BIOMECHANICS OF TENDONS AND LIGAMENTS 2 Flashcards
Different surrounding structures
- Fibrous sheath/retinacula e.g. hand
- Assist in joint stability
- Synovial sheaths +/- peritendinous fluid • Reduce friction
- Bursae e.g. subacromial • at sites of compression
CONNECTIVE TISSUE
CELLS:
fibroblasts
chondrocytes
osteoblasts and osteocytes
ECM component: fibres prosteoglycans glycoproteins tissue fluid
Collagen
- Most abundant protein in the body
* At least 28 types of collagen (….different structures, properties & functions)
Elastin
- 3 dimensional branching pattern
- Highly elastic, fatigue resistant
- Able to store & return energy
- In ligaments, elastin resists transverse and shear deformation
- Yellowish
- Aorta (30% elastin)
- Ligamentum flavum (75%) • Achilles tendon (4.4%)
Proteoglycans (PGs)
- Most abundant non-fibrous proteins
- Core protein attached to glycosaminoglycan (GAG) side chains- negatively charged, which attracts water
- PG distribution varies along the length of the tendon
- Decorin is the most abundant PG in tendon, helps transfer loads between collagen fibrils & regulate collagen fibrillogenesis
- Lubricin provides lubrication allowing gliding at tendon surface
- Cartilage associated proteoglycans predominate in areas of tendon subjected to compression (attract water to resist compression)
Composition & structure - Ligament
- Fibroblasts 10-20%; ECM 80-90%
- Mainly type I collagen, lesser III, IV, V
- Varying amounts of elastin
- Collagen/elastin ratio determines stability/mobility
- Varied collagen arrangement - resists forces in several directions
RESIST FORCE IN MULTIPLE DIRECTIONS
Composition & structure - Tendon
- Similar composition to ligament (10-20/80-90 ratio)
- Mainly type I collagen (> than ligament) *stronger
- Less type III collagen (< ligament)
- Small amounts of elastin
- Proteoglycans – mainly decorin
- Collagen aligned along long axis
- resists uniaxial tensile loads (anisotropic)
RESIST FORCE IN ONE DIRECTION
Tendon Hierarchical Structure
Tropocollagen > microfibril > fibril (primary structural unit) > fiber > fascicle (visible to naked eye) > tendon with ectotenon and endotenon (interfasicular matrix)
Paratenon
(additional loose connective tissue layer) surrounds tendons in regions away from joints, to facilitate movement of tendons below the skin.
Synovial sheath
(additional covering where a tendon passes around a joint) to ensure smooth gliding past surrounding structures.
Mechanical behaviour
- Depends on the nature and direction of applied forces (anisotropic)
- Heterogeneous - varies along the tendon
- Tendons & ligaments are viscoelastic
- Behaviour is time and history dependent
- Combination of “elasticity” (ability to return to original state, depends on collagen/elastin) & “viscosity” (resistance to deformation; depends on PG/GAG)
Structural vs. material properties
- Material properties are normalized for the object’s size and shape and describe the properties of the underlying material from which the object is made.
- Structural properties depend on the object’s size and shape.
stress and strain
Forces and deformation values depend on size of structure (CSA & length) and its composition
Stress and strain depend on the composition of the structure but are independent of its size.
T = abruptly failures
L = progressive failure
Rate dependent and time dependent properties
- Creep
- Stress-relaxation
- Hysteresis
- Loading rate
- Temperature
Stress - relaxation
• If tissue is stretched to fixed length, the force will decay with time
