Achilles Tendon Rupture: Who Is At Risk?

One injury that’s always on the back of my mind is an Achilles tendon rupture. Why the concern? To start with, this injury involves some hefty down time, and a possible surgery. There is never a convenient time to have your Achilles tear. Adding to the inconvenience is the lengthy rehab process which can take months if not years to restore full function. Above all though, my biggest worry is that Achilles tendons are known to tear at anytime, without prior warning. Very little is understood about the nature of these ruptures so they’re almost impossible to predict.

Incidence

The incidence of Achilles ruptures has been reported to be anywhere 2 to 18 ruptures per 100,000 people.1 A study conducted in Finland over a 15 year period found that over 80% of Achilles ruptures during that time period were sport related.2 The injury also tends to mostly affect guys in their 30s and 40s.3 My demographic.

Achilles ruptures are prevalent in a wide range of sports, though more so in ones that require some form of sudden acceleration or jumping such as soccer and volleyball. Both sprinting and distance running have also been implicated as a possible causative factor for several Achilles problems. The study out of Finland found badminton accounted for a substantial amount of the tendon ruptures, but I feel that might be a regional thing. Non-sports related tears, which are much less common, mostly occur during slips and falls.

Men are somewhere in the vicinity of 2 to 12 times more likely to rupture their Achilles than women.4 Why women seem to be more protected from Achilles ruptures is somewhat of a mystery. This may simply represent the greater participation of males in sport, or an indication that other yet undiscovered factors, such as gene expression, are at play.

Functional Anatomy

The Achilles is the thickest and strongest tendon in the human body, and strangely enough one of the most likely to spontaneously rupture. It gets its name from the great warrior of Homer’s Iliad. To make her son invincible to physical harm, Achilles’ mother dipped him into the river Styx. The heel by which she held him was the only part not touched by the water thereby making it his only vulnerable spot. After leading the Greek forces against Troy, Achilles was killed by a poison arrow that struck him in the heel.

The basic function of any tendon is to transfer force created from a muscle to a bone. The Achilles serves as the attachment for the grastrocnemius and soleus muscles of the calf onto the calcanues (heel bone). It is important for a number of basic movements like walking, jumping, or raising up on your toes. The fibers of the Achilles spiral downward instead of traveling in a straight path. This allows for elongation and elastic recoil of the tendon, as well as providing a means to store energy that can be released during locomotion. This spiraling, while beneficial in many ways, may also cause a self-strangulation that diminishes blood flow to the tendon.

Because of its location and function the Achilles must withstand a tremendous amount of force. Normal walking produces load through the tendon equivalent to several times your bodyweight. Higher level activities, like jumping or hopping, further increase that load with the peak force reaching as high as 12 times bodyweight with running.5

At rest a tendon has a wavy configuration. As the tendon is stretched it starts to lose this wavy-ness. If it stretches less than 4% of its length–within the limit of most everyday loads–the fibers rebound like an elastic and can regain their original configuration. At a strain level between 4 and 8 percent the collagen fibers start to slide past each other and the cross-links fail, forming microtears. At stretch levels greater than 8 percent macroscopic rupture can occurs. 6

Tendon Stress Strain Curve

Due to its size and strength, the rupture of a healthy Achilles tendon is considered unlikely even under heavy loads. Researchers have found that ruptured tendons often show signs of chronic degeneration.4

Normal tendons are mostly made of a substance called collagen with a very small amount of a stretchy material called elastin. Approximately 95% of the collagen is of the strong Type 1 variety. Ruptures Achilles tendons contain a substantial portion of Type 3 collagen which is not as strong or resistant to forces.

In most cases, the tendon was going bad long before the rupture occurred, even without the presence of pain or other warning signs. So what causes the Achilles to weaken?

Why good tendons go bad

Lack of inflammatory response to minor injury

Historically, overuse tendon conditions have been considered a result of an inflammatory process. Treatment therefore was focused on reducing inflammation. The normal healing process in tendons produces an inflammatory response which over time allows the tissue to slowly regain its normal structure and strength. Not too long ago, many Achilles problems were termed tendinitis, meaning inflammation of the tendon. Microscopic examination of degenerated tendon tissue however, often does not reveal any of the telltale signs of inflammation.6,7

The microtrauma that occurs during overuse may not be at a sufficient level of injury to cause an inflammatory response required to begin the repair process, thus leading to long term degeneration and weakening. This has led to Achilles problems being relabeled under the more general term tendinopathy.

