Achilles Tendon Disorders:
Etiology and Epidemiology
Tero A.H. J7rvinen, MD, PhDa,b,c,*,
Pekka Kannus, MD, PhDa,b,d,
Nicola Maffulli, MD, MS, PhD, FRCS(Orth)e,
Karim M. Khan, MD, PhDf
aDepartment of Orthopaedic Surgery, Tampere University Hospital, Tampere, Finland
bMedical School and the Institute of Medical Technology, University of Tampere, Tampere, Finland
cThe Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
dAccident and Trauma Research Center and the Tampere Research Center of Sports Medicine,
UKK Institute, Tampere, Finland
eDepartment of Trauma and Orthopaedic Surgery, Keele University School of Medicine,
fDepartment of Family Practice & School of Human Kinetics, 2150 Western Parkway,
University of British Columbia, Vancouver, British Columbia, Canada V6T 1V6
The tendinous portion of the gastrocnemius and soleus muscles merge to
form the Achilles tendon, which is the largest and strongest tendon in the human
body [1,2]. The Achilles tendon has a high capacity to withstand the tensional
forces that are created by the movements of the human body.
The number and the incidence of tendon injuries, in general, have increased
substantially during the last few decades [1–5]. It is estimated that tendon injuries
account for 30% to 50% of all injuries that are related to sports. The increase in
tendon problems has been dominated by problems with the Achilles tendon,
which are common among athletes and the general public.
1083-7515/05/$ – see front matter D 2005 Elsevier Inc. All rights reserved.
* Corresponding author. The Burnham Institute, 10901 North Torrey Pines Road, La Jolla,
E-mail address: email@example.com (T.A.H. J7rvinen).
Foot Ankle Clin N Am
10 (2005) 255–266
Achilles tendon injuries have been divided into spontaneous ruptures and
overuse injuries. Generally, Achilles tendon problems arise from two different
origins: (1) some symptoms are caused solely by the excessive loading-induced
injury or degeneration of the Achilles tendon (without any predisposing systemic
diseases); and (2) sometimes a systemic disease, such as rheumatoid arthritis,
manifests with Achilles tendon symptoms . Only a minority (~2%) of all
Achilles tendon complaints and injuries are a result of a systemic, predisposing
disease; most tendon problems in a population can be traced to sports and
exercise-related overuse [1,6].
Chronic injuries: Achilles tendinopathy
Epidemiology of Achilles tendinopathy
Many terms have been used to describe (Achilles) tendon disorders. Because
of the highly confusing terminology for (Achilles) tendon disorders, it recently
was recommended that the clinical syndrome—characterized by a combination of
pain and swelling (diffuse or localized) in and around the Achilles tendon,
accompanied by impaired performance—should be called Achilles tendinopathy
[7,8]. Based on histopathologic findings, tendinopathy can be divided into
peritendinitis and tendinosis (tendon degeneration), and these entities may coexist
in the same, painful Achilles tendon; however, the division cannot be made
reliably in the clinical setting [3,4,7,8]. Some investigators avoid the term ‘‘de-
generation’’ because they believe it often is interpreted as meaning an irreversible
pathologic process, whereas tendinosis likely is reversible. We do not attribute
anything to the term degeneration other than to mean the findings that are seen
on histopathologic samples.
Achilles tendon overuse injuries are associated commonly with strenuous
physical activities, such as running and jumping [1,3,4,9]. The occurrence of
Achilles tendinopathy is highest among individuals who participate in middle-
and long-distance running, orienteering, track and field, tennis, badminton,
volleyball, and soccer [5,9–17]. Johansson  and Lysholm and Wiklander 
reported an annual incidence of Achilles disorders to be between 7% and 9%
in top-level runners.
In the studies with extensive material, the most common clinical diagnosis
of Achilles disorders is tendinopathy (55%–65%), followed by insertional
problems (retrocalcaneal bursitis and insertional tendinopathy; 20%–25%)
[5,9–11,17]. In a cohort study with an 11-year follow-up, Kujala et al 
found questionnaire-reported Achilles tendon overuse injury in 79 of 269 male
orienteering runners (29%) and 7 of 188 controls (4%); the age-adjusted odds
ratio was 10.0 in runners compared with controls.
Kvist [5,10] studied the epidemiology of Achilles tendon disorders in a
large group of competitive and recreational athletes who had Achilles tendon
jA¨rvinen et al 256
problems. In this report of 698 patients, 66% had Achilles tendinopathy and
23% had Achilles tendon insertional problems. In 8% of the patients, the
injury was located at the myotendinous junction, and 3% of the patients had
a complete tendon rupture. Eighty-nine percent of the patients were men.
