In this article we look at the Sesamoid bones found within a horses hoof and investigate commonly found sesamoid injuries, why a horse may develop a Sesamoid injury and what treatments are available if they do.
Where are Sesamoid bones in a horse
Sesamoids are two little bones positioned at the back of a horses fetlock joint.
Every horse has two proximal sesamoid bones on each limb, meaning each horse has eight proximal sesamoid bones. They also have one distal sesamoid bone in each limb.
1. Proximal Sesamoid Bones
The two proximal sesamoid bones found in each limb are roughly the shape of a triangle and act as a point of insertion for the suspensory ligament. They are situated next to each other and provide stability to the suspensory apparatus.
2. Distal Sesamoid Bones
A horse also has a Distal Sesamoid Bone located in each foot which is known as a navicular bone. This is situated on the palmar aspect of the coffin joint between the second and third phalanx (coffin bone).
Navicular is a widely found condition in many horses across all disciplines and requires immediate medical attention.
The purpose of Sesamoid Bones
Their purpose is to anchor the suspensory ligaments, allowing the horses fetlocks to operate and move properly and provide weight-bearing support to the fetlock joint.
Due to their location and the amount of movement and pressure subjected to that area of a horses foot, sesamoids are extremely vulnerable to injury which can lead to pain and discomfort for the horse and be extremely complicated to treat.
Injuries to a Sesamoid Bone
In many cases where a horse has injured a sesamoid bone, it is often an injury experienced through high-speed movement. Because of this it is commonly found hoof problem in horses who lead an active lifestyle, such as sports horses and younger more energetic animals.
The injury can be a strain resulting in inflammation of the sesamoid bone and surrounding ligaments, or even a fracture of the sesamoid bone itself.
In the majority of cases the horse will show immediate signs of equine lameness.
As sesamoids are surrounded by an intricate design of ligaments, any injury to the sesamoid bone will naturally increase the likelihood of an injury to one or more of these supportive ligaments. On the other hand, if an injury occurs to one of the surrounding ligaments first this can then lead to a fracture within the sesamoid bone.
Put simply, sesamoid bones are an extremely important area of a horses anatomy to understand and particularly if caring for the wellbeing of an active or competing horse.
Sesamoid injuries in sports horses
As mentioned above, it is common for professional-level sports horses to experience sesamoid injuries.
It is widely thought to be the most common fracture within racehorses and is common in many high-paced disciplines such as barrel racing, showjumping, polo, 3-day eventing and racing.
Top-level racehorse trainers are known to have regular MRI scans carried out on their horses legs to prevent poor performance and avoid the risk of further injury. Prevention is as important as cure and having the ability to see first-hand any potential issues are of high importance to many sports horse trainers. Regular MRI scans are not as available to the majority of trainers however due to the price prohibitive nature of MRI technologies.
As with any athlete, the ongoing wellbeing and management of a sports horse is of great importance. For this reason many competing horses are kitted out with the latest and greatest products and alternative therapies aimed at supporting the horse and .
The most common sesamoid fractures in Standardbreds and Thoroughbreds are caused by overextension and often are associated with suspensory ligament damage. Many injuries occur towards the end of a race when fatigues has set in and hyperextension of the fetlock joints is greatest. This is seen across many disciplines all over the world.
Many trainers will try and reduce training on hard surfaces and provide the horse with plenty of time to rehabilitate after any active exercise.
How to diagnose a Sesamoid Bone injury
Depending on the extent of the injury, the degrees of lameness in a horse with a sesamoid injury will vary.
In more serious cases pain is visible with any degree of movement in the fetlock area. The horses ligaments will likely be operating at less than 50% of their normal flex, so mobility levels will be greatly reduced.
In some cases the horses fetlocks will be hot to touch, often a sign of an internal injury, along with swelling of the fetlock itself.
In milder cases the horse will show signs of discomfort but it can be frustrating to self-diagnose milder sesamoid injuries due to the location and inability to see inflammation, heat or swelling in the bone itself.
It’s also worth remembering; if a ligament surrounding the sesamoid has been damaged and caught early then further trauma to the sesamoid can potentially be avoided.
A sesamoid injury is a ‘medical emergency’ and thus vital to seek professional advice.
Sesamoid Bone Disorders
Although horses can experience an injury to their Sesamoid Bones the condition, if developed over a period of time, can also be classified as a disorder.
Sesamoiditis is the name given to this disorder where by the horses sesamoid bones become inflamed causing pain (and lameness) in the ball of the foot.
Sesamoiditis, as opposed to a specific injury, is usually caused by repetitive use and is a common condition found in athletic sports horses who place extreme pressures on their sesamoid bones. In particular horses who exert regular impact on their legs such as show jumpers, barrel racing horses and polo ponies are more susceptible to degenerate sesamoid issues.