Poor blood supply

Generally, the better blood supply an area of the body has, the better it is able to heal due to the influx of the materials carried through the blood that are needed to speed along the repair process. Most ruptures occur in the area 2 to 6 cm above the tendon’s insertion point on the heel. It is not fully understood why this area in particular is the most likely to tear. It was once thought that this was due to the area receiving a poor blood supply. This theory has been called into question by several studies. Some studies show that there are less blood vessels in this “vulnerable” part of the tendon while others have shown that blood flow is evenly distributed.4 Because of the twisting alignment of the tendon fibers, another theory is that blood supply to this area gets choked off during activity leading ultimately to slower healing.

Blood flow also influences the temperature of the tissue. This may be another mechanism by which the tendon can be damaged. The elastic energy stored in tendons can be converted into heat, effectively raising the temperature of the tissue. Once the temperature inside the tendon reaches a certain point, the cells of the tendon are susceptible to damage. Normally the body would rely on a good circulation to cool the overheating tissue that might occur with activity or exercise, but this is not possible in regions that are poorly vascularized.

Medication

Certain commonly used medications have been shown to be related to Achilles problems.8 Fluoroquinolone antibiotics such as ciproflaxacin (Cipro) have been linked to many cases of Achilles tendonapthy and spontaneous ruptures. The use of corticosteroids, commonly used to treat inflammatory conditions, also interfere with the healing process and may result in weakening of the tendon, whether taken orally or injecting directly into the tendon. The drug interactions involve changes at the cellular level and are difficult to quantify and so there is debate among researchers as to the significance of the effect these drugs play in tendinopathy.

Mechanical factors

Over pronation. There is evidence that the rolling in of the ankles associated with over pronaton produces a whipping action of the Achilles that could lead to damage with overuse. [1] The tendons of an over pronator demonstrate a bowed shape in standing. The changing position of the heel during the gait cycle would cause the tendon to move side-to-side, as opposed to straight up and down, producing abnormal directional stress on the tendon. This curving will also cause the ground forces to travel unevenly through the tendon, straining one side more than the other. This effect would also apply to someone with high arches or a pes cavus foot.

Training Errors. This would include a sudden increase in frequency or intensity of activity such as a runner increasing their mileage too quickly, training frequently on hills, or running on the cambered part of the road. Training regimens that don’t allow adequate healing time and exercising past the point of fatigue can also be detrimental to the health of the tendon.

Decreased flexibility or ankle mobility. The Achilles is one of the only major tendons that uses its full stretch capacity. When ankle motion is restricted the tendon must absorb the load of the body over a short time with less range of motion.7

Footwear. Many athletic shoes feature a heel that’s elevated around 12 mm higher than the front of the shoe, which over time can cause inflexibility of the calf muscles and a loss of dorsiflexion range of motion. A stiff heel counter may add compression forces to the tendon. The argument could also be made that a shoe with a stiff, inflexible sole places increased demands on the Achilles.

Poor proprioception. Proprioception refers to a person’s ability to sense where their body is in space. A simple example would be attempting to balance with your eyes shut. Elite athletes usually demonstrate higher levels of proprioception, and it is a skill that diminishes with both age and inactivity. A person returning to sports or exercise after a prolonged layoff my lack sufficient proprioception and body awareness to guard their Achilles from undue or non-uniform stresses.

Ankle weakness. Weakness or poor endurance of other muscles in the calf may transfer workload to the Achilles eventually leading to overload. 

Mechanism of Rupture

The movements that cause complete tearing of the tendon can be divided into three main categories.4

  1. Pushing off with the weight bearing forefoot while extending the knee, as a sprinter would do at the start of the race.
  2. Sudden, unexpected dorsiflexon. This could occur with stepping off the curb unexpectedly or falling into a hole
  3. Violent dorsiflexion of plantar flexed foot as occurs with landing from a height

As accidents are hard if not impossible to control, and it may be unreasonable to ask an athlete to not participate in a sport that requires pushing off with their foot (which would eliminate most sports) it would be near impossible to control the mechanism of injury behind the rupture. A better strategy for prevention would be to address the factors that cause the tendon to degrade in the first place.

Prevention

Because little is known about the exact nature of this injury, there is no proven method for preventing ruptures. If tendon degeneration is the major factor for rupture, a goal of any prevention strategy should include:

  • Restoring the tendon to good health, getting it as strong and resilient as possible
  • Removing external stresses that can cause microtrauma and wearing down of the tissue

1. Exercise

Exercise so far is the only treatment that has shown the ability to affect tissue collagen alignment. Athletes who subject their Achilles to repetitive loads have shown larger cross sectional area, which would most likely reduce the likely hood of rupture.5 A balance must be struck between a sufficient amount of activity that would cause the tendon to strengthen, an adequate recover time to allow complete healing.

