Persistent ankle pain following a sprain: A review of imaging

Abstract

The initial diagnosis of an "ankle sprain" is not always correct. Prolonged pain, swelling and disability sufficient to limit the activity and refractory to treatment following an ankle injury are not typical of an ankle sprain and should alert the clinician of the possibility of an alternative or an associated diagnosis. There are several conditions that can be misdiagnosed as an ankle sprain and those include ankle syndesmosis injuries, sinus tarsi syndrome, ankle and hind foot fractures, osteochondral lesions, posterior tibialis and peroneal tendons abnormalities, spring ligament damage, impingement syndromes and reflex sympathetic dystrophy. In this review, we discuss the imaging features of these conditions that can clinically mimic an ankle sprain. It is crucial to remember that unresolved ankle pain following an injury is not always just due to a "sprain".

Full text

REVIEW ARTICLE
Persistent ankle pain following a sprain: a review of imaging
Ramy Mansour &Zaid Jibri &Sridhar Kamath &
Kausik Mukherjee &Simon Ostlere
Received: 23 December 2010 / Accepted: 21 February 2011 / Published online: 5 March 2011
#Am Soc Emergency Radiol 2011
Abstract The initial diagnosis of an “ankle sprain”is not
always correct. Prolonged pain, swelling and disability
sufficient to limit the activity and refractory to treatment
following an ankle injury are not typical of an ankle sprain
and should alert the clinician of the possibility of an
alternative or an associated diagnosis. There are several
conditions that can be misdiagnosed as an ankle sprain and
those include ankle syndesmosis injuries, sinus tarsi
syndrome, ankle and hind foot fractures, osteochondral
lesions, posterior tibialis and peroneal tendons abnormali-
ties, spring ligament damage, impingement syndromes and
reflex sympathetic dystrophy. In this review, we discuss the
imaging features of these conditions that can clinically
mimic an ankle sprain. It is crucial to remember that
unresolved ankle pain following an injury is not always just
due to a “sprain”.
Keywords Ankle pain .Ankle sprain .MRI .Ultrasound
Introduction
Acute ankle injuries are extremely common, with an
estimated one ankle inversion injury per 10,000 people
each day [1]. Eighty-five percent of these injuries are
sprains, with inversion injuries of the lateral ligaments
accounting for 85% of these injuries. Regardless of the
treatment provided, ankle sprain prognosis is excellent [2]. In
this article, we use the term “ankle sprain”to refer to lateral
ligament complex sprain, the most common ankle ligament
injury [2]. Chronic discomfort and swelling, lasting for more
than 6 weeks, sufficient to limit the activity and refractory to
treatment are not typical of ankle sprains and probably imply
a more significant injury [3]. A wide range of conditions
related to the ankle or hind foot are often responsible,
involving ligamentous, osseous, chondral and tendinous
pathologies. These include ankle syndesmosis injuries, sinus
tarsi syndrome, spring ligament damage, missed fractures,
osteochondral lesions, posterior tibialis and peroneal tendons
abnormalities, impingement syndromes and reflex sympa-
thetic dystrophy. In this article, we start with discussing
lateral ankle ligaments sprains and also deltoid ligament
injuries. This is followed by describing the conditions that
could cause persistent ankle pain and could initially be
misdiagnosed as isolated lateral ligaments sprains.
Choice of imaging modalities
Weight-bearing standard AP, lateral and mortise radio-
graphs are the first radiological investigations for unre-
solved ankle sprain [4]. CT is excellent at providing fine
bony detail, but is rarely required given that there is
sufficient access to MRI [5]. Ultrasound may be used to
investigate focal soft tissue pathology. It also has the added
advantages of allowing dynamic studies necessary for
assessing tendinous conditions and in the guidance of
combined steroid and local anaesthetic injections that can
help localise the source of pathology [6]. MRI is usually the
modality of choice when investigating persistent ankle pain
following a sprain as both soft tissue and bony abnormal-
ities can be readily detected.
R. Mansour :Z. Jibri (*):S. Kamath :K. Mukherjee
Department of Radiology, University Hospital of Wales,
Cardiff CF14 4XW, UK
e-mail: zjibri@doctors.org.uk
S. Ostlere
Department of Radiology, Nuffield Orthopaedic Centre,
Oxford OX3 7LD, UK
Emerg Radiol (2011) 18:211–225
DOI 10.1007/s10140-011-0945-8

