Pod Biomechanics Exam 1

Motion: triplanar, supination and pronation

Axis: distal-medial-dorsal to proximal-lateral-plantar. 16 deg from sagittal plane, 42 from transverse, and 48 from frontal

Motion: Biplanar and coupled. Dorsiflexion with inversion and plantarflexion with eversion.

Axis: 45 deg from frontal and 45 from sagittal, parallel to transverse plane.

STJ pronated = increased 1st Ray motion

STJ supinated = decreased 1st Ray motion

Motion: Triplanar. Pronation and supination.

Axis: oriented similarly to subtalar joint

Motion: Single plane, dorsiflexion and plantarflexion

Axis: Perpendicular to sagittal plane, parallel to front and transverse planes

Biaxial - vertical axis (transverse plane, ab and adduction) and horizontal axis (sagittal plane, dorsi and plantarflexion)

2 separate motions!

Biaxial: longitudinal axis and oblique axis.

Longitudinal axis: perpendicular to frontal plane (75 deg from frontal plane). Inversion and eversion

Oblique axis: oblique to sagittal and transverse. 8 deg from sag, 15 from transverse. Dorsiflextion w/ abduction and plantarflexion w/adduction

Body in motion stays in motion, and body at rest stays at rest, unless acted upon by another force.

vector that has magnitude and direction

Mass that moves from point A to B with a linear velocity (i.e. walking). Linear force = axial force.

Speed = distance/time. No direction.

velocity = displacement/time with direction.

displacement = distance

the rate at which an object changes its velocity.

a = change in velocity/time

i.e. going from 30mph to 60 mph is acceleration. or, changing direction also considered accel.

F= mass x acceleration

Momentum = mass x velocity

quantity of motion a mass has.

has force potential.

It takes a certain force over a time period to change the momentum.

change in momentum = force x time

How do you minimize force (i.e a punch coming at you w/ momentum?). Increase the time (move your head back).

Vectors. Have a direction and speed.

When a force is exerted on an object, that object pushes back with an equal and opposite force.

Ground reactive forces from the earth push back on our feet.

change in momentum = force x time. They increase the time.

body of mass rotating around axis to produce linear momentum. Degrees per minute.

ang. mom = inertia x angular velocity

inertia = amt. of energy it takes to start or stop an object

same as linear. change in momentum - change in acceleration (bc velocity changes). To produce ang. accel, apply a force called a torque or moment.

= force x distance from fulcrum (moment arm)

if two forces are equal, but one force is applied 2x farther from the fulcrum, it will produce 2x the torque.

Point in an object where it has its smallest amount of inertia around any axis that contains that point

it's easier to rotate object around an axis if that axis lies within its center of mass.

The farther a mass is spread out, the greater its inertia (or ability to resist change in velocity)

Fulcrum is between the force (effort) and the load (inertia)

example: tricep with elbow as fulcrum and hand with the load

intermediate strength

Lever mechanical advantage - length of effort arm divided by length of resistance arm

Strongest. Fulcrum at one end, force (effort) at other end with load in the middle. (wheel barrel, or door on hinge)

when effort arm is long, it's strong.

calf is effort, load is body weight and fulcrum is toes.

Weakest bc moment arm is smaller, but fastest.

Fulcrum at end, effort in middle, load at other end. i.e. elbow, bicep and load on hand. (bicep attaches to forearm).

Most joints are Class 3.

Every change in form or function of a bone is followed by adaptive changes (bone remodeling)

Compression stabilizes bone

Rotation/angular movements cause instability if excessive or outside normal range (muscle action keeps angulations low and stabilizes joint motion)

soft tissues (ligaments) will elongate under prolonged tension.

• elasticity = returns to normal shape, usually with force of short duration.
• plasticity = doesn't return to shape, long duration force.

Born with ligaments of high elastic content (abnormal collagen/elastin ratio)

Ligaments go through plastic deformation. Pronation in childhood becomes excessive and leads to bone and joint adaptation.

process by which the body can vary muscle contraction in response to external forces. Specialized structures: golgi tendon bodies, muscle spindle, joint proprioception.

Muscle, bone, ligaments and proprioception

External: body mass in motion, gravity

Internal: rotation/angular movement around joint

• 1. Static
• 2. Steady motion (moving at a constant velocity)

instability occurs when a force displaces the object from its original position (equilibrium)

Static Equilibrium

• Balance is improved when:
• -center of mass is lower
• -base of support is wider
• (crouched low with feet spread apart = most balanced position)

Momentum is conserved in the system. The only negligible loss of kinetic energy is in heat and friction. KE is, for the most part, conserved.

Momentum is conserved but kinetic energy is lost to a form outside the system.

I.e. foot hitting earth. Foot velocity changes (decelerates), earth moves but because of its mass its unperceivable.

the energy a moving body has just because it's moving. Energy is ability to do work.

KE = 1/2mv^2

A body's unrealized potential to do work. Something not in motion has PE, but when it moves it has KE.

• 1. Body weight
• -gravity
• -free falling mass
• 2. Earth as it reacts to foot
• -vertical force
• -horiz. force (friction)
• 3. Internal forces
• -tension, compression, rotation

Can apply increasing force on a bone, and up to the yield point, it will bounce back (elastic region). Beyond the yield point (plastic region) the bone is deformed/injured.

