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The anatomy of horse legs joints is complex. Formed from multiple different structures, each joint in horses’ legs are unique, which aids optimal function during performance. In the forelimb and hindlimb, the joints differ in form and function. As riders, it is vital to understand the structure of joints in order to enhance quality of movement and comfort.
Joints allow the musculoskeletal system to move efficiently through different ranges of motion. The horse’s legs are made up of a type of joint called synovial joints, which are the only type of joint which allows large movement patterns.
Synovial joints consist of the end of two long bones, covered in a smooth, lubricating tissue, called articular cartilage. To keep the joint stable through movement, it is contained within a fibrous capsule, called the joint capsule.
The joint capsule, although having a tough exterior, has a thin inner lining too. The thin inner lining contains additional lubrication and reduces friction in motion. This lubrication is called synovial fluid. The fluid is packed with naturally occurring ingredients such as hyaluronic acid and hyaluronate to maintain joint hydration, further preventing friction during movement. Feeding ingredients such as hyaluronic acid and glucosamine HCL can be key in topping up levels of these naturally occurring synovial fluid components, especially through periods of hard or increasing workload.
Ligaments connect bone to bone to further support joint integrity. Meanwhile, tendons insert into bone from muscles, with muscle contraction facilitating movement of joints.
The shoulder joint located in the forelimb of the horse. At the shoulder, the joint attaches the scapula to the humerus. This joint has limited movement, unlike the human’s shoulder joint, only moving in flexion and extension. The horse's shoulder facilitates propulsion of the entire forelimb and is a major generator of power in the stride.
The carpal joint is more commonly referred to as the horse’s knee joint and is located in the forelimb.
The carpus joint is one of the most complex joints in the horse’s leg, made of three smaller joints and nine bones. The carpus is made up of the radiocarpal, intercarpal and carpometacarpal joints. Meanwhile, nine smaller bones sit in two rows, with the longer bones of the radius and cannon bone sitting above and below, respectively. These bones are held together by a series of ligaments and assist in shock-absorption up the limb.
The stifle joint is located in the hindlimb of the horse, and despite its location, is considered as the equivalent of a human’s knee. It is made up of the femur, tibia and patella bones and works to move the hind leg up and forward. Its action makes it critically in hindlimb propulsion. There are also unique soft tissue structures in the stifle, similar to humans, called menisci. Menisci acts as shock absorbers, as well as reducing friction between joint surfaces.
The hock joint is also exclusive to the hindlimb of the horse, sitting between the tibia and tarsal bones. The hock is also known as the tarsal joint and is likened to the ankle in humans.
The hock is actually made up of four joints, three of which function to absorb impact and have low range of motion. Like the forelimb’s carpus joint, it also has two rows of smaller bones, however with the tibia and metatarsal bones sitting above and below respectively.
The fetlock joint is located on all four limbs. It allows flexion and extension movements and is a vital shock absorber, energy storage system, and stabiliser for the limbs. Multiple tendons from muscles in the leg insert into or close by to the fetlock, giving it it’s powerful function. However, due to its exposed site and not having many structures to absorb impact from the ground, it can be a common site for injury.
The pastern joint consists of the proximal phalanx and middle phalanx bone, and is located just below the fetlock in all four limbs. This joint has limited movement but is still vital in locomotion. It can only move in flexion and extension. However, it aids in shock absorption and influences propulsion in the stride.