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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]

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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]

Severity

The severity of capped hock depends on the underlying cause, how significant the swelling is, whether the horse is experiencing pain or lameness, and what work the horse is expected to perform.

Capped hock can result in minimal swelling and may be difficult to detect in mild cases. In more severe cases, the swelling is more exaggerated and obvious.

In cases where the swelling is mild, capped hock is considered a cosmetic issue. In such cases, the horse’s athletic performance is not likely to be affected, but some disciplines have penalties for conformation issues. [3] More complicated cases that affect the underlying structures, potentially impacting performance, are considered more serious.

In some cases, there may be more serious disease or injury in the capped hock such as dislocation of the superficial digital flexor tendon, abnormalities of the bones, or gastrocnemius tendinitis. [1][8] The conditions may be present whether a capped hock is visible or not and are associated with more severe pain and lameness.

The trauma that caused capped hock can also result in wounds in the area. [8] If this is the case, the horse is at risk of developing an infection that could affect the deeper structures of the joint. [8]

In severe cases, the swelling of the bursa leads to abscesses in the hock, which can lead to pain and lameness. Abscesses require surgical treatment and appropriate wound care to prevent infection. [7] Robust wound care for any open skin in the area is recommended.

Additionally, in severe cases, the underlying causes of capped hock can lead to bone loss or the development of fluid-filled or semi-solid cavities in the bones. [8]

Diagnosis

Diagnosis is usually based on observing the characteristic swelling at the point of the hock during physical examination. [1]

Other diagnostic tools help to confirm the diagnosis and rule out other possible conditions. These may include: [1][8][13][14]

  • Needle aspiration (withdrawing liquid from the swelling for testing)
  • Ultrasound
  • Nuclear Scintigraphy (X-ray with contrast)
  • X-rays
  • Endoscopy or bursoscopy (inserting a camera into the bursa)

Treatment

Treatment aims to reduce the swelling, support the joint, and ease pain and disability. Treatments include: [1][4][15]

In cases where capped hock is accompanied by a wound, thorough wound care is required to prevent deeper infection.

Prognosis

The prognosis for a horse with a capped hock depends on the underlying cause, the severity of the condition, and the success of the treatment.

In general, horses, especially young horses, with mild to moderate cases of capped hock have a good prognosis for life and return to full function. [1] Early treatment and complete rest are recommended.

In cases where the inflammation is chronic, or where there is loss of bone tissue due to disease, infection, inflammation, or other cause, the prognosis for a return to full athletic function is guarded. [8]

Prevention

Capped hock in horses is often preventable. Strategies aim to keep the horse free from injury, prevent them from lying on hard ground, and maintain overall health and condition. Considerations include: [3][4][8]

  • Taking extra precautions while transporting the horse and ensuring appropriately sized and padded trailers
  • Providing sufficient space when horses are housed together to prevent overcrowding
  • Managing social hierarchy in a herd to avoid physical altercations between horses
  • Providing adequate high-quality bedding to cushion the horse’s limbs while it is at rest
  • Removing any hard objects from stalls and high traffic areas
  • Ensuring stalls are wide enough
  • Providing consistent farriery from a qualified professional
  • Providing a high-quality, forage-first diet

Summary

Capped hock is inflammation that causes the calcaneal bursa to swell, making a bump of varying size over the bony point of the horse’s hock. This condition is cosmetic in mild cases, but in severe cases can cause lameness and pain.

  • The cause of capped hock is usually injury to the bursa, but can also be disease in the related structures of the hock.
  • Horses that tend to kick, get kicked, or bump against hard objects are more likely to develop capped hock.
  • Along with the characteristic swelling, other symptoms include pain, localized heat, decreased movement, and possibly lameness.
  • Diagnosis is based on physical examination and confirmed with imaging techniques such as endoscopy and ultrasound.
  • Treatment aims to reduce swelling, pain, and disability as well as supporting the joint. This may include medications, cold therapy, massage, and bandaging. The horse usually needs to rest while recovering.
  • The prognosis for mild cases is good, while more severe cases have a guarded prognosis for a return to full athletic capacity.

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References

  1. Raghuvanshi, P. D. et al., Capped Hock in a Gelding and Its Management. Indian Veterinary Journal. 2017.
  2. Post, E. M. et al., An Anatomic Study of the Calcaneal Bursae in the Horse. Veterinary Surgery. 2007. View Summary
  3. Loch, W. and Bradley, M., Unsoundness and Blemishes in Horses. University of Missouri Extension. 1995.
  4. Pascoe, E. and Baxter, G., Hock health: wear and tear can break down these critical joints. Here are the latest targeted treatment options. Practical Horseman. 2008.
  5. Wright, I. M. and Minshall, G. J., Injuries of the Calcaneal Insertions of the Superficial Digital Flexor Tendon in 19 Horses. Equine Veterinary Journal. 2012. View Summary
  6. Dyson, S., Incomplete Tears of the Medial Calcaneal Insertion of the Superficial Digital Flexor Tendon of a Hind Limb in Three Horses. Journal of Equine Veterinary Science. 2014.
  7. Boswell, J.C., Capped Hock. Merck. 2015.
  8. Baxter, G. M., Ed., Adams and Stashak’s Lameness in Horses. Seventh edition. Wiley-Blackwell, Hoboken, NJ. 2020.
  9. Clegg, P., Differential Diagnosis of a Swollen Hock in the Horse.Clinical Practice. 2003.
  10. Adams, S.B. Bursitis in Large Animals. Merck. 2022.
  11. Schramme, M. and Schumacher, J. Chapter 83 – Management of Bursitis. In: Equine Surgery (Fifth Edition). W.B. Saunders. 2019.
  12. Dik, K. J. and Leitch, M., Soft Tissue Injuries of the Tarsus. Veterinary Clinics of North America: Equine Practice. 1995.
  13. Ingle-Fehr, J. and Baxter, G. M., Endoscopy of the Calcaneal Bursa in Horses. Veterinary Surgery. 1998.
  14. Smith, R. K. and Cauvin, E., Ultrasonography of the Hock. UK-Vet Equine. 2018.
  15. Nagar, M. and Gahlot, T. K., A Clinical Study on Musculo-Skeletal Affections of Hindlimb in Equines. Veterinary Practitioner. 2015.