Human Anatomy Week 8 - Foot and Ankle (Notes)

Talocrural Joint

The talocrural joint, or ankle joint, is a synovial hinge joint formed between the tibia, fibula, and talus.
The joint doesn't move perfectly in a straight plane during sagittal plane motion.
The distal tibia, medial malleolus, and lateral malleolus of the fibula create the mortis (concave part of the joint)
The trochlea (concave part of the joint) is inferior to the mortis, and is the dome-shaped part of the talus covered in thick cartilage.

### Talocrural Joint Ligaments

The medial collateral ligament (deltoid ligaments) consists of four components: anterior tibiotalar, tibionavicular, tibiocalcaneal, and posterior tibiotalar.
The medial collateral ligament originates at the tibia and extends to the talus, navicular, and calcaneus.
It prevents eversion and is stronger than its lateral counterpart.
The anterior talofibular ligament (ATFL), calcaneofibular ligament, and posterior talofibular ligament, form the lateral collateral ligament.
The ATFL is the most commonly sprained ligament.
The posterior tibiofibular ligament supports the joint posteriorly and is not part of the talocrural joint.
The tendons and muscles of the leg, such as the fibular tendons and muscles, provide lateral stability.

Talocrural Joint Motion

The primary motions at the talocrural joint are dorsiflexion and plantar flexion.
These movements play a crucial role in normal walking gait.
Lack of dorsiflexion or plantar flexion can lead to short steps.

### Talocrural Joint Blood Supply and Innervation

The posterior tibial artery and fibular artery supply the ankle joint.
The tibial and deep fibular nerve innervate the talocrural joint.

Subtalar Joint

The subtalar joint is a planar synovial joint formed between the talus and calcaneus.
Two articulations exist between the talus and calcaneus: a posterior aspect and an anterior aspect.
The posterior articulation is larger and has an uneven surface, with the talus sitting superior to the calcaneus.
The anterior articulation between the talus and the anterior facet of the calcaneus is in a separate joint space.
The sinus tarsi, a space between the anterior and posterior articulation, contains important ligaments that support the joint.
The cervical and interosseous talocalcaneal ligaments are situated within the sinus tarsi.
The sustentaculum tali, a projection on the calcaneus, supports the head and neck of the talus.

### Subtalar Joint Ligaments

The interosseous and cervical ligaments act together to anchor the talus to the calcaneus.
The plantar calcaneonavicular ligament, otherwise known as the spring ligament, supports the head and neck of the talus and helps stabilize the subtalar joint.
The medial aspects of the talocalcaneal ligaments are very small and connect the posterior tubercles of the talus and calcaneus.
The deltoid ligament provides support on the medial side of the subtalar joint.
The talocalcaneal ligaments connect the posterior tubercles of the talus to the calcaneus and support the joint posteriorly.
The calcaneofibular ligament contributes to the support of the ankle joint and the subtalar joint on the lateral side.

### Subtalar Joint Motion

The primary motions at the subtalar joint are inversion and eversion.
The subtalar joint works together with the talocrural joint and the joints of the midfoot.
Inversion is turning the sole of the foot towards the midline.
Eversion is turning the sole of the foot away from the midline.
These movements, alongside dorsiflexion/plantar flexion and abduction/adduction, contribute to pronation and supination.

Subtalar Joint Blood Supply

The talus has a limited blood supply due to the presence of articular cartilage on most surfaces.
Fractures to the talus are at high risk for necrosis due to the limited blood flow.

### Transverse Tarsal Joints

The transverse tarsal joints are made up of two joints: the talonavicular on the medial side of the foot and the calcaneocuboid joint on the lateral side.
The talonavicular joint allows for a ball and socket configuration but does not fully function as one due to its limits.
The calcaneocuboid joint is often referred to as the 'chopper joint' because of its concave and convex surfaces, which allow for a planar joint motion.

Transverse Tarsal Joints Ligaments

The long plantar ligament, situated deep to the plantar fascia, runs from the calcaneus to the bases of the lateral three metatarsals and helps support the arches.
The deep plantar calcaneonavicular ligament, also known as the spring ligament, stabilizes the subtalar and talonavicular joints.
The plantar calcaneocuboid ligament, or short plantar ligament, connects the anterior inferior surface of the calcaneus and cuboid and stabilizes the calcaneocuboid joint.
The tibialis posterior tendon and ligament play a role in stabilizing the transverse tarsal joints and supporting the arches of the foot.
The bifurcate ligament (dorsal calcaneocuboid ligament) provides additional stability dorsally.

