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 acts with the stifle during all movements. This is called a reciprocal apparatus; when the hock flexes, the stifle flexes, when the hock extends, the stifle extends and vice versa.

This reciprocal apparatus allows the horse to “sit” onto their hind end, which is crucial for hind end engagement during upper-level dressage and jumping. When this reciprocal apparatus is compromised, the horse can experience poor performance and hock pain. [4]

Signs and Symptoms of Hock Lameness

The symptoms of hock lameness that your horse may experience range from subtle to obvious. Most clinical signs are seen during performance and present as the horse feeling “off” when asked to push from the hind end.

Common signs of hock problems can include:

  • Shortened hind end gait
  • Reluctance to engage from the hind end
  • Reduced spring over jumps
  • Shifting weight when standing still
  • Resistance to going downhill
  • Stiffness that resolves during warm-up
  • Heat and swelling in the hock area
  • Stiffness and reactivity when asked to pick up the hind legs
  • Soreness in the back or stifle from movement compensation [5]

Causes of Hock Lameness

Hock lameness is usually a result of repeated concussion and shock absorption during activities such as jumping, collected work, and travelling down steep hills.

Horses with conformational flaws of the hind limbs are more likely to develop hock issues. Horses born with sickle hocks, straight hocks, or cow hocks are more prone to arthritis and injury due to the altered function of the joints. [2] No one breed is more prone to hock lameness.

Hock lameness can also be caused by arthritis, injury, inflammation, developmental issues or bone problems.

Arthritis or Bone Spavin:

Osteoarthritis (also known as degenerative joint disease) involves progressive deterioration of the cartilage, bone and other components of the joint due to wear and tear.

Bone spavin is a term used to describe degenerative arthritis of the smaller hock joints. It is seen in older horses and commonly causes hindlimb lameness.

The hock is especially prone to arthritis, specifically in the three lower joints because of their role in shock-absorption.

Arthritis is characterized by changes in the cartilage and bone that can inhibit normal motion and increase inflammation. This is an extremely common issue in senior horses that can contribute to poor performance and result in early retirement. [6]

Osteochondritis Dissecans (OCD):

OCD is a developmental disease that can present as small bony fragments or chips breaking off within the hock joints. [6]

Horses with OCD have abnormal cartilage, resulting in the separation of the bone and cartilage from articular surfaces (joints). OCD can also result from excessive training causing lesions in the cartilage and bone.

Septic Arthritis:

Septic arthritis is inflammation of the hock joint caused by bacterial growth within the joint capsule. This serious and potentially life-threatening condition presents as severe lameness and heat in the joint.

Septic arthritis can be caused by bacterial introduction after injury, surgery, joint injection, or systemic infection in the bloodstream. [7]

Capped hocks:

A capped hock presents as warm swelling at the point of the hock. The bursae situated at the point of the hock usually provide a smooth surface for the digital flexor tendons to travel over.

When the bursae become inflamed (usually after trauma), the tendons do not have a smooth surface underneath them. Capped hocks can be asymptomatic or your horse may experience pain with every step.

This condition is caused by repeated concussive forces travelling up the limb, such as from a horse kicking a solid wall. If capped hocks are apparent, your veterinarian will investigate to rule out an underlying fracture. [8]

Fracture:

Like any bone in the horse’s body, the bones of the hock are susceptible to fracture from external trauma or repeated extreme concussion.

Hock fractures can involve fractures of any of the bones in the hock and present as extreme lameness with heat and tenderness on palpation. [9]

Ligament injury:

Because the ligaments of the hock are short and thick, ligament injury is relatively rare. However,