Comprehensive Study Notes: Anatomy and Kinematics of the Ankle and Foot

Institutional Context and University Information

• Institution: Brenau University.

• College: College of Health Sciences.

• Department: Department of Physical Therapy.

• Historical Foundation: Established in 1878.

• Subject Matter: The Ankle/Foot: Anatomy Review.

Primary Functions and Purposes of Ankle/Foot Joints

• Support and Absorption:

  • Supports total body weight.

  • Acts in shock absorption.

  • Adapts to various ground structures and forces.

• Stability:

  • Provides a base of support.

  • Acts as a rigid lever for propulsion.

• Mobility:

  • Facilitates locomotion.

  • Facilitates torque conversion.

Gross Anatomy of the Leg: Tibia and Fibula

• Tibial Torsion: A natural rotation present in the tibia bone.

• Fibula Presentation: The lateral malleolus of the fibula is situated more distal and posterior compared to the tibia.

• Ankle Mortise: Formed by the union of the fibula (lateral malleolus) and the tibia (medial malleolus).

• Interosseous Membrane: Connective tissue spanning between the tibia and fibula.

Muscular Anatomy and Neural Innervation

Posterior Compartment (Tibial Nerve)

• Gastrocnemius: Medial and lateral heads; Innervated by levels $L5, S1, S2$.

• Soleus: Innervated by levels $S1, S2$.

• Tibialis Posterior: Innervated by levels $L4, L5, S1$.

• Flexor Digitorum Longus: Innervated by levels $L5, S1, S2$.

• Flexor Hallucis Longus: Innervated by levels $S2, S3$.

• Plantaris: Located in the posterior compartment.

Lateral Compartment (Superficial Fibular Nerve)

• Fibularis (Peroneus) Longus: Innervated by levels $L5-S1$. Tendon travels through the groove on the inferior aspect of the cuboid to attach to the medial cuneiform and metatarsal I.

• Fibularis (Peroneus) Brevis: Innervated by levels $L5-S1$. Attaches to the fibular trochlea of the calcaneus bone.

Anterior Compartment (Deep Fibular Nerve)

• Tibialis Anterior: Innervated by levels $L4-L5$. Originates from the subcutaneous surface of the tibia.

• Extensor Digitorum Longus: Innervated by levels $L5, S1$.

• Extensor Hallucis Longus: Innervated by levels $L5, S1$.

• Peroneus Tertius (Fibularis Tertius): Part of the anterior group.

Plantar Foot Musculature (Superficial to Deep Layers)

• Layer 1:

  • Abductor Hallucis.

  • Flexor Digitorum Brevis.

  • Abductor Digiti Minimi.

• Layer 2:

  • Quadratus Plantae (also known as Flexor Digitorum Accessorius).

  • Lumbricals 2-5 (quantity of 4).

• Layer 3:

  • Flexor Hallucis Brevis.

  • Adductor Hallucis.

  • Flexor Digiti Minimi Brevis.

  • Opponens Digiti Minimi (noted in some texts).

• Layer 4:

  • Dorsal Interossei (quantity of 4).

  • Plantar Interossei (quantity of 3).

Skeleton and Joint Classification of the Foot/Ankle

• Bone Count: 26 bones total (excluding the Tibia and Fibula).

  • Foot consists of 7 tarsal bones and 5 metatarsals (MT).

  • Phalanges.

• Joint Components: 25 distinct joint components.

• Major Joints:

  • Distal Tibiofibular Joint.

  • Ankle (Talo-crural) Joint: Classified as a hinge joint.

  • Sub-talar (Talocalcaneal) Joint.

  • Transverse Tarsal (Mid-Tarsal) Joint: Includes the Talocalcanealnavicular, Calcanealcuboid, and Talonavicular articulations.

  • Metatarsal Phalangeal (MTP) Joint.

  • Interphalangeal Joints.

• Arches:

  • Medial Longitudinal.

  • Lateral Longitudinal.

  • Transverse Arch.

• Foot Divisions: Forefoot, Midfoot, and Hindfoot.

Specialized Joint Anatomy

Superior Tibio-Fibular Joint

• Type: Planar/Synovial joint.

• Structure: Contains a fibrous capsule.

• Function: Operates in relation to the ankle joint.

