The Achilles tendon is subject to high forces with each step and therefore subject to wear-and-tear damage. There are many pathological conditions that affect the Achilles tendon, but the most common chronic conditions are tendinitis and bursitis, and the most common acute condition is Achilles rupture (often super-imposed on wear-and-tear). 

Structure and function

The Achilles tendon is the largest and strongest tendon in the human body. It attaches the posterior calf muscles (the gastrocnemius, soleus, and, less critically, the plantaris) muscles  to the calcaneus. 

Figure: The insertion of the Achilles tendon (red arrow)

The posterior calf muscles both actively plantar flex the ankle and resist passive dorsiflexion during walking, jumping, and running. Note that when the person places the ball of his or her foot on the ground during gait, body weight and momentum will force the ankle into dorsiflexion. Resisting this motion, and in turn decelerating the landing of the heel, is powered by the posterior calf muscles. Forces up to 3 times body weight may be applied to the tendon when this happens while walking; even greater forces are applied while jumping and running.

The Achilles tendon inserts into the posterior surface of the calcaneus.  The insertion begins about halfway between the plantar and superior surface of the calcaneus.

A bursa lies between the tendon and calcaneus above the insertion point: the so-called retrocalcaneal bursa. Another bursa lies posterior to the tendon between the tendon and skin, namely, the subcutaneous calcaneal bursa.  A bursa is a fluid-filled sac (the word shares its origin with the English word “purse”) that normally exists between tendons and bone in places where the bone surface may be prominent; this allows the tendon to glide more easily.  In the healthy state, the bursa is only a few cells thick, and the bursa is filled with only a small amount of lubricating fluid. However, when irritated, a bursa can become markedly thickened and filled with larger amounts of fluid. This condition is known as bursitis.


Patient presentation

Achilles tendonitis is a chronic condition characterized by pain and swelling in the Achilles tendon.  

Symptoms of tendonitis are produced by swelling and inflammation of the tissue that surrounds the Achilles tendon – the paratendon.  As such, the condition may be more appropriately described as an Achilles tenosynovitis (inflammation of the lining surrounding the Achilles tendon).  Inflammation of the tendon can be caused either by direct pressure from shoe wear or more commonly, as part of the healing response to over-use and micro-trauma.  

 There are two types of Achilles tendonitis: non-insertional tendonitis and insertional tendonitis

Non-Insertional Achilles Tendonitis:  In non-insertional (or mid-substance) Achilles tendonitis, the pathology is typically located 2 to 6 cm proximal to the insertion of the Achilles tendon to the calcaneus. 

Non-insertional Achilles tendonitis is often associated with a history of increased activity level (eg, starting a new training regimen or attempting to resume a normal activity level after an injury and enforced immobilization).  




Figure:  Location of Symptoms:  A patient presenting with non-insertional Achilles tendonitis (seen at left) will often describe pain and tenderness 2-6 cm from the insertion of the tendon into the calcaneus. The patient will often describe an increase in activity, such as starting a new training regimen or attempting to resume a normal activity level after an injury to another part of the foot or ankle.  Examination will usually reveal swelling and tenderness around the Achilles tendon. The location of the pain can help differentiate this from insertional tendinitis (seen at right) which presents with pain more distally.

Insertional Achilles Tendonitis: In so-called “insertional” Achilles tendonitis, the pathology is located at the insertion of the Achilles tendon to the calcaneus. Insertional Achilles tendonitis is a product of wear and tear at the attachment (“insertion”) of the tendon onto the calcaneus. This degeneration incites an inflammatory response and produces pain at the back of the heel. Eventually, the inflamed Achilles tendon may become calcified, forming bone-like fragments in the tendon.


The pathology associated with insertional Achilles tendonitis includes the “terrible triad”:

  1. degeneration of the Achilles tendon near the insertion site,
  2. an inflamed retrocalcaneal bursitis, and
  3. a Haglund’s deformity (a prominent bony lump on the heel




Figure: Location of pain in patients with the “terrible triad”: insertional Achilles tendonitis,  retrocalcaneal bursitis, and a prominent bony lump on the heel (known as a Haglund’s deformity). 


