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
Base of Support (BOS)
· All points at which the body contacts a supporting surface (ex: sitting in chair- ischial tuberosity, butt, feet on floor, etc)
· Equilibrium occurs when COM is within BOS
Resultant Joint Force (RJF) / Joint Reaction Force (JRF)
· Net muscle forces and bony contact forces (primary internal forces) acting at a joint
Torque Formula
· Torque = Force x Moment Arm
** Angle at which force is applied and muscle attaches to bone is CRITICAL for Net Torque**
· Internal Moment Arm: distance from internal force/ tendon insertion to joint (axis of rotation)
ex: distance from bicep tendon insertion to elbow joint
· External Moment Arm: distance from external force to axis of rotation
(ex: distance from free weight in hand to elbow joint)
** Longer moment arm = greater torque
* Internal torque > external torque in order to lift a weight
* Force that passes through axis of rotation does not produce torque (bc moment arm = 0)
Translation vs Rotation
· Translation: linear motion where all parts of body move in same direction (parallel) to other parts of body
(ex: skiing down mountain)
· Rotation: angular/circular motion about a pivot point where all points in body rotate simultaneously in the same angular direction (CW vs CCW)
(ex: tumbling down mountain)
Normal vs Tangential (Compression and Distraction) Force
· Normal Force: acts perpendicular to body segment
- creates a moment/torque, AKA moves the joint
· Tangential Force: acts parallel to a segment (acts along the axis)
- Compression forces stabilize a joint
* PT application: WB through arm to compress shoulder to promote muscle recruitment
- Distraction forces create traction (pull away from each other)
* PT application: cervical traction
MSK Levers
· 1st Class: axis of rotation is in the middle of opposing forces
(ex: c-spine axis of rotation in between extensors/internal moment arm and head weight/external moment arm)
· 2nd Class: axis of rotation is at one end of bone and muscle has greater advantage
- Internal Moment Arm > External Moment Arm
- ex: Calf raise bc GSC is at advantage over gravity
· 3rd Class (MOST COMMON): axis of rotation at one end of bone and external force has greater advantage over muscle
- External Moment Arm > Internal Moment Arm
- ex: 90° elbow flexion and holding a dumbbell
Mechanical Advantage
· Ratio of internal moment arm (IMA) to external moment arm (EMA)
· Most muscles are at mechanical disadvantage (EMA > IMA)
Force-Couples
· 2 or more muscles contract simultaneously and produce SAME amount of force but in OPPOSITE direction
· ex: opening a jar, turning a steering wheel
-ex in the body: PPT where hamstrings pulls ischial tuberosity down, rectus abdominis pulls pubic symphisis up
ECM Components (Fibers, Fluid, and Ground Substance)
1) Fibers (Collagen, Elastin)
2) Proteoglycans (PGs)
· Aggrecan: main PG in articular cartilage for skeletal growth and function
3) Glycosaminoglycans (GAGs)
· Hydrophillic
· Stiff and inflexible
· Resist compressive forces in cartilage
· Ex: Hylauronic Acid combines with PGs to resist compressive forces in cartilage, high vsicosity to lubricate synovial joints
4) Tissue Fluid
5) Glycoproteins
· Allow adhesion of fibroblasts, chrondroblasts/cytes, osteoblasts/cytes
· ex: laminin, fibronectin
- Ground Substance is PGs, GAGs, and Glycoproteins
Elastin
· High recoil (but decreases with age)
· In tissues that accommodate large volume changes (ex: ligamentum flava (in SC) arteries, bladder, uterus, aorta)
· Thinner than collagen, yellow
Attenuation and Radiodensity
· Attenuation: Reduction of x-ray beam as it traverses matter
(ex: bone attenuates (absorbs) matter greater than air)
· Radiodensity: determined by how tissue attenuates/absorbs x-ray signal (ex: bone attenuates more than air and thus has higher radiodensity and appears whiter on film)
ABCS of Radiography (X-Rays and CT)
·A: Alignment
- skeletal alignment, joint alignment
- Can identify fractures, spurs, etc
·B: Bone integrity/density
- excessive sclerosis (bone hardening)
·C: Cartilage Spaces
- joint space
- subchondral bone
·S: Soft Tissues
- joint capsule effusions
- periosteum
- muscle swelling or atrophy
T1 vs T2 Weighting for Imaging
· T1: highlights tissues with high fat content (for good anatomical detail)
- Tissues with quick longitudinal magnetization times will appear brighter (Fat)
·T2: good for detecting inflammation
- Tissues with longer transverse magnetization times will appear brighter (Fluid)
Functional MRI (FMRI)
· Used to visualize blood flow in the brain because blood flow usually follows nerve activity
Ligament Function
· Connects bone to bone
· Made of dense regular connective tissue
· Limits excessive motion
· Guides normal joint movement
· Innervated but limited vascular supply
Tendon Function
· Connects muscle to bone
· Made of dense regular connective tissue
· Transmits force
· Innervated with some vascular supply
Joint Capsule (2 Layers and Function)
· Fibrous Layer:
- Made of dense irregular connective tissue that’s continuous with periosteum
- Surrounds tendons and ligaments that insert near the joint
- Innervated and vascularized
·Synovial Membrane Layer:
- Lines fibrous capsule
- Lubricates joint
- Contains Type A Cells (remove debris, important for inflammation)
- Contain Type B Cell (produce hyaluron and PGs to help lubricate and resist compressive forces)
Cartilage Function
· Load-bearing, resist force in multiple directions
· Mostly avascular (Medial Meniscus is highly vascularized though)
· Dense irregular connective tissue