Imaging of foot in non trauma and non neoplastic diseases

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IMAGING OF FOOT

IN NON TRAUMA AND NON NEOPLASTIC ETIOLOGY

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INTRODUCTION Radiologic evaluation of the foot is often

a complex task given the relatively small size of structures, detailed intricacy of anatomy, multifaceted relationships and mechanism of the anatomic structures, and wide range of pathologic entities.

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ANATOMY

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OSSIFICATION CENTERSPrimary centers

Within the fetal period, ossification commences first in the metatarsals, followed closely by the distal phalanges, proximal and finally the middle phalanges.

this is a different order from that found in the hand, where the distal phalanges are the first to commence ossification.

The primary centres for the shafts of the metatarsals appear between 8-10 prenatal weeks, which is at a similar time to that for the metacarpals.

Metatarsals 2 -4 tend to appear before metatarsal 5, while the first metatarsal may not appear until 12 prenatal weeks.

The distal phalanges appear around the end of the 2nd and throughout the 3rd month of intra-uterine life and so may appear- before the shaft of the first metatarsal.

The Juvenile Skeleton, By Louise Scheuer, Sue Black

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The primary centres of ossification for the proximal phalanges appear in the 4th prenatal month, around 14-16 prenatal weeks.

The centres for the first to the third toes tend to appear in advance of those for the fourth and fifth toe.

As with the hand, the middle phalanges of the foot are the last of the long bones to commence ossification.

In summary, therefore, the primary centres of ossification for the metatarsals and phalanges are all present (with the probable exception of the middle phalanges of the lateral toes) by the end of the 5th prenatal month.

The normal sequence of appearance for the tarsal bones is relatively constant and well documented.

The calcaneus appears first, followed closely by the talus and then the cuboid. The remainder of the tarsal bones always appear after birth and the sequence begins with the lateral cuneiform and is followed by the medial and then the intermediate cuneiform, with the navicular being the last to commence ossification.The Juvenile Skeleton, By Louise Scheuer, Sue Black

6The Juvenile Skeleton, By Louise Scheuer, Sue Black

7The Juvenile Skeleton, By Louise Scheuer, Sue Black

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ANATOMY OF FOOT The foot is divided into the Hindfoot

Calcaneus Talus

Midfoot Cuboid Navicular Three cuneiforms

Forefoot Metatarsals Phalanges

The articulation between the hindfoot and the midfoot (midtarsal joint) is frequently referred to as Chopart’s joint Named after surgeon who performed amputations at the

calcaneocuboid, talonavicular joint The articulation between the midfoot and the forefoot is

referred to as the Lisfranc joint Named after French surgeon Francois Chopart (1743–1795) who

performed amputations of the foot at this level

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TENDONS AND MUSCLES There are three distinct groups or compartments of lower

leg musculature:

posterior,

lateral,

and anterior.

The posterior muscles are divided into superficial and deep

groups.

The superficial group consists of gastrocnemius, soleus, and

plantaris.

The gastrocnemius and soleus unite to form the Achilles

tendon that inserts into the tuberosity of the calcaneus.

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The Achilles tendon is not surrounded by a tendon sheath as are other

ankle tendons, but does have a peritenon covering.

The fibers of achilles tendon are homogeneous and low signal on all MR

pulse sequences.

On axial images the tendon has a flat or concave anterior surface.

Anterior to the tendon is a fat-containing space known as Kager’s fat pad.

Between the distal Achilles tendon and the posterior calcaneal tuberosity

lies the retrocalcaneal bursa.

The plantaris is a small muscle between the gastrocnemius and soleus;

this muscle is rudimentary and may be absent in 10% of the population.

Its long tendon runs along the medial border of the Achilles and inserts

into the calcaneus, the Achilles tendon itself, or the flexor retinaculum

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The deep group of posterior muscles consists of the flexor hallucis longus, flexor digitorum longus, and tibialis posterior.

All three muscles arise from the posterior tibia, fibula, and/or interosseous membrane.

The tendons begin above the level of the ankle and all three pass beneath the flexor retinaculum.

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The anterior compartment contains the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius muscles.

The lateral compartment muscles include the peroneus longus and brevis.

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IMAGING MODALITIES Radiograph USG CT MRI A multimodality approach is often necessary for

complete radiologic assessment. Radiography, sonography, and computed

tomography all play important roles in the radiologic assessment of the foot and ankle.

However, magnetic resonance imaging (MRI) is often the imaging modality of choice attributable to the superior soft tissue contrast resolution, multiplanar capability, lack of ionizing radiation, and ability to do post contrast imaging.

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RADIOGRAPHY Plain radiographs are instrumental in

the initial evaluation of foot disorders. Weight-bearing views should be

obtained when possible.

