Tissue Mechanics and Injury Flashcards
Describe the three zones in articular cartilage.
Zone 1: parallel fibers, smooth, reduced friction, distribute forces
Zone 2: mesh-like to hold water, absorbs compression
Zone 3: perpendicular, securely holds the calcified cartilage
What is active tension? What does it depend on?
Developed by the active contractile elements of the muscle
Depends on more cross-bridges being formed, by:
- Frequency of motor unit firing
- Numberofmotorunitsfiring
- Sizeofmotorunitsfiring
- Diameter of the axon in motor unit (conduction velocity)
Describe the basics of muscle breakdown. How can age, immobility and injury, individually affect muscles. Give three possible pain mechanisms.
Age: reduced cross sectional area (# and size of fibers), decreased ROM and power
Immobility: decreased force production (smaller fibers, impaired activation)
Injury: decreased force production (damaged sarcomeres, pain inhibition)
Possible pain mechanisms
• Reflex inhibition of motor units (to prevent further injury)• Central descending inhibition of injured muscles
• Decreased motivation (cognitive effective)
Is the healing process made of clear steps of is it more of a continuum? Explain.
The healing process is a continuum
Not distinct phases
The healing process overlap one another
No definitive beginning or end points
What is bone composed of? What are its two layers and two types of cells?
- Primarily type I collagen
- Mineral (Ca2+)
Two layers:
• Cancellous (spongy)
- Compact (cortical)
- Osteoblasts versus osteoclasts
What are the different structural properties that a tissue can have? What does a steep stress/strain curve represent? A gradual curve?
• The slope of the line represents the stiffness and compliance of the tissue
- Steep curve: high stiffness, low compliance
- Gradual curve: low stiffness, high compliance
What are the intrinsic, systemic and extrinsic factors that impact healing?
INTRINSIC
Extent of Injury
Edema
Hemorrhage
Poor vascular Supply
Tissue Separation
Muscle Spasm
Atrophy
Scarring
SYSTEMIC
Age
Obesity
Malnutrition
Hormone
Levels
Infection
General Health
EXTRINSIC
Drugs
Dressings
Temperature
Physical
Modalities
Exercise
Give the roles of white blood cells in general/ of leukocytes
- White blood cells – involved in the inflammatory process and categorization depends on the type and age of injury, or if bacteria present
- Mononuclear Leukocytes (agranular): monocyte/macrophage, lymphocyte
- Polymorphonuclear Leukocytes (granular): eosinophil, basophil, neutrophil
What are the signs and symptoms of the fibroblastic repair phase? What are the two main things that are happening during this phase?
- Signs and symptoms include:
- Touch tenderness, pain with stretch to injured site
- Disappears with scar formation
- Deposit new material to reconstruct the injured tissue
- Formulate granulated tissue (highly vascularized)
- Revascularization
- Scar Formation
How are differences in stress-strain determined in ligaments? What happens to ligaments when then have intermittent tensile loads? Are ligaments more, equally or less resistant to tensile stree that tendons? Why?
Differences in stress-strain reflects varied proportion of collagen and type
Similar mechanics to tendons
Increased thickness and strength with intermittent tensile loads
Slightly less resistant to tensile stress than tendons because they must be oriented in multiple directions (but withstand a wider variety of force directions)
Describe the basics of ligaments breakdown.
What happens to its physical properties? What could an external load do to a ligament?
Insertion sites weaken with age, reducing strength and stiffness of tissue
Very sensitive to loading and loading history – without load rapid deterioration of biochemical and mechanical properties (reduced strength and stiffness)
When a ligament is taught for a particular joint position, an external load that results in any deformation of the tissue will exceed the elastic state and the ligament will fail
Ex: ACL tears - stops the tibia to sliding forward on the femur. ACL becomes very tight when you plant your foot on the ground, so if it gets hit at that same time (external load), we will see a tear (ex: soccer)
Describe the behavioural properties (3)
Structural Properties
- Load, force and elongation
- Stress and Strain
Viscoelasticity
Time/Rate-Dependent Properties
- Creep
- Stress Relaxation
- Strain Rate Sensitivity
What are some examples of inert structures? Describes one way that pain can increase in these structures.
- Ligaments, bursae, fascia, nerve roots, capsules, dura mater
- Non-contractile
- Pain is provoked by stretching the tissue
- Pain increases with ACTIVE AND PASSIVE movements (often end-range)
- In the SAME direction
- Resisted movements are not painful
What are some examples of contractile structures? Describes two ways that pain can increase in these structures. Give an example
- Muscle, tendon, tendon-periosteal (TP) junction
- Pain increases with ACTIVE AND RESISTED movements
- In the SAME direction
- Pain increases with PASSIVE movements
- In the OPPOSITE direction
- E.g., painful active and resisted elbow flexion, and passive elbow extension
What are the characteristics of a resting position of an articular joint? Would we see a CPP or a LPP?
