Anatomy and Biomechanics of the Ankle Joint

Ankle Joint

The ankle joint is formed by the convergence of the bones of the leg, the tibia and fibula. The tibia is the only bone that intervenes in the knee joint. Therefore, it is responsible for force transmission from the tibial plateau to the lower extremity. The fibula has a guiding or stabilizing function in the ankle joint.

Bone Surfaces

  1. Fibula: A thin bone, very rotated on itself, with a head at the outer edge of the knee where the crural biceps is fixed. It has a twisted body and a lower extremity called the external malleolus.
  2. Tibia: Curved. The tibial diaphysis is triangular, with an edge facing forward, called the tibial crest or shin. The lower extremity presses into the bones of the foot. It is apparently flat but has an internal trochlear surface and a protrusion, the internal tibial malleolus.

Bones of the Foot

These are arranged in different layers: an upper layer (tarsus), a middle layer (metatarsus), and an anterior layer (phalanges or digits). The tarsus is composed of the talus, calcaneus, navicular, cuboid, and three wedge-shaped bones called cuneiforms (1st, 2nd, and 3rd). The metatarsus is composed of five metatarsal bones. The 1st, 2nd, and 3rd metatarsals articulate with the three cuneiforms, and the 4th and 5th metatarsals articulate with the cuboid. The talus is the only bone that articulates with the bones of the leg.

Articulations

The ankle is formed by three joints:

  1. Tibiofibular Joint: The upper tip of the fibula is associated with the tibial plateau.
  2. Proximal Ankle Joint: Formed by the tibiofibular joint and the talus.
  3. Distal Ankle Joint: Formed by the talocalcaneal joint and the talocalcaneonavicular joint.

Other joints include:

  • Tarsometatarsal Joints
  • Metatarsophalangeal Joints
  • Naviculocuneiform Joints (between the navicular and cuneiforms)
  • Interphalangeal Joints

The ankle joint can be defined according to various parameters:

  • Function: The ankle is responsible for foot movement.
  • Structure: It is a trochlear joint. The tibia has a posterior malleolus that serves as a stop for ankle extension, preventing the talus from impacting the tibia.

Tibiofibular Joints

These joints connect the proximal and distal extremities of the tibia and fibula.

  • Upper Tibiofibular Joint: The tip of the fibula articulates with the surface of the tibial plateau. It is an arthrodial joint.
  • Lower Tibiofibular Joint: It has no cartilaginous surface and is an amphiarthrosis. The tibial surface is slightly concave, as if to embrace the surface of the fibula. It has anterior and posterior ligaments. The mechanics of this joint are associated with the movement of the talocrural joint.

Talocalcaneal Joint

Also known as the subtalar joint, it has three parts:

  • Head: Articulates with the calcaneus below and the navicular in front.
  • Body: Shaped like a pulley (talar pulley).
  • Neck: The lower longitudinal side of the talus articulates with the upper face of the calcaneus.

Ligaments include the interosseous ligament and the anterior and posterior talocalcaneal ligaments.

  • Posterior: An arthrodial joint with sliding movement.
  • Anterior: An arthrodial joint occupied by a projection of the calcaneus called the calcaneal apophysis, which supports the head of the talus in the lower part.

The talus and calcaneus are united by strong and short ligaments designed to withstand efforts during walking, running, and falling.

Tarsometatarsal Joints

Also known as Lisfranc’s joint, it is constituted by a succession of closely overlapping arthrodial joints. These joints unite the anterior part of the cuneiforms and cuboid with the posterior part of the metatarsal bases, covering the edges and proximal bones of the five metatarsals. They are held together by strong ligaments.

Metatarsophalangeal Joints

These joints are located between the heads of the metatarsals and the bases of the first phalanges. They allow for flexion, extension, and slight abduction and adduction.

Interphalangeal Joints

These joints allow for the flexion and extension of the toes. There are two interphalangeal joints in each toe except the big toe, which has only one. The first, or proximal, interphalangeal joint connects the head of the first phalanx with the base of the second phalanx. The second, or distal, interphalangeal joint connects the head of the second phalanx with the base of the third phalanx.

Ligaments

The ligaments are primarily lateral, fixing from the tip of the malleolus to the opposite bone.

