Foot study notes - A complete summary of the foot. Images provided to accompany the text. PDF

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A complete summary of the foot. Images provided to accompany the text....

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Foot: Study Notes Bones The human foot is a highly developed, biomechanically complex structure that serves to bear the weight of the body as well as forces many times the weight of the human body during propulsion. The bones of the foot can be divided into three categories: Tarsals (7) – A set of seven irregularly shaped bones. They are situated proximally in the foot, in the ankle area. Metatarsals (5) – These bones connect the phalanges to the tarsals. There are five in number – one for each digit. Phalanges (14) – The bones of the toes. Each toe has three phalanges – a proximal, intermediate and distal (except the big toe, which only has two phalanges).

Tarsals  The tarsal bones are 7 in number. They are named the calcaneus, talus, cuboid, navicular, and the medial, middle, and lateral cuneiforms. •

Talus: The talus is the most superior of the tarsal bones. The talus is the second largest tarsal bone, and it is situated above the calcaneus. The superior aspect of the body of the talus is elevated to fit into a socket formed by distal ends of the tibia & fibula to form the ankle joint. The upper(trochlear) surface articulates with the distal end of the tibia. The medial surface articulates with the medial malleolus of the tibia. Lateral surface articulates with the lateral malleolus of the fibula. Posterior to the sulcus tali is a large facet for articulation with the calcaneus (subtalar joint). The talus projects forward to articulate with the intermediate tarsal bone, the navicular, on the media side of the foot (Talonavicular joint). The main function of the talus is to transmit forces from the tibia to the heel bone (known as the calcaneus). Whilst numerous ligaments attach to the talus, it is not a site of muscle attachment or origin.

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Calcaneus: The calcaneus is the largest of the tarsal bones located in the heel of the foot and bears the weight of the body as the heel hits the ground. The posterior aspect of the calcaneus is marked by calcaneal tuberosity, to which the Achilles tendon attaches (bursa separates the bone from the tendon). The lateral surface of the calcaneus is smooth expect for slightly raised areas. One of them is the fibular trochlear, the tendons of the fibularis longus + brevis are bound to the trochlear as they pass over the lateral side of the calcaneus. The medial surface of the calcaneus is concave and has a prominent feature known as the sustentaculum tali. The tali has a facet for articulation with the middle facet of the talus. The calcaneal surface and the sulcus tali of the talus together form the tarsal sinus (large gap visible in skeleton when foot is viewed on the lateral aspect). Anteriorly, there’s a Calcaneocuboid joint – between the calcaneus and the cuboid.

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Navicular: Intermediate tarsal bone on the medial aspect of the foot. It is a boat-shaped bone and located between the talus posteriorly and the 3 cuneiform bones anteriorly. The navicular articulates with 4 bones: the talus and the 3 cuneiforms. It occasionally articulates with a fifth, the cuboid (laterally). A distinct feature on the plantar surface of the navicular, is a tuberosity for the attachment of the tibialis posterior tendon. It forms the uppermost portion of the medial longitudinal arch of the foot and acts as a keystone of the arch.

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Cuboid: In the distal row, at lateral side of the foot. The cuboid articulates posteriorly with the calcaneus, medially with the lateral cuneiform and anteriorly with the bases of the lateral two metatarsals. The inferior surface of the cuboid is marked by a groove for the fibularis longus muscle.

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Cuneiforms: The three cuneiforms (lateral, intermediate and medial) are wedge shaped bones. They articulate with each other, but also articulate posteriorly with the navicular bone and anteriorly with the bases of the medial 3 metatarsals. The medial and lateral cuneiforms project farther distally than the middle cuneiform to create a mortise for the base of the second metatarsal that articulates with the middle cuneiform. This configuration creates a keystone effect and contributes to the stability of the midfoot.

