Os tarsale IV (T4)
The fourth tarsal bone (T4) is on the lateral (outer) side of the distal tarsus. It is unique in that it spans both tarsal rows, articulating proximally with the calcaneus and the central tarsal bone, and distally with the fourth metatarsal (lateral splint) bone. It forms the lateral column of hock weight support and participates in the proximal intertarsal, distal intertarsal, and tarsometatarsal joints. While bone spavin more commonly affects the medial distal tarsal joints, T4 can be involved in degenerative changes or fractures.
The hock is complex with multiple joint compartments. Bone spavin is one of the most common hind-limb lamenesses and primarily affects the distal intertarsal and tarsometatarsal joints. T4 slab fractures are less common but do occur.
## 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 Bone spavin is osteoarthritis (degenerative joint disease) of the distal tarsal joints, principally the distal intertarsal and tarsometatarsal joints. Repeated compression and rotation da
Hind-limb lameness localized to the hock should be evaluated with flexion tests, joint blocks, and radiography. Many cases of distal tarsal osteoarthritis are manageable.
## 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 Bone spavin is osteoarthritis (degenerative joint disease) of the distal tarsal joints, principally the distal intertarsal and tarsometatarsal joints. Repeated compression and rotation damage cartilage, narrow the joint spaces, and stimulate new bone formation. The result is progressive hind-limb lameness that is one of the most common causes of performance limitation in sport horses. ## Causes Repetitive concussion, conformational faults (straight or sickle hocks), and athletic activities that heavily load the hocks (jumping, dressage, western performance) are the main drivers. Mineral imbalances have been suggested but evidence is limited. ## Diagnosis History of gradual hind-limb lameness that may warm out of, positive flexion tests, and a characteristic “stabbing” or short stride are suggestive. Radiographs show joint-space narrowing, sclerosis, and periarticular new bone. Diagnostic analgesia of the distal tarsal joints confirms the source of pain. ## Treatment Non-steroidal anti-inflammatory drugs, intra-articular corticosteroids, corrective shoeing, and workload modification are first-line measures. Chemical or surgical arthrodesis (facilitated ankylosis) can be considered when medical management fails and the goal is pain-free fusion of the low-motion joints. ## Recovery and Prognosis Many horses remain useful with medical management. Complete fusion, whether spontaneous or surgical, can restore comfort. Advanced bilateral disease may ultimately limit athletic career length. ## Prevention Selection for good hock conformation, balanced shoeing, and sensible training progression reduce risk but cannot eliminate it in high-level athletes. Signs include: gradual hindlimb lameness; shortened stride or toe dragging; positive hock flexion test; bony enlargement on the medial lower hock in advanced cases; stiffness after rest
The hock is complex with multiple joint compartments. Bone spavin is one of the most common hind-limb lamenesses and primarily affects the distal intertarsal and tarsometatarsal joints. T4 slab fractures are less common but do occur.
Hind-limb lameness localized to the hock should be evaluated with flexion tests, joint blocks, and radiography. Many cases of distal tarsal osteoarthritis are manageable.
See the Fourth Tarsal Bone (Right) on our interactive 3D horse model. Open 3D Model