Introduction

• Racehorse or ex-racehorse injury; most commonly involve distal radius, radial carpal bone, intermediate and third carpal bones.
• Cause: racing injury, acute or chronic.
• Signs: forelimb lameness Musculoskeletal: gait evaluation, synovial distension, pain on flexion Musculoskeletal: manipulative tests.
• Diagnosis: local anesthesia (intra-articular block Forelimb: joint anesthesia), radiography Forelimb: radiography, arthroscopy Joint: arthroscopy - overview, scintigraphy Bone: scintigraphy.
• Treatment: arthroscopy - chip removal Radiocarpal: arthroscopy Intercarpal: arthroscopy.
• Prognosis: depends on severity and age of injury.
• See also:
  • Carpus: fracture - slab.
  • Carpus: fracture - comminuted.
  • Accessory carpal: fracture.
  • Musculoskeletal: fracture.
  • Musculoskeletal: fracture - first aid.

Pathogenesis

Predisposing factors

• Repetitive training and loading of the carpal joints.
• Inappropriate training regimens Musculoskeletal: effects of training and exercise Musculoskeletal: training surfaces and regimens - racehorses.
• Poor carpal conformation, such as back-at-the-knee, is often considered significant, but so far this has not been statistically proven.
• Poor foot conformation and shoeing.

Pathophysiology

• The end result of stress-related subchondral bone injury caused by repetitive loading:
  • Initially this is adaptive but with continued loading it becomes non-adaptive bone remodeling and pathological.
  • This is seen in radiographs of the carpal bones Forelimb: radiography as bone sclerosis and remodeling of the subchondral bone, which is evident at the time of fracture.
• Once the bone is damaged it is predisposed to fracture, as an apparent one-off event, during training or racing.
• Osteochondral fragments, by definition, involve only one joint surface within the midcarpal or antebrachiocarpal joints. There can be single or multiple fragments in one joint, multiple joints or multiple legs.
• There are differences between racing breeds as to the site of osteochondral chip fractures, which are explained by gait and sites predisposed to stress-related subchondral bone injury.
• Acute overload injury, particularly in fatigued horses, does occur in the absence of pre-existing bone pathology in occasional cases, and usually involving the antebrachiocarpal joint.
• Dorsal sites in the carpus are more prone to fragmentation because of the biomechanics of the carpal joints. Individual sites within the midcarpal and antebrachiocarpal joint are affected by the breed of the animal, its racing requirements, training regimens, surfaces it trains and races on, and carpal conformation.
• Palmar osteochondral fragmentation is much less common.:
  • Those involving the proximal articular margin of the accessory carpal bone or other bones of the antebrachiocarpal joint may occur as one-off events such as falls, carpal hyperflexion, or recovery from a general anesthetic.
  • The most commonly affected bone is the proximal palmar articular margin of the radiocarpal bone either alone or in combination with comminuted palmar radiocarpal fractures and/or concurrent intermediate, ulnar or palmar distal radial fractures.
  • Midcarpal joint palmar carpal fragments are more often seen in combination with dorsal joint fragmentation and may be migrants from dorsally.

Diagnosis

Treatment

Prevention

Outcomes