Bowed tendon
Encyclopedia
Tendinitis/tendonitis is inflammation
of a tendon
. Many times, the tendon tissue is torn. A bowed tendon is a horseman's term for a tendon after a horse has sustained an injury that caused the tendon fibers to be torn, and then healed with "bowed" appearance.
When the SDFT is damaged, there is a thickening of the tendon, giving it a bowed appearance when the leg is viewed from the side. Bows usually occur in the middle of the tendon region, although they may also be seen in the upper third, right below the knee or hock (high bows), and lower third, just above the fetlock
(low bows).
For pictures of bowed tendons and the structures involved, see http://www.poolhousevets.co.uk/equine_tendon.html and http://www.horsetackreview.com/dbpix/bowedtendon-l.jpg.
Excessive strain on a tendon
can damage its collagen fibers. This is most commonly seen in performance horses that gallop or jump, who usually strain a tendon as a result of fetlock overextension when their weight is loaded on one leg. The overextension of the fetlock causes overstretching of the flexor tendons, resulting in the rupture of tendon fibers. Horses in intense training, especially those that were not conditioned properly, may damage many collagen fibers. This may occur gradually or suddenly.
After the fibers are torn, the tendon hemorrhages and collects fluid (edema
), creating swelling and lameness
in the area as well as increasing the pressure. The increase in pressure may damage the tendon
further by destroying the cross-linking of undamaged collagen fibers and preventing the flow of blood
to the area.
The SDFT
The middle third of the SDFT is most likely to suffer from tendinitis for several reasons.
The SDFT is narrower in its middle third than its top or bottom sections, making it weaker. The top and bottom of the SDFT has a better supply of blood
as well, with the top third supplied by the vessels
from the knee, and the bottom third supplied by the vessels in the fetlock. The middle third has a poor supply of blood, relying on the tiny vessels of the peritendon (the membrane that surrounds the tendons). If this supply is for some reason compromised, the collagen fibers in the area may die, weakening the tendon in that area and making it more likely to tear.
The SDFT branches at the fetlock, creating a sling under the back of the joint. Thus, overextension of the fetlock
is more likely to overstretch the SDFT than the DDFT, which simply travels straight down behind the fetlock and pastern, to attach to the coffin bone.
Other Factors
Each of these factors encourage the overextension of the fetlock
and knee during work. Several of these factors at once can add up.
Horses with bandage bows usually respond to sweats or poultices. These treatments must be applied under a bandage that is not tightly fitted and the bandage should only be left on for a few hours. Cold hosing, NSAIDs and DMSO may also help.
It is important not only to palpate the SDFT but the branches of the SDFT, the DDFT, check ligament, and suspensory ligament as well. These structures could have been damaged at the same time as the SDFT. Both legs should be checked, although tendinitis usually only occurs in one leg.
When the tendon is healed, it will still have a thickened, bowed appearance that feels firm and woody. However, all heat, lameness, and pain should disappear.
For the first several months, large area turnout is discouraged, since even a small amount of running or playing could easily re-injure the weakened tendon. As the tendon heals, it is loaded in increasing amounts. The use of diagnostic ultrasonography is extremely valuable in guiding changes in workload.
The best way to ensure that an injured horse returns to full work is to rehabilitate the animal correctly. This includes slowly bringing the horse back into training, and giving the horse light exercise each day as the tendon is healing. An impatient trainer who rushes to bring the horse back to intense training is likely to cause re-injury of the tendon.
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
of a tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
. Many times, the tendon tissue is torn. A bowed tendon is a horseman's term for a tendon after a horse has sustained an injury that caused the tendon fibers to be torn, and then healed with "bowed" appearance.
