Beware: when the shoulders get tight, tendons and ligaments of the leg could be in danger! The number one cause of sports injury (or pleasure injury) is muscle fatigue. The same is true for injury to tendons.
Bowed tendon, stretched tendon or stretched ligament are colloquial terms used for many decades by lay horsemen that have transferred into the veterinary dialog about injuries to the horse’s leg, but their descriptive terminology doesn’t do justice to the pathology that is at hand.
Tendon and ligament structures are both made of strong, connective tissue that does not tear easily, nor does it stretch. The fibers are longitudinal, running along the length of the tendon or ligament. When a load of tension is put on these fibers, the connective tissue is designed to remain rigid in order that the limb might move in the appropriate manner for which it was designed.
Ligaments are attached at each end to bone. They support joints so that the joint movement is limited to the appropriate angles normal to the joint. When the joint moves at angles not normal for forward locomotion of the animal, the ligaments are not capable of protecting either the joint or themselves. The forces on the ligament run perpendicular to the strength of the ligament, allowing for the tissue to become damaged. As long as the muscles that support and move the joint are healthy and moving correctly, the tendons and ligaments can protect the joint. They in turn will be protected. Ligament damage is often caused by a traumatic blow to the joint from an oblique angle to the joint, and not by the animal itself, if the muscles are doing their job. If the muscles are weak or in spasm, then the joint itself can cause ligament damage when it moves outside its normal range of motion.
Tendons are attached at one end to bone, the other to a muscle. The muscle acts as the puppeteer, contracting and relaxing, while the tendon acts as the string which is attached to the puppet. It moves the joint on its bony attachment because the stretching muscle at its other end is moving. Tendons don’t stretch. The joint of the limb moves in a normal manner when all of the muscles surrounding the limb are moving in concert with one another. The muscles must have checks and balances to move the limb smoothly through various tempos of motion, and each muscle must be working correctly in order to achieve this choreography. If one muscle is weak or in constant spasm, then the whole dance is affected, the joint does not move smoothly, joint fluid is trapped in pockets in the joint, and the tendon of the weak muscle is asked to carry weight that it is not designed to carry. The joint no longer moves correctly, and forces that are now oblique to the correct angle of movement are affecting all the tendons and ligaments involved.
WHY INJURIES OCCUR
When the forces on the tendons become more than the tendon is designed to carry, the tendon tears along the direction of its fibers. Tendons don’t get chopped in half in this case, but are shredded into individual fibers that cannot carry any load or support the joint or the limb – like a string that frays and breaks small fibers while it hangs on for dear life to the puppet below. The movement of the limb becomes uncontrollable and uncoordinated. The weak muscle is now in danger of more damage as well. And the joint or joints themselves are in danger of becoming damaged, broken, or chipped.
Which brings us back to the bowed tendon or stretched tendon idea. If the muscle is receiving abnormal neural input, such as a signal from the brain that it should be contracting in the face of no need to contract (stress), then the muscle will use up its food stores and become weak. It will begin to have poor oxygen distribution. It will fail to relax after the stretch or flexion. Long before the tendon is bowed or torn, the muscle is undergoing chemical damage within its cells. The cells of the spasming muscle cannot excrete waste products or receive oxygen adequately. It will become acutely more firm, and swell, and later become smaller. This is often found in the shoulders of horses with bowed tendons. The same applies to inflamed tendon sheaths of the hind leg. The semitendinosis and semimembranosis become weak, inflamed and eventually smaller, causing irritation within the tendon sheath, with swelling, heat and often sterile infection. The same cycle is at play.
Routine chiropractic and acupuncture reduce the likelihood of injury due to fatigue.
Dr Amy Hayek is a veterinarian certified by the AVCA and IVAS. She is co-host of the television show “Harmonizing Your Horse’s Health.” Her practice is located in South Carolina but she is licensed in several states and is available for long distance nutritional consulting. She is an instructor at Parker University of Chiropractic and conducts numerous continuing education seminars for both professionals and other equine enthusiasts. Contact her at www.hyhh.tv or 843-860-8336.
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