Keeping the structure and function of tendons and ligaments healthy is vital for the comfort of the horse's mobility.
Horse and human alike, tendons and ligaments are tough, strong bands of soft connective tissue – collagen-rich materials that hold various body structures together.
Tendons usually connect muscles to bones; ligaments typically connect bones to other bones. Like other connective tissues, they consist of three elements: cells, fibres (primarily collagen and elastin), and extracellular matrix. Tendon and ligament injuries are important causes of lameness, and rehabilitating these injuries is an expensive and time-consuming affair associated with variable success rates, mainly due to the tendency for injury to reoccur.
In the equine stifle, for example, there are three bones - the femur, patella, and tibia. Would you believe that 14 ligaments stabilise these three bones, including the important cranial and caudal cruciate ligaments, and medial and lateral collateral ligaments. The strong, cord-like tendons connect the large muscle groups responsible for flexing and extending the stifle joint (the quadriceps and hamstring muscles) to various bones in the limb, such as the tibia.
What they're made of
Sorry, science-y. Tendons and ligaments are strong bands of tissue with similar (macro and micro) structures. The cells in these structures are responsible for producing the fibres and extracellular matrix found in these highly specialised connective tissues, and they're also responsible for adapting them to meet the athletic demands and needs of the horse.
Now we get to collagen, without doubt the most important protein of the connective tissues. Collagen is a special type of strong, structural protein that provides support throughout the entire body, and helps form, amongst other tissues, bones, connective tissues, cartilage, skin and joints. It's thread-like, or stringy by temperament and constitutes a whopping 25-30% of the entire protein content in the body.
Collagen possesses immense firmness and is the most important constituent of ligaments and tendons. However, as we age, so levels of collagen diminish. Literally speaking, the absence of collagen can lead the body to disintegrate.
There are several types of collagen, with the fibres in tendons and ligaments primarily Type I collagen fibres. Individual collagen fibres combine and link together to form microfibres, then fibrils, then fascicles. Several of these fascicles ultimately form a tendon or ligament, which is then encased in a thin sheath.
Small amounts of elastin are also found in tendons and ligaments, and as its name implies, elastin gives connective tissues their elastic properties.
How they work
The primary function of ligaments is to stabilise the joints, with the main purpose of a tendon being to transmit the force to allow joint movement, created by muscles, to bone.
The collagen fibres play an essential role in the proper functioning of both tendons and ligaments – they’re crimp shape, so when the tendon or ligament is loaded during motion, the collagen fibres stretch out, as in un-crimp, to absorb the load. If the load is too high, or if there's been micro-trauma on micro-trauma over time, the collagen fibres will overstretch, the bonds and links between adjacent collagen molecules collapse, and injury occurs.
In horses, the majority of tendon injuries (97-99%) occur to the forelimb tendons, with the superficial digital flexor tendon (SDFT) injured in over 75% of cases, although if you've had a navicular diagnosis with severe lameness, the DDFT (deep digital flexor tendon) is usually affected - it's this injury that usually leads people to transitioning their horses barefoot. The remaining injuries tend to occur to the suspensory ligament.
When things go wrong
Once a tendon or ligament is injured, there is an inflammatory reaction manifested by heat, pain, and usually significant swelling. Local blood vessels constrict and cytokines (inflammatory mediators) are released in the injured area, which break down the damaged collagen fibres, resulting in a hole in the tendon or ligament.
Scar tissue is then slowly produced to fill in the defect; however, the new tissue is not identical to the original tendon matrix tissue. Instead, the scar tissue is dis-organised, has a higher proportion of Type III collagen than normal tendons or ligaments, and limits fibre and fascicle movement.
The extracellular matrix in the area of the injury is also less organised than in a normal, healthy tendon or ligament, and it possesses different biomechanical properties. As a result, healed tendons and ligaments are less elastic than healthy connective tissues, making them prone to re-injury, and are extremely frustrating to manage due to this risk - horse and human, and I speak from personal experience, both horse and flipping human as in me!
Therapies for injuries
We've probably all heard of the many therapies for soft-tissue injuries, everything from box rest to magnetic field application (I'm a big fan of this); shock wave therapy and most likely non-steroidal anti-inflammatory drugs (NSAIDs). Major surgical procedures include tendon splitting (perforating the affected area with a tendon knife through a skin incision), to neurectomy (removing a short length of a specific nerve in the affected area), to tendoscopy (scoping and flushing a tendon).
Unfortunately, not all of these therapies have been proved to be successful, with many questionable, and some potentially harmful. None appear any more or less effective than another for returning horses to athletic function without re-injury.
So, what to do
The first step is probably obvious: rest the injury, apply cold therapy to reduce the inflammation, and call the vet. It's then all about the long haul of repairing the injury and restoring comfortable movement.
This type of injury can result in haemorrhage and delivery of inflammatory cells, so reducing the initial influx of blood and fluid is really important. Hence, initial therapy is two-fold - cold-therapy to reduce the inflammation, then heat to get healthy blood flowing through the injurious site again to begin repair.
So, cold therapy first - intermittent application of ice baths and/or cold hosing for 24-48 hours after the injury will limit the amount of potentially injurious cells to the tendon lesion site. Then we need to warm the local tissues to encourage a healthy blood flow back into the site and deliver the much-needed components for the repair, as well as draining/detoxing the cellular debris away from the affected area.