Dorsal-Plantar (DP) and Oblique - are standard projections of the forefoot.

Comparison views of the contralateral foot is not routinely ordered but can be helpful in difficult cases

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ULTRASONOGRAPHY Sonography readily demonstrates the

tendons and peritendinous pathologies, Dynamic examination during flexion and

extension maneuvers Synovial pathologies can be evaluated Small amount of fluid along the

posterior tibial and common peroneal tendons in normal subjects.

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•No thickening •Homogeneous echogenicity •No hypoechoic or hyperechoic foci •Nil neovascularisation

Neovascularization in the distal third of tendon Thickened – ‘Spindle Shape’

Abnormal Diagnosed by 1 or more of the following findings

1.Tendon thickening with heterogeneous echogenicity 2.Hypoechoic foci representing intrasubstance tears (defined as linear hypoechoic foci associated with discontinuity of tendon fibres) 3.Calcifications and enthesiophytes at the tendon attachment 4.Neovascularization

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CT CT has become an invaluable additional tool, particularly

for visualizing complex anatomic regions such as the midfoot and for judging articular surface integrity.

The foot and ankle are usually imaged with 2- to 3-mm thick sections obtained in the axial plane (axial with respect to the long axis of the body) with the patient supine and the foot in neutral position.

Imaging of only the affected extremity is recommended, with the contralateral extremity removed from the scan plane when possible, to minimize streak artifact and optimize field of view and positioning for the area of interest.

When possible, direct coronal oblique sections are also obtained. With the knee flexed and the foot flat on the scan table, the gantry is tilted towards the knee as far as possible to place the tibia nearly parallel with the plane of section.

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Helical CT is useful in the trauma setting due to difficulty positioning caused by pain, splints and concomitant injuries.

Helical 1-mm images are obtained in the axial plane with 1:1 pitch, yielding essentially isotropic images and high-quality multiplanar reconstructions.

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MRI Magnetic resonance (MR) imaging has

opened new horizons in the diagnosis and treatment of many musculoskeletal diseases of the foot.

It demonstrates abnormalities in the bones and soft tissues before they become evident at other imaging modalities.

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DISEASES OF FOOT AND ANKLE Congenital variants and abnormalities Tendon abnormalities Impingement syndromes Infections Arthritis

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CONGENITAL VARIANTS

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Accessory ossicles of the feet are common developmental variants with almost 40 having been described. The more common ones include:

os peroneum os subfibulare os subtibiale os tibiale externum (accessory navicular) os trigonum os calcaneus secundaris os intermetatarseum os supratalare bipartite hallux sesamoid os supranaviculare

Knowledge of their presence is helpful so that they are not misdiagnosed as fractures.

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Secondary ossification centers are sometimes confused

for fractures.

The os trigonum may be mistaken for the much less

common Shepherd fracture of the posterior process of

talus.

Os trigonum syndrome is a mechanical tenosynovitis

caused by tethering of the flexor hallucis longus tendon

by the os trigonum.

An os supranaviculare can simulate a navicular fracture.

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Accessory ossicles may be painful. CT features that have

been associated with pain include degenerative sclerosis

and irregularity, subchondral cyst-like changes and vacuum

phenomenon at the synchondrosis .

A bipartite medial cuneiform is an uncommon variant that is

occasionally symptomatic and can be involved in trauma .

The corticated nature of sesamoids in the forefoot

distinguishes them from acute fracture fragments and is

usually readily apparent on CT.

Less noticed are the pathologic and potentially

symptomatic entities of these normal structures, including

fracture, osteonecrosis and degenerative change.

Os peroneum - “An os peroneum is a small accessory bone located just proximal to the base of the 5thmetatarsal and located within the substance of peroneus longus...”

Os tibiale externum (accessory navicular) is a large ossicle adjacent to the medial side of the navicular bone. The tibialis posterior tendon often inserts with a broad attachment onto the ossicle, which may cause a painful tendinosis due traction between the ossicle and the navicular.

Os trigonum - “An os trigonum is one of the bony ossicles of the foot and can be mistaken for a fracture. it sits posterior to talus on the lateral foot radiograph.”

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CONGENITAL ABNORMALITIES OF FOOT

Pes cavus Congenital talipes equinovarus

(idiopathic club-foot) Rocker bottom foot. Tarsal coalition

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PES CAVUS Pes cavus refers to a descriptive term for

a type of foot deformity with an abnormally high longitudinal arch of the foot (caved in foot).

It can be associated with certain neuromuscular disorders such as

Charcot-Marie-Tooth disease : considered one of the commonest associations in the western world

conditions that cause spastic paralysis spinal anomalies

spinal dysraphisms spina bifida

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A lateral view is the key to assessment as the dorso-plantar view can sometimes be normal unless there an associated abnormality 2.

