sartoris & resnick (1985) - tarsal coalition

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33

RADIOLOGIC

VIGNETTE

TARSAL

COALITION

DAVID J .

SARTORIS

and D O N A L D L. RESNICK

Tarsal coalition,

or

fusion , refers to the union of

2 or more tarsal bones into a single structure, with

consequent absence of normal relative motion be-

tween them (1,2). The connection may be fibrous

(syndesmosis), cartilaginous (synchondrosis),

or

osse-

ous (synostosis) (1,3). Congenital cases are thought to

arise from altered differentiation and impaired segmen-

tation of primordial mesenchyme, resulting in failure

of joint formation (3,4). Incorporation of accessory

ossicles into tarsal articulations has also been pro-

posed as an etiology (5,6). Acquired causes include

trauma, previous surgery, infection, osteoarthritis,

and rheumatoid arthritis (1,3).

Paleopathologic re-

mains have documented the occurrence of this condi-

tion as early as

900-950

AD

(7,8). This vignette

describes the epidemiologic, clinical, radiographic,

and scintigraphic features of the various forms of

tarsal coalition.

Epidemiology

The overall prevalence of tarsal coalition in the

general population is approximately 1 (6,9). In some

instances, particularly those with multiple tarsal fu-

sions,

a

familial tendency has been noted (3,8). Auto-

soma1 dominant inheritance with variable penetrance

has been proposed, based on

a

39 incidence among

first-degree relatives of 31 affected individuals in 1

From the Radiology Service, Veterans Administration

David

J .

Sartoris, MD; Donald L. Resnick, MD.

Address reprint requests to Donald L. Resnick, MD, Radi-

ology Service, VA Medical Center, 3350 La Jolla Village Drive, San

Diego, CA 92161.

Submitted for publication August 16, 1984; accepted in

revised form September

4,

1984.

Medical Center, San Diego, California.

study

8).

Tarsal coalitions may be isolated phenom-

ena or may be associated with congenital malforma-

tion syndromes, including hereditary symphalangism,

Apert’s acrocephalosyndactyly, and the hand-foot-

uterus syndrome (3,10,11). Many cases of peroneal

spastic flatfoot are accompanied by tarsal fusions,

although the former finding may also be caused by a

previous fracture, osteoarthritis, tuberculosis, juvenile

chronic arthritis, or other conditions (12-15).

Clinical manifestations

Signs and symptoms of tarsal coalition general-

ly develop during the second or third decade

of

life

(3,16). This delayed presentation ofa congenital prob-

lem has been attributed to the conversion of fibrous or

cartilaginous union to osseous fusion, the former being

rarely symptomatic (2,3). Typically, vague foot pain

exaggerated by vigorous use or prolonged standing is

noted, often beginning after minor trauma

or

unusual

activity (1,17). Physical examination reveals intermit-

tent or constant peroneal muscular spasm, restricted

subtaiar joint mobility, pes planus, and valgus posi-

tioning of the foot (1,3). Concomitant spasm of the

tibialis anterior may, however, result in varus deformi-

ty, and pes cavus has also been observed (1,3). Tarsal

coalition may present as an incidental radiographic

finding in an asymptomatic individual (3).

Radiographic classification

Solitary tarsal coalitions are categorized

according to the bones that are united (1,3). Calcaneo-

navicular fusions are slightly more common than talo-

calcaneal fusions, whereas talonavicular and calcaneo-

cuboid involvement occur far less frequently (3,9).

Arthritis and Rh eumatism,

Vol. 28,

No. 3 March 1985)



332

SARTORIS

AND

R E S N I C K

Figure 1.

Oblique view demonstrating osseous fusion between the

calcaneus and navicular

arrow).

Secondary degenerative changes

are present in the talonavicular articulation.

Coalitions involving multiple bones or unusual sites

are characteristically associated with other congenital

abnormalities

3).

In general, radiographic findings in

tarsal fusion can be classified as either primary (direct

or indirect visualization of the fibrous, cartilaginous,

or osseous bridge) or secondary (adaptive alterations

in the affected or adjacent bones and articulations) in

type.

Calcaneonavicular coalition.

Normally, an ar-

ticulation does not exist between the calcaneus and the

navicular

3).

