Abstract
Background: Calcaneal stress injuries are fairly common overuse
injuries in military recruits and athletes. We assessed the anatomic
distribution, nature, and healing of calcaneal stress injuries in a group of
military recruits.
Methods: Military recruits who underwent magnetic resonance imaging
for the evaluation of exercise-induced ankle and/or heel pain were identified
from the medical archives. The magnetic resonance images, plain radiographs,
and medical records of these patients were evaluated with regard to fracture
type and the natural history of the injury.
Results: Over ninety-six months, magnetic resonance imaging revealed
calcaneal stress injuries in thirty recruits in a population with a total
exposure time of 117,149 person-years, yielding an incidence of 2.6 (95%
confidence interval, 1.6 to 3.4) per 10,000 person-years. Four patients
exhibited a bilateral injury. Of the thirty-four injuries, nineteen occurred
in the posterior part of the calcaneus, six occurred in the middle part of the
calcaneus, and nine occurred in the anterior part of the calcaneus, with 79%
occurring in the upper region and 21% occurring in the lower region. The
calcaneus alone was affected in twelve cases. In twenty-two cases, stress
injury was also present in one or several other tarsal bones. A distinct
association emerged between injuries of the different parts of the calcaneus
and stress injuries in the surrounding bones. In only 15% of the patients was
the stress injury visible on plain radiographs. With the numbers available,
there were no significant differences between the patients with calcaneal
stress injuries and unaffected recruits with regard to age, height, weight,
body mass index, or physical fitness.
Conclusions: The majority of stress injuries of the calcaneus occur
in the posterior part of the bone, but a considerable proportion can also be
found in the middle and anterior parts. To obtain a diagnosis, magnetic
resonance imaging is warranted if plain radiography does not show
abnormalities in a physically active patient with exercise-induced pain in the
ankle or heel.
Level of Evidence: Prognostic Level II. See Instructions
to Authors for a complete description of levels of evidence.
Stress injuries of the calcaneus were first reported in the German
literature in
19371,2.
The first extensive study, published in 1944, described seventy-one cases of
such injuries among military recruits in the United
States3. Since then,
only a few large studies have been
documented4-8.
Calcaneal stress injuries are considered to be fairly common, especially in
military
recruits9-11.
In addition to military recruits, athletes are often
affected12. In
previous studies, nearly all calcaneal stress injuries were found to involve
the posterior part of the
bone3,7,10.
Previous research has suggested several risk factors for calcaneal stress
injuries, including poor physical condition and inadequate
footwear3,13,14.
The previous large studies on calcaneal stress injuries are more than
thirty years old and involved the use of plain radiographs as the diagnostic
tool. Currently, scintigraphy and magnetic resonance imaging are considered to
be the most reliable imaging methods for the diagnosis of bone stress
injuries. Both methods have excellent sensitivity, but magnetic resonance
imaging offers higher specificity and is considered to be the most
sophisticated technology currently available with which to diagnose and
describe bone stress
injury12.
The purpose of the present study, therefore, was to assess the anatomical
distribution, nature, clinical course, and healing of calcaneal stress
injuries in a large military recruit population on the basis of magnetic
resonance images and medical records. In addition, the risk factors for and
the incidence of calcaneal stress injuries were assessed.
The present study was conducted at a Finnish military hospital. Material
was obtained from the magnetic resonance imaging archives of the hospital to
cover the study period of eight years (from April 1, 1997 through March 31,
2005). We identified all recruits who had been referred for a magnetic
resonance imaging examination because of exercise-induced ankle and/or heel
pain. The criteria for inclusion were exercise-induced ankle and/or heel pain
during military service, a physical examination by an orthopaedic surgeon, and
evidence of a calcaneal stress injury on magnetic resonance imaging. We
excluded patients with a known recent injury and those with an infection
involving the ankle and/or foot. The original medical records and magnetic
resonance images of all patients who had undergone magnetic resonance imaging
were obtained for reevaluation to ensure that no stress injuries were missed.
