My thoughts on suspensory ligament injuries.
The suspensory apparatus which supports the fetlock joint acts like a sling preventing hyperextension and limiting palmar flexion. However, not on its own. A little-known fact which helps a conditioned barefooted horse is a well-formed back of the foot which also acts as a stopper. The digital cushion not only helps to stop ligaments and tendons from over stretching but also cushions the descent of the fetlock. The suspensory ligament is vital for support of the fetlock and along with the suspensory and stay apparatus allow the horse to rest.
The loading phase is where the suspensory apparatus which supports the fetlock joint acts like a sling to propel the horse forward. As the limb loads, the superficial digital flexor muscle creates tension and its tendon reaches full tension in the load phase. The suspensory ligament and distal sesamoidean ligaments are a passive support system to the fetlock and the suspensory ligament reaches peak strain mid-stance phase. The fetlock should also be supported by a well developed digital cushion, therefore, the fetlock should not be descending too low and hyperextending like many horses with an underdeveloped back of the foot. This is why shod jumping horses have so many suspensory ligaments injuries, they are missing their stopper!
Swelling or damage to the suspensory ligament or its branches is called suspensory desmitis. Proximal suspensory desmitis is damage to the ligament where it joins the cannon bone, this injury may cause fragmentation bone to be torn away. These sort of injuries are difficult to diagnose because they are deep and under other ligaments and sometimes made even more difficult because it's common that some of the evolutionary remnants can be muscle. It can be more common in racehorses because of failure to recognise subtle lameness. The lameness is exaggerated on softer ground and in a circle. Suspensory Body desmitis injuries are mostly found in the foreleg and at first causes intermittent lameness, it can be usually diagnosed by heat swelling and pain from touching the area. This type of injury is the most common and becomes severe if untreated because of the horse being able to function in its early stages. Prolonged swelling in this injury can cause splint bone fractures.
Suspensory ligament branch Injuries are common in athletic/sports horses, branches are more vulnerable basically because they are smaller. This injury is easily diagnosed because the swelling can be seen and is sometimes accompanied by proximal sesamoid bone fractures on the branch attachments.
Distal sesamoidean ligament Injuries are serious because they are an integral part of the stay apparatus and fundamental to the support of the fetlock. These injuries are difficult to diagnose because the swelling is deep within the tissue. They can also cause fractures to the base of the sesamoid bones.
Tendons and ligaments swell, bleed and scar when damaged and this scar tissue is rarely as strong as the original structure as it just wraps the damaged ligament, so key to healing is damage limitation and early diagnosis. The rule of thumb is the more fibres that are torn the longer it will take to heal and ultrasound can be used throughout the healing process to check and evaluate a horse's progress. Anti-inflammatory, ice and cold water can also be used to check the swelling. By nature ligament injuries are slow to heal because of the lack of blood vessels and generally take months to recover, also current treatments are unproven. The recommended rehabilitation at the moment is stall rest and hand walking which in my opinion goes against the horses healing mechanism, research is definitely needed in this area. New treatments are shock wave therapy, oxygen chambers and using stem cells of bone marrow to stimulate healing and growth.
Degenerative suspensory ligament desmitis (DSLD) I am not convinced this is a disease I have become very weary of anything that is called a disease in the equine world. This problem is not the same as in humans where it has been found to be genetic. I understand that performance horses will have injuries by the very nature of having a rider and their intense activity, however, I'm sure that these injuries would be a lot less in conditioned barefooted horses that lived in a more natural environment. The strength, structure, health and back of the foot development of these horses is far superior and would prevent a lot of injuries. I believe along with many barefoot advocates that many of these injuries are also caused by an underdeveloped back of the foot. The tendons and ligaments of the lower limb allow the fetlock joint to sink as the hoof lands in stride or after a jump, this then stores energy to allow the leg and horse to spring forward into the next stride. Nevertheless, one of the most important functions of this mechanism is performed by the digital cushion frog and lateral cartilages, which is the stop. The digital cushion not only helps to stop the ligaments and tendons from over stretching but also cushions its descent. Pete Ramey states that he has never seen a horse with a suspensory ligament injury that had good development of the back of the foot. Therefore, because most shod domestic horses have an underdeveloped inadequate digital cushion it makes them more susceptible to these type of injuries. I would imagine that there are quite a few factors involved here, but It would be more than interesting to see how many of these injuries happen to barefoot horses in comparison to shod. I'm going to take more that an educated guess and say that shoeing, diet, poor training, poor riding and unnatural boarding are major contributing factors in not only the cause but also the slow healing of these injuries as well. Finding of a study by the University of Georgia seem to contradict Pete's statement. They say that the problem is not limited to the suspensory ligament and it can be an underlying systemic disorder affecting tissues with a high content of connective tissue and been proven that it is to do with the lack of production of nitric oxide. Also, in this disorder which shows unique in its bilateral distribution and has an uncommon healing response. Where healing takes place with cartilage and not collagen so the ligament is weak and horses often breakdown. Does this prove Pete and my thinking wrong, well perhaps, however, I feel this systemic disorder maybe a dietary issue and may have a magnesium deficiency at its root? My reasoning is that magnesium is known to stimulate the production of nitric oxide. This is just me not believing in disease as much as everyone else and putting two and two together. The first thing that changes when a horse goes barefoot is its diet and maybe this is another reason why Pete has never seen a suspensory ligament injury in a horse with good back of the foot development and it's the dietary changes that also helps to sort and corrects this problem? We had a horse that had bilateral distribution, swollen fetlocks and he in his early days with us used to stamped quite a lot, he was hammered hunting even though he had this problem. He also had hip and hock issues which are not surprising and came to us to retire still lame after 3 months of physiotherapy treatment with vets advise to bar shoe him. His diet change along with our other horses and he responded very well and also later improved again with a barefoot trim. He had a great 8 years with us before his previous life before caught up with him at 26. They are an indicator of suspensory failure, but this horse coped very well with this feature and was still extremely athletic and quick he would tear around the field most days and he would jump anything if he set his mind to it. One day next doors put some hay out for their sheep and he popped a four-foot fence from a stand still.
Post legged horses like the Paso find it more difficult to round into collection than other breeds this makes them more susceptible to suspensory injuries. Where other post legged breeds such as the thoroughbred with their longer backs and being more rangy galloping horses are less prone. Any horse that is not taught to round under a rider will be more susceptible to this type of injury. Horses with DSLD issues first undergo suspensory ligament degeneration. Post leggedness can be a conformational issue but in these cases, it is more than likely that Post leggedness is a posture problem brought on by underlying systemic disorder affected tissue or the horse trying to make itself more comfortable. Coon footedness then seems to be a progression of the issue where the branches of the suspensory ligament are inelastic and do not support the fetlock joint correctly allowing the pasterns to drop.
To summarise, yes, performance horses are more susceptible to this kind of injury, however, a well-formed back of the foot would certainly reduce these injuries. As Pete Ramey points out he has never seen a suspensory injury on a horse which had good back of the foot development. Rounding and not using the hindquarters correctly is another issue that contributes. As well as diet, conformation issues such as post-leggedness, and breeding, all make a horse more vulnerable to this kind of issue. I may be wrong, but all in all DSLD, in my eyes has all the hallmarks of another made up disease and maybe a combination of individual circumstances.