Middle of single support (one foot on ground, one at highest point in air)

double support

• Decrease body weight
• Minimize how far center of mass falls
• Maximize time of applied force to change momentum
• smooth walking (i.e. limping is less energy efficient

fat pad and skin of heel, STJ pronation, MTJ pronation, knee flexion (increases time to minimize force), ankle plantarflexion, phasic muscle contraction

Supinated position. Doesn't pronate, loss of shock absorption.

abnormal internally rotated femur due to tight soft tissues. treatable.

externally rotated femur due to tight soft tissues. treatable.

lack of normal external twisting of femur. increased angle. leads to internally rotated femur (intoeing). Not very treatable since the problem is the bone.

Too much external rotation of femur. smaller angle. outtoeing. Not very treatable since it's the bone.

Angle of neck to shaft of femur.

• Increased: coxa valgum/genu varum (bow-legged)
• Decreased: coxa varum/genu valgum (knock-kneed)

From birth to adult, decreases from 135-140 to 126-128 degrees

• Birth - 2: bowlegged
• 2 - 4: straight
• 4 - 7: knock kneed
• 7 - 12: straight
• 13 - 18: knock kneed
• Adult should be straight or slightly knock kneed

knees are hyperextended. Due to ligamentous laxity. affects girls more. sagittal plane.

• Birth - up to 75 degrees.
• By age 15, decreased to 10 degrees.

Knees and hips straight but feet are rotated either out or in. Tibia, like the femur, starts inwardly rotated and needs to rotate externally.

Could also be caused by position of fibula and tibia to each other (fibia should be slightly posterior to tibia)

At birth they are straight. Progressively externally rotate until they are 15 to 18 degrees external. Thus, it's normal for fibula to be posterior to tibia.

Pigeon-toed/intoed

out-toe, duck feet

soft-tissue problem at the KNEE that causes intoeing, even though it looks like an ankle problem

In the womb, foot is adducted and inverted. Children are flat footed and everted. Adult should have vertical heel and straight forefoot.

torsion twist from 20 degrees to 40 in a valgus direction (lack of twist=forefoot varus, too much twist=forefoot valgus)

transverse external rotation from 35 to 20 deg (lack of rotation=forefoot adductus, too much=forefoot abductus)

twist and rotation from varus to vertical.

• lack of twist/rotation = inverted/varus
• excess twist/rotation = everted/valgus

the motion of the body is known, and the forces must be extrapolated from position-time curves

adding forces to making something do what u want it to do

measures the tendency for a structure to rotate

tibialis posterior muscle decreases internal rotation of the foot! (answer on test)

Tendency of bone to bend

i.e. stress fractures : no outward physical change, nothing visible. but when it breaks, it becomes an external moment. Test Q!

Results in visible motion (has an outright physical change). Most common form of a moment in kinematics.

If GRF on lateral calcaneus, will cause eversion. If on medial, will cause inversion.

GRF pushes back with equal and opposite force!

Interval of time from heel strike of one foot to heel strike of same foot. consists of 2 phases: stance and swing.

the distance covered on one foot during one complete gait cycle

the distance covered on one foot during one-half of the gait cycle

number of steps/minute when a person walks normally

weightbearing portion of gait cycle. starts at heel strike of one foot to toe-off of opposite foot.

Periods of stance phase: contact period, midstance period, propulsive period.

Non-weight bearing portion. Toe off of one foot to heel strike of same foot. 40% of gait cycle.

heel strike to forefoot loading (or opposite toe-off)

forefoot loading (or opposite toe-off) to heel lift

heel lift to toe-off

limits inversion and eversion

limits inversion

limits inversion

limits eversion

• Anterior talo-fibular
• Calcaneofibular - limits STJ supination
• Posterior talo-fibular

• superficial deltoid
• deep deltoid

strongest portion of superficial deltoid, limits eversion of STJ and ankle

For every degree of sagittal plane motion, there are three degrees of transverse and frontal plane motion

shock absorption and adaptation to uneven terrain

Creates rigid lever for propulsion and prepares foot for heel contact

(foot doesn't propel well from a pronated position)

non-weight bearing (swing phase), occurs in gait, calcaneus does all the work (moves in all 3 planes), tibia has little influence

weight bearing (stance phase), occurs in gait, both calcaneus and talus do the work, tibia has great influence

calcaneus goes back to only moving in frontal plane

• Pronation (dorsiflexion, abduction, eversion)
• Supination (plantarflexion, adduction, imversion)

talus does equal and opposite motion as calcaneus. tibia does same transverse plane motion as talus!

• pronation: calcaneus everts, talus plantarflexes and adducts
• supination: calcaneus inverts, talus dorsiflexes and abducts

internally rotated (because talus is adducted)

externally rotated (because talus is abducted)

Heel strike to forefoot loading

at heel strike, STJ is supinated then undergoes rapid pronation throughout contact period. Neutral position just after heel strike.

forefoot loading to heel lift

STJ is slowly supinating, still pronated just before heel lift. Neutral position around heel lift.

Heel lift to toe off

STJ is supinated and still supinating even more (a rigid lever)

• 1st half: STJ pronates
• 2nd Half: STJ supinates

Remember in OKP, calcaneus does all the work! In pronation, it everts, abducts and dorsiflexes. In supination, it inverts, adducts and plantarflexes.

STJ neither pronated nor supinated. Measure non-weight bearing.

• Amount of max STJ inversion and max STJ eversion. Then use NP = (total ROM/3) - eversion
• where ROM = measured calcaneal inversion + measured calcaneal eversion. If negative, NP is everted. If positive, NP is inverted. Normal is 0-2 degrees inverted.