Anatomy of Ankle and Talocrural Joint

Bones of the Ankle

• Sesamoid bones act as pulleys to reduce stress on tendons.
• There are two sesamoid bones in the big toe joint situated within the flexor hallucis brevis tendons.
• The axis of rotation in a joint defines the direction of movement.
• There are three axes of rotation: anterior-posterior, mediolateral, and longitudinal.
• Ankle motion primarily occurs in the sagittal plane, but some movement in the frontal and transverse planes are necessary for complete plantarflexion and dorsiflexion.

Talocrural Joint

• The talocrural joint is formed by the tibia, fibula, and talus.
• Its axis of rotation is oblique to both the sagittal and frontal planes, requiring multi-planar movement.
• Dorsiflexion range typically varies between 0-16.5 degrees or 0-25 degrees, depending on weight-bearing status.
• Plantarflexion range is typically around 0-50 degrees.
• The talus rolls anteriorly and glides posteriorly during dorsiflexion.
• Conversely, the talus rolls posteriorly and glides anteriorly during plantarflexion.

Subtalar Joint

• The subtalar joint is defined as a single degree of freedom hinge with a tri-planar axis.
• Its axis is located about 42 degrees superior to the sagittal plane and about 16-23 degrees medial to the transverse plane.
• Inversion-to-eversion movement ratio is approximately 2:1 or 3:2.
• Pronation involves the coupled motion of dorsiflexion, abduction, and eversion.
• Supination involves the coupled motion of plantarflexion, adduction, and inversion.
• Pronation helps the body absorb forces during walking.

Extrinsic Muscles

• Extensor digitorum brevis is located on the dorsum of the foot.
• Extensor hallucis brevis is located on the dorsum of the foot.

Intrinsic Muscles

• First layer:

  • Abductor hallucis
  • Flexor digitorum brevis
  • Abductor digiti minimi

• Second layer:

  • Quadratus plantae: assists with toe flexion in the sagittal plane.
  • Lumbricals: extend the interphalangeal joint.

• Third layer:

  • Flexor hallucis brevis
  • Adductor hallucis
  • Flexor digiti minimi brevis

• Fourth layer:

  • Plantar interossei
  • Dorsal interossei: assist with MTP joint flexion, IP joint extension, and toe abduction and adduction.

Ligaments of the Ankle Joint

• The ankle joint is stabilized by ligaments.
• The anterior talofibular ligament, calcaneofibular ligament, and posterior talofibular ligament are crucial for ankle stability.

Ankle Instability

• Instability can result from ligament damage.

Plantar Fascia

• It originates at the medial tubercle of the calcaneus and inserts in three locations on the forefoot: medial, central, and lateral.
• The central band, also known as the plantar aponeurosis, is the thickest and most frequently involved in plantar fasciitis.
• It helps raise and stabilize the arch during gait via the windlass mechanism.

Plantar Fasciitis

• It's a degenerative process affecting the plantar fascia, characterized by:
  • Insidious onset of heel pain, especially during the first steps after rest.
  • Heel pain that often alleviates with moderate activity but worsens throughout the day or after prolonged standing or walking.
  • Risk factors include age, weight, and specific activities.

Calcaneal Spur

• Calcaneal spurs are bony projections on the calcaneus.
• There are two types: dorsal and plantar spurs.
• Their development might be related to degenerative, inflammatory, traction, repetitive trauma, and bone-formers theories.
• Calcaneal spurs are not the cause of plantar fasciitis, and removing the spur may not always alleviate pain.

Morton's Neuroma

• It's a compression neuropathy affecting the common digital plantar nerve.
• Typically occurs in the third intermetatarsal space (66% of cases).
• It's not a true neuroma, but a benign fibrotic thickening caused by nerve irritation.
• Risk factors include chronic trauma, high arches, tight footwear, nerve ischemia, repetitive impact, intermetatarsal bursitis, and nerve entrapment.

Hallux Valgus

• The great toe deviates laterally away from the midline towards the lesser toes.
• Angles less than 15 degrees are considered normal, while angles of 20 degrees or greater are considered abnormal.
• It causes medial prominence of the first metatarsal head and can lead to inflammation of the overlying bursa and soft tissues.
• Predisposing factors: poorly fitting footwear, age, female gender, family history, pes planus, Achilles tendon contracture, and ligamentous laxity.

Pes Planus

• Flat feet can be caused by genetics, injury, or underlying medical conditions.
• The congenital vertical talus is an example of a genetic factor leading to a rigid flatfoot deformity.

This quiz explores the anatomy and mechanics of the ankle, focusing on the role of sesamoid bones and the talocrural joint. It covers axes of rotation, motion in different planes, and the ranges of dorsiflexion and plantarflexion. Test your knowledge of these essential concepts in lower limb anatomy.