Foot & Ankle Biomechanics

Author: Mark Karadsheh

Topic updated on 03/13/13 11:46am

Ankle Biomechanics

Ankle joint
- consists of
  - tibial plafond
  - medial malleolus
  - lateral malleolus
  - talus
- motion
  - main motion
    - plantar flexion
    - dorsiflexion
  - secondary motions
    - inversion/eversion
    - rotation
Distal tibiofibular joint
- consists of
  - distal fibula
  - incisura fibularis
    - concave surface of distal lateral tibia
- motion
  - fibular rotates within incisura during gait
  - mortise widens when ankle goes from plantar to dorsiflexion
  - syndesmosis screws limit external rotation
Joint reaction force
- ankle joint
  - 5 times body weight with walking on level surfaces

Hindfoot Biomechanics

Subtalar joint
- consists of articulation between
  - talus
  - calcaneus
- motion
  - inversion/eversion
  - plays no role in plantar and dorsiflexion
Transverse tarsal joint (Chopart joint)
- consists of
  - talonavicular articulation
  - calcaneocuboid articulation
- motion
  - inversion of subtalar joint locks the transverse tarsal joint
    - allows for a stable hindfoot/midfoot for toe-off
  - eversion of subtalar joint unlocks the transverse tarsal joint
    - allows for supple foot to accommodate ground just after heel strike
  - plantar aponeurosis is primary structure of load/force transfer between hindfoot and forefoot during stance

Midfoot Biomechanics

Consists of
- intercuneiform joints
- naviculocuneiform joint
- tarsalmetatarsal joints (lisfranc joints)
  - divided into three columns
    - medial column
      - first metatarsal
      - medial cuneiform
      - navicular
    - middle column
      - second and third metatarsals
      - middle cuneiform
      - lateral cuneiform
    - lateral column
      - forth and fifth metatarsals
      - cuboid
Motion
- lateral column is the most mobile
  - allows for flexibility when walking on uneven ground
- middle column is the least mobile
  - allows for rigidity during push-off
- medial column carries most of load while standing

Forefoot Biomechanics

Consists of
- metarsalphalangeal joints
- proximal interphalangeal joints
- distal interphalangeal joints
Joint reaction forces
- second metatarsal experiences more stress during gait
  - most commonly metatarsal to have a stress fracture

The Gait Cycle

Overview
- one gait cycle is measured from heel-strike to heel-strike
- consists of
  - stance phase
    - period of time that the foot is on the ground
    - ~60% of one gait cycle is spent in stance
  - swing phase
    - period of time that the foot is off the ground moving forward
    - ~40% of one gait cycle is spent in swing
Phases of the gait cycle
- stance phase ("I Like My Tea Presweetened")
  - initial contact
    - definition
      - occurs when foot contacts the ground
    - muscular contractions
      - hip extensors contract
  - loading response (initial double limb support)
    - definition
      - occurs after initial contact until elevation of opposite limb
    - muscular contractions
      - ankle dorsiflexors (tibialis anterior) contract eccentrically to control plantar flexion moment
      - quads contracts to stabilize knee and counteract the flexion moment (about the knee)
  - mid-stance (single limb support)
    - definition
      - from elevation of opposite limb until both ankles are aligned in coronal plane
    - muscular contractions
      - hip extensors and quads undergo concentric contraction
  - terminal stance (single limb support)
    - definition
      - from when ankles are aligned to until the opposite to when heel strikes in contralateral limb
    - muscular contractions
      - toe flexors contract
  - pre-swing (second double limb support)
    - definition
      - from initial contact of opposite limb to just prior to elevation of ipsilateral limb
    - muscular contractions
      - hip flexors contract to propel advancing limb
- swing phase ("In My Teapot")
  - initial swing (toe off)
    - definition
      - from elevation of limb to point of maximal knee flexion
    - muscular contractions
      - hip flexors contract
  - mid-swing (foot clearance)
    - definition
      - following knee flexion to point where tibia is vertical
    - muscular contractions
      - ankle dorsiflexors contract to ensure foot clearance
  - terminal swing (tibia vertical)
    - definition
      - from point where tibia is vertical to just prior to initial contact
    - muscular contractions
      - hamstring muscles decelerate forward motion of thigh
Center of gravity (COG)
- 5cm anterior to S2 vertebral body
- displaced 5cm horizontally and 5cm vertically during adult male step
Determinants of gait
- pelvic rotation
  - pelvis rotates 4 degrees medially (anteriorly) on swing side
    - lengthens the limb as it prepares to accept weight
- pelvic tilt
  - pelvis drops 4 degrees on swing side
    - lowers COG at midstance
- knee flexion in stance
  - early knee flexion (15 degrees) at heel strike
    - lowers COG, decreasing energy expenditure
    - also absorbs shock of heel strike
- foot mechanisms
  - ankle plantar flexion at heel strike and first part of stance
- knee mechanisms
  - at midstance, the knee extends as the ankle plantar flexes and foot supinates
  - restores leg to original length
  - reduces fall of pelvis at opposite heel strike
- lateral displacement of pelvis
  - pelvis shifts over stance limb
    - COG must lie over base of support (stance limb)

