Functional Anatomy of the Ankle

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Introduction

Understanding the anatomy of the ankle is essential for correct diagnosis and treatment of common ankle injuries. Chronic ankle pain, acute and chronic sprains, fractures, tears and inflammation may be a result of routine daily activities or professional and recreational sports. This article will address the complexity of the ankle joint and its osseous, soft tissue, neural and vascular components and how they relates to function.

Anatomy Basic Vocabulary

Axes: lines around which an object rotates. The rotation axis is a line that passes through the centre of mass. There are three axes of rotation: saggital passing from posterior to anterior, frontal passing from left to right, and vertical passing from inferior to superior. The rotation axes of foot joints are perpendicular to the cardinal planes; therefore, motions at these joints result in rotations within three planes. Example: supination involves inversion, internal rotation, and plantar flexion.

Bursae: reduces friction between the moving parts of the body joints. It is a fluid-filled sac. There are four types of bursae: adventitious, subcutaneous, synovial, and sub-muscular.

Capsule: one of the characteristics of the synovial joints. It is a fibrous connective tissue which forms a band that seals the joint space, provides passive and active stability and may even form articular surfaces for the joint.

Closed pack position: most of the area of joint contact between the two sides of the joint. In this position, joint stability increases. The closed pack position for interphalangeal joints is at full extension.

Degrees of freedom: the direction of joint movement or rotation, with six being a maximum, including three translations and three rotations.

Ligament: fibrous connective tissue that holds the bones together.

Open (loose) pack position: least amount of joint contact area where joint stability is reduced.

Planes of movement: describe how the body moves. Up and down movements (flexion/extension) occur in a saggital plane.Sideway movements (abduction/adduction) are done in the frontal plane. Movements in the transverse plane are rotational (internal and external rotation).

Ankle Structure

The ankle joint includes three bones: the talus, tibia and fibula. There are three borders forming the ankle joint: the lateral, medial and superior. The mortise joint of the ankle is a hinge connecting the ends of the tibia and fibula to the talus.

• Lateral border of the joint: the articular facet of the lateral malleolus
• Medial border of the joint: the articular facet of the medial malleolus
• Superior border of the joint: the inferior articular surface of the tibia and the superior margin of the talus.

Bones and Articulations of the Ankle

The lower leg and foot constitute the ankle. The following bony elements of the ankle joint are part of this structure:

• Distal tibia
• Distal fibula
• Talus

Bones	Articulation	Characteristic	Key Palpation
Talus Tibia Fibula	Talocrural joint ("ankle joint" or TC joint)	It is framed laterally and medially by the lateral and the medial malleolus and from the top by the tibia and the talus	To palpate the tibia, first find tibial tuberosity on the anterior aspect of the leg. This is the location of the quadriceps inserted via the tendon. Next, ask the patient to rotate the leg inward. Move your finger slightly up and out along the oblique line. Ask the patient to dorsiflex and invert the foot to identify the tibialis anterior. Continue upwards along the oblique line, and you will feel a bony landmark called Gerdy’s tubercle on the lateral condyle of the tibia. To palpate the proximal ends of the tibia, bring the patient's knee into flexion to visualise a joint line between the femur and tibia. The patient performs lateral and medial rotation while you palpate the joint line where the movement occurs. This is the medial and lateral condyle of the tibia. Move your fingers down from the tibial tuberosity along the anterior border of the tibia. On the distal end of the tibia, you will palpate the medial malleolus.
Talus Calcaneus	Subtalar joint (ST joint)	Three facets of the talus and the calcaneus are part of the ST joint.	To find calcaneus, palpate distally to the lateral malleolus. It is located directly under the talus. To locate the head of the talus, find medial and lateral malleoli. Place the thumb on the medial and your index finger on the lateral malleolus and move your fingers anteriorly. You feel a dip located behind the tendon. To verify that you are on the head of the talus, evert the patient's ankle while plantar flexed. You should feel the medial aspect of the head of the talus projecting into your contact.
Tibia Fibula	Inferior tibiofibular joint (ITF joint)	ITF is an articulation between the fibular notch of the distal tibia and the fibula. Provides stabilisation to the ankle mortise.	To palpate the fibula start at the tibial tuberosity. Move your finger lateral until you feel a bony landmark located more posteriorly. The head of the fibula is almost in direct line with tibial tuberosity. To confirm this landmark, ask the patient to evert the foot, and you can visualise the belly of the peroneus longus, which originates on the head of the fibula. The shaft of the fibula is covered with the muscle belly of the peroneus longus and brevis, so it is difficult to palpate. The distal part of the fibula ends with lateral malleolus.