Lateral complex ankle sprain
Inversion sprains are the commonest injuries in athletes,
accounting for 21% of all sporting injuries. Injury is more
likely in the plantar-flexed ankle when the narrowest part of
the talar dome articulates at the mortise joint [1,4]. The
anterior talofibular ligament is involved in 95% of sprains,
and in 20%, both the anterior talofibular ligament and the
calcaneofibular ligaments are injured. The posterior talo-
fibular ligament is not usually injured unless there is a frank
dislocation of the ankle joint [7].
In clinical practice, ankle sprains have been classified
into three grades. In grade I (mild) sprains, the ligament
fibres are mostly stretched. Grade II (moderate) sprains
represent partial ligament tears. In grade III (severe)
sprains, the ligament is completely ruptured [1].
Ligament integrity can be assessed indirectly by stress
radiographs or more directly and accurately by ultrasound
or MRI [6,8,9]. In a recent study, the accuracy of MRI,
ultrasound and stress radiography in the diagnosis of
anterior talofibular ligament injury was 97%, 91% and
67%, respectively [10]. On ultrasound, the normal anterior
talofibular and calcaneofibular ligaments are readily visible
as echogenic bands [6]. On MRI, the ligaments are easily
identified on T1- and T2-weighted images as thin hypo-
intense bands well defined by the high signal of the
surrounding fat [9]. The posterior talofibular ligament can
appear inhomogeneous on T1-weighted MR images due to
areas of fatty tissue located between the ligament fibres and
this should not be mistaken for a ligament tear [9]. Acutely
Fig. 1 Anterior talofibular ligament injury. aT1-weighted axial MRI
showing thickened and indistinct anterior talofibular ligament indicat-
ing an acute tear (arrows). bSagittal T1-weighted MRI of the same
patient showing a non-bony talocalcaneal coalition at the middle
subtalar joint (open arrow)
Fig. 2 T2-weighted axial MR image showing a chronic tear of the
anterior talofibular ligament. The ligament is absent allowing focal
expansion of the joint space with an effusion (arrows)
212 Emerg Radiol (2011) 18:211–225

damaged ligaments can show discontinuity, detachment,
changes in thickness and irregularity (Fig. 1). There may be
obliteration of surrounding fat and increased signal on T2-
weighted images both in the surrounding bone and the
ligament itself, indicating oedema or haemorrhage [9,11,
12].
In patients with persistent pain, MRI remains the
imaging method of choice because it can also detect the
Fig. 3 Ultrasound of the anterior talofibular ligament. aAxial oblique
view showing a normal ligament (arrows). bAxial oblique image of
another ankle, showing chronic tear of the anterior talofibular
ligament. The ligament is thickened and hyper-vascular (arrows).
There is fluid in the anterolateral gutter (asterisk). Ffibula, Ttalus
Fig. 4 Axial proton density (PD) fat-saturated MR image showing
thickening with high signal intensity within the anterior tibiofibular
ligament consistent with an acute injury (arrow)
Fig. 5 Sinus tarsi syndrome with posterior impingement. aT1 sagittal
MRI showing low signal infiltrating the sinus tarsi instead of the
normally high signal of fat (arrowhead). bSTIR sagittal MR image
showing an abnormal high signal within the sinus (arrowhead). There
is also evidence of posterior impingement with oedema in the os
trigonum (arrow) and posterior synovitis (open arrow)
Emerg Radiol (2011) 18:211–225 213

common associated pathologies such as osteochondral
lesions and occult fractures [5]. Chronic lateral ankle
instability is the most common long-term complication of
grade III sprains with 10–20% of sprains presenting in this
manner [2,3]. Healed tears show thickening, while
incompetent ligaments show thinning, elongation, waviness
or absence of the ligament (Fig. 2). Oedema is rarely
encountered [5].
Ultrasound can also be used to detect abnormalities of
the ligaments [6]. In acute injures, the ligament is replaced
by amorphous hypoechoic mass, and tears are evident as
interruptions in ligament continuity. In chronic cases, the
ligament may appear attenuated or absent, or thickened
(Fig. 3)[6,13].
Deltoid ligament injuries
The deltoid ligament attaches the medial malleolus to
multiple tarsal bones and also to the spring ligament. It
has a superficial layer and a deep layer. The deep
component is intraarticular [14]. Isolated deltoid ligament
injuries are uncommon [15]. Deltoid ligament injuries are
Fig. 6 The spring ligament. aPD fat-suppressed coronal image
showing normal superomedial portion of the spring ligament (arrow)
deep to the posterior tibialis tendon (open arrow). bT1-weighted
coronal image showing a torn spring ligament with thickening and low
signal intensity (arrows). cPD fat suppression coronal image of the
same ankle in bshowing an increased signal within the thickened
injured spring ligament (arrows). Ttalus, Ccalcaneus
214 Emerg Radiol (2011) 18:211–225

