10-Year-Old Paint Horse Mare

Signalment & History

  • This patient presents for left thoracic limb lameness that occurred while turning at the canter.
  • On physical examination, her vitals are normal. There is Grade 4 lameness of the left thoracic limb, moderate soft tissue swelling, and pain on palpation of the left carpus.DLMPO carpus DMPLO carpus DP carpus 2 DP carpus Flexed lateral carpus Lateral carpus



The soft tissues surrounding the left carpus are moderately thickened. There is a comminuted fracture within the fourth carpal bone, with multiple angular, well-defined fracture fragments. There is a mild palmar, lateral, and proximal displacement of the fracture fragments. Multiple ill-defined fissure lines are present within the fourth carpal bone, with mild sclerosis of the surrounding trabecular bone. There is a mild amount of angular, amorphous mineral opacity within the soft tissues on the palmarolateral aspect of the fourth carpal bone.


  • This patient is diagnosed with a comminuted, subacute, mildly displaced, fourth carpal bone fracture, with soft tissue swelling (likely edema, with or without hemorrhage)


Fractures of fourth carpal bones of horses

  • Fractures of the fourth carpal bone are uncommon in horses
  • They appear to be the end result of abnormal concentrations of force on the bone resulting in bone failure
  • Fractures typically arise at a 45 degree angle to the direction of the applied force
  • They can occur in both racing and pleasure horses and may be the result of either direct trauma or abnormal force concentration in the carpus


  • Field JR, Zaruby JF. Repair of a fracture of the fourth carpal bone in a yearling standardbred horse. Can Vet J. 1994;35: 371-2