Distal Tibio-Fibular Joint

• Type: Fibrous joint (syndesmosis).

• Structure: Contains a large lateral talar facet which allows for increased translation.

• Ligaments: Anterior and posterior tibiofibular ligaments, and the interosseous ligament.

Talo-Crural (Ankle) Joint

• Morphology: The articular surface is narrow posteriorly and wide anteriorly.

Ligamentous Anatomy of the Ankle

Medial Ligaments (Deltoid Ligament)

• The Deltoid ligament is exceptionally strong. It consists of:

  • Tibionavicular ligament.

  • Tibiocalcaneal ligament.

  • Posterior Tibiotalar ligament.

  • Anterior Tibiotalar ligament.

• Purpose: Prevents eversion and excessive abduction.

Lateral Ligaments

• Anterior Talo-Fibular (ATF): Most frequently injured.

• Posterior Talo-Fibular (PTF).

• Calcaneofibular.

• Purpose: Prevents inversion and excessive adduction.

Compartments and Tarsal Tunnel

• Tarsal Tunnel Contents:

  • Tendon of Tibialis Posterior.

  • Tendon of Flexor Digitorum Longus.

  • Posterior Tibial Artery (Pulse located midway between the heel and medial malleolus).

  • Tibial Nerve.

  • Tendon of Flexor Hallucis Longus.

  • Structure: Bound by the Flexor Retinaculum.

• Anterior Compartment Retinacula:

  • Superior extensor retinaculum.

  • Inferior extensor retinaculum.

• Lateral Compartment Retinacula:

  • Superior fibular retinaculum.

  • Inferior fibular retinaculum (located at the fibular trochlea on the calcaneus).

Osteokinematics: Talo-Crural (Ankle) Joint

While described as moving in a single sagittal plane, motion is actually Tri-planar (occurring in all 3 cardinal planes):

• Sagittal Plane: Dorsiflexion and Plantarflexion.

• Frontal Plane: Eversion and Inversion.

• Transverse Plane: Abduction and Adduction (rotation).

Movement Ranges and Axis

• Dorsiflexion: $0-20^{\circ}$. Coupled with Eversion/Abduction.

• Plantarflexion: $0-50^{\circ}$. Coupled with Inversion/Adduction.

• Inversion: $0-30^{\circ}$.

• Eversion: $0-20^{\circ}$.

• Closed Packed Position: Maximum Dorsiflexion (due to the wider anterior talus).

Arthrokinematics

Tibiofibular Joints

• Superior Tibio-fibular Joint:

  • Dorsiflexion: Superior/Posterior glide of fibula on tibia.

  • Plantarflexion: Inferior/Anterior glide of fibula on tibia.

• Distal Tibio-fibular Joint:

  • Dorsiflexion: Superior/Anterior glide; Mortise widens/separates due to the wide anterior talus.

  • Plantarflexion: Inferior/Posterior glide.

Talo-Crural Joint (Ankle)

• Open Chain (Convex Talus on Concave Tibia):

  • Rule: Rolls in the same direction of the moment arm; glides in the opposite direction.

  • Dorsiflexion: Talus rolls anteriorly and glides posteriorly.

  • Plantarflexion: Talus rolls posteriorly and glides anteriorly.

• Closed Chain (Concave Tibia on Convex Talus):

  • Rule: Glides and rolls in the same direction of the moment arm.

  • Dorsiflexion: Tibia rolls and glides anteriorly.

  • Plantarflexion: Tibia rolls and glides posteriorly.

Sub-Talar Joint Mechanics

Definitions

• Supination: A composite motion involving Inversion, Adduction, and Plantarflexion.

• Pronation: A composite motion involving Eversion, Abduction, and Dorsiflexion.

• Clinical Distinction: Inversion/Eversion are used for open chain motion; Supination/Pronation describe the observed closed chain position.

  • Calcaneal Varus: Associated with Supinated position.

  • Calcaneal Valgus: Associated with Pronated position.

Osteokinematics

• Open Chain: Calcaneus moving on Talus.

  • Sub-talar Inversion range: $0-20^{\circ}$.

  • Sub-talar Eversion range: $0-10^{\circ}$.

• Closed Chain: Talus moving on a stable calcaneus (Newton’s 3rd Law).