Maintaining regrowth of collagen and tissue formation is hugely important. Vit.C’s primary role is in the manufacture of collagen, with rosehips being one of the best natural sources of Vitamin C, reportedly 60 times more than citrus fruit.
Collagen fibres also have large amounts of two amino acids, hydroxylysine and hydroxyproline, both of which can be found in linseed. These two amino acids are important for formation of all types of collagen and are needed to provide the different collagen types with their appropriate amount of strength and flexibility.
Several studies have also shown that linseed supports connective joint tissue, and also helps support comfort of injured joints.Sulphur and omega-3 fatty acids are also all important to collagen production, with calendula and garlic both high in sulphur (remember, feed the whole garlic cloves, crushed - not the dried stuff which has the natural bioactive dried out of it). Linseed, again, proves invaluable as it contains the omegas in balanced ratios.
Vitamin E is also very useful for cell and connective tissue regrowth - this is found in abundance in fresh, growing grass, but during the winter months it depletes so needs to be supplemented, with the UK feed recommendation at 2000iu/day. With free radical damage to the cellular framework and injury being alleviated by antioxidants like Vitamins A, C and E, Vitamin E will also prove useful for helping to lessen scar tissue formation and scarring of the internal tissues.Silica deficiency is also known to result in peripheral bone deformities, poorly formed joints, and reduced contents of cartilage and collagen, so nutritional supplements containing silica are also considered useful.
My 2-penneth-worth of humble opinion
Box rest is the vet solution. However, I am of the school that goes with the saying, ‘Rest the injury, not the horse.’ Here's why.
I've had my share of tendon/ligament injuries over the years as we all have, but back in 2013 I ruptured my Achilles Tendon. Not fun. Apart from being completely debilitating, not to mention seriously painful, I also found that if I sat and rested the injury, as instructed, my whole body seized up, pins and needles set in, and I could barely put my leg down, let alone my foot. I felt as if I'd aged 50 years, and as an added non-benefit, my limited movement added very unwelcome kilos to my midriff. Not easy when you've got horses, sheep, dogs, cats, chickens, and a family et-al to care for.
So, presented with a no-choice scenario, I decided to treat myself like I would a horse, as in slow, gentle, careful movement. My blood flowed, pins and needles stopped, and I was able to shuffle reasonably comfortably. It was only when I sat down that the spasms hit, which were breath-stoppingly painful. Movement, for me, was key.
Back to the horse and yes, we know the injury has to be rested, but no movement is more detrimental to a healthy recovery, reason being that what fixes injuries such as these is a healthy, stimulated, nutrient-rich, healing blood supply getting to the damaged site, and what creates a healthy circulation is - movement. Plus – for a horse, being encapsulated in a small stable is so desperately un-natural for a horse's well-being (sitting still on the sofa drove me nuts), plus it means that the only movement stabled horses can do is small, sharp turns which force the joint to pivot sharply (otherwise they collide with the stable wall), which puts enormous strain on the injurious site and potentially risks re-damaging it and prolonging the lameness. To me, box rest is like a ripple effect coming off a 2-pronged BBQ fork, with the fork handle representing Box Rest:
- Fork Prong 1 - Restriction of Movement - leads to sluggish circulation, leads to blocked lymphatic system, leads to Puffy Leg syndrome (can also lead to infection), leads to longer healing process.
- Fork Prong 2 - Not Allowed To Be A Horse - no equine company/no natural grazing, leads to depressed horse, leads to depressed immunity, leads to longer healing process.
Vets are conventionally trained to treat ‘symptoms’, so when an injury such as this needs fixing, the easiest thing to do - and least risky for any comeback on the vet - is to lock the horse up in a stable. For weeks on end. However, without considering the consequences, who’s getting fried on the end of the fork? One very fed-up horse, and one very worried - and frustrated - owner, having to deal with half-a-ton of depressed horse, who's either developing attitude, or worse, ongoing chronic stress.
Furthermore, horse isn’t healing. And ... let’s not forget those stomach-lurching vet bills because they keep having to come out because horse isn’t healing. A major benefit for horses with injuries such as these are regular slow, gentle in-hand walking out in straight lines with very big circular turns at the end to avoid the sharp pivot. Take them up a quiet lane with plenty of herby hedgerow to browse on - they'll really thank you for it.
Also if you’re able to, get them out into a small grassy enclosure or even a dry lot with hay where they can see their buddies, and allow them to take a few pottery steps within their comfort zone to maintain gentle movement and graze naturally to maintain sanity.
I've witnessed many horses with injuries such as these get sound all by themselves when allowed to stay being horses - our Blas for one, and in 2017 our Carmen who tore her RF DDFT. I've also had two clients tell me that they secretly followed this principal without daring to tell their vets, who were then amazed at their client's horse's swift recovery!
And as for my Achilles? Much better within 6-months, but then Stupido here decided to run a Half-Marathon . . . say no more. Finally completely healed a year later, and just as I was about to start half-marathons again, Stupido slipped on the stairs and broke my ankle with a double fracture. 10-months on I'm still wearing the compression sock ... nuff said!