Equine Joint Anatomy & Common Conditions – [Complete Guide]

Joint Anatomy
Types of Joints
Limb Joints
Joint Disease
Joint Health

The horse’s skeletal system consists of over 200 bones connected by tendons, ligaments, and cartilage. Joints are the anatomical structures where two or more bones come together.

Joints facilitate the horse’s movement, providing flexibility and enabling key functions such as walking, running, jumping, and turning. They also support weight distribution and absorb shock to protect bones during movement.

However, the joints in a horse’s body are prone to injury and disease. Sport horses are at highest risk of joint problems, but all equines are at risk given their large size and active lifestyles.

Horse owners should have a basic understanding of equine joint structure and function, as well as common joint conditions in horses, so they are equipped to make appropriate management and medical decisions when problems arise.

Equine Joint Anatomy

Joints are complex structures where two or more bones meet, enabling movement and providing stability. Each joint has its own blood supply, nerves, and is supported by muscles, which contribute to its stability. ^[1]

Connective tissue plays a critical role in the function and structure of joints. Various types of connective tissue, such as tendons, ligaments, cartilage, and the joint capsule, work together to ensure the functions smoothly and remains stable under the strain of movement and weight-bearing activities.

Proper joint function is essential for a horse’s performance and overall well-being. To better understand joint health, horse owners and caretakers should familiarize themselves with key anatomical terms related to joints. ^[2]^[3]^[4]

Bursa: Small fluid-filled sac between a tendon and a bone that serves to reduce friction around the joint.
Tendon sheath: Connective tissue sac that is similar in structure to a bursa, but smaller. Surrounds a muscle tendon at places where the tendon crosses the joint and contains lubricating fluid to allow for smooth motion.
Joint capsule: Sac-like envelope that forms a sleeve around a synovial joint, enclosing its cavity. The joint capsule provides stability to the joint surface. It is also a significant source of nerve endings that play a role in joint pain.
Articular cartilage: Smooth covering of the joint which allows for ease of movement and mobility. Articular cartilage also prevents damage of underlying bone tissue.
Synovium/Synovial membrane: The 1-3 cell thick lining of the joint capsule that covers all joint surfaces except articular cartilage. This is where synovial fluid is made.
Synovial fluid: Thick fluid secreted by the synovial membrane and found in the joint cavity (space between bones) that lubricates joints and reduces friction. Synovial fluid also provides nourishment to articular cartilage since blood vessels are not present in that area.
Hyaline cartilage: Translucent cartilage found on many joint surfaces.
Ligaments: Strong bands of connective tissue that hold bones together in a joint. Some ligaments also keep organs in place.
Tendons: Strong, flexible bands of tissue that connect muscle to bone.
Fibrocartilage: A type of transitional tissue that is a blend between hyaline cartilage and dense fibrous connective tissue. Mainly found in the discs of the spine and at the insertion of ligaments and tendons.

Types of Equine Joints

Horses have several types of joints in their bodies, each featuring different types of connective tissue and allowing for varying degrees of movement, or in some cases, none at all.

Types of joints include fibrous, cartilaginous and synovial joints.

Fibrous

Fibrous joints are fixed joints where fibrous connective tissue holds two bones together. They are usually immovable and do not contain a joint cavity.

Fibrous joints can be further classified into the following sub-types: ^[1]

Sutures: Joints found only in the cranium (skull). Sutures are slightly mobile at birth to allow the fetal head to pass through the birth canal and remain open until the brain reaches full size. After that, sutures fuse and become immobile.
Gomphoses: Immobile joints found between teeth and their sockets in mandible and maxillae (jaw bones).
Syndesmoses: Slightly movable joints which maintain union between long bones including the humerus, radius, third metacarpal bone, femur, tibia, and third metatarsal bone.

