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What is a ruptured Achilles Tendon?

This post explains the

• anatomy of the calf and Achilles
• structure of the Achilles Tendon
• factors affecting rupture of the tendon

What is the Achilles Tendon?

Well it’s the long cord that attaches your calf muscles to the heel bone (Calcaneum) at the back of your lower leg.

It comes in all shapes and sizes – from long and thin to short and thick but they all do the same job – transfer forces from the calf muscles to the foot and vice versa. I say muscles because you have two muscle groups in the calf and they both perform slightly differing functions.

Gastrocenmius muscle gives the calf its distinct shape. This muscle itself has two distinct parts (heads) to it – medial and lateral.

These heads are attached to either side of the back of the knee and actually cross the knee joint to be attached to the lower end of the thigh bone (femur) by strong flat tendons.

The medial head is larger than the lateral which can sometimes be absent although I don’t think I’ve ever seen it.  The terms medial and lateral are explained in the Medical Terms Explained post.

The two heads come together about half way down the lower leg and blend with a sheet of fibrous tissue (aponeurosis) which joins onto the tendon of the third muscle –Soleus.

Soleus is attached to the upper ends of two lower leg bones namely the tibia and fibula and so is deep to the gastrocnemius muscle. From here its fibres pass posteriorly to its tendon which blends with the gastrocnemius and other fibres extend further down the leg to attach directly to the Achilles tendon almost to its lower end.

Achilles tendon (or more correctly tendocalcaneus) is the thickest and strongest human tendon. It begins near the middle of the lower leg and reaches up to 15cm long before attaching to the heel bone (calcaneus).

This diagram shows the back of the leg with the gastrocnemius muscle cut away to show the deeper Soleus muscle in its entirety.

The Gastrocnemius muscle sits over the upper part of the Soleus. There is another muscle which is small and this called Plantaris (this can be absent in many people).

Plantaris is not shown in the diagrams but it starts on the lateral side of the femur and passes obliquely down the leg to attach to the medial side of the Achilles tendon or directly onto the medial aspect of the heel bone (calcaneus).

STRUCTURE OF ACHILLES TENDON

The tendon consists of budles of connective tissue fibres called type 1 collagen fibres. Collagen is the main structural protein in the body which provides the strength to the tendon. Collagen is present in bone, tendons, cartilage and scar tissue. The tendon is between 4mm and 6mm thick, it does not contract and it can handle forces up to 12.5 times bodyweight. By my calculations that is over a ton for someone weighing just under 13 stones!!

RUPTURE OF ACHILLES TENDON

This generally takes place 2 – 5 centimetres above the insertion of the tendon into the calcaneum. It generally ruptures with and audible ‘snap’ and patients report being struck on the back of the leg by an object and turn to find nothing and no-one there. There is actually not a great deal of pain with a total tear. If it is painful then that may be a sign that the tear is only partial.

Factors contributing to rupture of the Achilles Tendon are

• high velocity sports – to otherwise healthy tendons
• pre-existing damage to the tendon
• age related degenerative changes in tendon
• rheumatoid arthritis
• Certain antibiotics (Fluoroquinolones are often used for genitourinary infections)

You now have an understanding of where the Achilles Tendon is and what it is made of, and what muscles are attached to it.
You know where the tendon ruptures and what factors may cause a rupture.

Other Achilles Related Posts