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Force=?
mass x acceleration
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When do we infer the existence of forces?
when we observe masses being accelerated (or distorted)
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What are some forces that influence human movement?
- gravity
- muscles
- wind
- water
- ligaments
- reaction forces
- bones
- external weights
- friction
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How do we depict forces?
using vectors
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What four characteristics do vectors have?
- point of application
- line of application
- direction
- magnitude
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Where is the point of application of gravity?
COG
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Where is the point of application of outside forces (including muscle forces)?
muscle's point of attachment to the moving bone
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Where is the line of application for gravity?
vertical
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Where is the line of application for outside forces (including mm)?
follows muscle or tendon fibers local to the joint being analyzed
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What is the direction of gravity?
down
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What is the direction of outside forces (mm)?
toward center of muscle belly
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What is the magnitude of gravity and outside forces?
arbitrary, drawn to scale
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What are the rules for vector analysis?
1.
name joint at which movement occurs
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Rules for vector analysis
2.
determine what segment is moving, what segment is stable, and joint where movement takes place
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Rules for vector analysis
3.
determine plane of movement in which movement occurs, and axis around which joint moves in this plane
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Rules for vector analysis
4.
draw simple diagram that illustrates body in plane you named. Estimate location of relevant joint axis, and label it on your diagram w/ a "cross." Even if movement takes place in more than one plane, analyze only one plane at a time
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rules for vector analysis
5.
focus analysis on moving segment, and begin by considering force of gravity
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Rules for vector analysis
6.
following rules for gravity forces, depict force of gravity as vector. Determine vector's moment arm and determine moment that gravity produces around joint's axis in the plane depicted
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Rules for vector analysis
7.
consider other forces, especially muscle forces, that act on moving segment
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Rules for vector analysis
8.
decide which muscle forces act in a direction that produces moments that oppose gravity's moment
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Rules for vector analysis
9.
follow rules for muscle forces to depict these muscle forces as vectors
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Rules for vector analysis
10.
determine each muscle vector's moment arm with respect to the joint axis
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What terms are synonymous with torque?
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Moment:
- a turning effect, produced by a force at some distance from an axis of rotation [M=Fs]
- M= moment's magnitude
- F=force (N or lbs)
- s=force's moment arm (length-cm/in)
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moment arm:
length of perpendicular distance from line of application of gravity to the joint's axis
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Just as a FORCE produces straight line acceleration in a object at rest, a MOMENT produces..
- an angular acceleration in an object around an axis of rotation [M=Ir]
- I=moment inertia
- r=angular acceleration
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What is a moment of inertia?
- rotational equivalent of mass in its mechanical effect, that is, the resistance to a change of state during rotation
- a mass's moment of inertia depends on how that mass is distributed about an axis of rotation
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Kinematics:
study of direction, extent, and speed of motion
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What motions are possible in the lateral axis of the tibio-femoral (knee) joint?
flexion and extension
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What is the close-packed position of the tibio-femoral (knee) joint?
extension
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What motions are possible in the longitudinal axis of the tibio-femoral (knee) joint?
tibial rotation
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What motion is possible at the patello-femoral joint?
tracking only
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What is the function of the medial collateral ligament of the knee?
- resists valgus stress
- limits knee extension
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Where is the location of the medial collateral ligament of the knee?
runs from medial epicondyle of the femur to medial proximal tibia
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What is the function of the lateral collateral ligament?
- resists varus stress
- limits knee extension
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Where is the location of the lateral collateral ligament of the knee?
runs from lateral epicondyle (femur) to the head of the fibula
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What is the function of the ACL?
- provides 90% stability to knee joint
- limits knee extension and rotation
- limits excessive forward movement of tibia relative to a stable femur OR
- limits excessive backward movement of the femur on a stable tibia
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Where is the location of the ACL?
attaches to depression in front of intercondyloid eminence of tibia and passes up, backward, and lateral to attach to back of lateral condyle of femur
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What is the function of the PCL?
