Anatomy of the Ankle and Foot (Tobillo)

Anatomical Components of the Ankle and Foot

The anatomy of the ankle (Tobillo), as presented by L.T.F. Mijal Hirsch Fischer, is composed of a complex arrangement of bones, joints, ligaments, and musculature. The primary skeletal structures of the lower leg and foot include the Tibia, the Peroné (fibula), the Tarso (tarsus), the Metatarsos (metatarsals), and the Falanges (phalanges). These components collectively facilitate movement, balance, and weight distribution during locomotion.

The Tarsus (Tarso): Proximal, Intermediate, and Distal Groups

The Tarso is organized into three distinct functional and anatomical groups. The Grupo proximal consists of the Astrágalo (talus) and the Calcáneo. The Hueso intermedio del tarso is represented by the Navicular (also known as the Escafoides). Finally, the Grupo distal is composed of four bones: the Cuboides and the three Cuneiformes (cuñas), specifically the medial, intermediate, and lateral cuneiforms. These bones are viewed through both medial and lateral orientations to fully understand their spatial relationships.

Detailed Anatomy of the Tarsal Bones

The Astrágalo is the most superior bone of the foot, situated directly on top of the Calcáneo. It plays a critical role in the ankle joint by articulating with the Tibia and Peroné, as well as articulating with the Navicular bone on the medial side of the foot. The Calcáneo is identified as the longest bone of the tarsus; posteriorly, it forms the anatomical heel, while anteriorly and laterally, it articulates with the Cuboides and the Astrágalo. The Navicular or Escafoides resides between the Astrágalo (posteriorly) and the three Cuneiformes (anteriorly). It features a distinct Tuberosidad for the insertion of the Tibial posterior muscle. The Grupo Distal includes the three Cuñas (Cuneiformes: Medial, Intermedia, and Lateral), which articulate posteriorly with the Navicular and anteriorly with the first $3$ metatarsals. The Cuboides articulates with the Calcáneo posteriorly and with the base of the $2$ lateral metatarsals anteriorly.

Metatarsals and Phalanges

The Metatarsianos are numbered from $I$ to $V$ in a medial-to-lateral direction. The first metatarsal (ortejo) articulates with $2$ sesamoid bones (huesos sesamoideos). The lateral faces of the metatarsals from $II$ to $V$ articulate with one another. The Falanges comprise the digits and are categorized into three levels: Falanges proximales ($1^{a}$), Falanges mediales ($2^{a}$), and Falanges distales ($3^{a}$). On the dorsal view of the right foot, the bones are identified sequentially: $1.$ Astrágalo, $2.$ Calcáneo, $3.$ Navicular, $4.$ Primer cuneiforme, $5.$ Segundo cuneiforme, $6.$ Tercer cuneiforme, and $7.$ Cuboides.

Clinical Divisions and Joints: Lisfranc and Chopart

The foot is clinically subdivided into the Hindfoot, Midfoot, and Forefoot. Two significant functional joints are defined within these regions. Lisfranc's joint (Articulación de Lisfranc) serves as the transition between the Tarsal bones (Cuneiformes and Cuboides) and the bases of the Metatarsals. Chopart's joint (Articulación de Chopart) is the transverse tarsal joint located between the hindfoot (Talus/Astrágalo and Calcaneus) and the midfoot (Navicular/Escafoides and Cuboides). These zones are essential for structural integrity and movement mechanics.

Ligamentous Structures and Bursas

The stability of the ankle is maintained by several key ligaments. On the lateral side, the primary ligaments are the $1.$ Astrágalo-peroneo anterior, $2.$ Astrágalo-peroneo posterior, and $3.$ Ligamento calcaneo-peroneo. On the medial side, the stabilization is provided by the deltoid group: $1.$ Tibioastragalino anterior, $2.$ Tibionavicular, $3.$ Tibiocalcáneo, and $4.$ Tibioastragalino posterior. Additionally, specialized fluid-filled sacs called Bursas reduce friction near the heel: the Bursa retro-calcánea (located between the Tendón de Aquíles and the calcaneus) and the Bursa calcánea subcutánea (located superficially at the posterior heel).

Functional Architecture: Arches of the Foot

The foot is supported by three primary arches that manage weight-bearing. The Arco Longitudinal Lateral is formed by the Calcáneo, Cuboides, the $5^{to}$ metatarsal, and the $5^{to}$ dedo; its mechanical stability is aided by the Peroneo lateral largo and Peroneo lateral corto muscles. The Arco Longitudinal Medial is higher and more flexible, comprising the Astrágalo, Escafoides, $1^{a}$ cuña, $1^{er}$ metatarsal, and the $1^{er}$ dedo; it is supported by the Tibial posterior, Flexor largo propio del dedo gordo, Flexor largo común de los dedos, and Peroneo lateral largo. The Arco Transverso (Transverse Arch) transitions from the posterior tarsal region (Cuneiformes and Cuboides) to the anterior metatarsal region.