The study design was approved by the Medical Ethics Committee of the
institution.
In Finland, military service is compulsory for all men but is voluntary for
women. The duration of the service varies from six to twelve months. Men are
expected to complete their service by their thirtieth birthday, but the
majority enter and complete it before turning twenty-one years old. An average
of 23,000 male and 370 female recruits enter into military training of the
defense forces annually. To establish the total exposure time for the
population at risk within the catchment area of the military hospital, dates
of entry into and transfer or discharge from military service were recorded
for every recruit. Using these dates, we reached the total exposure time of
117,149 person-years over the study period of ninety-six months. The equipment
used and the military training program were constant for all recruits during
the study period.
The patients in the study were first managed nonoperatively in the primary
health-care unit. As the result of an unclear diagnosis and prolonged pain,
they were then referred to an orthopaedic surgeon. The surgeon examined the
patients to determine the onset and duration of pain and its relation to
physical activities. The maximum areas of tenderness in the ankle and heel
were identified, and plain radiographs of the affected area were made. The
standard views were anteroposterior, mortise, and lateral views of the ankle;
lateral oblique and anteroposterior views of the foot; and lateral and
superoinferior views of the heel. The patients were then evaluated with use of
a 1.0-T magnetic resonance scanner with an extremity coil (Signa Horizon; GE
Medical Systems, Milwaukee, Wisconsin). Magnetic resonance images of the ankle
were acquired in at least two different planes; of these, the sagittal and
axial T1-weighted spin-echo sequence images (repetition time, 500 to 680 msec,
with two signals averaged; echo time, 10 to 15 msec, with two signals
averaged; 256 × 192 to 224 matrix) and T2-weighted fast-spin echo
sequence images with fat suppression (repetition time, 4400 to 6000 msec, with
two signals averaged; effective-echo time, 80 to 90 msec, with two signals
averaged; echo train length, 8 to 12; 256 × 224 matrix) were the most
common. The field of view was 18 to 20 × 18 to 20 cm, and the slice
thickness was 3.0 to 4.0 mm, with a 0.5 to 1.0-mm interslice gap. Additional
sequences, such as a STIR (short-tau-inversion-recovery) sequence (repetition
time, 5400 msec, with two signals averaged; echo time, 17 msec, with two
signals averaged; tau inversion, 140 msec, with two signals averaged; 256
× 224 matrix; field of view, 32 to 48 × 24 to 48 cm; slice
thickness, 4.0 to 5.0 mm; 0.5 to 1.0-mm interslice gap), were acquired as
well. Two patients also underwent scintigraphy.
All magnetic resonance images were reevaluated by a musculoskeletal
radiologist (M.K.). For evaluation purposes, the calcaneus was divided into
three anatomic regions: the anterior part, the middle part, and the posterior
part (Fig. 1-A). The calcaneus
was also divided into upper and lower regions to determine the location of
injury as accurately as possible (Fig.
1-B). Calcaneal stress injuries were classified into lower-grade
(grade-I, II, or III) injuries, which were associated with periosteal,
endosteal, and muscle edema, and more advanced (grade-IV) injuries, which were
associated with a visible fracture line on magnetic resonance
imaging15-17.
The lower-grade injuries were evaluated together because of the difficulty of
differentiating between such injuries in the calcaneus, which consists
essentially entirely of trabecular bone. All other positive magnetic resonance
imaging findings, including stress injuries to other tarsal bones, were also
reported.
Background information, such as military service data and physical fitness,
was retrieved for all recruits in the catchment area of the hospital (117,149
person-years). The available computer-based statistics included data on the
age, gender, height, weight, and length of military service of every recruit.
