Pathomechanics of the Foot

Question 1

Abnormal Motion of the foot

Answer 1

Abnormal Pronation

Abnormal Supination

Restricted motion (1 or more joints ROM inadequate for normal locomotion, maybe caused by destructive joint disease, trauma, muscle spasm or contracture, congenital coalitions of bone)

Question 2

Abnormal Pronation of the foot

Answer 2

a) to compensate for an osseus abnormality within the foot
b) to compensate for osseus or soft tissue abnormality extrinsic to the foot
c) in response to forces which load the medial side of the foot prematurely
d) as a result of muscle imbalance caused by neuromuscular disorders
e) as a result of tonic muscle spasm initiated by pain in the articular or periarticular tissue

Question 3

Osseus abnormality within the foot - abnormal compensatory pronation

Answer 3

most common cause of pathology within the foot

Question 4

Deformities of the foot which are compensated by abnormal pronation of the foot

Answer 4

i) forefoot varus
ii) rearfoot varus
iii) forefoot valgus
iv) lateral postural instability during propulsion by a plantarflexed 1st ray
v) plantarflexed 5th ray

Question 5

Forefoot varus

Answer 5

Very common cause of abnormal compensatory pronation

Forefoot is inverted positon relativ eot hindfoot

Pronation through STJ allows forefoot to evert until medial side touches the ground

Foot remains in pronated position during early propulsion making it very unstable and prone to trauma

Question 6

Forefoot valgus

Answer 6

Opposite of forefoot varus

Forefoot is everted relative to hindfoot

Everted position causes less pronation to occur during midstance

At heel lift, forefoot deflects to lateral side of causing lateral instability

To avoid inversion sprain, pronation occurs at the STJ to compensate

Pronation occurring during propulsive phase makes foot unstable and vulnerable to trauma

Common in pes cavus type foot

Question 7

Plantarflexed first ray

Answer 7

Presents and acts like a forefoot valgus

Question 8

Rearfoot varus

Answer 8

Heel inverted relative to lower 1/3 of leg when subtalar joint is in neutral position

Normally entire foot will present inverted as foot follows the heel into inversion

Pronation must occur early in stance to bring medial side of the heel and forefoot to the ground

Foot is more pronated earlier in stance

Question 9

Tibial Varum (Bow legs), how it affects the foot

Answer 9

Foot is inverted and adducted as it bears weight

Necessitating pronation fo hindfoot to bring forefoot foot to the horizontal

Compensatory pronation may leave the foot hypermobile and structurally unstable during propulsion

Question 10

Internal tibial and internal femoral torsion

Answer 10

Foot tries to avoid “pidgeon toed” alignment by abducting the foot on the leg

Accomplished by subtalar joint pronation (Abduction is component of pronation)

Question 11

Gastrocnemius shortening

Answer 11

Shortened Achilles tendon resists dorsiflexion at the ankle

As tibia moves over foot, castroc resists dorsiflexion, GRF pronates STJ and midtarsal joints to produce dorsiflexion component of pronation in these 2 joints

This is how tight heel cord is implicated in plantarfasciitis

Question 12

Factors prematurely load the medial side of the foot

Answer 12

1. extreme obesity
2. external femoral torsion or external tibial torsion
3. Rearfoot valgus

Question 13

External femoral torsion/External tibial tortion

Answer 13

foot more externally rotated than normal

Forward progression of body weight causes forces to be prematurely supported by medial heel and of the foot

Alignment causes eversion of the heel, pronates the foot excessively

Question 14

Rearfoot valgus

Answer 14

Heel everted relative to lower leg when subtalar joint is in neutral

Heel already in everted position, foot predisposed to excessive pronation

Question 15

Muscle Imbalance caused by neuromuscular disorders

Answer 15

Good example of this spastic peroneus brevis, very strong pronator of STJ, when in spasm, overpowers tib post, foot pronates abnormally at STJ

Question 16

Tonic Muscle Spasm

Answer 16

Trauma and inflammatory disease (RA), can stimulate pain receptors producing tonic muscle spasm, which splint the joint thus preventing unwanted motion

Question 17

Forefoot deformity caused by abnormal STJ pronation

Answer 17

If foot is in pronated position during propulsive period in stance, entire foot becomes hypermobile

Most distal osseus segments become most unstable

Pathological subluxations develope at metatrsus and phalanges

Hallux abductovalgus
Hallus limitus
Hallus rigidus
Splayfoot
Tailor's bunion ( 5th MTP joint)

Question 18

!st MTP Joint Deformities

Answer 18

Abnormal STJ pronation causes subluxation of the 1st MTP joint

Transverse plane - Hallux Abductovalgus

Sagittal plane - Hallux Limitus/Rigidus

May also be caused by RA, gout, any degenerative joint disease, trauma

Question 19

Hallux Abductovalgus

Answer 19

Abnormal STJ pronation is primary cause of most hallux abductovalgus deformity

Progressive deformity

Hypermobile 1st metatarsal head inverts relative to the hallux

Valgus subluxation of hallux at MTP joint

Base of prox phalanx subluxes laterally on 1st MTP joint

Hallux abducts, presses into 2nd toe

1st ray may also sublux at its base, 1st metatarsal adducts, increasing severity of deformity

Heredity and Shoe fit may also play a role