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First Posted: Mar 21, 2009
Oct 13, 2012

Horse Tendons and Ligaments

by Debora Johnson
  

New Treatment for tendon injuries: Study Evaluates Injectable Treatment for Tendon Injuries

What Is It?

"...NEXT (nonsurgical exogenous crosslink therapy, sometimes called ECM2 or exogenous crosslink modification of the extracellular matrix) involves chemical modification--using the plant-derived reagent genipin, which Hedman noted the FDA classifies as nontoxic--of connective tissue to improve mechanical and nutritional properties. Although it sounds complicated, the theory behind NEXT is relatively simple, he said.

Essentially, when tissue is injured (specifically tendons, which are Hedman's current research focus) a veterinarian can hypothetically inject genipin into the lesion. The reagent is designed to provide internal bracing to collagen tissues (the main substance of which tendon is comprised) while increasing nutrient flow into the tissue. Genipin's protein crosslinking activity confers a high tensile strength when injected into collagen. ..."

Tendon Angles and Lameness

My farrier, Don Roof, has always stressed the importance of the angles of the horses's hooves. Improper angles can cause major damage to your horse that can become permanent. He has done wonders with some of my horses over the past 30 years. "There is no one way to trim the feet...you trim to the conformation of each horse, or to whatever is causing the horse problems." Horse tendons need to be able to stretch as much as one to three inches. Overstretching can cause injury such as a rupture of the tendon fibers as well as other problems.

Horse Tendon and Ligament Chart
One Step at a Time: Hoof Trimming and Leg Stress

Anatomy and Physiology of Tendons and Ligaments

Tendons and ligaments are made from the same basic tissue and have the same basic structure. The tissue is a very strong fibrous material that groups together in bundles, forming long cords.

Tendons join muscle to bone and as a result, when the muscle contracts, the bone moves. Most tendons are designated as either flexor or extensor. Flexor tendons allow a joint to bend inward, toward the body (joint closes), and extensor tendons allow a joint to extend (joint opens).

Ligaments join bone to bone. They are stabilizing structures that essentially hold bones together and stop them from overextending, over flexing or over rotating.

There are four main tendons and ligaments at the back of the horse's leg that do the majority of the work: suspensory ligament, inferior check ligament, deep digital flexor tendon and the superficial digital flexor tendon. In a horse's forelegs, these four structures are the most commonly injured tendons and ligaments. When injury does occur in these structures, the infamous "bowing out" along the back of the leg is visible-in layman's terms, the horse has a bow.

For an excellent article on Tendons and Ligaments: Tendon and Ligament Injuries, By Janice Posnikoff, DVM

Tendon Injury Signs

  • Heat
  • Swelling
  • If there is no lameness, but heat and swelling in the tendon area is present, call your vet immediately. If a tendon or a ligament is involved it can be time sensitive. Strains and sprains should be dealt with within 48 hours if at all possible so that further damage does not develop. Stall rest or a paddock area where the horse will not be chased will help in the healing process. Too much time in the stall aggravates some horses. They get anxious. When let out they get "stupid" and will often reinjure themselves. Tendon injuries can happen in an instant. Your vet will tell you how to proceed.

  • Lameness
  • Visual bows or a dropped hip that cannot hold any weight
  • Ruptures of the tendon fibers
Types of Tendon Injuries

  • Deep digital flexor tendon: Tarsal and digital tendon sheaths of the deep digital flexor tendon.
  • Displacement of the superficial digital flexor tendon from the point of the hock. (Disorders of the Shoulder and Elbow)
  • Tendinitis (Bowed tendon) Inflammation of a tendon can be acute or chronic, with varying degrees of tendon fibril disruption.
  • Hindlimb Tendon Ruptures. Laceration of the entire Achilles tendon involving both the gastrocnemius and superficial flexor tendons.
  • Displacement of Superficial Flexor Tendon from the Point of the Hock. Damage to the medial attachment of the superficial flexor tendon as it passes over the tuber calcaneus can cause a lateral luxation of the tendon.
  • Navicular Disease. (Podotrochlosis, Podotrochlitis) Navicular disease is essentially a chronic degenerative condition of the navicular bursa and navicular bone that involves damage to the flexor surface of the bone and the overlying deep digital flexor tendon with osteophyte formation on the lateral and proximal borders of the bone.
  • Flexion Deformities. (Contracted tendons, Club foot, Knuckling) Flexor tendon disorders are associated with postural and foot changes, lameness, and debility.
  • Lascerations can also cause tendon injuries.
  • Tendons/Merck Vet Manual

Re-Injury

Re-injury often causes long term problems. There are a number of factors that are considered in a re-injury: previous injury, healing stage of previous injury, and the horse's work schedule after the injury was sustained. It is key to try not to stress the horse after an injury. It is really important to go slowly and practice patience! Movement can be beneficial as it encourages blood flow and circulation, keeps the horse happy mentally, and gives the horse some natural exercise while he is healing. However, I must point out that not all agree with this train of thought. Your vet is the one who will explain the protocol for your horse's recovery.

