some range of motion during the weeks or months between surgeries. This design has practical advantages for patients. In a study comparing the two approaches in knees with at least five years of follow-up, articulating spacers produced about 30 degrees more range of motion in the final knee (111 degrees vs. 82 degrees) and significantly better physical function and patient satisfaction scores. Infection eradication rates were essentially the same between the two types, around 84 to 86 percent in that study.
Articulating spacers have become the more popular choice for most patients, particularly in the knee, because the functional benefits don’t come at the cost of infection control.
Living With a Spacer
The weeks between surgeries can be challenging. Weight-bearing is traditionally restricted, meaning many patients use a walker or crutches and limit how much force they put through the joint. Some newer cement-on-cement articulating spacer designs have allowed patients to walk with full weight-bearing during the interval period, but this depends on the specific spacer type and your surgeon’s protocol.
A spacer is not a functioning joint replacement. Even articulating spacers provide limited function compared to a real implant. The goal during this period is infection clearance, not full mobility. Most patients experience a significant improvement in quality of life once the second surgery is complete and the new permanent implant is in place.
Success Rates
Two-stage revision with an antibiotic spacer clears the infection in the large majority of cases. Multiple studies report infection control rates as high as 95 percent. Even in more complex situations involving patients who have had multiple prior surgeries, success rates around 87 to 88 percent have been reported. These are strong numbers for what is often a difficult clinical problem, since periprosthetic infections involve bacteria embedded in biofilms on implant surfaces and in surrounding bone.
Risks and Complications
Spacers are effective, but the overall treatment process carries real risks. One study of 82 hip spacer cases found a 58.5 percent overall complication rate across both stages, which reflects the complexity of treating deep joint infections rather than problems with the spacer concept itself.
Mechanical complications during the spacer period include spacer dislocation (17 percent in that study), spacer fracture (about 10 percent), and fracture of the surrounding bone (nearly 14 percent). These are more common in the hip than the knee, partly because of the forces involved in bearing any weight through a temporary device.
Because the spacer releases antibiotics that are also absorbed into the bloodstream, kidney problems are a known concern. Acute kidney failure occurred in about 6 percent of cases in one series, with most cases manageable through conservative treatment, though a small number of patients required temporary dialysis. This risk is higher in older patients and those with pre-existing kidney issues. Your surgical team will monitor kidney function with regular blood tests during the spacer period.
After the second surgery, dislocation of the new permanent implant is also a notable risk, reported at 23 percent in one study. This is higher than the dislocation rate after a first-time joint replacement, because the surrounding muscles and soft tissues have been through two major surgeries and an extended period of limited use.