Description of a Tendinitis in Horses
Tendinitis usually involves disruption of the tendon fibers. It is most commonly seen in the superficial digital flexor tendon (SDFT) in a front leg—the tendon that runs down the back of the leg, closest to the surface. Tendinitis is uncommon in the deep digital flexor tendon (DDFT) of a front leg or either the SDFT or DDFT in a hindleg.When the SDFT is damaged, there is a thickening of the tendon, giving it a bowed appearance when the leg is viewed from the side. Bows usually occur in the middle of the tendon region, although they may also be seen in the upper third, right below the knee or hock (high bows), and lower third, just above the fetlock
Fetlock
Fetlock is the common name for the metacarpophalangeal and metatarsophalangeal joints of horses, large animals, and sometimes dogs. It is formed by the junction of the third metacarpal or metatarsal bones proximad and the proximal phalanx distad...
(low bows).
For pictures of bowed tendons and the structures involved, see http://www.poolhousevets.co.uk/equine_tendon.html and http://www.horsetackreview.com/dbpix/bowedtendon-l.jpg.
Causes and Factors of Tendinitis in Horses
Excessive StrainExcessive strain on a tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
can damage its collagen fibers. This is most commonly seen in performance horses that gallop or jump, who usually strain a tendon as a result of fetlock overextension when their weight is loaded on one leg. The overextension of the fetlock causes overstretching of the flexor tendons, resulting in the rupture of tendon fibers. Horses in intense training, especially those that were not conditioned properly, may damage many collagen fibers. This may occur gradually or suddenly.
After the fibers are torn, the tendon hemorrhages and collects fluid (edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
), creating swelling and lameness
Lameness (equine)
Lameness in horses and other equidae is a term used to refer to any number of conditions where the animal fails to travel in a regular and sound manner on all four feet...
in the area as well as increasing the pressure. The increase in pressure may damage the tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
further by destroying the cross-linking of undamaged collagen fibers and preventing the flow of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
to the area.
The SDFT
The middle third of the SDFT is most likely to suffer from tendinitis for several reasons.
The SDFT is narrower in its middle third than its top or bottom sections, making it weaker. The top and bottom of the SDFT has a better supply of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
as well, with the top third supplied by the vessels
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
from the knee, and the bottom third supplied by the vessels in the fetlock. The middle third has a poor supply of blood, relying on the tiny vessels of the peritendon (the membrane that surrounds the tendons). If this supply is for some reason compromised, the collagen fibers in the area may die, weakening the tendon in that area and making it more likely to tear.
The SDFT branches at the fetlock, creating a sling under the back of the joint. Thus, overextension of the fetlock
Fetlock
Fetlock is the common name for the metacarpophalangeal and metatarsophalangeal joints of horses, large animals, and sometimes dogs. It is formed by the junction of the third metacarpal or metatarsal bones proximad and the proximal phalanx distad...
is more likely to overstretch the SDFT than the DDFT, which simply travels straight down behind the fetlock and pastern, to attach to the coffin bone.
Other Factors
- Poor conformation: long, sloping pasterns and a long-toe, low-heel shape to the hoofHoofA hoof , plural hooves or hoofs , is the tip of a toe of an ungulate mammal, strengthened by a thick horny covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole...
(seen commonly in ThoroughbredThoroughbredThe Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed...
s) predisposes a horse to tendinitis.
- Poor trimming and shoeing: such as a farrierFarrierA farrier is a specialist in equine hoof care, including the trimming and balancing of horses' hooves and the placing of shoes on their hooves...
that causes a hoof shape that predisposed the horse to tendon injuries (such as a long-toe and low-heel), or one that shoes a horse with toe grabs, which artificially create a long-toe and low heel by lifting the toe up.
- Improper conditioning: such as working a horse at an intensity that it has not yet been conditioned for, working an unfit horse, and continuing to work an extremely fatigued horseHorseThe horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
.
- Poor footing: working a horse on uneven or slippery footing can cause tendon strain, as well as deep, “thick” footing.
Each of these factors encourage the overextension of the fetlock
Fetlock
Fetlock is the common name for the metacarpophalangeal and metatarsophalangeal joints of horses, large animals, and sometimes dogs. It is formed by the junction of the third metacarpal or metatarsal bones proximad and the proximal phalanx distad...
and knee during work. Several of these factors at once can add up.
