Chapter Three - Tissue Mechanics and Injury Flashcards
Why is it important to understand the functional demands and the tissues’ response?
Our musculoskeletal systems must adapt in appearance and composition in response to functional demand
These demands can change with immobilization, inactivity, or training
Understanding the functional demands and the tissues’ response, we can modify the stresses on joint structure during rehabilitation to optimize function
What is a tissue?
• An aggregate of cells that have similar structure and function
All joints in the body are composed of what? Give some examples of this type of tissue.
• All joints in the body are composed of connective (inert) tissue
- Bones
- Bursae
- Capsules
- Cartilage
- Discs
- Menisci
- Ligaments
• Tendons
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 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

What are the two cellular components of the ECM? When are they there? Give some examples for each type
• Resident Cells – Always present but depends on tissue
- Fibroblasts (collagen)
- Osteoblasts (bone)
- Chondroblasts (cartilage)
- Circulating Cells – If inflamed or damaged• Lymphocytes
- Macrophages
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)

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 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

What is hyaline cartilage and where can we find it?
Lines articulating bones and distinguishes synovial joints
Type II collagen throughout the ECM and compresses on the proteoglycan (PG) molecules that hold onto water during load
Articular cartilage has much more PG than other joint structures
Limited blood supply, nutrient diffusion with compression
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 fibrocartilage?
Type I > type II collagen
Collagen density to keep the water in the tissue (versus hyaline cartilage that
utilizes collagen and chemical water attraction)
Limited blood supply, nutrient diffusion with compression
E.g., meniscus
• Circumferential fibers (deep zone)• Radial fibers (superficial zone)
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

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 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 different kinds of strains that we can do to a tissue?

Viscoelasticity: give the definition of elacticity, and viscosity. What does an elastic tissue do, and a viscous one?
- Elasticity: returning to the original length or shape of the material after the load has been removed
- Also known as deformation (proportional to the amount of force)
- Elastic tissue: return to resting length when force is removed
- Viscosity: the material’s resistance to flow
- Force applied to viscous material display time/rate dependent properties
• Viscous tissue: creeps under constant load (plastic does not return shape)
What are the three time/rate dependent porperties? Give a small definition for each
- Creep: continuous change in shape with prolonged force application
- Stress Relaxation: a tissue is stretched to a fixed length and held constant, the force needed to maintain that length reduces over time
- Strain-Rate Sensitivity: more force is required to deform a tissue rapidly versus slowly

Which type of bone withstands greater force with less deformation than the other? What does frequent loading of low magnitude do to a bone? What about a single load of high magnitude?
- Cortical bone withstands greater force with less deformation than cancellous bone
- Greater compression versus tension
- The amount of strain required to reach failure (fracture) is less in cortical bone
- Frequent loading of low magnitude: stress fracture
- Single load of high magnitude: complete failure (fracture)
How are differences in stress-strain determined in tendons? What does continuous compression do to a tendon? What does tensile loads over long periods of time do?
Differences in stress-strain reflects varied proportion of collagen and type
Cross-sectional area, material and tendon length determine the amount of force
that a tendon can resist and the amount of elongation that it can undergo
Continuous compression modifies composition to resemble cartilage (reducing tensile strength)
Tensile loads over long periods will increase tissue size, collagen concentration and cross-linking
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)
What are the three things that cartilage does to resist load? What does compression do? What does varied orientations of fibers do?
• To resist load…
Stress developed in the fibrillar portion of ECM
Swelling pressures developed in the interstitial fluid
Frictional drag resulting from fluid flow through the ECM
- Compression reduces volume and increases pressure to push fluid out (rapid initial deformation becoming gradual and stops)
- Varied orientation of fibers through zones creates non-linear behaviour
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