Cartilaginous

Cartilaginous joints are slightly moveable or immovable and are united by fibrocartilage, hyaline cartilage, or both. Cartilaginous joints are further classified as either primary or secondary, depending on the type of cartilage that is involved. ^[1]

Primary cartilaginous joints, also known as synchondroses, are joints that contain only hyaline cartilage and can be either temporary or permanent. A temporary example is the growth plate, which enables bone lengthening during development. In contrast, permanent synchondroses retain their hyaline cartilage and do not ossify; an example can be found in the joints between the ribs. ^[1]

Secondary cartilaginous joints, called symphyses, are composed of thick and strong fibrocartilage. Examples of symphyses include the pubic symphysis in females and the intervertebral discs between the vertebrae. These joints provide both stability and flexibility. ^[1]

Synovial

Synovial joints are the most common type of joint in the horse’s body and the most prone to injury or disease. ^[1]

Synovial joints are made up of two bone ends covered by articular cartilage, which allows for smooth movement. Their defining feature is the presence of a joint cavity, which is surrounded by an articular capsule. This capsule is lined by a thin synovial membrane, whose cells secrete synovial fluid to lubricate the joint and reduce friction during movement. ^[2]

The bones in a synovial joint are connected by ligaments, which can be classified as extrinsic or intrinsic. ^[2]

Extrinsic are located outside the articular capsule.
Intrinsic are fused to or incorporated into the wall of the articular capsule.

These ligaments help stabilize the joint and control its range of motion.

Most synovial joints also receive additional support from muscles and tendons that work across the joint to enhance stability and movement.

Some synovial joints feature a fibrocartilage structure between the articulating bones, either in the form of articular discs, which are small and oval-shaped, or a meniscus, which is larger and C-shaped. These structures help improve joint stability and shock absorption.^[2]

The extent of movement in synovial joints varies, and the different subtypes are based on the types of movements they allow. These include: ^[1]^[2]

Hinge joints: Formed where a convex end of one bone meets the concave end of another, allowing movement along a single axis. Examples include fetlock joints.
Planar joints: Involve two flat bones of similar size, permitting gliding motion in multiple directions. Examples include inter-carpal (knee) and inter-tarsal (hock) joints.
Pivot joints: Feature a rounded portion of a bone enclosed by another bone and ligament, allowing rotational movement around one axis. Examples include the atlantoaxial joint between the first and second cervical vertebrae.
Ball-and-Socket joints: Consist of a rounded bone head (ball) fitting into a concave part (socket), enabling movement in multiple directions, including flexion, extension, abduction, adduction, and rotation. Examples include the horse’s hip and shoulder joints.

Equine Limb Joints

The joints in a horse’s limbs are particularly susceptible to injury or disease, often leading to lameness. This is because the limbs endure significant strain, especially in horses involved in work or competition. ^[3]

Understanding the structure and function of these limb joints is crucial for owners and caretakers to make informed decisions when addressing lameness or other performance-related concerns.

Fetlock

The fetlock joint is where the cannon bone, proximal sesamoid bones, and first phalanx (long pastern bones) meet. It is present in both the forelimbs and hind limbs of the horse. ^[5]

The fetlock joint serves as a shock absorber and plays a key role in the horse’s ability to walk, trot, and gallop. It allows flexion and extension in the lower limb, bearing significant weight and impact during movement, particularly in performance horses.

Of all the horse’s joints, the fetlock is most prone to injury. ^[3]

Carpal (Knee)

The carpus, commonly referred to as the knee, is located on the forelimbs and consists of three distinct joints: ^[6]

Antebrachiocarpal (Radiocarpal) Joint: This joint connects the forearm bones (radius and ulna) to the first row of carpal (wrist) bones. It has a high range of motion, allowing significant flexion and extension, which is essential for the horse’s ability to bend and move the foreleg.
Intercarpal (Middle Carpal) Joint: Located between the two rows of carpal bones, this joint also allows a high degree of movement. It contributes to the overall flexibility and motion of the knee, enabling the horse to navigate various terrains and perform maneuvers.
Carpometacarpal Joint: This joint connects the second row of carpal bones to the metacarpal bones (cannon bone) and has a low range of motion. Its primary role is to provide stability rather than movement, supporting the structure of the lower limb during weight-bearing activities.

Together, these carpal joints allow the forelimb to flex and extend, helping the horse move its front legs smoothly. They contribute to mobility and stability, enabling quick directional changes and controlled landings during jumping.

Shoulder (Humeral)

The shoulder joint is one of the largest joints in the horse’s body, where the scapula and humerus meet. Located above the forelimbs, it provides a wide range of motion, enabling the horse to swing its foreleg forward. ^[4]

This joint is vital for stride length and overall fluidity of movement, especially in activities requiring agility and speed.

