Bones
Joints and Joint Movments
Second part of the first lecture
Purpose of the skeletal system
to protect internal organs
to provide rigid kinematic links
to provide muscle attachment sites
to facilitate muscle action and body movement (support weight)
Facts
Bone is one of the most dynamic and metabolically active tissues in the body
Bone is highly vascular with an excellent capacity for self-repair and can alter its
properties and configuration in repose
to change in mechanical demand
Bone has a high content of inorganic mateirals, in the from of mineral salts (Calcium
and Phosphate) that combine with
an organic matrix
The inorganic mineral salts make bone hard and rigid and account for approximately
65-70%
The organic component makes bone flexible and resilient and accounts for
approximately 5%
Water accounts for approximately 25%
Types of Bone Tissue
Cortical bone (compact)- is the dense structure that forms the cortex of a bone (outer
shell)
Cancellous bone (trabecular)- is the loose mesh structure filled with red marrow,
surrounds by the cortex
Types of Bone
Long- cylindrical shaft with a central cavity
ex: clavicle, humerus, radius, ulna, femur, tibia, fibula, metacarpals
Short - small, solid
ex: carpals and tarsals
Flat - flat
ex: sternum, scapula, ribs, pelvic bones, patella)
Irregular ex: vertebrae, bone of the skull and ear
Joints
Articulation of adjacent bones forms joints
Types
Synarthrotic (Fibrous)
bones are attached by fibrous connective tissue allowing no movement
Ex: sutures of the skull (immovable)
Amphiarthrotic (Cartilaginous)
bones are attached by cartilage connective tissue reinforced by fibrous tissue
allowing little or no movement
Ex: fibrocartilage (intervertebral discs) discs between the vertebra
Diarthrotic (Synovial)
the bones are capped with hyaline cartilage and articulate within a capsule (synovial
capsule) that is lined by a
membrane that secrets a viscous fluid (synovial fluid)
Types of Synovial Joints
Ball and Socket
The ball like head of one bone fits into the socket of another,
Allowing for all movements
Ex: Shoulder and Hip joints
Hinge
A rounded, C-shaped surface of one bone swings about the rounded surface of the
other
Permitting only flexion/extension
Ex: elbow, ankle and interphalangeal joints
Saddle
The concave surfaces of 2 bones articulate.
Allowing for all movements, although rotation is limited
Ex: carpometacarpal joint of the thumb
Condyloid (Ellipsoid)
This is a portion of a ball and socket joint, in which rotation is not allowed.
Ex: radiocarpal joint (the wrist)
Pivot
A ring of one bone rotates about the process of another bone. Only rotation is
permitted.
Ex: the atlas and axis
Irregular (Gliding)
2 opposing surfaces of bone glide across one another
Ex: carpal joints
Kapit & Elson, 1993
Motions Defined
Sagital Plane
Flexion- joint angle decreases
Extension -joint angle increases
Dorsi-flexion- movement of the foot upward
Plantar-flexion- movement of the foot downward
Frontal Plane
Adduction- movement toward the midline or central axis of the body
Abduction- movement away from the midline of the body
Inversion- movement of the sole of the foot toward the midline
Eversion- movement of the sole of the foot away from the midline
Lateral Flexion- (R or L) - side bending of the head or trunk
Elevation- movement that raises a segment, usually refers to the scapula
Depression- movement that lowers a segment usually refers to the scapula
Upward Rotation- a twist about an axis on the scapula, toward pointing the glenoid
cavity up
Downward Rotation- a twist about an axis on the scapula toward pointing the
glenoid cavity down
Transverse Plane
Medial Rotation- inward (toward midline) rotation of a segment about its long axis
Lateral Rotation- outward (away from the midline) rotation of a segment about its
long axis
Rotation (R or L)- rotation of a segment (trunk or neck)
Horizontal Flexion- Flexion in the Transverse Plane
Horizontal Extension- Extension in the Transverse Plane
Pronation-rotation about the radioulnar joint toward the midline
Supination- rotation about the radioulnar joint away from the midline
Protraction- forward rotation of a segment (scapula)
Retraction- rearward rotation of a segment (scapula)
General
Circumduction- movment of a segment in such as way that it describes a cone with
the proximal end forming the
vertex.