In cases of bony coalition, which gener-

ally occurs in children between the ages of 8 and 12

(2,3), routine frontal and lateral radiographs may fail to

demonstrate the site of union between these struc-

tures, although a

45”

medial-oblique view of the foot

establishes the diagnosis (Figure

1 1,3) .

Close ap-

proximation of the adjacent calcaneal and navicular

cortices, particularly in association with bone sclerosis

or irregularity, suggests fibrous or cartilaginous fusion

1,3).

Secondary radiographic signs are less pro-

nounced than those accompanying talocalcaneal coali-

tion, and include hypoplasia of the talar head (1,3)

(Table

1).

Clinical manifestations are also less severe:

spastic flatfoot may be evident, although the condition

is commonly asymptomatic. This coalition may predis-

pose to ankle sprain (3,18). Fracture of an osseous

calcaneonavicular bridge has also been reported 6).

Talocalcaneal coalition.

Fusion of the talus and

the calcaneus occurs most commonly at the level of

the sustentaculum tali and involves the middle facets

of the anterior subtalar joint. Rarely are the anterior

facets or posterior subtalar joint affected (3,17). Talo-

calcaneal coalition is seen more frequently in males

and occurs bilaterally in up to

25

of patients (3,17).

Ossification occurs between the ages of 12 and

16

(2).

Osseous coalitions may be overlooked on standard

frontal and lateral radiographs, or even simulated in

normal feet (3,19). Plain

film

radiography, utilizing

oblique or axial (Harris-Beath views) projections (Fig-

ure

2),

and conventional tomography are more diag-

nostic (1,3). Close apposition, eburnation, or sclerosis

of adjacent articular surfaces implies fibrous or carti-

laginous union (3). The latter may be confirmed by

contrast arthrography of

t h e

talocalcaneonavicular

joint, during which failure of normal opacification of

the fused posterior portion

of

the articular cavity is

noted (Figure 3) (3,20).

The numerous secondary radiographic signs

of

talocalcaneal coalition are summarized in Table 1.

Subtalar rigidity leads to dorsal subluxation of the

navicular, resulting in periosteal elevation and reactive

bone formation at the attachment of the talonavicular

ligament

(1,17).

An osseous outgrowth, or “beak,” is

formed at the dorsal aspect of the talar head adjacent

to the talonavicular articulation (Figure

4 .

Less con-

stantly, a similar excrescence develops on the proxi-

mal-dorsal surface of the navicular (1,3). These find-

ings, best recognized in the lateral projection, are also

observed in diffuse idiopathic skeletal hyperostosis,

acromegaly, rheumatoid arthritis, and other conditions

with altered motion of the talonavicular joint (1,3).

Table

1.

Secondary radiographic signs of tarsal coalition

Calcaneonavicular

Hypoplasia

of

head

of

talus

Talocalcaneal

Osseous excrescence at dorsal aspect of talus

Narrowing of posterior talocalcaneal joint space

Broadening or rounding

of

lateral process

of talus

Ball-and-socket tibiotalar articulation

Failure of visualization

of

middle facets of anterior subtalar joint

Concave undersurface of talar neck with asymmetry

of

talocalcaneonavicular joint



RADIOLOGIC

VIGNETTE

333

A B

Figure 2. Axial Harris-Bea th) views at the level

of

the sustentaculum tali. A , Normal side. B, Osseous talocalcaneal coalition arrow).

Figure

3.

Tornogram lateral view) following contrast injection of talocalcaneona vicular joint rev ealing

absence of opacification posteriorly in region of sustentaculum tali, due to nonosseous talocalcaneal coalition

arrow).



334

SARTORIS

AND

RESNICK

Figure 4 Radiograph (lateral view) showing prominent osseous

excrescence arising from dorsal aspect

of

talar head. Obliteration

of

articular interval between talus and calcaneus also suggests coali-

tion.

However, they are readily distinguished from osteo-

phyte formation related to osteoarthritis of the ankle

or midfoot, and should not be mistaken for excres-

cences which may develop normally at the insertion of

the capsule of the ankle joint in the talar neck (3,21).

