Joint and Connective Tissue (EXAM 1)

Cells

• Role: produce ECM

• Fibroblast = basic cell

• Differentiates to become a more specialized connective tissue cell
  ▪ Chondroblast/cyte
  ▪ Tenoblast/cyte
  ▪ Osteoblast/cyte

Collagen

• Type I

  • is found in most/all connective tissues

  • most of the body’s total collagen

  • Resists tensile stress

• Type II
  ▪ Mainly found in cartilage and nuclei of IV discs
  ▪ Gives compressive strength

Elastin

Found in tissues that require more deformation and elasticity

• Arteries (30% elastin)

• Ligamentum Nuchae (75% elastin)

• Achilles Tendon (4% elastin)

ECM

• most of vol in tissue

• proteins + water

• Has Both Fibrillar (collagen + elastin) and Interfibrillar (H2O, PGs, GAGs) things

PGs + GAGs

Proteoglycans (PG’s)

• protein w/ carb linked to it

Glycosaminoglycans (GAG’s)
▪ Carb portion of the PG
▪ Responsible for water content in the ECM

****Increases in # PGs + GAGs → increases water****

• which will make it easier to resist compressive loads (cartilage + interverbral discs)

ex: Hyaline cartilage

Ligament (cell, fibrillar component, nutrition source, and optimal mechanical stressor)

Cell: Fibroblast

Fibrillar Component: Type I Collagen w/ varying amount of Elastin

• fibrils are organized in line w/ the applied tensile forces (from joint movement or external forces)

• ****(not very good @ resist tensile forces)***

  • changes based on joint position

  • NOT uniform in the structure

• ratio (Collagen/Elastin) depending on role of ligament (stability or mobility)

Nutrition source: blood supply (even though not very vascular)

Optimal mechanical stressor: tension + shear

Tendon (cell, fibrillar component, nutrition source, and optimal mechanical stressor)

Cell: Fibroblast, Tenoblasts, Tenocytes

Fibrillar Component: Mainly type I collagen (more than ligament)

• Fibers are uniform and in the SAME direction of tensile loading (contrast to ligament)

• ****( very good @ resist tensile forces)***

• ***force produce by muscle = strain experience by tendon***

Nutrition source: blood supply (limited → hard for tendon to heal)

Optimal mechanical stressor: tensile loading to stay healthy

• Impacts collagen content and cross-linking

Hyaline Cartilage (cell, fibrillar component, nutrition source, and optimal mechanical stressor)

Cell: Chondroblast, Chrondrocyte

Fibrillar Component: 90-95% Type I collagen

• Fibers are uniform and in the SAME direction of tensile loading (contrast to ligament)

Interfibrillar Components: PG’s (aggrecan), GAG’s, (chondroitin sulfate/keratin sulfate, hyaluronan)

Nutrition source: diffusion for nutrition (synovial fluid) via compression

Optimal mechanical stressor: compression

Bone

Cell: Fibroblasts, osteoblasts, osteocytes, osteoclasts, progenitor cells

Fibrillar Component:

• Type I Collagen w/ hydroxyapatite crystals (helps give more compressive strength)

Interfibrillar Components: PG’s (aggrecan), GAG’s, (chondroitin sulfate/keratin sulfate, hyaluronan)

Nutrition source: blood supply

Optimal mechanical stressor:

Wolff’s law

• bone loading (via weight bearing + muscle contraction)

  • load bones → stronger bones

Bone structure

Cancellous Bone

• Spongy inner layer

• Trabeculae (calcified tissue) are laid down according to loading patterns
  placed on the bone

• Form Follows Function”

Cortical Bone

• Outer layer

• Thin but dense and compact

Periosteum

• Fibrous

• Covers bone except for articular surface

• has undifferentiated cells that can turn into OB/OC as well as a capillary network

Common changes occurring with injury, exercise, and immobilization for each
connective tissue

Tendon

• exercise: daily activity is in toe region or early parts of elastic region

  • strengthens tendon

• injury: happens w/ repeated loading plastic region w/ NOT enough recovery

• immobilization: bad for tendon

Ligament

• exercise: become stronger + stiffer (strengthens ligament)

