Bone & Fractures Flashcards
What is the function of the skeleton?
- Rigid supportive framework: Anchoring for organs/structures
- Movement: muscles use bones as levers
- Protection: CNS, organs
- Mineral store: calcium, phosphate ions
- Blood cell production: RBCs/WBCs
What are the 3 regions of bones?
Diaphysis
Metaphysis
Epiphysis
What is the difference between periosteum and endosteum?
Periosteum: Lining on the outside of the bone
Endosteum: Lining on the inside of the bone
Where is compact (cortical) bone found?
Outer layers of diaphysis and flat bones
What is the function of Harversian systems (osteons) and Haversian and Volkman’s canals?
- Haversian systems (osteons): functional component of bone, lamelli form nested concentric cylinders
- Haversian and Volkman’s canals: convey blood vessels through bone
What are the components of Haversian systems (osteons)?
- Haversian canal: hole running parallel to long axis of bone
- Lamelli: each ring around the canal
- Lacunae: hollows containing osteocytes
- Canaliculi: canals between lacunae, allow osteocytes to pass info, waste, O2
What are the characteristics of spongy (trabecular, cancellous) bone?
- Forms meshwork
- Trabeculae - few layers thick
- Spaces lined with endosteum & filled with marrow
What is the difference between osteoblasts, osteoclasts and osteocytes?
Osteoblasts: Form new bone matrix
Osteocytes: Osteoblasts trapped inside bone matrix after forming new bone
Osteoclasts: Break down bone matrix
What are the 4 types of cells found in bone tissue?
- Osteoprogenitor cells (osteoblasts, clasts, cytes)
- Matrix
- Fat cells
- Hematopoietic cells: make RBCs, WBCs within bone marrow
What is bone matrix made up of?
- Collagen fibres
- Glycoproteins
- Calcium salts
What are the components of bone matrix?
- Lamelli: layers of matrix
- Lacunae: hollows containing osteocytes
- Canaliculi: canals between lacunae, allow osteocytes to pass info, waste, O2
What happens during bone remodelling?
- Bone resorption by osteoclasts
- Release of osteocytes within osteon, form osteoblasts to lay down new bone
- Cell to cell communication
- Muscle pull appears to be significant stimulus
- Very specific cell responses to load rate, magnitude, timing of bouts
What is ossification?
Process of laying down new bone
What happens during ossification?
Osteoblasts secret matrix
- collagen fibres/glycoproteins
= osteoid
Osteoblasts secrete matrix vesicles
- enzyme accumulate Ca & phosphate ions in matrix
= bone mineral precipitation
What are the 2 forms of ossification?
Endochondral
Intramembranous
What is endochondral ossification and what does it enable?
Process of new cartilage being converted into bone, enables complex cartilaginous shapes to be ossified
When does endochondral ossification occur?
- Formation of long bones in embryo
- Growth in length of long bones
- Found in epiphyseal plates in growing bones
What are the 2 centres of endochondral ossification?
Primary centre:
- Near the centre of the diaphysis
Secondary centre:
- Growth plate
- Held between epiphysial bone plate and trabecular bone in metaphysis
- Allows bones to increase in length while maintaining strength
What is intramembranous ossification?
Process of bone matrix being laid down in fibrous tissue, doesn’t involve cartilage - formation of flat bones
What happens during intramembranous ossification?
Osteoblasts lay down spicules of bone which combine together to form sheets of bone
What are examples of flat bones?
- Skulls, parts of face
- Body of scapula
- Ribs
What happens during osteoporosis?
- Osteoclasts more active than osteoblasts
- Bone loses mass, density, becomes porous and easy to break
Why does osteoporosis occur?
Due to age or changes in hormonal levels
What is one of the implications of osteoporosis?
Vertebral compression - slouched posture, rounded cervical vertebrae
What happens in ageing bone?
- Loss of 1% per year, 2-3% after menopause
- Decreased Ca & fibres, causes bone to become more brittle
- Cortical bone thins from inside out, greater internal space
- Bigger Haversian canals, can withstand stress as well
- Increase porosity, osteoblasts
What are other age-related changes?
