Biomechanics of the Foot and Ankle

# bones in the foot

28

talo-navicular bulge

?

Foot Orthotic Theories

Balanced Orthotic Theory Podiatric theory developed by Root Capture STN at midstance with molding procedure Purpose of rearfoot and forefoot posts are to control excessive foot pronation Total-Contact Foot Orthotic Theory Incorporates stabilization of the medial and lateral longitudinal arches by providing total plantar contact Foot impression is taken in resting calcaneal stance Goal of orthotic is to reduce abnormal stresses on symptomatic tissues

Foot Posture Index Forefoot Components

Bulging in the region of the talonavicular joint -- positive bulging is common with pronated feet Height and congruence of the medial longitudinal arch -- careful observation of the arch congruence should be the main element with this measure with arch height factored in secondarily -symmetrical rainbow, flat, or high/assymetrical Abduction/adduction of the forefoot on the rearfoot -- too many toes sign

Lateral column

Calcaneus, cuboid, MT 4&5 + phalanges supinators load this column

Why do foot orthoses work?

Change lower limb kinematics -pronation Assist with shock attenuation -lateral column overload Augment lower limb neuromotor control -newer theory

Guiding Principles with Orthotic Prescriptions

Correct deformity by no more than 50% (i.e. LLD ½ inch is corrected with no more than ¼ inch lift on short side) Prioritize correction of malalignments at the rear foot first -where gait sequence starts Be conservative initially as small changes often work well Increase wear time gradually (1-2 hours on first day with incremental increases)

Subtalar Pronation

During subtalar pronation in weight bearing, the calcaneus moves into eversion (frontal plane) while the talus moves into abduction (transverse plane) and plantar flexion (sagittal plane). Movements of the midtarsal joints into abduction and eversion result in greater movement of the foot in the sagittal plane. Results in lowering of the medial longitudinal arch as the foot approaches and adapts to the ground. unlocks "bag of bones" to absorb shock

Transverse plane

Forefoot adduction 0°-20° Forefoot abduction 0°-10° Occurs at mid tarsal joint 2:1 add- abd

Frontal plane

Inversion 0°-35° Eversion 0°-20° Occurs at subtler joint - coach of the foot

The Foot Posture Index (FPI-6) procedure

Patient should stand in their relaxed stance position with double limb support. Instructions: "Stand still, with arms at side and look straight ahead." Assessment should take 2-3 minutes to complete with patient in relaxed standing. Each component of the test is rated between -2 and +2. The final FPI score will be a whole number between -12 and +12. REFERENCE VALUES: Normal = 0 to +5 Pronated = +6 to +12 (large pos #) Supinated = -1 to -12

Common Overpronation Pathologies for over pronation

Plantar Fasciitis Heel Pain/Heel Spurs Achilles Tendinopathy Medial Tibial Stress Syndrome (PTT) Patellofemoral Pain Syndrome

Balanced Orthotic Theory

Podiatric theory developed by Root Capture STN at midstance with molding procedure Purpose of rearfoot and forefoot posts are to control excessive foot pronation

Types of Foot Orthoses

Soft Semi-rigid Rigid

Low Arch (Pes Planus)

The functional consequence of a flat foot is midfoot instability due to loss of the rigid lever. -esp spring ligament (could rupture) Plantarflexion of the talus occurs resulting in subluxation of the posterior facet of the subtalar joint. Loads the plantar calcaneonavicular ligament, which eventually may rupture.

Rearfoot

calcaneus, talus

The Foot Posture Index (FPI-6)

A diagnostic tool aimed at quantifying the degree to which a foot can be considered to be in a pronated, supinated, or neutral position. Intended to be a simple assessment tool for scoring and determining overall foot posture. FPI-6 has been subjected to a rigorous validation process and found to be a reliable clinical tool that measures foot posture in multiple planes and anatomical segments. 3 mid foot, 3 forefoot

Standing Assessment

Assess arch height -done w/ FPI Find subtalar neutral -hold that position -relax and observe foot height Observe rearfoot and forefoot position -if 1st ray is off ground, not ability to adapt Relax and observe change in arch height and foot Palpate bony landmarks for leg length discrepancy -from hip all the way down the chain

Sagittal plane

Dorsiflexion 0°-20° Plantarflexion 0°-50° Occurs at talocrual joint 2:1 ratio

Gait Assessment Tips

Expose the area distal to the calf and have the patient walk barefoot Look at only one leg at a time Focus on what is happening at heel strike, midstance, and push off -away - mid foot -toward - forefoot Encourage patient to walk at a normal cadence -can see more when it's faster

Midtarsal Joint

Functions as the "star player" of the foot. Responsible for the transformation mechanism from flexible base to rigid lever during gait. When the talonavicular and calcaneocuboid joint axes are parallel (subtalar joint is pronated or neutral), the foot is flexible. -arrows lined up on medicine bottle, unlocked When the midtarsal joint axes are not parallel (subtalar joint is supinated), the foot is rigid.

The Father of Function

Gary Gray "The magic of the foot is its ability to quickly transform from mobile adaptor to stabile propeller."