• injury:

• immobilization: bad for ligament

Hyaline cartilage

• exercise: compression helps deliver nutrients (strengthens hyaline cartilage)

  • resists shear forces

• injury: osteoarthritis

• immobilization: bad for cartilage

Bone

• exercise: moderate compressive load/stress → bones = stronger + denser

  • more stress and less strain compare to tensile load/stress

• injury: fracture

• immobilization: bad for cartilage

More examination into injury of Tendon, Ligaments, and Bone

Tendon injury:

• Tendonitis: Repetitive loading into the plastic region of the curve without
  sufficient recovery before the next bout of loading (repeated microfailure)

• Tendon rupture: Single bout of excessive loading that results in macrofailure

Ligament injury:

• Instability: Repetitive sub-maximal loading into the late elastic region of the curve without sufficient recovery before the next bout of loading

• Sprain: A bout of loading into the plastic region (early, grade 1; late, grade 2)

  • some part of ligament is injured

• Rupture: (e.g. ACL tear)= Single bout of excessive loading that results in
  macrofailure

  • whole ligament is injured

Bone injury:

• Stress fracture: Repeated low loads/creep strain into plastic region of the curve causes microdamage of stress/strain curve

• Fracture: single bout of high stress into macrofailure of stress/strain curce
  

Mechanical properties of connective tissue (load/deformation )

• Describes the properties of tissue

Toe region: taking rest or slack

Elastic region:

• steep slope = high load and small deformation —> stiff

• more horizontal = small load and high deformation —> more compliant

Plastic region:

• more deformation for small load → microfailures in tissue

  • removing load does NOT stop failure, need to reintroduce ECM for healing

Mechanical properties of connective tissue (load/deformation ). w/ elongation

• relies on structural size

  • increase in Cross-Sect area (thickness) —> increase in stiffness

  • increase in # long fibers —> decrease in stiffness (more compliant)

Mechanical properties of connective tissue (stress/strain curves)

• Describes material properties/qualities of tissue

• curve changes based on speed of load, injury/immobilization, and tissue type

Mechanical Properties terminology

Load: any force applied to a tissue

Deformation: the result of an applied force

• Tensile loads create elongation

• Compressive loads create compression

Stiffness: resistance to deformation

Compliance: ease of deformation

Stress: Force per unit area (S= F/A)

Strain: % change in length (L2-L1)/L1

Relationships between CSA, length, and material (EXCEPTION)

Increased CSA should increase stiffness but depends on material a well

• An injured tendon can be thicker but weaker (b/c not having good material)

How does the stress/strain curve change in the presence of injury or immobilization?

look at the graphs

Viscoelastic properties of connective tissue (creep, stress-relaxation, strain
rate sensitivity)

Creep: force sustained while length/deformation changes over time

Stress-Relaxation: force to maintain a certain strain decreases over time

• try less hard over time to keep deformation

Strain Rate Sensitivity: stiffness increases when loaded quickly

• Fast calf raises v. slowed and controlled calf raises

Viscoelasticity in PT is used by stretching, joint mobilization, tendon loading, and plyometrics

Synovial joints

Uniaxial joints (1 dg of freedom —> flex/ext)

• Hinge joint

• Pivot joint

Biaxial joints (2 dg of freedom —> flex/ext, deviations)

• Condyloid joint

• Saddle joint

Triaxial joints (3 dg of freedom —> flex/ext, abd/add, med/lat rotation)

• Plane joint

• Ball-and-socket joint

Joint types

Fibrous: more for stability

• sutures + syndesmotic joints

Cartilagenous: more for weight-bearing and more mobile than fibrous

• pubic symphysis + intervertebral joints

Synovial:

• more for mobility

Use the Physical Stress Theory to predict changes in connective tissue based on the
intensity and frequency of applied stimulus?

more stuff on Bone

Cortical bone

• Can bear greater stress with less strain

• Strain of just 2% will result in failure —→ vertical slope)
  

Cancellous bone
▪ Less stiff (less stress for the same amount of strain)
▪ Can bear strain of up to 75%

Increased Tendon strained is linked to what?

increased production of force by the muscle

Bone can take that much deform til it break