Lower Ox - Foot Biomechanics, UCBL

talocrural joint movements

major → dorsiflexion, plantarflexion

minor → abduction, adduction

clinically insignificant → eversion, inversion

subtalar joint movements

major → eversion, inversion, abduction, adduction

clinically insignificant → dorsiflexion, plantarflexion

midtarsal joint (transverse tarsal or chopart’s joint)

two axes but functionally uniaxial → longitudinal axis + oblique axis

joint only pronates + supinates

midtarsal joint longitudinal axis movements

major → eversion, inversion

clinically insignificant → dorsiflexion, plantarflexion, abduction, adduction

midtarsal joint oblique axis movements

major → dorsiflexion, plantarflexion, abduction, adduction

clinically insignificant → eversion, inversion

closed chain pronation

dorsiflexion at ankle joint

talus adduction + plantarflexion

calcaneal eversion + abduction at subtalar joint

tibia internal rotation

knee flexion

medial cuneiform inversion

navicular eversion

medial longitudinal arch depresses

midtarsal joint axes get more parallel than in STN → foot become more flexible + mobile

function of pronation

unlock the joints of the foot, allowing foot to be a mobile adapter to allow ambulation on uneven surfaces

facilitates shock absorption in the lower extremity by allowing flexion of the knee secondary to internal rotation of the tibia

closed chain supination

plantarflexion at ankle joint

talus abduction + dorsiflexion

calcaneal inversion + adduction at subtalar joint

tibial external rotation

knee extension

medial cuneiform eversion

navicular inversion

medial longitudinal arch elevates

midtarsal joint axes become less parallel than in STN → foot becomes more rigid

function of supination

increase rigidity of foot and provide a rigid lever for push off

subtalar neutral (root’s alignment)

neither down pronated nor up supinated

plantar surface of calcaneus is perfectly parallel to supporting surface

hindfoot is normal when bisection of calcaneus is at 90 degrees to supporting surface

root’s normal alignment occurs just before TSt during gait when STJ is in neutral position and MTJ is fully locked → does not occur while standing in double support relaxed standing

normal foot alignment in STN open chain

hindfoot varus

forefoot varus

normal foot alignment in stance closed chain

calcaneal eversion

tibial varus

foot biomechanics for normal walking

4-6 degrees of STJ pronation necessary to provide adequate shock absorption + accommodation to even ground terrain

foot needs proper arch support at 2nd rocker

foot should have normal plantarflexion of 1st ray at 2nd and 3rd rockers to allow 1st metatarsal head to maintain ground contact while the rest of the foot inverts during propulsion

foot should have greater range of 1st MTP dorsiflexion at 3rd rocker for propulsion

pronation in gait cycle

the supinated foot begins to pronate to adapt to terrain at heel strike

pronation continues until early midstance

tibial internal rotation subtalar joint everts, foot pronates, flexible forefoot shock absorption

supination in gait cycle

foot begins to resupinate to provide a rigid lever from which to propel during heel off/toe off

tibial external rotation, subtalar joint inverts, foot supinates, rigid propulsion

foot needs proper arch support at 2nd rocker

longitudinal arch support

ligaments → plantar calcaneonavicular ligament (spring ligament) + plantar aponeurosis

muscles → tibialis anterior, tibialis posterior, flexor digitorum longus, flexor hallucis longus, abductor hallucis, flexor digitorum brevis

axis of 1st ray

foot should have normal plantarflexion of 1st ray at 2nd + 3rd rockers to allow the 1st metatarsal head to maintain ground contact while the rest of the foot inverts during propulsion

inadequate plantarflexion of 1st ray causes subluxation of 1st MTP joint + gradually leads to hallux limitus or rigidus deformity