A Haglund’s deformity is a bony prominence associated with the upper part of the calcaneus. This is sometimes called a “pump bump.” This prominent bone tends to form gradually over many years, and can eventually cause irritation by disrupting nearby structures, including the retrocalcaneal bursa and the Achilles tendon. The bony prominence also creates discomfort by rubbing up against the back of footwear, the so-called  “heel counter” of the shoe. 




Figure: An xray showing both a “pump bump” (red arrow) as well as calcification of the Achilles tendon insertion (green arrow) (Modified from

When a Haglund’s deformity is present, the retrocalcaneal bursa can become inflamed. This inflammation can result in exquisite tenderness along the posterior aspect of the heel. 

Achilles tendon rupture:  The most common acute injury to the Achilles tendon is a complete rupture.  This injury typically occurs in men in their 30s and 40s. The inciting event often is an athletic activity that requires a sudden acceleration or changes in direction (ex. basketball, tennis, soccer).  Ruptures typically occur 2 to 5 cm proximal to insertion into the calcaneus. 

Achilles tendon ruptures usually occur when an athlete loads the Achilles immediately prior to pushing off. This can occur when suddenly changing directions, starting to run, or preparing to jump. A sudden change in direction requires the calf muscle to contract while still lengthening (eccentric loading).  This subjects the Achilles tendon to a large loading force which can tear it. To be clear: the tendon tears because of the large internal forces generated by the eccentric contraction of the calf muscle and applied to the Achilles, and not because of an external force. In such a sense, it may be said that the patient tore the tendon himself.

Although Achilles tendon tears are more common in middle aged men who exercise intensely but intermittantly (the so-called “weekend warrior”), the diagnosis must be considered in any patient who reports an acute mechanism of injury (or acute change in symptoms) implicating the heel or soft tissues above it. In those patients, the examiner can exclude an Achilles tendon rupture) with the Thompson test. (see figure).  

The Thompson test, as shown, takes advantage of the fact that squeezing the patient’s calf muscles with the knee flexed should induce plantar flexion of the ankle if and only if the Achilles is intact. 

Figure: The starting position for the Thompson test. The patient lays prone on the examining table. The affected leg is flexed 90, perpendicular to the table (blue lines). The examiner firmly squeezes the gastrocnemius (black arrows). The examiner examines the ankle for plantar flexion

Figure: Thompson test: The Normal (negative) response, namely plantar flexion of the ankle produced by  the examiner’s  pressure on the gastrocnemius,  indicating that the tendon is NOT torn

Two points are worth noting: 

  1. The nomenclature of the Thompson test can be confusing: a “positive” Thompson test is the absence of motion (whereas “positive” using means something was affirmatively observed). It is therefore helpful to describe the results as “positive for rupture” or “negative for rupture”.

  2. The Thompson test is necessary because testing active ankle plantar flexion can be misleading: an intact posterior tibialis and the flexors of the toe, which are both (weak) ankle flexors as well, might mask a torn Achilles. With these tendons intact, a patient with a ruptured Achilles may still be able to actively flex the ankle, especially without resistance.

A patient presenting with Achilles tendon rupture will often describe a sharp intense pain in the back of their heel at the time of the injury. Patients often initially report that they were “struck in the back of the heel” only to realize that this was not the case, as there was no one around them.

After the injury, patients may have some swelling. If they can walk at all, it will be with a marked limp.

Note that Achilles tendonitis or a partial rupture of the calf muscle (gastrocnemius) as it inserts into the Achilles can also cause symptoms that suggest a tendon rupture. The Thompson test is helpful (indeed essential) here.

At times, an Achilles tendon rupture is obvious on physical examination: a substantial defect in the Achilles 2-5 cm proximal to where it normally inserts into the heel bone is appreciated, beyond the positive Thompson test.


Objective Evidence

X-rays will usually be negative in cases of non insertional Achilles tendonitis, unless there is calcification of the Achilles tendon. (Calcification is relatively rare except in older patients.) Cases of insertional Achilles tendonitis may reveal a calcaneal spur on x-ray.

