Introduction Flashcards
1
Q
Role and function of human bones
A
- Provides mechanical support
- Produces red blood cells
- Protects internal organs
- Provides rigid mechanical links and muscle attachment sites
- Facilitates muscle action and body movement
- Serves as active ion reservoir for calcium and phosphorus
2
Q
Composition and Structure of Bone
A
- Inorganic Components (e.g., calcium and phosphate) 65-70% Dry Weight
- Organic Components (e.g. Collagen) 25-30%Dry Weight
- Water (25-30%)
- protein matrix (mainly collagen) upon which calcium salts (especially phosphate) are deposited (25-30% of dry weight)
- bone salts ≈ 65-70% of dry weight
- osteocollagenous fibers determine strength and resilience
- osteon (haversian system) - basic structural unit of bone
3
Q
Bone remodeling process
A
*Continues
Bone remodeling also help maintain mineral homeostasis by transferring calcium and other ions into and out of bone.
Osteoclasts and osteoblasts are the major cell types involved in bone remodeling.
Osteoclasts erode bone matrix whereas osteoblasts secrete it.
The epiphyses, or epiphyseal plates, are growth centers where new bone cells are produced until the epiphysis closes during late adolescence or early adulthood.
The inner layer of the periosteum, a double-layered mem-brane covering bone, builds concentric layers of new bone on top of existing ones specialized cells called os-teoblasts build new bone tissue and osteoclasts resorb bone tissue.
4
Q
Biomechanical Characteristics of Bone
A
- Physical Activity
- Lack of Activity
- Gravity
- Hormones
- Age & Osteoprosis
- Bone Deposits (myositis Ossificans)
5
Q
Bone Response to Stress
A
- bones respond to certain kinds of training by hypertrophying
- Wolff’s law, the densities, and to a lesser extent, the sizes and shapes of bones are de-termined by the magnitude and direction of the acting forces
- Increased or decreased mechanical stress leads to a predominance of osteoblast or osteoclast activity, respectively.
- osteoporosis –increase porosity of bone, decrease in density and strength, increase in vulnerability to fractures
- piezoelectric effect – electric potential created when collagen fibers in bone slip relative to one another, facilitates bone growth
- use of electric and magnetic stimulation to facilitate bone healing
• shape of bone reflects its function
o tennis arm of pro tennis players have cortical thicknesses 35% greater
than contralateral arm (Keller & Spengler, 1989)
6
Q
Types of Bone
A
- axial skeleton
- appendicular skeleton
- Long Bones
- Short Bones
- Flat Bones
- Irregular Bones
- Sesamoid Bones
7
Q
axial skeleton
A
skull, thorax, pelvis, & vertebral column
8
Q
appendicular skeleton
A
upper and lower extremities
9
Q
condyle
A
- a rounded process of a bone that articulates with another bone
- e.g. femoral condyle
10
Q
epicondyle
A
- a small condyle
* e.g. humeral epicondyle
11
Q
facet
A
- a small, fairly flat, smooth surface of a bone, generally an articular surface
- e.g. vertebral facets
12
Q
foramen
A
- a hole in a bone through which nerves or vessels pass
* e.g. vertebral foramen
13
Q
fossa
A
- a shallow dish-shaped sec-tion of a bone that provides space for an articulation with another bone or serves as a muscle attachment
- glenoid fossa
14
Q
process
A
- a bony prominence
* olecranon process
15
Q
tuberosity
A
- a raised section of bone to which a ligament, tendon, or muscle attaches; usually created or enlarged by the stress of the muscle’s pull on that bone during growth
- radial tuberosity
16
Q
Long Bone Structure
A
- cortical or compact bone
- (porosity ~ 15%)
- periosteum: outer cortical membrane
- endosteum: inner cortical membrane
17
Q
Mechanical Loading of Bone
A
• elasticity: ability to return to normal state after stretch
elastic limit: stretch beyond this limit will cause permanent damage
• plasticity: stretched too far such that does not return to its normal state
18
Q
Stress-Strain Relationships
A
- Elastic modulus – slope of the stress-strain curve in the elastic region (measure of stiffness)
- Plastic modulus – slope of the stress-strain curve in the plastic region
- Area under stress strain curve is measure of energy absorbed
19
Q
Behavior of Bone Under Compression
A
- under compression structure shortens and widens
- maximum compression stress occurs on plane perpendicular to applied load
- failure mechanism is mainly oblique cracking of osteons
- example: fractures of vertebrae weakened by age, fracture of femoral neck
20
Q
Compressive Loading-Vertebral fractures
A
cervical fractures: spine loaded through head
e.g., football, diving, gymnastics, once “spearing” was outlawed in football the number of cervical inju-ries declined dramatically
lumbar fractures: weight lifters, linemen, or gymnasts: spine is loaded in hyperlordot position
21
Q
Tensile Loading
A
Main source of tensile load is muscle.