Musculature of the Leg: Anterior and Lateral Compartments

The muscles of the leg are divided into specific functional groups. In the Anterior compartment, the Tibial anterior originates from the lateral surface of the tibia and the interosseous membrane, inserting into the medial cuneiform and first metatarsal to perform dorsiflexion and inversion. The Extensor largo del primer ortejo (Extensor hallucis longus) originates from the medial fibula and interosseous membrane, inserting into the dorsal distal phalanx of the first toe to perform dorsiflexion and extension of that toe. The Extensor largo de los dedos (Extensor digitorum longus) originates from the medial fibula and inserts into the middle and distal phalanges of the four lateral toes to extend the toes and perform dorsiflexion. The Tercer peroneo (Peroneo anterior) originates from the distal fibula and inserts into the $5^{o}$ metatarsal, aiding in eversion and dorsiflexion. In the Lateral compartment, the Peroneo lateral largo (Peroneus longus) originates from the fibular head and lateral tibial condyle, inserting at the medial cuneiform and first metatarsal for eversion and plantiflexion. The Peroneo lateral corto (Peroneus brevis) originates from the inferior $2/3$ of the fibular shaft and inserts at the base of the $5^{o}$ metatarsal for eversion.

Musculature of the Leg: Posterior Compartments (Superficial and Deep)

The posterior leg is divided into deep and superficial groups. The Grupo profundo (Deep Group) includes the Poplíteo, which originates from the lateral femoral condyle and inserts on the proximal posterior tibia as a stabilizer. The Flexor largo del dedo gordo originates from the posterior fibula and inserts onto the plantar surface of the distal phalanx of the first toe to perform flexion. The Flexor largo de los dedos originates from the medial posterior tibia and inserts onto the distal phalanges of the four lateral toes for flexion. The Tibial posterior originates from the posterior interosseous membrane and inserts into the Navicular and medial cuneiform, performing inversion and plantar flexion. The Grupo superficial (Superficial Group) includes the Gastrocnemio (Gemelos), which originates above the femoral condyles and inserts into the Tendón del calcáneo (Achilles tendon) for knee flexion and plantiflexion. The Sóleo originates from the posterior fibular head and proximal tibia/fibula shaft, inserting into the Tendón del calcáneo for plantiflexion. The Plantar delgado originates from the lateral supracondylar line of the femur and inserts into the Tendón del calcáneo for knee flexion and plantiflexion.

Intrinsic Musculature of the Foot: Dorsal and Plantar Regions

The intrinsic muscles of the foot are categorized by their location. The Región dorsal contains the Extensor corto de los dedos, which originates from the Astragalar sulcus and lateral calcaneus, inserting into the middle and distal phalanges of the $2^{o}$, $3^{o}$, and $4^{o}$ toes to facilitate toe extension. The Extensor corto del primer dedo (also known as Pedio) originates from the astrágalo-calcáneo sulcus and inserts into the proximal phalanx of the first toe to extend it.

The Región plantar is organized into four layers. The Primera capa (First Layer) includes the Abductor del dedo gordo (origin: internal calcaneal tuberosity; insertion: base of the $1^{er}$ phalanx; action: abduction), the Abductor del $5^{to}$ dedo (origin: external calcaneal tuberosity; insertion: base of the $1^{er}$ phalanx; action: abduction), and the Flexor corto de los dedos (origin: internal calcaneal tuberosity; insertion: middle phalanges of toes $2-5$; action: proximal interphalangeal flexion). The Segunda capa (Second Layer) includes the Cuadrado Plantar (origin: internal and external calcaneal tuberosity; insertion: Flexor digitorum longus tendons; action: distal interphalangeal flexion) and the Lumbricales (origin: between Flexor longus tendons; insertion: Extensor longus tendons; action: metatarsophalangeal flexion and distal interphalangeal extension). The Tercera capa (Third Layer) includes the Flexor corto del dedo gordo (origin: Cuboides, cuneiforms, and Navicular; insertion: proximal phalanx of the first toe), the Flexor corto del $5^{o}$ dedo (origin: Peroneus longus sheath and $5^{o}$ metatarsal), and the Aductor del dedo gordo (origin: bases of metatarsals $2-4$ and Cuboides). Finally, the Cuarta capa (Fourth Layer) contains the Interóseos dorsales (origin: interosseous spaces; action: abduction) and Interóseos plantares (origin: medial side of the last $3$ metatarsals; action: adduction).