The ankle anatomy is a complex hinged synovial joint that is formed by three bones: the tibia, the fibula and the talus bone. These bones are connected by a very strong ligaments that maintain the joint stability.

Ankle Anatomy Bones

Ankle joint if formed by:

  1. Tibial plafond.
  2. Talus bone.
  3. Medial malleolus
  4. Lateral malleolus

The ankle mortise is formed by:

  1. Tibial plafond
  2. Medial malleolus
  3. Lateral malleolus

Ankle mortise articulates with the dome of talar body. The dome of talar body is wider anteriorly, so the mortise widens and ankle becomes more stable in dorsiflexion.

Motions at ankle joint are:

  1. Plantar flexion (23 to 48 ْ ).
  2. Dorsiflexion (10 to 23 ْ ).
  3. Inversion / Eversion and Rotation.
Ankle Anatomy bones
Ankle Anatomy bones

The Distal Tibiofibular joint

The distal tibiofibular joint is classified as a syndesmosis, except for approximately 1 mm of the inferior portion, which is covered in hyaline cartilage.

The joint consists of a concave tibial surface and a convex or plane surface on the medial distal end of the fibula. There is an elongation into the joint by the synovium of the talocrural joint, the fibers of which are oriented inferiorly and laterally.

The fibula serves as a site for muscular and ligamentous attachment, providing stability for the talus at the talocrural joint.

The tibia is the second longest bone of the skeleton and is a major weight-bearing bone.

As at the proximal tibiofibular joint, support for this joint is provided primarily by ligaments.

The Tibiofibular joint is stabilized by four ligaments, collectively known as the Syndesmosis ligaments , these include:

  1. the inferior interosseous ligament (the primary stabilizer),
  2. the anterior inferior tibiofibular ligament,
  3. the posterior inferior tibiofibular ligament,
  4. the inferior transverse ligament.

The inferior interosseous ligament is the primary stabilizer of the Tibiofibular joint.

The Special tests to identify a Syndesmosis ligaments injury include external rotation test and squeeze test.

Syndesmosis ligaments
Syndesmosis ligaments

The Tibiotalar joint (Talocrural)

The tibiotalar joint is the articulation between the talus and the distal tibia. The talus serves as the link between the foot and the leg through the ankle joint and functions to distribute the body weight posteriorly toward the heel and anteriorly to the midfoot.

The talus is divided into an anterior head and a posterior neck and body:

  1. Body: The superior dome-shaped surface of the body articulates with the tibia. The body is convex in the anteroposterior (A-P) direction and slightly concave in the mediolateral (M-L) and superior directions. The shape of this articulating surface can be compared with that of a cone, with the base of the cone facing laterally and the apex medially. Since the superior aspect of the body of the talus is wedge shaped with the wider portion anterior, no varus/valgus movement is possible when the ankle is positioned in maximum dorsiflexion, unless the mortise or the tibiofibular ligaments are compromised.
  2. Neck: The neck of the talus is a narrow region between the head and the body of the talus, and it is medially inclined. Its rough surfaces serve as attachments for ligaments. Inferior to the neck of the talus is the sulcus tali, which, when the talus and the calcaneus are articulated, roofs the sinus tarsi and is occupied by the talocalcaneal interosseous and cervical ligaments.
  3. Head: The plantar surface of the head has three articular areas separated by smooth ridges. The most posterior and largest of the articular areas is oval, slightly convex, and rests on a shelf-like medial calcanean projection called the sustentaculum tali. The other two articulating facets connect the talus with the navicular and the plantar calcaneo-navicular ligament.
talus anatomy
Talus anatomy

The medial malleolus extends distally to approximately onethird of the height of the talus, whereas the lateral malleolus extends distally to approximately two-thirds the height of the talus.

The fibrous capsule of the ankle joint is relatively thin on its anterior and posterior aspects. It is lined with synovial membrane and reinforced by the collateral ligaments.

No tendons, with the exception of a small slip from the posterior tibialis, attach to the talus. However, the talus serves as the attachment for many ligaments.

The talus receives its blood supply from the branches of the anterior and posterior tibial arteries and is very susceptible to aseptic necrosis, particularly with proximal fractures.

talus blood supply
Talus blood supply

The Tibiotalar joint Ligaments:

The most important ligaments of the Tibiotalar joint can be divided into two main groups: lateral collaterals and medial (deltoid) collaterals.

Lateral Collaterals Ligaments:

The lateral collateral ligament complex consists of three separate bands, which function together as the static stabilizers of the lateral ankle. Each of the lateral ligaments has a role in stabilizing the ankle and/or subtalar joint, depending on the position of the foot. As such, these ligaments are commonly involved in ankle sprains.

1. Anterior Talofibular Ligament ATFL:

This thickening of the anterior capsule extends from the anterior surface of the fibular malleolus, just lateral to the articular cartilage of the lateral malleolus, to just anterior to the lateral facet of the talus and to the lateral surface of the talar neck.

The anterior talofibular ligament (ATFL) is an intracapsular structure and is approximately 2–5-mm thick and 10–12-mm long.

The ATFL functions to resist ankle inversion in plantarflexion. Regardless of ankle position, the ATFL is usually the first ankle ligament to be torn in an inversion injury. The accessory functions of the ATFL include providing resistance against anterior talar displacement from the mortise and resistance against internal rotation of the talus within the mortise.