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Qbank (6 Questions)

TAG

(OBQ10.123) Which of the following descriptions of muscle activity during normal gait is correct? Topic

Review Topic

1. Gastrocnemius-soleus contracts eccentrically during heel strike
2. Gastrocnemius-soleus contracts concentrically during heel strike
3. Gastrocnemius-soleus contracts concentrically during swing phase
4. Tibialis anterior contracts concentrically during toe-off
5. Tibialis anterior contracts eccentrically after heel strike

PREFERRED RESPONSE ▶

DISCUSSION: One stride (heel strike to heel strike of one leg) of normal gait has been divided into the stance (62%) and swing (38%) phases. The stance phase is further divided into heel strike, foot flat, and toe off. Proper gait requires coordinated contraction of the leg muscles. The tibialis anterior (TA) muscle fires eccentrically at heel strike to lower the foot to the ground, while the gasto-soleus (GS) complex is dormant. The TA then relaxes, while the GS eccentrically contracts as the body’s weight is transferred forward over the foot during foot-flat. As the foot propels the body forward during toe-off, the GS contracts concentrically, while the TA remains dormant. As swing commences, the TA then fires concentrically producing dorsiflexion to clear the foot over the ground while the GS relaxes. Certain conditions like cerebral palsy result in improper firing of the muscles during the gait cycle, resulting in altered gait mechanics.

REFERENCES:

1. Mann RA, Haskell A. Biomechanics of the foot and ankle. In: Coughlin MJ, Mann RA, Saltzman CL, eds. Surgery of the Foot and Ankle, 8th ed. Philadelphia, PA: Mosby Elsevier; 2007:4-8.

2. Perry J. Gait Analysis: Normal and Pathological Function. Thorofare, NJ: Ankle Foot Complex; 1992:52-87.

Question Authors:

Aaron Bott MD, Ben Taylor MD,

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(OBQ07.58) Which of the following does NOT occur during the normal push-off stance of the gait cycle? Topic

Review Topic

1. subtalar joint inversion
2. transverse tarsal joint locks
3. external rotation of the lower extremity
4. tightening of the plantar fascia
5. loosening of the spring ligament

PREFERRED RESPONSE ▶

DISCUSSION: During the normal gait cycle, the foot changes from a flexible structure at heel strike to a rigid structure at toe-off. The mechanisms that bring about this conversion are (1) tightening of the plantar aponeurosis, (2) progressive external rotation of the lower extremity, which begins at the pelvis and is passed distally across the ankle joint to the subtalar joint, and (3) stabilization of the transverse tarsal joint which results from progressive inversion of the subtalar joint. Van Boerum and Sangeorzan cite triceps surae insufficiency, obesity, posterior tibial tendon dysfunction, or ligamentous laxity in the spring ligament or other ligaments as possible causes for flatfoot.

