Exam 4 (Biomechanics) Flashcards
What determines the type and function of connective tissue?
1) Composition and percentage of cells (fibroblasts, chondrocytes, osteoblasts)
2) Extracellular matrix (ECM) components (fibers, proteoglycans, glycoproteins, tissue fluid)
Collagen General Function
· Resists tensile (stretch) forces (minimal elongation under tension)
· Types I- VI are most abundant
Collagen Types (I-IV) , Function, and Synthesis
1) TYPE I: “crimped”/ overlapping layout, resists tensile loads, most abundant
· Bone
· Ligament
· Tendons
· Reinforces Fibrocartilage
· Joint Capsule
· Intervertebral discs
* “Uncrimping” occurs in Toe-region of stress-strain curve
2) Type II: withstands tensile/compressive forces
· Articular cartilage
· Hyaline Cartilage
· Nucleus pulposus
· Eye
· SYNTHESIZED BY: chondroblasts
3) Type III: most pliable, greater ability to stretch, synthesized during wound repair
· Blood vessels
· Bladder
· Uterus
· Skin
· GI Tract
· Embryonic tissue
* Pliable for tissues that need to expand
· SYNTHESIZED BY: Fibroblasts
4) Type IV:
* Separates tissue compartments and surrounds smooth muscle and nerve cells
Collagen Fiber Arrangements/Alignments and Mechanical Stress
· Arrangements/alignment reflects the mechanical stress acting on the tissues
· Can form:
- fibrils to resist tensile loads
- sheets/mesh to anchor/link tissues
Why is re-injury more prominent in early healing stages? (Type III vs Type I Collagen Fibers)
· Type III (more pliable/weaker) is laid down initially and then replaced by Type I (stiff)
Result of Collagen Synthesis
· Formation of Tropollagen (from Procollagen) which joins together to form fibrils with distinct cross bands (transverse and longitudinal)
· Fibrils then form fibers and bundles of fibers
*Cross bands are what provides resistance to tensile loads
Connective Tissue Diseases/Disorders
1) Marfan Syndrome: gene mutation that affects elastin fibers
· Results in lack of resistance in tissues
· Prone to aortic rupture (decreased resistance causes increased risk of rupture)
2) Ehlers-Danlos Syndrome (13 Types): gene mutation that affects Type III collagen
· Joint pain/hyper-mobility/instability/hyper-extensibility/organ prolapse, etc.
3) Osteogenesis Imperfecta (8 Types): genetic mutation of Type I collagen
· Easily fracture bones, bone deformities, barrel-chest, scoliosis, hearing loss, discolored teeth, respiratory issues, short stature, etc
Impact of the Loss of PGs during early stages of Osteoarthritis?
· PGs (combined to hylauronic acid) are lost during early stages of Osteoarthritis resulting in:
- decreased ability of tissue to absorb water - decreased ability to withstand compressive forces
- Increased subchondral bone stress (bone on bone)
Clinical Significance of PGs and early Osteoarthritis
· PGs are lost during early OA
· DECREASED ability of tissues to absorb water and withstand compressive forces results in INCREASED stress on subchondral bone (bone on bone with no cartilage so bones are now weight bearing)
Classification of Connective Tissue
1) Proper
· Dense (Regular vs Irregular)
· Loose
2) Supportive
· Cartilage
· Bone
3) Special Properties
· Adipose
· Hematopoietic
· Mucous
Kinematics vs. Kinetics
· Kinematics: study of motion WITHOUT regard to the forces contributing to that motion
· Kinetics: study of the effect of forces on the body and resulting motions they created
Biomechanics
Forces acting on and with biological systems
Newtons 1st Law of Motion: Law of Inertia
· Law of Inertia: a body will remain at rest or constant motion until acted upon by an external force
· Inertia: Energy required to displace an object/body, directly proportional to object’s mass (ex: bigger person is harder to push over vs. smaller person)
Newton’s 2nd Law of Motion: Law of Acceleration
· Law of Acceleration (Linear): Linear acceleration is directly proportional to the force causing it, occurs in same direction as force, and is inversely proportional to mass of object
· Law of Acceleration (Angular):
Angular acceleration is directly proportional to the torque causing it and inversely proportional to mass moment of inertia
· If acceleration = 0 then sum of forces = 0 (ex: when standing still or moving at constant speed)
* ex: more torque required to push escalade vs. mini cooper)
* Mass moment on inertia changes based on mass distribution around axis of rotation
Newton’s 3rd Law: Law of Action-Reaction
· Law of Action-Reaction: For every action (force/torque) there is an equal and opposite reaction (force/torque)
*ex: force from pt pulling TB apart and force from TB pulling together
* ex: ground reaction force while standing
Internal vs External Force
· Internal: act within the body
(ex: muscles)
· External: Act on the body
(ex: gravity, ground reaction forces, etc.)
Types of Forces on MSK
1) Unloaded
2) Tension (ends pull in opposite directions)
3) Compression (ends push in same direction) (present during weight bearing)
4) Bending (one side stretches and other compresses)
5) Shear (body segments go in opposite directions)
6) Torsion (twist)
7) Combined Loading (combo. of any or all above forces)
Stress-Strain Curve
· Strain on tissue when a stress/stretch/force is applied
· All tissues have this
· 4 Regions:
1) Nonlinear Toe Region: uncrimping of collagen fibers (Type I)
2) Elastic Region/Linear Region: tissue stretches and then returns to original shape
3) Plastic Region: tissue stretches and then change/deformation in tissue occurs
* Ideal region for PTs
4) Ultimate Failure Point: stretch resulting in rupture/damage
Importance of Time on Viscoelastic Tissues during the Stress-Strain Curve
· Viscoelastic tissues change with time during the stress-strain curve
· Slope increases as rate of loading and rate of force increase (how fast/slow a stretch/force is applied)
Ground Reaction Force (GRF)
· Force that is equal and opposite to force exerted by the foot (tri-planar)
Center of Pressure (CoP)
· Point of application of GRF (then needs to be absorbed)
· Multi-directional
· Changes throughout movement
* ex: heel strike during gait means COP at heel
Center of Mass (CoM) vs Center of Gravity (CoG)
· CoM: point where mass is equally distributed
- changes with movement
- depends on shape, mass distribution, and density
- can be inside or outside of object
- Normal CoM: Anterior to S2 (static standing)
* ex: pole vaulting would shift CoM posteriorly
· CoG: point where weight is evenly distributed (balance with response to gravity)
Dense Connective Tissue (Regular vs Irregular)
· Dense Regular: high stress resistance in a SINGLE direction (due to organized collagen arrangement)
- innervated but poorly vascularized
*ex: Tendons and ligaments
· Dense Irregular: mechanical stress resistance in ALL directions and protects organs (due to woven collagen arrangement)
*ex: Fascia, periosteum, peri and endomysium, dermis, glands, organs
Loose Connective Tissue
· Multi-directional stress resistance (NOT mechanical stress) due to meshwork of collagen and elastin arrangement
· Well vascularized and innervated
* ex: Viscera, fascia, endothelia