Tendon & Ligament

Question 1

Ligaments join ___ to ____

Answer 1

Ligaments join BONE to BONE

Question 2

Tendons join ____ to _____

Answer 2

Tendons join MUSCLE to BONE

Question 3

Choose the TWO correct functions of tendons:

• Elastic energy storage and release
• Protect the muscle tissue
• Transmit muscular forces

Answer 3

Tendon functions:

• Elastic energy storage and release
• Transmit muscular forces

Question 4

What is the main function of ligaments?

Answer 4

Restrain joints

Question 5

What is the main type of collagen found in ligaments and tendons?

Answer 5

Type I collagen

Question 6

What is the name of the connective tissue surrounding each tendon fascicle?

Answer 6

The endotenon (also known as the endotendineum). This is the connective tissue WITHIN the tendon, surrounding each bundle of fibres (fascicles).

Question 7

The specialised elongated fibroblast-like cells found in tendons are called…?

Answer 7

Tenocytes

Question 8

Put these in order of hierarchy from the largest to smallest unit:
Collagen fibre Collagen molecule
Whole tendon Fascicle
Collagen fibril

Answer 8

Hierarchy, largest to smallest:
1 - Whole tendon
2 - Fascicle (bundle of collagen fibres)
3 - Collagen fibre
4 - Collagen fibril
5 - Collagen molecule

Question 9

What is the composition of tendon/ligament? HINT: there are THREE main substances. Give proportions too!

Answer 9

60-70% water
25-30% collagen type I
0.3% glycosaminoglycans

Question 10

What is crimp? What role does it play in the function of tendon/ligament?

Answer 10

Crimp is the WAVY PATTERN in the collagen. It allows the fibres to stretch slightly, thereby contributing to the tissue’s ability to cope with mechanical stress.

Question 11

Under a microscope, non-fatigue-loaded (i.e. normal) tendon exhibits aligned collagen fibrils. What would the collagen fibrils look like in a tendon that has LOW LEVEL fatigue load?

Answer 11

Low level fatigue loaded tendons exhibit kinked fibre deformations.

Question 12

Under a microscope, low level fatigue loaded tendons exhibit kinked fibre deformations. What would the collagen fibres look like under MODERATE level fatigue load?

Answer 12

Moderate level fatigue loaded tendons exhibit kinked fibre deformations with widening of the spaces between the fibres.

Question 13

Under a microscope, moderate level fatigue loaded tendons exhibit kinked fibre deformations with widening of the spaces between the fibres. What would the collagen fibres look like under HIGH LEVEL fatigue load?

Answer 13

High level fatigue loaded tendons exhibit severe matrix disruption. The fibres are thinning and there are discontinuities within the matrix.

Question 14

What shape are tenocytes? And how are they arranged/located within the tissue?

Answer 14

Tenocytes are elongated, and found in chains between collagen fibres. They have long, wide, flat cell processes (the processes aren’t tendril-like).

Question 15

Tenocyte nuclei can be either ‘blastic’ or ‘cytic’. How could you differentiate between under a microscope?

Answer 15

Blastic = shorter and fatter
Cytic = thinner and longer

Question 16

What is the function of the tenocyte?

Answer 16

In developing tendons, tenocytes produce the collagen and arrange the molecules into fibrils. But their function is less well understood in the mature tendon. It is believed that perhaps the blastic (round/fat) tenocytes produce collagen for repair, and the cytic (long/thin) tenocytes maintain normal tissue function.

Question 17

Why do tenocytes need to be tolerant to hypoxia (low O2) and hyperthermia (high temp)?

Answer 17

Tendons are very poorly vascularised (low O2 levels). Some tendons are very elastic, which would result in a lot of heat energy being generated within the tissue.

Question 18

Why do tenocytes have a low metabolic activity rate? And what does this indicate about their general ability to repair/remodel the tendon?

Answer 18

Tendons are very poorly vascularised. Tenocytes have a LIMITED ability to do repair/remodel the fibrils.

Question 19

What is a bursa and what is its function?

Answer 19

It is a small fluid-filled sac (lined with a synovial membrane) that acts as a lubricated cushion to permit frictionless movement of a tendon over bone. Smooth gliding!

Question 20

What is a tendon sheath and what is its function?

Answer 20

An elongated bursa that wraps around the tendon to allow frictionless movement of the tendon over bone and under a retinaculum (which is a band of connective tissue). Smooth gliding!

Question 21

How many polypeptide chains in a molecule of collagen?

Answer 21

Three! Collagen is a triple helix.

Question 22

Collagen is translated as ___________. How does this become collagen?

Answer 22

Collagen is translated as procollagen. Enzymes cleave the ends off to leave a molecule of collagen.

Question 23

What guides the formation of the shape of the collagen fibrils?

Answer 23

Collagen is exported from the tenocyte through cytoplasmic furrows, which guides the formation of fibril shape.

Question 24

Tenocytes are initially round and fat, and bunched together. What happens to them as more collagen is produced?

Answer 24

As collagen is secreted during development and growth, the tenocytes become more distantly spaced. They are joined by long, flat processes.

Question 25

Do muscles and tendons develop together or independently?

Answer 25

Muscles and tendons develop independently very early on in development.

Question 26

Choose the correct word to finish this sentence:

Tendons arise from from regions near the diaphysis/joints/ligaments.

Answer 26

Tendons arise from regions near the joints.

Question 27

In the adult, the tendon is continuous with the endomysium. TRUE or FALSE?

Answer 27

TRUE. The endomysium is loose connective tissue surrounding each individual muscle fibre. The tendon is continuous with this, resulting in an extremely strong integrated connection between muscle and tendon.

Question 28

What is an enthesis?

Answer 28

Site of insertion of a tendon, ligament, capsule or fascia into bone. It is calcified fibrocartilage that is firmly linked to the bone surface.

Question 29

What is an avulsion fracture? And is it more common in younger or adult bone?

Answer 29

This is when the bone fractures deep to (under) the enthesis (the bone is weaker than the enthesis and tendon!). This type of fracture is more common in younger animals, often at synchondroses (cartilagenous areas that aren’t yet bone, e.g. growth plate).

Question 30

Does ligament/tendon degeneration usually occur with or without inflammation?

Answer 30

Without inflammation. -opathy is more common that -itis.

Question 31

Name one tendon and one ligament that commonly display obvious degeneration due to the animal’s activity.

Answer 31

• Cranial cruciate ligament in DOGS, especially jumpy ones (analogous to human ACL tear).
• Superficial digital flexor tendon in HORSES, especially eventers and National Hunt racers.

Question 32

Degeneration = fatigue damage accumulates SLOWER/FASTER than cells can repair it. Which is correct?

Answer 32

Degeneration occurs when fatigue damage accumulates faster than cells can repair it.

Question 33

Are repair tissues better or worse than the original tendon/ligament? How/why?

Answer 33

The repair strategy produces MECHANICALLY INFERIOR tissue. The fibres aren’t as well organised as the original, and it is more vascularised. This results in less tensile strength.

Question 34

Mesenchymal stem cell (MSC) treatment is still quite experimental. Example: stem cells from the bone marrow of horse’s sternum were aspirated and expanded. 10 million bone marrow (BM)-MSCs were injected into the superficial digital flexor tendon (SDFT). How did this affect the tendon?

Answer 34

• Increased collagen content, and improves collagen arrangement.
• Reduced cellularity.
• Resulted in a more tendon-like repair tissue (less scar-like).