often associated with lateral ankle ligaments injuries and
malleolar fractures [14,16]. The main mechanism of injury
is ankle eversion [2]. The severity of these injuries can be
classified similarly to that of lateral ligament complex
injuries. The MRI appearances depend on the severity of
these injuries and range from loss of the striated appearance
of the ligament with amorphous signal intensity on T1-
weighted imaging to complete discontinuity of the ligament
[14].
Ankle syndesmotic injuries
Ankle syndesmotic injury is a recognised cause of prolonged
ankle pain and disability [15]. The distal tibiofibular
syndesmosis is maintained by the tough interosseous
ligaments, as well as the anterior and posterior tibiofibular
ligaments. Syndesmotic injuries occur more commonly in
skiing and soccer, where twisting injuries are prevalent. The
proposed mechanism of injury is forced external rotation of
the foot combined with internal rotation of the leg [17]. It
can be detected by stress radiography or by ultrasound [6,
18]. MRI is the imaging modality of choice due to the
significant association of syndesmotic injury with other
pathologies such as fractures, osteochondral lesions of the
talar dome, joint incongruity and distortion of the tibiofibular
recess [19]. Acute syndesmotic injury to the anterior tibio-
fibular ligament would result in oedema around or within the
ligament on MRI (Fig. 4). In chronic injury, the ligament will
appear disrupted or thickened without oedema.
Subtalar sprain—“sinus tarsi”syndrome
The sulcus tali and the sulcus calcanei form a tunnel known
as the sinus tarsi, which is occupied by the strong cervical
Fig. 7 Ultrasound of the superomedial portion of spring ligament
(coronal oblique views). aThe spring ligament is thickened (asterisk).
bThere is also hyper-vascularity within the spring ligament on
Doppler imaging (arrow). PT posterior tibialis tendon, Ttalus, S
sustentaculum tali
Fig. 8 Osteochondral lesion. aAP Radiograph of the ankle reported
as normal. bSTIR coronal MR image showing a small osteochondral
fracture (arrow)
Emerg Radiol (2011) 18:211–225 215

and interosseous talocalcaneal ligaments, fat and the medial
origin of the inferior extensor retinaculum. The most
common cause of sinus tarsi syndrome is ankle sprain, the
remainder are due to rheumatological conditions, ganglion
cysts and foot deformities such as flat foot secondary to
posterior tibialis tendon damage [20,21]. On MRI, sinus
tarsi syndrome results in alteration of the normal fat signal
of the sinus tarsi. This can be manifested as diffuse
infiltration of the sinus with decreased signal intensity on
T1- and T2-weighted images, which correlates with fibrosis
seen pathologically. Another recognised pattern is diffuse
low-signal intensity on T1 and high signal on T2-weighted
images, which is related to inflammatory changes (Fig. 5)
[22,23]. The torn ligaments themselves may be visible
within the sinus. Partially torn ligaments can appear
irregularly thickened [23].
Fig. 9 Osteochondral fractures of the talar dome in two different
patients. aSTIR coronal MRI showing an undisplaced (stage I)
osteochondral fracture with oedema (arrow). bT1-weighted image of
another ankle showing a partially detached (stage II) osteochondral
fracture of the lateral corner of the talar dome (arrow) along with an
undisplaced (stage I) lesion affecting the medial corner (open arrow)Fig. 10 Lateral talar process fracture. aPlain AP radiograph of the
ankle showing oblique fracture of the medial malleolus following an
inversion injury (open arrow). The lateral talar process fracture
(arrow) was overlooked. bCoronal reconstruction CT image,
performed because of continuing pain following internal fixation of
the malleolar fracture, showing the lateral talar process fracture
(arrow)
216 Emerg Radiol (2011) 18:211–225

