Anatomy of the talus and the surrounding bony
and articular structures

Maurice Laude
Laboratory of Anatomy and Organogenesis, Amiens Medical School



The talus is the tarsal homologue of the carpal lunate. The fundamental difference between these two homologous structures derives from the weight-bearing function of the talus: in the bipedal stance and gait pattern typical of humans, the talus is the only bone through which the entire body weight load is channelled, before being distributed to the arches of the foot.

MORPHOLOGY OF THE TALUS

The talus (astragalus) sits at the top of the tarsal skeleton. It is squat in a dorso-plantar direction, and elongated in a posteroanterior direction. It has a single ossification centre, which is present at term and becomes indented at around 6 months to produce the “peanut” pattern described by paediatric radiologists.

The talus has six surfaces:

# A SUPERIOR SURFACE
(Fig. 1), which articulates with the tibia. The long axes of the neck and the body make an angle of 150° to 160°; this angle is reduced in pes planus (flat foot).

# A MEDIAL SURFACE
(Fig. 2), which also articulates with the tibia.

# A LATERAL SURFACE
(Fig. 3), which articulates with the fibula. It has a mean vertical concavity of 115°; this angle is increased in pes planus, and reduced in pes cavus.

# AN INFERIOR SURFACE
(Fig. 4), which articulates with the calcaneus.

# A POSTERIOR SURFACE
(Fig. 5)

# AN ANTERIOR SURFACE
(Fig. 6), which articulates with the navicular bone. The long axis of the head is rotated ca. 45° medially; this angle is reduced in pes planus.

# ACCESSORY BONES
(Fig. 7) may be found, especially an os trigonum, which may be have an articular facet. An os trigonum should not be mistaken for a Shepherd’s fracture.


JOINTS INVOLVING THE TALUS

The talus is involved in the formation of three joints, with synovial recesses and passive ligamentous restraints, as seen on

# THE LATERAL VIEW
(Fig. 8);

# THE MEDIAL VIEW
(Figs. 9 and 10);

# THE POSTERIOR VIEW
(Fig. 11); and

# THE SUPERIOR VIEW
(Fig. 12), which shows the right talocalcaneal joint opened up, with the talus dislocated anteriorly and medially.


MUSCLES AND VESSELS AROUND THE TALUS

These structures form the soft tissues, which are shown divided and reflected on

# A LATERAL VIEW
(Fig. 13);

# AN ANTERIOR VIEW
(Fig. 14);

# A MEDIAL VIEW
(Fig. 15); and

# A POSTERIOR VIEW
(Fig. 16).

# THE ARTERIES OF THE TALUS
(Figs. 17 and 18). These vessels play an important role: the rate of osteonecrosis secondary to fracture has been reported to be 50% after talar neck fractures, and 75% after fracture-dislocation of the talar neck.

According to a recent study by Cologne anatomists, there are no intraosseous anastomoses between the different vessels. Following trauma, revascularization would need to be derived from capsular vessels and from the remaining periosteal supply.

This view contrasts with the conclusions by Féri, who, in an excellent study performed at Nantes, found that intraosseous anastomoses are plentiful.

Vascular foramina are widest and most numerous on the superior aspect of the talar neck, near the roof of the sinus tarsi, and close to the insertion of the deep fibres of the medial ligament.


RELATIONS OF THE TALUS

These are shown in sectional views of the kind routinely obtained with CT or MR imaging:

# ON A CORONAL SECTION OF THE RIGHT HINDFOOT
(Fig. 19);

# ON A HORIZONTAL SECTION OF THE ANKLE JOINT
(Fig. 20). This view clearly shows that the structures stabilizing the ankle joint, and above all the talus, are the tendons and muscles surrounding the joint, which provide active restraints whose proprioception must be optimal and enhanced to prevent recurrence of ankle sprains.

# ON AN OBLIQUE CORONAL SECTION OF THE POSTERIOR TARSUS
(Fig. 21);

# ON A CORONAL SECTION THROUGH THE MID-TARSAL JOINT SPACE
(Fig. 22).


BIOMECHANICS OF THE TALUS

Passive aspects

# TRABECULAR PATTERNS
(Fig. 23). The trabecular patterns are shaped by the fact that, when the foot is in weight-bearing contact with the ground, there is a medial sagittal arch, a major posterior support on the calcaneus, as well as lateral support, with an anterior transverse arch.

