New Research: Your Achilles Tendon Is an Efficient and Twisted Mess

By Chris Centeno, MD /

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achilles tendon injuries

As a physician, like every other doctor, I was taught that the Achilles was the biggest single tendon in the human body. The first day of medical school I was also told that half of everything they would teach me would eventually be proven wrong. So this past week, researchers added yet another thing that all doctors believe is true and blew it away. Turns out the Achilles isn’t one tendon but three twisted tendons! This discovery has major implications for how we fix these torn tendons, so if you’re planning on Achilles surgery, you better make sure your doctor got the memo.

The Achilles Tendon Explained

The Achilles tendon lives at the back of the ankle where it stretches from the gastrocnemius and soleus muscles (the muscles that form the calf muscle) down to the back of the calcaneus (the heel bone). The Achilles tendon is strong and thick, a bit like an industrial-strength rubber band, and for good reason: it is put under a lot of pressure every day. With every step we take, the tendon is constantly stretching and compressing. Add physical activities to the mix (e.g., sports, dance, running, etc.), and the Achilles tendon can experience enormous stress.

Despite its strength, when the Achilles tendon becomes overworked or has too much loading, injuries are common, which can include tendinopathy (aka tendinosis), partial tears, complete nonretracted tears (where the tendon is torn but still together) and full ruptures (a complete tear where the tendon snaps back like a rubber band). Additionally, Quinolone antibiotics (e.g., Cipro and Levaquin) have also been shown to cause Achilles tendon ruptures.

See the video for more info on this horrible medication-induced tendon disease.

Invasive surgeries are often recommended for Achilles tears, which involve sewing the torn pieces of the tendon back together. Recoveries are lengthy, complication and failure rates are high, and one study found that Achilles tear surgery is no better than simply immobilizing and bracing the ankle for a few weeks.

The Achilles Tendon’s Role in the Interconnected Musculoskeletal System

Your body is very interconnected. This is despite the fact that you’ve likely been taught to view it as this piece or that piece. Let’s explore how that works with the foot, ankle, knee, and spine.

Biomechanical forces on the Achilles tendon, such as those that create instability following a bad ankle sprain, for example, have been shown to be one catalyst that can lead to knee arthritis. How can the ankle affect the knee? The deep muscles that live behind the knee connect to tendons that bridge all the way down to the Achilles tendon. So if there is pain in the back of the knee, the source could be instability in the Achilles tendon, and if left unaddressed, this could cause more damage, such as knee arthritis.

This interconnected musculoskeletal system also works in reverse. A pinched or otherwise irritated nerve in the low back (the S1 nerve) can present as a problem in the knee, the calf, or all the way down into the Achilles tendon. You may not even have pain in the back, just chronic tightness in your calf. This happens because the S1 nerve branches down through the length of the leg and into the calf muscle giving it instructions for how to behave.

So why is the body’s strongest tendon so vulnerable to Achilles tendon injuries? The answer seems to lie in the fact that it’s not one tendon, but three twisted ropes.

Turns Out Your Achilles Is One Twisted Tendon!

The new study investigated specifically the forces of the three different calf muscles (soleus, lateral gastrocnemius, and medial gastrocnemius) on the Achilles tendon. What’s new about this research is that it identified that the Achilles tendon has three different and twisted subtendons. All three muscles have different functions, so this makes sense that all three connect via different tendon “ropes” to the heel bone, creating different degrees of stress on the tendon. The study suggests that it’s this “nonuniform loading” (pressure on a twisted tendon) that may make it so vulnerable to injury.

Translation? Think back to that thick industrial-strength rubber band. As a whole rubber band, it can stand up to heavy forces, but if we have smaller rubber bands that make up one whole structure and we twist them, one of those smaller and weaker bands can get loaded in a weird way and snap or become damaged.

What does all this look like? Check out the diagram below. The MG and LG parts represent the medial gastroc and lateral gastroc muscle tendons within the Achilles (inside and outside calf). The SOL part represents the soleus tendon, which is a deep postural muscle involved in standing that lives under the calf muscle. Look at the way these three subtendons twist as they go from top to bottom (proximal to distal) and you’ll get a real sense of why the Achilles is so vulnerable to injury.

