English
Capped hock refers to inflammation and swelling over the bony point of a horse’s hock joint. The “cap” may be soft or firm to the touch and is usually the result of injury or repeated rubbing.
Alongside the characteristic swelling, the horse may have difficulty moving, lack appetite, or experience pain. Affected horses may also have other joint, bone, or soft tissue problems in the same joint.
Factors such as kicking habits, inadequate bedding, and poor stall design increase the risk of developing this condition. Diagnosing capped hock involves physical examination as well as imaging techniques. Treatment focuses on reducing inflammation and pain with medications, cold therapy, massage, and rest.
By understanding causes of this condition as well as the anatomy of the hock, horse owners can take proactive steps to minimize the risk of capped hock and identify and treat it promptly if it develops.
Capped Hock in Horses
Capped hock, also known as calcaneal bursitis or distention of the calcaneal bursa, is a general term for inflammation, swelling, thickening, or callusing over the bony point of the hock. The hock is the large joint at the bottom of the horse’s hind leg, similar to the human ankle. [1][2][3][4]
A horse is said to have a “capped” appearance when there is noticeable enlargement at the back of the hock. [4][5][6]
The “cap” may be filled with fluid, making it feel soft and squishy, or it can be firm if there is significant thickening of the skin and underlying tissues. [1] The skin over the affected area is usually intact, but severe cases can progress into secondary abscesses. [7]
Although capped hock is typically a cosmetic issue, moderate and severe cases can lead to pain and lameness. [1][4][8]
Bursitis
Capped hock is a form of bursitis, which describes inflammation of the bursa. Bursae are present in most joints, and are fluid-filled sacs that reduce friction within a joint space.
The most common locations for bursitis in horses are in the shoulder, elbow, and hock joints. [10] Bursitis and injury to a bursa may result in pain, limited motion, and decreased functional mobility.
Two types of bursitis can occur in horses: [10][11]
- Congenital bursitis: inflammation of a normal bursa that horses are born with
- Acquired bursitis: formation and inflammation of a new bursa beneath the skin, where one didn’t exist before
Capped hock in horses is usually an acquired form of bursitis.
Hock Anatomy
The hock is a complex joint. It plays an important role in the horse’s mobility and stability. To understand capped hock, it is useful for horse owners to familiarize themselves with the hock’s anatomy.
Bursa
The subcutaneous calcaneal (SC) bursa is the structure most affected in cases of capped hock. The SC bursa lies between the skin and the calcaneus bone at the point of the hock.
The SC bursa specifically reduces friction between the skin, calcaneus bone, and underlying structures of the hock. In doing so, it facilitates smooth movement of the tendons as they glide over the bony prominence of the hock as the horse moves. [8]
The location of this bursa makes it susceptible to injury and repetitive pressure like kicking hard surfaces or bumping against walls or other objects. [4] Injuries of this nature are usually associated with capped hock.
Bone Structure
The hock joint comprises several bones collectively referred to as the tarsus. These include: [8]
- Calcaneus: the bone that forms the point of the hock, akin to the human heel bone. The calcaneus usually lies just under the skin and is protected by the subcutaneous calcaneal bursa. When the horse has capped hock, the swelling of the bursa covers this bony prominence.
- Tibia: the long bone extending from the stifle (knee) to the hock.
- Tarsal Bones: includes the central tarsal bone and third tarsal bone, these small bones contribute to the hock’s structure.
Joints
The hock is a complex joint because it comprises multiple points of connection where bones come together and interact. These points of articulation allow the joint to perform a wide range of movements and functions.
The articulations of the hock include: [8]
- Tibiotarsal Joint: the primary joint which allows the horse to walk and bear weight. It enables the hock’s flexibility and movement.
- Smaller Joints: these include the proximal intertarsal, distal intertarsal, and tarsometatarsal joints. These joints contribute to the overall stability and function of the hock.
Ligaments and Tendons
Several ligaments and tendons support the hock, ensuring stability and facilitating movement.
These include: [8]
- Collateral Ligaments: structures on either side of the hock that provide lateral stability.
- Long Plantar Ligament: structure that runs along the back of the hock, helping to stabilize the joint.
- Gastrocnemius Tendon: also known as the Achilles tendon, this structure extends from the calf muscles to the hock, facilitating the extension of the hock joint.
- Superficial Digital Flexor Tendon: structure that runs parallel to the gastrocnemius tendon and aids in flexing the hock.
Capped hock can result from trauma or inflammation of any of these structures. If capped hock is accompanied by a wound, these tendons are at risk of developing infections. [9]
Causes
Cases of capped hock arise when the SC bursa becomes inflamed and swells, resulting in a visible “cap” of tissue over the bony prominence at the back of the hock. [5][6] This condition is acquired as a result of injury to the hock joint. [9]
Typically, capped hock is caused by damage to the subcutaneous calcaneal bursae. [9] This may be due to pressure or friction, such as from rising from a hard surface, or as a result of a kick or bump to the area. The trauma instigates an inflammatory response which brings fluids into the bursa, causing swelling. [7]
Many cases of capped hock are associated with instances where a horse kicked a fixed object like a wall or trailer. [8] In rarer cases, capped hock is related to disease in the structures attached to the hock such as the gastrocnemius and the digital flexor tendons. [9]
Other possible causes are tendonitis and inflammation of the ligaments that lead to secondary inflammation in the bursa. [8]
Risk Factors
Since capped hock is usually related to an injury, the risk factors for capped hock relate to the risk of injury to the hock. [8]
Other considerations in assessing a horse’s risk for this condition include: [3]
- Size of and padding in trailers
- Stall size and design
- Inadequate bedding requiring the horse to lie on hard surfaces
- Inadequate turnout leading to restlessness
- Improper shoeing and hoof care
- Poor conformation
- Being housed in close quarters with other horses that may kick
In addition, the nature and degree of work performed by the horse may be predisposing to injuries associated with all forms of bursitis, including capped hock.
Symptoms
The characteristic symptom of capped hock is a visible swelling over the point of the hock. This is typically obvious as it changes the shape of the leg.
Additional symptoms depend on severity and may include: [6][12]
- Lameness
- Pain
- Hock that feels hot to the touch