ACHILLES TENDON: ANATOMY AND FUNCTION
By CEO Robert Forster, PT
The Achilles tendon is one of the most robust tendons in the body, and for good reason: Three relatively large and extremely strong muscles in the calf (the gastrocnemius, soleus, and plantaris) all attach to the back of the heel bone (calcaneus) via the Achilles, and the forces they generate during running and jumping are immense, among the biggest in the body.
That’s why, despite the Achilles’ robustness, it is still at risk for injury, and it behooves you not to abuse it with poor training habits, but rather protect it with regular stretching and calf strengthening. The fact is, all injuries to the Achilles hold the risk of complete tendon rupture-which Los Angeles Lakers fans witnessed firsthand in May 2013 when player Kobe Bryant suddenly was lost for the playoffs along with his team’s hopes. As his untimely collapse on the hardwood demonstrated, the Achilles tendon sometimes suffers spontaneous rupture with no history of previous injury or pain. But more often, those huge forces manifest themselves much earlier with telltale pain.
To understand why the Achilles is particularly vulnerable to the stress of running, a short physiology lesson is in order. During on land, steady-state running, the calf muscles perform an “eccentric” contraction-that is, they lengthen in a controlled release of their contraction on the landing to stabilize the foot and slow down the forward progression of your body weight as the shin bone moves over the foot. Add the push off that comes with acceleration or an uphill grade, and the calf now additionally performs a “concentric” contraction, which contracts and shortens the muscle. The Achilles, being attached to the calf’s three prime movers, is not only worked the entire time, but worked at G forces several times your body weight. Sure, it’s designed to handle it. During a toe raise exercise, in which the calf muscles contract concentrically, an average untrained man can do it with 200 pound on his shoulders, and a well trained man with more than 400 pounds. But that’s a lot of stress on the Achilles and its constituent parts. Like other tendons in the body (but not all), the Achilles is encased in a sheath called a paratenon that produces a lubricating fluid designed to prevent friction. Heavy, excess movement and under-lubrication (from poor warm-up, dehydration, or pure overuse) ramp up that friction, which you’ll feel as pain.
How You Feel the Pain
There are three different conditions of Achilles tendon dysfunction-Achilles tendonitis, Achilles paratenonitis, and Achilles tendonosis-and you feel similar pain signatures from each one. But with careful observation and palpation (what PTs call poking people and asking, “Does that hurt?”), we can make an exact diagnosis.
Achilles tendon, like all tendons, is composed of collagen fibers that are constantly reacting to the stress of the forces created during activities of daily life and exercise. In normal use, the body has no problem keeping up with the repair needs of fibers that get damaged (microtears) from the stresses of walking, running, and jumping. Achilles tendonitis occurs when the volume and intensity of these activities creates a stress load that outpaces the body’s ability to repair the microdamaged fibers. Chronic inflammation results; pain soon follows. Achilles tendonitis pain is provoked by high exertion activities such as sprinting, running up hills, and jumping, but more moderate activities such as walking up stairs or even just walking will cause pain if you let it progress. Stiffness in the tendon may be present in the morning and after periods of inactivity. There may be increased soreness at the end of the day; often the pain is worse when you’re barefoot and lessened when wearing a shoe with a slight heel. You’ll know it’s Achilles tendonitis when the Achilles tendon is tender when you pinch it between your finger and thumb. Maybe, under close inspection, it’s minimally swollen.
Achilles Paratenonitis (Sheath Inflammation)
Achilles paratenonitis is caused by an inflamed tendon that irritates the sheath (paratenon) as the tendon slides back and forth with muscle contractions. The pain associated with this condition is often exquisite and easy to recognize. It hurts when you perform any movements of the ankle, including simple range-of-motion exercises. Also, the whole length of the tendon is swollen and enlarged from the end of the calf muscle to the heel bone (as opposed to a bulbous swelling mid tendon, as you will read about below) and acutely tender to relatively light palpation ( finger pressing). In extreme cases, there exists an audible “crepitus” noise that feels like there is sand between the tendon and its sheath. This indicates that a scar is forming between these two structures in reaction to inflammation of the tendon fibers.
Achilles TendonosisWhen the body’s repair mechanisms fail to maintain the health of the tendon and the repair process fails, the inner substance of the tendon breaks down. This is a tendonosis, which appears as a firm, bulbous nodule about the size of a pea somewhere in the middle of the length of the Achilles tendon. Even after the acute swelling and pain go away, this nodule persists and creates more of an ache during and after activities. The nodule represents scar tissue surrounding the area of damaged collagen. If left untreated, it becomes the weak spot, vulnerable to complete rupture. Note: Don’t confuse tendonosis with heel bursitis (calcaneal bursitis), a condition characterized by pain and swelling at the back of the heel bone. It may be associated with inflammation of the Achilles tendon, but is a more recalcitrant condition that typically requires a comprehensive clinical approach to resolve. If you observe a swollen or enlarged bump at the back of the heel bone in one or both of your feet, you’ll have to come in and see a guy like me for an evaluation.