- Thinning of articular cartilage
- Calcification
- Disk changes
- Reduced transfer of nutrients
- Parathyroid hormone > calcitonin
How are fractures classified in terms of the mechanism of the break?
- Greenstick: Bent
- Spiral: Twisted
- Comminuted: Broke into lots of pieces
- Transverse: Clean, flat, horizontal break
- Compound: Break is through the skin
- Vertebral compression
How are fractures classified in terms of the end result of the fracture?
- Closed vs open (compound)
- Simple vs multi-fragmentary
- Stable vs unstable
- Displaced vs undisplaced
- Articular vs extra-articular: involving/not involving the joint
- Complications, e.g. near vessels, nerves etc
- Impacted (compacted): shunted into itself
What are the mechanisms of injury for fractures?
- Unloaded
- Tension (pulling away)
- Compression
- Bending
- Shear (two pieces of bone moving laterally away from each other)
- Torsion
What are the physical signs of a fracture?
- Abnormal movement
- Crepitus (grating between bone ends)
- Deformity
- Bruising around fracture
- Tenderness
- Pain on stressing the limb (bending/longitudinal compression)
- Impaired function
- Swelling
What other tissues can be injured by a fracture?
Joints Ligaments Soft tissues (blood vessels, nerves, muscles, skin, viscera)
What are the types of paediatric fractures?
- Greenstick
- Buckle (torus)
- Epiphysial fractures
What are the 6 steps of fracture healing?
1) Increase in blood flow:
- WBCs, fibro/osteoblasts
- Blood clot (procallus)
- Periosteum confines space, speeds healing process
2) Osteoblasts lay down bone
3) Formation of bony callus:
- 6-8 weeks
- Cast removed
- Primarily trabecular bone, very susceptible to re-fracture
4) Modelling
5) Remodelling
6) Healed fracture - 2 years
What occurs during stage 1 of fracture healing?
Inflammatory (first few days)
- Large hematoma
- Leukocytes/macrophages remove dead muscle/bone fragment
- Delicate fibrin network bridges fracture fragments
- Stimulates growth of osteoblasts
What occurs during stage 2 of fracture healing?
Callus (following 2 weeks)
- Fibrin network organised and reinforced by collagen fibres
- Capillaries bring O2/nutrients
- Osteoblasts form fibrocartilaginous matrix (osteoid)
- Osteoid becomes calcified, soft callus becomes visible (2-3 weeks)
- Osteoid is mineralised, fracture fragments cemented together - hard callus (6-12 weeks)
What occurs during stage 3 of fracture healing?
Remodelling (12-18 months)
- Osteoclasts remove immature woven bone
- Osteoblasts lay down lamellar bone along lines of mechanical stress
- Lamellar bone contains Haversian systems, making it much stronger
What are some of the early complications of fractures?
- Wound infection
- Fat embolism
- Shock lung (actue respiratory distress syndrome)
- Chest infection
- Disseminated intravascular coagulation
- Compartment syndrome
What are some of the late complications of fractures?
- Deformity
- Osteoarthritis of related joints
- Avascular necrosis
- Traumatic chondromalacia
- Complex regional pain syndrom
What are the reasons for fractures not healing?
- 10% of the time biological (natural problem)
- 90 of the time technical (not set right)
What are some of the complications for failure in fracture healing?
- Mal-union: heals with residual deformity
- Delayed union: takes longer
- Non-union: fracture gap fills with scar tissue instead of bridging callus
- Pseudoarthrosis: movement is excessive around fracture site, cavity forms with synovial fluid
- Rotation of bone segments (bad)
- Some angulation or displacement is OK
What is the treatment for fractures?
- Reduction
- Stabilisation
- Immobilisation of fracture site
- Rehabilitation of soft tissues and joints
What are the methods of reduction?
- Traction: e.g. Hamilton Russell traction
- External splints/braces/Plaster of Paris (POP), fibreglass
- External fixation: drilled through skin into bone
- Internal fixation: drilled into bone under skin
