The ankle and foot regions belong to the body’s lower extremities or lower limbs. These parts support the upper body’s weight, maintain balance, and allow various movements(1).
Anatomy of the Ankle
The ankle is part of the lower limb that encompasses the leg’s distal portion and the foot’s proximal portions. The ankle joint (talocrural joint) allows the foot’s dorsiflexion (raising the foot upwards) and plantar flexion (pointing the foot downwards)(2). Three joints comprise the ankle joint: tibiotarsal (upper ankle joint), talocalcaneonavicular, and subtalar joints. The last two joints are also called the lower ankle joints(3). The interior surfaces of the tibia (shinbone), fibula (calf bone), and the superior surface of the talus make up the upper ankle joint. Meanwhile, the talus (ankle bone), calcaneus (heel bone), and navicular bone form the lower ankle joint. The joints are supported by a set of ankle ligaments: the medial collateral or deltoid ligament and lateral collateral ligament(4).
Bones of the Foot
There are 26 bones in the foot divided into tarsal bones, metatarsal bones, and phalanges(5). Tarsals consist of seven irregularly shaped bones that make up a strong weight-bearing platform. These bones are homologous to the carpal bones in the wrist and are divided into three groups(6):
- Proximal tarsal bones: talus and calcaneus
- Intermediate tarsal bone: navicular
- Distant tarsal bones: cuboid and three cuneiform bones (lateral, intermediate, and medial)
Five metatarsals connect the distal aspects of the cuneiform bones and cuboid bone to the base of the foot’s phalanges supporting the body’s weight(7). Metatarsal bones are homologous to the metacarpals of the hand. Phalanges are bones that make up the fingers and toes. There are 56 phalanges in the body, with 14 on each hand and foot. The lateral four toes consist of three phalanges (proximal, middle, and distal). Meanwhile, the hallux (great toe) consists of only two phalanges (proximal and distal)(8).
Joints of the Foot
Aside from the ankle joint that connects the foot with the leg, the foot’s bones articulate among themselves through numerous synovial joints(9). A synovial joint is a common joint type wherein the articulating surfaces have no direct contact with each other. The four groups of foot joints are: intertarsal, tarsometatarsal, metatarsophalangeal, and interphalangeal(10).
- Intertarsal are joints between the tarsal bones. These joints include the subtalar (talocalcaneal), talocalcaneonavicular, calcaneocuboid, cuneonavicular, cuboideonavicular, and intercuneiform joints.
- Tarsometatarsal joints consist of the articulations between the tarsals and metatarsals.
- Metatarsophalangeal (MTP) are the joints between the metatarsals’ heads and corresponding bases of the foot’s proximal phalanges.
- Interphalangeal are the joints between the phalanges of the foot. There is only one interphalangeal joint in the great toe, while the other four toes have a proximal (PIP) and a distal (DIP) interphalangeal joint.
Muscles of the Foot
The foot muscles contribute to the toes’ movements, the foot’s plantar flexion, dorsiflexion, eversion, and inversion(11). In eversion, the sole of the foot is turned and faces laterally. Meanwhile, the sole is directed medially during inversion(12). The foot muscles are divided into two groups: plantar and dorsal. The dorsal group has two muscles, while the plantar muscles are further divided into three subgroups: lateral, central, and medial. The dorsal foot muscles extend the toes and are in the dorsum (area facing upwards while standing). These muscles include the extensor digitorum brevis and extensor hallucis brevis(13). The deep fascia of the foot is located beneath the subcutaneous tissue, surrounding the intrinsic foot muscles. The three groups of plantar foot muscles are(14):
- Lateral plantar muscles act on the fifth toe - These muscles are the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi.
- Central plantar muscles act upon the four lateral toes - These muscles are the flexor digitorum brevis, quadratus plantae, four lumbricals, three plantar interossei, and four dorsal interossei.
- Medial plantar muscles act upon the hallux or great toe - These muscles are the abductor hallucis, adductor hallucis, and flexor hallucis brevis.
Ankle and Foot Imaging Techniques
The standard initial imaging modality to assess the ankle and foot is conventional radiography. It has a superior spatial resolution of osseous (bony) structures compared to magnetic resonance imaging (MRI)(15). Radiography also offers strong contrast resolution to differentiate between bone, metal, fat, calcification, and soft tissues. This modality provides a detailed anatomic assessment of the bones to help identify and diagnose fractures or injuries(16).
Computed Tomography (CT)
Like radiography, CT utilizes ionizing radiation to generate images. This cross-sectional imaging technique provides a non-invasive method to visualize complex anatomical structures(17). CT is most commonly used in ankle and foot imaging to characterize complex injuries or detect radiographically occult fractures. CT can easily distinguish metal, bone and calcifications, soft tissues, gas, and fat(18).
Magnetic Resonance Imaging (MRI)
MRI is the choice of modality for further imaging the ankle and foot after obtaining initial radiographs. This imaging technique assesses the ligaments and tendons, neurovascular structures (tarsal tunnel and plantar fascia), and the osseous structures(19). MRI can detect radiographically occult fractures or ankle impingement syndromes and characterize various injuries(20).
- Riegger, C. L. (1988). Anatomy of the ankle and foot. Physical therapy, 68(12), 1802-1814.
- Lezak B, Massel DH. Anatomy, Bony Pelvis and Lower Limb, Metatarsal Bones. [Updated 2020 Jul 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK549872/
- Dartmouth.edu. Basic Human Anatomy. Chapter 17: The ankle and foot. Retrieved from: https://www.dartmouth.edu/~humananatomy/part_3/chapter_17.html
- Lezak B, Massel DH. op. Cit.
- Bansal, G. J. (2006). Digital radiography. A comparison with modern conventional imaging. Postgraduate medical journal, 82(969), 425-428.
- Solomon, M. A., Gilula, L. A., Oloff, L. M., Oloff, J., & Compton, T. (1986). CT scanning of the foot and ankle: 1. Normal anatomy. American Journal of Roentgenology, 146(6), 1192-1203.
- Rosenberg, Z. S., Beltran, J., & Bencardino, J. T. (2000). MR imaging of the ankle and foot. Radiographics, 20(suppl_1), S153-S179.