Bio Mechanics of Joints

8/2/2019 Bio Mechanics of Joints

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JointsDefinition:

Joint is the articulation between any of

rigid component parts of the skeletonwhether bones or cartilage by differenttissues.


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Functions of the joints:

1) Allowing movements of body segments by

providing the bones with a mean of moving orrather of being moved.

2) Providing stability without interfering with thedesired motion.

The function of the joints depends upon:

A. The shape of the contours of the contacting

surfaces.

B. How well it fits together.


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Classification of humanJoints according to structure

SynarthorosesLimeted or no movement

DiarthrosesFree movement

SynostosesBone is connected to bone by bone

Synchonroses

Bone is connected to bone byCartilage or fibrocartilage

SyndesmosesBone is connected to bone by a fibrous

Connective tissues

SynovialThere is synovial membrane and

Synovial fluid


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According to the degree of freedom ofmovement

One degree of freedom of movement.

Two degree of freedom of movement.

Three degree of freedom of movement.

According to the number of axes of rotation:

Uniaxial.

Biaxial.

Multiaxial.


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Classification of synovial joints

ExampleMechanicalClassification

Anatomical classification

Elbow jointUniaxialHinge joint

Atlanto axial joint,Superior radio-ulnar joint

UniaxialPivot joint

Knee jointBiaxialCodyloid joint

Carpometacarpal joint ofthe thumb

BiaxialSaddle joint

Wrist jointTriaxialElbsoid joint

hip joint and shoulderjoint

TriaxialBall and socket

Midtarsal jointsof footNonaxialGliding joint


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Classification of motion

Rotation

Is motion about an axis,causing points on therotating body to travil

different distancesdepending upon theirdistance from the point ofrotation

Translation

Produces a linearmovement in which allpoints in the body travel

the same distanceregardless of theirlocation in the body, mostcartilaginous and fibrous

joints allow translation, or

linear movements. Synovial joints allow

rotation and translationmovements


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Terminology

Concave: hollowed or rounded inward.

Convex: curved or rounded outward.

Congruent: The surfaces of the joint are

equal

Incongruent : The surfaces of the joint are

not equal


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Joint Shapes

Ovoid one surface is convex, other surface is concave

What is an example of an ovoid joint?

Sellar (saddle)

one surface is concave in one direction& convex in the other, with the opposing surface convex& concave respectively

What is an example of a sellar joint?


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Relationship Between Physiological &Accessory Motion

Biomechanics of joint motion

Physiological motion

Result of concentric or eccentric active muscle contractions

Bones moving about an axis or through flexion, extension,abduction, adduction or rotation

Accessory Motion

Motion of articular surfaces relative to one another

Generally associated with physiological movement

Necessary for full range of physiological motion to occur

Ligament & joint capsule involvement in motion


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Arthrokinematics

Arthrokinematicsmeans motions of

bone surfaces within the joint are :

Roll, Slide, Spin, Compressionand Distraction

(5 motions)


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Roll

A series of points on one articulating surface come into contact witha series of points on another surface

Rocking chair analogy; ball rolling on ground Example: Femoral condyles rolling on tibial plateau

Roll occurs in direction of movement

Occurs on incongruent (unequal) surfaces

Usually occurs in combination with sliding or spinning In rolling, equidistant points touch each other in the

course of motion.


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Spin

Occurs when one bone rotates around a stationary longitudinalmechanical axis

Same point on the moving surface creates an arc of a circleas the bone spins

Example: Radial head at the humeroradial joint duringpronation/supination; shoulder flexion/extension; hipflexion/extension

Spin does not occur by itself during normal joint motion

In spinning, the contact point of one surface rotates arounda longitudinal axis.


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Slide

Specific point on one surface comes into contact with aseries of points on another surface

In sliding, a point of a shallow concave gliding surface sweeps over a largersurface of the other convex joint body. (sometimes referred to as a GLIDE)Surfaces are congruent.Combined rolling-sliding in a joint

The more congruent the surfaces are, the more slidingthere isThe more incongruent the joint surfaces are, the morerolling there is


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Slide (glide)


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Compression

Decrease in space between two joint surfaces

Adds stability to a joint

Normal reaction of a joint to muscle contraction

Distraction -

Two surfaces are pulled apart

Often used in combination with joint mobilizations toincrease stretch of capsule.

CONGRUENCE OF ARTICULAR


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CONGRUENCE OF ARTICULARSURFACES

a) CLOSE-PACKED POSITION OF THEJOINT .

b) LOOSE- PACKED POSITION


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Kinematic chain

It is a combination of several successivelyarranged joints constituting a complexmotor system.

Kinematic chainis when a number of linksare united in series.


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Body link System and KinematicChains:

Body link system: Body linkis the distance between joint axes and it unites

joint axes.

A body link is the central straight link that extendsbetween two joint axes of rotation. In the case of handsand feet, the terminal links are considered to extend fromthe wrist and ankle joint centers to the center of themass of these so- called and members.

Link systems are interconnected by joints thatpredetermine the particular type of motion permitted tothe functional segments.

The link system is used to make calculations regardingdifferent body segments in different positions.


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Kinematic chains

OPEN CHAIN

The distal end terminates free inspace.

It has a characteristic degree offreedom.

The distal segments possess higherdegrees of freedom than the proximalone.

Such linkage system allows the degreeof freedom of many joints in the chainto be pooled giving the segmentsgreater potential for achieving a varietyof movements than can any one jointcould possibly have on its own

CLOSED CHAIN

The distal segment is fixed and

the terminal joint meets with greatresistance which restraints itsfree motion.

e.g. chinning oneself on horizontalbar or stance phase of gaitcycle.

2) end segments are united to form aring when one link moves, the otherlinks will move in a predictable

pattern e.g. rib cage


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Walking and ascending and descendingstairs are examples of alternation betweenopen and closed chains

Open kinematic chainsare the mostcommon type in the human body


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Factors Affecting Range ofMotion:

1. Shape of articular surfaces.2. Restraining effect of the ligaments and muscles crossing the joint as well as

overlying skin.3. Controlling and restraining action of the muscles e.g. hamstring muscles

tightness when attempting to touch the floor.4. Body build: Mesomorph and ectomorph have usually a greater flexibility

than endomorph.5. The bulk of tissue in the adjacent segments.6. Personal exercise habits.7. Current state of physical fitness.8. Age.9. Heredity.

N.B.: Apparent range of motion can be affected by the close relationshipthat exists between certain joints. E.g. relationship of pelvic tilting tomovement of the hip and relationship of the shoulder girdle articulation tomovement of the shoulder joint

Bio Mechanics of Joints

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