Use of magnetic resonance imaging to diagnose distal sesamoid bone injury in a horse.

This research article covers a case study of diagnosing a horse with a distal sesamoid (navicular) bone injury using magnetic resonance imaging (MRI), which was not detectable through traditional radiographs. The 5-year-old horse showed severe lameness in its left forelimb of four months’ duration, but no abnormalities were seen in initial X-rays. However, MRI revealed increased bone density and damages in the navicular bone, resulting in a blunt traumatic injury that caused bone proliferation.

Case Presentation

• The 5-year-old Appaloosa mare was observed for a severe lameness in its left forelimb which lasted for 4 months. This condition became apparent when the horse walked or trotted, and was even more noticeable when the horse circled to the left.
• The horse showed signs of pain when hoof testers were placed over the frog (soft under part) of the left front hoof. Moreover, the temporary numbing of the foot through a palmar digital nerve block made the lameness disappear, suggesting the pain was the cause of the lameness.

Diagnosis Methods

• Initial radiographs did not show any abnormal findings, belying the severe lameness and the acute pain the horse was experiencing.
• Magnetic resonance imaging (MRI), however, revealed increased bone density in the navicular bone – specifically within the medullary cavity. On top of this, defects were detected in the fibrocartilage and subchondral bone of the flexor cortex.
• These findings could only be seen using MRI and not through traditional radiographs, highlighting the superior diagnostic capabilities of MRI in detecting such conditions.

Conclusion and Implications of the Research

• Despite four months of observation and care, the horse’s condition did not improve. Due to the poor prognosis for the return to soundness and ongoing pain, the decision was made to euthanize the mare.
• Postmortem examination revealed an adhesion between the deep digital flexor tendon and the flexor cortex defect on the navicular bone. Further histologic evaluation showed diffuse replacement of marrow trabecular bone with compact lamellar bone, changes that were consistent with a blunt traumatic injury to the navicular bone.
• The key takeaway from this research is the utility of MRI in capturing the symptoms of navicular bone injury that is not usually evident in traditional radiographs. Additionally, the research also pushes for considering navicular injury as a potent plausible cause of sudden severe lameness in a horse’s forelimb even when no fracture is evident.