Running was the main sports activity in patients who presented with an
Achilles tendon disorder (53%); persons who were runners represented 27%
of all patients who were studied in the sports medicine clinic where the research
Chronic Achilles tendon disorders are more common in older athletes than
in young athletes (teenage and child athletes) . In a report of 470 patients
who had Achilles tendinopathy and insertional complaints, only 25% of subjects
were young athletes and 10% were younger than 14 years; most of these younger
patients were diagnosed with calcaneal apophysitis (Sever’s disease) . Pa-
tients who had unilateral Achilles tendinopathy seem to have a high risk of
sustaining Achilles tendinopathy in the uninvolved leg as well; almost half of
the patients who had the Achilles tendinopathy (41%) developed symptoms
of this in the contralateral leg during the 8-year follow-up .
Etiology of Achilles tendinopathy
Sports injuries can be caused by intrinsic or extrinsic factors, either alone
or combination . In acute trauma, extrinsic factors predominate, whereas
overuse injuries generally are multi-factorial in origin. In chronic tendon dis-
orders, an interaction between these two types of factors is common .
The basic etiology of the Achilles tendinopathy is known to be multi-factorial,
because several extrinsic and intrinsic factors were identified that predispose to
these problems (Boxes 1 and 2; Fig. 1) [21,22]. In the epidemiologic studies,
various malalignment of the lower extremity and biomechanical faults are
claimed to play a causative role in two thirds of the athletes who had Achilles
tendon disorders. Kvist [5,10] found in his large series on chronic Achilles tendon
overuse injuries that some kind of predisposing malalignment of the lower
extremity was found in 60% of patients who had an Achilles tendon disorder
(see Box 1); however, the mechanisms by which these factors contribute to the
pathogenesis of Achilles tendinopathy remain in dispute . The most com-
mon, and perhaps the most important, malalignment in the ankle is caused
by hyperpronation of the foot. Increased foot pronation was proposed to be
associated with Achilles tendinopathy . Kvist [5,10] demonstrated that
limited subtalar joint mobility and limited range of motion of the ankle joint were
more frequent in athletes who had Achilles tendinopathy than in those who had
other complaints. In addition, forefoot varus correlates with Achilles tendino-
pathy [5,10,24,25]. Recently, Kaufman et al  observed that increased hindfoot
inversion and decreased ankle dorsiflexion with the knee in extension is
associated with Achilles tendinopathy.
In addition to hyperpronation and the other aforementioned malalignments,
leg length discrepancy is one of the more controversial potential contributing
etiology of achilles tendon disorders
factors . The traditional orthopedic view is that discrepancies of less than
20 mm are not clinically important . In elite athletes, however, a discrepancy
of more than 5 mm to 6 mm may be symptomatic and, consequently, for a
discrepancy of 10 mm or more, a built-up shoe or shoe insert has been recom-
mended to prevent overuse symptoms. It must be recognized that the true oc-
currence of these proposed biomechanical alterations, their magnitude and, above
all, their clinical importance is not well-known .
The importance of muscle weakness and imbalance, as well as disturbed
musculotendinous flexibility, in the development of Achilles tendon disorders
also is a matter of debate; however, muscular strength, power, endurance, and
flexibility are an important part of physical performance, and thus, can be
important in the prevention of certain sports injuries, particularly tendon inju-
ries . If the muscle is weak or fatigued, the energy-absorbing capacity of
Box 1. Predisposing intrinsic factors related to Achilles
tendinopathy in sports
Constitution: weak or strong
Local (anatomic) factors on the lower limb
Foot hyper- or hypopronation
Forefoot varus or valgus
Hindfoot varus or valgus
Pes planus or cavus
Leg length discrepancy
Muscle weakness and imbalance
jA¨rvinen et al258
the whole muscle–tendon unit is reduced, and the muscle no longer protects the
tendon from strain injury and subsequent inflammation and pain . Recently,
good short-term improvements have been reported in chronic Achilles tendinosis
with heavy-load eccentric training, a rehabilitation program that is based on
increasing the length, tensile strength, and force of the muscle–tendon unit
Box 2. Predisposing extrinsic factors related to Achilles
tendinopathy in sports
Corticosteroids (local and systemic)
Excessive loads on the lower extremities
Speed of movement
Type of movement
Number of repetitions
Heat or cold
etiology of achilles tendon disorders
Healing and tissue
repair and regeneration
→ Partial rupture
Healing by conservative
or surgical therapy, usually
with scar formation
Complete tendon rupture
overuse symptoms, tendinopathy
Fig. 1. The pathophysiologic mechanisms of Achilles tendon overuse injuries and disorders, which
also may lead to Achilles tendon ruptures.