### Transverse Tarsal Joints Motion

The transverse tarsal joints contribute to motion in the foot.
Pronation involves dorsiflexion at the talocrural joint, eversion at the subtalar joint, and abduction of the foot.
Supination involves plantarflexion at the talocrural joint, inversion at the subtalar joint, and adduction of the foot.

Other Joints in the Foot

The cuneonavicular, cuboideonavicular, tarsometatarsal, intermetatarsal, metatarsophalangeal, and interphalangeal joints are all gliding planar joints, allowing for minimal movement.
The metatarsophalangeal joints are ellipsoid joints, while the interphalangeal joints are hinge joints.

Arches of the Foot

The arches of the foot are formed by the bones, the plantar fascia, and muscles.
The arches of the foot are important for shock absorption, stability, blood flow, and distributed weight bearing.
The three arches are the medial longitudinal, lateral longitudinal, and transverse tarsal arch:
Medial Longitudinal Arch: Formed by the calcaneus, talus, navicular, and all cuneiforms, with the talus and navicular serving as the keystone bones.
Lateral Longitudinal Arch: Formed by the calcaneus, cuboid, and fifth metatarsal, with the cuboid serving as the keystone.
Transverse Tarsal Arch: Formed across the middle of the foot.

### Arches of the Foot Support Structures

The arches of the foot are supported by a number of structures including:
Muscles: Tibialis anterior, tibialis posterior, flexor hallucis longus, flexor digitorum longus, abductor hallucis, fibularis brevis, fibularis tertius, abductor digiti minimi.
Ligaments: Plantar calcaneonavicular ligament (spring ligament), long plantar ligament, short plantar ligament.
Fascia: Plantar aponeurosis.

### Dorsal Surface of the Foot

The dorsal surface of the foot has less soft tissue coverage compared to the plantar surface.
The dorsalis pedis artery runs from the anterior tibial artery.
The superficial fibular nerve innervates the dorsum of the skin.
The sural nerve provides sensory innervation along the lateral surface of the foot.
The deep fibular nerve innervates the extensor hallucis brevis and extensor digitorum brevis muscles.

Plantar Surface of the Foot

The plantar surface is composed of thick epithelial tissue, thick stratum corneum (dead cells), and the plantar fascia, which lies underneath the epidermis, dermis, and hypodermis.
The plantar fascia functions to support the arches of the foot and extends from the calcaneus to the base of the digits.
The plantar fascia can be divided into three compartments: central, medial, and lateral.

### Plantar Neurovascular Supply

The plantar neurovascular supply is provided by the posterior tibial artery.
The posterior tibial artery courses around the medial malleolus and, after passing under the flexor retinaculum, branches into the medial and lateral plantar arteries.
The tarsal tunnel syndrome occurs when the artery and nerve are impinged under the flexor retinaculum, causing numbness and tingling on the plantar foot.

### Cutaneous Innervation of the Foot

The saphenous nerve, a branch of the femoral nerve, innervates the medial aspect of the leg towards the medial malleolus.
The superficial fibular nerve innervates the anterolateral leg and the dorsum of the foot.
The deep fibular nerve innervates between the first and second phalanges.
The sural nerve innervates the lateral side of the foot.
The medial plantar nerve and lateral plantar nerve are on the plantar side.

### Plantar Muscles

There are four muscle layers on the plantar surface of the foot, consisting of abductor hallucis, abductor digiti minimi, flexor digitorum brevis, quadratus plantae, lumbricals, adductor hallucis, flexor hallucis brevis, flexor digiti minimi brevis, and interossei.

### First Layer of Plantar Muscles

Abductor Hallucis: Fills in the medial arch.
Abductor Digiti Minimi: Mirrors abductor hallucis on the lateral side.
Flexor Digitorum Brevis: Located in the central component.
All three muscles are innervated by the S2 and S3 nerve roots.

### Second Layer of Plantar Muscles

Quadratus Plantae: Helps align the pull of the tendon to create a straight pull.
Lumbricals: Help stabilize the toes.
Both muscles are innervated by the S2 and S3 nerve roots.

Third Layer of Plantar Muscles

Adductor Hallucis: Pulls the big toe towards the midline.
Flexor Hallucis Brevis: Flexes the big toe.
Flexor Digiti Minimi Brevis: Flexes the little toe.
The muscles are all innervated by the S2 and S3 nerve roots.

### Fourth Layer of Plantar Muscles

Interossei:
- Plantar interossei: Help adduct the toes.
- Dorsal interossei: Help abduct the toes.
All muscles are innervated by the S2 and S3 nerve roots.