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Metatarsals: There are 5 metatarsals, numbered I – V from medial to lateral. Each metatarsal consists of a distal head and proximal base, which are joined by an elongated shaft of bone. Metatarsal I (great toe) is the shortest and thickest. The plantar surface of the head of metatarsal I articulates with two sesamoid bones. The second metatarsal is the longest. The sides of the bases of metatarsal II-V articulate with each other. The first metatarsal articulates with the first cuneiform, the second with all 3 cuneiforms, the third with the third cuneiform, the fourth with the third cuneiform and the cuboid, and the fifth with the cuboid. The lateral side of the base of metatarsal V has a prominent tuberosity and it’s an attachment site for the tendon of fibularis brevis muscle.

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Phalanges: Bones of the toes. Each toe has three phalanges – a proximal, intermediate and distal (except the big toe, which only has two phalanges). The head of the distal phalanx is nonarticular & flattened. In each toe, the total length of the digits combined is much shorter than the length of the associated metatarsal.

The ankle joint is a hinged synovial joint with primarily up-and-down movement (plantarflexion and dorsiflexion. •

Articulating surfaces The ankle joint is formed by three bones; the tibia and fibula of the leg, and the talus of the foot. Distal end of the fibula is anchored to the larger distal head of the tibia by strong tibiofibular ligaments, producing a bracket shaped socket, which is covered in hyaline cartilage. This socket is known as a mortise. When viewed from above, the articular surface of the talus is much wider anteriorly than it is posteriorly. As a result, the body of the talus fits snugly into the mortise formed by the bones of the leg. During dorsiflexion, the anterior part of the bone is held in the mortise, and the joint is more stable

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Ligaments  The ankle joint is stabilized by the medial (deltoid) & lateral ligaments.

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Medial ligament is large, strong and triangular. Apex is attached to the medial malleolus and it consists of four separate ligaments, which fan out from the malleolus, attaching to the talus, calcaneus and navicular bones. The primary action of the medial ligament is to resist overeversion of the foot. Subdivided into four parts: (1) Tibionavicular part: attaches in front of the tuberosity of the navicular and the margin of the plantar calcaneonavicular ligament (spring ligament), which connects the navicular bone to the sustenaculum tali of the calcaneus. (2) Tibiocalcaneal part is more central, attaches to the sustenaculum tali of the calcaneus. (3) Posterior tibiotalar part attaches to the medial tubercle of the talus. (4) Anterior tibiotalar part is deep to the Tibionavicular and Tibiocalcaneal parts + attaches to the medial side of the talus.

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The lateral ligament originates from the lateral malleolus. It resists over-inversion of the foot. It is comprised of three distinct and separate ligaments: (1) Anterior talofibular spans between the lateral malleolus and lateral aspect of the talus. (2) Posterior talofibular spans between the lateral malleolus and the posterior aspect of the talus. (3) Calcaneofibular spans between the lateral malleolus (malleolus fossa) and the lateral surface of the calcaneus.

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Movements  The ankle joint is a hinge type joint, with movement only possible in one plane. Thus, plantarflexion and dorsiflexion are the only movements that occur at the ankle joint. Eversion and inversion are produced at the other joints of the foot, such as the subtalar joint.

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Neurovascular The arterial supply is derived from the malleolar branches of the anterior tibial, posterior tibial and fibular arteries. Innervation is provided by tibial and deep fibular nerves.

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Clinical Ankle sprain: An ankle sprain refers to partial or complete tears in the ligaments of the ankle joint. It usually occurs in a plantarflexed weight-bearing foot, which is excessively inverted. The lateral ligament is more likely to be damaged for two main reasons: The lateral ligament is weaker than the medial ligament. The lateral ligament resists inversion. The anterior talofibular ligament is the lateral ligament most at risk of irreversible damage. Fracture  A Pott’s fracture is a term used to describe a bimalleolar (medial and lateral malleoli) or trimalleolar (medial and lateral malleoli, and distal tibia) fracture. This type of injury is produced by forced eversion of the foot. Forced eversion pulls on the medial ligaments, producing an avulsion fracture of the medial malleolus. The talus moves laterally, breaking off the lateral malleolus. The tibia is then forced anteriorly, shearing off the distal and posterior part against the talus. When a fracture is noted on an X-ray, important to consider that they may be ligamentous distortion.