Fixing the Achilles Without Surgery?

Now that we know that the Achilles is broken into subtendons, restoring normal function through surgery just got a lot harder! Now the surgeon needs to carefully align these three twisted subtendons, but since most surgeons don’t know that these exist, you’re more likely than not to end up with a misaligned tendon. Hence, if you have a partial tear or even a tear that you’ve been told is complete, it’s likely better to use a precise ultrasound-guided injection of your own platelets or stem cells to help the area heal and let the body do the heavy lifting and reconnecting of its own subtendons. However, if you do need a surgery, make sure your surgeon has gotten the memo that unless he carefully aligns these bands within the Achilles, you may well end up with an untwisted and less functional tendon.

The upshot? What’s fascinating here is that what many physicians consider is one structure, is actually not. Like the ACL and PCL ligaments in the knee, the body has developed the Achilles into parts that serve different functions. While this gives the tendon more flexibility in supporting walking, running, and jumping by more accurately transferring forces from three different muscles to the heel bone, it also creates areas of weakness as we age. In addition, it now creates much more work for any surgeon sewing a torn Achilles back together. Therefore, for most tendon tears, it’s likely better to make sure it’s aligned and then stimulate the body to heal with a precise injection of orthobiologics and let it figure out where everything goes!

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7 thoughts on “New Research: Your Achilles Tendon Is an Efficient and Twisted Mess

  1. Karim

    I’d like to know if you have any clue about recurrent tendo Achilles rupture? I got ruptured twice in my left leg and I got ruptured after Six years in my right leg.plz if you have any answer to help I’d be glad.

    1. Regenexx Team Post author

      Karim,

      There are several different issues that can occur in the Achilles tendon, but more important is to track down what’s causing the problem. We’d need to take a full medical history and examine you to see what’s going on in your case. If you’d like us to take a look, please submit the “Are You a Candidate” form to the right of the blog.

    2. Chris Centeno Post author

      Yes, the first place I would look is for an irritated S1 nerve in the back causing chronic tightness in the calf muscles and placing the Achilles under too much stretch. Next would be lost dorsiflexion in the ankle doing the same thing.

  2. sid weiler

    I am diebetic type 2 an my left foot arch going flat footed i have a cracked heel bone an my Dr wants to cut just below my calf mussel at the tendon to make it longer what do you think of this surgery

    1. Regenexx Team

      Hi Sid,
      Please see: https://regenexx.com/blog/gastrocnemius-recession-recovery/ We would never recommend this surgery to one of our patients as we have many less invasive ways to treat this common problem. We have a location in Sarasota, FL. If you’d like to see if we could help in your case, please submit the Candidate form here, or give us a call at 855 622 7838

  3. Karen

    I have had micro tears in both Achilles’ tendons since 2009 (diagnosed as tendinitis by MRIs). I had PT off and on for several years, then learned to live with gradually changed/then reduced physical activity, and pain after use followed by ice etc. i recently had new MRIs and x-rays showing a 50% tear near insertion, with a 2 cm bone spur and a significant large calcification in the tendon, and significant inflammation of the bursa. Also a 70% tear in right Achilles without spur but also with calcification. Surgeon recommended open surgery on left to include removing bone spur and calcification and grafting tendon from a nearby tendon. He recommended surgery based on having pain in the left vs. the right Achilles, which has a larger tear. He said he wouldn’t recommend surgery on right solely based on size of tear if it wasn’t causing me pain. My question: do the spur and calcifications disqualify me from having a Regenexx procedure vs. the open surgery? Surgery is imminent and I would like to avoid it and the long rehab if possible. Many thanks!

    1. Regenexx Team

      Hi Karen,
      We’d need to see the imaging through the Candidacy process. To do that, please submit the “Are You a Regenexx Candidate” form here. https://regenexx.com/conditions-treated/foot-and-ankle/

Chris Centeno, MD

Regenexx Founder

Chris Centeno, MD is a specialist in regenerative medicine and the new field of Interventional Orthopedics. Centeno pioneered orthopedic stem cell procedures in 2005 and is responsible for a large amount of the published research on stem cell use for orthopedic applications.
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