The body mass index values for all of the patients and unaffected controls
were determined from these statistics by dividing the body weight (in
kilograms) by the square of the body height (in meters). Aerobic and physical
fitness levels were ascertained during the first weeks of service. The aerobic
fitness level for all subjects was measured with use of a twelve-minute
running test, and the muscle strength level was assessed on the basis of five
measures (the distance of horizontal jump and the number of sit-ups, push-ups,
pull-ups, and back-lifts), which were then used to determine the individual
physical fitness scores for all subjects in the study.
To test differences between groups, the Kruskal-Wallis test was used for
the continuous skewed data and the independent-samples t test was used for the
continuous data. Differences in the cross-tables were determined with the
Pearson chi-square test. The level of significance was set at p = 0.05. The
statistical analysis was performed with use of SPSS software (version 12.0.1
for Windows; SPSS, Chicago, Illinois).
The incidence of stress injuries of the calcaneus was calculated by
dividing the number of recruits with a stress injury of the calcaneus (as
identified on magnetic resonance imaging) by the total exposure time. The
confidence interval was set at 95%, and the incidence is presented per 10,000
recruits per year.
On the basis of magnetic resonance imaging, thirty male recruits with a
mean age of twenty-one years (range, eighteen to twenty-six years) exhibited a
stress injury of the calcaneus over the period of eight years. This finding
yields a person-based incidence of 2.6 (95% confidence interval, 1.6 to 3.5)
per 10,000 person-years. The occurrence of stress injuries in the calcaneus
was 1.4 per 10,000 recruits. Four patients had bilateral involvement; thus, a
total of thirty-four different calcaneal stress injuries were evaluated.
Because of the calcaneal stress injury, five of the thirty patients were
relieved from the military training program and two were transferred to
military duties that did not require physical performance. The patients were
suspended from physical training for an average of twenty-four days (range,
three to seventy-three days). Patients became symptomless and returned to
normal training activity within an average of seventy-seven days (range,
twenty to 223 days) after first seeking medical attention. This length of time
includes leaves and failed attempts to resume the training program. In only
five cases (15%) was the stress injury found or suspected on the basis of
plain radiographs and then confirmed with magnetic resonance imaging
(Figs. 2-A and 2-B). In the
cases of the other patients, there was no indication of a stress injury on the
plain radiographs. The median time from the beginning of military training to
the onset of pain was sixteen days (range, three to 250 days).
With regard to the anatomical region of involvement, nineteen stress
injuries (56%) occurred in the posterior part of the calcaneus, six (18%)
occurred in the middle part, and nine (26%) occurred in the anterior part
(Fig. 1-A). In five cases the
injury involved both the posterior and middle parts of the bone, and in three
cases the injury extended from the upper region to the lower region of the
posterior part of the bone. In these eight latter cases in which the injury
involved two anatomic areas, it was considered as one injury and the location
was assigned on the basis of the predominant area of involvement. When the
entire bone was divided into upper and lower regions, twenty-seven (79%) of
the thirty-four injuries involved the upper region and seven (21%) involved
the lower region (Fig.
1-B).
In nineteen cases the stress injury was located in the right foot, and in
fifteen cases it was located in the left foot. There was no relationship
between the anatomic distribution of bone stress injuries and the side of
involvement. Twenty (59%) of the thirty-four injuries were higher-grade
(grade-IV) stress injuries with a fracture line that was visible on magnetic
resonance imaging (Figs. 2-B,
3-A, and 3-B), but fourteen
injuries (41%) were lower-grade (grade-I, II, or III) injuries that were
manifested only as bone marrow edema. The higher-grade (grade-IV) injuries
predominated in the posterior part of the calcaneus (representing fourteen of
nineteen injuries) and the anterior part of the calcaneus (representing five
of nine injuries). In contrast, the lower-grade (grade-I, II, and III)
injuries predominated in the middle part of the bone (representing five of six
injuries).
In twelve feet, the stress injury was found to affect the calcaneus alone.