Spring ligament (calcaneonavicular ligament)
The spring ligament is closely associated, both anatomical-
ly and functionally, with the posterior tibialis tendon. It
consists of superomedial calcaneonavicular, medioplantar
calcaneonavicular and inferoplantar calcaneonavicular liga-
ments. The tibiospring ligament is part of the superficial
layer of the deltoid ligament that attaches to the super-
omedial portion of the spring ligament. The spring ligament
proper and the tibiospring ligament stabilise the talocalca-
neonavicular joint and serve as a secondary stabiliser of the
medial plantar arch [14]. It was shown that the super-
omedial component of the spring ligament should be
readily visible on MRI in all individuals, while the inferior
component is visible in about 91% and the medial
component in about 77% [24].
It is common for the superomedial calcaneonavicular
ligament to be abnormal with advanced posterior tibialis
tendinopathy [21] However, acute injury in isolation of
posterior tibialis tendinopathy is an under-diagnosed con-
dition and several cases have been reported in the literature
[25–27]. On MRI, torn ligaments can exhibit abnormal
heterogeneous signal or thickening (Fig. 6)[28,29]. A full
thickness gap is virtually diagnostic of a tear [29]. The
superomedial calcaneonavicular ligament can also be
clearly detected on ultrasound [30–32]. The injured
ligament will be thick, hypoechoic and have some internal
vascularity (Fig. 7).
Osteochondral lesions
Osteochondral fracture of the talar dome is the commonest
missed fracture associated with inversion sprains [11].
Lateral dome lesions most commonly occur at its middle
third, and they present as tenderness anterior to the lateral
malleolus. These lesions are usually acute shearing injuries
caused by contact between the corner of the talar dome and
the fibula during inversion or compression injuries. Medial
dome lesions occur at its posterior third, and present as
tenderness posterior to the medial malleolus. Talar fractures
were rarely encountered in the Ottawa Fracture Rules trial
[33]. A significant proportion of patients are able to
ambulate and do not present with tenderness on the
posterior aspect of the malleoli necessary to meet the
Ottawa Rules for radiography [34,35].
The severity of an osteochondral talar dome fracture can
be assessed using the Berndt–Harty staging system, which
Fig. 12 Fracture of the anterior process of calcaneus. aLateral
radiograph of the ankle with no detectable fracture. bCorresponding
STIR sagittal MR image showing an undisplaced fracture of the
anterior process of the calcaneus (arrows)
Fig. 11 Lateral ankle radiograph showing fracture of the posterior
talar process (arrow)
Emerg Radiol (2011) 18:211–225 217

Fig. 15 Axial PD fat-saturated MR image demonstrating pernoeus
brevis tendon split surrounded by high signal intensity indicative of
fluid (arrow)
Fig. 14 Peroneal tendon dislocation. aPlain AP radiograph with a
typical avulsion fracture at the origin of the peroneal retinaculum from
the lateral aspect of the distal fibula (arrows). bAxial oblique
ultrasound image showing the avulsed fragment (arrows) attached to
the peroneal retinaculum (arrowheads). cLongitudinal ultrasound
image. The peroneal tendon (asterisk) is dislocated and lies deep to
the avulsed distal fibula fragment (arrow). LM lateral malleolus
Fig. 13 Plain foot radiograph showing os peroneum fracture. The
patient was clinically tender over the os peroneum
218 Emerg Radiol (2011) 18:211–225