On a lateral view there is: increase in the calcaneal inclination

angle angle of the longitudinal arch greater

than 170 degrees the mid-talar axis either extends above

the 1st metatarsal or intersects the shaft distal to its midpoint

Hibb's angle less than 150 degrees.

CALCANEAL INCLINATION ANGLE The calcaneal inclination

angle is drawn on a weightbearing lateral foot radiograph between the calcaneal inclination axis and the supporting surface.

It is a measurement that reflects the height of the foot framework, but is affected by abnormal pronation or supination of the foot:

low: 10-20 degrees medium: 20-30 degrees high: 30+ degrees

ANGLE OF THE LONGITUDINAL ARCH The angle of the

longitudinal arch is one of the angles drawn on the weightbearing lateral foot radiograph. The angle is formed between the calcaneal inclination axis and a line drawn along the inferior edge of the 5th metatarsal.

The normal angle is 150-170 degrees.

MID-TALAR AXIS

The mid-talar axis represents a line drawn down the longitudinal axis of the talus and can be drawn on lateral and DP radiographs.

lateral view: line should bisect the shaft of the first metatarsal

DP view: line should intersect (or pass just medial to) the base of the first metatarsal

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HIBB'S ANGLE

Hibb's angle is formed between the line representing the long axes of the calcaneum and the first metatarsal. The intersection of the lines represents apex of the deformity.

Normally Hibb's angle is greater than 150 degrees .

Hibb's angle less than 150 degrees indicates pes cavus.

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Pes cavus

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CONGENITAL TALIPES EQUINOVARUS (IDIOPATHIC CLUB-FOOT) It is a congenital deformity comprising

four elements: (a) an equinus position of the heel; (b) a varus position of the hindfoot; (c) adduction and a varus deformity of the

forefoot; (d) talonavicular subluxation.

Before the ossification of the navicular bone at 2 to 3 years of age, only the first three elements can be verified radiographically.

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CONGENITAL TALIPES EQUINOVARUS (IDIOPATHIC CLUB-FOOT) Relatively common; the incidence is 1 or

2 /1000 births Boys are affected twice as often as girls. The condition is bilateral in one-third of

cases. Similar deformities are seen in

neurological disorders, e.g. myelomeningocele, and in arthrogryposis.

It’s mostly a problem passed from parents to children (genetic), and it may run in families.

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There can be an immense number (estimated at 200) of associations which include:

chromosomal anomalies 18q deletion syndrome trisomy 18 Wolf-Hirschhorn syndrome

other syndromic conditions Freeman Sheldon syndrome Meckel Gruber syndrome Roberts syndrome

renal anomalies prune belly syndrome renal agenesis

connective tissue disorders Marfan syndrome Ehlers-Danlos syndrome

spinal anomalies caudal regression syndrome diastematomyelia spina bifida

skeletal dysplasias diastrophic dysplasia

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In the clubfoot deformity, the Kite anteroposterior talocalcaneal angle

is less than 20 degrees, the lateral angle is less than 35 degrees, and the TFM angle is greater than 15

degrees In the determination of the Kite

anteroposterior talocalcaneal angle, the lines of the angle normally intersect the first and fourth metatarsals; in the clubfoot anomaly, these lines fall lateral to the normal points.

Lateral radiograph of the right foot shows that the long axes of the talus and calcaneus are nearly parallel. The longitudinal arch is abnormally high. AP radiograph of the right foot shows abnormally narrow talocalcaneal angle, with severe adduction and supination of the forefoot.

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ROCKER BOTTOM FOOT (CONGENITAL VERTICAL TALUS)

It’s a rare neonatal condition usually affects both feet.

The foot is turned outwards (valgus) and the medial arch is not only flat, it actually curves the opposite way from the normal, producing the appearance of a “rocker-bottom” foot.

Passive correction is impossible The only effective treatment is by operation,

ideally before the age of 2 years.

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Associations aneuploidic syndromic

trisomy 13 trisomy 1818q deletion syndrome

non aneuploidic non syndromicspina bifidaarthrogryposis

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RADIOGRAPH: Radiographic features are characteristic: The calcaneum is in equinus and the talus

points into the sole of the foot, with the navicular dislocated dorsally onto the neck of the talus.

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TARSAL COALITION Tarsal coalition refers to the fusion of two or more

tarsal bones to form a single structure. This fusion may be complete or incomplete, and

the bridge may be fibrous (syndesmosis), cartilaginous (synchondrosis), or osseous (synostosis).

Various bones may be affected, but most commonly the coalition occurs between the calcaneus and navicular bone.

Pain, particularly associated with prolonged walking or standing, is a typical presenting symptom.

On physical examination, peroneal muscular spasm and restricted joint mobility (the so-called peroneal spastic foot) are revealed.

