Orthotic and Podiatric Biomechanics Flashcards
Orthotic device
added to the body part to enhance function, prevent pain, or injury
Podiatry
Branch of medicine dedicated to the diagnosis, treatment, and prevention of foot and ankle disorder
History of Podiatry: Ancient Egypt (2400 BC)
Earliest recorded foot treatments on tomb painting; later found in ebers papyrus
History of Podiatry: Ancient Greece and Renaissance (500 BC - 1500 AD)
- Hippocrates wrote about treatment of corns
- Leonardo da Vinci’s anatomical drawings
History of Podiatry: 19-20th century
- 1895-1911 first podiatry society and school opened
- Dr.william scholl popularized commercial arch supports
- Dr. Merton Root: father of podiatric biomechanics identified normal and abnormal foot function using analysis; introduced functional foot orthotic, devised a foot and lower extremity classification scheme, introduced a standardized orthosis casting method with the foot held around the subtalar joint neutral potion
Root Theory
Defined neutral foot alignment as the biomechanical standard
Inversion-eversion
Subtalar joint motion
Supination-pronation
Motion of the ankle complex (foot relative to tibia
Subtalar joint
- Very important joint within the foot for podiatrists
- Located between talus and calcaneus
- Joint axis normally directed toward the great two, can be palpated for
- deviations cause pain during walking
Subtalar joint axis: medial deviation
Axis shifts inward
- flat foot, fallen arch
Subtalar joint axis: lateral deviation
Axis shifts outward
- high arch, rigid foot
Measuring STJ ROM
- Patient Position: Typically measured in prone position, with foot hanging freely off the edge of the table
Measurement position - One hand stabilizes the leg
- The other passively inverts and everts the foot to assess motion
- Place goniometer between the malleoli
- Maximally invert the STJ
- Zero goniometer then maximally evert
- Neutral position is usually found 1/3 from full inversion and 2/3 from full eversion
Uncompensated Rearfoot Varus
- The calcaneus and forefoot remain inverted even when the STJ is in neutral
- The foot fails to evert fully, preventing the medial side from making proper ground contact
Compensated Rearfoot varus
- The person compensates by overpronating the STJ especially during weight-bearing, allowing the medial heel to touch the ground
- This compensation can lead to instability, excessive stress on soft tissue, and overuse injuries
Orthotic intervention for rearfoot varus
A medial heel wedge can be used to support the calcaneus and
help maintain STJ neutral, reducing compensatory stress.
Uncompensated Forefoot Varus
- The plane of the metatarsal heads is inverted relative to the rearfoot when the subtalar joint (STJ) is neutral.
- The first metatarsal does not make contact with the ground, leading to excessive weight on the lateral forefoot.
Compensated Forefoot Varus
- The person compensates by pronating the STJ during midstance and terminal stance to allow the first metatarsal to contact the ground.
- This excessive pronation may lead to joint instability, overuse injuries, and medial knee stress
Orthotic Solution for Forefoot Varus
- A medial forefoot wedge can provide support the forefoot and maintain subtalar neutral.
Uncompensated Forefoot Valgus
- The metatarsals are everted relative to the calcaneus when the STJ is neutral.
- This results in excessive weight distribution on the medial forefoot, potentially causing instability
Compensated Forefoot Valgus
- During midstance and late stance, the STJ supinates away from neutral to adjust for the forefoot’s excessive eversion.
- This compensation can lead to lateral instability, ankle sprains, and inefficient propulsion
Orthotic solution for forefoot valgus
A lateral forefoot wedge can help support the forefoot and maintain subtalar neutral
Dynamic Rearfoot motion
Tracks Talus and Calcaneus Motion
* Used during weight-bearing movements like walking and running on a treadmill.
Reveals Misalignment in Motion
* Video analysis shows tibia-calcaneus misalignment throughout the stance phase.
Loaded vs. Unloaded Foot Differences
* Rearfoot motion under load can differ significantly from passive range of motion assessments.
Traditional vs. Modern Assessment
* Older method: Examining shoe wear patterns to infer foot loading.
* Modern method: Motion analysis provides real-time, precise data.
Internal shoe wear
- Wear along the inside edge of the shoe, near the big toe and medial heel.
- Low arch, pronation
Central Shoe Wear
Wear under big toe. Neutral foot gait naturally rests on the first toe, without excessive rotation during the stride.
- Normal arch and ankle position
External shoe wear
Wear along the outer edge of the shoe, near the little toe and lateral heel.
- High arch, supination
Impact of Orthoses
- Orthotic may appear to correct motion, but it might only treat the symptom rather than the underlying cause
- usually caused by: Muscle weakness/imbalances, flexibility deficits, leg structure
Center of Pressure (CoP) and Ground Reaction Force (GRF)
CoP identifies where the GRF acts, allowing calculation of the moment about the STJ axis.
Pronatory Effect
if CoP is lateral to the STJ axis, the GRF
creates a pronation moment, attempting to roll the foot inward
Supinatory Effect
If CoP is medial to the STJ axis, the GRF creates a supination moment, attempting to roll the foot outward.
No Moment about the STJ
If CoP is directly beneath the STJ axis, there is no moment or torque, as the forces are balanced.
Sources of moments of STJ axis
- Muscles create moments such as the posterior tibial (PT) muscle, which resists the
pronation moment caused by the GRF - If the pronation moment is excessive, it may lead to posterior tibial tendon dysfunction
- Plantar fascia action and bone-on-bone forces at the end range of motion also provide
resistance to the GRF
Reducing Moments and relieving symptoms
- Identifying the painful structure support orthotic design that reduce or shift stress.
- Extrinsic wedges, posts, pads, cast skives, and shoe modifications can shift CoP relative to the STJ axis.
- Footwear plays a crucial role in transmitting GRFs and influencing the effectiveness of foot orthotics.
