Bone growth Flashcards
When does bone growth start?
Before birth
When does bone growth end?
Puberty
Which part of bone is very poorly vascularised?
The hyaline cartilage
What effect do sex steroids have on bone?
They stimulate bone growth spurt but also promotes the closure of epiphyseal plates
What happens to the growth plate towards the end of bone growth?
- Growth in cells ceases, cell proliferation slows and the plate thins
- The plate is invaded by blood vessels, epiphyseal and diaphysial vessels unite
- A visible line may be left on an X ray
Which bones have one ossification centre
- Capals
- Tarsals
- Ear ossicles
How many ossification centres do most bones have?
More than 2
How many ossification centres does the humerus have?
3
What are the effects on bone growth caused by having multiple ossification centres?
- Rate of bone growth varies both bone to bone and within the same bone
- Weak points within the bone change
What are the zones of the epiphyseal plate?
- Ossification zone
- Calcification zone
- Hypertrophic zone
- Growth (proliferating) zone
- Resting zone
What happens in the resting zone?
Matrix production
What are the defects associated with the resting zone?
Diatrophic dysplasia: defective collagen synthesis/processing of proteaglycans
Results in shortened stature and shorter arms and legs
What happens in the Growth zone?
Cell proliferation
What are the defects associated with the growth zone?
• Achondroplasia • Malnutrition • Irradiation injures All above result from the deficiency of proliferation and/or matrix synthesis • Gigantism: Increased proliferation
What happens in the hypertrophic zone?
Calcification of the matrix
What are the defects associated with the hypertrophic zone?
• Rickets
• Osteomalacia
Both caused by an insufficiency of calcium or phosphate for normal calcification
What is the difference between rickets and osteomalacia?
- Rickets is more paediatrics related because of the growth plates
- Osteomalacia involves the periosteum
What happens in the Metaphysis?
Bone formation and vascularisation
What are the defects associated with the metaphysis?
- Osteomyelitis: bacterial infection
- Osteogenesis imperfecta: Abnormalities with the osteoblasts and collagen synthesis (brittle bone disease)
- Scurvy: Inadequate collagen turnover(which is why it also affects the skin)
What does bone growth and development require?
- Calcium
- Phosphorus
- Vitamins A, C and D
- Balance between growth hormone, thyroid and parathyroid hormones, oestrogen and androgens
What percentage of bone is cortical bone?
80
Where is cortical bone found?
In the shafts of long bones
Describe the structure of cortical bone
Concentrically arranged in lamellae- Haversian system
What is the function of cortical bone?
Mechanic strength
What may cause damage to the bone/ cause the bone to fracture?
Direct or indirect violence may result in deficits at the fracture sit leading to non-union
What percentage of bone is cancellous/trabecular bone?
20%
Where is cancellous/trabecular bone located?
At the ends of long bones, vertebral bodies and flat bones
Describe the structure of cancellous/trabecular bone
Meshwork of trabecular with intercommunicating spaces
What is the function of cancellous/trabecular bone?
Metabolic
How would cancellous/trabecular bone likely be damaged?
Honeycomb structure fails as the result of compression
In cortical and cancellous bone, what are the differences between:
1) The periosteum
2) Cell turnover
3) Blood supply
1) Cortical bone has a thicker periosteum, Cancellous bone has a thin periosteum
2) Cortical bone has a slow turnover, Cancellous bone has a rapid turnover
3) Cortical bone has a slow blood supply and Cancellous bone has a rich blood supply
What needs to be thought about in the mechanism of injury of a fracture?
Direction of force:
• Direct vs angular?
• Rotational?
• Was there compression?
Energy transfer:
• Cause?
• Site? (how close was it to other tissues?)
What is imaging used for in fracture treatment?
- Site and the bones involved
- Clues on any soft bone injury (e.g. are there fragments? Can it be realigned? etc.)
- Clues on energy transfer: Wide displacement? Comminuted? Multiple fracture sites?
- Pathological bone?
- Paediatric bone: What are the effects on the growth plates and bone density
What are the different definitions of a fracture?
- Complete or incomplete
- Site
- Open to surface
- Contaminated
- Soft tissue injury
- Joint involvement
- No. of pieces
- Alignment
- Degree of separation
What are the types of fracture?
- Transverse- across the bone horizontally
- Linear - across vertically
- Oblique non displaced - Diagonally
- Oblique displaced - Diagonally and separated
- Greenstick (mainly in children) chunk on side of bone
- Communited - broken into fragments
- Spiral - Around the bone and twisted
What are avulsion fractures?
Fragment of the bone is separated from the main mass
What is a buckled fracture?
- Otherwise known as an impacted fracture, torus fracture
* Ends are driven into each other, commonly seen in arm fractures in children
What is a compression/ wedge fracture?
Usually involves vertebrae (seen more commonly in patients with osteoporosis or in cancer patients)
What is a pathologic fracture?
Caused by a disease that weakens the bones
What is a stress fracture?
Hairline crack
What complications are limb threatening/ a non-union risk?
- Dislocation
- Comminuted
- Compound
- Compartment syndrome
- Vascular/nerve injury
- Soft tissue injury
- Pathological bone
How long does a fracture take to heal and what is the healing time dependent on?
- 2-10 weeks
- Severity and position
- Age
What effect on bone cells does age have?
• Decrease of osteoblasts
What effect on bone cells does osteoporosis have?
• Increases osteoclasts
What are the 3 major phases of fractures and callus formation?
1) Reactive phase
2) Reparative phase
3) Remodelling phase
What happens in the reactive phase of callus formation ?
- Fracture and inflammatory phase (haematoma)
* Fibroblasts in the periosteum proliferate to form granulation tissue around fracture site
What happens in the reparative phase of callus formation?
30-40% of callus formation
• Callus formation: osteoblasts quickly form woven bone to bridge the gap
• Woven bone is weak as the collagen fibres are arranged irregularly
• Lamellar bone is laid down - collagen is organised in regular sheets to give strength and resilience
What determines if osteoblast or chondroblasts are the main cell in callus formation?
- Osteoblasts = loading/ forces being applied
* Chondroblasts = less weight bearing
What happens in the remodelling phase?
Remodelling by osteoclasts restore original bone shape
What is conservative treatment?
- Simple fracture with low risk of non-union
- Dependent on natural healing process
- +/- immobilisation
- Rehabilitation
What happens in intervention?
- Fractures with limb threat or risk of non union
- Augment natural healing with replacement or strengthening
- +/- immobilisation
- Rehabilitation