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The vast majority (90%) of tarsal coalitions are either:

calcaneonavicular (~ 45%)usually involves the anterior process of the

calcaneus the anteater nose sign may sometimes be seenbest seen on an oblique film

talocalcaneal (~ 45%)usually involves the middle facetbest seen on the lateral viewC-sign - complete posterior ring around the talus

and sustentaculum tali talar beak sign due to impaired subtalar movement

The remainder of the coalitions (calcaneocuboid, talonavicular, cubonavicular) are much less common .

The anteater nose sign refers to an anterior tubular prolongation of the superior calcaneus which approaches or overlaps the navicular on a lateral radiograph of the foot. This fancifully resembles the nose of an anteater and is an indication of calcaneonavicular coalition .

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TALO CALCANEAL COALITION

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TALOCALCANEAL COALITION

A continuous C shaped arc is seen on lateral radiograph of ankle which is formed by medial outline of dome of talus and posteroinferior aspect of sustentaculum tali .

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TALAR BEAK SIGN The talar beak sign is seen in cases

of tarsal coalition, and refers to a superior projection of the distal aspect of the talus. It is most frequently encountered in talocalcaneal coalition . It is thought to result from abnormal biomechanic stresses at the talonavicular joint.

(A) Harris view shows bulbous sustentaculum tali, with rounded inferiorcontour and overgrowth in expected region of middle subtalar facet. (B) Lateral radiograph shows dysmorphic sustentaculum tali, with bony overgrowth and rounding of its inferior contour. Continuity of sustentaculum tali contour with that of medial talus is the C-sign (C) Lateral radiograph shows talar beak arising at talonavicular joint and curving away from joint and dysmorphic sustentaculum tali and C-sign (D) Lateral radiograph shows rounded lateral process of talus and dysmorphic sustentaculum tali Bony prominence at dorsal margin of talar head has features of both osteophyte and beak, perhaps because this is an older patient who has developed osteoarthritis

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EPIDEMIOLOGY OF TENDON ABNORMALITIES Achilles tendon: occur in atheletes esp

runners. Tibialis posterior: in middle age obese

women Peroneal tendons: pateints with previous

lateral ankle sprains Other tendons are rarely injured.

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TENDON ABNORMALITIES Tendinosis(collagen degeneration and

vascular ingrowth) Paratendinosis(inflamation of the

paratenon) Tenosynovitis(inflamation of the tendon

sheath) Partial tear Complete tear( tendon rupture) Tendon dislocation and entrapment These conditions often coexist, and overlap in their

clinical,gross, and histologic manifestations can make them indistinguishable at MR imaging

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TENDINOSIS The MR imaging characteristics of

tendinosis include a fusiform shape focal areas of increased tendon girth associated with increased signal intensity

within the tendon on T1-weighted and protondensity–weighted images.

T2 signal intensity alterations are noted when significant intrasubstance degeneration is present.

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Tendonosis-Neovascularisation

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TENOSYNOVITIS AND PERITENDINOSIS Caused by inflammation or mechanical

irritation of the tendon sheath and peritenon, respectively.

MR images reveal fluid accumulation, synovial proliferation, or scarring within the tendon sheath or adjacent soft tissues.

Stenosing tenosynovitis occurs when synovial proliferation and fibrosis surround the tendon, causing entrapment and even rupture.

It manifests as areas of intermediate to low signal intensity in the soft tissues around the tendon with all MR imaging sequences.

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fluid is noted within the tendon sheath of the tibialis posterior tendon. The tendon itself is of normal echotexture with no evidence of tendinopathy. Tenosynovitis

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PERITENDINOSIS

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Tenosynovitis

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Tenosynovitis

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Peritendinitis & chronic tendinosis TA

Peritendinitis & chronic tendinosis TA

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PARTIAL /COMPLETE RUPTURE OF TENDONS Ultrasonography :

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PARTIAL /COMPLETE RUPTURE OF TENDONS MRI Findings:

Partial rupture manifests on T1-weighted and proton-density–weighted images and occasionally

on T2-weighted images as an area within the substance of the tendon having a signal intensity similar to that seen in advanced tendinosis.

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Partial tear

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ACHILLES TENDON INJURIES Achilles tendon injuries may be

classified as noninsertional or insertional.

The former group includes diffuse acute and chronic peritendinosis, tendinosis, and a rupture 2–6 cm above the insertion of the tendon on the calcaneus.

The latter group includes insertional Achilles tendinosis, which may be associated with Haglund deformity of the calcaneus.

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Weinstabi et al classified Achilles tendon lesions into four types on the basis of MR imaging findings.

Type I represents inflammatory reaction; Type II, degenerative changes; Type III, partial rupture; Type IV, complete rupture.