is based on the integrity of the articular cartilage and
condition of the underlying bone. Stage I fractures are
undislocated compression fractures of subchondral bone,
with sparing of the overlying cartilage. Stage II fractures
appear as partially detached osteochondral fragments.
Stage III fractures result in complete detachment without
displacement, while stage IV fractures are displaced
[36].
Osteochondral fractures may be visible on the plain AP
radiograph, although the findings may be subtle and require
very careful attention. Displaced fragments are more likely
to be detected on the plain radiograph than those which are
undisplaced. However; it is not unusual for the initial
radiograph to be normal (Fig. 8). Small fragments are rarely
visible [37]. Such fractures remain painful if they do not
heal or if they form loose bodies. MRI is the best way to
detect these fractures and to assess the fracture stage [37]
(Fig. 9). It was also shown that multidetector CT can be
accurate in detecting these fractures [38]. However, MRI
has the advantages of assessing the integrity of the articular
cartilage and also the bone marrow changes. Cartilage-
sensitive techniques, such as T2-weighted turbo spin-echo
and fat-suppressed 3D spoiled gradient echo have improved
visualisation [39]. Subchondral oedema may imply trabec-
ular micro-fracture or bone bruising. The signal intensity of
the osteochondral fragment itself is useful. Hyper-intensity
on T1-weighted images indicates viable bone marrow,
whilst low signal intensity in both T1- and T2-weighted
images indicates necrosis. MR and CT arthrography have
been used for staging purposes with a better accuracy [40,
41].
Missed fractures
One cause for an apparently sprained ankle is a missed
fracture. The second most commonly missed fractures (after
osteochondral fractures of the talar dome) involve the
lateral talar process (Fig. 10). It is commonly referred to as
the “snowboarder’s talus fracture”[42]. Whilst standard
radiographic views can detect such fractures, as many as
50% are missed [43]. CT readily shows this injury. Failure
to detect this fracture can have severe consequences: the
fracture is intra-articular and mainly affects a young age
group, and so may fail to heal, resulting in non-union and
chronic pain [43].
The posterior talar process is a rare fracture site that is
nevertheless frequently missed (Fig. 11). In the largest
published series, only three out of 20 patients presented
acutely following the injury [44]. Whilst it might be
possible differentiate this fracture from the os trigonum by
its rough and irregular surface, a definitive diagnosis is
often made using MR imaging.
Fig. 16 Axial (a) and sagittal (b) PD fat-saturated MR images
demonstrating partial tear of the posterior tiblialis tendon surrounded
by high signal intensity indicative of fluid (arrow). MM medial
malleolus
Emerg Radiol (2011) 18:211–225 219

Fractures of the anterior process of the calcaneus
account for up to 15% of all calcaneal fractures. These
are regularly misdiagnosed as an ankle sprain because
most patients can continue to bear weight on that ankle
(Fig 12)[45].
The fractures most commonly associated with sprains
are those of the proximal fifth metatarsal [2]. As it is the
distal site of attachment of both peroneus brevis tendon and
the lateral cord of the plantar aponeurosis, forcible
inversion of a plantar-flexed foot can cause complete
avulsion fractures. Fractures involving the very proximal
tip may be missed, resulting in a misdiagnosis as an ankle
sprain [46].
The os peroneum is a sesamoid bone found in up to 20%
of adults and is located within the peroneus longus tendon
at the region of the cuboid tunnel [47]. There have been
case reports of fractures of the os peroneum initially
diagnosed as a simple sprain [48,49]. This fracture can
be seen on plain films, MRI and ultrasound. Fracture of the
os peroneum is nevertheless a rare injury (Fig. 13). It is part
of the spectrum of “painful os peroneum syndrome”which
includes acute or healed os peroneum fractures and
diastasis of multi-partite os peroneum. Os peroneum
fracture is associated with peroneus longus tendon tears
and stenosing tenosynovitis [50,51].
Tendon injuries
Peroneal tendons
Various forms of peroneal tendon pathology, including
tenosynovitis, tendon or retinaculum rupture and disloca-
tion can result in chronic symptoms following an ankle
injury. Peroneal tendon subluxation or dislocation is
associated with traumatic resistance dorsi-flexion and
eversion. Plain radiographs may show an avulsion fracture
of the lateral aspect of the distal fibula due to the
detachment of the superior peroneal retinaculum
(Fig. 14a). Chronic ankle instability with superior peroneal
Fig. 17 Transverse (a) and
longitudinal (b) ultrasound
images of the posterior tibialis
tendon several months following
a twisting injury showing a
longitudinal split in the tendon
(arrow)
220 Emerg Radiol (2011) 18:211–225

