Functional Anatomy of the Ankle
Introduction[edit | edit source]
Understanding the anatomy of the ankle is essential for the diagnosis and treatment of common injuries. Chronic ankle pain, acute and chronic sprains, fractures, tears and inflammation may result from routine daily activities or professional and recreational sports. This article will discuss the ankle joint and its osseous, soft tissue, neural and vascular components, and explore how they relate to function.
Key Terms[edit | edit source]
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: sagittal passing from posterior to anterior, frontal passing from left to right, and vertical passing from inferior to superior. The rotation axes of the foot joints are perpendicular to the cardinal planes. Therefore, motion at these joints results in rotations within three planes. Example: supination involves inversion, internal rotation, and plantarflexion.
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: the position where there is the most congruency of the joint surfaces. 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; there is a maximum of six, including three translations and three rotations.
Ligament: fibrous connective tissue that holds the bones together.
Open (loose) pack position: position with least amount of joint congruency where joint stability is reduced.
Planes of movement: describe how the body moves. Up and down movements (flexion/extension) occur in the sagittal plane. Sideway movements (abduction/adduction) occur in the frontal plane. Movements in the transverse plane are rotational (internal and external rotation).
Ankle Structure[edit | edit source]
The ankle joint includes three bones: the talus, tibia and fibula. The ankle joint has three borders: 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.
- The lateral border of the joint = the articular facet of the lateral malleolus.
- Medial border of the joint = the articular facet of the medial malleolus.
- The superior border of the joint = the tibia's inferior articular surface and the talus's superior margin.
Bones and Articulations of the Ankle[edit | edit source]
The lower leg and foot constitute the ankle. The following bony elements of the ankle joint are part of this structure:
|Bones||Articulation||Characteristics||Key palpation points|
|Talocrural joint ("ankle joint" or TC joint)||The TC joint is framed laterally and medially by the lateral and the medial malleolus. The superior portion of the joint is formed by the tibia's inferior articular surface and the talus's superior margin.||To palpate the tibia, first find the tibial tuberosity on the anterior aspect of the leg. This is where the quadriceps muscle inserts into the tibia via the quadriceps tendon. Next, ask the patient to rotate their 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 the joint line between the femur and tibia. The patient performs lateral and medial rotation while you palpate the joint line where the movement occurs. You will be palpating the medial and lateral condyles of the tibia. Move your fingers down from the tibial tuberosity along the anterior border of the tibia. You will palpate the medial malleolus on the distal end of the tibia.|
|Subtalar joint (ST joint)||The three facets of the talus and the calcaneus form the ST joint.||To find the calcaneus, palpate distally to the lateral malleolus. It is located directly under the talus.
To locate the head of the talus, find the medial and lateral malleoli. Place your thumb on the medial malleolus 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 plantarflexed. You should feel the medial aspect of the head of the talus projecting.
|Inferior tibiofibular joint (ITF joint)||The ITF joint is an articulation between the fibular notch of the distal tibia and the fibula.
It helps stabilise the ankle mortise.
|To palpate the fibula, start at the tibial tuberosity. Move your finger laterally 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. This enables you to 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 the lateral malleolus.|
Ankle Kinematics[edit | edit source]
Ankle kinematics can vary between individuals. Factors that affect ankle range of motion include activities of daily living (with geographical and cultural differences), age, gender, and the method used to assess range of motion. For example, ankle range of motion in females aged 9 to 20 years is generally higher than in males. However, after the age of 60 years, it has been found that females experience a greater decline in ankle range of motion than males.
|Joint||Type of Joint||Plane of Movement||Motion||Kinematics||Closed pack position||Open pack position|
|TC joint||Hinge||Mainly sagittal;
Concomitant transverse and frontal plane
|Plantarflexion and dorsiflexion -
during plantarflexion, the foot adducts and inverts.