- A specific loose packed position
- Minimal congruency between surfaces
- Capsule and ligament have greatest laxity
- Passive separation of joint surfaces, therefore greatest swelling
• Usually the mid-position for the joint
Describe the four stages of bone healing
What is the maturation phase? What is its timeframe? What happens to fibers? What is the apperance of the wound at this point?
Long-term process (3 week to multiple years)
Realignment collagen fibers (no new)
Increases in stress and strain to realign for maximum tension efficiency (more cross-linking bonds)
Fibers to orient themselves along stress line
Normal appearance and function but rarely as strong as the original tissue
Describe the composition of tendons (bone to muscle)
- Similar make up as ligaments
- More type I collagen thought to be an adaptation to larger tensile forces
- Primarily aligned in one direction
Whats is a fibrocartilaginous junction? What is its function?
Gradual change in tendon structure, divided into four zones
Diffuses the load at the tissue-bone interface, perhaps to help prevent injury
What is the difference in cartilage healing between an injury that doesn’t reache the subchondral bone and one that does? Why?
Does not reach the subchondral bone (there is no vascular supply!): becomes necrotic, no healing
If the subchondral bone is reached: access to blood supply
• May resemble healthy tissue, but biochemically and mechanically differ
Fibrillation, fissures and degenerative changes occur
What is the inflammatory response? What is its timeframe? What are its clinical signs? What happens, at the tissue level, during the inflammatory response?
Early, almost immediate response to the injury
0 to 4 days
A protective response intended to eliminate the initial cause of cell injury as well as the necrotic tissues resulting from the original injury
Clinical signs of acute inflammation:
HEAT, REDNESS, SWELLING, PAIN, LOSS OF FUNCTION
Direct injury to the cells that disrupts blood vessels
Immediate coagulation and development of a fibrin clot leading to homeostasis of the injured tissue
Platelets release chemical messengers that change the metabolism of the tissue and initiate the inflammatory response
The later stages of healing can only occur once the inflammatory phase occurs
What are the two main fibrous components of the ECM? One of them has two types, name and describe them.
• Fibrous Component
Collagen – white fibrous, steel-like
strength, rigid
Elastin – yellow fibrous, elastic properties
- Collagen type 1: thick fibers, little elongation• Resists tensile forces well
- Collagen type 2: thinner, less stiff fibers• Resists compression and shear
How is a scar formed?
- Initial fibrin clot breaks down and granulation tissue created
- Fibroblasts, collagen and capillaries (highly vascularized, connective tissue)
- Reddish granular mass filling in the gaps during healing
- Capillary growth accumulates fibroblasts -> ECM synthesis
- Collagen deposited randomly but increases strength of scar (proportionately)
- Fibroblasts diminish with increases in strength (Less collagen that is being laid down)
What are the two characteristics of the cellular response during tissue injury?
Describe the physiology of what happens and the two cell movements that we see in each characteristic.
a) WBCs (white blood cells) leave the vessels moving into the tissues (extravascular space)
• Triggered by chemical mediators supporting dilation and permeability
- Margination: leukocytes adhere to the endothelial cell well of vessel
- Diapedesis: squeezing between cells to leave the vessel
b) Seek and destroy foreign substances
- Chemotaxis: chemical gradient attracts leukocytes to injury site
- Phagocytosis: recognize foreign substance (e.g., bacteria), engulf, degrade
Describe the composition of ligaments (bone to bone)
Cells make up 10-20%
ECM makes up 80-90%
Primarily composed of type I collagen fibrils that are densely packed into fiber bundles arranged in line with the applied tensile force
Depending on the ligament there may be varying directions of tensile force therefore ligaments run in multiple directions (e.g., MCL)
What are some tissue modifiers?
- Age
- Immobility
- Disuse
- Injury
- Medication
• Pain
What is a tissue?
• An aggregate of cells that have similar structure and function
What is the maturation remodeling phase? Use a graph to describe it.
What is passive tension What happens when the muscle is stretched?
Tension developed by passive, non-contractile components of muscle
Parallelelasticcomponents
When the muscle is stretched they resist and contribute to the tension (only in tension stretch not shortening)
- Epimysium
- Perimysium
- Endomysium
Series elastic component
• Tendon (stretch exerts a pull on the tendon)
What are the three types of contractions that a sarcomere can do?
