Source: Clyde Vet Group
The annular ligament (AL) is a part of a horse’s anatomy that encircles and stabilizes the tendons in the fetlock area, which is the joint between the horse’s cannon bone and the pastern.
This ligament plays a critical role in supporting the fetlock joint, especially during movement, by preventing excessive splaying of the tendons around the joint, thus ensuring smooth and coordinated motion.
Certain breeds struggle with this injury more than others. For instance, the breeds Paso Fino, Warmbloods, and Native Ponies (e.g. Dales pony, Dartmoor pony, and Welsh Mountain pony) are just some breeds that can suffer from annular ligament injuries.
Trauma to the annular ligament may lead to acute inflammation and pain, but usually, the onset is more chronic, over weeks and months. Bearing this in mind, preventative measures can be taken to prevent a full-blown injury.
In this article, we will examine the anatomical structures involved in this injury, the causes, and supportive therapy to prevent this injury from occurring.
The anatomical structures involved in an annular ligament injury
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An annular ligament injury involves an interplay of structures within the equine limb, particularly those associated with the fetlock joint. Understanding how these structures relate to one another provides the pathway for understanding the injury and how to prevent it.
Flexor tendons
Flexor tendons in a horse’s limb, including the superficial flexor tendon, accessory ligaments of the flexor tendon, and deep digital flexor tendons, play a critical role in flexing the digit and supporting the horse’s weight during movement. These tendons run along the back of the leg, passing through the fetlock and into the hoof.
Superficial Digital Flexor Tendon
This tendon extends down the back of the leg and is critical for flexing the fetlock, pastern, and coffin joints. The inferior check ligament helps to support the deep flexor tendon. Injuries to these structures can increase the load on the annular ligament, leading to a potential injury.
Digital Flexor Tendon Sheath
The digital flexor tendon sheath surrounds the flexor tendons near the fetlock and pastern. Chronic inflammation of the DFTS due to infectious or non-infectious tenosynovitis leads to effusion of the sheath and fibrosis and thickening of the DFTS capsule, including the AL.
Furthermore, tendon sheath sepsis is a complication from DFTS and AL injury that can be life-threatening and needs urgent medical attention.
Commonly injured collateral ligaments
Collateral ligaments provide lateral (side-by-side) stability to joints. While not directly related to annular ligament injuries, damage to collateral ligaments can impact joint stability and affect the overall health of the limb, potentially influencing the treatment and management of annular ligament injuries.
Suspensory ligament injury
The suspensory ligament injury supports the fetlock joint by preventing excessive extension – a leading cause of annular ligament injury. Any injuries to this ligament weaken the surrounding ligaments and tendons setting up an environment for further injury.
Palmar/Plantar Annular Ligament
The terms plantar annular ligament (hindlimb) and palmar annular ligament (forelimb) refer to the same structure, indicating its location. This ligament encircles the tendons at the back of the fetlock, playing a critical role in stabilizing these tendons. Injuries or inflammation in this area can cause or contribute to annular ligament constriction syndrome (ALCS).
Annular ligament constriction syndrome or annular ligament syndrome as it’s commonly known is a condition characterized by tightening or constriction of the AL, around the tendons at the back of the fetlock joint. This develops when the AL becomes too tight due to inflammation and swelling. This restricts the movement within the tendon sheath, particularly the superficial and deep digital flexor tendons, leading to increased pressure and friction.
Cruciate Ligaments
These ligaments are primarily associated with the knee joint, however, they play a role in overall joint stability and any weaknesses in the surrounding structures will place pressure on the annular ligament.
The primary role and importance of the annular ligament
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The primary role of the annular ligament is to stabilize the tendons that pass over the fetlock joint, preventing them from bowing outwards during movement. This stabilizing function is essential for several reasons:
Tendon alignment
By maintaining the proper alignment of the tendons, the AL ensures efficient force transmission from the muscles in the horse’s lower limb to the hoof, facilitating smooth movement.
Joint support
The ligament supports the fetlock joint by limiting excessive movement that could lead to joint instability or injury.
Shock Absorption
During high-impact activities like show jumping and galloping, the AL contributes to the shock-absorbing capacity of the fetlock, protecting both the joint and the tendons from injury.
The causes of annular ligament injury
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Now that you’ve received a better understanding of the anatomy involved in this injury and the importance of the AL, let’s examine how this ligament can sustain injury.
AL injuries are more commonly associated with activities that place stress on the fetlock joint. These activities can vary but often the reason lies with competitive sports and training exercises.
