Functional Anatomy of the ligaments on the medial and lateral sides of the ankle.
The Ankle
Sprain of the lateral ankle ligaments is the most common injury seen by healthcare providers who treat sports injuries to the lower extremity. Ankle injuries constitute 25% of all sports-related injuries, including 21% to 53% of basketball injuries and 17% to 29% of all soccer injuries.
Anatomy and Biomechanics
The ankle is a simple hinge joint. The usual movements at the talo-crural joint are plantar and dorsiflexion only.The stability of the talocrural joint depends on both joint congruency and the supporting ligamentous structures. The ankle joint has a fibrous capsule that encircles the joint completely and is thickened laterally.
Medial and Lateral Ligaments
The syndesmotic ligaments, responsible for maintaining stability between the distal fibula and tibia, consist of:
1. the anterior tibiofibular ligament,
2. the posterior tibiofibular ligament,
3. the transverse tibiofibular ligament,
4. the interosseous ligament, and
5. the interosseous membrane.
From the lateral malleolus, three ligaments fan out to provide stability.
The lateral ankle ligaments, responsible for resistance against inversion and internal rotation stress, are:
1. the anterior talofibular ligament (ATFL),
2. the calcaneofibular ligament (CFL) and
3. the posterior talofibular ligament (PTFL).
The medial supporting ligaments are:
1. the superficial and deep deltoid ligaments, which are responsible for resistance to eversion and external rotation stress and are less commonly injured.
Figure 1 Lateral (A) and Syndesmotic   (B) ligaments of the Ankle
A number of aspects of the biomechanics of the ankle joint will assist in the understanding of ankle joint injuries.
- with the ankle in neutral position the CFL is almost perpendicular to the long axis of the talus and is under tension,
- with the ankle in neutral position the ATFL is parallel to the long axis of the talus and is not under tension
In plantar flexion the relationship is reversed.
The ATFL resists ankle inversion in plantar flexion, and the CFL resists ankle inversion during dorsiflexion.?
Anterior TaloFibular Ligament (ATFL)
The relatively weak anterior talofibular ligament passes from the anterior surface of the fibula malleolus to the talus. This ligament is actually a thickening in the anterior ankle capsule and blends imperceptibly into it. A torn anterior talofibular ligament is, therefore, a capsular injury. Ligament is 20 mm long, 10 mm wide, and 2 mm thick and it passes from the lateral malleolus to the neck of the talus. Distance from tip of fibula to center of fibular attachment of anterior talofibular ligament is 10 millimeters;
With the foot plantigrade, its fibers are oriented 75 deg to the floor; with plantar flexion, its fibers approach vertical orientation.
Primary stabiliser to inversion in plantar flexion in the unloaded state, first ligament to be torn in inversion regardless of the position, tension increases in plantar flexion, in plantar flexion the ATFL aligns with the long axis of the fibula, in the neutral position ATFL resists anterior drawer
The accessory functions of the ATFL are resistance to anterior talar displacement from the mortise, clinically referred to as the anterior drawer, and resistance to internal rotation of the talus within the mortise.
The orientation of ATFL depends on position of ankle joint. In plantar flexion, it is parallel to long axis of foot, whereas in dorsiflexion, it is aligned with the tibial and fibular shafts. Strain in ATFL is minimum in dorsiflexion & neutral; it increased as ankle is moved progressively thru plantar flexion.
CalcaneoFibular Ligament (CFL)
The calcaneofibular ligament is a extra-articular round and cordlike ligament which connnects tip of distal fibula (attached proximally to the lateral malleolus) to small tubercle on posterior & lateral aspect of calcaneus (distally to the tubercle of the lateral surface of the calcaneus).
It thus crosses two joints: talocrural and the talocalcaneal.
Because the CFL spans both the lateral ankle joint and lateral subtalar joint, it contributes to both ankle and subtalar joint stability.