The ATFL requires the lowest maximal load to produce failure of the lateral ligaments, although it has the highest strain of failure in that group.

This ligament is tested by anterior drawer test of the ankle

2. Calcaneofibular Ligament CFL:

The calcaneofibular ligament (CFL), an extra-articular structure covered by the fibular (peroneal) tendons, is larger and stronger than the ATFL. It fans out at 10–40 degrees from the tip of the fibular malleolus to the lateral side of the calcaneus, paralleling the horizontal axis of the subtalar joint.

This ligament effectively spans the ankle and subtalar joints, which have markedly different axes of rotation. Thus, its attachment is designed so that it does not restrict motion in either joint, whether they move independently or simultaneously.

As the ankle joint passes from dorsiflexion to plantarflexion, the CFL is less able to resist talar tilt to inversion, although the ATFL is more able to resist this tilt.

3. Posterior Talofibular Ligament PTFL:

The posterior talofibular ligament (PTFL) is the strongest of the lateral ligament complex, and serves to indirectly aid talofibular stability during dorsiflexion due to its anatomic location, where it can act as a true collateral ligament and prevent talar tilt into inversion.

The PTFL is rarely injured except in severe ankle sprains. The ligament is coalescent with the joint capsule, and its orientation is relatively horizontal. Its attachment on the talus involves nearly the entire nonarticular portion of the posterior talus to the groove for the flexor hallucis longus (FHL) tendon, and anteriorly to the digital fossa of the fibula, which transmits the vessels that supply the talus and the fibula.

This ligament is tested by Posterior drawer test of the ankle

4. Lateral Talocalcaneal Interosseous:

The lateral talocalcaneal interosseous (LTCIL) ligament is sometimes included in this group as it does play a role in lateral ankle and subtalar stability (see Talocalcaneal Ligaments).

In dorsiflexion, the PTFL is maximally stressed, and the CFL is taut, whereas the ATFL is loose. Conversely, in plantarflexion, the ATFL is taut, and the CFL and PTFL become loose.

Ankle Anatomy ligaments
Ankle Anatomy ligaments – Lateral Collateral

Medial Collaterals Ligaments:

The medial collateral ligaments form a triangular-shaped ligamentous structure known as the deltoid ligament of the ankle which consists of both superficial and deep fibers.

The superficial fibers of deltoid ligament consist of the following:

  1. Tibionavicular fibers: These fibers extend from the medial malleolus to the tuberosity of the navicular and serve to resist lateral translation and external rotation of the talus.
  2. Posterior talotibial fibers: These fibers travel in a posterolateral direction from the medial malleolus to the medial side of the talus and medial tuberosity of the talus. These fibers resist ankle dorsiflexion and lateral translation and external rotation of the talus.
  3. Calcaneotibial fibers: These thin fibers extend from the medial malleolus to the sustentaculum tali. The fibers are oriented in such a way that they resist abduction of the talus, calcaneus, and navicular, when the foot and ankle are positioned in plantar flexion and eversion.

The deep fibers of deltoid ligament consist of the following:

  1. Anterior talotibial fibers: The fibers of this strong ligament extend from the tip of the medial malleolus to the anterior aspect of the medial surface of the talus. These fibers are oriented in such a way that they resist abduction of the talus, when it is in plantar flexion and eversion. Such is the strength of these fibers that an injury to this ligament is often associated with an avulsion fracture

The superficial fibers of the deltoid ligament of the ankle specifically limited talar abduction or negative talar tilt and that the deep layers of the deltoid ligament of the ankle ruptured with external rotation of the leg, without the superficial portion being involved.

The strength of the ankle ligaments from weakest to strongest is the ATFL, PTFL, CFL, and deltoid complex.

Medial Deltoid ligaments
Medial Deltoid ligaments

Ankle joint Biomechanics:

The ankle joint sustains the greatest load per surface area of any joint of the body. Peak vertical forces reach 120% of body weight during walking and they approach 275% during running.

The joints and ligaments of the ankle and foot complex act as stabilizers against these forces and constantly adapt during weight-bearing activities, especially on uneven surfaces. It is estimated that an average 180-lb man absorbs 76.2 tons on each foot while walking 1 mile and that the same man absorbs 121.5 tons per foot while running 1 mile.

Approximately 60% of this weight-bearing load is carried out by the rearfoot, and 28% by the metatarsal heads.

Although the ankle and foot complex normally adapts well to the stresses of everyday life, sudden or unanticipated stresses to this region have the potential to produce dysfunction.

References:

  1. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.
  2. Millers Review of Orthopaedics -7th Edition Book.
  3. Rasmussen O, Kromann-Andersen C, Boe S. Deltoid ligament. Functional analysis of the medial collateral ligamentous apparatus of the ankle joint. Acta Orthop Scand. 1983 Feb;54(1):36-44. doi: 10.3109/17453678308992867. PMID: 6829280.
  4. Rasmussen O, Tovborg-Jensen I. Mobility of the ankle joint: recording of rotatory movements in the talocrural joint in vitro with and without the lateral collateral ligaments of the ankle. Acta Orthop Scand. 1982 Feb;53(1):155-60. doi: 10.3109/17453678208992194. PMID: 7064676.