Lateral Ligament

It extends from the tip of the fibula to the talus and calcaneus, with three groups of fibers that limit inward movement. This is the ligament most commonly injured.

  • Anterior Fiber: From the anterior tip of the malleolus to the neck of the talus, limiting extension.
  • Middle Fiber: From the tip of the fibula to the side of the calcaneus, limiting extension.
  • Posterior Fiber: From the internal face of the malleolus to the talus, limiting flexion.

Medial Ligament

Thicker and wider than the lateral ligament, it has a glenoid ligament reinforcement that extends from the tip of the tibia to the navicular.

Ankle Movements

The ankle functions on several axes, allowing for various movements.

  1. Transverse Axis:
    • Dorsiflexion (Flexion): The back of the foot approaches the anterior part of the leg. The arches of the foot flatten. Range of motion is 20-30 degrees.
    • Plantarflexion (Extension): The opposite movement, where the toes flex. The arches of the foot are elevated. Range of motion is 30-50 degrees.
  2. Anteroposterior Axis:
    • Pronation: Greater support on the inner zone of the foot.
    • Supination: Greater support on the outer zone of the foot.
  3. Longitudinal Axis: Prolongation of the tibia. Abduction and adduction movements are performed, which are functions of the knee or hip.

Limitations of Movement

  1. Flexion:
    • Impact of the anterior part of the tibia with the neck of the talus.
    • Tension from the posterior and lateral ligaments.
    • Muscle tone of the triceps surae.
  2. Extension:
    • Ankle flexors.
    • Anterior part of the joint capsule and lateral ligaments.
    • Impact between the posterior side of the tibia and the talar pulley.

Muscles

The posterior muscles are larger because they are responsible for propelling the body during walking. This is explained by the action-reaction principle: the tip or heel of the foot exerts pressure on the floor, and the floor responds with a force of equal magnitude but in the opposite direction. These muscles are extrinsic to the foot, meaning they insert into the bones of the tarsus or toes. There are also intrinsic muscles of the foot that move the ankle. These muscles are arranged in compartments and are mostly multiarticular, crossing multiple joints.

Extrinsic Muscles

These muscles originate outside the foot (tibia, fibula, and femur) and insert into the bones of the foot. They are polyarticular. As a tendon passes along the front or behind the ankle, it acts as a flexor or extensor.

Intrinsic Muscles and Lumbricals

  • Dorsal Interossei (4): Located in the center of the foot, they originate on the metatarsals and terminate on the toe closest to the second toe.
  • Plantar Interossei (3): Insert on the medial side of the three outermost metatarsals and terminate on the corresponding metatarsal.

These muscles form the fleshy mass of the sole of the foot.

  1. First Plantar Layer:
    • Abductor Hallucis: Separates the big toe from the second toe.
    • Flexor Digitorum Brevis: Flexes the second to fifth toes.
    • Abductor Digiti Minimi: Separates the fifth toe.
  2. Second Plantar Layer:
    • Quadratus Plantae: Flexes the second to fifth toes.
    • Lumbricals (4): Flex the distal phalanges of the second to fifth toes.
  3. Third Plantar Layer:
    • Flexor Hallucis Brevis: Flexes the proximal phalanx of the big toe.
    • Adductor Hallucis: Adducts the big toe towards the second toe.
    • Flexor Digiti Minimi Brevis: Flexes the proximal phalanx of the fifth toe.
  4. Fourth Plantar Layer:
    • Dorsal Interossei: Muscles between the four metatarsals.
    • Plantar Interossei: Three muscles.
  5. Dorsal:
    • Extensor Digitorum Brevis: Extends the proximal phalanges of the first to fourth toes.

Plantar Arches

The plantar arches are located in the foot to accommodate the soft tissues between the bones and the ground, facilitate adaptation to walking on different terrains, and facilitate cushioning and propulsion functions.

Medial Plantar Arch

  1. Osseous Surface: Posterior lower apophysis of the calcaneus, navicular, first cuneiform, first metatarsal, and talus. Support is provided by the head of the first metatarsal (at the base of the head, there are two sesamoid bones located between the tendons).
  2. Ligaments: Deltoid and calcaneonavicular ligaments, which prevent the navicular from dropping.
  3. Muscles: Posterior tibialis, flexor hallucis longus, flexor digitorum longus, anterior tibialis, and long peroneal, which form a belt that helps prevent the navicular area from dropping.
  4. Tendons: Prevent the descent of the medial arch, which is closely related to the plantar fascia. It is not designed to withstand sustained pressure, even if low intensity, requiring recovery between propulsions.

