Bone Growth and Fractures Flashcards
Describe endochondral ossification.
Bone is formed onto temporary cartilage model
Cartilage model grows then chondrocytes mature and hypertrophy and growing cartilage model starts to calcify
Chondrocytes far from blood vessels less able to gain nutrients so start to died. Fragmented calified bone matrix left behind acts as structural framework for bony material
Osteoprogenitor cells and blood vessels from periosteum invade the area, proliferate and differentiate into osteoblasts which start to lay down bone matrix (in the primary ossification center first in the shaft, and then in the secondary ossification center in the epiphysis)
Describe the process of cessation of bone growth.
- Growth in height ceases at the end of puberty
- Sex steroids stimulate growth spurt but promote closure of epiphyseal plates
- Growth in length ceases, cell proliferation slows and plate thins
- Plate is invaded by blood vessels, epiphyseal and diaphyseal vessels unite
- May leave a line visible on x rays
How many ossification centers are there in bone ?
Some have only one
• Carpals, tarsals, ear ossicles
Most bones have 2+
• Head of humerus has 3
Why are ossification centers clinically important ?
- Appearance in age varies, so allows estimate of skeletal vs chronological age (can radiologically estimate age)
- Represent areas of bone that are subject to damage or trauma (area of growth plate damage)
Is the rate of growth of different bones the same ? Explain.
No, rate of growth varies
• From bone to bone
• Within same bone
Identify the zones of the epiphyseal plate, describing each.
“Ossification zone: Osteoclasts and osteoblasts from the diaphysial side break down the calcified cartilage and replace with mineralized bone tissue.
Calcification zone: Chondrocytes undergo apoptosis. Cartilaginous matrix begins to calcify.
Hypertrophic zone: Chondrocytes stop mitosis, and begin to hypertrophy
Proliferating (growth) zone: Chondrocytes undergo rapid mitosis
Resting zone: Quiescent chondrocytes are found at the epiphyseal end”
Identify the function of the resting zone of the epiphyseal plate, a possible disease associated with it, and the underlying defect.
RESTING ZONE
Function: Matrix Production
Example of disease: Diastrophic dwarfism
Defects: Defective collagen synthesis/ processing of proteoglycans
Identify the function of the growth zone of the epiphyseal plate, a possible disease associated with it, and the underlying defect.
GROWTH ZONE
Function: Cell Proliferation
Example of disease: Achondroplasia, Malnutrition, Irradiation injury
Defect: Deficiency in cell proliferation and/or matrix synthesis
Example of disease: Gigantism
Defect: Increased cell proliferation
Identify the function of the hypertrophic zone of the epiphyseal plate, a possible disease associated with it, and the underlying defect.
HYPERTROPHIC ZONE
Function: Calcification of matrix
Example of disease: Rickets (More common in children), osteomalacia (more common in adults)
Defect: Insufficiency of calcium or phosphate for normal calcification
Identify the function of the metaphysis of the epiphyseal plate, a possible disease associated with it, and the underlying defect.
METAPHYSIS
Function: Bone formation and vascularisation
Example of disease: Osteomyelitis
Defect: Bacterial infection
Example of disease: Osteogenesis imperfecta
Defect: Abnormality of osteoblasts and collagen synthesis
Example of disease: Scurvy
Defect: Inadequate collagen turnover
Normal growth and development of bone requires ___ (more than one thing) ? Can these affect healing of bone ?
– Calcium
– Phosphorus
– Vitamins A, C and D
– Balance between growth hormone, thyroid and parathyroid hormones, oestrogen and androgens
Yes, abnormalities in these can have an effect on fracture healing
Identify the following for cortical bone.
- Other names
- Percentage of human bones
- Location
- Structure
- Function
- Periosteum thickness
- Turnover rate
- Blood supply
- Fracture patterns
- Other names: Cortical bone, compact bone
- Percentage of human bones: 80%
- Location: Shaft of long bones
- Structure: Concentrically arranged lamellae - Haversian systems
- Function: Mechanically strong
- Periosteum thickness: Thick
- Turnover rate: Slow
- Blood supply: Slow
- Fracture patterns: Direct or indirect violence may result in deficits at the fracture site leading to non-union.
Identify the following for cancellous bone.
- Other names
- Percentage of human bones
- Location
- Structure
- Function
- Periosteum thickness
- Turnover rate
- Blood supply
- Fracture patterns
- Other names: Cancellous bone, trabecular bone
- Percentage of human bones: 20%
- Location: Ends of long bones, vertebral bodies, flat bones
- Structure: Meshwork of trabeculae with intercommunicating spaces
- Function: Metabolic
- Periosteum thickness: Thin
- Turnover rate: Rapid
- Blood supply: Rich
- Fracture patterns: Honeycomb structure fails as the result of compression (e.g. a fall from height compacts the bone)
What are the factors making up mechanism of injury ? Why is this important ?