Fractures of the body of the talus and of the calcaneus, and talar neck fractures, occur along vertical lines. What Destot called the “talar ball” is ideally shaped to dislocate, popping out like the stone of a ripe cherry. It may dislocate backwards, where the dorsal stop provided by the “third malleolus” accounts for fractures of that bony protuberance. More often than not, it will dislocate forwards, where the only restraints encountered are the extensor tendons and their retinacula.

# THE FORCE LINES, SEEN FROM ABOVE
Figure 24 shows the medial longitudinal arch (shaded grey), and the lateral longitudinal arch (unshaded). The deep layer of the spring ligament (plantar calcaneonavicular ligament) and the tendon of tibialis posterior support the head of the talus gliding inwards and under the forefoot, rather like a soft and elastic curtain loop.

Active aspects

# AXIS OF THE ANKLE JOINT
(Fig. 25). This axis slopes downwards, outwards, and backwards, which accounts for the fact that the plane of dorsiflexion and plantar flexion is angled 15° forwards and outwards in relation to the sagittal plane.

# ACTION OF THE PERIARTICULAR MUSCLES
This action is shown on the medial view (Fig. 26) and the lateral view (Fig. 27). The periarticular muscles permit 20° of dorsiflexion, under the control of the L4 and L5 nerve roots, and 40° of plantar flexion, under the control of the L5 and S1 roots.

# MECHANICAL AXIS OF THE SUBTALAR (TALOCALCANEAL) JOINT
(Fig. 28). This axis affects also the mid-tarsal joint and, distally, the joints of the forefoot. As described by Henke, it runs from the craniomedial aspect of the talus to the lateral tubercle of the posterior process of that bone.

The talus sits in the ankle mortise, whose grip in conjunction with tibialis posterior has been much emphasized by Pol Le Coeur. In a recent CT study of the joint, performed together with Mertl, we were unable to reproduce Le Coeur’s findings regarding the contributory action of tibialis posterior.

The calcaneus, navicular, and cuboid allow gliding and rotation, permitting the foot to turn inward (supination, inversion) or outward (pronation, eversion).

A knowledge of the morphological and topographical anatomy of the talus, including a familiarity with the more frequently encountered departures from the textbook patterns, is essential. Dissection, which should be performed by all junior surgeons, is the key to the surgical approaches to the talus.

Fig 1 Figure 1

Superior (dorsal) aspect of the talus, showing the angle between the axes of the body and the head of the talus

1- trochlea

2- neck

3- talonavicular ligament

4- anterior capsular ligament

5- lateral tubercle of posterior process

6- medial tubercle of posterior process (Stieda’s tubercle)

7- groove for the tendon of flexor hallucis longus

Fig 2 Figure 2

Medial aspect of the talus

1- facet for tibial malleolus

2- medial (deltoid) ligament, deep component

3- entrance to sinus tarsi

4- posterior annular ligament (roof of the canal of the flexor hallucis longus tendon)

5- superficial component of medial ligament attached to talar neck

Fig 3 Figure 3

Lateral aspect of the talus - angle of inclination of the neck

1- facet for fibular malleolus

2- anterior talofibular ligament

3- posterior talofibular ligament

4- lateral talocalcaneal ligament

5- entrance to sinus tarsi

6- cervical ligament

Fig 4 Figure 4

Inferior (plantar) aspect of the talus

1- sulcus tali

2- and 2’ the two laminae of the interosseous talocalcaneal ligament

3- facet for spring ligament

4- facet for navicular bone

5- middle articular surface (facet for sustentaculum tali)

6- posterior articular surface (facet for posterior articular surface of calcaneus)

7- tendon of flexor hallucis longus

8- posterior talocalcaneal ligament

Fig 5 Figure 5

Posterior aspect of the talus

1- trochlea with inclined lateral edge

2- facet for fibular malleolus

3- posterior talocalcaneal ligament

4- tendon of flexor hallucis longus between the two bundles of the annular ligament

