statics and compensation

During static stance, what proportion of body weight is supported by each forefoot and each heel?

Each forefoot and each heel supports ¼ of the body weight.

How is weight distributed among the metatarsal heads in the forefoot?

1st metatarsal head bears 2 parts, while each lesser metatarsal head bears 1 part, creating a 2:1:1:1:1 ratio.

What muscle must contract for the forefoot to bear weight during static stance?

Gastrocnemius; its contraction causes plantarflexion via the Achilles tendon

In normal static stance, what is the position of the subtalar joint?

Neutral position (calcaneal bisection perpendicular to the ground).

What is the result of midtarsal joint being maximally pronated?

The joint locks, providing stability during static stance.

Define “dynamic gait.”

Movement of foot bones while bearing weight, due to ground reaction forces and body mass acceleration.

What kind of forces increase joint instability during dynamic gait?

Bending (rotational/tensile) forces.

What provides emergency stability during sudden motion at joints?

Ligaments and joint capsules.

What are common consequences of kinetic instability in the foot?

Ligament sprains, ruptures, avulsion fractures, and joint degeneration (e.g., arthritis).

What is compensation in foot biomechanics?

Structural, positional, or functional adjustments to offset deviations elsewhere in the body.

What joint is the primary site for compensation in the foot?

Subtalar joint (STJ), with midtarsal joint (MTJ) assisting due to triplanar motion.

What type of foot deformity is associated with STJ pronation during midstance and propulsion?

Forefoot varus.

What causes compensation in rearfoot varus?

STJ pronation during midstance to distribute ground reactive forces

What condition involves a rigid, structurally plantarflexed first ray?

Rigid plantarflexed first ray; may lead to STJ supination and lateral instability.

What causes forefoot supinatus, and what is the compensation?

Caused by soft tissue contracture or tight gastro/soleus complex; compensation is LMTJ supination

What occurs when the center of weight shifts medially in the foot?

The 1st and 2nd metatarsals bear more than 50% of the weight; associated with an abducted forefoot.

What occurs when the center of weight shifts laterally in the foot?

Lateral metatarsals bear more weight; associated with an adducted forefoot.

What defines the base of support in static stance?

Lateral and posterior foot margins, metatarsophalangeal joints; toes do not bear weight without muscle function.

What is required for forefoot to bear weight during static stance?

Achilles tendon force must exceed tibial load to load metatarsal heads.

What is phasic muscle activity during gait?

Timed contraction of muscles to resist rotatory forces and maintain joint stability during gait.

What stimulates proprioceptive reflexes that stabilize joints?

Ligament and capsule stretch during subluxation or sudden motion.

What is the role of ligaments in emergency joint stabilization?

They decelerate joint motion and stimulate muscle contraction to maintain joint integrity.

Define subluxation in the context of foot biomechanics.

Partial joint dislocation due to hypermobility or unresisted forces.

What are common pathologies from subluxation in young versus adult feet?

Young: abnormal bone development.
Adult: degenerative joint disease (e.g., traumatic arthritis).

How does the foot normally compensate for an inverted forefoot due to terrain?

If inversion is within ROM, forefoot compensates; if not, rearfoot also inverts.

How does the foot compensate when the terrain causes forefoot eversion?

Both rearfoot and forefoot evert together, but forefoot may evert slightly more.

What happens if forefoot inversion cannot match rearfoot eversion?

Incomplete compensation; MTJ unlocks and weight shifts to 2nd metatarsal head.

What prevents forefoot from compensating for rearfoot supination?

Osseous restraining mechanism of the locked midtarsal joint.

What is the most common biomechanical cause of "I’ve fallen and I can’t get up" syndrome?

Sudden demand for subtalar joint supination causing instability.

Why are the subtalar and midtarsal joints suited for compensation?

They allow triplanar motion, enabling adjustments across three planes.