Tendon Structure and Common Injuries

The connective tissue that surrounds muscle fibers and muscle fascicles (small bundles of muscle and nerves) converge and exit the muscle belly to become the tendon, which is white, glossy and smooth. Tendons are exquisitely designed to perform their job: connect skeletal muscles to the bones, transmit muscle force and slide during movement. Tendons have great tensile strength and a component of elasticity. Whereas muscle can withstand mechanicl forces up to 77 lbs/sq.in., the average strength of human tendons ranges from 4,000 to 18,000 lbs/sq.in.

Composition of Tendons

Tendons are composed primarily of structural protein which is known as fibrous collagen. Compared with many tissues, tendons have poorly developed blood supply in contrast with muscles and bones with which they associate. As a result, it may not be surprising that it is difficult to get tendons to heal fully after laceration or trauma.1

Tendons may be very short relative to their width or they may be long and slender. Shorter, broader tendons include the attachments for the major muscles of the trunk, limbs, and head. The long, slender tendons that serve the digits of the hands and feet have special modifications.2

Tendon Injuries in Animals

Tendons can be stretched, partly torn, or ruptured. Strained tendons follow sudden wrenching or twisting injuries. The tendons of the forepaws (front and back) are strained most often. The signs of tendon injuries are lameness, pain on bearing weight, and painful swelling over the course of the tendon. Rupture of the Achilles tendon at the hock joint can be caused by sudden and extreme flexion of the hock. This injury tends to occur in Greyhounds and sporting and performance breeds. The Achilles tendon is the one most often severed in dog fights and car accidents. Rupture of the Achilles tendon causes a dropped hock. A ruptured Achilles tendon should be surgically repaired.

Inflammation in the tendon is called tendinitis. This injury follows strenuous field or road work and overuse of the limb.3

Rupture or Displacement of the Tendons of the Toe

Injuries to the flexor tendons of the dog's foot can occur when an animal is running and obtaining maximum traction on rough surfaces. Racing and hunting dogs are at increased risk for this type of tendon injury. If a flexor tendon of a toe is ruptured or torn loose, the toe is no longer maintained in its normal arched position. Instead of the toe being bent with the toenail touching the ground, the bones of the toe are in a straight line, the toe is flat, and the nail sticks up. This injury appears to be painless to the dog; the owner will simply notice that the dog now has one or more flat toes, when yesterday the foot appeared to be normal. Surgery is the only corrective measure for ruptured tendons of the toes, but flat toes are not debilitating to dogs.4


  1. Skeletal muscle structure, function & plasticity. Richard L. Lieber
  2. Connective tissue and its heritable disorders. Peter M. Royce, Beat U. Steinmann
  3. Dog Owner's Home Veterinary Handbook. Debra M. Eldredge, Liisa D. Carlson, Delbert G. Carlson, James M. Giffin
  4. The Dog's Drugstore: A Dog Owner's Guide to Nonprescription Drugs. Ph.D. Richard W. Redding, Myrna Papurt