During dorsiflexion, it abducts and everts.
|Normal range of motion (ROM):
between 12 and 20 degrees of dorsiflexion, and between 50 and 56 degrees of plantarflexion
|ST joint||Condyloid||Mainly transverse||Inversion and eversion||Average ROM is
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[edit | edit source]
There are three bursae located in the ankle region:
- Achilles bursa
- Retrocalcaneal bursa
- Medial malleolus bursa
Ankle Joint Capsule[edit | edit source]
The articular capsule surrounds the joints. Superiorly, it is attached to the borders of the articular surfaces of the tibia and malleoli and inferiorly, to the talus around its upper articular surface. Anteriorly, the joint capsule 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 the subtalar joint (in 15% of individuals)
The capsule and collateral ligaments support the talocrural joint and provide proprioceptive feedback from the mechanoreceptors, free nerve endings and Ruffini endings located in the ligaments.
Ligaments of the Ankle[edit | edit source]
The 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 the medial collateral ligament as a structure composed of 6 bands, with 3 consistent bands. The 3 consistent bands are the tibionavicular ligament (TNL), tibiospring ligament (TSL), and deep posterior tibiotalar ligament (dPTL). The three inconsistent ligaments are the deep anterior tibiotalar ligament (dATL), tibiocalcaneal ligament (TCL), and superficial posterior tibiotalar ligament (sPTL).
The lateral collateral ligaments are made of the anterior and posterior talofibular and calcaneofibular ligaments.
The subtalar joint ligaments include the lateral talocalcaneal ligament, medial talocalcaneal ligament, and interosseous talocalcaneal ligament.
The distal tibiofibular joint is held together by the interosseous tibiofibular ligament, and the anterior, posterior and transverse tibiofibular ligaments.
|Key Ligaments||Origin||Insertion||Action/Role||Key palpation|
Tibionavicular ligament (TNL)
Tibiospring ligament (TSL)
Deep posterior tibiotalar ligament (dPTL)
Deep anterior tibiotalar ligament (dATL) Tibiocalcaneal ligament (TCL)
Superficial posterior tibiotalar ligament (sPTL)
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 ligament (TNL)||Anterior colliculus of the medial malleolus||Dorsomedial side of the navicular bone||The 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. The TNL runs next and slightly posterior to the ATTL and almost covers a portion of the ATTL. Ankle plantarflexion and eversion will create tension in the ligament.|
|Tibiospring ligament (TSL)||Anterior portion of the anterior colliculus of the medial malleolus||Superior border of the superomedial portion of the calcaneonavicular (spring) ligament||The TSL controls abduction of the talus.||To palpate the spring ligament, find the sustentaculum tali and navicular tuberosity. Place your thumbs on each of the bony prominences. In between your 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||The 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. The ATTL runs between these two structures. Place your thumb in-between as you evert and plantarflex the ankle to create tension in 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 inferior to the medial malleolus. The rigid structure under your finger is the sustentaculum tali; from this point, only soft tissue (fat pad) can be palpated. The TCL runs inferior to the medial malleolus. Foot eversion with create tension in 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 the tibialis posterior and flexor digitorum longus covering the ligament. Dorsiflexion and eversion will assist with PTTL palpation.|
|Lateral collateral ligaments:
|Lateral collateral ligaments:
Limit the excessive inversion motion of the ankle.
Control extreme of dorsiflexion and plantarflexion 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 the 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 the ankle and subtalar joint.
Resists varus stresses to the calcaneum in dorsiflexion.
|To palpate the calcaneal tubercle: Palpate the 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 as the fibularis longus and brevis tendons cover this ligament.|
Muscles of the Ankle[edit | edit source]
The lower leg muscles are divided into four compartments: the anterior compartment, the posterior compartment (superficial and deep), and the lateral compartment.