Ankle Kinematics

Joint	Type of Joint	Plane of Movement	Motion	Kinematics	Closed pack position	Open pack position
TC joint	Hinge	Mainly saggital Concomitant transverse and frontal plane	Plantarflexion &Dorsiflexion During plantarflexion, the foot adducts and inverts. During dorsiflexion, it abducts and everts.	Normal range of motion : 12 and 20 degrees of dorsiflexion 50 and 56 degrees of plantarflexion	Maximum dorsiflexion	Plantaflexion
ST joint	Condyloid	Mainly transverse	Inversion &Eversion	The average ROM: 30 degrees inversion / 18 degrees eversion	Full inversion	Inversion/plantarflexion
ITF joint	Syndesmotic		Small range of gliding movements	No active movements	Maximum dorsiflexion	Plantarflexion

Ankle Bursae

There are three bursae located in the ankle region:

• The Achilles Bursa
• Retrocalcaneal Bursa
• The medial malleolus bursa

Ankle Joint Capsule

The articular capsule surrounds the joints, and is attached, above, to the borders of the articular surfaces of the tibia and malleoli, and below, to the talus around its upper articular surface. The joint capsule anteriorly is a broad, thin, fibrous layer. Posteriorly, the fibres are thin and run mainly transversely, blending with the transverse ligament. Laterally the capsule is thickened and attaches to the hollow on the medial surface of the lateral malleolus.

The ankle joint capsule communicates with the following structures:

• Flexor hallucis longus tendon sheath
• May communicate with subtalar joint (15%)

The capsule, together with collateral ligaments, they support the talocrural joint, and provide a proprioceptive feedback from the mechanoreceptors, free nerve endings and Ruffini endings located in the ligaments.

Ligaments of the Ankle

Medial collateral ligament ( deltoid ligament ) structure has not been described consistently. The criteria proposed by Milner and Soames are currently used as a point of reference. They describe medial collateral ligament as a structure composed of 6 bands, with 3 of them being consistent. The 3 consistent bands are the tibionavicular ligament (TNL), tibiospring ligament (TSL), and deep posterior tibiotalar ligament (dPTL). The three inconsistent ligaments are deep anterior tibiotalar ligament (dATL), the tibiocalcaneal ligament (TCL), and the superficial posterior tibiotalar ligament (sPTL).

Lateral collateral ligaments are made of anterior and posterior talofibular, and calcaneofibular ligaments.

Subtalar joint ligaments include lateral talocalcaneal ligament, the medial talocalcaneal ligament, and the interosseous talocalcaneal ligament.

Distal tibiofibular joint is held together by the interosseous tibiofibular ligament, the anterior, posterior and transverse tibiofibular ligaments.