Tension can stimulate tissue growth.
Fracture due to tensile loading is usually an avulsion. Other injuries include sprains, strains, inflammation, bony deposits.
When the tibial tuber-osity experiences excessive loads from quadriceps muscle group develop condition known as Osgood-Schlatter’s disease.
22
Q
Behavior of Bone Under Shear
A
- created by the application of compressive, tensile or a combination of these loads
- deformation occurs internally in an angular manner
- note that tensile and compressive loads also produce shear stress
- clinically shear fractures are most often seen in cancellous bone
- examples: femoral condyles and tibial plateau
23
Q
Behavior of Bone Under Bending
A
- bending subjects bone to a combination of tension and compression (tension on one side of neutral axis, compression on the other side, and no stress or strain along the neutral axis)
- magnitude of stresses is proportional to the distance from the neutral axis
24
Q
Behavior of Bone Under Torsion
A
- Caused by a twisting force
- produces shear, tensile, and compressive loads
- tensile and compressive loads are at an angle
- often see a spiral fracture develop from this load
- load applied to cause twist about an axis
- magnitude of stress proportional to distance from neutral axis
- shear stresses distributed over entire structure
- maximal shear stresses act on planes parallel and perpendicular to neutral axis
- clinically bone fails first in shear with initial crack parallel to neutral axis; second crack along plane of max-imum tension
25
Synarthrosis (fixed)
Structural Name : Fibrous
Degree of movement: Fixed
Example: Skull
Synostosis: the degree of movement is null, because these joints unite using bone(pelvic bones).
Synchondrosis: the degree of movement is low, because these joints unite through thick cartilage (sternal ribs).
Synfibrosis and syndesmosis : the degree of movement is limited, because these are held together by fibrous connective tissue (symphysis pubis).
26
Amphiarthrosis
Structural Name : Cartilage
Degree of movement: Slightly mobile
Example: Spine
27
Diarthrosis
Structural Name : Synovial
Degree of movement: Very mobile
Example: Shoulder
```
Consists of the following:
• Joint cavity with synovial fluid
• Synovial membrane and capsule
• Surrounded by ligaments for support
• The bone coated by articular cartilage
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28
Types of Diarthrosis
Arthrodia:
It can be found in the hand, metacarpal, foot and metatarsal joints.
There are zero degrees of freedom for movement.
Trochlea Arthrosis:
Found in knee, humero-ulnar joint, interphalangeal joints
There is one degree of freedom for movement.
Trochoid:
Found in: articulation of the proximal and distal radio-ulnar, tarsometatarsal. There is one degree of freedom for movement.
Saddle:
Two Degree of freedom
Example: trapezoid-metacarpal joint
Condylararthrosis
Example: metacarpophalangeal joints
Radio carpal joint
Two Degree of freedom
Enarthrosis:
Most moveable 3 degrees of freedom
Example: glenohumeral joint and hip joint
Amphiarthrosis:
Example: Sacroiliac joints and the Proximal tibiofibular joint
29
Function of articular fibrocartilage
* distributing loads over joint surfaces
* improving the fit of articulations (very important for stability)
* limiting slip between articulating bones
* protecting the joint periphery
* lubricating the joint
* absorbing shock at the joint
* It is impossible to replicate currently.
30
Composition of articular cartilage
Chondrocyte: sparsely distributed cells in articular cartilage the amount of the cartilage made from chondro-cytes Is less then 10% of the tissue volume.
Collagen: Most abundant protein in the body. It provides structural organization of the fibrous ultrastructure. Its basic biological unit is tropocollagen. The most important mechanical properties of collagen is the tensile stiffness and strength.
Proteoglycan (PG): protein-polysaccharide molecules monomers or aggregates
Water: Most abundant component in the articular cartilage. The concentration is 80 % in surface and de-crease linearly in the different zone and it to reach 65% in the zone deep. The water play a role of exchange between the synovial fluid and the chondrocytes. A large quantity of water be extra-cellular which allow to himself associate with fibrilla of collagen and to play a role mechanical.
* important to know that chondrocyte are only 10% and water is 80%
31
Biomechanical behavior of articular cartilage
* Fluid phase & solid phase
* Highly stressed material ( can resist Compression tension and shear)
* Nature of articular cartilage viscoelasticity
* The articular cartilage is regarded as a porous medium filled of liquid. (like a sponge filled with water)
* A material viscoelastic change its behavior mechanical according to rate of application of load
* The behavior of a material viscoelastic is the creep and the stress relaxation.
* The stress relaxation: is the deformation is constant and load is measured (decreases) in func-tion of time
* Creep: is when load remains constant and the deformation is measured in function of time
* Permeability due to water and proteoglycan
* Articular cartilage is a highly porous material and low permeability.