The CFL is long and strong, resembling a collateral ligament of other hinged joints. It is 2 cm long, 5 mm wide, and 3 mm thick. The calcaneal attachment of CFL is 13 mm from subtalar joint, & that insertion of anterior talofibular ligament onto talus is 18 mm posterior to subtalar joint.
It is in close contact (beneath) with medial peroneal sheath, but is not associated with either the ankle capsule or peroneal tendon sheath. The calcaneofibular ligament is part of the medial wall of the peroneal tendon sheath.
CFL attaches posteriorly on calcaneus to form 133-deg angle with fibula when ankle is in?neutral dorsiflexion-plantar flexion. It is lax in normal, standing position due to relative valgus orientation of calcaneus. Calcaneofiblar ligament may be lax until supination force is applied; greatest strain occurrs when inversion moment is applied with ankle in dorsiflexion. It is stressed in dorsiflexion/inversion and extreme inversion. In plantar flexion it stabilises the subtalar joint.
Because of its unique anatomical orientation, calcaneofibular ligament also has major role in stabilization of subtalar joint; it thus acts primarily to stabilize sub-talar joint & limit inversion. The CFL provides stability to inversion and torsional stresses to both the ankle and subtalar joints. It is rarely injured in isolation. Isolated rupture of the calcaneofibular ligament probably does not cause demonstrable ankle laxity;
Posterior TaloFibular Ligament (PTFL)
The anterior and posterior talofibular ligaments blend in with the joint capsule (unlike ?the calcaneal fibular ligament); thus capsular tears accompany tears of the 2 talofibular ligaments. The transverse tibiofibular ligament is often considered part of posterior talofibular ligament complex and acts to deepen posterior aspect of ankle joint;
The posterior talofibular ligament arises from the nonarticular surface of posteromedial fibula, runs horizontally and inserts onto lateral tubercle of talus; it connects posterolateral tubercle of the talus to the medial aspect of the lateral malleolus.
It is strongest of the lateral ligaments. It is? short, thick, very strong and poorly positioned to resist inversion stress in any position or arc of motion. It prevents posterior and rotatory subluxation of the talus.
The fibers are oriented horizontally, and tensed only in extreme dorsiflexion. The PTFL is under greatest strain in ankle dorsiflexion and acts to limit posterior talar displacement within the mortise as well as talar external rotation. When the posterior talofibular ligament is under tension it can either rupture or avulse the posterolateral corner of tibia (Volkmann's triangle).
Deltoid Ligament
The medial side of Ankle Joint is stabilized by deltoid ligament. The deltoid (medial collateral) ligament is a strong triangular ligament made up of superficial and deep components that arise from the anterior, distal, and posterior borders of the medial malleolus. It is a strong ligament that runs from tip of medial malleolus? tonavicular, sustentaculumtali and posterior area of talus.
The superficial portion consists of three parts;
a. the tibionavicular,
b. tibiocalcaneal (along plantar calcaneonavicular (spring) ligament, inserting onto the sustentaculumtali of the calcaneus), and
c. posterior tibiotalar ligaments (medial tubercle of talus).
Superficial deltoid ligament primarily resists eversion of hindfoot. Tibionavicular portion suspends spring ligament and prevents inward displacement of head of talus, while tibiocalcaneal portion prevents valgus displacement. Superficial deltoid is also partially covered by tendon sheaths & crural fascia.
The deep portion
consists only of the anterior tibiotalar ligament. It originates from inferior & posterior aspects of medial malleolus and inserts on medial and posteromedial aspects of the talus (it originates on posterior border of anterior colliculus, intercollicular groove, & posterior colliculus). It is oriented transversely & inserts into entire nonarticular surface of medial talus. The deep deltoid extends function of medial malleolus & prevents lateral displacement of talus and prevents external rotation of the talus; latter effect is pronounced in plantar flexion, when deep deltoid tends to pull talus into internal rotation.