Jumping
In disciplines such as showjumping, eventing, and fox hunting where horses are required to clear obstacles of various heights and widths, the act of jumping puts strain on the fetlock joint. As the horse launches and lands, the AL supports the fetlock, but any injury to the fetlock joint can put pressure on the AL causing it to bulk.
Dressage
Less strenuous than show jumping or eventing, dressage still puts strain on the lower limbs due to the level of precision movements required. Sharp turns, launches, and sudden stops create an environment for strains, tears, and tendon sheath damage which in turn affects the AL.
Racing
Thoroughbred and standardbred racing involve high-speed galloping, which generates a significant force across the fetlock joint and puts increased pressure on the AL.
Repetitive exercise or overexercise
Repetitive movements over and over can cause micro-trauma to the AL. On its own, this would not present a major problem, however, overexercise doesn’t just cause small injuries to the AL, but also affects the tendons and fetlock joint. Together, these biostructures suffer more wear and tear than necessary and therefore begin to suffer from excessive friction and force. This leads to inflammation and swelling in any one of these areas, weakening the structures of the lower limb.
This is a common problem faced by horses who compete in showjumping, racing, dressage, or any other activity that requires a great deal of practice. One supportive therapy for combating this problem comes from Chemipower and Tartu University. Recognizing the need for an effective aid to help horses recover from high-impact exercises, they developed a carnosine-based gel, called Carnogel that supports muscle, tendon, and ligament health whilst preventing the adverse effects of muscle fatigue, such as inflammation.
How to prevent annular ligament injury
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While is it impossible to eliminate these injuries, there are several measures you can take to minimize them. Here we discuss six practical actions that will help you minimize injuries.
Proper conditioning and training
A well-designed conditioning program is essential for building the strength and flexibility needed to prevent AL injuries.
Slowly introduce intensity and frequency of exercise and ensure that the horse does appropriate warming exercises beforehand. Incorporate a variety of training exercises that will evenly develop different muscle groups, giving the tendons and ligaments a chance to adapt and recover from training.
Strength-building exercises will improve joint stability as well as tendon and ligament resilience. This is what you need to keep your horse from suffering AL injuries.
Supportive therapy
Using a carnosine-based gel that is specifically developed to increase the health of the muscle, tendons, and ligaments alongside other preventative measures, will provide all-round protection against AL injury.
Carnosine is a naturally occurring amino acid compound found in the muscles of horses that actively combats inflammation and acts as an antioxidant. It also reduces the destructive side effects of the byproducts of strenuous exercise, allowing your horse’s muscles to recover from exercise faster.
Using the gel before and after exercise will provide a protective mechanism against AL injury because it will strengthen the muscles, tendons, and ligaments.
Buy CarnoGel as a supportive therapy for muscle, tendon, and ligament health.
Appropriate footwear
The proper footwear acts as a protective mechanism against injury. Just like a human runner needs the correct footwear for running long distances and/or interval training, so too a horse must have anti-injury footwear.
Ensure that the footwear or protective gear is properly fitted according to the size of the hoof. Shock absorbent pads should be correctly fitted to ensure an even surface when the horse lands on their feet. Also, different surfaces require the appropriate footwear and this can make a huge difference to the health of your horse’s limbs.
Regular veterinary check-ups
Not only are veterinary check-ups essential but your assessments of your horse’s health and physical condition act as early preventative measures.
Routine evaluations help you to spot early signs of stress and strain on ligaments. Inspect your horse’s limbs as often as you can and look for signs of swelling, restlessness, and favoring one limb over another.
Veterinary exams will include evaluations of limb conformation, gait analysis, and palpation of the legs and joints.
Safe environment
Keep paddocks and turnout areas free from hazards that could cause injury. Regularly inspect fences, gates, and ground surfaces for potential risks.
Training and competing on surfaces that are not too hard, deep, or uneven can significantly reduce the stress on the annular ligament. Regular maintenance of riding surfaces to keep them level and shock-absorbent is essential.
Nutrition
A balanced diet supports overall health and the strength of connective tissue. Omega 3 fatty acids, amino acids, vitamin C, glucosamine, and chondroitin are all helpful for maintaining joint, tendon, and ligament health. [1]
Concluding words
Annular ligament injuries in horses present a significant challenge to their health, performance, and well-being. As we have explored, these injuries are not only a result of acute trauma but often develop over time due to repetitive strain on the fetlock joint.
Understanding the intricate anatomy involved, from the annular ligament itself to the supporting tendons and ligaments, provides a foundation for effective prevention and management strategies.
Proper conditioning, supportive therapies like the use of a carnosine-based gel, appropriate footwear, regular veterinary check-ups, a safe environment, and balanced nutrition form a comprehensive approach to safeguarding the health of these magnificent animals.
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