5- posterior fibres of tibiotalar portion of medial ligament

6- posterior portion of talofibular ligament

Fig 6 Figure 6

Anterior (distal) aspect of the talus - angle of head rotation

1- facet for navicular bone

2- facet for spring ligament

3- anterior talofibular ligament

4- cervical ligament

5- anterior tibiotalar fibres of medial ligament

Fig 7 Figure 7

Accessory bones

p.tr.: os talonaviculare dorsale (Pirie’s bone)

o.tr.: os trigonum

1- accessory articular facet for tibia on talar neck

Fig 8 Figure 8

Lateral aspect of the joints of the right ankle region

1- anterior inferior tibiofibular ligament

2- anterior oblique capsular reinforcement

3- talonavicular ligament

4- dorsal cuboideonavicular ligament

5- the two limbs of the bifurcate ligament

6- dorsal calcaneocuboid ligament

7- extensor digitorum brevis

8- cervical ligament

9- anterior talofibular ligament

10- lateral talocalcaneal ligament

11- calcaneofibular ligament

12- posterior intermalleolar ligament

13- posterior talofibular ligament

14- posterior talocalcaneal ligament

Fig 9 Figure 9

Medial aspect of the joints of the right ankle region - superficial layer

1- anterior oblique capsular reinforcement

2- talonavicular ligament

3- deep portion of spring ligament

4- medial ligament, superficial tibiotalar portion

4’ medial ligament, superficial portion attached to spring ligament

4’’ medial ligament, superficial tibiocalcaneal portion

5- medial ligament, deep component

6- posterior intermalleolar ligament

Fig 10 Figure 10

Medial aspect of the joints of the right ankle region - deep layer

1- superficial component of medial ligament, cut and reflected

2- anterior portion of deep component of medial ligament

3- posterior portion of deep component of medial ligament

4- medial tubercle of posterior process

5- talonavicular joint capsule, opened

6- cartilaginous dorsal surface of the spring ligament

Fig 11 Figure 11

Posterior aspect of the joints of the right ankle region

1- posterior inferior tibiofibular ligament

2- posterior intermalleolar ligament

3- posterior talofibular ligament, on the posterior process of the talus

4- posterior talocalcaneal ligament

5- fibulotalocalcaneal ligament of Rouvière and Canela Lazaro

6- calcaneofibular ligament

7- deep (tibiotalar) portion of medial ligament

8- superficial portion of medial ligament

Fig 12 Figure 12

Superior aspect of the right talocalcaneal (subtalar) joint, opened and dislocated

1- sinus tarsi

2- interosseous talocalcaneal ligament

3- cervical ligament

4- posterior articular surface of calcaneus

4’- talar facet for posterior calcanean articular surface

5- proximal joint surface of navicular bone

5’- head of talus

6- cranial surface of sustentaculum tali

6’- talar articular facet for sustentaculum tali

7- flexor hallucis longus tendon

8- dorsal surface of spring ligament, covered in cartilage

9- bifurcate ligament

10- dorsal calcaneocuboid ligament

11- posterior talocalcaneal ligament

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Fig 13 Figure 13

Lateral aspect of right ankle, skin reflected. Standard approach to talus

1- inferior extensor retinaculum

2- tendon and synovial sheath of peroneus tertius

3- tendons and synovial sheaths of extensor digitorum longus

4- extensor digitorum brevis, bound down by the inferior extensor retinaculum

5- tendons and synovial sheaths of peroneus brevis (superficial) and peroneus longus (deep), bound down by the inferior peroneal retinaculum

6- tendons and synovial sheaths of the peroneal muscles under the superior peroneal retinaculum

7- abductor digiti minimi

8- Achilles tendon (tendo calcaneus), with pre- and retro-Achilles bursae

9- posterior peroneal vessels with malleolar and posterior talar branches and tributaries

Fig 14 Figure 14

Anterior aspect of the right ankle, skin reflected

1- inferior extensor retinaculum, with its two medial bands

2- tendon and synovial sheath of tibialis anterior, piercing the proximal band of the inferior extensor retinaculum