The deltoid ligament (especially the anterior fibers) is brought into tension during plantarflexion. In dorsiflexion, medial and lateral stretch of the middle and posterior ligamentous fibers plays the predominant role in ankle stability. Eversion in neutral evaluates superficial deltoid ligament complex; external rotation stress evaluates syndesmotic ligaments and additionally - the deep deltoid ligament;
Other Ligaments:
Lateral talocalcaneal ligament
Lies between ATFL and CFL
Posterior and Anterior (inferior) tibiofibular ligament
The posterior and anterior tibiofibular ligament attaches the fibula to the tibia to strengthen the tibiofibularsyndesmosis. Damaged in more severe injuries. Associated with syndesmosis injury.
The origin of the posterior tibiofibular ligament is broad, covering most of the horizontal distal surface of the tibia. As the ligament fibers sweep laterally and distally to insert on the fibula they fit over the trochlea. When injured, combined rotation of the foot and dorsiflexion of the ankle may be painful.
Other Issues:
Amkle Stability
The stability of the ankle is achieved mainly by the tibionavicular fibers of the deltoid and the lateral ligaments. The lateral ligaments maintain the intrinsic stability of the talus and its mortise by developing a fairly uniform ligamentous force about it.
As plantarflexion occurs, all the lateral ligaments remain taut, and because of this passive talar mechanism, movement of inversion and adduction occurs. This movement is assisted dynamically in the early phases of gait by the intrinsic plantarflexors on the medial side of the ankle, which are active throughout stance a are all the extrinsic ankle and foot plantarflexors. Because of this talar mechanism, in the absence of muscular contracture the talus still cannot move freely in its mortise during passive plantarflexion. The anterior talofibular ligament and the similarly oriented fibers of the deltoid ligament are brought into tension during plantarflexion and contribute equally to ankle stability.
In dorsiflexion, medial and lateral stretch of the middle and posterior ligamentous fibers plays the predominant role. The differences in ankle stability may thus be related to interpersonal variation in the strength of the ligaments and the orientation of the axes of rotational and translational motions of the ankle joint and tarsal mechanism.
Ankle Injury
The body of the talus is widest anteriorly. Therefore, the ankle is most stable in dorsiflexion when the anterior aspect of the talus articulates with mortise. Most inversion ankle injuries occur in plantar flexion when the ankle is least stable.
The sequence of tearing in plantar flexion inversion injury is:
1. Lateral capsule
3. CFL
4. Posterior talofibular ligament (PTFL)
5. Deltoid ligament
6. Fracture
Clinically, the most commonly sprained ankle ligament is the ATFL, followed by the CFL. The anterior talofibular ligament need not necessarily be completely torn to allow damage to the calcaneofibular ligament. The calcaneofibular ligament may be injured without damage to the anterior talofibular ligament in the uncommon situation of inversion stress applied across a dorsiflexed ankle.
The PTFL is rarely injured. An inversion injury may be likened to opening a book. The posterior talofibular ligament is located at the binding and, therefore, is not generally torn as the injury progresses.
The incidence of ligamentous injury tends to match both the mechanism of injury and relative ligamentous strength. The strength of the ankle ligaments from weakest to strongest is the ATFL, PTFL, CFL, and deltoid ligament.
Lateral ankle sprains occur as a result of landing on a plantar flexed and inverted foot. These injuries occur while running on uneven terrain, stepping in a hole, stepping on another athlete's foot during play, or landing from a jump in an unbalanced position. During periods of ankle unloading, the ankle rests in a position of plantar flexion and inversion. If the ground or another object is met unexpectedly by the unloaded foot, lateral ligament injury may occur.
Other Injuries around the ankle
Of seven ligaments arising from the two malleoli, only four connect to the talus, and none of these four are the strongest ligaments surrounding the ankle joint.
The other three ligaments connect more distally to the calcaneus, and are the strongest. This structure has led to the concept that the subtalar joint must be considered a constrained joint and its inversion-eversion movements are integrally involved in the stability of the ankle.