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ULTRA SONOGRAPHY A patient with isolated paratendinitis

demonstrates a normal intratendinous structure,

whereas peritendinous effusion, irregularities of tendon margins and adhesions related to scarring of the

paratenon, heterogeneous appearance of the pre-

Achilles tendon fat pad, are the main findings

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PERITENDINITIS

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ULTRASONOGRAPHY Achilles tendinosis is demonstrated as tendon swelling, which is often bilateral,

and textural heterogeneity with intratendinous focal hypoechoic areas

US can reveal subtle changes in the fibrillar pattern, including thickening, fragmentation and disappearance of specular echoes

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Achilles peritendinosis manifests at MR imaging as linear or irregular areas of altered signal intensity in the pre–Achilles tendon fat pad, a finding that indicates the presence of edema or scarring of the peritenon. The tendon itself is normal.

Achilles tendinosis manifests on axial MR images as loss of the anterior concave or flat surface of the Achilles tendon and on sagittal images as fusiform thickening of the tendon.

Areas of increased signal intensity within the tendon are also noted.

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PARTIAL TEAR At MR imaging, partial Achilles tendon tears

demonstrate heterogeneous signal intensity and thickening of the tendon without complete interruption.

Differentiation between partial tear and severe chronic Achilles tendinosis may be difficult apart from clinical history.

Acute partial tears are often associated with subcutaneous edema, hemorrhage within the Kager fat pad, and intratendinous hemorrhage at MR imaging, whereas chronic tendinosis does not usually demonstrate increased subcutaneous or intratendinous signal intensity on T2-weighted images.

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COMPLETE TEAR Complete Achilles tendon rupture

manifests as discontinuity with fraying and retraction of the torn edges of the tendon.

In acute rupture, the tendon gap demonstrates intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images, findings that are consistent with edema and hemorrhage,

In chronic ruptures, scar or fat may replace the tendon

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HAGLUND’S DEFORMITY Haglund's deformity represents

insertional tendinitis with a posterosuperior calcaneal bony prominence and retrocalcaneal tendo Achilles bursitis

94Chronic partial rupture with extensve scar formation and bursitis

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HAGLUND SYNDROME The Haglund syndrome refers to the

triad of insertional achilles tendinopathy retrocalcaneal bursitis and and retro tendo-achilles bursitis This results in pain at the back of the

heel. It is associated with calcaneal spurs,

and the wearing of high heels (thus the colloquial term "pump-bump") or stiff backed shoes in general.

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METABOLIC DISORDERS INVOLVING ACHILLES TENDON The Achilles tendon is the tendon most frequently involved in

metabolic disorders

In gout, deposition of urate tophi may result in intratendinous nodules or diffuse thickening of the tendon,

Heterozygous familial hypercholesterolemia, an inherited disorder leading to premature atherosclerosis,

US can depict striking bilateral tendon swelling and a high-grade textural heterogeneity and disappearance of the fibrillar pattern with focal or diffuse hypoechoic areas, the intratendinous xanthomas, before these become clinically apparent

On MR Fusiform thickening of the Achilles tendon associated with intrasubstance heterogeneity and stippling are consistent with the presence of xanthoma.

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Xanthoma of the Achilles tendon in a patient with familial hypercholesterolemia

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POSTERIOR TIBIAL TENDON DYSFUNCTION Acute or chronic dysfunction of the

posterior tibial tendon encompasses a spectrum of abnormalities ranging from tenosynovitis and tendinosis to partial or complete rupture of the tendon.

Acute tenosynovitis is related to overuse and is usually encountered in young, athletic individuals. At MR imaging, fluid is seen within the tendon sheath

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POSTERIOR TIBIAL TENDON RUPTURE Chronic posterior tibial tendon rupture

typically develops in women during the 5th and 6th decades of life and is associated with progressive flat foot deformity.

The tear is commonly noted behind the medial malleolus, where the tendon is subjected to a significant amount of friction.

Acute partial or complete rupture of the posterior tibial tendon in young, athletic individuals is less common and is usually seen at the insertion of the tendon on the navicular bone.

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MR imaging classification of chronic posterior tibial tendon ruptures divides these injuries into three types.

Type I partial tear consists of an incomplete tear with fusiform enlargement, intra-substance degeneration, and longitudinal splits

Type II partial tear of the posterior tibial tendon. On axial images, a decrease in the diameter of the tendon, usually without signal intensity alterations. The caliber of the tendon may be equal to or less than that of the adjacent flexor digitorum longus tendon

Type III posterior tibial tendon tears there is complete disruption of the tendon fibers

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Type 1

Type 2

Type 3

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ARTHROPATHIES IN FOOT AND ANKLE Osteoarthritis Crystal artropathy(gout) Rheumatoid arthritis Seronegative arthropathies Septic arthritis Charcot arthropathy(neuroarthropathy)

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OSTEOARTHRITIS Trauma is the most common predisposing factor,

including injuries such as lateral ligament tear with resultant instability and/or osteochondral injury, as well as intraarticular fracture,Degenerative arthropathy, or osteoarthritis, commonly affects the ankle.