3- tendon and synovial sheath of extensor hallucis longus

4- tendons and tendon sheaths of extensor digitorum longus

5- peroneus tertius

6- extensor digitorum brevis

7- anterior tibial neurovascular bundle

8- lateral perimalleolar branches

9- medial perimalleolar branches

Fig 15 Figure 15

Medial aspect of the right ankle, skin reflected

1- proximal band of inferior extensor retinaculum, binding down the tendon of tibialis anterior and its synovial sheath

2- tendons and synovial sheaths of tibialis posterior, flexor digitorum longus, and flexor hallucis longus, bound down by the flexor retinaculum

3- flexor retinaculum

4- posterior tibial neurovascular bundle, with malleolar branches and tributaries

5- abductor hallucis

Fig 16 Figure 16

Posterior aspect of the right ankle, skin reflected

1- Achilles tendon, divided

2- pre- and retro-Achilles bursae

3- origin of short saphenous vein

4- tendons and synovial sheaths of peroneal muscles

5- tendons and synovial sheaths of toe flexors and tibialis posterior

6- posterior tibial neurovascular bundle giving off intermalleolar anastomosing branches

7- posterior peroneal neurovascular bundle

8- posterior process of talus

9- posterior capsuloligamentous reinforcements

Fig 17 Figure 17

Superior aspect of the right talus - arterial supply

ta: anterior tibial artery

dt: lateral tarsal artery

st: artery of the sinus tarsi

tp: posterior tibial artery

fp: (posterior) peroneal artery

1- branch to neck of talus

2- medial osteoligamentous branches

3- posterior periosteal branches

Fig 18 Figure 18

Medial aspect of right talus - arterial supply

t.a.: anterior tibial artery

t.p.: posterior tibial artery

1- branch to neck of talus

2- branch to roof of sinus tarsi

3- branches to deep fibres of medial ligament

Fig 19 Figure 19
Coronal section of the right hindfoot, seen from the front
f.: fibula and fibular malleolus
t.: tibia and tibial malleolus
1- interosseous membrane
2- subtalar joint (posterior part)
3- subtalar joint (anterior part, between the talus and the sustentaculum tali)
4- sinus tarsi, with the two laminae of the interosseous talocalcaneal ligament, and the artery of the sinus tarsi giving off nutrient branches
5- calcaneofibular ligament
6- lateral talocalcaneal ligament
7- tendons and synovial sheaths of the peroneal muscles bound down by the inferior extensor retinaculum
8- abductor digiti minimi
9- plantar calcaneocuboid ligament
10- flexor digitorum brevis
11- plantar aponeurosis
12- abductor hallucis
13- quadratus plantae
14- medial inframalleolar canal (of Cruveilhier) with the two plantar neurovascular bundles
15- tendon and synovial sheath of flexor hallucis longus
16- tendon and synovial sheath of flexor digitorum longus
17- tendon and synovial sheath of tibialis posterior; all three tendons bound down by the flexor retinaculum
18- medial ligament (superficial and deep fibres)

Fig 20 Figure 20
Horizontal section of the right ankle joint, proximal aspect
f.: fibular malleolus
T.: tibial malleolus
1- talus
2- posterior malleolus
3- tendons and synovial sheaths of the peroneals bound down by the superior peroneal retinaculum
4- posterior peroneal vessels
5- Achilles tendon, with pre- and retro-Achilles bursae, and plantaris (where present)
6- posterior tibial neurovascular bundle
7- tendon and synovial sheath of flexor hallucis longus
8- tendon and synovial sheath of flexor digitorum longus
9- tendon and synovial sheath of tibialis posterior
10- tendon and synovial sheath of peroneus tertius
11- tendons and synovial sheaths of extensor digitorum longus
12- tendon and synovial sheath of extensor hallucis longus
13- tendon and synovial sheath of tibialis anterior
14- inferior extensor retinaculum
15- anterior tibial neurovascular bundle