At its typical site, talocalcaneal coalition may

lead

to

eversion of the calcaneus, or premature degen-

erative arthritis of the posterior subtalar articulation

(3). Either of these phenomena results in apparent

narrowing

of

the posterior subtalar joint space, a

secondary radiographic sign seen in as many as60 of

patients (3,17). Valgus angulation of the calcaneus

resulting from talocalcaneal fusion leads to broaden-

ing, or rounding of the lateral process of the talus in

approximately

50

of patients (1,3,17). Furthermore,

in the presence of a talocalcaneal coalition, the func-

tions of inversion and eversion which are normally

performed by the subtalar articulations are assumed

by the tibiotalar joint (3,22). This phenomenon con-

verts the normally mesa-shaped superior talar joint

surface

to

a rounded convexity which articulates with

a correspondingly concave distal tibia, a finding that is

termed the “ball-and-socket” ankle joint (Figure 5

(322).

The middle facets of the anterior subtalar joint

are normally seen in tangent ona properly-positioned

lateral radiograph of the foot (Figure

6).

Failure to

visualize this articulation is a helpful ancillary sign of

talocalcaneal coalition, although technical error may

result in false-positive diagnoses (3,17). Comparison

radiographs of the uninvolved foot may be useful in

detecting talocalcaneonavicular joint asymmetry and

associated concavity of the plantar aspect of the talar

neck (3,17). The reliability of these signs depends upon

comparable positioning on the 2 sides

of

the body

(3,171.

Talonavicular coalition. Conventional radio-

graphs, particularly the lateral view, are usually ade-

quate for the diagnosis of this uncommon variety of

tarsal fusion (Figure

7)

(1,3). Osseous bridging occurs

between the ages of 3 and

5

years, and may be

asymptomatic or associated with peroneal spasm (1,2).

Abnormalities of the fifth digit of the hand may occur

concomitantly, and both autosomal dominant and re-

cessive inheritance patterns have been observed

(10,23).

Calcaneocuboid coalition. This extremely rare

entity is readily diagnosed in its osseous form by

routine radiography (1,3). Calcaneocuboid fusion may

be asymptomatic, coexistent with peroneal spasm,

bilateral, or associated with other congenital anoma-

lies (1,3).

Figure

5 Frontal view illustrating typical appearance

of

the “ball-

and-socket’’ ankle joint.



RADIOLOGIC

VIGNETTE

5

A

Figure 6.

A ,

Lateral view of talocalcaneal coalition showing obscuration of middle facets of anterior subtalar oi nt arrowhead), with associated

narrowing

of

the posterior subtalar articulation. B , Lateral view

of

normal foot, for comparison.

Figure

7. Osseous fusion (lateral view) between the talus and navicular

arrow).



336

SARTORIS AND RESNICK

Miscellaneous coalitions. Sporadic case reports

of isolated naviculocuneiform and cubonavicular co-

alition exist (24,25).

Newer imaging m odalities

Recently, skeletal scintigraphy using Y9mT~

methylene diphosphonate has been found to be useful

as a noninvasive screening procedure for subtalar

coalition (16,26). Positive findings include augmented

radionuclide accumulation in the region of the subtalar

joint, as well as in the dorsal aspect of the talus or

talonavicular joint (Figures

8

and

9)

(16,26). The

former probably results from accentuated stress on

articular surfaces adjacent to the site of fusion, where-

as the latter is probably secondary to the same mecha-

nism that produces dorsal talar and navicular excres-

cences (26).

High-resolution computed tomography has re-

cently been shown to be an extremely valuable tech-

nique in the identification and charactlkization of

talocalcaneal coalitions (Figure 10) (16,27). Its advan-

tages include noninvasiveness, precise evaluation

O f

adjacent osseous and soft tissue structures, potential

for demonstration of associated abnormalities, and an

ability to simultaneously image the opposite foot (16).

Figure 8. Skeletal scintigram of both feet (frontal view) revealing

augmented radionuclide accumulation in the tarsal region

of

the

right foot.

Figure 9

Lateral image of right foot (shown in Figure

8)

localizes the increased activity to the subtala r and

talonavicular joint area s.



RADIOLOGIC VIGNETTE

337

Figure 10 Computed tomographic image at the level of sustentacula tali demonstrating osseous bridging of

the middle facets

of

the anterior subtdlarjoinl on the right arrow).The normal appearance of this articulation

is seen in the left foot.

Acknowledgment.

Special thanks are extended to

Geri Hubble

for

typing the manuscript.

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SARTORIS AND RESNICK

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