Ex: a combination of Flex/Ext and Add/Abd
Hyperextension- extension of a joint in such a way as to exceed a joint angle of 180
degrees
Hyperflexion- flexion of a joint beyond the normal range of motion
Planes and Axes
Classification
Fibrous Irregular Hinge & Pivot Condyliod & Saddle Ball & Socket
Number of Planes 0
0
1
2
3
Number of Axis
0
1
2
3
0
MACHINES
Types of Machines in the Body
1. Levers
2. Pulleys
3. Wheel and Axle
Function - Any machine may be described as having one or more of these four functions
1. To balance 2 or more forces (e.g. levers)
2. To provide an advantage in force (e.g. wrench vs screwdriver
3. To provide an advantage in the range of linear motion and speed of movement
4. To change the effective direction of the applied force (e.g. pulley)
Mechanical Advantage
1. Refers to an advantage in muscle, where the muscle force applied is less than the
resistance moved
2. Can be greater than, equal to or less than one.
MACHINES
Levers - Are a simple machine with 5 components
1. Fulcrum - the axis of rotation
2. Point of force application (F)
3. Point of opposing force application (resistance- R)
4. Moment Arm associated with the force (FA)
5. Moment Arm associated with the resistance (RA)
Levers-Moment Arms
1. are the physical connections between the fulcrum and the points of both force
applications (F and R)
2. are measured as the perpendicular distance from the line of action of the force (or
resistance) to the axis of
rotation
Levers
1. Lever systems only act in rotational motion and as such the lines of force (F and
R) cannot pass through
the axis of rotation if motion is to occur. Any force that acts through the axis of
rotation will not produce a
moment
Levers - Moment Arms
1. Force Moment Arm (FMA) - the perpendicular distance from the axis of
rotation to the line of action of the
force
2. Resistance Moment Arm (RMA) - the perpendicular distance between the axis
of rotation and the line of
action of the resistive force
Levers 1. The product of the magnitude of the force and its moment arm is the rotary effect
of that force - moment or
torque
2. The mathematical expression for a lever system in equilibrium is:
(F)(FMA) = (R)(RMA)
Levers - When classifying levers we only need to look at 3 of the 5 components (there
are 3 classes)
1. the point of force application (F)
2. the point of resistance application (R)
3. the fulcrum or axis of rotation (A)
Levers - Classes
1. First Class - ( Most Efficient)
A) The fulcrum always lie between the force and resistance (F-A-R)
B) A first class lever performs all four machine functions
1. Balances forces
2. Changes direction of applied force
3. Modifies force (e.g increases force)
Note: Longer FMA
4. Modifies speed and/or range of motion
Note: Longer RMA
C) Examples
1) Force = Neck Extensors
Axis = Atlas Vertebrae
Resistance = Head Weight
2) Other First Class Examples
Force = Triceps Brachii
Axis = Elbow Joint
Resistance = Weight in hand
3) Example 3
Force = Calves
Axis = Ankle Joint
Resistance = Foot pedal
2. Second Class
A) Resistance is in the middle
1) Force - Resistance - Axis (F-R-A)
2) The Force arm is ALWAYS longer than the Resistance arm
3) The lever type only favors force production
4) Examples a) Wheelbarrow
b) Door
c) Rowing a boat
5) Body Examples
a) Toe raise
Force = Calves
Resistance = Body weight
Axis = Ball of the foot
b) Example Two - A Push-up
Force = Arms
Resistance = Total body weight
Axis = Feet
3. Levers - Third Class
A) Force is in the middle
1) Resistance - Force - Axis (R-F-A)
2) The Resistance arm is ALWAYS longer than the Force arm
3) Third Class (Least Efficient)
4) This lever type provides an advantage in the range of linear motion and
speed of movement
5) Examples a) Racquets
b) Bats
c) Deep sea fishing
6) Body Levers - Third Class (Most Common in the human body)
a) Example- Bicep Curl
Axis = Elbow
Force = Brachialis
Resistance = Weight in the hand