An MRI can give a detailed view of the soft tissue.  However, this test is not routinely indicated in the initial assessment of Achilles tendonitis.  

Figure: Achilles tendon rupture as seen on MRI (from

Ultrasound is usually less expensive than an MRI, but may not be available in all settings. Further, use of ultrasound may be limited by the examiner’s lack of skill or experience.

Plain x-rays will be negative in patients who have suffered an Achilles tendon rupture unless the Achilles injury involved an avulsion (traumatic displacement of a bony fragment from the calcaneus). Avulsions are rare, except in older patients with weaker bone.

Achilles rupture can be seen on ultrasound or MRI. However, these studies are usually not needed as a good history and well-performed physical exam should cinch the diagnosis. However, an MRI may be justified when the history or physical exam is ambiguous, or the quality of the tendon is in question (and whether it is amenable to repair) in the setting of chronic tendinopathy.  

Figure: Achilles tendinopathy as seen on MRI. The tendon is shown in continuity but is abnormally thickened. 


Achilles tendon rupture is a common injury that occurs at an incidence of 2.66 per 1000 person years or 18 per 100,000 population (PMID: 23386750). Middle-aged males are the largest group affected by this injury, and most injuries occur during athletic participation, most commonly basketball, soccer, or tennis.

Insertional Achilles tendonitis with its associated “terrible triad” of heel pain typically occurs in middle-aged individuals who are overweight, though this condition is also seen in young, active runners.  The exact incidence of this bimodal distribution has not been recorded.

Non-Insertional Achilles tendinitis is often associated with an increase in activity level/overuse and tends to occur in patients in their 30s and 40s.  According to Jarvinen et al., the reported annual incidence of Achilles tendonitis is between 7-9% in top-level runners (PMID: 15922917).

Differential diagnosis

There are four common causes for pain near the back of the heel:

  1. non-insertional Achilles tendonitis, 
  2. insertional Achilles tendonitis (with or without bursitis)
  3. paratendonitis (inflammation of the sheath surrounding the Achilles tendon, rather than of the tendon itself), and 
  4. Achilles tendon rupture.  

The Thompson test will identify an Achilles tendon rupture. The precise location of the pain should distinguish non-insertional Achilles tendonitis vs insertional Achilles tendonitis.  

Red flags

Acute pain in the vicinity of the Achilles tendon or weakness of plantar flexion rupture should be considered a “red flag” for an Achilles tendon rupture, prompting the examiner to perform he Thompson test. 


Treatment options and Outcomes

Achilles tendonitis 

Most patients with Achilles tendonitis can be treated effectively with rest, followed by a gradual return to normal activities.

The key elements of non-operative treatment include activity modification, shoe wear modification (a heel lift will unload the tendon), anti-inflammatory medication, and stretching and strengthening exercises. 

A tight calf muscle will increase the force going through the Achilles tendon and predispose the tendon to micro-tearing. 

Using a heel lift reduces the “stretch” on the Achilles during walking and thereby reduce the stress on the tendon.  

Because the forces applied to the Achilles tendon during activities are proportional to body weight, losing weight (even a small amount) can be very helpful, though attaining weight loss is difficult and maintaining it even harder.

Surgical debridement, that is, the removal of the damaged tissue with meticulous repair of the remaining tendon, may be chosen if non-operative treatment fails.  One setting where surgery may be considered more readily is that of a high-level athlete with a Haglund’s deformity. Surgery usually involves removing the prominent excess bone and the thickened inflamed retrocalcaneal bursa and debriding the Achilles tendon.

Recovery from surgery can be prolonged. Initially, the leg is immobilized to allow the wound to heal. Once the wound is healed, gentle range of motion exercises can be started. Some patients are limited in weight-bearing for the first six weeks during the healing process. Gradually, activity can be increased. Improvement in strength continues for several months and may take over one year. 

Stiffness of the ankle, rupture of the tendon, and deep vein thrombosis are known potential complications. Infection is uncommon but if it occurs it is a very serious problem because loss of skin and soft-tissue in this area is very hard to treat.