Classic signs include joint space narrowing,marginal osteophytes, intraarticular body formation, subchondral cysts, and subchondral sclerosis.

Osteoarthritis is also quite common at the midfoot, typically resulting in dorsal spurring at multiple articulations (also called “dorsal proliferative change”).

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GOUT Gout is a metabolic disorder characterized by recurrent

episodes of arthritis associated with the presence of monosodium urate monohydrate crystals in the synovial fluid leukocytes and, in many cases, gross deposits of sodium urate (tophi) in periarticular soft tissues.

Serum uric acid concentrations are elevated. The great toe is the most common site of involvement

in gouty arthritis; the condition known as podagra, which involves the

first metatarsophalangeal joint, occurs in approximately 75% of patients.

Other frequently affected sites include the ankle, knee, elbow, and wrist.

Most patients are men, but gouty arthritis is seen in postmenopausal women as well.

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RADIOGRAPHIC FEATURES Erosions, which are usually sharply marginated, are initially

periarticular in location and are later seen to extend into the joint

an “overhanging edge” of erosion is a frequent identifying feature

Intraosseous defects are present secondary to formation of intraosseous tophi .

Lack of osteoporosis, helps differentiate this condition from rheumatoid arthritis.

If erosion involves the articular end of the bone and extends into the joint, part of the joint is usually preserved.

In chronic tophaceous gout, sodium urate deposits in and around the joint are seen, creating a dense mass in the soft tissues called a tophus, which frequently exhibits calcifications

Characteristically, tophi are randomly distributed and are usually asymmetric; if they occur in the hands or feet, they are more often seen on the dorsal aspect

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RHEUMATOID ARTHRITIS OF FOOT In the foot, rheumatoid arthritis has a predilection

for the metatarsophalangeal joints, especially the fifth.

Periarticular osteopenia is variably present. Although the intertarsal, subtalar, and ankle joints

may be involved. Involvement at the ankle can create a characteristic

erosion of the synovial recess at the distal tibiofibular joint.

Joint destruction and capsular distension can result in deformities including subluxation/ dislocation

Chronic inflammatory tenosynovitis can result in tendon tear and dysfunction, causing additional deformity; posterior tibial tendon dysfunction is particularly common.

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PSORIATIC ARTHRITIS seronegative arthropathy and enthesopathy, where

erosions and bone proliferation occurs. In the foot, this typically affects the metatarsophalangeal

and interphalangeal joints. Interphalangeal erosions may result in the pathognomonic

“pencil-in-cup” appearance. Acro-osteolysis can occur along with nail involvement. Proliferative bone formation manifests as periostitis and in

areas of bone erosion fluffy bone production occurs. Occasionally, if severe, erosions may result in ankylosis or

joint destruction (arthritis mutilans). Enthesial involvement resulting in erosions or “fuzzy spurs”

may occur at the plantar fascia or other tendon, ligament, or fascial attachment sites.

Bursitis may also occur with focal soft-tissue swelling.

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SEPTIC ARTHRITIS/OSTEOMYELITIS Septic arthritis of the foot and ankle, like

any other region,may occur secondary to penetrating trauma/direct implantation, postoperatively, due to contiguous spread, or hematogenous spread.

The imaging features consist of a joint effusion, with loss of the sharp cortical margins of the subarticular bone.

Joint space loss is rapid in acute septic arthritis, and marginal erosions may develop mimicking an inflammatory arthropathy

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Osteomyelitis of the foot and ankle is usually seen in susceptible populations, particularly diabetic or paralyzed patients.

In these patients, contiguous spread is by far the most common mode of infection, arising via skin ulceration.

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diabetic patient

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NEUROPATHIC OSTEOARTROPATHY Neuropathic osteoarthropathy is an arthritic

process that is often aggressive, resulting from repetitive micro- and macrotrauma that heals ineffectively due to ischemia and reduced nociception.

Disease may be seen in various neurological conditions involving the foot/ ankle such as leprosy, common in diabetics with peripheral neuropathy.

In diabetic population, the Lisfranc joint and intertarsal joints are most commonly involved, followed by the Chopart joint, subtalar and tibiotalar joint, and the metatarsophalangeal joints.

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Radiographically in the early stage diffuse soft tissue swelling and occasionally mild offset of a joint.

The disease progress rapidly, with erosions and even frank joint destruction.