1st MTP joint

foot should have greater range of 1st MTP dorsiflexion at 3rd rocker for propulsion

any restriction of dorsiflexion mechanism will lead to joint subluxation + pain

continued use for active propulsion could lead to eventual ankylosis + rigid deformity hallux rigidus

pes planus/pes planovalgus

excessive pronation of the foot

gait deficits → soft gait, lack of 1st rocker, prolonged 2nd rocker, lack of 3rd rocker

lack of 1st rocker → diminished heel strike + controlled plantarflexion

prolonged 2nd rocker → excessive midstance duration

lack of 3rd rocker → reduced push off efficiency

major clinical signs of pes planus

hindfoot eversion → everted by more than 6 degrees (6-10 degrees = moderate, 10+ degrees = severe)

medial longitudinal arch depression → navicular drop test (>10mm)

forefoot abduction → toe sign test (> 1.5 toes visible laterally)

compensation in flexible excessive hindfoot varus

hindfoot is positioned in a rolled inward position → abnormal pronation

compensation in rigid excessive forefoot varus

forefoot is positioned in a rolled inward position → abnormal pronation

unnecessary destructive compensatory motion occurs in other planes of motion of STJ

excessive motion may be compensatory for structural deformities

compensatory mechanism may occur during midstance in flexible foot

hypermobile 1st rat + great toe dorsiflexion while walking → in abnormal pronated foot: 1) 1st ray can move into dorsiflexion to compensate for everted position that occurs in forefoot, 2) great toe can keep dorsiflexed position at 2nd rocker to compensate the lower MLA to provide stability to medial aspect of foot (windlass)

windlass mechanism

dorsiflexed position of great toe

great toe provides stability to medial aspect of foot through windlass mechanism of plantar aponeurosis

causes of pes planus - congenital

idiopathic hypermobile feet

developmental delay

down syndrome

generalized ligamentous laxity

congenital vertical talus

tarsal coalition

congenital talipes calcaneovalgus

causes of pes planus - neurological

spasticity of gastrocnemius + soleus (CP)

charcot-marie-tooth dz

peripheral neuropathy

causes of pes planus - muscular/tendinous/ligamentous

generalized ligamentous laxity

posterior tibial tendon dysfunction (PTTD)/posterior tibial tendonitis

achilles tendon contracture

hip extensor weakness/inhibition

knee osteoarthritis (OA) in lateral compartment

causes of pes planus - acquired causes

obesity

pregnancy

chronic overuse

weakening of ligaments + tendons over time

calcaneal fractures

midfoot injuries (lisfranc injury)

overuse injuries

structural malalignment, muscle weakness or imbalance, loss of structural integrity → abnormal excessive pronation → overuse injury

overuse injuries due to excessive pronation may result in 2nd metatarsal stress fractures, plantar fasciitis, posterior tibialis tendinitis, achilles tendinitis, medial tibial stress syndrome (shin splints), medial knee pain

2nd metatarsal stress fracture or callus

excessive forefoot varus in STN open chain → talus adducts, plantarflexes, lower extremity internal rotation → midtarsal joint hypermobile → cuboid pulley less efficient → peroneal tendon less functional → hypermobile 1st ray → stress on 2nd metatarsal → metatarsals splay → stress fracture, calluses

ox tx for flexible pes planus

functional improvement/correction for better alignment → semirigid or rigid FOs w/medial wedge in hindfoot area, MLA support, or both

ox tx for CP pes planovalgus

children → UCBL ox or AFOs

adolescents → post op AFOs

ox tx for infant idiopathic hypermobile feet pes planus

total contact concept for better alignment → SMO

ox tx for rigid pes planus

accommodation, stability, pain relief → accommodative FOs, custom molded accommodative shoes or ox (rocker bottom soles or extra depth shoes may reduce pressure + improve gait)

functional FOs

orthopedic device designed to promote structural integrity of joints of foot + lower limb by resisting GRFs that cause abnor

goals of functional FOs

stop, reduce, or slow abnormal compensatory motion of the joints of the foot as the foot + leg interact w/GRFs

indications for functional FOs

to support abnormal structural positions of the forefoot

to support rearfoot deformity

to resist abnormal forces from the leg that cause abnormal pronation or supination of the foot due to the abnormal medial or lateral distribution of extrinsic forces across the subtalar joint

