Case Report: Calcium sulfate antibiotic beads and bone morphogenetic protein-2-loaded hydroxyapatite and allograft for the treatment of infected delayed union in a dog.

Abstract

A 6-year-old male German Shepherd dog was presented with a closed, highly comminuted fracture of the left tibia caused by a fall. The fracture was stabilized using a plate-and-rod construct that was further protected with an external skeletal fixator. However, the surgery resulted in an external torsional deformity of the left tibia. Therefore, 23 weeks after the first surgery, an additional deformity-correction surgery was performed based on the tibial torsion angle measured from computed tomography scans. At 28 weeks after the first surgery, osteomyelitis at the osteotomy site in the left tibia, caused by methicillin-resistant, was diagnosed based on culture and antimicrobial susceptibility testing, and this infection was considered to hinder bone healing. At 28 weeks after the first surgery, a third surgery was performed in which calcium sulfate antibiotic beads and antibiotic-impregnated collagen sponges, together with hydroxyapatite and allografts loaded with recombinant human bone morphogenetic protein-2, were grafted for treatment of osteomyelitis and to promote bone healing. Six weeks following the application of antibiotic beads and bone graft materials, clinical bone union was observed. Complete bone healing was confirmed using radiographic imaging, and functional recovery was verified using objective gait analysis. The implant was subsequently removed to prevent stress shielding and the associated peri-implant bone loss. In conclusion, a tissue engineering strategy combining local antibiotic delivery using calcium sulfate antibiotic beads with bone graft substitutes loaded with recombinant human bone morphogenetic protein-2 can overcome the limitations of systemic antibiotic therapy and may be a viable option for treating infected tibial delayed union.