- Direct trauma to a tendonTendonA tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
: such as when a horse hits its front leg with a hind hoof.
Bandage Bows
Bandage bows are caused by applying a bandage too tightly, creating an acute pressure injury to the tendons. The compression may cause the area to swell once the bandage is removed, giving a "bowed" appearance. However, the damage is usually just to the skin and not to the tendon itself.Horses with bandage bows usually respond to sweats or poultices. These treatments must be applied under a bandage that is not tightly fitted and the bandage should only be left on for a few hours. Cold hosing, NSAIDs and DMSO may also help.
Signs of Tendinitis in Horses
Signs of acute tendinitis include swelling, heat, and pain when the affected area is palpated. If mild, swelling may not be readily apparent, although there will still be heat and pain in the area, as well as mild lameness. If more severe, the injury is usually accompanied by moderate lameness (2-3 on a scale of 5) with obvious swelling.It is important not only to palpate the SDFT but the branches of the SDFT, the DDFT, check ligament, and suspensory ligament as well. These structures could have been damaged at the same time as the SDFT. Both legs should be checked, although tendinitis usually only occurs in one leg.
When the tendon is healed, it will still have a thickened, bowed appearance that feels firm and woody. However, all heat, lameness, and pain should disappear.
Treatment of Tendinitis in Horses
Initial treatment of a bowed tendon should concentrate on anti-inflammatory therapies, including cold water or ice therapy, and anti-inflammatory medications on the direction of a veterinarian. The horse should be confined to a small area until the severity of the injury can be assessed with ultrasound. Standing bandages are helpful, but care should be taken to avoid applying them too tightly.Controlled exercise
Generally speaking, the most important aspect of long-term therapy is controlling the level of exercise. A balance must be struck between two competing ideas:- The injured tendon is weakened, making it prone to further injury with excessive exercise.
- Tendons strengthen along lines of tension, which requires exercise.
For the first several months, large area turnout is discouraged, since even a small amount of running or playing could easily re-injure the weakened tendon. As the tendon heals, it is loaded in increasing amounts. The use of diagnostic ultrasonography is extremely valuable in guiding changes in workload.
Adjunctive therapies
Many adjunctive therapies have been attempted to improve the quality of healing or to speed the recovery process. There is no consensus in the veterinary community as to which treatments are the most effective.- A tissue regenerating bioscaffold material, being developed by TR BioSurgical, has unique properties that permits angiogenesisAngiogenesisAngiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
and produces fetal-like repair mechanisms, known to be involved in tissue turnover and repair. The new bioscaffold is currently being evaluated for a variety of connective tissue disorders in veterinary medicine. The bioscaffold structure is responsible for its non-immunogenic property and its ability to upregulate a variety of genes involved in tissue repair, as evidenced by gene microarray analysis and lead to a fetal like or regenerative tissue response. Depending on the tissue type, cells that bind to this bioscaffold will have significant, measurable increases in select tissue repair factors, including aggrecanAggrecanAggrecan also known as cartilage-specific proteoglycan core protein or chondroitin sulfate proteoglycan 1 is a protein that in humans is encoded by the ACAN gene. This gene is a member of the aggrecan/versican proteoglycan family...
, connective tissue growth factor (CTGF), transforming growth factorTransforming growth factorTransforming growth factor is used to describe two classes of polypeptide growth factors, TGFα and TGFβ....
s (TGF-β1 and TBF-β3), bone morphogenic protein (BMP-2) and other repair factors. These factors are important for cellular ingrowth, extracellular matrix turnover, scarless wound healing, and sustained vasculogenesisVasculogenesisVasculogenesis is the process of blood vessel formation occurring by a de novo production of endothelial cells.-Process:Though similar to angiogenesis, the two are different in one aspect: The term angiogenesis denotes the formation of new blood vessels from pre-existing ones, whereas...