to reposition the calcaneus to a more correct position at the heel strike

to provide a normal degree of contact phase shock absorption

to immobilize the subtalar joint

functional FOs in flexible pes planus

provide varus moment on heel w/medial heel wedge

posting MLA pad or increasing arch during mod to support MLA

posting medial forefoot wedge (extrinsic) if forefoot deformity led to abnormal hindfoot function in stance

building medial metatarsal platform during mod (intrinsic) to support MLA + allow normal plantarflexion of 1st ray if forefoot deformity led to abnormal hindfoot function in stance

having a metatarsal length trimline to allow greater rage of 1st MTP dorsiflexion

FOs

redistribute contact from heel strike to toe off to compensate for alteration in foot architecture assoc w/neuropathies, bony structural changes, + muscle imbalances

align/support the foot, prevent/correct/accommodate deformities, improve overall foot function

types of FOs

corrective → rigid

supportive → semirigid

accommodative → soft

accommodative FOs

protect plantar surface for individuals w/fixed deformities or neuropathic feet

low durometer + flexible materials → plastazote or similar

supportive FOs

several layers of materials each w/different durometer

top cover → lowest durometer → superfoam, spenco, trilam

midlayer → shock absorption → PPT, ultacloud

base layer → highest durometer, supportive → copoly, pelite, cork

corrective FOs

reserved for flexible deformities like mild varus/valgus deformities oro a nearly normal foot w/slight biomechanical deficits

any ox capable of controlling functional foot + leg pathology by maintaining foot in its neutral position or close to it

fabricated from high durometer materials, low temp plastics, or thermoplastics → polypro or carbon fiber

UCBL FOs

for flexible severe varus/valgus deformities

types of FO trimlines

sulcus → at the sulcus

full → at distal edge end of foot ox or shoe

metatarsal/three-quarter length → just proximal to metatarsal heads

FO forefoot extension

material added to bottom of topcover, just distal to front of ox

used to provide additional cushion, control, or accommodation

used to prevent an insert (metatarsal length trimline) from moving forwards in the shoe

FO Morton’s extension

material added under the 1st metatarsophalangeal joint from distal end of ox shell

designed to limit 1st metatarsophalangeal ROM

hallux limitus or rigidus

FO reverse Morton’s extension

material extends from distal aspect of shell to the sulcus under 2-5 metatarsal heads to accommodate the 1st metatarsal or promote 1st ray ROM

FO hindfoot posting w/out inclination angle

used to stabilize the foot against GRFs during initial contact phase of gait

FO hindfoot posting wedge

for pts w/severe excess pronation +/or flat feet → hindfoot varus wedge can be applied to increase subtalar joint control, post is placed over entire heel area w/thicker side on medial side of FO

prefab hindfoot post has a 4 degree inclination wedge, the inclination degrees of the hindfoot post are determined to provide 50% correction of a hindfoot deformity

when the hindfoot is aggressively posted more than 3-4 degrees of varus posting, the distal medial aspect of the ox shell loses contact w/ground as if a forefoot varus deformity were present → in this case, a medial forefoot post is used to counteract the included apparent forefoot varus

FO forefoot posting wedge

inverted/varus orientation of forefoot can be treated by placing a wedge on medial side of ox under 1st MTP joint

in case of forefoot valgus abnormality a post can be placed on lateral side of ox → this will also encourage increased propulsion through the hallux

forefoot deformity must corrected to its fullest extent → 8 degrees forefoot varus condition req a 8 degree forefoot medial wedge

metatarsal pad

tearshaped mod added to top of ox under top cover

begins midshaft of metatarsals + terminates just proximal to the heads of the metatarsals

it acts to shift pressure from metatarsal heads to metatarsal shafts → usually centered at 3rd metatarsal

metatarsal bars

piece of metatarsal bar, usually 3mm thickness, added to the distal edge of the ox shell + covers the distal part of the ox shell

it is designed to transfer force off of the metatarsal heads + onto the metatarsal necks + shafts