Lameness in the horse’s hock joint is one of the most common causes of altered hind end gait.

Hock lameness is characterized by shortened gait, weight shifting, stiffness when your horse picks their hind legs up, and reduced springiness off the ground when the horse picks up a canter or jumps.

Most performance horses will experience some form of hock lameness in their careers. Hock problems are most common in horses being asked to carry large amounts of weight on their hind ends, such as jumpers and upper-level dressage horses.

Vigilance and medical imaging of the hock are key to early detection and intervention. The good news is there are many effective treatment options for horses with hock lameness, keeping horses sound and pain-free after diagnosis.

Prevention of hock lameness starts with good management. Keep your horse at an appropriate body weight, support their joint health with a good nutritional program and watch for signs of soreness.

The Hock Joint

The hock is a group of joints that work to flex and extend the lower limb of the horse. The hock is considered a hinge joint because its movement is limited to flexion and extension in one plane (front to back). [1]

While the hock is usually thought of as a single joint, it is actually an area consisting of four separate joints that are each involved in moving the horse’s hind leg.

The four joints in the hock – consisting of one upper and three lower joints – include: [2]

  • Tibio-tarsal joint
  • Proximal inter-tarsal joint
  • Distal inter-tarsal joint
  • Tarso-metatarsal joint

The upper and largest joint is the tibio-tarsal joint. This joint is considered high-motion and responsible for most movement within the hock.

The lower joints are smaller and are considered low-movement but high shock absorbing. [3]

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Anatomy

These four joints include connections between the following ten bones:

  • Tibia
  • Talus
  • Calcaneus
  • Central tarsal bone
  • Fused 1st and 2nd tarsal bones
  • 3rd and 4th tarsal bone
  • 2nd, 3rd, and 4th metatarsal bone. [1]

The tibio-tarsal joint connects the horse’s tibia to its talus (a smaller bone within the hock). Unlike humans, this joint does not include the fibula, since the end of the horse’s fibula is incorporated into the end of the tibia. [2]

The proximal inter-tarsal joint is the junction between the talus and calcaneus and the central and 4th tarsal bones. The distal inter-tarsal joint articulates the numbered tarsal bones and the metatarsals. Finally, the tarso-metatarsal joint consists of the numbered tarsal bones and the metatarsals.

Ligaments

Three ligaments ensure the stability of the hock: [2]

  • Lateral collateral
  • Medial collateral
  • Long plantar ligament

Cartilage pads in the joint with synovial fluid in between allow for smooth movement throughout the range of motion.

The hock also has up to three bursae (fluid-filled pillows), allowing for smooth continuation of tendons down the horse’s lower leg. [2]

Function of the Hock

The joints within the hock perform two main functions:

  • Shock absorption
  • Propulsion [2]

Shock Absorption

The horse’s hock acts as a major shock absorber for the horse’s hind end. The anatomy of the hock allows the joint to be in a flexed position during the early portions of the stance phase (i.e. when the hoof makes contact with the ground).

This flexed position allows concussion to travel through the soft tissues and up the limb, reducing damaging concussive forces directly on the small structures of the lower limb. [3]

The hock also absorbs any torque created by breakover during the gait cycle. Breakover is the point of the gait cycle when the horse moves the heel off the ground onto the front of the hoof.

The breakover point is a location on the hoof where the most force is generated to propel the body forward. This point is similar to the ball of the foot on a human. [19]

For these reasons, the hock is very susceptible to damage and strain. [3] This shock absorption also allows for propulsion during push-off.

Propulsion

The major muscles that extend the hock are the biceps femoris and semitendinosus muscles. Extension of the hock allows for the horse’s body to be propelled forward. [1]

The major muscles responsible for flexing the hock are peroneus tertius (also known as the fibularis tertius), tensor fasciae latae, and extensor digitorum lateralis and longus. [2]

Flexion of the hock allows the limb to be lifted off the ground, propelled forward, and placed back on the ground without the toe dragging.

The hock is a unique joint in that it