1. Biomechanics of the joint
Joints
Definition:
Joint is the articulation between any of rigid component parts of the skeleton whether bones or cartilage by different tissues.

2. Functions of the joints:
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:
The shape of the contours of the contacting surfaces.
How well it fits together.

4. 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.

5. Classification of synovial joints
Example
Mechanical Classification
Anatomical classification
Elbow joint
Uniaxial
Hinge joint
Atlanto axial joint, Superior radio-ulnar joint
Pivot joint
Knee joint
Biaxial
Codyloid joint
Carpometacarpal joint of the thumb
Saddle joint
Wrist joint
Triaxial
Elbsoid joint
hip joint and shoulder joint
Ball and socket
Midtarsal joints of foot
Nonaxial
Gliding joint

6. 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

7. 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

8. 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?

9. 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

10. Arthrokinematics Arthrokinematics means motions of
bone surfaces within the joint are :
Roll, Slide, Spin, Compression
and Distraction
(5 motions)

11. 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.

12. 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.

13. Slide
Specific point on one surface comes into contact with a series of points on another surface
In 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 is
The more incongruent the joint surfaces are, the more rolling there is

14. Slide (glide)

15. Compression – Distraction -
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.

16. CONGRUENCE OF ARTICULAR SURFACES
a) CLOSE-PACKED POSITION OF THE
JOINT .
b) LOOSE- PACKED POSITION

17. 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.

18. Body link System and Kinematic Chains:
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.

19. 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.

20. 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

21. 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

22. Factors Affecting Joint Stability ( Resistance to Displacement)
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.
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.
Fascia: Accordingly to the location and function of the fascia, it may vary from thin to tough and fibrous membranes.
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.
Atmospheric Pressure: It plays a role mainly in the hip joint.

23. Factors Affecting Range of Motion:
Shape of articular surfaces.
Restraining effect of the ligaments and muscles crossing the joint as well as overlying skin.
Controlling and restraining action of the muscles e.g. hamstring muscles tightness when attempting to touch the floor.
Body build: Mesomorph and ectomorph have usually a greater flexibility than endomorph.
The bulk of tissue in the adjacent segments.
Personal exercise habits.
Current state of physical fitness.
Age.
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