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 Uncommon fractures are those seen infrequently in clinical practice. Diagnosis relies on a high index of suspicion and appropriate imaging. Management follows standard orthopedic principl
## Overview Periosteal proliferation is the production of new bone by the outer layer of the bone (periosteum) in response to irritation, trauma, or instability. It appears on radiographs as irregula
## 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 Uncommon fractures are those seen infrequently in clinical practice. Diagnosis relies on a high index of suspicion and appropriate imaging. Management follows standard orthopedic principles for the bone involved. ## Causes Trauma or fatigue in atypical locations. ## Diagnosis Radiographs or advanced imaging. ## Treatment Rest, external support, or internal fixation as indicated. ## Recovery and Prognosis Variable. ## Prevention Risk management appropriate to the horse’s use. Signs include: acute or subacute lameness; swelling; radiographic fracture in an uncommon location
## Overview Periosteal proliferation is the production of new bone by the outer layer of the bone (periosteum) in response to irritation, trauma, or instability. It appears on radiographs as irregular new bone and may be accompanied by local swelling if active. Mature proliferation is often incidental. ## Causes Trauma, inflammation, or chronic stress. ## Diagnosis Radiographs correlated with clinical signs of heat or pain. ## Treatment Rest and anti-inflammatories for active cases. No treatment needed for quiet, mature bone. ## Recovery and Prognosis Good. Bony enlargement may persist. ## Prevention Avoidance of repetitive trauma. Signs include: radiographic new bone; local swelling or pain if active; may be incidental when mature
## 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 (Left) on our interactive 3D horse model. Open 3D Model