In twenty-two cases, however, one or several other tarsal bones were also
affected. The most commonly affected bones were the talus
(Figs. 3-A and 3-B), the
navicular, and the cuboid. Injuries of the upper part of the calcaneal body
were associated with stress injuries of the talus, and injuries of the
anterior part of the calcaneus were associated with stress injuries of the
cuboid. In two of the thirteen feet with injuries in the upper region of the
posterior part of the calcaneus, excess fluid was also noted in the
retrocalcaneal bursa.
The examination by the orthopaedic surgeon revealed positive findings in
twenty-one of the thirty-four feet. Ten feet had tenderness in the calcaneus,
and eight had tenderness in other areas. Fifteen feet had soft-tissue edema
around the ankle joint or heel. Pes planus was reported in association with
three feet. Almost all of the ankles were stable; only two patients displayed
minor amounts of joint laxity. For thirteen feet, the clinical findings were
recorded in the medical record as normal. All patients were managed with
reduced activity; none had cast treatment or surgery.
Twenty-five patients returned to duty after recovery and completed the
service uneventfully. Of the five patients who were temporarily discharged
from the training program, four resumed and completed the program uneventfully
within two years after the injury. One patient had met the minimum length of
the military service obligation at the time of the injury discharge and did
not return to duty. The average time from the onset of pain to the date of
diagnosis of a stress injury on magnetic resonance imaging was fifty-five days
(range, twenty to 170 days).
With the numbers available, there were no significant differences between
the patients with calcaneal stress injuries and the controls in terms of
average height (178.7 cm for patients compared with 178.7 cm for controls, p =
0.9), weight (71.6 kg for patients compared with 73.8 kg for controls, p =
0.4), or body mass index (22.4 kg/m2 for patients compared with
23.6 kg/m2 for controls, p = 0.4). In addition, age (20.0 years for
patients compared with 20.0 years for controls, p = 0.3), length of military
service (nine months for patients compared with nine months for controls, p =
0.6), aerobic fitness (2503 m for patients compared with 2476 m for controls,
p = 0.8), or muscle strength (16.2 points for patients compared with 15.0
points for controls, p = 0.2) did not reach significance as risk factors for
stress injuries of the calcaneus.
All previous larger studies of calcaneal stress injuries were conducted
more than thirty years ago when plain radiographs were the only imaging
technology available. With use of magnetic resonance imaging and scintigraphy,
stress injuries can be documented and characterized with higher accuracy than
is the case with use of plain
radiographs12.
Injuries can be detected earlier throughout all parts of the bone. Notably,
lower-grade (grade-I, II, and III) injuries associated with only edema can
also be seen.
Stress injuries of the calcaneus are considered to be common. The authors
of some studies of military recruits in the United States have claimed that
such injuries represent the most common type of stress injury to the
foot7,11.
However, considerable differences in the incidence of such injuries have been
described in different military recruit populations. The incidence in the
present study was quite low but was consistent with that in a study of
recruits in the Israeli
army18. Both Israel
and Finland maintain conscription forces, with the military service program
being mandatory for all male citizens. The higher incidence reported in United
States recruits may be explained by the inadequate shoewear that was used when
those studies were conducted decades ago. This variation also can possibly be
attributed to differences in military training programs, equipment, or the
heterogeneity of the samples of recruits.
Previous studies have indicated that stress injuries of the calcaneus are
almost always located in the posterior part of the
bone3,8,10.
Although most of the injuries in the present study were located in the
posterior part of the bone, a considerable proportion (26%) of the injuries
involved the anterior part of the bone and 18% involved the middle part of the
bone. Only 56% of the injuries in the present study involved the posterior
third of the bone, in contrast to 95% to 100% of the injuries in previous
studies involving the use of conventional radiographs. The likely explanation
for this difference is the greater sensitivity of magnetic resonance imaging
in the detection of stress injuries in the middle and anterior parts of the
calcaneus. The vast majority of the calcaneal stress injuries in the present
study occurred in the upper part of the bone, an observation that was not
reported in the previous studies conducted with plain radiographs.