Supine Assessment

Great toe extension mobility (PROM) -min 60 deg for push-off, 80-90 better -deficiency passes to mid foot First ray mobility (flexible, semi-flexible, or rigid) -flexible - moves up & down well relative to 2nd semi-flexible - moves up OR down well relative to 2nd (PFs) rigid - moves NEITHER up NOR down well relative to 2nd Midtarsal joint mobility Subtalar neutral and relative arch height in NWB -most roll out, tendency to pronation Leg length assessment -bridge 1st -1 cm Clin Sig (3/8") -beware of scoliosis Active and passive ankle mobility Gastrocnemius and hamstring flexibility Special tests -ant drawer -varus/valgus -squeeze ant tib/fib lig

Total-Contact Foot Orthotic Theory

Incorporates stabilization of the medial and lateral longitudinal arches by providing total plantar contact Foot impression is taken in resting calcaneal stance Goal of orthotic is to reduce abnormal stresses on symptomatic tissues -diabetics use this -not trying to put in subtalar neutral

Gait Analysis

Initial Contact (heel strike to foot flat) ➔ supination Midstance (foot flat to heel rise) ➔ roll into pronation -midtarsal jt unlocked Push off (heel rise to toe off) ➔ back toward supination

Specific Shoe Features

Last - straight, semi-curved, curved -relationship of mid foot to forefoot Heel counter - firm, deep, normal -if you pinch and it collapses, no ctl -pronators need a lot of ctl Fasteners - lacing styles -metatarsalgia - skip 1st couple of eyelets -can lace up higher for pronators Forefoot width and depth -narrow heel w/ wide toe box would be ideal

High Arch (Pes Cavus)

Less common and less well understood than pes planus. High arch foot posture may include inverted hindfoot, inverted midfoot, and adducted forefoot. The "peek a boo" sign is an indication of an inverted subtalar joint. -can see calcaneus from the front

Common Pathologies Associated with Supinated Feet

Metatarsalgia Lateral Ankle Instability Plantar Fasciitis Stress Fractures

Subtalar Supination

Occurs from the start of midstance phase of gait (foot flat) until the end of stance (toe off). In the closed kinetic chain, the calcaneus moves into inversion (frontal plane) while the talus moves into adduction (transverse plane) and dorsiflexion (sagittal plane). Movement of the midtarsal joints into adduction and inversion results in less movement of the foot in the sagittal plane. These movements result in an elevation of the medial longitudinal arch. locks - elevation of medial longitudinal arch

Subjective Examination

Onset Date of most recent onset Mechanism of injury Symptom Behavior Location of symptoms Aggravating and easing factors Previous History Prior history of ankle and foot injury Treatment for prior episodes Patient Goals

Prone Assessment

Ops leg in combat crawl Find subtalar neutral. Measure rearfoot position (degrees of inversion or eversion) relative to the lower extremity (line of tib) Measure the forefoot position (varus or valgus) relative to the rearfoot with foot in subtalar neutral position. -midfoot 2-3 deg of inv normal -forefoot varus/valgus - most pronators have a lot of forefoot varus (8 or more) relative to mid foot in subtalar neutral Subtalar ROM Soleus flexibility Hip IR/ER mobility

Functional Standing Assessment

Perform functional activities: Single leg balance -medial deviation = pronation -poor balance/ankle stability Single leg calf raises -at height calcaneal inv due to post tib tendon Balance reach test -w/ foot - strength/ flexibility/ motor control Squat test -toes forward -forefoot collapse can lead to knee problems, shin splints, consider posting forefoot w/ orthotic

Subtalar Joint

Pronation and supination are triplanar motions in the subtalar joint. In the closed kinetic chain, pronation occurs during the first 25% of the stance phase of gait, as the foot approaches and adapts to the ground. Supination occurs from the start of midstance phase of gait (foot flat) until the end of stance (toe off). Subtalar joint effectively functions like the "coach" of the foot. -positions other its

Soft or Accomodative Orthotics

Provide cushioning, decrease shear forces, and redistribute plantar pressures Materials include plastizote, pelite, and poron Often utilized with diabetic patients and supinators Typically custom molded

Semi-rigid Foot Orthotics

Provide flexibility and control to the malaligned foot Broad category including everything between soft and rigid Can be prefabricated or customized -1/3 the cost

low arch runners

ST injuries knee injuries ?

Foot Posture Index Rearfoot Components

Talar Head Palpation - palpation for talonavicular congruence in relaxed stance position -not subtalar neutral -more on med or lat side Supra and infra lateral malleolar curvature -- observation and comparison of the curves above and below the lateral ankle malleoli -symmetrical or lower curve concave/vex Calcaneal frontal plane position -- inversion or eversion of the calcaneus (angular measurements not required) -too many toes/peek-a-boo

Footwear Selection

Types of running shoes Motion control - pronated foot Stability - neutral foot -70% would do well w/ this Cushion - supinated foot

Rigid Foot Orthotics

Used to control abnormal motion -pes planus Very durable but may be uncomfortable due to rigidity -blisters Examples could include acrylic plastics or carbon fiber mesh composites -turn shoe into "walking boot" -great for turf toe Can be prefabricated or custom fabricated

high arch runners

lateral & bony injuries

Forefoot

metatarsals, phalanges base of 2nd MT is most freq fx in Lisfranc inj

Midfoot

navicular, cuneiforms, and cuboid

Medial column

talus, navicular, cuneiforms, MT 2&3 + phalanges pronators load this column

Low Arch (Pes Planus) - Clinically

this results in severe hindfoot eversion posture. Often associated with the "too many toes sign." - when viewed from behind - forefoot abduction calcareous everted Looking from behind, more toes are seen on the lateral side of the involved foot.