Elbow

The elbow joint connects the humerus, ulna, and radius in the foreleg. This joint plays an important role in the horse’s ability to flex and extend its forelimbs during movement. It stabilizes the leg during weight-bearing and aids in propulsion. ^[4]

Tarsal (Hock)

The tarsal joint, or hock, is made up of four joints that allow varying degrees of movement, similar to the carpal joints in the forelimbs. These include: ^[6]

Tibiotarsal joint: The largest joint of the hock where all movement occurs
Proximal intertarsal joint: Allows for low motion
Distal intertarsal joint: Allows for low motion
Tarsometatarsal joint: Allows for low motion

The hock joint is crucial for generating power and propulsion in the hind limbs. It acts like a lever during movement, enabling the horse to push off the ground, which is essential for galloping and jumping.

Stifle

The stifle joint functions similarly to the human knee, playing a major role in supporting the horse’s weight and aiding in flexion and extension of the hind limbs. It provides stability during movement and is vital for actions such as walking, running, and jumping.

The stifle is the largest joint in a horse’s body, consisting of the femorotibial and femoropatellar joints. ^[7]

Sacroiliac

The sacroiliac (SI) joint connects the pelvis (ilium) to the spine, transferring the force generated by the hind limbs to the rest of the body. Although it has minimal movement, it stabilizes the horse’s back and plays a key role in balance and coordination, especially during high-intensity activities like jumping or racing. ^[8]^[9]

The surrounding soft tissues are prone to strain or injury, which can cause low-grade lameness or reduced performance in horses. Issues with this joint are increasingly recognized as contributing to performance problems in sport horses. ^[8]^[9]

Common Joint Problems in Horses

Joint problems are one of the most common reasons for loss of performance in horses. In addition to the cost of managing equine joint disease, these issues can also become a welfare concern for some horses. ^[10]

Several factors contribute to joint injury and disease in horses, including:

Age (wear and tear)
Concussive stress
Repetitive strain
Fitness level
Body condition

Common joint conditions in horses include:

Arthritis
Bursitis
Osteochondrosis

Proper management and early intervention are essential to maintaining joint health and minimizing the impact on a horse’s performance and well-being.

Arthritis

Arthritis commonly affects equine synovial joints. This condition describes inflammation of the joint, which results in pain, stiffness, and reduced mobility.

Arthritis may arise for any of the following reasons: ^[2]

Aging
Damage to articular cartilage
Autoimmune disease
Bacterial infections
Viral infections
Unknown causes

There are more than 100 different forms of arthritis that can affect horses. However, osteoarthritis (also known as degenerative joint disease) is most common in horses. This condition often develops due to injury or as part of the normal aging process. Overweight and obese horses are also prone to osteoarthritis. ^[1]^[2]

Arthritis causes the articular cartilage to thin, triggering pain in surrounding tissues. As the cartilage wears down, the bones in the joint are exposed to more pressure, leading to an increased production of synovial fluid. ^[1]^[2]

As osteoarthritis progresses, the bone tissue beneath the damaged articular cartilage becomes thickened and irregular, making movement painful. In the early stages, mild activity that “warms up” the joint can help reduce symptoms, but pain and stiffness often worsen after exercise. ^[2]

In advanced cases, affected joints may be difficult to use effectively, leading to decreased mobility and exercise intolerance. There is no cure for osteoarthritis, but treatment such as management changes, weight loss, and low-impact exercise may help reduce pain and inflammation. ^[2]

Bursitis

Bursitis involves inflammation of the bursa near a joint. This condition causes pain, swelling, localized heat, and tenderness of the bursa and surrounding area. It may also lead to joint stiffness. ^[2]^[11]

Bursitis in horses can be caused by overuse, trauma to a joint, or sepsis (infection). The condition can be further classified as: ^[11]

True bursitis: Inflammation in a naturally occurring bursa such as trochanteric (hip) bursitis, supraspinous bursitis (fistulous withers), and bicipital (elbow) bursitis.
Acquired bursitis: Development and inflammation of a subcutaneous bursa where one was not previously present. Fluid accumulates with acquired bursitis and is known as hygroma. Examples of acquired bursitis include capped elbow and capped hock.