Fig 21 Figure 21
Oblique coronal section of the posterior tarsus, seen from the front
1- distal part of tibial malleolus
2- talus
3- medial ligament (superficial and deep fibres)
4- tendon and synovial sheath of tibialis posterior, reinforcing the medial ligament
5- tendon and synovial sheath of flexor digitorum longus, under the medial border of the sustentaculum tali
6- tendon and synovial sheath of flexor hallucis longus, under the sustentaculum tali
7- plantar neurovascular bundle
8- quadratus plantae
9- abductor hallucis
10- flexor digitorum brevis
11- plantar aponeurosis
12- plantar calcaneocuboid ligament
13- abductor digiti minimi
14- calcaneus
15- peroneal muscles in their synovial sheaths, bound down by the inferior peroneal retinaculum
16- extensor digitorum brevis
17- entrance to sinus tarsi, with vessels entering and leaving there
18- tendon and synovial sheath of peroneus tertius
19- tendons and synovial sheaths of extensor digitorum longus
20- anterior tibial neurovascular bundle, giving off nutrient branches to the bone
21- inferior extensor retinaculum
22- tendon and synovial sheath of extensor hallucis longus
22- tendon and synovial sheath of tibialis anterior

Fig 22 Figure 22
Coronal section through the midtarsal joint space of the right foot, seen from the front
1- head of talus
2- fibrocartilage on the surface of the strong spring ligament
3- tendon and synovial sheath of tibialis posterior, medially reinforcing the spring ligament and supporting the head of the talus
4- tendons of flexor digitorum longus and flexor hallucis longus, united by a common expansion andproviding additional support for the talus
5- abductor hallucis
6- medial plantar neurovascular bundle
7- flexor digitorum brevis
8- thickened plantar aponeurosis
9- quadratus plantae
10- lateral plantar neurovascular bundle
11- abductor digiti minimi
12- tendons and synovial sheaths of the peroneal muscles
13- plantar calcaneocuboid ligament
14- calcaneal facet for cuboid bone
15- the two limbs of the bifurcate ligament
16- extensor digitorum brevis
17- tendons and synovial sheaths of peroneus tertius and extensor digitorum longus
18- anterior tibial neurovascular bundle
19- tendon and synovial sheath of extensor hallucis longus
20- tendon and synovial sheath of tibialis anterior
21- talonavicular ligament

Fig 23 Figure 23
Bony architecture of the foot, medial view
P.: body weight
R.: ground reaction
1- trabecular system of the posterior calcaneus
2- trabecular system under the attachment of the Achilles tendon
3- plantar trabecular system
4- fracture line through body of talus
5- fracture line through neck of talus
6- posterior dislocation in the subtalar joint resulting in fracture of the posterior malleolus
7- anterior dislocation of the talus

Fig 24 Figure 24

Force lines in the right foot, seen from above

Shaded: medial longitudinal arch;

unshaded: lateral longitudinal arch

lig.gl.: spring ligament

Tp.: tibialis posterior

Fig 25 Fig 25b Figure 25
Ankle joint axis

T: tibia

f.: fibula

t.: talus

L: lateral

M: medial

Fig 26 Figure 26
Medial view of muscle action patterns
Ta.: tibialis anterior
Ext. H.: extensor hallucis longus
Ext. D.: extensor digitorum longus
TRI.: triceps surae
Tp.: tibialis posterior
Fl. D.: flexor digitorum longus
Fl. H.: flexor hallucis longus
1- dorsiflexion
2- plantar flexion

Fig 27 Figure 27
Lateral view of muscle action patterns
Ext. D. lg.: extensor digitorum longus
Fib. Ter.: peroneus tertius
Fib. br.: peroneus brevis
Fib. lg.: peroneus longus
TRI: triceps surae
1- dorsiflexion
2- plantar flexion

Fig 28 Figure 28

Superior view of right foot - mechanical axis of talocalcaneal articulation (axis of Henke)

Ext. H.: extensor hallucis

Ext. D. lg.: extensor digitorum longus

T. a.: tibialis anterior

T. p.: tibialis posterior

Fl. D. lg.: flexor digitorum longus

Fl. H.: flexor hallucis longus

TRI: triceps surae

Fib. lg.: peroneus longus

Fib. br.: peroneus brevis

Fib. ter.: peroneus tertius

1- varus - adduction and supination of the foot (inversion)

2- valgus - abduction and pronation of the foot (eversion)

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