retinaculum instability is considered a risk factor for
peroneal tendon dislocation [52]. Ultrasound is a good
method of determining the position of the tendons in
relation to the retinaculum or fracture (Fig. 14b, c). The
tendons can clearly be seen on MRI as hypointense
structures on both T1- and T2-weighted images. In
general, T1 images provide excellent anatomical detail
whilst T2-weighted images best define the sites of
pathology as in tenosynovitis. In pernoneal tendons
dislocation, axial MR images reveal the position of the
tendons out of the retromalleolar sulcus. Longitudinal
peroneal tendon splits can also be clearly demonstrated on
the axial MR images (Fig. 15). Care must be taken to
differentiate peroneal tendon abnormalities from the
recognised normal variants like a bifurcated peroneal
tendon and the presence of accessory muscles such as
peroneus quartus [53].
Chronic peroneal tenosynovitis is often misdiagnosed
initially as an ankle sprain in patients with a history of
inversion injuries [54]. On MRI, this would manifest as
fluid within the tendon sheath. The tendon itself usually
appears normal. A potential pitfall is the appearance of fluid
as a consequence of a calcaneofibular ligament tear [43,
54].
Posterior tibialis tendon
Posterior tibialis muscle contraction results in plantar
flexion and inversion. It maintains the tone of the medial
longitudinal arch of the foot. Multiple case reports have
been published involving posterior tibialis tendon rupture
diagnosed initially as ankle sprain [55–57]. In children and
younger patients, the trauma may be sufficiently severe to
result in complete avulsion from the navicular tuberosity
[55]. In the middle-aged and elderly patients, minor sprains
can induce rupture in a degenerate tendon posterior and
distal to the medial malleolus [56]. Some patients exhibit an
acute flat foot deformity. Delay in detection results in
weakening of the ligaments of the medial longitudinal arch,
and subsequent painful, irreversible foot deformities
remedied only by arthrodesis, as opposed to soft tissue
repair [58,59]. As with the peroneal tendons, both MRI and
Fig. 18 PD fat-saturated axial MR image showing low signal
intensity soft tissue thickening in the anterolateral gutter consistent
with scarring (arrow) suggestive of anterolateral impingement which
supported the clinical findings
Fig. 19 Lateral radiograph of the ankle showing osteophytes at the
dorsal aspect of the talar neck and in the anterior lip of the distal tibia
(arrows). These osteophytes are associated with anterior ankle
impingement syndrome
Emerg Radiol (2011) 18:211–225 221

ultrasound can readily detect partial tears, chronic tendon-
itis, rupture and dislocation (Figs. 16,17)[60].
Impingement syndromes
Ankle impingement is the painful restriction of ankle range
of movement secondary to soft tissue or bony abnormality.
Sprain is the leading cause of impingement syndromes.
They are defined according to their anatomical position,
most commonly anterolateral, posterior and anterior im-
pingement. Anteromedial and posteromedial impingement
are rare and less well-defined entities [61,62]. Treatment is
the same for all types which includes conservative
management followed by arthroscopic resection of im-
pinged tissue if there is no response to non-operative
treatment [63].
Anterolateral impingement
In anterolateral impingement syndrome, the synovial
membrane hypertrophies and scars in response to repeated
sprains. This condition can cause severe morbidity and
pain, particularly amongst athletes and the younger popu-
lation. It is estimated that the incidence of anterolateral
impingement syndrome is 3% following ankle sprains [63,
64]. The resultant soft tissue mass can become trapped in
the mortise joint at the anterolateral gutter [64]. The patient
can present with swelling and a vague exertional pain over
the anterolateral ankle. This condition can be exacerbated
by osteophyte bone impingement. The MRI findings of
abnormal soft tissue mass in the anterolateral gutter which
is of low signal intensity on T1 and a low or an
intermediate signal on T2 or proton density-weighted
images is suggestive of anterolateral impingement
(Fig. 18)[65]. A meniscus-like hyalinised lesion is
sometimes seen in the advanced cases of anterolateral
impingement as a hypo-intense structure on both T1- and
T2-weighted images [65,66]. MR arthrography proved
accurate in the assessment of the anterolateral recess. The
absence of a normal fluid filled recess between the
anterolateral soft tissue and the anterior surface of fibula
suggests the diagnosis. The diagnosis should only be made
when it is supported by clinical signs of impingement
[66].
Posterior impingement
The os trigonum is an accessory sesamoid bone found in
2.5–15% of normal feet. In some people, fusion produces
a prominence known as the Steida process. While most
people with os trigonum or Steida process are asymp-
tomatic, repeated compression can lead to bony contu-
sion and synovitis involving both the ankle and subtalar
joints. This is often seen in soccer players and ballet
dancers [67]. The impingement can also be purely related
to soft tissue compression between the posterior tibia and
the calcaneus. Most patients with this condition give a
history of ankle sprain weeks earlier. Posterolateral
capsular thickening and synovitis of the posterior joint
recess with oedema in the adjacent bones including the os
trigonum are recognised MRI findings of posterior
Fig 20 Reflex sympathetic dystrophy in a patient with a history of
ankle sprain. Coronal (a) and sagittal (b) PD fat-saturated MR images
of the ankle showing patchy bone marrow oedema around the
posterior subtalar joint and involving multiple tarsal bones with ankle
effusion and surrounding soft tissue swelling
222 Emerg Radiol (2011) 18:211–225

