Can Antibiotic Beads Have An Impact In Osteomyelitis Cases?
How To Create The Antibiotic Mixture
Calcium sulfate is a commercially available product (OsteoSet, Wright Medical) but it is not FDA-approved to be sold with an impregnated antibiotic. Therefore, it is necessary to add the antibiotic of your choice to the calcium sulfate. One would mix the calcium sulfate, curing solution and antibiotic (vancomycin 500 mg or tobramycin/gentamicin 1 g) together and pour them into the pellet template that comes with the kit. Allow the pellets of 3 or 4 mm to harden in an exothermic reaction. After two minutes, they are ready to be implanted into the wound. Proceed to perform primary closure of the wound. Doing so facilitates a higher concentration of eluted antibiotic.
You can see the antibiotic pellets on X-ray for up to three months. We have found sterile serous drainage from the wound in a number of our wounds postoperatively. This represents the breakdown product of the calcium sulfate beads. Be advised that placing too many calcium sulfate beads may result in significant exudate production, which may delay primary wound closure. Kelly, et. al., in a large study of the use of calcium sulfate as a bone graft substitute, reported that 4 percent of cases may have postoperative drainage with complete resolution after four to six weeks.8 One should be careful to differentiate this drainage from continued infection or fibrous tissue.
It’s important to achieve a balance between the need for a large number of beads for the desired antibiotic effect versus having too many and the resulting complication of serous drainage. We normally use five of the 4 mm pellets in a single ray resection and 15 to 20 in a mid-foot amputation without a delay in wound healing from serous drainage.
What The Literature Reveals
As with most treatment options regarding osteomyelitis, there are few reports regarding the efficacy of calcium sulfate antibiotic beads in a clinical setting. Similar to PMMA, its use is considered off-label and without FDA approval. Using calcium sulfate beads as an antibiotic delivery system packed within bony defects has been reported in the literature with good success.
No studies to date have reported on using the modality in the soft tissues as adjunctive therapy to amputation surgery or for soft tissue infections. Its proximity to bony stumps may be of concern for increased incidence of bony regrowth. However, we have not experienced any bony regrowth when we have used these beads adjacent to amputation sites including digit, ray and midfoot amputations.
Other reports have emerged fairly recently in the literature. Reporting on an animal model study, Nelson, et. al., noted an 84.6 percent cure with calcium sulfate antibiotic beads alone compared with 41.7 percent with debridement alone and 35 percent with systemic antibiotics.13
McKee, et. al., reported on 25 patients with culture-confirmed long bone osteomyelitis. All patients were treated with local debridement, systemic oral antibiotics and absorbable calcium sulfate beads impregnated with tobramycin. In 92 percent of cases, the researchers found no clinical and radiographic signs of infection at a mean 28-month follow-up. In eight cases, they noted sterile draining sinus postoperatively.14
Turner, et. al., reported on a single patient they treated for intramedullary osteomyelitis with calcium sulfate tobramycin beads. They achieved resolution of infection with filling of dead space cavity at 31 months.12
Calcium sulfate is biodegradable, an important consideration in that it eliminates the need for removal and associated costs. We have found this surgical adjunct to be of value when performing a delayed closure of a problem wound site. Complete resorption of the beads occurs at six months or sooner and you can follow this clinically with serial radiographs. It also has the advantage of a more reliable elution profile of antibiotic than traditional PMMA as more antibiotic is delivered in the postoperative period. The antibiotic is completely released over a two- to three-month period with high concentrations detectable for at least four weeks.
Calcium sulfate beads seem to be a viable bioabsorbable alternative to PMMA antibiotic beads in the adjunctive treatment of musculoskeletal infections, and warrant further study.