Key Ligaments	Origin	Insertion	Action/Role	Key palpation
Deltoid ligament: Tibionavicular ligament (TNL) Tibiospring ligament (TSL) Deep posterior tibiotalar ligament (dPTL) Deep anterior tibiotalar ligament (dATL) Tibiocalcaneal ligament (TCL) Superficial posterior tibiotalar ligament (sPTL)			Deltoid ligament: Provides medial stability to the ankle Limits the extreme motion of eversion across the talocrural, subtalar and talonavicular joints Resists valgus stresses coming from the lateral to the medial side of the ankle joints Prevents lateral tilt of the talus
Tibionavicular (TNL)	Anterior colliculus of the medial malleolus	Dorsomedial side of the navicular bone	TNL controls abduction of the talus.	To palpate the navicular bone: The patient is supine, leg straight, and foot in neutral. Find the bony prominence midway between the calcaneus and the base of the 1st metatarsal. The navicular bone extends in the lateral direction to the third metatarsal. TNL runs next and slightly posterior to ATTL and almost covers a portion of ATTL. Ankle plantarflexion and eversion will create tension on the ligament.
Tibiospring (TSL)	Anterior portion of the anterior colliculus of the medial malleolus	Superior border of the superomedial portion of the calcaneonavicular (spring) ligament.	TSL controls abduction of the talus	To palpate spring ligament, find the sustentaculum tali and navicular tuberosity. Place your thumbs on each of the bony prominences. In between the thumbs lies the spring ligament. To tighten the ligament, stretch the bones apart.
Anterior Tibiotalar (ATTL)	Tip of the medial malleolus	Non-articular part of the medial talar surface	ATTL controls plantarflexion together with talofibular ligament	Palpate between talus and tibia. Place the foot in eversion and plantarflexion. Palpate the talus and the front of the malleolus, and the ligament runs between these two structures. Place your thumb in-between as you evert and plantarflex the ankle to create tension on the ligament
Tibiocalcaneal (TCL)(middle)	Anterior colliculus of the medial malleolus anterior to the origin of the anterior tibiotalar and tibiospring ligaments	Posterior part of the sustentaculum tali, posterior to the proximal origin of the superomedial portion of the calcaneonavicular ligament.	TCL controls abduction of the talus	To palpate sustentaculum tali: The patient is supine, foot in neutral. Find the medial malleolus and palpate straight inferior to the medial malleolus. The rigid structure under your finger is sustentaculum tali; from this point, only soft tissue (fat pad) can be palpated. TCL runs inferior to the medial malleolus. Foot eversion with create tension on the ligament.
Posterior Tibiotalar (PTTL)	Apex of the medial malleolus	Non-articular posterior part of the medial talar surface.	PTTL inhibits dorsiflexion	Difficult to palpate due to tendons of tibialis posterior and flexor digitorum longus covering the ligament. Dorsiflexion and eversion will assist with PTTL palpation.
Lateral collateral ligaments: Anterior Talofibular Posterior Talofibular Calcaneofibular			Lateral collateral ligaments: Limit the excessive inversion motion of the ankle Control extreme of dorsiflexion and plantar flexion of the ankle joint
Anterior Talofibular (ATFL)	Anterior edge of the lateral malleolus of the fibula	The neck of the talus	Supports the ankle joint	To palpate the neck of the talus: The patient is supine. Find the dome of the talus. Slide your fingers distal from the dome, and you will feel the neck of the talus. Foot inversion will create tension on the ligament
Posterior Talofibular (PTFL)	Distal part of the lateral malleolar fossa of the fibula	Lateral tubercle of the talus	Supports the ankle joint	Hard to palpate due to tendons of fibularis longus and brevis covering the ligament. Ankle dorsiflexion and inversion will assist with palpation.
Calcaneofibular (CFL)	Depression located anterior to the apex of the lateral malleolus of the fibula	Tubercle on the lateral calcaneal surface	Supports both ankle and subtalar joint Resists varus stresses to the calcaneum in dorsiflexion	To palpate calcaneal tubercle: Palpate lateral malleolus. Move your fingers straight down to find a bony prominence on the lateral aspect of the calcaneus. Palpation of the CFL is difficult due to tendons of the fibularis longus and brevis covering the ligament.

Muscles of the Ankle

The lower leg muscles are divided into four compartments: the posterior compartment (superficial and deep), the anterior compartment, and the lateral compartment.

a.      Posterior compartment of the leg

b.     Anterior compartment of the leg

c.      Lateral compartment of the leg

Resources

• Aparisi Gómez MP, Aparisi F, Bartoloni A, Ferrando Fons MA, Battista G, Guglielmi G, Bazzocchi A. Anatomical variation in the ankle and foot: from incidental finding to inductor of pathology. Part II: midfooot and forefoot. Insights Imaging. 2019 Jul 31;10(1):69.
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