What Is It?

The hock joint of a dog is analogous to the ankle joint of humans. The shin bone, called the tibia, is connected to the hock joint, which then joins the talus bone (one of the bones of the paw). The fibula (splint bone) runs along the full length of the tibia. Ligaments on the inner and outer part of the hock joint hold the bones together. The hock joint’s side has two important ligaments, making a total of four main ligaments that hold the hock together. Instability can be due to tearing of ligaments that hold the hock’s bones in place, a fracture of the fibula, or a fracture of the bottom of the tibia bone.
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Who Gets It?

Any dog or cat can suffer from hock instability, as it is usually due to trauma.
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What Are The Signs?

Hock instability results in a sudden onset of lameness. There may be pain, swelling, and heat associated with the affected joint as well.
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How Is It Diagnosed?

Hock instability can be diagnosed relatively easily on a physical exam. The veterinarian must test the hock by trying to open the joint from the outside and inside (medial and lateral) sides of the joint with the hock in both extension and flexion. The hock must also be stressed by twisting it from side to side (internal and external torsion) to see if the ligaments are stable. It is important to determine what structures have been compromised in the injury leading to the joint’s instability. This can be done by taking stress radiographs, in which forces are applied to the hock in a different direction, and radiographs are taken. A variety of radiograph positions and views are needed to identify if and where a bone fracture is.
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Why Did This Happen To My Dog?

Hock instability is created when ligaments that hold the hock’s bones in place are torn when the fibula is fractured, or when the bottom of the tibia is fractured. These occur due to trauma, which can include a fall, accident, or similar event.
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How Is It Treated?

Treatment requires surgery, but the surgery technique employed depends on the type of injury that is present, ligament damage versus a fracture.

If a fracture is present, surgery using pins, wires, and screws to repair the fracture is performed. To minimize arthritis development in the joint, the fracture must be perfectly aligned, and the pin must not penetrate the joint.
If a ligament is torn, screws are placed in the bones above and below the joint, and a heavy permanent suture is tied around screws to simulate the ligament. With time, scar tissue develops to add support to the surgically repaired joint.
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What Is The Prognosis For My Dog?

The best outcome for injuries that cause instability of the hock is with surgery. If instability is due to a broken bone, the damage is more easily and successfully repaired than if caused by torn ligaments.
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Hock Instability/Dislocation