Achilles tendon rupture

Achilles tendon ruptures can be treated with either surgical repair or relative immobilization.  If the ruptured tendon is ignored (or not correctly diagnosed) the tendon ends will retract, leading to failure of the calf muscle and a dysfunctional lower leg.

The medical literature suggests that ruptures treated with surgery are less likely to re-rupture, though there are complications (such as wound breakdown) that are unique to surgery. A published expected-value decision analysis on this issue (PMID: 12435641)  reported that the optimal management strategy is highly dependent on patient preferences.

Non-operative treatment consists of placing the foot in a downward position [equinus] initially, a position that encourages the torn ends to contact each other. Once there is some healing, the foot can be advanced to a more neutral position. Early weight-bearing and controlled active plantar flexion has been shown to improve non-operative treatment.  However, care must be taken to avoid excessive dorsiflexion (extension), a position that encourages the torn ends to separate from each other.

It is important to monitor the status of the Achilles throughout non-operative treatment. This can be done by examination or via ultrasound. If there is evidence of gapping or non-healing, surgery may need to be considered. 

The primary advantage of non-operative treatment is avoiding an incision in an area, by dint of location and vascularity that is at higher risk for wound healing problems and infection.  The main disadvantage of non-operative treatment is that the recovery appears to be somewhat slower and the re-rupture rate appears to be higher.

Operative treatment of Achilles tendon ruptures involves opening the skin and identifying the torn tendon. This is then sutured together to create a stable construct.  By suturing the torn tendon ends together, and assuring continuity even if the ankle is not in full plantar flexion, the patient can be mobilized more quickly.

Figure: Operative repair of  Achilles tendon rupture. The proximal (blue arrow) and distal (red arrow) ends of the tendon are shown. The surgeon here is about to weave a suture through the body of the tendon to provide a firm attachment. (modified from

Risk factors and prevention

Factors that are associated with a higher risk for Achilles rupture include age between 30-50, male sex, playing recreational sports (most typically soccer, basketball, and tennis), prior steroid injections, and taking fluoroquinolone antibiotics.

Regular calf stretching, as shown in the figures, can help improve the Achilles tendon’s mechanical compliance (“stretchability” in layman’s terms) and makes it more resilient.



Figure: A consistent calf stretching program is an important part of treatment and prevention of Achilles injuries. Leaning against the wall with one foot forward and the back heel kept on the ground will stretch the Achilles and posterior calf muscles.



Figure: Controlled exercises where the Achilles tendon is being lengthened while the calf muscle contracts, such as the “Heel drop”shown here,  may help prevent (or treat) Achilles tendonitis. In this exercise, patients stand on their toes while positioned on the edge of a ledge such as a stair. They then slowly lower their heels down below the ledge simultaneously stretching and strengthening the Achilles tendon. This can be done with both legs at a time (bilaterally) or for a more concentrated effort, one leg at a time. It can also be done with the knees straight (putting force on the gastrocnemius) or the knees bent (putting force on the soleus).

Patients should gradually work up to performing 5 sets of 10 repetitions. These exercises should be performed 5-6 days per week during the active treatment phase and then 3 times per week to minimize the chance of developing recurrent symptoms. It is critical that this exercise is approached cautiously, as it has the potential to put excessive pressure on the Achilles. Patients should always warm up first (ex. get their blood flowing on an exercise bike for 5-10 minutes) before performing these exercises.

Using a heel lift or a shoe with a moderate heel can help reduce the stress on the tendon.   


In Greek mythology, Achilles was dipped into the River Styx by his mother Thetis, to coat his body with a shield of protection. Thetis grasped Achilles by the heel (on the eponymous tendon) when she dipped him, leaving that one area not washed by the river, and in turn unprotected. From that comesthe term “Achilles heel”, connoting a person’s area ofvulnerabilityy. 

Key terms

Achilles tendonitis; insertional; non-insertional; Achilles tendon rupture; Haglund’s deformity; retrocalcaneal bursitis; Thompson test


Bedside skills for the diagnosis of disorders of the Achilles include the ability to take a detailed but focused history and perform a thorough musculoskeletal examination. Additionally, students should be able to perform and interpret the Thompson test.