Session III - Clinically Relevant Research

The Efficacy of Gentamycin Impregnated Resorbable Calcium Phosphate Cement in Treating Osteomyelitis in a Rat Model

Brian D. Solberg, MD, Andrew P. Gutow, MD, Michael R. Baumgaertner, MD

Yale University School of Medicine, New Haven, Connecticut, USA; Atlanta, Georgia, USA

The use of poly-methylmethacrylate (PMMA) beads as a carrier for local antibiotic delivery has been shown to be effective in the eradication of infection in an osteomyelitis model. Although there is data to suggest that prefabricated calcium phosphate cement (CPC) beads perform similarly(1), there has been no data to study the performance of CPC placed into a bony defect utilizing a void fill technique. The purpose of this study was to test the effectiveness of CPC as a carrier of gentamycin for the treatment of chronic osteomyelitis utilizing a technique in which CPC paste fills the three- dimensional void and then sets in a rat model.

Methods: Sixty retired female breeder Sprague-Dawley rats were infected with Staphylococcus Aureus using the model by Korkusuz et al. All animals were followed radiographically and clinically for signs of infection. At 7 weeks post infection, all animals were debrided and broken into 4 treatment groups: (A) Debridment only, (B) Debridment + Daily intraperitoneal gentamycin (0.2 mg/kg/day), (C) Debridment + Gentamycin impregnated CPC in a void filled model (1.0 mg/kg), (D) Debridment + Gentamycin impregnated PMMA beads (1.0 mg/kg). Tibiae were harvested at T=0 (control) (n=6), T=3 weeks (n=3/group), T=5 weeks (n=4/group) and T=7 weeks (n=4/group) and analyzed using quantitative bacteriologic analysis expressed as CFU of bacteria per gram of bone. Statistical analysis was performed using Student's T-test.

Results: The quantitative counts for all groups are shown graphically below. All animals displayed clinical and radiographic manifestations of osteomyelitis at the time of debridment. Six animals were lost to peri-operative complications and 4 were left as sentinel animals. The quantitative counts for Group C (CPC) and D (PMMA) were significantly less (p<0.003) than Group A (Debridment alone) or Group B (IP Gentamycin) at all time points after time 0. There was no difference between Group C or D at any time point. The quantitative values for Groups C and D at the 7 week time point were below the sensitivity of the quantitative assay (50 CFU/gm bone) and were thus assigned a value of 1.

Discussion: PMMA is currently a favored local delivery system for antibiotics in a chronic osteomyelitis setting, however, disadvantages include foreign body issues and the need for later removal. This data demonstrates that when placed using a void fill technique, CPC is an effective local delivery system for antibiotics in a chronic osteomyelitis model. Calcium phosphate cement is known to be remodeled into bone in a fracture setting; investigation will ascertain whether this same phenomena occurs in an infection model.

Conclusion: Calcium phosphate cement is an effective adjuvant in treating chronic osteomyelitis in a rat model using a void fill placement technique.

1. Korkusuz F. et al: Experimental Implant Related Osteomyelitis Treated by Antibiotic-Calcium Hydroxyapetite Ceramic Composites. J Bone Joint Surg 75-B: 111-114,1993