JointsDefinition:

Joint is the articulation between any of rigid component parts of the skeleton whether bones or cartilage by different tissues.

Functions of the joints:

1) Allowing movements of body segments by

providing the bones with a mean of moving or rather of being moved.

2) Providing stability without interfering with the desired motion.

The function of the joints depends upon:A. The shape of the contours of the contacting

surfaces.

B. How well it fits together.

Classification of humanJoints according to structure

SynarthorosesLimeted or no movement

DiarthrosesFree movement

SynostosesBone is connected to bone by bone

SynchonrosesBone is connected to bone by

Cartilage or fibrocartilage

SyndesmosesBone is connected to bone by a fibrous

Connective tissues

SynovialThere is synovial membrane and

Synovial fluid

• According to the degree of freedom of movement

• 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.

Classification of synovial joints

Anatomical classificationMechanical Classification

Example

Hinge jointUniaxialElbow joint

Pivot jointUniaxialAtlanto axial joint, Superior radio-ulnar joint

Codyloid jointBiaxialKnee joint

Saddle jointBiaxialCarpometacarpal joint of the thumb

Elbsoid jointTriaxialWrist joint

Ball and socketTriaxialhip joint and shoulder joint

Gliding jointNonaxialMidtarsal joints of foot

Classification of motion

• Rotation• Is motion about an axis,

causing points on the rotating body to travil different distances depending upon their distance from the point of rotation

• Translation• Produces a linear

movement in which all points in the body travel the same distance regardless of their location in the body, most cartilaginous and fibrous joints allow translation, or linear movements.

• Synovial joints allow rotation and translation movements

Terminology

Concave : hollowed or rounded inward.Convex : curved or rounded outward.Congruent: The surfaces of the joint are

equalIncongruent : The surfaces of the joint are

not equal

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?

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

Arthrokinematics

• Arthrokinematics means motions of

bone surfaces within the joint are :

Roll, Slide, Spin, Compression

and Distraction

(5 motions)

Roll

• A series of points on one articulating surface come into contact with a 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.

Spin

• Occurs when one bone rotates around a stationary longitudinal mechanical axis

• Same point on the moving surface creates an arc of a circle as the bone spins

• Example: Radial head at the humeroradial joint during pronation/supination; shoulder flexion/extension; hip flexion/extension

– Spin does not occur by itself during normal joint motion

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

Slide

Specific point on one surface comes into contact with a series of points on another surfaceIn sliding, a point of a shallow concave gliding surface sweeps over a larger surface 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 sliding there isThe more incongruent the joint surfaces are, the more rolling there is

Slide (glide)

• 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 to

increase stretch of capsule.

CONGRUENCE OF ARTICULAR SURFACES

• a) CLOSE-PACKED POSITION OF THE

JOINT .

• b) LOOSE- PACKED POSITION

Kinematic chain

• It is a combination of several successively arranged joints constituting a complex motor system.

• Kinematic chain is when a number of links are united in series.

Body link System and Kinematic Chains:

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

joint axes.• A body link is the central straight link that extends

between two joint axes of rotation. In the case of hands and feet, the terminal links are considered to extend from the wrist and ankle joint centers to the center of the mass of these so- called and members.

• Link systems are interconnected by joints that predetermine the particular type of motion permitted to the functional segments.

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

The kinematic chain may be open or closed.

• In a closed kinematic chain, the distal segment is fixed and the end segments are unite to form a ring or a circuit.

• When one link moves all the other links will move in a predictable pattern. e.g. the rib cage.

• In an open kinematic chain, the distal segment terminates free in space.

• Each segment of an open chain has a characteristic degree of freedom of motion; the distal possessing a higher degree of freedom than the proximal ones.

• Such linkage system allows the degrees of freedom of the many joints in the chain to be pooled giving the segments (particularly those more distal) greater potential for achieving a variety of movements than any one joint could possibly have on its own.

• e.g. when reaching forward to pick up a small object from a high shelf.

Kinematic chains

OPEN CHAIN

The distal end terminates free in space.

It has a characteristic degree of freedom.

The distal segments possess higher degrees of freedom than the proximal one.

Such linkage system allows the degree of freedom of many joints in the chain to be pooled giving the segments greater potential for achieving a variety of movements than can any one joint could possibly have on its own

CLOSED CHAIN

The distal segment is fixed and

the terminal joint meets with great resistance which restraints its

free motion.

e.g. chinning oneself on horizontal bar or stance phase of gait

cycle.

2) end segments are united to form a ring when one link moves, the other links will move in a predictable

pattern e.g. rib cage

• Walking and ascending and descending stairs are examples of alternation between open and closed chains

• Open kinematic chains are the most common type in the human body

Factors Affecting Joint Stability ( Resistance to Displacement)

1. Shape of the bony structure: e.g. depth of the acetabulum of the hip joint and shallowness of the glenoid fossa of the shoulder joint.

2. Ligaments Arrangement: the ligaments attach the ends of the bones that form a movable joint and help in maintaining them in the right relationship to each other.They check the movement when it reaches its normal limits and the resist the movements for which the joint is not constructed, e.g collateral ligament of the knee. The importance of this factor remains as long as the ligaments remain undamaged.

3. Fascia: Accordingly to the location and function of the fascia, it may vary from thin to tough and fibrous membranes.

4. Muscular Arrangement: They play part in the stability of joints especially in those joints whose bony structure contribute little to stability; e.g. rotator cuff of the shoulder have strong inwards pull on the humeral head toward the glenoid fossa.

5. Atmospheric Pressure: It plays a role mainly in the hip joint.

Factors Affecting Range of Motion:

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 relationship that exists between certain joints. E.g. relationship of pelvic tilting to movement of the hip and relationship of the shoulder girdle articulation to movement of the shoulder joint