Mechanical Behaviours Flashcards
What parts of a tissue resist tension loads
Collagen
Elastin
What is the primary mechanical function of collagen
Withstand axial tension
What’s creep
When a ligament is subjected to a load it initially lengthens quite rapidly over time
A constant load level is reached and the ligament continues to deform for the same constant loads until it plateaus
Ligament length change on passive stretch
What is viscoelastic stress relaxation
Ligament is deformed (lengthened) to a constant length and held at the length
Initially the stress in the ligament fibres is at max but keeping it at the constant length over time causes a relaxation of stress in the fibres and the end feel will reduced
How is rate dependency related to ligament rehab
If a ligament is stretched quickly then it’s resistance is increased
If rate of stretch application is decreased (by therapist on patient) then there is less internal resistance to the stretch
What is hysteresis
A viscoelastic behaviour in a ligament
- normal elastic response = elastic band - return to normal length
- visco-elastic response = rate of deformation on application of stretch is not the same as rate if return to original length - rate of return is slower
Permanent tissue elongation =
Ligament is loaded past 3% strain point of stress strain curve and so ligament fibres undergo permanent change in length and enter a plastic range - return to new length on unloading
What’s the the regions to the stress strain curve in ligaments and tendons
Toe region = collagen fibres start to uncrimp with increased strain on ligament
Linear / elastic region = strain increased and collagen fibres stretch with 100% elastic recoil and stress starts increasing
Plastic region = elastic region reaches yield point - limit of elasticity. Collagen fibres elastic recoil diminishes from yield point to failure point. In this region the fibres will have permanent length changes
Failure = structure is ruptured, no longer any stress
