Tendons and ligaments

Tendons

• non-elastic dense fibrous connective tissue

• Responsible for joining muscle to bone

• When a muscle contracts to move a joint, the tendon pulls on the bone

Function of tendons

• Tendons transmit force from muscle to bone

• Able to withstand high tensile loads while the muscle contracts (> 10X individuals weight during physical activity) and still retain flexibility

• They have a high energy storage capacity

• They are regarded as viscoelastic structures

• Viscolestic structures have both elastic and viscous behavior

• This implies that they can be stretched like an elastic band and return to their original shape – Human tendons and ligaments are elastic structures.

Chronic injuries

• Caused by overuse of particular part of your body either through sports or exercises or occupational activities

• Develop slowly and last a long time, over several months and possibly years

Acute injuries

• Injuries happen suddenly, sudden onset

Ligaments

• are strong bands of fibrous connective tissue which connect bones to bones

• Are elasticated to allow the movement of the joint

• more elastic and flexible than tendons

• BLOOD supply to both tendon and ligament is poor

Function of ligaments

• stretch and contract allowing shock absorption under stress

• protects joints and bones

• prevents excessive joint movement

• prevents joint dislocation

Structure of tendons and ligaments

Dense connective tissue:

• parallel-fibers of collagen

• Collagen fibres are arranged in a heirarchecal structure

• Sparsely vascularized

• Cellular (fibroblasts) – 20 %

• Extracellular (80%) - 70%

• H2O - 30%

• solids – collagen and elastin fibres, groundsubstance: GAGs and proteoglycan proteins

Major building block of tendons and ligaments

• protein fibres

• other proteins

• ground substances

• cells

• ECM is larger compared to the cells

Cells in tendons and ligaments

• the ability to synthesise all the ECM components (proteins)

• They have receptors on the cell membranes called integrins

• Integrins can sense a load being applied to the tendon and a signal is transmitted into the nucleus via an entire cascade of signals to produce specific proteins required in the ECM

Common tendon injuries

• Achilles tendon (heel)

• Rotator cuff tendons (shoulder)

Achilles tendinopathy

• Collagen disarray (disruption of the neat parallel collagen bundle structure)

• Increased ground substance (aggrecan is on the proteoglycans which are increased during an injury)

• Neovascularization (new blood vessel formation: angiogenesis)

• Areas of increased or decrease cell death (apoptosis)

• prominence of tenocytes

• Remember cells are responsible for synthesizing all the components of the ECM

Anterior Cruciate Ligament injuries

• Low in the general population

• A number of more Males are affected compared to Females

• 40% of all Knee injuries involve Ligament injury

• It is therefore one of the common knew injuries to date

Response to load

• Tenoblasts and tenocytes are components of tendon which able to respond to load

• They Initiate the adaptive response

• Load applied would initiate cellular proliferation.This mean more cells are produced

• ECM is increased