Antibiotic bone cement is a specialized material used in orthopedic surgery, combining traditional bone cement with antibiotics. This blend allows for the direct delivery of medication to a specific surgical site. It consists primarily of polymethyl methacrylate (PMMA) and incorporated antibiotics, forming a solid structure upon hardening. This innovative approach ensures that therapeutic concentrations of antibiotics are available precisely where they are needed, supporting better patient outcomes.
Purpose in Orthopedic Surgery
The primary role of antibiotic bone cement in orthopedic surgery is to prevent and treat infections, such as osteomyelitis or periprosthetic joint infection, which can be particularly challenging to manage. Bone has a limited blood supply, making it difficult for systemic antibiotics to reach adequate concentrations at infection sites. This local delivery bypasses poor blood perfusion in bone, achieving high antibiotic levels directly at the surgical area.
It also minimizes systemic side effects from high doses of oral or intravenous antibiotics. Targeted delivery reduces overall body exposure to medication, benefiting patient health. This localized approach is particularly valuable in preventing infections around implanted prostheses, where even a low-grade infection can lead to significant complications. It provides a sustained release of antibiotics, maintaining a protective environment around the implant for an extended period.
How Antibiotics Are Released
Antibiotics are incorporated into bone cement by mixing them into the polymethyl methacrylate (PMMA) powder. This creates a composite material where antibiotic particles are embedded within the cement matrix. The release of these antibiotics from the hardened cement occurs in two distinct phases.
Initially, a rapid burst release of antibiotics occurs from the cement surface, typically within 24 to 48 hours after implantation. This immediate high concentration helps to combat any bacteria introduced during surgery. Following this initial burst, a slower, more sustained release occurs over weeks or even months, as antibiotics diffuse out of the cement matrix. Factors that influence this release include the antibiotic’s solubility, the porosity of the cement, and the total surface area of the cement exposed to body fluids.
Commonly chosen antibiotics, such as gentamicin, tobramycin, and vancomycin, are selected for heat stability, broad-spectrum activity, and ease of incorporation. These antibiotics are effective against common pathogens like Staphylococcus aureus (including methicillin-resistant strains) and Gram-negative bacteria such as Pseudomonas aeruginosa. Combining multiple antibiotics can also broaden the spectrum of coverage and potentially reduce the risk of resistance development.
Common Uses in Joint Procedures
Antibiotic bone cement is frequently used in orthopedic procedures, especially total joint replacements for hips and knees. It often prevents infection in primary joint arthroplasty, particularly in higher-risk patients. This preventive use aims to establish a protective antibiotic concentration around the new implant from the moment of surgery.
Beyond prevention, it plays a significant role in revision surgeries for infected prostheses. In these cases, it is often part of a two-stage exchange arthroplasty. During the first stage, the infected prosthesis is removed, and a temporary cement spacer loaded with high doses of antibiotics is inserted to clear the infection. After a period of antibiotic treatment, a second surgery is performed to replace the spacer with a new, permanent prosthesis.
It also applies to other scenarios with elevated infection risk, such as open fractures or certain bone tumor resections. In these situations, local antibiotic delivery helps manage or prevent post-operative infections, contributing to better healing and outcomes.
Important Considerations
While antibiotic bone cement offers benefits, several factors warrant consideration. One concern is potential antibiotic resistance development, particularly with prolonged exposure to sub-inhibitory concentrations. Careful antibiotic selection and appropriate dosing are important to maintain efficacy and mitigate this risk. Some studies suggest that the amount of antibiotic added to 40 grams of PMMA bone cement should not exceed 8 grams to avoid compromising the cement’s mechanical strength.
Adding antibiotics can affect bone cement’s mechanical properties, potentially reducing its strength or increasing porosity. This is true if high antibiotic concentrations are used, as they can form voids within the cement as they elute. Despite this, studies indicate that the compressive strength of antibiotic-impregnated bone cement remains above minimum accepted standards, even after antibiotic elution.
Patients may also experience adverse reactions, such as allergic responses to the antibiotic or cement components. While high antibiotic concentrations are desired at the surgical site, excessively high levels can be toxic to local tissues, including bone-forming cells. Long-term effectiveness is also a consideration; while it provides sustained release, the elution rate decreases over time, and the protective effect may diminish, sometimes necessitating further intervention or revision surgery. Therefore, patient follow-up is important to monitor for signs of persistent infection or other complications.