The Cause of Injury
Unless you hurt yourself by running too many hills, Achilles injuries in runners are almost always related to overpronation. Over pronation is defined by the degree the heel bone (calcaneus) angles inward toward the mid-line of the body during the stance or weight-bearing phase of the running gait. Whether overpronation occurs in both feet due to inherent anatomy issues or only in the foot of the long leg (in an attempt to collapse that arch and “shorten” the long leg to match the short leg), an over pronated foot creates problems for the Achilles tendon in two ways:
First, the excessive inward inclination of the heel associated with overpronation creates an odd angle of pull for the Achilles at its attachment on the heel bone. Second, the corresponding instability of a pronated foot makes the calf muscle work extra hard to create stability.
As I mentioned earlier, the calf muscles function both concentrically and eccentrically during running. Of the two types of contractions, the eccentric (lengthening) contraction puts the most stress on the Achilles tendon. During the landing, the calf muscles work via the Achilles tendon in an eccentric contraction to slow down the forward progression of the shin bone, then switch to a concentric contraction to stabilize the foot and ankle and create the force needed to push o the ground. Over pronators have a problem because their heel bones remain too far tilted inward, meaning that the foot and ankle are less stabilized and too flexible when it comes time to push off.
These two factors, a too-tilted heel bone and an unstable/too flexible foot, cause the Achilles to struggle to pull up on the back of the heel bone and generate the right force needed for a good push off.
Rehabilitation of the Achilles
Rehabilitation of Achilles tendon injuries, like all injuries, is guided by the PRICE acronym previously outlined. As we like to say in PT land, “You must pay the PRICE of your injury to get better quickly and avoid chronic problems in the injury re-injury cycle.” Here, I’ll apply the PRICE protocol specifically to rehabbing Achilles problems:
P for PROTECT: Because calf muscles and Achilles tendons are active almost all the time in daily life, take care of them by wearing supportive shoes with good arch support, a sturdy heel counter, and a heel rise (which reduces the Achilles’ need to stretch when you land during a running or walking step). This is why, when the Achilles tendon is injured, we advocate the elimination of barefoot activities, sandals, flat soled shoes, and flip flops, and even advocate heel lifts.
R for REST: Limit all activities of daily living and workouts that provoke any pain. Even if the pain minimizes after the tendon warms up with use, it doesn’t mean the damage being done is minimized. To allow the body to begin to repair the damage, spare the tendon from further stress by replacing running with cross-training activities (e.g., stationary bike or elliptical machine) that cause no pain during or after the workout. Then begin slow running, per the walk/run protocol.
I for ICE: To control runaway inflammation and swelling, apply ice three to five times per day for 20 minutes. By controlling inflammation, you prevent Achilles tendonitis from becoming paratenonitis or tendonosis. You will also limit the amount of scar tissue that forms and shorten your recovery.
C for COMPRESSION: It is difficult to apply effective compression on the Achilles tendon because there’s a risk of a wrap or strap irritating the sheath even more. Apply ice with compression three times per day.
E for ELEVATION: Elevating your leg above your hips or (better yet) above your heart is an effective strategy to control and reduce swelling in the Achilles. When done simultaneously with ice, it is even more beneficial.The first goal of Achilles tendon injury rehab is to control the early inflammation and swelling with the strategies of the PRICE protocol. This limits the loss of range of motion, muscle weakness, and scar tissue formation that will lengthen your rehabilitation program. Secondary goals include regaining full range of motion, eliminating scar tissue, and restrengthening the calf muscles that assist them during running. As with all running injuries, a key is correcting your running gait mechanics, which will limit pronation and stress on the Achilles. If your Achilles issues are unilateral (on one side only), it strongly implicates a leg length discrepancy that needs to be solved. Finally, after the pain is gone, the stronger your calf muscles get, the less stress will be placed on the Achilles. Strengthen the calf to its full capacity with toe raises, with a gradual increase up to 1.5 times your body weight in your hands or on your shoulders. Proper running shoes and a scientific approach to your training that includes all the principles of Periodization will help minimize your chances of re-injury. The use of heel lifts in your shoes, or wearing a shoe with more heel height, will take a significant amount of stress off the Achilles tendon by reducing the stretch on the Achilles when you walk or run. Heel lifts of one eighth to one quarter inch (3 to 6 mm) can be purchased at better national brand pharmacies. They must be worn in both shoes.