Often in the late stage there is excessive bone production (sclerosis and spurring), and subchondral cystic change which in addition to deformity leads to the classic appearance of chronic neuropathic osteoarthropathy.

Articular surfaces degenerate over time and may fragment, becoming distorted, incongruent, and generally disorganized, with debris and body formation.

Neuropathic osteoarthropathy has been characterized radiographically as dislocation, debris, disorganization, deformity, and increased density.

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DIABETIC FOOT MR imaging has been shown to be highly sensitive in the

detection and staging of a number of musculoskeletal infections including cellulitis, soft-tissue abscesses, and osteomyelitis.

MR imaging has greater specificity and better spatial resolution than bone scintigraphy and also has the capacity to provide a quicker diagnosis.

Differentiation between neuroarthropathy and infection may be difficult with any imaging technique.

At MR imaging, neuroarthropathy exhibits characteristic findings including bone fragmentation, dislocations, cortical and periosteal thickening, joint effusion, and soft-tissue swelling. In most cases, the bone marrow appears hypointense on both T1- and T2-weighted images.

In osteomyelitis, on the other hand, the bone marrow appears hypointense on T1- weighted images and hyperintense on T2-weighted images.

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COMPRESSIVE NEUROPATHIES The most common compressive

neuropathies of the ankle and foot are tarsal tunnel syndrome and Morton neuroma

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TARSAL TUNNEL SYNDROME Tarsal tunnel syndrome is characterized

by pain and paresthesia in the plantar aspect of the foot and toes.

This syndrome is most frequently unilateral, as opposed to carpal tunnel syndrome, which is typically bilateral.

Nerve entrapment or compression can occur at the level of the posterior tibial nerve or its branches producing different symptoms depending on the site of compression

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Intrinsic and extrinsic causes of posterior tibial nerve compression have been identified.

Intrinsic lesions that often produce tarsal tunnel syndrome include Accessory muscles, Ganglion cysts, Neurogenic tumors, Varicose veins, lipomas, synovial hypertrophy, and scar tissue.

Extrinsic causes Foot deformities, Hypertrophic and accessory muscles, accessory ossicle (os trigonum), and excessive pronation

In about 50% of cases, the cause of tarsal tunnel syndrome cannot be identified.

Relief of symptoms following retinacular release is frequently seen in these idiopathic cases.

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MORTON NEUROMA Morton neuroma (interdigital neuroma) is

actually a fibrosing degenerative process produced by compression of a plantar digital nerve.

The condition has a female predilection and is frequently seen between the heads of the third and fourth metatarsals, although all web spaces may be involved.

The nerve becomes thickened, and associated bursitis is often present.

Exquisite tenderness is elicited on lateral compression of the metatarsals.

The pain can radiate to the toes and may be accompanied by numbness

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MR imaging has proved highly accurate in the diagnosis of Morton neuroma,

manifests as a dumbbell shaped mass located between the metatarsal heads and having intermediate to low signal intensity on both T1- and T2-weighted images.

T1- weighted sequences are probably more helpful because the hypointense neuroma is made more conspicuous by the surrounding hyperintense fat.

The low signal intensity of Morton neuroma is attributed to the presence of fibrous tissue.

Morton’s neuroma

Transverse view: Hypoechoic focus between 3rd and 4th interspace.

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MORTON NEUROMAS

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OSTEONECROSIS

Osteonecrosis of the ankle and foot typically occurs in the talus as a consequence of talar neck fractures with vascular compromise of the bone at the level of the sinus tarsi.

Osteonecrosis of the tarsal navicular bone can occur in children (Kohler disease)

Manifests radiographically as sclerosis, irregularity, and fragmentation of the bone.

A form of osteonecrosis of the tarsal navicular bone has also been described in adults (Mueller-Weiss syndrome).

Osteonecrosis of the ankle and foot region is also frequently seen in the second metatarsal head (Freiberg disease), with sclerosis and flattening of the metatarsal head seen at conventional radiography, and in the first metatarsal sesamoid bone

Freiberg disease. (A) T2 image shows extensive bone marrow edema and subchondral impaction (arrow) and effusion suggesting more acute changes. (B) Proton density images show subchondral fracture with impaction of cortex and subchondral bone plate (arrow). (C) Axial, (D) sagittal images of late-stage Freiberg disease with secondary osteoarthritis and subchondral cyst (arrow). Collapsed subchondral bone with a low-grade stress response.

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PIGMENTED VILLONODULAR SYNOVITIS Pigmented villonodular synovitis (PVNS) is

characterized by inflammatory proliferation of the synovium associated with deposits of hemosiderin.

It can be present in any joint, tendon sheath, or bursa but is most frequently seen in the knee, hip, ankle, and elbow.

When it originates in the tendon sheaths, the term giant cell tumor of the tendon sheaths is often used.

