Tissue mechanics: tendons and ligaments

what are tendons and ligaments made up of

they are both composed of dense connective tissue and are biologically active

what do tendons connect

they connect muscle to bone

what do ligaments connents

they connect bone to bone

what are the function of tendons

force transmission

macroscopic movements

alter stress field within the bone

compliance

proprioception

store elastic energy

what are the functions of ligaments

microscopic movement

force transmission is a minor function

maintains optimal joint alignment

provide joint stability

compliance

proprioception

what are tendons and ligaments classified as

they are classified as connective tissue

what are the 3 categories of connective tissue

connective tissue proper, supporting connective tissue, specialized connective tissue

what are characteristics of loose connective tissue proper

it is a packing material within and between muscle sheaths. it is delicate and not very resistant to stress or strain

what are characteristics of dense connective tissue proper

it is less flexible and more resistant to stress

what are examples of supporting connective tissue

bone and cartilage

what are examples of specialized connective tissues

adipose tissue and hematopoietic tissue

what are the components of tendons and ligaments

20% cells 80% ECM

what is ECM composed of

it is composed of fibers like collagen and elastic and ground substance (non-fibrous part) like glycoproteins, proteoglycans, inorganic components and water

what are the cells that make up tendons and ligaments

primarily fibrocytes/tenocytes

what are fibrocytes called when manufacturing proteins

they are called fibroblasts

what do fibroblasts do

they manufacture components of the ECM

what happens after fibroblasts secrete (pro)collagen into the ECM

the procollagen assembles into tropocollagen which eventually assembles into tendons and ligaments

how much water is in tendons

they are 55-70% water

how much dry matter are in tendons

they are 30-45% dry matter

what makes up the dry matter of tendons

75-85% collagen (95% type 1 and 5% type 3 or 5) <3% elastin and 102% proteoglycans

what is the collagen fiber arrangement in tendons like

it is a nearly parallel arrangement of fibers

how much water is in ligaments

it is 55-65% water

how much dry matter is in ligaments

35-45% dry matter

what is the dry matter of ligaments made up of

70-80% collagen (type 1)

5-15% elastin

1-3% proteoglycans

what is the fiber arrangement of collagen in ligaments

ligaments have a less parallel fiber arrangement

what do the parallel fiber arrangements in tendons allow for

it makes tendons equipped to withstand high unidirectional loads

what do the less parallel alignment in ligaments allow for

it allows ligaments to sustain predominantly tensile stresses in one direction and smaller stresses in other directions

what do load deformation curves represent

they represent the structural properties of the tissue

what does deformation produced by a load depend on

it depends on the size of the structure

what is tensile stress

it is externally applied tensile load per cross-sectional area of the tendon or ligament to which it is applied

what is used to determine cross sectional area

ultrasonography and mri are used to determine it

what is tensile strain

its the elongation/unit length of a material in response to tensile load

what is used to measure tenson elongation, strain and tissue stiffness during movement

noninvasive ultrasound method can be used to measure them

are tendons and ligaments viscoelastic

yes they are

what is hysteresis

it is when the output of a system depends on its input. when a viscoelastic material is loaded and unloaded, the unloading curve is different from the loading curve

what does the difference between two hysteresis curves represent

it represents the amount of energy that is lost during loading, if loading and unloading are repeated several times, different curves can be obtained

what are the 3 modes of failure

rupture (tearing)

failure through the enthesis (attachment point near bone)

avulsion failure (pulling away of bony attachment)

which is more sensitive to strain rate, ligaments or tendons

tendons are more sensitive to it

what do higher strain rates do to tendons and ligaments

it increases the stiffness of tendons and ligaments

when is avulsion fracture more likely to occur

it is more likely to occur with lower strain rates

when is failure by substance rupture more likely to occur

it is more likely to occur for higher strain rates

what does heat above 55-60 degrees Celsius do to tendons and ligaments

it can produce irreversible shrinkage as a result of denaturation

when do viscoelastic properties of tendons and ligaments increase

they increase with increased temperature which increases stress relaxation and creep

when is maximal tissue strength achieved

it is achieved around the time of skeletal maturity

what do tendons and ligaments of the very young and very old have in common

they both have lower ultimate stress and strain and decreased stiffness

what does cortisol and other glucocorticoids do to tendons and ligaments

they reduce the synthesis of type 1 collagen, which might make healing tendons and ligaments more susceptible to reinjury

what does relaxin do to tendons and ligaments

it softens and increases the extensibility of the pelvic ligament during pregnancy and reduce stiffness of patellar tendons in women

what does growth hormone do to tendons and ligamens

it increases collagen synthesis and turnover

what is tissue remodeling

its the adaptation of biological tissues to changes in the mechanical stresses to which they are subjected on a regular basis

what does the specific adaptation to imposed demand (SAID) principle explain

it explains remodeling in response to alteration in external loading in soft tissues

what does joint immobilization do to tendons and ligaments

it reduces the tensile forces normally applied to tendons and ligaments during joint movement

what does immobilization do

it reduces the load to failure and stiffness and decreases the strain/elongation to failure

when does frequency of avulsion failures increase

it increases with immobilization compared with mid substance failures

what does early mobilization within the physiological limits of the healing tissue strengthen

it strengthens the unions, speeds healing and reduces scar tissue adhesions

what does increased loading do to the tendon

it can lead to tendon hypertrophy and increased strength and stiffness

at approximately what percentage of the ultimate stress do tendons typically function

they typically function at 30-40% of their ultimate stress

at approximately what percentage of the ultimate stress do ligaments typically function

they typically function at 5-10% of their ultimate stress