Bone Pathology Flashcards
Where are osteocytes found?
In lacunae
How are osteocytes sustained?
Canaliculi
What do osteocytes do?
Maintain matrix
What is mechanotransduction?
Osteocytes can tell if stress moving through bone
Initiate bone modelling in response
What are active osteoblasts involved in?
Growth
Remodelling
Fracture healing
What can osteoprogenitor cells differentiate into?
Osteoblasts
Chondrocytes
Where are osteoprogenitor cells found?
Periosteum
Endosteum
What do osteoclasts do?
Resorb bone
How many nuclei do osteoclasts have?
Multinucleated
Which hormone stimulates osteoclasts?
Parathyroid hormone
Which cells express RANK-L?
Osteoblasts
Which cells express RANK?
Osteoclast precursor
What is osteoprotegrin (OPG)?
Binds to RANK-L > blocks it from interacting with RANK
How does parathyroid hormone stimulate osteoclasts?
Increases expression of RANK-L on osteoblasts > bind to RANK on osteoclast precursor > stimulate osteoclast differentiation
What cells do the periosteum and endosteum contain?
Osteoprogenitor cells
Resting osteoblasts
What is in the dense outer layer of the periosteum?
Fibroblasts
Fibrous tissue
Blood supply
Nerves
What type of cartilage is the model built from in endochondral ossification?
Hyaline
How does endochondral ossification work?
Chondrocytes - Proliferate - Hypertrophy - Degenerate Osteoblasts move in - Colonise strips of cartilage left by growth plate > ossify cartilage
How do flat bones develop?
Intramembranous ossification
What is intramembranous ossification?
Mesenchymal stem cells differentiate directly into osteoprogenitor cells
- Start producing osteoid
What is osteoid?
Bone matrix
What cell lays down osteoid?
Osteoblasts
What does osteoid contain?
Type I collagen
Other proteins
- Few glycosaminoglycans
- Growth factors and cytokines
How is osteoid secreted by osteoblasts?
Secrete
- Collagen
- Secretory vessels
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
