Os carpale IV (C4)
The fourth carpal bone (C4) is the lateral bone of the distal row of carpal bones. It articulates proximally with the ulnar carpal bone, medially with the third carpal bone, and distally with the fourth metacarpal (lateral splint) bone. It is part of the weight-bearing column of the carpus. The carpus is a common site of injury in racehorses. Chip fractures and slab fractures of the carpal bones (including C4) are treated arthroscopically when indicated. The distal row of carpal bones is subject to high compressive and shear forces during high-speed work.
Carpal chip and slab fractures are common in racehorses. Diagnosis is by radiography (multiple views) and arthroscopy. Prognosis depends on the size and location of the fragment and concurrent joint damage.
## Overview Fractures in horses range from minor chip fractures to catastrophic long-bone breaks. Prognosis depends on the bone involved, whether the fracture is open or closed, the age of the horse,
## Overview Osteoarthritis of the carpometacarpal joint is degenerative joint disease of the lower knee joint. It is less common than middle-carpal osteoarthritis but causes similar signs of knee swe
## Overview Periosteal new bone formation is extra bone produced by the periosteum (the outer layer of bone) in response to trauma, inflammation, or instability. It is seen on radiographs at sites of
Swelling or lameness localized to the knee after racing or hard work should be evaluated promptly. Many carpal chips are managed arthroscopically with a good return to work.
## Overview Fractures in horses range from minor chip fractures to catastrophic long-bone breaks. Prognosis depends on the bone involved, whether the fracture is open or closed, the age of the horse, and the degree of displacement. Adult long-bone fractures often carry a poor prognosis. ## Causes Trauma, fatigue failure, or pathologic bone weakness. ## Diagnosis Clinical signs plus radiographs. Advanced imaging for complex or articular fractures. ## Treatment Internal fixation, external coaptation, or conservative management depending on the fracture. Many adult weight-bearing long-bone fractures result in euthanasia. ## Recovery and Prognosis Highly variable. Foals and certain locations (for example, some splint or chip fractures) have better outcomes. ## Prevention Risk reduction through training management and safe environments. Signs include: acute lameness; swelling; crepitus; non-weight-bearing in severe cases; radiographic fracture line
## Overview Osteoarthritis of the carpometacarpal joint is degenerative joint disease of the lower knee joint. It is less common than middle-carpal osteoarthritis but causes similar signs of knee swelling, reduced flexion, and lameness that worsens with work. Radiographs show joint-space narrowing and osteophytes. ## Causes Repetitive loading, previous injury, or conformational stress. ## Diagnosis Lameness examination, diagnostic analgesia, and radiographs. ## Treatment Intra-articular medication, systemic anti-inflammatories, and workload adjustment. ## Recovery and Prognosis Fair. Management is ongoing. ## Prevention Sensible training and early treatment of joint inflammation. Signs include: carpal swelling; lameness worse after work; reduced carpal flexion; radiographic osteoarthritis
## Overview Periosteal new bone formation is extra bone produced by the periosteum (the outer layer of bone) in response to trauma, inflammation, or instability. It is seen on radiographs at sites of previous injury, splint bones, or stress remodeling. Clinical importance depends on whether it is actively inflamed or mechanically interfering. ## Causes Trauma, periostitis, or chronic instability. ## Diagnosis Radiographs correlated with palpation and lameness examination. ## Treatment Rest and anti-inflammatories for active inflammation. Mature, non-painful new bone often requires no treatment. ## Recovery and Prognosis Good once inflammation settles. The bony enlargement may remain. ## Prevention Avoidance of repetitive trauma. Signs include: radiographic periosteal reaction; local swelling or pain if active; may be incidental if mature
Carpal chip and slab fractures are common in racehorses. Diagnosis is by radiography (multiple views) and arthroscopy. Prognosis depends on the size and location of the fragment and concurrent joint damage.
Swelling or lameness localized to the knee after racing or hard work should be evaluated promptly. Many carpal chips are managed arthroscopically with a good return to work.
See the Fourth Carpal Bone (Right) on our interactive 3D horse model. Open 3D Model