impingement (Fig. 5). Tenosynovitis of flexor hallucis
longus is a commonly associated MRI finding due to the
course of the tendon between the medial and lateral
tubercles of the talus [68,69].
Anterior impingement
Anterior ankle impingement is most commonly encoun-
tered in soccer players and ballet dancers, and is the result
of a radiographically visible osteophyte arising from the
anterior lip of the distal tibia, which may be complemented
by a second osteophyte originating from the opposing
dorsal surface of the talus. Bony formation is thought to be
driven by a combination of focal chondral degeneration,
repeated dorsi-flexion and/or direct trauma [66]. Neverthe-
less, such bony formations are also found in asymptomatic
athletes [70]. Plain radiographs are sufficiently sensitive in
detecting the osteophytes, with standard lateral views
detecting anterior and more anterolateral osteophytes
(Fig. 19), and an oblique view for detecting more
anteromedial osteophyes [71,72]. MRI is useful in the
appreciation of the abnormal mechanics and in particular
the presence of extra-articular causes of impingement that
may not be detected at arthroscopy. MRI shows synovitis
and capsular thickening in the anterior recess of the
tibiotalar joint with bone marrow oedema in the anterior
part of the talus and anteriorly in the distal tibia in addition
to the described osteophytes [73].
Reflex sympathetic dystrophy
It is characterised by extreme burning pain, a history of
trauma and evidence of sympathetic dysfunction. Most
patients describe a previous injury that can be minor or
severe, and this includes sprains [74]. There are three
clinical stages of reflex sympathetic dystrophy. Stage 1 is
characterised by burning pain and warmth sensation. In
stage 2, the pain diminishes with the onset of vasoconstric-
tion. In stage 3, the skin can become smooth or cyanotic
with the onset of muscle atrophy [75]. The underlying
pathophysiology remains uncertain. Radiographs often
exhibit non-specific soft tissue swelling and subperiosteal
bone resorption [76]. MR imaging findings of reflex
sympathetic dystrophy vary depending on the stage of this
condition. In one study, patients with the warm form (stage
1) of reflex sympathetic dystrophy showed periarticular
marrow oedema at MRI (Fig. 20). There were also
inconstant findings on MRI including soft tissue oedema,
joint effusion, and rarely, subchondral band of low signal
intensity on T1 weighted images [77]. In another study,
stage 1 reflex sympathetic dystrophy demonstrated contrast
enhancement of the periarticular or subcutaneous tissues
and skin thickening on MRI. Muscle and fascial oedema
was also occasionally demonstrated. In stage 2 and 3, there
was no evidence of contrast enhancement. In stage 3,
muscle atrophy was seen on MRI [75].
Tarsal coalition
One study has found a much higher incidence of calcaneo-
navicular coalitions than anticipated in patients who
sustained ankle sprain supporting the view that coalition
increases the susceptibility to sprain (Fig. 1)[78]. Tarsal
coalition refers to an abnormal bony, cartilaginous or
fibrous union of two or more bones of the foot. It affects
about 1% of the population, with 50% of the cases thought
to be bilateral [79]. While the majority of cases are
congenital, some occur due to infection, trauma or surgery.
The commonest form is calcaneonavicular coalition, fol-
lowed by talocalcaneal coalition. The consequence of
coalition is an anatomical, often sub-clinical, restriction of
motion at the mid or hind foot.
Conclusion
Persistent ankle pain following a “sprain”is not always just
due to a sprain. Chronic discomfort and swelling sufficient to
limit the activity and refractory to treatment is not typical of
ankle sprains and probably imply a more significant pathology
that could be related to the ankle or the hind foot. It is
important to recognise the causes of unresolved ankle pain
which would lead to an accurate approach in its evaluation.
Plain radiograph is the first-line investigation whilst MRI is
usually the modality of choice when investigating persistent
ankle pain following a sprain as both soft tissue and bony
abnormalities can be readily detected.
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