REFERENCES:

1. Mann RA: Biomechanics of the foot and ankle, on Coughlin MJ, Mann RA (eds): Surgery of the Foot and Ankle, ed 7. St Louis, MO, Mosby, 1999, pp 2 – 35

2. Van Boerum DH, Sangeorzan BJ: Biomechanics and pathophysiology of flat foot. Foot Ankle Clin 2003;8:419 – 430 PMID:14560896 (Link to Abstract)

Question Authors:

Greg Galano MD, Patrick McCulloch MD,

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(OBQ06.6) Which of the following structures is the primary site of force transfer between the hindfoot and forefoot during the stance phase of gait? Topic

Review Topic

1. Plantar aponeurosis
2. Achilles tendon
3. Lisfranc ligament
4. Posterior tibial tendon
5. Anterior tibial tendon

PREFERRED RESPONSE ▶

DISCUSSION: During ambulation, the transverse tarsal joints are parallel during the heel strike phase of stance, when the calcaneus is in eversion, allowing the midfoot to be supple for shock absorption of the body's weight. During the push-off phase of stance the subtalar joint moves to inversion, which makes the foot rigid so that it can create a rigid lever arm for propulsion. The referenced study by Erdemir et al found that plantar aponeurosis forces gradually increased during stance and peaked in late stance, with maximum tension reaching 96% of total body weight. The authors concluded the plantar aponeurosis transmits large forces between the hindfoot and forefoot during the stance phase of gait.

REFERENCES:

1. Erdemir A, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA. Dynamic loading of the plantar aponeurosis in walking. J Bone Joint Surg Am. 2004 Mar;86-A(3):546-52. PMID:14996881 (Link to Abstract)

Question Authors:

Ben Taylor MD,

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(OBQ06.222) The primary antagonist of the anterior tibial tendon is innervated by which of the following nerves? Topic

Review Topic

1. Superficial peroneal nerve
2. Deep peroneal nerve
3. Tibial nerve
4. Posterior tibial nerve
5. Sural nerve

PREFERRED RESPONSE ▶

DISCUSSION: The primary antagonist of the anterior tibial tendon is the peroneus longus, which is innervated by the superficial peroneal nerve. The peroneus longus (PL) and tibialis anterior (TA) are antagonists to each other as the PL plantarflexes and everts, while the TA dorsiflexes and inverts the foot. The cited cadaveric study by Silver found that the plantarflexors of the ankle were six times as strong as the dorsiflexors.

REFERENCES:

1. Silver RL, de la Garza J, Rang M. The myth of muscle balance. A study of relative strengths and excursions of normal muscles about the foot and ankle. JBone Joint Surg Br. 1985 May;67(3):432-7. PMID:3997956 (Link to Abstract)

Question Authors:

Ben Taylor MD,

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Videos

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Groups

ABOS II: Foot & Ankle Biomechanics

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Evidence & References Show References

Level of Evidence 5 and Other Journal Articles (includes Case Reports, Expert Opinions, Personal Observations, and Biomechanic Studies)

Erdemir A, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA. Dynamic loading of the plantar aponeurosis in walking. J Bone Joint Surg Am. 2004 Mar;86-A(3):546-52. PMID:14996881 (Link to Abstract)

Textbooks

Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
AAOS Comprehensive Orthopaedic Review, Jay R. Leiberman. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2009
Orthopaedic Knowledge Update 10, John M Flyn. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2011
Hoppenfeld SP. Surgical Exposures in Orthopaedics: The Anatomic Approach. Lipponcott, Williams, and Wilkins, Philadelphia, PA, Copyright 2009
Orthopaedic In-training Examination (OITE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
Self-Assessment Examination (SAE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
Mann RA, Haskell A. Biomechanics of the foot and ankle. In: Coughlin MJ, Mann RA, Saltzman CL, eds. Surgery of the Foot and Ankle, 8th ed. Philadelphia, PA: Mosby Elsevier; 2007:4-8.
Perry J. Gait Analysis: Normal and Pathological Function. Thorofare, NJ: Ankle Foot Complex; 1992:52-87.

Undefined

Mann RA: Biomechanics of the foot and ankle, on Coughlin MJ, Mann RA (eds): Surgery of the Foot and Ankle, ed 7. St Louis, MO, Mosby, 1999, pp 2 – 35
Van Boerum DH, Sangeorzan BJ: Biomechanics and pathophysiology of flat foot. Foot Ankle Clin 2003;8:419 – 430 PMID:14560896 (Link to Abstract)
Silver RL, de la Garza J, Rang M. The myth of muscle balance. A study of relative strengths and excursions of normal muscles about the foot and ankle. JBone Joint Surg Br. 1985 May;67(3):432-7. PMID:3997956 (Link to Abstract)

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Foot & Ankle Biomechanics

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