It is noteworthy that magnetic resonance imaging detected lower-grade
stress injuries, which accounted for 41% of the injuries in our study. These
grade-I, II, and III injuries could not be detected with plain radiographs,
yet they caused considerable pain for the patients. Of all stress injuries of
the calcaneus that were detected with magnetic resonance imaging, only a small
proportion (15%) were found with radiographs. Therefore, we believe that a
magnetic resonance imaging scan should be acquired when physicians working
with athletes or military recruits suspect a calcaneal stress injury, even if
plain radiographs reveal normal findings.
Calcaneal stress injuries often were associated with stress fractures
involving other bones of the foot and ankle. Notably, calcaneal stress
injuries in the anterior and upper parts of the bone were associated with
stress injuries of the cuboid and talus. Therefore, we may conclude that if a
stress injury is seen in the calcaneus, one should be suspected in the other
tarsal bones as well, particularly because stress fractures of the navicular
and the talus can permanently damage the foot if left
untreated19,20.
No significant relationship was found between the incidence of calcaneal
stress injuries and background variables such as weight and physical fitness.
Three feet had a minor pes planus deformity that may have created a
predisposition to the calcaneal stress injury. Other possible causes might
include other abnormal foot structure patterns, the biomechanics of the foot,
and/or limb-length
inequality21,22.
Apart from the three feet with pes planus, however, no other major
abnormalities were found in the present study. This finding was expected,
however, because men with major abnormalities of the feet are excused from
military service.
Calcaneal stress injuries have been considered to be low-risk stress
injuries as no displaced fractures have been documented in previous studies,
to our
knowledge3,8,15,23.
On the basis of the present study, we agree that calcaneal stress injuries can
still be regarded as benign, low-risk injuries. It is noteworthy, however,
that they can cause considerable hardship for military recruits and athletes
trying to focus on their training programs. Our patients were compelled to
refrain from the training program for weeks or even months, and a substantial
number were relieved from the military training program altogether.
In conclusion, calcaneal stress injury should be considered in the
differential diagnosis of exercise-induced ankle or heel pain in soldiers and
athletes. Although stress injuries of the calcaneus have been previously
diagnosed with use of conventional radiographs, magnetic resonance imaging has
a superior sensitivity for lower-grade injuries and injuries located in the
anterior and middle parts of the bone. Roughly half of calcaneal stress
injuries occur in the posterior third of the bone, and the other half occur in
the middle and anterior thirds combined. Moreover, stress injuries to the
different parts of the calcaneus are commonly associated with stress injuries
to the surrounding bones. ?
Note: The authors thank Harry Larni for the skillful artwork and
the Radiological Society of Finland and the Pehr Oscar Klingendahl Foundation
for personal grants supporting the study.
Asal. Über Entstehung und
Verhütung der Spontanfrakturen an den unteren Extremitäten.
Veröffentl. Gebiete. Herressaanitätsw.
1937;104:
32.10432
1937
Scheller F.
Überlastungsschäden am Knochengerüst junger Männer.
Med Welt. 1939;13:
1333.131333
1939
Hullinger CW. Insufficiency fracture of
the calcaneus similar to march fracture of the metatarsal. J Bone Joint
Surg Am. 1944;26:
751-7.26751
1944
Winfield AC, Dennis JM. Stress fractures
of the calcaneus. Radiology. 1959;
72: 415-8.72415
1959
[PubMed]
Leabhart JW. Stress fractures of the
calcaneus. J Bone Joint Surg Am.
1959;41:
1285-90.411285
1959
[PubMed]
MacDonald RG. Early diagnosis and
treatment of stress fractures of the calcaneus. J Am Podiatry
Assoc. 1966;56:
533-6.56533
1966
Darby RE. Stress fractures of the os
calcis. JAMA. 1967;200:
1183-4.2001183
1967
[PubMed][CrossRef]
Hopson CN, Perry DR. Stress fractures of
the calcaneus in women marine recruits. Clin Orthop Relat Res.