In the foot, this lesion predominantly involves the peroneal and flexor tendon sheaths

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PVNS can occur at age 20–50 years and may manifest as a focal mass or as a generalized lesion involving the entire joint space.

Pressure erosions may be present in the diffuse form.

These lesions manifest clinically as joint pain and swelling of long duration, and most are slowly progressive.

At pathologic analysis, PVNS is characterized by synovial inflammation with giant cell proliferation, collagen, and lipid-laden macrophages.

Treatment of PVNS often consists of resection of the lesion.

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characteristic MR imaging features due to the paramagnetic effect of hemosiderin, which produces focal areas of hypointensity with all pulse sequences,

mixed with hypointense areas on T1-weighted images and hyperintense areas on T2-weighted images.

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PLANTAR FASCIITIS Plantar fasciitis is a painful condition caused

by repetitive injury to the proximal plantar fascia, at or near its origin from the calcaneus.

Individuals with pes planus and overpronation are predisposed.

Although spur formation at the inferior calcaneus is often implicated in this process, it actually has little association with pain;

Although plantar fascial thickening may be suggested on the lateral radiograph, this finding is not necessarily related to acute, symptomatic fasciitis

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MR imaging is useful in distinguishing plantar fasciitis from other causes of heel pain and in excluding plantar fascia tears.

On sagittal and coronal MR images, the normal plantar fascia appears as a thin, hypointense structure extending anteriorly from the calcaneal tuberosity.

The plantar fascia has a normal thickness of 3.22 mm ± 0.53 and flares slightly at the calcaneal insertion.

When inflammatory changes take place, it becomes thickened (up to 7–8 mm) and demonstrates intermediate signal intensity on T1-weighted and proton-density– weighted images and hyperintensity on T2- weighted images .

These changes are most prominent in the proximal portion of the plantar fascia at or near its insertion on the calcaneus.

Signal intensity changes may also be present in the subcutaneous fat, in the deep soft tissues, and in the calcaneus near the fascial insertion.

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SINUS TARSI SYNDROME The sinus tarsi is a lateral space located between the talus and

the calcaneus. It contains the cervical and interosseous talocalcaneal ligaments,

the medial roots of the inferior extensor retinaculum, neurovascular structures, and fat.

Sinus tarsi syndrome is caused by hemorrhage or inflammation of the synovial recesses of the sinus tarsi with or without tears of the associated ligaments.

This disease entity commonly occurs following an inversion injury and is often associated with tears of the lateral collateral ligaments.

It may also be related to rheumatologic disorders and abnormal biomechanics such as flat foot deformity secondary to posterior tibial tendon tear.

Patients with sinus tarsi syndrome present with hindfoot instability and pain along the lateral aspect of the foot.

The MR imaging characteristics of sinus tarsi syndrome include the obliteration of fat in the sinus tarsi space. The space itself is replaced by either fluid or scar tissue, and the ligaments may be disrupted.

Osteoarthritis of the subtalar joint and subchondral cysts may be present in advanced cases.

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Sinus tarsi syndrome (STS) is a clinical finding that mainly consists of pain and tenderness of the lateral side of the hindfoot, between the ankle and the heel.

Aetiology STS probably occurs following one single or a series

of ankle sprains that also result in significant injuries to the talocrural interosseous and cervical ligaments.

This causes instability of the subtalar joint in supination and pronation movements.

In summary, STS can be primarily described as an instability of the subtalar joint due to ligamentous injuries that result in synovitis and scar tissue formation in the sinus tarsi. Haemorrhage or inflammation of the synovial recesses of the sinus tarsi can also cause scarring without tears of the associated ligaments.

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Plain film Osteoarthritis of the subtalar joint and intraosseous

cysts may be present in advanced cases.CT Shows secondary bony changes earlier than plain

films.Bone scan - scintigraphy Inflammatory changes may be attributed to the sinus

tarsi / subtalar region.MRI Probably the best test to show changes in the tissues

of the sinus tarsi including inflammation, scar tissue formation or ligamentous injuries.The T1-hyperintense fat in the sinus tarsi space is replaced by either fluid or scar tissue, and the ligaments may be disrupted. Ganglion cysts in the region of the sinus tarsi may compress the posterior tibial nerve.

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Diffuse fluid signal or oedema around the interosseous ligaments in the sinus tarsi.

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CONCLUSION The initial evaluation should always

commence with plain radiographic assessment.

MR imaging is the modality of choice for optimal detection of most soft-tissue disorders of the tendons,ligaments, and other soft-tissue structures of the ankle and foot.

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Imaging of foot in non trauma and non neoplastic diseases

Health & Medicine

Transcript of Imaging of foot in non trauma and non neoplastic diseases