Tendons of the Lower Leg

Tendons attach muscles and bone, and are classified as flexors (flex a joint) or extensors (extend a joint). However, some tendons will flex multiple joints and extend another (the flexor tendons of the hind limb, for example, will flex the fetlock, pastern, and coffin joint, but extend the hock joint). In this case, they are classified according to whether they flex or extend the joints of the digit.

The following tendons are the main tendons found in the lower leg. When they pass over a joint, they are protected in a tendon sheath, which contains synovial fluid as a lubricant:

  • Common digital extensor: the common digital extensor muscle becomes tendon at the bottom third of the radius and continues down the front of the leg. The tendon pulls upward to extends the carpal, pastern, and coffin joints. It is the major extensor tendon of the leg. However, unlike the flexor tendons, a horse with a damaged or non-functional "extensor unit" (i.e., tendon and musculature) is not lame, but rapidly learns to compensate by "flicking" the lower limb using the carpal or tarsal extensor units.
  • Lateral digital extensor: the lateral digital extensor muscle becomes the lateral digital extensor tendon at the proximal portion of the metacarpus. The tendon continues down the front of the leg and inserts into the proximal portion of the first phalanx. Important in the treatment of stringhalt in the hindlimb. Extends the carpal, pastern, and coffin joints.
  • Deep digital flexor: 3 tendons of the deep digital flexor muscle travel distally and join at the carpus, were they pass through the carpal canal, and travel distally along the back of the leg, finally inserting into the palmar side of the third phalanx. Below the knee/hock, the tendon is superficial to the suspensory ligament, but deep to the SDFT. Fairly commonly injured by horses doing fast work, the DDFT is round in cross section.
  • Superficial digital flexor: Runs down the back of the leg, behind the carpus and cannon, branches below the fetlock and inserts into the distal side of the 1st phalanx and proximal side of the 2nd phalanx. Flexes the elbow, carpus and lower joints. Additionally, the superior check ligament inserts into this tendon from the caudal side of the radius. The SDFT is the most commonly injured tendon, and appears oval or flattened in cross section.

Note: Department of Veterinary Pathology, Faculty of Agricultural and Veterinary Sciences, São Paulo State University, Via de Accesso Prof Paulo Donato Castellane s/n, Jaboticabal, CEP 14884-900, SP, Brazil.

"An inflammatory process was induced by intratendinous injection of bacterial collagenase into the superficial digital flexor tendon (SDFT) of the left thoracic limb of 10 horses. One week later, the tendons in five of the horses (group 1) were treated with glycosaminoglycan polysulphate (GAGPS), and the tendons of the other five (group 2) were treated with saline solution. The horses were euthanased 150 days after the collagenase injections, and samples of the SDFTs were frozen at -14 degrees C, sectioned at 5 to 7 mum longitudinally and transversely, and stained by the picrosirius red method. Morphometric analysis was used to quantify the organized and disorganized bundles of collagen in the samples from groups 1 and 2. Significantly more organized bundles of collagen were observed in the tendons treated with GAGPS." PubMed

Note: "...One important consideration for PRP optimization involves the concentration of white blood cells (WBCs). Although WBCs are often included because of their anti-microbial properties, which are believed to improve healing in infected wounds (one common use of PRP), PRP is often used to treat uninfected tendons or joints. Thus, the most recent data on PRP generated by Fortier's laboratory indicates that PRP low in WBCs is more beneficial in tendon healing.

At present, the commercial growth of PRP products exceeds substantial research. Horse owners are encouraged with work with a veterinarian experienced in PRP when using this therapy." Optimize Platelet-Rich Plasma for Best Results

For More Information:

The Conservative Approach for Healing Horses
Improving the Outcome after Tendon and Ligament Injuries
Tendon Healing: Objective Measurement Method Reported (Ultrasonographic tissue characterization (UTC))
Tendon Sheath Effusion, Tenosynovitis
Leg Problems Most Prevalent in Horses

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