What is the anatomy of dog's tendons?
21 Jun, 2019
What are tendons?
Tendons are dense, cordlike connective tissue that attach muscles to the bone or cartilage. Tendon fibres are comprised of collagen and tenocytes which are rod or spindle shaped cells. These fibres blend with periosteum (bone) fibres which are made of similar substances. By weight, tendons are approximately 55% water.
Tendon fibres are a collection of collagen fibrils. Tendon fibres are bundled and surrounded by endotenon to form fascicles. The endotenon provides a vascular (blood flow), lymphatic and neural (nervous system) transmission routes. Fasicles are bound by the epitenon to form the tendon. Like the endotenon, the epitenon supplies the tendon with blood, lymphatics and nerves.
Tendon fibres are arranged in a parallel, crimped pattern. The crimped pattern facilitates 1 – 3 % elongation of the fibres which gives the tendon its tensile strength and buffers the tendon from sudden mechanical loading. The arrangement of tendon fibres also reduces friction and allows the tendon to glide over bony structures like joints.
Further, some tendons are enclosed in a sheath which is covered by synovial cells. Such tendons are typically those that are required to bend sharply over a joint. Being covered by synovial cells helps lubricate the tendon, facilitates gliding and reduces friction. Tendons that are not enclosed in a sheath are those that move in a straight line only. An example of such a tendon in humans is the well known Achilles’ tendon.
What is the role of tendons?
The role of tendons is to transmit the force produced by the muscle to the bone to create movement. As stress and strain are initially applied to a tendon, the crimped pattern of collagen fibre bundles are straightened under strain. When the tension is released, then elastin fibres in the extracellular matrix of the tendon brings the tendon fibres back to a resting state.
If stress and strain is continued being applied to the tendon when the collagen fibres are already straightened, then the limit of the tendon is reach. This is the “stiffness” felt in the strained tendon.
Once the limit of the tendon is reached, if stress and strain are continually added to the tendon, then the collagen fibres will begin to fail and cause micro-tears in the fibres. Continued strain at this point will ultimately result in a complete tendon rupture.
Tips for keeping dog’s tendons healthy
As approximately 55% of the tendon’s weight is water, ensuring your dog is well hydrated is essential for maintaining healthy tendons. Dogs hydrate themselves by drinking water and from their food. Raw meat, bone and vegetable matter are excellent source of hydration.
Like ligaments, tendons require regular loading to maintain their strength, mass and mechanical function. Providing the dog regular and varied weight bearing exercise such as off lead running and play, walking over uneven surfaces, hill walking, and water walking are all good exercise options to effectively load dogs’ tendons.
A common cause of tendon pathologies in dogs is overuse injuries, where the tendon is repetitively overloaded. Tips for avoiding tendon injury includes:
- ensuring dogs are given rest and recovery time after strenuous or repetitive work,
- avoiding asking (or allowing) the dog to perform repetitive tasks,
- treating minor tendon strains early, so the tendon can restore its strength and function before performing again.
The next article will discuss causes and treatment for tendon injuries and chronic conditions.
Please also see related articles:
Until next time, enjoy your dogs.
Fischer, M.S & Lilje, K. E, 2014 Dogs in motion, 2nd edition, VDH Service GmbH, Dortmund, Germany
James, R., Kesturu, G., Balian, G., & Chhabra, A. B. (2008). Tendon: biology, biomechanics, repair, growth factors, and evolving treatment options. The Journal of hand surgery, 33(1), 102-112.