- provides additional stability to the knee joint
- limits knee extension and rotation
- limits excessive backward movement of tibia relative to stable femur OR
- limits excessive forward movement of femur on a stable tibia
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Where is the location of the PCL?
connects posterior intercondylar area of tibia to medial condyle of femur
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What are menisci?
cartilaginous structures that are shaped concave superiorly, and continuous w/ tibia inferiorly
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Where are the menisci attached?
medial and lateral attached to small depressions b/w condyles of tibia (intercondyloid fossa)
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Are the menisci attached attached in the center?
no, unattached and their shape narrows to a thin shelf in the center
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Arthrokinematics
During Knee extension:
Open chain
- tibia glides anteriorly on femur
- tibia rotates externally (screw-home mechanism)
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Arthrokinematics
During knee extension
Closed chain:
- femur glides posteriorly on tibia
- femur rotates internally on stable tibia (screw-home mechanism)
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Arthrokinematics
During knee flexion
Open chain:
- tibia glides posteriorly on femur
- tibia rotates internally
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Arthrokinematics
During knee flexion
Closed chain:
- femur glides anteriorly on tibia
- femur rotates externally on stable tibia
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What causes these roll and glide knee joint movements?
shapes of tibial and femoral surfaces DO NOT cause these movements
tibial glide is produced by muscle forces
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During open chain knee extension:
The tibia rolls-
- anteriorly
- quadriceps pull on tibia causes it to glide anteriorly
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During open chain knee flexion:
tibia rolls-
- posteriorly
- hamstring's pull on tibia causes it to glide posteriorly
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The screw home mechanism is driven by 3 forces:
- 1. shape of medial femoral condyle
- 2. passive tension in ACL
- 3. lateral pull of quadriceps muscle
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What unlocks the knee?
- knee to the knee
- popliteus
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What muscles move the knee?
- rectus femoris
- vastus lateralis
- vastus medialis
- biceps femoris
- semitendinosus
- semimembranosus
- gastrocnemis
- popliteus
- plantaris
- gracilis
- sartorius
- possibly tensor fascia latae
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What are the extensors of the knee?
- rectus femoris
- vastus lateralis
- vastus medialis
- vastus intermedius
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What are the knee flexors that cross 2 joints?
- biceps femoris -long head
- semitendinosus
- semimembranosus
- gastrocnemius
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What are the knee flexors that cross 1 joint?
- biceps femoris -short head
- popliteus
- plantaris
- gracilis
- sartorius
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What are the internal rotators of the tibia w/ respect to the femur?
- semitendinosus
- semimembranosus
- popliteus
- gracilis
- sartorius
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What are the external rotators of the tibia w/ respect to the femur?
- biceps femoris
- possibly tensor fascia latae
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Does the patella track only superiorly?
no, as knee extends, patella pulled in lateral direction because of larger size, direction, and cross-sectional area of vastus lateralis
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What is the Q-angle?
- quadriceps angle
- a measure of overal line of pull from quadriceps
- formed in frontal plane by two line segments
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What two line segments form the Q-angle?
- from ASIS to the mid-patella --representing overall line of force by quads
- from tibial tuberosity to mid-patella, representing long axis of patellar tendon
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Increases or decreases in Q-angle are associated w/...
increased peak patellofemoral contact pressures
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What is the normal Q-angle for males?
14 deg
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What is the normal Q-angle for females?
17 deg
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Biomechanics of patellofemoral joint are effected by:
patellar tendon length and Q-angle
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The posterior line of pull of vastus medialis oblique causes the patella to:
stay securely in intertrochlear groove during its glide superiorly w/ knee extension
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What factors oppose lateral pull of patella?
(What causes patella to track normally?)
- fibers of vastus medialis oblique
- lateral facet of groove is steeper than medial--forcing patella more medial
- medial patello-femoral ligament --esp important in last 20 deg
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How do we manage lateral "bowstringing" forces on the patella?
- increase control by hip abd mm
- increase control by hip ext rot mm
- increase control of quads
- increase control of mm that support arch of foot
- MODIFY activites that creaste unnecessarily large stress on PF joint...particularly working in large angles of knee flexion
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PROM:
passive movements end-feels
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End-feel:
quality of resistance to movement that examiner feels when coming to the end point of a particular movement
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What do end-feels provide the therapist with?
critical info about what structure is/are limiting motion
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Normal end-feels:
- capsular
- ligamentous
- bony
- soft tissue approximation
- muscular
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Pathologic end-feels:
- muscle-spasm
- capular (abnormal)
- boggy
- internal derangement
- empty
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At the end of available passive movement into knee extension, further extension is normally limited by 4 ligaments we have discuss, making the normal end-feel...
ligamentous
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At end of available passive movement into knee rotation, further rotation is normally limited by 4 ligs, making normal end-feel...
ligamentous
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At end of available passive movement into knee flexion, further flexion limited by tissue of hamstrings againsts gastroc-soleus mm, making normal end-feel...
soft tissue
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