  • Supination (Heel Strike): Calcaneal inversion + Talar abduction and dorsiflexion. Result: "Lock home" at the knee, lateral tibial rotation, raising of the arch (rigid lever).

  • Pronation (Mid-stance): Calcaneal eversion + Talar adduction and plantarflexion. Result: Lowering of the arch (flexible lever), medial rotation of the tibia (preparing for knee flexion).

Arthrokinematics (Open Chain)

• Convex Calcaneus on Concave Talus.

• Inversion: Posterior facet rolls medially and glides laterally; Anterior/middle facet glides medially.

• Eversion: Posterior facet rolls laterally and glides medially; Anterior/middle facet glides laterally.

Mid-Tarsal and Forefoot Joints

Mid-Tarsal Joints

• Acts as a link between hindfoot and forefoot. Allows forefoot to stay on the ground regardless of hindfoot position.

• Talonavicular Joint: Convex talus to concave navicular. Shared capsule with subtalar joint. Supported by the Spring Ligament (Plantar Calcaneonavicular).

• Calcaneocuboid Joint: Separate capsule, saddle-shaped. Supported by Bifurcate/Dorsal Calcneocuboid, Short Plantar, and Long Plantar ligaments.

• Osteokinematics: Forefoot Moving on Hindfoot.

  • Inversion (Supination): Navicular glides lateral and dorsal; Cuboid glides medial and plantar.

  • Eversion (Pronation): Navicular glides medial and plantar; Cuboid glides lateral and dorsal.

Tarsometatarsal (TMT) Joints

• 1st MT: Most mobile.

• 2nd MT: Most stable (articulating with three cuneiforms).

• 5th MT: Most mobile (> 1st).

• Supination Twist: Inversion rotation to compensate for hindfoot pronation ($1st/2nd$ ray DF; $4th/5th$ ray PF).

• Pronation Twist: Eversion rotation to compensate for hindfoot supination ($1st/2nd$ ray PF; $4th/5th$ ray DF).

Metatarsophalangeal (MTP) Joints

• 1st MTP: Unique for having 2 sesamoid bones on the plantar surface.

• Function: Extension mobility is critical for terminal stance and stabilization during push-off.

Arch Support and the Windlass Mechanism

• Medial Longitudinal Arch Bones: Calcaneus, Talus, Navicular, 1st MT.

• Passive Supports: Plantar fascia, Plantar ligaments, Spring ligament.

• Dynamic Support (Windlass Mechanism): Present with digit extension. Effectively increases the arch height.

• Muscular Contributors:

  • Tibialis Posterior (Primary contribution).

  • Peroneus Longus (Primary contribution).

  • Flexor Digitorum Longus.

  • Flexor Hallucis Longus.

  • Intrinsics (primarily for stabilization during propulsion).

Sensory Distribution

• Saphenous Nerve: Medial leg and foot.

• Sural Nerve: Lateral foot.

• Superficial Fibular Nerve: Dorsum of foot (except 1st webspace).

• Deep Fibular Nerve: 1st interdigital space (webspace between 1st and 2nd MT).

• Medial Plantar Nerve: Medial sole.

• Lateral Plantar Nerve: Lateral sole.

• Tibial Nerve: Heel area.

Questions & Discussion (Reflection Points)

• Question: Describe a mechanism of injury that would injure the lateral ligaments?

  • Response Context: Inversion ankle sprains, often involving plantarflexion (injury to ATF).

• Question: Describe the function of the tarsal tunnel structures? Based on these medial structures, name two pathologies that may occur and describe why/how.

  • Pathology examples: Tarsal Tunnel Syndrome (compression of the tibial nerve); Tibialis Posterior Tendinopathy.

• Question: What % of body weight do you think is distributed over the 1st MTP joint during gait?

• Question: Your patient is having paresthesia between the 1st/2nd distal MT area that occurs consistently into mile 3 of their run. They also describe a deep aching sensation in the anterior leg. What would be your first concern?

  • Differential Diagnosis: Deep Fibular Nerve entrapment or Anterior Compartment Syndrome.

• Question: What happens to the arch if a patient has limited DF or tightness in the calf muscle (Gastrocnemius Passive Insufficiency)?

  • Response Context: Compares to the inability of the muscle to lengthen over multiple joints, potentially leading to compensatory arch collapse (pronation) to gain required ROM for gait.