1977;128:
159-62.128159
1977
[PubMed]
Greaney RB, Gerber FH, Laughlin RL, Kmet
JP, Metz CD, Kilcheski TS, Rao BR, Silverman ED. Distribution and natural
history of stress fractures in US Marine recruits. Radiology.
1983;146:
339-46.146339
1983
[PubMed]
Weber JM, Vidt LG, Gehl RS, Montgomery
T. Calcaneal stress fractures. Clin Podiatr Med Surg North Am.
2005;22:
45-54.2245
2005
[CrossRef]
Yale J. A statistical analysis of 3,657
consecutive fatigue fractures of the distal lower extremities. J Am
Podiatry Med Assoc. 1976;66:
739-48.66739
1976
Spitz DJ, Newberg AH. Imaging of stress
fractures in the athlete. Radiol Clin North Am.
2002;40:
313-31.40313
2002
[PubMed][CrossRef]
Shaffer RA, Brodine SK, Almeida SA,
Williams KM, Ronaghy S. Use of simple measures of physical activity to predict
stress fractures in young men undergoing a rigorous physical training program.
Am J Epidemiol. 1999;149:
236-42.149236
1999
[PubMed]
Rome K, Handoll HH, Ashford R.
Interventions for preventing and treating stress fractures and stress
reactions of bone of the lower limbs in young adults. Cochrane Database
Syst Rev. 2005;2:
CD000450.2CD000450
2005
Kiuru MJ, Niva M, Reponen A,
Pihlajamäki HK. Bone stress injuries in asymptomatic elite recruits: a
clinical and magnetic resonance image study. Am J Sports Med.
2005;33:
272-6.33272
2005
[PubMed][CrossRef]
Kiuru MJ, Pihlajamäki HK,
Perkiö JP, Ahovuo JA. Dynamic contrast-enhanced MR imaging in symptomatic
bone stress of the pelvis and the lower extremity. Acta Radiol.
2001;42:
277-85.42277
2001
[PubMed][CrossRef]
Fredericson M, Bergman AG, Hoffman KL,
Dillingham MS. Tibial stress reaction in runners. Correlation of clinical
symptoms and scintigraphy with a new magnetic resonance imaging grading
system. Am J Sports Med. 1995;
23: 472-81.23472
1995
[PubMed][CrossRef]
Giladi M, Alcalay J. Stress fractures of
the calcaneus—still an enigma in the Israeli Army. JAMA.
1984;252:
3128-9.2523128
1984
[PubMed][CrossRef]
Burne SG, Mahoney CM, Forster BB, Koehle
MS, Taunton JE, Khan KM. Tarsal navicular stress injury: long-term outcome and
clinicoradiological correlation using both computed tomography and magnetic
resonance imaging. Am J Sports Med.
2005;33:
1875-81.331875
2005
[PubMed][CrossRef]
Bradshaw C, Khan K, Brukner P. Stress
fracture of the body of the talus in athletes demonstrated with computer
tomography. Clin J Sport Med.
1996;6:
48-51.648
1996
[PubMed][CrossRef]
Korpelainen R, Orava S, Karpakka J,
Siira P, Hulkko A. Risk factors for recurrent stress fractures in athletes.
Am J Sports Med. 2001;29:
304-10.29304
2001
[PubMed]
Kaufman KR, Brodine SK, Shaffer RA,
Johnson CW, Cullison TR. The effect of foot structure and range of motion on
musculoskeletal overuse injuries. Am J Sports Med.
1999;27:
585-93.27585
1999
[PubMed]
Boden BP, Osbahr DC, Jimenez C. Low-risk
stress fractures. Am J Sports Med.
2001;29:
100-11.29100
2001
[PubMed]