32
Lubrication of Articular Cartilage
From an engineering perspective, two types of lubrication
- boundary lubrication
- fluid film lubrication: when the load is applied the pressure is dissipated with out modifying the mechanical re-sistance of the cartilage
33
Wear on articular cartilage
Can happen with fatigue, age and interfacial wear. We main types of wear fatigue and interfacial.
• Interfacial wear: occuring when bearing surfaces come into direct contact with no lubricant film separating them
o adhesive wear
o abrasive wear
• Fatigue wear: not from surface to surface contact but from the accumulation of microscopic damage within the bearing material under repetitive stress
three mechanisms
• Repetitive collagen-PG matrix stress could disrupt the collagen fibers, the PG macromolecules, or the in-terface between the two.
• Repetitive and massive exudation and imbibition of interstitial fluid may cause a PG washout from the carti-lage matrix near the articular surface, with a resultant decrease in stiffness and increase in permeability of the tissue.
• When associated with synovial joint impact loading
34
Ligaments
functions are:
o Maintain a good position of the joint in the posture
o Connect bone to bone (example knee See picture to right)
o Augment mechanical stability of joints and define guide motion
o Prevent excessive motion
o This is why when there is a ligament tare we have increased movement in the joint. We get joint instability. Surgery is needed to regain stability to return to normal function
35
Tendon
Function:
• Attach muscle to bone
• Position muscle belly in optimal position with respect to joint
o There is a relationship of the size of the muscle belly and the length of the tendon. If we change the relationship you will rupture the tendon
36
Outer structure and insertion into the bone:
It is hard to replicate because in as small as a micron. When we look at the bone attachment we move from the bone to the collagen fibers. These area is call enthesis.
Differences related to function of outer Structure of ligament and tendon:
o both are surrounded by a loose areolar connective tissue
• In tendon : called as the paratenon more structured than that of ligaments forms a sheath
• to protects the tendon
• to enhances gliding
37
Unloaded collagen fibers
have a wavy configuration
38
Loaded collagen fibers
straighten out
39
Maturing and aging
* During maturation (up to 20 years of age), the number and quality of cross-links increases, resulting in in-creased tensile strength of the tendon and ligament.
* The collagen content of tendons and ligaments also decreases during aging contributing to the gradual de-cline in their mechanical properties.
40
Nonsteroidal anti-inflammaroty drugs (NSAD)
Short term administration of NSAIDs would not be deleterious for tendon healing but rather would increase the rate of biomechanical restoration of the tissue.
41
Mobilization and Immobilization
Like bone, ligament and tendon appear to remodel in response to the mechanical demand (ex. Astronaut) Physical training has been found to increase the tensile strength of tendon and the ligament-bone interface.
42
Kinematic Chains
A combination of several joints uniting successive segments constitutes a kinematic chain.
43
Biomechanics of Movement
Biomechanics is the application of mechanical principles to biological systems.
o Human Biomechanics of Movement
• It is a multidisciplinary science that is interested in the study of the movement of the human body as a whole and segments of it.
o Two types of movement
o Kinetic
• It studies the forces determining the movement of bodies
o Kinematic
• It studies the geometry and the movement of space-time motion of a body
o Axis of Motion: change of position of a body in space according to the Cartesian coordinate system
o "x", frontal axis through the center of gravity (CG) of the body from left to right
o"y", longitudinal axis through the CG of the body from back to front
o"z", sagittal axis through the CG of the body from bottom to the top
Planes divided by the axis
o Transverse plane divides the body into 2 asymmetric halves: the upper & lower hemi-body
o Sagittal plane divides the body into two symmetrical halves: left and right
o Coronal plane divides the body into two asymmetric halves: the anterior and posterior
44
Types of Movement
o Translational Motion: all points along the body at the same time, the same distances in the same direction they have the same displacement vector
o Rotatory Motion: all points of a body run through the same angle, in the same direction at the same time.
o Natural Human Motion: There is always a combination of rotational and translational motion. Abduc-tion and adduction, Flexion and extension,
Rotation. These can all happen when we take into consider-ation the axis and plane.
45
Examples of Natural Human Motion
o Abduction and adduction: Motions that occur on the frontal plane around a sagittal axis
• Abduction occurs when an extremity (arm or leg) or part of an extremity (hand, fingers, etc.) is moved away from the center or midline of the body
• Adduction occurs when an extremity or part of an extremity is moved toward the midline
o Flexion and extension: Motions that occur on the sagittal plane around the frontal axis
• Flexion: describes the bending of a joint on the plane so that the joint angle is smaller
• Extension: describes the bending of a joint on this plane so that the joint angle is larger
o Rotation: Motions that occur on the transverse plane around the longitudinal axis
• Internal rotation describes turning motions toward the midline
• External rotation describes turning motions away from the midline of the body
