Anatomy of the Achilles

Function of the Achilles Tendon

Tendons function in our bodies to transmit the energy generated by a muscle to the bones or joints they are attached to. They stretch and recoil when muscles contract and relax which causes movement of the bone or joint.

The Achilles tendons are well used tendons in your body as they function to allow you to walk, run, jump, or stand on your toes. These movements occur when the calf muscles, or gastrocnemius and soleus muscles, contract and the Achilles tendon is pulled upwards. When the tendon is pulled upwards the foot is pushed downward and the heel lifts due to flexion of the subtalar, or talocalcaneal, joint.

With every step we take, our Achilles tendons carry our entire body weight so it makes sense that it is the thickest, strongest and most powerful tendon in the body. Additional force is placed on the Achilles tendon when you sprint, widen your stride, walk on unlevel or rough terrain, or push off for a jump - up to 12 times our own body weight.

Anatomy of the Achilles Tendon

The Achilles tendon, also known as the calcaneal tendon, is a white fibrous cord located at the back of the ankle. It is the thickest and most powerful tendon in your body. The Achilles Tendon is essential in the flexion of the subtalar joint (also known as the talocalcaneal joint) in the ankle which exists between the calcaneus (heel bone) and the talus bone. Flexion of the subtalar joint allows us to walk, run, jump, and lift ourselves up on our toes.

Tendons are located throughout your entire body and function to connect muscle tissue to bone. The Achilles tendon connects the calf muscles, called the gastrocnemius and soleus muscles, to the tuberosity of the calcaneus, also called the heel bone or os calcis.

The Achilles tendon is made up of strands of protein called collagen that run parallel to each other and are bundled closely together within the Achilles tendon. The smallest collagen component is called a collagen fibril or tenocyte. These small strands are bundled together within a collagen fiber. Several collagen fibers are bound together and make up the next layer within the tendon called the fascicle. The fascicle, combined with the subfascicles, form 3 different levels of collagen. These levels are referred to as the primary, secondary and tertiary fiber bundles.

The endotenon surrounds the fascicle to stabilize and bind them together within the Achilles tendon. The endotenon are then bound together by the final layer of the tendon, called the peritendon, which is made up of 3 layers as well. The epitenon is the interior layer, closest to the endotenons which contains the vascular, lymphatic, and nerve supply.

Next is the mesotenon which is filled with a thin, lubricating fluid that allows for the Achilles tendon to glide when the gastrocenemius and soleus muscles in the calf contract.

The paratenon is the outer layer binding all of the Achilles tendon together and is part of the deep fascia that runs throughout your entire body. Unlike other tendons in the body, the Achilles tendon does not have a true synovial sheath covering it, rather it is surrounded by this loose outer covering of fatty tissue.

Although tendons contain blood vessels and nerves, compared to other parts of the body the Achilles tendons have a relatively poor supply of blood. They receive the least amount of blood between 3/4" and 2 1/2" above where the Achilles tendon attaches to the calcaneus heel bone making this area the weakest part of the Achilles tendon and the slowest area to heal.

Achilles Bursae

Bursae are sacs that are lined with synovial tissue. These sacs provide cushioning between tissue and bone where needed throughout the body. There are 2 bursae located near the insertion of the Achilles tendon at the heel bone, the retrocalcaneal bursa and subcutaneous calcaneal bursa.

The retrocalcaneal bursa lies between the Achilles tendon and the posterior, or back, surface of the calcaneus bone. This is a "true" bursa that is present from birth.

The larger subcutaneous calcaneal bursa lies overtop of the tendon at the lower part of the heel where the Achilles tendon joins to the heel bone. This bursa develops as you age (called an "adventitious" bursa) to protect the tendon from friction that can damage soft tissue.

Healing the Achilles Tendon

Tendons are similar to elastic bands, in that they stretch. If your Achilles tendon is injured and you continue to stretch and strain it, tough and inflexible scar tissue will replace the Achilles tendon's normally elastic fibrous tissue. An inelastic tendon hurts during exercise, is more susceptible to further injury, and can become a constant pain even while you walk. An Achilles tendon injury or tendonitis (also spelled tendinitis) that is left untreated can become a chronic condition that is extremely difficult to cure. So, if your Achilles is injured, it's important to treat it and heal as fast as possible.

Unfortunately, an Achilles tendon is dense and fibrous with limited blood vessels which does not allow for ample blood flow. As a result, the Achilles tendon heals slowly by nature.

However, the trick to treating any tendon injury is getting it to heal quickly, with minimal scar tissue formation, and with as much proper realignment of the tendon fibers as possible. By healing your Achilles tendon tissue faster and more completely, you maintain more elasticity in the fibers. A more elastic tendon is less prone to further pain and injury than a tight, unhealthy tendon that is held together with scar tissue.

The good news is, reducing scar tissue and healing faster is possible with the combination of cold compression therapy, ultrasound therapy and Blood Flow Stimulation Therapy! Even with optimum healing, there is always less elasticity in a previously injured tendon compared to an Achilles tendon that has never been injured. However, it's crucial that you heal your Achilles injury the best you can. That way, your chance of a further injury and chronic pain is significantly reduced.

The Legend of the Achilles Heel

The name "Achilles tendon" derives from the story of the ancient Greek hero, Achilles. According to legend, as a baby he was dipped in the river Styx by his mother, the goddess Thetis, causing him to become (supposedly) immortal and invincible. This was proved to be untrue during the Trojan War, where Achilles (by then a grown man and the mightiest Greek warrior) was killed by a single arrow, which pierced his heel. This was due to the fact that Thetis had held that particular ankle while dipping him in the Styx, causing that spot to be the only "mortal" place on his body. Thus, the terms "Achilles tendon" and "Achilles heel" derive from this story.

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