0 - 1%
5 - 8%
1 - 3%
3 - 5%
Fig. 2. A schematic presentation of the development of chronic tendon disorders. According to current
concepts, repetitive tendon strain (3-5-8% strain) may lead to cumulative fiber microtrauma. If the
reparative capacity of the tendon tissue is exceeded, inflammation, edema, pain and tendon
degeneration (overuse injury) can ensue.
jA¨rvinen et al260
[26–30]. This concept, however, is open to speculation because the studies do
not provide conclusive evidence on whether muscular weakness, imbalance and
musculotendinous tightness are the causes or consequences of injuries.
By one definition, an overuse tendon injury is caused by repetitive strain
of the affected tendon such that the tendon can no longer endure tensile stress.
As a result, tendon fibers begin to disrupt microscopically, and inflammation
and pain result (Fig. 2) . Of the extrinsic risk factors, excessive loading of
the lower extremities and training errors were said to be present in 60% to 80%
of the patients who had Achilles tendon overuse injuries (see Box 2; see Fig. 1)
[5,10,22]. The most common of these include running too long a distance,
running at too high an intensity, increasing distance too greatly or intensity too
rapidly, and performing too much uphill or downhill work [5,10,22,25]. Mo-
notonous, asymmetric, and specialized training, such as running only (ie, with-
out cross-training), as well as poor technique and fatigue are further risk factors
for Achilles tendon overuse injuries (see Box 2). Poor environmental conditions,
such as cold weather, hard ground surface, and slippery/icy surface also were
suggested to promote Achilles tendon problems [1,3,21,23,31]. The lack of high-
quality prospective studies limits the strength of the conclusions that can be
drawn regarding these extrinsic risk factors.
Achilles tendon ruptures
Although the incidence of Achilles tendon ruptures is difficult to deter-
mine accurately, it is generally agreed that the incidence has increased in
the industrialized countries in recent decades [1,2,32–35]. The incidence of
ruptures of the Achilles tendon in the city of Oulu, Finland was approxi-
mately 18 per 100,000 in 1994 , 6 per 100,000 in Scotland in 1994 ,
37.3 per 100,000 in Denmark (a single county of 220,000 inhabitants) , and
17.9 per 100,000 in a single-hospital district (93,000 inhabitants) in eastern
Of all spontaneous tendon ruptures, complete Achilles tendon tears are
associated most closely with sports activities. Schfnbauer  found in his study
population that 75% of all Achilles tendon ruptures were related to sports,
whereas Plecko and Passl  found that the proportion of sports-related Achilles
tendon ruptures was 60%. In the material of 430 tendon ruptures that were
analyzed by Jo ´zsa et al , the number of sports-related Achilles ruptures was
similar (62%) to the two aforementioned studies, whereas only few (2%) ruptures
of other human tendons were sports related.
The distribution of Achilles tendon ruptures according to different sports
varies considerably from country to country, according to the national sports
traditions. For example, in northern and middle Europe, soccer, tennis, track and
field, indoor ball games, downhill skiing, and gymnastics are the most common
etiology of achilles tendon disorders
sports during which the Achilles tendon ruptures take place [1,2]. In North
America, American football, basketball, baseball, tennis, and downhill skiing
dominate the statistics [1,2].
There also are indications that patients who have spontaneous Achilles tendon
ruptures are at increased risk for sustaining a rupture in the contralateral Achilles
tendon as well .
Etiology of a spontaneous Achilles tendon rupture
The exact cause of Achilles tendon ruptures is not known, because most
of the patients who sustain a spontaneous rupture never had any symp-
toms (tenderness, stiffness, discomfort, diagnosed disease in the region of
the ruptured Achilles tendon) before the rupture [1,2,40]. Histopathologic
studies on ruptured Achilles tendons show, however, that almost all of these
subjects have clear degenerative changes, such as hypoxic and mucoid
degeneration, poor vascular supply, tissue and cell necrosis, calcification, and
tendolipomatosis, as well as irregular, degenerated collagen fibers at and
around the rupture site [41–44]. Furthermore, there is evidence that professional,
white-collar workers are overrepresented among patients who have Achilles
tendon ruptures . Taking these findings together, it is believed that a
sedentary lifestyle (possibly by contributing to poor circulation and subsequent,
hypoxic degeneration of the Achilles tendon), together with mechanical fac-
tors (sudden or repetitive movements), lead to spontaneous tears of the Achil-
les tendon [38,40]. A substantial proportion of Achilles tendon ruptures occur
in situations in which degeneration of the tendon cannot be traced as an etio-
logic factor, however. In these cases, the rupture is more a consequence of the
remarkably high forces that are involved in the performance (eg, high or triple
The biomechanically undesired positions of the ankle and foot, such as fore-
foot or calcaneal valgus and varus malalignments that cause horizontal, axial,
and rotational alterations on the collagen fibers of the Achilles tendon during
running are important predisposing factors to rupture [1,2,40].