.,,,,,,.
- Carbon fiberCarbon fiberCarbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
implants have been proven to be ineffective: these fibers are extremely strong, but inflexible, causing increased strain on adjacent normal tissue. - Surgical drainage (tendon splitting) of core lesion tissue is controversial, but likely has some benefit in the early phases where the tear is filled with fluid. Once the lesion has granulatedGranulation tissueGranulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size it heals...
, this procedure is of questionable benefit. - Extracorporeal shockwave therapy is now more commonly used as an adjunctive therapy.
- Proximal check ligament desmotomy has been shown to return horses to work faster, but is thought by some to predispose to suspensory ligament injury.
- Mesenchymal stem cellMesenchymal stem cellMesenchymal stem cells, or MSCs, are multipotent stem cells that can differentiate into a variety of cell types, including: osteoblasts , chondrocytes and adipocytes...
s, derived from the affected horse's bone marrow or fat are currently being used as a potential therapy for SDFT tendinitis and other injuries.
Prognosis of Tendinitis in Horses
The prognosis for return to full work depends on:- The damage to the tendon: if there was not obvious disruption of the tendon fibers, or if the damage was minimal and healed quickly and completely, the horse has a better prognosis for returning to full work.
- The treatment used: horses with moderate or severe tendinitis have a better prognosis if managed conservatively (rested, brought back to work slowly), with about 50-60 percent returning to training. If they undergo surgery and are rehabilitated correctly, up to 70-80 percent return to full work.
- Use of the horse: horses that are used for athletic events that strain their tendons (eventingEventingEventing is an equestrian event comprising dressage, cross-country, and show jumping. This event has its roots in a comprehensive cavalry test requiring mastery of several types of riding...
, racing) are less likely to return to their previous level of performance than those in less strenuous work (dressageDressageDressage is a competitive equestrian sport, defined by the International Equestrian Federation as "the highest expression of horse training." Competitions are held at all levels from amateur to the World Equestrian Games...
, pleasure and trail riding).
- New treatments developed by VetCell Bioscience Ltd. and Vet-StemVet-StemVet-Stem is a privately held company that offers veterinarians a service to provide adipose-derived stem cell regenerative medicine therapy for horses and dogs and cats suffering from tendon, ligament and joint injuries...
involve the use of autologous mesenchymal stem cells to regenerate torn tendons.
The best way to ensure that an injured horse returns to full work is to rehabilitate the animal correctly. This includes slowly bringing the horse back into training, and giving the horse light exercise each day as the tendon is healing. An impatient trainer who rushes to bring the horse back to intense training is likely to cause re-injury of the tendon.
Prevention of Bowing and Reducing the Risk of Re-injury to Tendons
- Checking the Legs: especially after hard work, it is important to feel each leg for swelling and heat, and to palpate it for pain.
- Correct Trimming and ShoeingHorseshoeA horseshoe, is a fabricated product, normally made of metal, although sometimes made partially or wholly of modern synthetic materials, designed to protect a horse's hoof from wear and tear. Shoes are attached on the palmar surface of the hooves, usually nailed through the insensitive hoof wall...
: a good farrierFarrierA farrier is a specialist in equine hoof care, including the trimming and balancing of horses' hooves and the placing of shoes on their hooves...
will trim the horse's feet correctly, preserving the pastern-hoof angle, and will properly support the horse’s heels.
- Bandaging: using properly applied exercise bandagesPolo wrapsPolo wraps are bandage materials, usually made of fleece, for a horse's legs. They can be quite stretchy compared to other bandaging materials, and are used mainly for protection during ridden work, longeing, and turnout.-Uses of polo wraps:...
can help prevent the overextension of the fetlock.
- Correct Conditioning: with a base of long, slow distance work, and a fitness schedule that is not increased too rapidly.
- Suspending Training: if any sign of heat, swelling, or pain is detected.