# Shared Flashcard Set

## Details

biomechanics of hip, knee, and ankle
ABC boards for certification in orthotics
54
Health Care
10/16/2010

Term
 orthosis and forces
Definition
 when an orthosis applies a force to the body there is an equal and opposite force also applied to the orthosis by the body
Term
 applying corrective forces
Definition
 essential to consider were and how the orthosis must apply corrective forces
Term
 failure to consider forces being placed on the orthosis by the body
Definition
 may cause structural failure or distortion of the orthosis
Term
 orthoses and pressure
Definition
 in clinical practice, forces must be applied over as large of an area as possible to reduce pressure-P(pressure)=F(force)/A(area)
Term
 basic function of an orthosis
Definition
 resist or control angular motion at a joint-varus, valgus, knee hyperextension, etc
Term
 orthosis control angular motion at a joint by...
Definition
 applying a system of linear forces each pushing on a different part of the body in a specific direction
Term
 control of angular motion
Definition
 required because many of these linear forces are applied at a distance from the joint's center of rotation
Term
 force at a distance
Definition
 force acting at a distance from a joint causes a "turning force" known as a moment.
Term
 magnitude of force calculation
Definition
 M(moment)=F(force)x D(distance)
Term
 M(moment)=F(force)x D(distance)
Definition
 D (know as the lever arm) is defined as the perpendicular distance from the joint center to the line of action of the force.
Term
 applying oblique rather then perpendicular forces
Definition
 -if this happens forces will be less then effective in generating the required moment because the lever arm will be smaller
Term
 critical function of most lower limb orthosis
Definition
 the creation of moments
Term
 increasing lever arm
Definition
 -clinically useful strategy-enables required moment to be generated while reducing the size of the force required
Term
 reducing force
Definition
 reduces pressure on tissue which increases comfort.
Term
 ways to reduce pressure
Definition
 -increase lever arm-increase area over which pressure is applied-increase both
Term
 maximizing pressure reduction
Definition
 -increase both lever arm and the area over which pressure is applied.
Term
 orthotic system of forces
Definition
 -in order to work successfully force systems in orthosis must be set up in equilibrium to balance each other
Term
 equilibrium relates to
Definition
 both the forces applied as well as the moments created by these forces
Term
 to control angular motion at a joint
Definition
 minimum number of three forces is required.-three point pressure system
Term
 effective three point pressure system
Definition
 -2 forces must be applied to the concave side of the joint.-these forces must balance with the third force working in the opposite direction.
Term
 3rd opposition force
Definition
 this force should be located as close as possible to the center of joint rotation
Term
 mathematical expression of three point pressure system
Definition
 F2=F1+F3
Term
 clinical importance of force systems
Definition
 it is important to recognize that it is impossible to alter one force in a three point pressure system without influencing the other two forces in the system
Term
 applying forces in orthosis
Definition
 important to use straps in the direction that the force is required to act
Term
 force systems for two joints
Definition
 if two joints are adjacent to each other some of the forces in a force system maybe shared. this can reduce the overall number of forces required to control joints.
Term
 significance of the masses of the orthosis and shoes
Definition
 The larger the mass to be accelerated and decelerated, the greater the muscle forces that are required
Term
 mass considerations
Definition
 whenever possible it is beneficial to minimize mass of the distally applied orthosis in order to reduce demand
Term
 kinematics
Definition
 -study of motion
Term
 kinetics
Definition
 -study of the effects of forces
Term
 ground reaction force (GRF)
Definition
 due to gravity the weight of body acts vertically downward. equal opposite vertical force acting upward is the ground reaction force
Term
 when is there no GRF?
Definition
 swing phase
Term
 GRF in static situations
Definition
 -all forces remain constant, with the magnitude equal to the body weight
Term
 GRF in dynamic situations
Definition
 forces typically vary in a repetitive fashion
Term
 GRF and center of rotation
Definition
 -when line of action lies at a distance from the the center of rotation it creates a external moment-greater the perpendicular line of action for GRF to joint cen
Term
 GRF joint alignment
Definition
 -GRF close, smaller external moment-GRF farther, larger external moment-GRF through joint, no external moment
Term
 presence of an external moment tends to cause:
Definition
 -motion at a joint-usually (not always) requires an opposing internal muscle moment to create equilibrium (control the motion)
Term
 balancing moments in dynamic situations
Definition
 moments generated by the muscles maybe greater or less then external moments in order to control angular motion at the joints
Term
 desirable effect of GRF at joints
Definition
 may reduce or remove the need for muscle activity at a joint.-paraplegic patient with KAFOs can achive hip stability by aligning the GRF posterior to the hip joints
Term
 exact magnitude of external and internal moments:
Definition
 influenced by the accelerations and inertial effects of the individual joint segments
Term
 normal gait basic definition
Definition
 highly controlled, coordinated, repetitive series of limb movements whose function is to advance the body safely with minimum energy expenditure
Term
 5 attributes of normal walking
Definition
 1. foot clearance in swing2. adequate step length3. prepositioning of foot for initial contact4. stability in stance phase5. conservation of energy
Term
 joint deviations in pathological gait
Definition
 potential deviations can occur in all phases of the gait cycle as well as all three planes
Term
 forward progression of the tibia
Definition
 -facilitated by the three rockers of gait
Term
 GRF in pathological gait
Definition
 -common feature is that the magnitude of the first peak of the GRF is excessively high in early stance, but the second peak in terminal stance is insufficient.
Term
 if GRF is less then body weight
Definition
 limb is not supporting the body weight sufficiently to remain functional as a support
Term
 if limb can not support weight sufficiently
Definition
 contralateral limb may make heavy contact with the floor generating an excessive first peak of GRF
Term
 normal gait patterns and GRF
Definition
 segments move in ways that align the knees and hip joints closely to the GRF so as to minimize lever arms and produce sufficient moments making gait efficient
Term
 3 GRF alignment changes at knee in gait
Definition
 1 during loading response moment changes from extension to flexion2 in midstance-flexion to extension3 preswing-extension to flexion
Term
 GRF stability in stance
Definition
 GRF aligned anterior to the knee and posterior to the hip-creates external hip and knee extension moments producing stability
Term
 GRF stability in stance
Definition
 GRF aligned anterior to the knee and posterior to the hip-creates external hip and knee extension moments producing stability
Term
 when segments are misaligned:
Definition
 GRF is also misaligned relative to the joints causing abnormal lever arms and moments that destabilize or excessively stabilize joints
Term
 what is external rotation angle of the ankle joint?
Definition
 -20-30 degrees
Term
 what is external rotation angle of the ankle joint?
Definition
 -20-30 degrees
Term
 reason for external rotation angle of ankle joint
Definition
 -motion of the ankle is then comparable with the antero-lateral movement of the center of gravity.
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