An antibiotic hip spacer is a temporary, specialized orthopedic implant used to treat an infected total hip replacement, known as periprosthetic joint infection (PJI). This device is utilized as part of a two-stage revision procedure, the established method for clearing chronic infections from the joint area. The first stage involves removing the infected hip prosthesis and surrounding tissue, followed immediately by the insertion of the antibiotic spacer. It functions as a placeholder and a localized drug delivery system during the infection-fighting treatment.
The Role of the Antibiotic Hip Spacer
The spacer serves two functions following the removal of the infected hardware. Its primary medical purpose is to provide a continuous, high concentration of antibiotics directly to the infected joint space and surrounding bone tissue. The polymethyl methacrylate (PMMA) bone cement used to construct the spacer is heavily loaded with powdered antibiotics. These antibiotics slowly leach out into the surrounding environment over several weeks. This localized delivery is highly effective against bacteria and minimizes systemic side effects.
The second mechanical function of the spacer is to maintain the anatomical space within the hip socket and femur. By keeping the joint structures separated, the spacer prevents the surrounding soft tissues, such as muscles and ligaments, from contracting and scarring down. This preservation of tissue tension and anatomical alignment is important for the success of the second stage of surgery. Without the spacer, re-implantation of a permanent hip prosthesis would be technically more challenging, potentially leading to complications like leg length discrepancy or joint instability.
Physical Appearance and Construction
The antibiotic hip spacer is engineered to approximate the shape of a normal hip joint. It is typically constructed from antibiotic-loaded bone cement, the same material used to secure permanent implants. The spacer often appears as an opaque white or slightly yellowed structure due to the mixing of the cement powder with high-dose antibiotics. It generally mimics the hip’s ball-and-socket configuration, allowing for some movement during the treatment phase.
Spacers are categorized as either custom-molded or prefabricated. Custom-molded spacers are created by the surgical team in the operating room, using molds or by hand-packing the cement around a metal rod to form a stem and femoral head shape. Prefabricated, or modular, spacers are commercially available in various sizes. These often incorporate a metal core for increased mechanical strength and stability, allowing the temporary device to better withstand the forces of limited movement.
Life with a Temporary Spacer
Patients live with the spacer implanted for six to twelve weeks while the infection is being eradicated. During this time, the patient usually receives a course of systemic antibiotics, often administered intravenously at home. The primary limitation is the restriction on weight-bearing, necessary to prevent mechanical failure, such as fracture or dislocation of the cement device. Most patients are restricted to non-weight-bearing or limited touch-down weight-bearing on the affected leg. They must use crutches or a walker for mobility.
The spacer is not designed to handle the full force of body weight, and increased activity can lead to complications like instability or breakage. Before the second stage of surgery can proceed, blood tests and joint fluid aspirations are performed to confirm that infection markers have normalized. This confirms the bacteria have been successfully cleared from the hip joint.
Once infection clearance is confirmed, the antibiotic spacer is surgically removed. It is then replaced with a new, permanent hip prosthesis, completing the two-stage revision process.