Bone Pathology Flashcards by Srishti D

Where are osteocytes found?

In lacunae

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How are osteocytes sustained?

Canaliculi

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What do osteocytes do?

Maintain matrix

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What is mechanotransduction?

Osteocytes can tell if stress moving through bone

Initiate bone modelling in response

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What are active osteoblasts involved in?

Growth
Remodelling
Fracture healing

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What can osteoprogenitor cells differentiate into?

Osteoblasts

Chondrocytes

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Where are osteoprogenitor cells found?

Periosteum

Endosteum

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What do osteoclasts do?

Resorb bone

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How many nuclei do osteoclasts have?

Multinucleated

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Which hormone stimulates osteoclasts?

Parathyroid hormone

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Which cells express RANK-L?

Osteoblasts

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Which cells express RANK?

Osteoclast precursor

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What is osteoprotegrin (OPG)?

Binds to RANK-L > blocks it from interacting with RANK

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How does parathyroid hormone stimulate osteoclasts?

Increases expression of RANK-L on osteoblasts > bind to RANK on osteoclast precursor > stimulate osteoclast differentiation

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What cells do the periosteum and endosteum contain?

Osteoprogenitor cells

Resting osteoblasts

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What is in the dense outer layer of the periosteum?

Fibroblasts
Fibrous tissue
Blood supply
Nerves

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What type of cartilage is the model built from in endochondral ossification?

Hyaline

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How does endochondral ossification work?

Chondrocytes
- Proliferate
- Hypertrophy
- Degenerate
Osteoblasts move in
- Colonise strips of cartilage left by growth plate > ossify cartilage

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How do flat bones develop?

Intramembranous ossification

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What is intramembranous ossification?

Mesenchymal stem cells differentiate directly into osteoprogenitor cells
- Start producing osteoid

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What is osteoid?

Bone matrix

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What cell lays down osteoid?

Osteoblasts

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What does osteoid contain?

Type I collagen
Other proteins
- Few glycosaminoglycans
- Growth factors and cytokines

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How is osteoid secreted by osteoblasts?

Secrete

Collagen
Secretory vessels

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What do the secretory vessels released by osteoblasts contain?

Alkaline phosphatase | Pyrophosphatase

What do the proteins in the secretory vessels of osteoblasts do?

Increase concentration of calcium and phosphate locally to cause precipitation

What is the most common form of calcium phosphate found in bone?

Hydroxyapatite

What is woven bone?

Growing/healing bone

Compared to woven bone, what is the strength and production rate of lamellar bone?

Stronger | Slower production

What is the normal annual turnover of bone?

5-10%

How is bone remodelled?

Removes tunnel of bone Rebuilds new osteon Occurs in lamellar, not woven bone

What is a fracture?

Disruption in integrity of living bone

What are the fracture types by orientation of the fracture line?

Transverse Oblique Spiral

Other than by the orientation of the fracture line, what other fracture types are there?

``` Displaced Open (compound) vs closed (simple) Comminuted Pathological Stress ```

What is a comminuted fracture?

Bone broke into 2+ pieces

What is a pathological fracture?

Something wrong with bone and it fractures

What is a stress fracture?

Repeated low force injury to normal bone

Can stress fractures be seen in an x-ray?

Usually, no

What are the stages of fracture healing?

1) Inflammatory phase - Bleeding and haematoma formation - Vascular granulation tissue 2) Reparative phase - Soft callus - Hard callus 3) Remodelling phase

What does a haematoma contain in a fracture?

Growth factors | Cytokines

What does vascular granulation tissue contain?

Fibroblasts | New capillaries

What is soft callus made of?

Cartilage

What is hard callus made of?

Bone

What happens during haematoma formation?

Fibrin mesh creates framework Damaged matrix releases trapped growth factors and cytokines Stem cells activated to start repair Stem cells start to differentiate very early depending on local stability

What can osteoprogenitor cells differentiate into during the inflammatory phase, from most to least stable?

Osteoblast Chondroblast Fibroblast

When does the inflammatory phase occur?

Hours-days

What does the soft callus do?

Holds fractured ends together but poor structural stability

What happens to the periosteum during soft callus formation?

Repairs itself over outside

When does soft callus formation occur?

Days-weeks

What kind of ossification occurs to form the hard callus?

Endochondral in unstable areas | Intramembranous in stable areas

What kind of bone is a hard callus?

Woven

What is the shape of the hard callus?

Thickened spindle

What is the structural integrity of a hard callus?

Stable and (pain-free) but not as strong as normal bone

When does hard callus formation occur?

Weeks-months

What happens during remodelling in fracture healing?

Osteoclasts followed by osteoblasts Woven bone > lamellar bone Along lines of stress

What is the result of remodelling in fracture healing?

Completely reconstituted bone

When does remodelling occur?

Months-years

What is the goal of clinical management of fractures?

Union = unite broken ends | To allow bone healing as fast as possible and without complications

How are the goals of clinical management of fractures achieved?

Minimise gap = reduction of fracture Minimise strain/movement = fixation Minimise any other factors slowing healing

What are factors that slow healing?

``` Age >40 years Multiple medical comorbidites NSAIDs and corticosteroids Smoker Poor nutrition Open fracture with poor blood supply Multiple traumatic injuries Local infection ```

What is non-union?

Fracture which will not heal, no matter how long you persist with primary management

What is pseudoarthrosis?

Also called non-union and false joint Has no chance of mending without intervention Body perceives fragments as separate bones and doesn't attempt to unite them

What interventions can be done in non-union?

Bone grafting Further stabilisation Treat infection Stop smoking

What is delayed union?

Fracture which isn't healing as fast as expected

What are the risk factors for delayed union?

Similar to those for non-union

What can delayed union result in?

Non-union

What is mal-union?

Healing of bone in unacceptable position

What problems can mal-union cause for the patient?

Disability Post-traumatic osteoarthritis Cosmetic

Which type of fracture is especially at risk of infection?

Open

What effect does osteomyelitis have on healing bone?

Disrupts vessels in periosteum/Haversian canals > infected fragments of necrotic bone

What is the most common bacteria causing osteomyelitis?

Staphylococcus aureus

What other infection can osteomyelitis lead to?

Sepsis

What is osteonecrosis/avascular necrosis?

Fractures can interrupt blood supply > leave part of bone ischaemic

Which bones are particularly at risk of avascular necrosis?

Neck of femur | Scaphoid