Anterior Compartment[edit | edit source]
Ankle dorsiflexion is performed by all the muscles within the anterior compartment. In addition:
- tibialis anterior and extensor hallucis longus invert the foot during dorsiflexion
- extensor digitorum longus everts the foot during dorsiflexion
- there is eccentric control of foot lowering during heel strike
- there is concentric control for toe clearance during the swing phase of gait
|Tibialis Anterior||Lateral condyle of the tibia, the proximal two-thirds of the lateral surface of the tibia, the interosseous membrane, the deep surface of the fascia cruris, and the intermuscular septum between it and the extensor digitorum longus||Medial cuneiform and the base of the first metatarsal||Deep peroneal nerve (L4, L5, S1)||Dorsiflexes the ankle,
inverts the foot
|Extensor Digitorum Longus||The proximal half of the medial surface of the fibula, the lateral tibial condyle, and the interosseous membrane||Distal and middle phalanges of digits two to five.||Deep peroneal nerve (L4, L5, S1)||Extends toes 2 - 5, dorsiflexes the ankle|
|Extensor Hallucis Longus||Anterior surface of the fibula and the adjacent interosseous membrane||The base and dorsal centre of the distal phalanx of great toe||Deep peroneal nerve (L4, L5, S1)||Extends great toe, dorsiflexes the ankle|
|Fibularis Tertius||Distal one-third of the fibula||The base of the fifth metatarsal||Deep peroneal nerve||Assists the extensor digitorum longus to dorsiflex, evert and abduct the foot, assists with dorsiflexion|
Superficial and Deep Posterior Compartments[edit | edit source]
The primary plantar flexors of the ankle are located in this compartment. Because of their insertion medial to the to the foot's midline, they also function as supinators.
Primary responsibilities include:
- transforming the foot into a rigid lever
- assisting with push-off during the gait cycle
- controlling tibia progression over the foot during initial contact through the push-off phase of the gait cycle
- controlling foot pronation during initial contact through the push-off phase of the gait cycle
Superficial Posterior Compartment[edit | edit source]
|Soleus||Soleal line, medial border of the tibia, head of the fibula, and posterior border of the fibula||The posterior surface of the calcaneus via the Achilles tendon||Tibial nerve (S1, S2)||Powerful plantarflexor of the ankle|
|Gastrocnemius||The lateral head: posterolateral aspect of the lateral condyle of the femur
The medial head: posterior surface of the medial femoral condyle and the popliteal surface of the femoral shaft
|Posterior surface of the calcaneus via the Achilles tendon||Tibial nerve (S1, S2)||Main plantarflexor of the ankle|
|Plantaris||Lateral supracondylar line of the femur, oblique popliteal ligament of the knee||Via the Achilles tendon into the posterior surface of the calcaneus||Tibial nerve (L5, S1, S2)||Helps with plantarflexion of the ankle
Assists with stabilising the tibia on the calcaneus to limit forward sway
Deep Posterior Compartment[edit | edit source]
|Flexor digitorum longus||The posterior surface of the tibia||Bases of distal phalanges of digits 2 - 5||Tibial nerve (S2, S3)||Flexes the second to fifth toes, assists with ankle plantarflexion|
|Tibialis posterior||The posterior surface of the tibia, the posterior surface of the fibula, and the interosseous membrane.||Navicular and medial cuneiform, bases of metatarsals 2 - 4, the second and third cuneiform, and the cuboid||Tibial nerve (L4, L5)||Plantarflexes and inverts the ankle, supports the medial arch by assisting with foot supination|
|Flexor hallucis longus||Distal two-thirds of the posterior surface of the fibula, the interosseous membrane, the posterior intermuscular septum of the leg, and the fascia of the tibialis posterior muscle.||The base of the distal phalanx of the great toe||Tibial nerve (S2, S3)||Flexes the great toe, and plantar flexes and inverts the ankle|
Lateral Compartment[edit | edit source]
The lateral compartment is also known as the peroneal compartment. The muscles located here are primarily responsible for ankle and foot eversion. There is some variation in the description of the lateral compartment in the literature, where the "absence of one or more muscle or the presence of supernumerary bundles or supernumerary distinct muscles" can be found.
