Researchers gain insight into Achilles tendon injuries

February 22, 2013

Topic: orthopaedic surgeons

A study found that patients of older age or a higher BMI tend to fare worse after sustaining a foot injury such as an Achilles tendon rupture than younger patients or patients with a lower BMI.

The Achilles tendon is an essential component of the foot, connecting the muscles in the back of the calf to the heel bone. Orthopaedic surgeons know from experience that if injured, the tendon can take a long time to heal, and now researchers know more about why that is.

Designed to last a lifetime
Danish researchers from Aarhus University and the University of Copenhagen used 50-year-old nuclear weapons test results to figure out why the healing process of Achilles tendons is slower than that of other parts of the body. They discovered that this tendon in particular remains exactly the same throughout the course of an individual's adult life.

"It's fascinating that some parts of the body are designed to last an entire lifetime," said senior researcher Katja Heinemeier. "The Achilles tendon can withstand very strong forces - up to 1,102 pounds when you're hopping, for example - and you might think that it would be exposed to minor injuries all the time, thus requiring constant repair and renewal. Not the Achilles tendon, however."

Heinemeier goes on to explain that the Achilles tendon is built like a steel cable that essentially has to last a person's entire life. It is also the largest tendon in the human body. If it is ruptured or tears for some reason, it is not easy for it to regain the strength that it once had.

Still susceptible to injury
Although the Achilles tendon can endure a great deal of stress, it can still sustain injury. For instance, a rupture is when the tendon fibers tear and separate from one another so that the tendon can no longer function normally, according to the American Academy of Orthopaedic Surgeons. Common symptoms of this ailment include pain and swelling near the heel, an inability to bend the foot downward or push off the injured leg, and a popping or snapping sound.

A rupture is commonly caused by an increase in the amount of stress a person places on his or her Achilles tendon. This may occur if the individual increases the intensity of a workout regimen or sports participation, falls from a significant height or steps into a hole.

The answer lies in the building blocks
The study's investigators looked at the Achilles tendon from individuals who lived during the Cold War. They found that carbon-14, a molecule present in the atmosphere at the time, remained on the tendons at very high concentrations decades later. This supports their hypothesis that the tendon's building blocks undergo very little renewal over time. In fact, they are essentially the same during a person's lifetime. This is different from many other parts of the body that constantly renew and repair.

Since the building blocks of the Achilles tendon have limited ability to rejuvenate, the healing process of this body part tends to be poor, which explains why it takes so long for tendon injuries to recover.

"Based on our results, we actually think that the cells living in the tendon are in a kind of hibernation state, and therefore don't manage to wake up and repair the tendon when it's injured," said Michael Kjaer, a professor at the University of Copenhagen. "The interesting results achieved by our research collaboration cutting across different fields of study now form a much better understanding of tendon function," said Michael Kjaer, a professor at the University of Copenhagen.

The study's findings can help researchers develop new treatments for tendon injuries. For instance, they now know that they should focus on trying to stimulate dormant tendon cells in order to facilitate healing. 

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