Arches of the foot The foot has three arches: two longitudinal (medial and lateral) arches and one anterior transverse arch. They are formed by the tarsal and metatarsal bones, and supported by ligaments and tendons in the foot. Their shape allows them to act in the same way as a spring, bearing the weight of the body and absorbing the shock produced during locomotion. The flexibility conferred to the foot by these arches facilitate functions such as walking and running. •

Medial longitudinal arch  The medial arch is the higher of the two longitudinal arches. It formed by the posterior end of the calcaneus and the heads of the metatarsals. Has dynamic muscular support from the tibialis anterior and posterior, fibularis longus and intrinsic foot muscles. Ligamentous support by the plantar ligaments in particular the long plantar, short plantar and plantar calcaneonavicular ligaments (spring ligament) and the plantar aponeurosis.

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Lateral longitudinal arch  The lateral arch is the flatter of the two longitudinal arches, and lies on the ground in the standing position. Formed by the posterior end of the calcaneus and heads of the metatarsals. Muscle support from the tendon of fibularis longus. Same ligamentous support as the medial.

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Transverse Arch  Highest in a coronal plane of the foot. It is formed by the metatarsal bases, the cuboid and the three cuneiform bones. Muscle support from fibularis longus and tibialis posterior. Ligamentous support by the plantar ligaments and the deep transverse metatarsal ligaments holding the bones together.

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Clinical

➢ Pes Cavus (High arches): Pes cavus is a foot condition characterised by an unusually high medial longitudinal arch. It can appear in early life and become symptomatic with increasing age. Due to the higher arch, the ability to shock absorb during walking is diminished and an increased degree of stress is placed on the ball and heel of the foot. Consequently, symptoms will generally include pain in the foot, which can radiate to the ankle, leg, thigh and hip. ➢ Pes Planus (Flat footed): Pes planus is a common condition in which the longitudinal arches have been lost. Arches do not develop until about 2-3 years of age, meaning flat feet during infancy is normal. Because the arches are formed, in part, by the tight tendons of the foot, damage to these tissues through direct injury or trauma can cause pes planus. However, in some people, the arches never form. The feet may ache after prolonged activity in adults.

Retinaculum Flexor retinaculum  A strap-like CT structure that attaches above to the medial malleolus and below and behind to the inferomedial surface of the calcaneus. The retinaculum is continuous above with the deep fascia of the leg and below with the plantar aponeurosis of the foot. Two tendons enter into the retinaculum which are the tibialis posterior tendon (most medial) and lateral to it is the tendon of flexor digitorum longus. Lateral to both tendons is the posterior tibial artery, then the posterior tibial vein and then the tibial nerve. Lateral to the tibial nerve is the tendon for flexor hallicus longus. They all pass through to enter the sole of the foot. Pulse of the posterior tibial artery can be palpated through the flexor retinaculum midway between the medial malleolus and the calcaneus. Extensor retinaculum  2 Extensor retinacula strap tendons of the extensor muscles to the ankle region and prevent tendon bowing during extension of the foot + toes. There’s a superior extensor retinaculum at the distal leg just superior to ankle joint and is attached to the anterior borders of the tibia and fibula. Tendons of extensor digitorum longus, extensor hallicus longus, tibialis anterior and dorsalis pedis artery pass through. The inferior extensor

retinaculum is Y- shaped. Base attaches to the lateral side of the upper surface of the calcaneus, crosses medially over the foot and one of its arms attach to the medial malleolus and the other arm wraps around the foot and attaches to the medial side of the plantar aponeurosis. Tendon of extensor digitorum longus and fibularis tertius pass through the lateral compartment. Dorsalis pedis , extensor hallicus longus and tibialis anterior pass thorugh the medial compartment....