Ankle and Foot: An Integrated Complex

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As an integrated complex, the ankle and foot function as a dynamic interface between the leg and the ground. This interface exhibits remarkable adaptability, being flexible enough to conform to irregular surfaces and absorb repetitive loads, while also being rigid and stable enough to support muscular propulsion and weight-bearing during walking and running.

Anatomical and Functional Organization

With 28 muscles acting across 32 joints or joint complexes, the ankle and foot regulate movement and posture. Based on anatomical configuration, they are divided into three regions:

  1. Hindfoot (posterior foot)
  2. Midfoot (middle foot)
  3. Forefoot (anterior foot)

Although movements can occur independently within each region, this is not common, particularly during the stance phase of walking. Most movements within these regions tend to augment or regulate movements initiated in other areas of the foot and leg, in response to muscular forces and ground reaction forces (GRF).

Dynamic Movements During the Stance Phase of Walking

The best way to summarize the kinematics of the ankle and foot is by describing key phases of the stance phase in walking, which begins with heel contact:

1. Initial Contact & Load Acceptance Phase

  • The ankle rapidly plantarflexes while the hindfoot everts (pronates).
  • During this load acceptance phase, dorsiflexors and supinators (invertors) contract eccentrically to absorb impact and control movement dynamics.
  • Simultaneously, the medial longitudinal arch (MLA) lowers gradually in response to weight-bearing.
  • Several structural components slow down this arch descent, including:
    • Spring ligament
    • Talonavicular joint capsule
    • Plantar fascia
    • Muscles such as tibialis posterior

These structures absorb energy, preventing excessive stress on the foot.

Clinical Considerations
  • Failure to regulate the magnitude and speed of hindfoot eversion and arch lowering can result in localized tissue overload, leading to pain and structural stress.
  • Treatments include:
    • Orthotics, specialized footwear, taping, activity modification, and muscle training (stretching, strengthening, and neuromuscular re-education).

2. Mid-Stance to Terminal Stance Phase

  • The previously internally rotated leg now rapidly transitions to external rotation.
  • The hindfoot shifts from eversion (pronation) to inversion (supination).
  • The gradual elevation of the medial longitudinal arch increases foot rigidity.
  • This increased rigidity enhances stability in both transverse and longitudinal axes, which is critical for push-off.
  • Tibialis posterior and intrinsic foot muscles contract concentrically to raise the arch and prepare the foot for propulsion.

3. Pre-Swing & Push-Off Phase

  • Just before toe-off, the heel rises, shifting body weight forward onto the metatarsal heads.
  • The windlass effect at the metatarsophalangeal (MTP) joints, combined with intrinsic and extrinsic muscle activation, ensures stability for forward propulsion.

Pathomechanics of the Ankle and Foot

Dysfunctions in the ankle and foot can arise from:

  1. Connective tissue injuries
  2. Muscular imbalances
  3. Peripheral nerve impairments
  4. Central nervous system pathologies
  5. Mechanical trauma

Due to their direct exposure to mechanical forces, the ankle and foot are particularly prone to injuries.

Acute Injuries

  • Inversion sprains
  • Avulsion fractures of the 5th metatarsal tuberosity
  • Hyperextension injuries of the hallux (turf toe)

Chronic Injuries

  • Plantar fasciitis
  • Peroneal tendon subluxation over the fibula
  • Posterior tibial tendon dysfunction
  • Heel spurs
  • Metatarsalgia

Microtrauma & Malalignment

  • Abnormal alignment can cause excessive biomechanical compensation, leading to muscular fatigue and connective tissue stress.
  • Frequent overuse results in inflammatory responses and pain.

Clinical Relevance: The Importance of Understanding Ankle & Foot Kinematics

  • A deep understanding of the foot’s anatomy and biomechanics is crucial for diagnosing pathomechanics.
  • Clinicians must assess muscle-joint interactions both in non-weight-bearing and weight-bearing conditions.
  • The interdependence between the ankle, foot, and proximal lower limb segments should also be carefully evaluated to optimize treatment strategies.