Lateral Plantar Arch

  1. Osseous Surface: Posterior external part of the calcaneus, cuboid, and fifth metatarsal. It is shorter and lower than the medial arch.
  2. Ligaments: Plantar ligaments.
  3. Muscles: Adductor digiti minimi, flexor digiti minimi, and opponens digiti minimi.
  4. Tendons: Short and long peroneal tendons.
Functions
  • It is more solid, making it more capable of receiving and maintaining pressure.
  • Supports weight in a sustained and constant manner.
  • Acceptable impulses are transmitted to the medial arch, decreasing the force to facilitate propulsion.

Anterior or Transverse Plantar Arch

  1. Osseous Surfaces: Heads of the five metatarsals (the highest point is the head of the second metatarsal). It is shorter and lower than the other arches.
  2. Means of Union: Few. There are ligaments that unite the dorsal part transversely.
  3. Muscles: Adductor hallucis and transverse ligaments.
Functions
  • Transmits pressure from the lateral arch to the medial arch.
  • Establishes or facilitates the establishment of plantar pads that facilitate the friction of the skin against the floor or shoes.
  • It is a weak arch.

Mechanisms of Walking

There are five phases:

  1. Initial Contact: Heel contact with the ground. The knee and hip are extended, and the ankle is in a neutral position.
  2. Loading Response: The foot is in plantar extension with a tendency towards supination. At this moment, the center of gravity is over the stance leg, and there is only one point of support.
  3. Mid Stance: The tibia and hip begin to extend. Body weight falls on the sesamoid bones.
  4. Terminal Stance: Double support continues. Hip extension continues, and the big toe flexes. If the ground is rigid, the big toe cannot extend, resulting in an elevation of the body or foot from the ground, favored by knee flexion and tension relief of the big toe.
  5. Pre-Swing: Before the big toe leaves the ground, the other foot is already in contact with the ground.

Shoes

  • Thickness: The sole should be thick enough.
  • Laces: Inelastic laces. They should be tied at the ankle, close to the instep, with two knots, not one, and the second one should be tighter. They should not be tied high around the ankle.
  • Length and Width: Adequate length and width. Shoes should be purchased in the afternoon when the foot is more swollen, supporting all the weight, and always with socks (to prevent infections or structural defects of the foot).
  • Heel: The heel should be higher than the forefoot (difference up to 100%).
  • Effects of Heels: Dorsiflexion of the toes, increased energy expenditure, decreased postural tone of the triceps surae, and shortening of the lever arm for propulsion, making movements more costly and causing hyperextension of the knee.

Intrinsic Muscles of the Foot

  • Extensor Digitorum Brevis (Pedis)
  • Dorsal Interossei
  • Plantar Interossei
  • Lumbricals
  • Flexor Digitorum Brevis
  • Flexor Hallucis Brevis
  • Abductor Hallucis
  • Adductor Hallucis
  • Flexor Digiti Minimi Brevis
  • Abductor Digiti Minimi
  • Opponens Digiti Minimi

Extrinsic Muscles of the Foot

  • Anterior Group:
    • Extensor Hallucis Longus
    • Extensor Digitorum Longus
    • Peroneus Tertius
    • Tibialis Anterior
  • Lateral Group:
    • Peroneus Longus
    • Peroneus Brevis
  • Posterior Group:
    • Flexor Digitorum Longus
    • Tibialis Posterior
    • Flexor Hallucis Longus
    • Triceps Surae
  • The anterior group performs dorsiflexion or other functions.
  • The lateral group performs plantarflexion or pronation/extension.
  • The posterior group performs plantarflexion/extension or other functions, depending on the muscle and its action on the knee (e.g., the gastrocnemius acts to flex the knee).
  • Supination is performed by the tibialis posterior.

Extrinsic muscles originate in the tibia, fibula, or femur and insert into the bones of the foot. Intrinsic muscles originate and insert within the bones of the foot, mainly in the sole, forming the fleshy mass of the sole.