Generally speaking, patients who have Achilles tendon rupture are younger
than those who have other tendon ruptures , and there is a clear male
predominance among this group of patients [6,38]. Although there are case
reports on pre-existing distinct intratendinous diseases as well as a wide range
of different generalized concurrent diseases (eg, rheumatoid arthritis, gout,
ankylosing spondylitis, chronic uremia, hyperparathyroidism) causing tendon
ruptures, they rarely are responsible (b2%) for Achilles tendon rupture and for
tendon ruptures, in general [1,6].
Several drugs can cause spontaneous tendon ruptures . Recent literature
provides strong evidence that the abuse of anabolic steroids increases the risk of
tendon rupture . Since the initial report by Ribard et al  that described
seven cases of Achilles tendinopathy (three were complicated further by spon-
taneous rupture of the tendon) after fluoroquinolone antibiotic treatment, several
jA¨rvinen et al262
similar cases have been reported around the world [47,48]. Thus, it has become
accepted that the fluoroquinolone antibiotics have an unspecific, toxic effect that
may cause tendonitis or spontaneous rupture of the Achilles tendon .
The issue of corticosteroids and the risk of tendon rupture is controversial
in the orthopedic literature [49,50]. In this context, it needs to be emphasized
that current literature that was derived from experimental or clinical studies
provides no convincing evidence either for or against (intratendinous or periten-
dinous) corticosteroid injections increasing the risk of tendon rupture (for a
review see ). Furthermore, rheumatologists have been injecting cortico-
steroids directly into the tendon tissue for decades without any evidence of
increased prevalence of tendon ruptures . A recent study, although small
in number of patients treated, indicates that the corticosteroids can be beneficial
and safe, even when injected directly into the tendon in athletes who have
Achilles tendinopathy . Thus, based on the current evidence on the topic, one
plausible explanation for the tendon ruptures that are seen after corticosteroid
injection is that rapid pain relief, and consequently, a quick return to strenuous
physical activity provides an opportunity for the degenerated tendon to rupture,
which merely is a final manifestation of the disease for which the corticosteroids
were applied .
The role of genetic background of the patient in Achilles tendon rupture is
almost unknown. There is evidence of a relationship between ABO blood groups
and spontaneous tendon ruptures. A strong association between blood group O
and Achilles tendon rupture was identified in a large series of patients in
Hungarian and Finnish populations [53,54]. The exact reason for the identified
relationship is unknown; the above described relationship has not been found in
other populations .
The Achilles tendon is the strongest tendon in the human body. The number
and incidence of Achilles tendon overuse injuries and complete, spontaneous
ruptures have increased in the industrialized countries during the last decades
because of the increased participation in sports.
The most common clinical diagnosis of Achilles overuse injuries is ten-
dinopathy, which is characterized by a combination of pain and swell-
ing in the Achilles tendon accompanied by impaired ability to perform
strenuous activities. Achilles tendinopathy is common in sports that require
strenuous physical activity. Extrinsic and intrinsic factors contribute to Achil-
Among the different ruptures of the human tendons, a complete rupture of
the Achilles tendon is the one that is associated most closely with sports.
Although histopathologic studies showed that ruptured Achilles tendons have
clear degenerative changes before the rupture, many Achilles tendon ruptures
take place suddenly without any preceding signs or symptoms. Considering that
etiology of achilles tendon disorders
professional white-collar workers are overrepresented among the patients
who have Achilles tendon rupture, in conjunction with the degenerative changes
that are identified in ruptured tendons, a potential mechanism for the causative
effect of a sedentary lifestyle on the increased incidence of spontaneous tendon
ruptures has been introduced.
This work was supported by grants from the Sigrid Juselius Foundation,
Helsinki, Finland; Tampere University Hospital Research Fund; the Research
Council for Physical Education and Sport Ministry of Education, Finland; and the
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