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
Describe what happens during the cross bridge cycle.
Describe the anatomy of a contractile unit (sarcomere).
- The arrangement is regular to give stripped appearance “striated muscle”
- (I) only actin “isotropic”, (A) actin and myosin “anisotropic”, (H) only myosin
What are the three types of contractions that a sarcomere can do?
Concentric
Eccentric
Isometric
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)
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 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 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
What are some tissue modifiers?
- Age
- Immobility
- Disuse
- Injury
- Medication
• Pain
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 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 is a PPM? What do you have to do to feel the end-feel using PPMs? What information can that give us?
- Physiological movements are used (PPM)
- Need full accessory movements for PPM to occur (movements beyond control)
- E.g., Bend finger – interphalangeal flexion plus slide
- Apply over-pressure (OP) at the end to determine end-feel
• Isometric muscle testing (strong, weak, painful, painless) – compared other side
- To determine tissue type (source of pain)
- Treatment guided by tissue and the specific lesion
What is an end feel? Is it normal or pathological? What is essential when using that technique?
• A sensation that the therapist feels in the joint and tissues at the end of available range of motion during passive movement
- May be normal or pathological (abnormal)
- Must compare the affected and unaffected sides
What are the three types of normal end feels? Give a brief description and an example for each.
Bone to Bone
• Abrupt stop in motion; two bone surfaces coming together (e.g., elbow ext)
Capsular or Soft Tissue Stretch
• Hard-ish stop in motion; spring or slight give (e.g., shoulder lateral rotation)
Soft Tissue Approximation
- Squishy, giving
- Movement stopped by limb hitting again soft tissue of another body part
• e.g., knee flexion
What are the five types of abnormal end feels? Give a brief description and an example for each.
Empty – movement stopped by pain before resistance is felt (e.g., 10/10 pain)
Spasm – involuntary, vibrant twang (e.g., recent #)
Springy Block – unexpected rebound, non-capsular pattern restriction (e.g., tear)
Abnormal Bone to Bone – early abrupt stop, crepitus or grating (e.g., post- immobilization)
Abnormal Capsular – early hard-ish stop before end range (e.g., frozen shoulder)
What is a capsular pattern of restriction? In what kind of joints can this occur? What happens and what does this suggest? How is a capsular pattern of restriction determined?
A characteristic pattern of expected proportional limitation of movement, specific to a particular joint
Exists only in those joints controlled by muscle, which have a joint capsule and are lined by a synovial membrane
Suggests that the entire capsule and/or synovial membrane of the joint is involved
Total joint reaction (e.g., post-immobilization)
Determined by passive movements
What are the two articular joint positions? Identify and describe the most stable one. What happens when it is swollen?
CLOSED PACKED POSITION (CPP) and LOOSE PACKED POSITION (LPP)
- Most stable position
- Greatest protection for the joint
- Usually avoided during assessment
- Greatest congruency of surfaces
- Capsule, ligaments under max tension• If swollen, CPP cannot be reached
Describe the loose packed position (LPP) of articular joints.
LOOSE PACKED POSITION (LPP)
- Any position other than CPP
- Not congruent
- Capsule and ligaments are relaxed
- Greatest room for swelling
- Naturally adopted for rest when painful
• Least amount of stress on structures
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 constant length phenomenon. What does it suggest? Give an example.
• Limitation of movement at one joint is dependent on the position at which another joint is held
• Restricting tissue is outside the joint
• Suggests a lesion in a tissue that spans two joints
E.g., lumbar disc lesion, irritates the sciatic nerveàpositive SLR
E.g., muscle adhesion in the two joint muscle
