PMMA is superior to hydroxyapatite for colony reduction in induced osteomyelitis

Staphylococcus aureus infection is a serious complication in patients receiving orthopaedic implants. Treatment with antibiotic-loaded cements can deliver high local concentrations and reduce toxic side effects associated with systemic antibiotic administration, but polymethylmethacrylate cement is nondegradable and may necessitate additional surgery for removal. Previous studies provide support for hydroxyapatite as a biodegradable carrier, but consensus has not been achieved. We hypothesized vancomycin-loaded hydroxyapatite was superior to vancomycin-loaded polymethylmethacrylate in reducing the number of bacterial colony-forming units in the setting of osteomyelitis. Osteomyelitis was induced in rats using an established model. Animals then were randomly assigned to a control group (no antibiotics), a group treated with vancomycin-loaded polymethylmethacry-late, and two groups treated with hydroxyapatite loaded with either low-dose or high-dose vancomycin. After 6 weeks we compared the number of colony-forming units per gram of harvested bone between groups. Vancomycin-loaded hydroxyapatite was inferior to vancomycin-loaded polymethylmethacrylate in reducing the number of bacterial colony-forming units and vancomycin-loaded polymethylmethacry-late was superior to the control group. We observed no difference between low- and high-dose vancomycin-loaded hydroxyapatite groups. The poor handling properties of hydroxyapatite paste may explain these findings. Based on these results, a hydroxyapatite carrier cannot be recommended for the treatment of osteomyelitis.