Muscles, Tendons, and Ligaments
Rippling beneath the skin are the muscles. Muscles are body tissues made up of long fibers that contract when they're stimulated, producing motion. The muscles are connected to the underlying bones with fibrous tissues called tendons. Ligaments are dense, stiff, stable bands of fibrous tissues that support and stabilize the joints — the places where two bones meet. In other words, they attach one bone to another. Ligaments limit range of motion, which is why your dog's front leg, for instance, bends backward but not upward.
Your dog's body has three types of muscles. Skeletal muscle plays a role in movement; smooth muscle enables the contractions of hollow organs such as blood vessels, the gastrointestinal tract, the bladder, and the uterus; and cardiac muscle ensures that the heart keeps beating. Skeletal muscles are the only ones that your dog can actually control. Smooth and cardiac muscles operate under the direction of the nervous system.
What the Muscles Do
Dogs have five muscle groups: the head and neck muscles; the dorsal (back) muscles; the thoracic, abdominal, and tail muscles; the forelimb muscles; and the hind-limb muscles. The muscles of the head and neck enable your dog to move his ears forward, up, or back. One muscle depresses the eyelid, while another raises the upper lip and dilates the nostrils. Muscles are also involved in chewing, moving the head and lower jaw, and flexing the neck and extending the shoulder. The dorsal muscles — the trapezius, the latissimus dorsi, and the lumbodorsal fascia — work to raise the head and shoulder, flex the shoulder, and anchor other muscles. The thoracic, or intercostal, muscles connect the ribs. The pectoral muscle helps to flex the shoulder, while abdominal muscles are important for a strong back and to stabilize the entire body. Your dog is able to wag his tail with the help of the caudalis and sacrococcygeus muscles. The various forelimb muscles are involved in flexing and extending the shoulders, supporting the shoulder joints, flexing and extending the elbows, and moving the front paws and toes. Your dog's rear end is controlled by the hind-limb muscles, which flex and extend the hip and knee joints and extend the foot.
Dogs can suffer muscle sprains and strains and tendon injuries. If your dog is limping, he may well have one of these injuries. These are common in canine “weekend warriors” — dogs that aren't well conditioned and then get taken out for strenuous exercise, such as a long walk, a trip to the park to chase flying discs, or a hike that involves jumping over obstacles such as fallen trees.
Sprains are partial or complete tearing of a muscle or ligament. Torn knee ligaments are especially common. Sprains often occur when a dog slips or slides on a hard, slick surface or falls off a piece of furniture. Once a dog has suffered a sprain, it's likely to recur, so keeping your dog in good condition is important.
Recurring sprains can cause joints to become unstable and may lead to arthritis. Never take the blase attitude that “It's just a sprain.” Sprains can be difficult to heal, often more so than a fracture. Signs of a sprain include tenderness in the area of the injury, swelling, bruising, and lameness. X rays can rule out a fracture and help evaluate the injury to the soft tissue.
Sprains are treated with rest. The easiest way to do that is to confine your dog to his crate or to a small room such as a bathroom or laundry room. Cold packs applied to the injured area for the first twenty-four hours can help bring down swelling. Use a gauze wrap to attach a chemical cold pack or a bag of frozen peas to the affected area, leaving it for fifteen to thirty minutes. Do this three or four times during the day. On the second and third days, apply warm — not hot — compresses to the area on a similar schedule. Your veterinarian may prescribe pain relievers (nonsteroidal anti-inflammatory drugs), but these can have the negative effect of causing your dog to use the limb before the injury has healed. Continue to rest him, and take him out to potty on leash to prevent him from running or jumping. Sprains can take as little as three weeks to heal or as long as several months. Healing occurs when the body replaces the torn portion of the ligament with new fibrous connective tissue.
Tendon injuries usually occur when the dog suddenly wrenches or twists a limb. The most common injury of this type in dogs is a ruptured Achilles tendon and is often seen in canine athletes such as racing greyhounds, hunting dogs, or agility competitors. Tendons can also become inflamed (tendonitis) after extensive running or other overuse of the leg. Tendon injuries have much the same signs and treatment as sprains. The exception is the ruptured Achilles tendon, which must be repaired surgically.