Eccentric strengthening of the gastrocnemius-soleus complex is often considered the gold standard for both the prevention and treatment of Achilles tendinopathy. In one study of 44 patients with Achilles problems, half were asked to perform eccentric calf exercises daily and the other half were instructed to perform concentric exercises for a period of 12 weeks. 82% of the patients using eccentric based exercise reported a return to their prior level of activity compared to only 36% in the concentric exercise group.6

Eccentric exercise is putting resistance on a muscle as it is lengthening. An example for the calf and Achilles would be raising up on your toes with both feet, then lowering yourself down slowly on just one leg. Don’t get to hung up on any one specific exercise though, since current evidence suggests that loading the tendon is the real key. 

2. Correcting overpronation.

From a biomechanical standpoint, the Achilles should line up with direction of motion at the ankle. The everted heel position associated with large degrees of pronation causes the whipping motion and non-uniform loading of the tendon described earlier. 

3. Restoring ankle dorsiflexion mobility.

Not only does limited dorsiflexion promote over pronation, it also forces the Achilles to have to work harder in a smaller range. Examples of ankle mobility exercises can be found here.

4. Wearing shoes with lower heel-toe differentials.

A shoe with an elevated heel holds the foot in a plantar flexed position and causes shortening of the calf muscles. Transitioning to low differential shoes should be done cautiously because you’re asking the Achilles to function beyond the range that it’s accustomed to. 

5. Manual therapy?

I mark this one as questionable because there isn’t strong evidence supporting the use of massage or soft tissue mobilization to either strengthen tendons or facilitate tendon healing. The general theory behind employing these techniques is that vigorous mobilization of the tissue produces increased blood flow and an inflammatory response, components necessary for complete healing.

6. Balance training

Balancing exercise help to increase proprioception and the body’s ability to make quick adjustments. It can also help beef up the strength of the ankle stabilizing muscles that can assist the Achilles. Balance training is particularly important after a prolonged absence from sports.

Once the tendon has ruptured

There is ongoing debate about which method of treatment is best for Achilles ruptures and usually it comes down to a personal choice made between the patient and their surgeon so I’m not going to devote much space going into the specifics of treatment. The three main options are:

  1. Conservative (non-surgical) management
  2. Percutaneous repair: sutures are places through the skin to approximate the ends of the torn tendon
  3. Open operative repair (maximally invasive): cutting through the skin to suture the two ends of the torn tendon together4

Each approach has its advantages and disadvantages. Surgical repair has been typically associated with less likelihood or re-rupture but carries the usual risks associated with surgery.

Recovery

Regardless of the treatment choice, the patient is usually placed in a cast or boot for a period of 4-6 weeks after which time therapy is started to restore normal strength and range of motion in the leg. Return to the prior level of activity is usually expected after 4 to 6 months although a full recovery can take much longer. A study of NFL players with ruptured Achilles showed that only 64% were able to return to play at the NFL level, and the players who did return saw a significant reduction in their performance compared to their pre-injury levels.9 It’s difficult to compare pro athletes to the general population, but this study highlights the challenge of returning to the full prior level of activity following this major injury.

Luckily, each year advances in surgical techniques and a better understanding of the rehabilitation process are producing quicker recovery rates and improved long term functional outcomes. Back in 1575, when this injury was first described, the surgeon Ambroise Pare recommended that a ruptured Achilles be wrapped in bandages and dipped in wine and spices. Medicine has come a long way, but no matter the time period prevention is always the best option.

References
1. Thompson J, Baravarian B. Acute and Chronic Achilles Tendon Ruptures in Athletes. Clin Podiatr Med Surg. 28 (2011) 117–135
2. Leppilahti J, Puranen J and Orava S. Incidence of Achilles tendon rupture. Acta Ortbop Scand.1996; 67 (3): 277-279
3. Gebauer M, Beil FT, Beckmann J, Sarvary AM, Eublacker P, Ruecker AH, et al. Mechanical evaluation of different techniques for Achilles tendon repair. Arch Orthop Trauma Surg. 2007;127:795-9
4. Maffulli N. Rupture of the Achilles tendon. J Bone Joint Surg Am. Jul 1999;81(7):1019-36.
5. Maquirriain J. Achilles tendon rupture: Avoiding tendon lengthening during surgical repair and rehabilitation. Yale J Bio Med. 84 (2011), pp.289-300.
6. Kader D, Saxena A, Movin T, Maffulli N. Achilles tendinopathy: some aspects of basic science and clinical management. Br J Sports Med. Aug 2002;36(4):239-49.
7. Cook J, Khan K, Purdam C. Achilles tendinopathy Manual Therapy (2002) 7(3), 121–130
8. Schepsis A, Jones H, Haas A. Achilles tendon disorders in athletes. Am J Sports Med. 2002;30(2):287-305.
9. Parekh S, Wray W, Brimmo O, et al. Epidemiology and outcomes of Achilles tendon ruptures in the National Football League. Presented at American Academy of Orthopaedic Surgeons 73rd Annual Meeting, Chicago, Mar 2006.

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