The hock (known as the ankle in man) connects the paw (talus and calcaneus bones) to the shin bones (tibia and fibula). This joint is held together by a set of ligaments primarily located on the inner and outer sides of the joint.
Cause of hock dislocation
Hock dislocation occurs with tearing of collateral ligaments or fracture of bones that make up the hock joint. The most common causes of a hock dislocation include being stepped on by a human; being hit by a car; getting the paw caught in a chain-linked fence; or getting the paw caught in a hole in the ground when running. Sometimes the injury will result in an open wound over the dislocated hock. This could potentially result in infection and delayed healing.
Signs and diagnosis
The clinical signs of a dislocated hock include lameness, swelling and abnormal movement of the joint (instability). In order to determine which ligaments or bones are fractured, stress X-rays (pressure is applied to hock during the X-ray) are done while the patient is under heavy sedation or full anesthesia. The information gathered from this study is critical to determine the type of surgical repair required. Prior to anesthesia and surgery, blood work is done in order to evaluate the health of the internal organs.
Surgery is frequently essential to correct a hock dislocation and involves repairing the fractured bone or reconstructing the torn ligament. If a fractured bone is found, surgical repair may require the use of a pin, wire, plate and screws (see figure right). If a torn ligament is present, one or more metal anchors are usually placed in the bones of the hock joint for attachment of a synthetic ligament. In some cases, there is extensive damage or fractures of the bones in the hock, and a fusion of the joint(s) is/are needed. This involves removing the cartilage from the joints, packing the affected joints with bone graft collected from the patient’s pelvis or shoulder and stabilizing the joint with screws or a plate and screws.
Surgical repair of a dislocated hock caused by a fracture has the best prognosis. Most of these patients respond very well to treatment with resolution of lameness. If arthritis of the joint develops, the pet may have some residual stiffness noted with heavy exercise or after long periods of rest.
The prognosis following repair of a torn ligament in the hock usually carries only a fair prognosis as arthritis will likely develop within the damaged joints, which may cause stiffness of the limb with heavy exercise, after weather changes or after napping. Medications can be prescribed to alleviate these signs. Uncommon complications associated with surgery include infection, breakage of the screws and cold sensitivity to the implanted screws (during cold weather).
For more information on this subject, speak to the veterinarian who is treating your pet.