Joints Flashcards by Niel Hayes

in simple terms what is a joint?

The articulation between 2 bones

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What do joints consist of?

Bones, ligaments, tendons, cartilage, joint capsule, bursa and muscle.

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Simply what is a ligament?

Fibrous tissue that connect bone to bone to maintain stability and prevent unwanted movement.

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Simply what is a tendon?

Fibrous tissue that connect bone to muscle to maintain stability, prevent unwanted movement and transfer force as well as crossing joints

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Simply what is cartilage?

A smooth material found at attachment sites where there will be friction between bones.

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What is a joint capsule

Tissue surrounding the joint further keeping it in place and stops unpermitted movement.
Every joint has 2 parts, an outer fibrous membrane and an inner synovial membrane which acts as a shock absorber as well as containing fluid (synovial fluid) which acts as a lubricant.

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What is a muscle?

Muscles cross joints and helps with stability but more importantly its what makes us move.

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What is bursa?

Fluid filled sacks that sit between muscles and joints to help reduce friction

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What is bursa?

Fluid filled sacks that sit between muscles and joints to help reduce friction

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What is a labrum?

A piece of cartilage that makes the socket of a joint deeper in order for the bone to have more stability in the socket.

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What are the 4 main types of connective tissue?

Connective tissue
Connective Cartilage Bone Blood. tissue proper (2) 1 Hairline (articular) 1 Compact
LOOSE (3) DENSE (3) 2 Fibrocartilage 2 Spongy
1 Areolar 1 Regular 3 Elastic
2 Adipose 2 Irregular
3 Reticular 3 Elastic

Dense regular are tendons and ligaments

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Connective tissue cells

Mesenchyme (stem cells) and can turn into chondroblasts, fibroblasts and osteoblasts depending on what connective tissue needs it. Fibroblasts can be found in both chondroblasts and osteoblasts.

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What connective tissue cells go to which connective tissue?

Cartilage: Chondroblast
Tendon: Tendoblast (Fibroblast)
Ligament: Fibroblast
Bone: Fibroblast and Osteoblast

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Where is collagen found?

In structures that undergo a lot of tensile force.

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What is collagen structure

Tipple helix structure.

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Structure of a muscle smallest to largest

Collagen
Microfibril
Fibril
Fascicle
Tendon

What does relaxed and loaded collagen look like?

Relaxed looks wavey and loose while loaded are straight and tight.

What is the composition of a ligament?

Cells (mostly fibroblasts) = 10-20%
•Extra cellular matrix (ECM) = 80-90%
– Water (~70% of the ECM)
– Solids (mostly collagen) ~30% of the ECM
• Collagen composition
– ~ 90% type 1 (Strongest)
– ~ 10% type 3 (can vary with pathology)
• Variable elastin content 
– Ligaments flava (spine)

Ligament vascularity

Blood vessel supply

Relatively thinly dispersed but important, it has slower healing rates than muscle.

Ligament innervation

Innervation
A) Mechanoreceptors (MN’s)
1. Under-recognised significance
2. Proprioception (Helps with orientation in space)
3. eg ACL strain à inhibition of quadriceps MNs and activation of hamstring MNs
B) Nociceptors

Ligaments as mechanoreceptors (ACL limits what?)

The ACL limits anterior tibial translation
Hamstrings are the primary muscular support
ACL-hamstring reflex

Ligament loading and de-loading

Loading
• ?cross sectional area
• ↑tensile strength & stiffness
De-loading
• ↓ Cross sectional area
• ↓ tensile strength & stiffness

tendon composition

Cells (fibroblasts/tenoblasts/tenocytes) = 20% 
• Extra cellular matrix (ECM) = 80%
– Water (60-75% of the ECM)
– Solids (mostly collagen) ~25-40% of the ECM
• Collagen composition
– ~ 95% type 1
– ~ 5% type 3 (can vary with pathology)
– Very small amounts of type 4 & 5
• Elastin content???

Tendon loading and de-loading

Loading
• ↑cross sectional area
• ↑collagen concentration & 
cross linkage
• ↑tensile strength & 
stiffness 
De-loading
• ↓ collagen content and 
cross linkage
• ↓ tensile strength & 
stiffness
• ↔ size

Tendon stiffness

Tendon stiffness varies from muscle to muscle the body e.g. the achilleas tendon is know to be relatively compliant The older you get the less stiff your tendons get

What are the 3 types of cartilage

``` Articular (hyaline) Fibrocartilage - More type 1 collagen - Little movement - eg spine Elastic - More elastin - found in the epiglottis ```

Cartilage composition

``` • Cells (mostly chondro-blasts & -cytes) = 10% • Extra cellular matrix (ECM) = 90% – Water (60-85%) – Collagen (~10-30%) • >90% type 2 – Proteoglycans (8-10%) • Mostly aggrecan bound to hyaluronan Elastin ```

Articular cartilage characteristics

• 1-7 mm thick, white, almost translucent • Has no innervation or nerves cells or interaction with nervous system therefore cant feel damages cartilage. • No blood vessels, low cell density. Which suggests it is difficult for cartilage to heal. • Functions – provide low friction surfaces – distribute load over a larger surface area

What is the nutrition for articular cartilage?

Avascular tissue –The chondrocytes are nourished by – Compressive loading squeezes fluid out of cartilage – Unloading allows fluid to flow back into cartilage • Under influence of osmotic pressure • Nutrients from synovial fluid is drawn into the cartilage • Cartilage health relies on repetitive loading cycles – Nutrient supply declines with constant loading AND in the absence of loading.

What does the meniscus do?

¨ Helps to ‘smooth’ the distribution of contact forces in the knee.

What do all synovial joints contain (6) and what do some synovial joints contain (4)?

``` All contain – Synovial fluid – Articular cartilage – Articular (joint) capsule – Synovial membrane – Blood vessels – Sensory nerves Some contain – Menisci – Peripheral labra – Fat pads – Bursae ```

What happens to joints when they age? (7 points)

1) Decreased water content in articular and fibro-cartilage and 2) increase in calcium deposits in articular cartilage which can both result in joint stiffness. 3) Increased collagen cross linkage, particularly ligaments. 4) Cartilage thinning. 5) Increased fibrous material in synovial membrane (i.e. cartilage deposits) which causes stiffer/less elastic joints. 6) Reduction in synovial membrane blood vessels have a decreased ability to produce and remove synovial fluid and reduce in healing capacity. 7) Joint diseases/degeneration such as osteoarthritis and rheumatoid arthritis.

Types of joint injuries (6)

``` Ligament sprains Bursitis Subluxation Dislocation Arthritis - Osteoarthritis - Rheumatoid arthritis ```

Ligament sprains

Occur due to stretching or taring of ligaments. Low blood supply which decreases healing ability and takes longer. sever injuries may require surgery or grafts.

Bursitis

Inflammation of bursae sacks.

Subluxation

One segment of a joint becomes displaced (partial displacement)

Dislocation

A full joint displacement

Arthritis - Osteoarthritis - Rheumatoid arthritis

Osteoarthritis Reduction of articular cartilage causing bones to rub together causing friction (leading to abrasion), damage and discomfort in the joint. Rheumatoid arthritis Due to inflames synovial membrane It is an auto immune disease where the immune system attacks the joint causes bone erosion causing inflammation and swelling. lasts a long period of time and is hard to manage