1) Direction of force
– Direct v angular
– Rotational
– Compression
2) Energy transfer
– Cause
– Site
Important because it determines the likely type of fracture and the likelihood/time frame of recovery.
What information does bone imaging, with regards to a fracture ?
• Site & bones involved • Clues on soft tissue injury • Clues on energy transfer: – Wide displacement – Comminuted – Multiple fracture sites • Pathological bone (bone fracture caused by disease that led to weakness of the bone structure, such as cancer or osterporosis) • Paediatric bone (greenstick fracture, fracture due to energy transfer onto hands/wrists upon falling)
Defined Comminuted fracture.
One which produces multiple bone fragments
Identify and describe pediatric bone fractures.
- Greenstick fractures: properties of bone not fully matured so bendiness and flexility of bone means end up with bendy bone with stress lines
- Energy transfer onto hands/wrists upon falling: epiphyseal plates not fully fused, compression of bone
Define fracture.
A complete or incomplete break in a bone
What are the descriptors of a fracture ?
Site Open to surface Contaminated (e.g. compound fracture) Associated soft tissue injury Joint involvement Number of pieces Alignment Degree of separation
Define compound fracture.
A broken bone pierces the skin, causing a risk of infection
Identify the main types of fracture patterns.
- Transverse (fracture line is perpendicular to the long axis of the bone, two fracture fragments.)
- Linear/Longitudinal (fracture line runs nearly parallel to the long axis of the bone)
- Oblique non-displaced (fracture line is at an oblique angle to the long axis of the bone BUT bone maintains proper alignment)
- Oblique displaced (fracture line is at an oblique angle to the long axis of the bone BUT bone does not maintain proper alignment)
- Spiral (fracture plane rotates along the long axis of the bone. Due to rotational force)
- Greenstick (bone bends and cracks, instead of breaking completely into separate pieces)
- Comminuted (results in more than two fracture fragments)
- Avulsion fracture (a fragment of bone is separated from the main mass)
- Buckled fracture (=a.k.a. impacted fracture, torus fracture, ends are driven into each other, commonly seen in arm fractures in children)
- Compression or wedge fracture (usually involves the vertebrae)
- Stress fracture (=hairline crack, small crack or severe bruising in a bone due to overuse)
- Pathologic fracture (caused by a disease that weakens the bones)
What kind of direction of force is needed to inflict a spiral fracture ?
Twisting torsion
Identify the factors influencing if the fracture is limb threatening / if there is non-union risk.
– Dislocation – Comminuted – Compound – Compartment syndrome – Vascular / nerve injury – Significant soft issue injury – Pathological bone
Define non-union.
Complication of a fracture wherein the fracture repair process is arrested.
How good is bone at healing, compared to articular cartilage ?
• Bone has a remarkable capacity to heal well (unlike articular cartilage).
Define Bone Remodelling Units and state their function.
– Units consisting of osteoclasts and osteoblasts
– Keep adult bone mass relatively constant in the face of developmental, physiological and physical demands
What are some factors which healing depends on ?
– Activity of osteoblasts in the local periosteum
– Severity and position of the fracture
– Age of the patient
How long does it take for a fracture to heal ?
Takes 2 -20 weeks for healing, depending on age of patient, severity and position of the fracture.
Describe the physiological process of fracture healing.
- REACTIVE PHASE (10% of healing time)
• Fracture and inflammatory phase (haematoma to bridge gap)
• Fibroblasts in the periosteum proliferate to form granulation tissue around the fracture site - REPARATIVE PHASE (30-40%)
• Callus formation-osteoblasts quickly form woven bone, to bridge the gap (chondrocytes also help)
• Woven bone is weak as the collagen fibres are arranged irregularly
• Lamellar bone laid down-collagen organised in regular sheets to give strength and resilience - REMODELLING PHASE (50%)
• Remodelling by osteoclasts to restore original bone shape
• Influenced by strains and stress on the bone
Describe treatment for fractures.
1. CONSERVATIVE HEALING – Simple fracture with low risk of non-union – Dependent on natural healing process – +/- immobilisation – Rehabilitation
- INTERVENTION
– Fractures with limb threat or risk of non union
– Augment natural healing with replacement or strengthening
– +/- immobilisation
– Rehabilitation
Distinguish between between a primary and secondary ossification centre.
PRIMARY OSSIFICATION CENTERS
- where bone first forms
- long bones (shaft or diaphysis)
- irregular bones (body)
SECONDARY OSSIFICATION CENTERS
- individual bones may have multiple secondary centers
- usually found in epiphysis
