Slocum Enterprises, Inc.

Joint Hinge for Repair of Shearing Injuries of the Canine Hock

By Barclay Slocum, DVM and Theresa Devine Slocum, MS

    Shearing injuries of the canine hock most commonly occur when the patient is dragged by a vehicle at the time of accident.  Most commonly, the resultant injury is the loss of the medial malleolus of the tibia.  The medial collateral ligament is often ruptured or lost to the abrasive action of the pavement.  Even though bone and ligaments are lost, the trochlear conformation of the talus and the lateral collateral ligament can provide a biomechanically stable, one degree of freedom joint in the hock if the function of the missing structures can be maintained during healing.

    The problem of shearing injuries is threefold: joint stability, management of infection, and maintenance of joint function.  If the loss of bone and ligament constitute one half of the joint, then stability by natural conformation will be lost, and reconstructive efforts should be salvaged by fusion.  If two thirds of the joint is left, then the joint hinge is a viable alternative.  Fortunately, skin loss is minimized during abrasion injuries of the hock, since the skin moves rather than being rigid.  This means that there is sufficient tissue available for coverage of the joint following debridement of foreign material, by sliding skin flap or other skin grafting techniques.  Stability of the soft tissue components by use of the joint hinge in a triangular conformation during the initial stages of healing can provide the conditions for optimal soft tissue healing during early revascularization of the damaged area.  In order to maintain joint function following revascularization, a kinesiotherapeutically appropriate apparatus, such as the Slocum^® joint hinge, must be used to maintain normal physiology of the joint motion.

    The secret to maintaining normal joint function is placement of the hinge center at the instant center of motion of the hock.  This can be accomplished by preplacement of a 3/32 pin at the center of motion and testing its position by placing a second pin in the tibia and joining this to the center hock pin by a wire.  As the joint is flexed and extended, the wire should neither shorten nor lengthen, indicating proper placement of the hock center pin.  The hock center pin needs to be perpendicular to the long axis of the tibia.  This can be accomplished by the multi-pin guide bar or hock hinge itself.  Once the joint center has been located, application of the hock hinge by the clamp shell external fixator will assure normal joint motion.  This joint motion is limited during the initial stages of healing to allow granulation and stability of the soft tissues, and later mobilized by removal of the triangulation bar for physiological normal motion and alignment of collagen fibers into a ligament-like support for the medial hock joint.