Horses who are overweight are also more prone to developing Sesamoiditis.
There are two widely described forms of Sesamoiditis found in horses: Periostitis form and Osteitis form.
1. Periostitis sesamoids are a type of sesamoid inquiry which occur as a result of damage to the bone-ligaments surrounding the sesamoid bones. This can result from injuries to the palmar/plantar annular ligaments within the horses fetlock joint or the suspensory ligament branches.
2. Osteitis sesamoids occur as a secondary result of horses with arteriosclerosis, thrombosis, and local ischaemic necrosis (pronounced is-kee-mik neh-kroh-sis) - where the bone itself dies due to a lack of blood flow to the bone itself.
Diagnosing Sesamoid injuries
Veterinary diagnosis is traditionally carried out using local nerve blocks alongside detailed lameness examinations.
Ultrasounds, Radiographs, X-rays and MRI scans can be used to help diagnose the exact issue.
X-rays will determine the precise location and configuration of the fractured bone whilst ultrasounds can be used to determine the extent of any soft tissue damage, especially to the suspensory ligaments.
MRI scans, if affordable, offer a valuable insight into both the bone and soft tissues of the horse and importantly without the need for anaesthesia. With ‘standing-MRI technology’ now widely available it provides a compelling reason for horse owners to use it’s non-invasive approach.
Advancements in thermal imaging technology now provides horse owners with a relatively low cost form of technology useful in diagnosing sesamoid injuries. Thermal imaging can indicate where the exact issue is and can be a valuable tool to establish the ongoing condition of your horses sesamoid bones.
Treating Sesamoid injuries
How to best treat a sesamoid injury entirely depends on the severity of the individual case. In many cases they are fully treatable with little to no lasting effects.
Rest and rehabilitation are key, with a period of time on box rest required.
No matter the severity of the injury it is important to reduce the inflammation within the fetlock area.
Vets will likely prescribe an anti-inflammatory medication (NSAID) and advise the horse is rested and confined to their stall for up to 30 days.
Many horses with sesamoid injuries will not be ridden for several months and certainly not competing for many months to come.
Some vets will suggest intra-articular treatments of the fetlock joint often with hyaluronic acid used to reduce inflammation in the actual joint.
In severe cases an operation may be required to repair/remove the sesamoid bone or repair the ligaments. Some horses will require bars in their shoes to provide further support to the joint and ligaments.
Using tack to support your horses Sesamoid injury
With technologies improving in magnetic therapy and other alternative therapies, many horse owners now look towards less conventional methods to support their horses ongoing sesamoids by using a plethora of devices or tack, whether for preventative measures or to treat an existing injury or condition.
Traditional cold-therapy is used by many owners where simply reducing the temperature of the horses legs (and sesamoids) can lead to a reduction in inflammation. Cold therapies include regular hosing and the use of specifically developed tack products such as specially developed ice boots. Understanding when to use 'hot therapy and cold therapy' is an important factor when looking to treat any condition, including sesamoid injuries.
Advanced magnetic therapy now provides owners with a long term solution which unlike traditional magnetic therapy creates no heat - this is of significant interest when looking to treat sesamoid inflammation and can be used both within the recovery stage and as a preventative measure. 
Recovery from a Sesamoid Injury
Sesamoid injuries are treatable and if effectively managed can create no lasting effects.
Recovery periods will vary based on the severity of the injury but in many cases will be a slow and steady approach.
Your horse will require plenty of rest and limiting their ability to overexert themselves during exercise. Owners will often look to exercise their horse on soft surfaces and pay close attention to their horses weight.
Preventative measures for sesamoid injuries
Applying the approach of ‘prevention is better than cure’ is widely regarded as the best way to manage any potential sesamoid issues, particularly in an active horse.
As sesamoid injuries are common in horses moving and turning at speed, ensuring rest and recuperation between exercising is advised. Holistic therapies such as massage and reflexology are widely used to boost this recovery process.
Many injuries occur whilst the horse is fatigued so keeping the horse fit and healthy is important to helping prevent an injury. Carrying out good shoeing and regular balancing of the feet can also play an important role.
In some cases owners carry out ‘preventive-measure MRI scans’ with a view to looking at the horses bone density and reviewing any potential area of concern and addressing it before any fracture or injury occurs.
Nothing can guarantee the prevention of sesamoid injuries, but continuous care and monitoring of the horses fetlock are essential in detecting any early signs.
Conclusion
Sesamoid injuries are a common condition found in active horses and as such are a widely reported issue across many professional equestrian disciplines.
Sesamoid ‘disorders’ are caused over a period of time whereas Sesamoid ‘injuries’ occur through a specific trauma or injury.
Understanding your horse and providing them with adequate ongoing care and protection is a part of working with any horse and as sesamoid injuries are so common there are now a wide range of solutions to help your horse through their injury and as a preventative measure.