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Reduction of Postoperative Spinal Implant Infection Using Gentamicin Microspheres

Stall, Alec C. MD; Becker, Ed MD; Ludwig, Steven C. MD; Gelb, Daniel MD; Poelstra, Kornelis A. MD, PhD

doi: 10.1097/BRS.0b013e318197e96c
Basic Science

Study Design. Three noncontiguous spinal implant sites in 1 rabbit were challenged with Staphylococcus aureus and local antibiotic prophylaxis was given with gentamicin in controlled-release microspheres (poly(lactic-coglycolic-acid) [PLGA]). Postoperative biomaterial-centered infection on and around the titanium rods was assessed using standard bacterial quantification essays.

Objective. To assess surgical site and biomaterial-centered infection reduction with controlled release gentamicin from microspheres against S. aureus.

Summary of Background Data. A postoperative biomaterial-centered infection can be devastating after successful thoracolumbar spinal surgery and puts a high burden on patients, families, surgeons, and hospitals, endangering both our healthcare budget and our ability to perform challenging cases in patients with increasing numbers of comorbidities. Systemic antibiotics often do not reach “dead-space” hematomas where bacteria harbor after surgery, whereas local, controlled release gentamicin prophylaxis through PLGA microspheres showed favorable pharmacokinetics data to achieve local bactericidal concentrations for up to 7 days after surgery.

Methods. A well published rabbit spinal implant model with systemic cephalosporin prophylaxis was challenged to create a baseline infection of ∼70% in control sites. We then challenged 3 noncontiguous titanium rods inside the laminectomy defect with 10e6 colony forming units S. aureus and randomly treated 2 sites with gentamicin PLGA microspheres and 1 site with PLGA carrier only (control). Standard quantification techniques were used to assess biomaterial centered and soft tissue bacterial growth after 7 days.

Results. After establishing reliable infection rates in control sites, the therapeutic arm of the study was started. Surgical site infections were found in 75% of control sites, whereas gentamicin microspheres reduced the incidence down to 38% in the same rabbits. Biomaterial-centered infection was reduced from 58% to 23% only in all sites challenged with 10e6 S. aureus.

Conclusion. Postoperative, biomaterial-centered infection was reduced at least 50% with intraoperative gentamicin microspheres in the face of systemic cephalosporin prophylaxis and high dose S. aureus in a laminectomy defect in rabbits. The data are statistically and clinically significant, and further animal testing is planned to confirm these results.

Postoperative biomaterial-centered infection after spinal surgery can be devastating. Using local gentamicin microspheres, significant reduction of Staphylococcus aureus surgical site and titanium implant-associated infection incidence was observed in a well published rabbit model. Further animal studies are planned to verify current data.

From the University of Maryland, Shock Trauma Center, Baltimore, MD.

Acknowledgment date: February 14, 2008. Revision date: August 14, 2008. Acceptance date: September 21, 2008.

The device(s)/drug(s) that is/are the subject of this manuscript is/are not FDA-approved for this indication and is/are not commercially available in the United States.

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Kornelis A. Poelstra, MD, PhD, University of Maryland, 22 South Greene St-Suite 11B, Baltimore, MD 21212; E-mail:

© 2009 Lippincott Williams & Wilkins, Inc.