The following muscles might be present in the lateral compartment:
- The peroneus quartus muscle (1-20% of cases)
- Bundles of the flexor digitorum longus
- The flexor digitorum accessorius longus muscle (6% of cases)
|Fibularis Longus||The head and superior two-thirds of the lateral surface of the fibula||The base of the first metatarsal and medial cuneiform||Superficial fibular nerve (L5, S1, S2)
May also receive additional innervation from common or deep fibular nerves
|Weak plantarflexor, supports the transverse arch of the foot|
|Fibularis Brevis||Inferior two-thirds of the lateral fibular surface and anterior and posterior intermuscular septa of leg||Lateral surface of the styloid process of the fifth metatarsal base||Superficial fibular nerve (L5, S1, S2)||Everts the foot, plantarflexes the ankle|
Innervation of the Ankle[edit | edit source]
Two main nerves innervate the muscles responsible for ankle movement: the tibial nerve and the common fibular nerve.
|Nerve||Origin||Branches||Motor fibres||Sensory fibres|
|Tibial nerve||L5, S1 and S2||Calcaneal nerve branches;
Medial and lateral plantar nerve
|Gastrocnemius, soleus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus||Occasionally supplies the area typically innervated by the deep fibular nerve|
|Common Fibular nerve||L4, S1, and S2||Superficial fibular nerve (SFN);
Deep fibular nerve (DFN)
|SFN: Fibularis longus and brevis
DFN: Tibialis anterior, extensor digitorum longus, extensor hallucis longus, extensor digitorum brevis (rarely innervated by the tibial nerve)
|SFN: skin of the anterolateral leg and dorsum of the foot (except the skin between the first and second toes)
DFN: lateral part of the ankle and foot regions, the skin between the first and second toes
Vascular Supply of the Ankle[edit | edit source]
The four arteries: popliteal, anterior and posterior tibial and fibular, supply the ankle region. Underdevelopment or complete absence of one vessel can occur, usually leading to increased development of the other artery. For example, under-development of the anterior tibial artery has been described in 0.5% to 10.9% of cases.
|Popliteal artery||Femoral artery||Anterior and posterior tibial arteries||Superficial posterior compartment including gastrocnemius, soleus and plantaris muscles|
|Anterior tibial artery||Popliteal artery||Posterior tibial recurrent artery;
Anterior tibial recurrent artery
|Proximal tibiofibular joint, knee joint, ankle joint, muscles and skin of the anterior compartment of the leg|
|Posterior tibial artery||Popliteal artery||Posterior tibial recurrent artery;
Anterior tibial recurrent artery;
Anterior medial malleolar artery;
Anterior lateral malleolar artery;
Dorsalis pedis artery
|Soleus muscle, popliteus, flexor hallucis longus, flexor digitorum longus and tibialis posterior|
|Fibular artery||Posterior tibial artery||Communicating branch (to the anterior tibial artery);
Perforating branch (to the posterior tibial artery)
|Popliteus, soleus, tibialis posterior, and flexor hallucis longus muscles|
Clinical Relevance[edit | edit source]
- When the common fibular nerve is damaged, an individual may be unable to dorsiflex and evert the foot and extend the digits.
- The area posterior to the medial malleolus tends to get injured frequently, causing tendon injury of the tibialis posterior, flexor hallucis longus or flexor digitorum longus and tibial nerve compression.
- Increased tissue stiffness in gastrocnemius and the hamstrings can lead to plantar fasciitis; calf muscle stretching may be one solution to this problem.
- Injuries to the ankle are painful and cause significant mobility limitations. Learn about ankle injuries here.
- One-third of all ankle fractures can result in tibiotalar joint dislocations. You can learn more about ankle fracture here.
- Chronic ankle instability may result from a poorly managed acute ankle ligament injury. Learn more about chronic ankle instability here.
- Individuals can still experience pain, functional instability, mechanical instability or recurrent sprain for 1 to 5 years after an acute ligament sprain. More information on ankle sprain can be found here.
- Bilateral extrinsic compression of the anterior tibial artery by the ankle's extensor retinaculum can cause intermittent claudication in both feet.
Resources[edit | edit source]
- Brockett CL, Chapman GJ. Biomechanics of the ankle. Orthop Trauma. 2016 Jun;30(3):232-238.
- Fraser JJ, Feger MA, Hertel J. MIDFOOT AND FOREFOOT INVOLVEMENT IN LATERAL ANKLE SPRAINS AND CHRONIC ANKLE INSTABILITY. PART 1: ANATOMY AND BIOMECHANICS. Int J Sports Phys Ther. 2016 Dec;11(6):992-1005.
References[edit | edit source]
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