Concentric
Eccentric
Isometric
Give a definition for angiogenesis. What causes it? What has to happend to lead to revascularization (4 steps)?
• Angiogenesis: lack of oxygen stimulates growth of endothelial capillary buds into the wound
The wound can then heal aerobically; increased oxygen delivery
Blood flow to deliver nutrients for tissue regeneration in the area
Vessels tend to be leaky so the tissue appears wet
- Proteolysis of basement membrane
- Migration and chemotaxis at the capillary tip
- Cell proliferation
- Increased permeability through gaps
Describe the basics of cartilage breakdown.
What happens when there’s a lack of cyclical loading? How can it affect other tissues, e.g. bones?
Disruption of synthesis and degradation in the ECM (softening)
Lack of cyclical loading (immobility, bed rest) deprives tissue stresses required for healthy function
• Decreased stress leads to changes in collagen (weaker bonds and unorganized structural changes)
Abnormal force transmission
Less water, increased stiffness, more force translated to other tissues (e.g., bone) and experiences earlier plastic zone
What happens as a muscle is being pulled apart?
When the muscle is being pulled apart, increase stretch
Passive increases while active decreases, but the overall tension increases as the muscle gets longer
At the black circle: total tension can become stronger than just with active tension
When muscle is shortened: everything is so tightly put together that there is no room to shortnen more, to contract
How are contractile tissue fibers grouped? What composes a myofilament? What is a cross-bridge?
- Thousands of fibers grouped into:
- Fascicles
- Myofibrils
- Myofilaments
- Myofilaments: actin, myosin, troponin
- Cross-bridge: Action potential releases Ca2+ to expose binding sites between actin and myosin
What is muscle tension? What is the optimal length, and what happens when a muscles in longer or shorter than its optimal length?
Direct relationship between tension development and muscle length
Optimal length: capable of developing a maximal tension
As a muscle is lengthened or shortened from the optimal length, the amount of tension generated is diminished
Shorter muscle, or too stretched = smaller ability to create a big tension
Passive (green) line in the graph: only contributes to shortening, not lengtening
What are different kinds of strains that we can do to a tissue?
What is the fibroblastic phase (scar forming)?
What is its time frame?
What are the two different possible pathways of scar forming? Which is the most common one? The fibroblastic phase depends on two things… what are they?
Begins within hours to days post-injury
2 days to 6 weeks
Either a REGENERATIVE process to replace necrotic cells with new cells of the same type; OR a REPARATIVE (generally what we see, more common) process to replace necrotic cells with collagen and form scar tissue (type I and III collagen)
Dependent on:
• the extent of the injury (severe vs. mild)
• type of tissue (if its cells can divide or not)
What is a quantitive way to describe the levels of tendon/ligament breakdown?
What are fibroblasts? What are their functions in injury?
Flat shaped cells in the dermis of skin and structural tissues including ligaments and tendons
Function in injury:
Synthesize collagen for wound closure (forming scar)
ECM remodeling – degradation and production of collagen
Which chemicals are released because of cell damage during the inflammatory phase, and what do they do?
What are the two types of response that we can observe?
• Injury to the tissue results in damage to the cells -> release of chemicals
- E.g., bradykinin and histamine
- Releases with injury, triggering free nerve endings, ↑ pain
- Triggers the inflammatory response (2), until:• Stimulus is removed
- Inflammatory mediators are eliminated
Vascular Response
Cellular Response
What is the extracellular matrix composed of (ECM)? What are its roles?
Non-fibrous component (Glycoproteins & Proteoglycans)
- Attracting and binding water
- Supporting substance for fibrous and cellular components
- Contributes to overall strength of connective tissue thereby protecting it
What is a musculotendinous junction?
Muscle cells intertwine with the tendon
Very sensitive to mechanical conditions and becomes flatter with low load
Weakens the junction increasing susceptibility to injury
Loading caution post-immobilization
Describe what happens during the cross bridge cycle.
How does homeostasis affect the inflammatory response during tissue healing?
- Within seconds, to stop blood loss
- Reflexive and transient vasoconstriction (decrease vessel size) -> allows the platelets to build up at the site of the injury, behind the vasoconstriction, and they start binding to the collagen, which generates a snowball effect to recruit more collagen
- Clot formation
- Adhesive platelets – to collagen molecules exposed by injury
- Plug formation – accumulated platelets
Describe the anatomy of a contractile unit (sarcomere).
- The arrangement is regular to give stripped appearance “striated muscle”
- (I) only actin, (A) actin and myosin (H) only myosin
Give some examples of types of bone fractures.