Bursitis may also be chronic or acute. These are differentiated as: ^[11]

Chronic bursitis: Can develop due to repeated trauma, fibrosis, and other chronic changes. Excess fluid accumulates and the bursal wall becomes thickened by fibrous tissue. Treating chronic bursitis in horses may require surgery. If infection is present, systemic antimicrobials are needed.
Acute bursitis: Usually develops from trauma or infection. This form of bursitis can be treated with rest, bandaging, ice/cold packs, needle aspiration of bursal contents, and injection of medication.

Septic bursitis may occur secondary to infectious osteitis of the hock or after a penetrating injury. This is a serious condition that is associated with pain and lameness and needs immediate veterinary care. ^[11]^[12]

It is usually treated with surgical debridement (removal of dead or infected tissue) and lavage as well as appropriate antibiotic therapy. ^[11]^[12]

Osteochondrosis

Also known as osteochondrosis dissecans (OCD), this equine developmental disorder is a condition where pieces of cartilage and/or bone break off into or near a joint. OCD causes joint effusion (fluid accumulation) and slight lameness. It often affects young horses in heavy work, and most commonly develops during the first year of the horse’s life. ^[6]

Osteochondrosis commonly affects the hock joint, leading to effusion or fluid buildup in the hock, known as bog spavin. It is often bilateral, meaning it affects both hocks. ^[6]

Bone fragments may be visible on diagnostic imaging and can be removed surgically. Affected horses usually have a very good prognosis. ^[6]

Synovitis

Synovitis describes inflammation of the joint capsule itself and can occur secondarily to other joint disease, including: ^[13]

Osteochondrosis
Osteoarthritis
Trauma
Poor conformation
Hemarthrosis (articular bleeding)
Synovial infection

Synovitis can be acute or chronic and results in distention (swelling) of the joint capsule. It may or may not cause lameness. ^[13]

Draining synovial fluid and medicating the joint with intra-articular corticosteroids may be helpful. Pressure bandages and stall rest can also help to reduce symptoms. Intra-articular injection of atropine may be used as treatment in some cases. ^[13]

If you suspect your horse is affected by a joint condition, consult your veterinarian for an accurate diagnosis and treatment plan.

Joint Health & Nutrition

You can support your horse’s joint health by maintaining them at a healthy weight, providing adequate turnout, ensuring regular farrier care, and following a gradual exercise program to improve fitness and conditioning.

Allow enough rest and recovery time after heavy exercise or injury to prevent long-term joint damage. Frequently check for early signs of joint pain, like stiffness, swelling, or reluctance to move, and seek veterinary care promptly.

Nutrition also plays a key role in supporting mobility and maintaining healthy connective tissue. Ensure your horse receives a balanced diet with adequate levels of key nutrients, such as vitamins, minerals and amino acids.

Deficiencies in these nutrients can lead to oxidative damage, poor tissue repair, and weakened connective tissues, making your horse more vulnerable to injury and joint issues. Feeding a complete vitamin and mineral supplement, such as Mad Barn’s Omneity® will help ensure your horse’s diet is properly balanced and supports overall joint health.

You can also consider research-backed equine joint supplements that include the following ingredients:

MSM (Methylsulfonylmethane): A natural sulfur-containing compound, MSM helps regulate inflammation and supports the repair of connective tissue.
Hyaluronic Acid: Found naturally in the synovial fluid of joints, it helps lubricate and cushion joints, improving mobility and reducing friction in the joint.
Omega-3 Fatty Acids: Omega-3’s such as DHA and EPA support the normal homeostatic regulation of inflammation and support overall joint health, especially in horses with joint concerns.

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Summary

Horses are prone to joint injury and degeneration due to high-impact exercise and natural wear and tear due to aging. Since the horse’s limbs endure significant stress, the limb joints are the most vulnerable to injury and disease.

Understanding equine joint anatomy and function can help owners prevent and manage common joint issues.
Horses have various types of joints, each allowing for different ranges of motion depending on their structure.
The most common joint conditions in horses include arthritis, bursitis, and osteochondrosis.
A balanced diet supports joint health at every life stage.