Mandibular fracture with subsequent sequestrum formation and tooth-root abscess in a 3-year-old mare.

Overview

• A 3-year-old mare sustained a mandibular fracture complicated by chronic bone infection (sequestrum) and a tooth-root abscess.
• Initial treatment involved removing the dead bone and cleaning the area, but persistent symptoms led to advanced imaging that identified infection in a tooth, which was then surgically extracted, resulting in full recovery.

Case Presentation and Initial Diagnosis

• A quarter horse cross mare, 3 years old, was brought to a veterinary college for a draining tract (persistent hole draining fluid) on the underside of the left mandible (lower jaw).
• The draining tract was linked to a previously sustained mandibular fracture.
• Diagnostic imaging was performed:
  • Radiography (X-rays) and ultrasonography (ultrasound) confirmed the presence of a sequestrum — a piece of dead bone separated from healthy bone due to chronic infection.

Treatment and Follow-up

• The fractured region underwent sequestrectomy, which is surgical removal of the dead bone, along with debridement (cleaning) of the mandible to remove infected or necrotic tissue.
• Following surgery, the mare was discharged from the clinic.
• However, three months later, the mare returned with continued drainage, indicating the problem was not fully resolved.

Advanced Diagnostic Imaging and Secondary Infection Discovery

• A CT scan (computed tomography) of the mare’s skull was performed to better visualize complex structures not fully elucidated by previous imaging methods.
• The CT scan revealed infection involving Tooth 310 (a specific tooth in equine dental notation), indicating that the tooth root was infected and serving as a persistent source of infection.
• This tooth infection was likely secondary to the initial mandibular fracture and chronic bone infection, highlighting a complication not detected by X-ray or ultrasound originally.

Final Treatment and Outcome

• The infected tooth was surgically extracted to remove the nidus of infection.
• After tooth removal, the mare was discharged again.
• At a one-month follow-up examination, clinical signs including drainage had resolved, indicating successful treatment.

Key Clinical Messages and Additional Insights

• The report emphasizes the critical utility of CT imaging in diagnosing dental involvement secondary to mandibular fractures. CT provides superior detail of bone and tooth anatomy, identifying occult infections not seen with radiographs or ultrasound.
• It also raises awareness about the growing issue of antibiotic resistance, particularly to trimethoprim-sulfamethoxazole, which is commonly used in equine medicine. Prolonged and frequent use of this antibiotic contributes to increasing resistance, complicating treatment options.
• This case underscores the importance of thorough diagnostic evaluation in persistent infections and cautions against reliance solely on standard imaging or prolonged antibiotics without addressing underlying causes.