Treatment of methicillin-resistant Staphylococcus epidermidis infection following repair of an ulnar fracture and humeroradial joint luxation in a horse.

This study documents the successful treatment of a serious bone and joint infection in a horse caused by methicillin-resistant Staphylococcus epidermidis using a combination of strong antibiotics and innovative localized therapy.

Understanding the Case

• The subject of the study was a 27-month-old Rocky Mountain Horse who had sustained a significant injury, causing a fracture in the ulna (foreleg bone) and the dislocation of the humeroradial joint. This injury is referred to as a Monteggia fracture.
• Open surgical reduction was performed to realign the fractured bones and the joint. The bone fracture was stabilized with a bone plate and screws.
• Post-surgery, the horse developed a serious infection at the surgical site.
• The infection was identified as methicillin-resistant Staphylococcus epidermidis (MRSE) – a bacterium resistant to a common type of antibiotic, making the infection harder to treat.

Diagnosis and Initial Treatment

• The MRSE infection was studied and found to be susceptible to four types of antibiotics: oxytetracycline, erythromycin, rifampin, and vancomycin.
• The horse was initially treated with oxytetracycline, however, the clinical response from the horse was not favorable, indicating that the infection was not effectively contained or eliminated.

Further Treatment and Outcome

• As a result, systemic (whole body) treatment using vancomycin and rifampin was started. Alongside this, an innovative measure was taken – vancomycin-impregnated polymethyl methacrylate (PMMA) beads were implanted directly at the surgical site. This would have addressed the infection locally, at its source, potentially improving the antibiotic’s effectiveness.
• Six months after the surgery and the start of this combined local and systemic treatment, the horse was sound both walking and trotting, signaling successful treatment.
• Bony union, i.e., efficient healing of the bones, was observed in radiographs of the elbow joint, indicating that the fracture had healed well and that the treatment had been successful.

Significance

• This case provides valuable insight into treating serious, drug-resistant infections in equine medicine. The innovative use of antibiotic-impregnated beads directly at the infection site demonstrates a potentially effective treatment pathway for similar future cases.
• It highlights the importance of tailoring treatment plans based on the unique needs of each case, particularly in the face of drug-resistant infections.