Trauma Flashcards
Why do bones heal? Why is it important?
- Due to evolution, we are genetically predisposed to heal fractures
- It’s important for bones to heal because we need bones for daily function
Do bones need external help to heal?
No
What is so special about tissue ‘bone’?
- It is the only tissue that heals without scarring
- Scarring can impede function
- Other tissues are often repaired using different tissues (e.g fibrous)
What are the changes in a bone after a break histologically and macroscopically?
- Histologically, there is no scar after a break because the bone is repaired using the bone tissue
- Macroscopically, a callus may be seen as scarring
What is a callous? What kind of tissue is it? When does it form? Where do you not want a callus?
- Bony and cartilaginous structure that forms a connecting bridge across a bone fracture during the repair.
- Same tissue as bone. Forms during secondary healing, not primary (surgery)
- You don’t want a callus at an articular surface as it would disrupt movement
What are the 3 major components of a long bone?
- Epiphyses (found at proximal and distal ends of the bone, covered with articular cartilage to help with joint movement)
- Diaphysis (shaft of bone)
- Metaphysis (conical expansion from diaphysis to epiphysis)
What are epiphyses? Where are they found? What do they carry? What are they covered with and why?
What kind of bone do they contain and why?
What marrow does it contain and why?
- Found at the proximal and distal ends od bone
- They carry the joint surface so often have a complex shape
- They are covered with articular cartilage to help with movement because articular cartilage is very smooth
- They contain airy spongey (cancellous bone) which helps reduce the overall weight of the bone and provide flexibility
- They contain red bone barrow which is essential for RBC turnover
What is cancellous bone (trabecular bone/spongy bone)?
- Porous bone
- Has many enclosed spaces to give it a honeycombed appearance
What is the diaphysis? What is it composed of? What cavities does it contain?
- Shaft of the bone
- Composed of compact cortical bone
- Has medullary cavities that have yellow marrow which contain a lot of fat
What can a diaphyseal fracture lead to?
-It can lead to fatty emboli due to the fatty yellow marrow in the medullary cavities
What is compact/cortical bone?
- Dense protective outer layer
- Less porous than trabecular bone
What is the metaphysis?
-Conical expansion from diaphysis to epiphysis
What is physis? Why is it important? What is it in adults?
- The growth plate
- Separates epiphyses from the metaphysis
- Allows longitudinal growth of bones in children
- It forms the epiphyseal scar that can be seen on radiographs
What is the epiphyseal scar?
Fusion of growth plates
What are the 2 membranes of long bones?
- Periosteum (outside of bone)
- Endosteoum (thin vascular membrane that lines medullary cavity)
What is the periosteum? What layers does it consist of and why is it important? Why is it thicker in children
- Outer-membrane of bone
- Consists of the deep cellular layer which acts as a stem-cell reserve
- Consists of the fibrous superficial layer which transmits nutrient arteries to the bone
- Periosteum is thicker in children so they can heal fractures quicker than adults
What is the endosteum?
-Thin vascular membrane that lines the medullary cavity
What arteries does the superficial fifibrous layer of the periosteum transmit to the bone?
Nutrient arteries
What are the 2 types of bone?
What are the 2 forms of bone?
-Types: cortical and cancelleous
Forms: Woven and lamellar
What is the difference between woven and lamellar bone?
- Woven bone (fibrous bone) = collagen fibres are randomly arranged. Immature form of bone when bone is formed rapidly e.g early stages of fracture, before bone remodelling. Mechanically weak
- Lamella bone = collagen fibres are arranged in parallel. Woven bone is remodelled into lamella bone. Almost all bones of healthy adults are made of lamella bone.
What form of bone makes up most bones of healthy adults?
Lamella bone
Where is cortical bone found? What is it composed of? What is its structure? What types of cells are found here?
What is cortical bone covered by?
What do the medullary cavities of cortical bone contain?
- Found on the outer portion of long bones and vertebrae
- Composed of osteons (long parallel columns)
- Osteons are made up of concentric rings of bone (lamellae) surrounding a central Harvesian canal
- (Harvesian canal contains lymphatics and blood vessels)
- Buried within lacunae (spaces) of bone are osteoctyes
- Cortical bone is covered by periosteum
- The medullary cavities contain yellow marrow (diaphysis mainly?)
What is spongey made up of? What are the spaces filled with?
- Made up of trabeculae
- Trabeculae connect with each other and to the endosteum
- The spaces between trabeculae are filled with red marrow (hematopoietic tissue) or yellow marrow (adipose tissue)
What are the 3 types of bone cells?
- Osteoblasts (produce osteoid- made from collagen and other proteins, unmineralised bone matrix). Bone forming cells
- Osteocytes (terminally differentiated osteoblasts)
- Osteoclasts (bone-reabsorbing cells)
What is the difference between osteon and osteoid?
- Osteon= functional unit of cortical bone
- Osteoid= unmineralised bone matrix, made up of collagen and other proteins
What cells do osteoblasts, osteocytes and osteoclasts differentiate from?
- Osteoblasts (lie on surface of bone): mesenchymal stem cells
- Osteocytes (buried within cortical and spongey bone, regulate remodelling, release FGF-23 for Pi excretion): mesenchymal stem cells
- Osteoclasts (multinucleate cells found on surface of bone, modified macrophages, responsive to inflammatory mediators): Haematopoietic stem cells
What is osteoclast differentiation?
- RANK-L binds RANK on osteoclasts, stimulating its differentiation
- RANK-L is produced by osteoblasts and osteocytes in response to PTH and activated vit D
- GM-CSF (cytokine secreted by T cells) is required for osteoclast activation
- OPG is a decoy receptor produced by osteocytes, preventing activation of RANK
What is osteoblast differentiation?
- Osteocytes activate the Wnt pathway of osteoblasts, promoting its differentiation
- PGE2, NO, ATP activate Wnt pathway
- Sclerostin and dickkpoff inhibit the pathway
- Without sclerostin, sclerostosis occurs which can entrap cranial nerves causing neurological problems
What are the 8 mechanisms of injury (MOI)?
- Falls
- Twisting
- Blunt trauma
- Penetrating trauma
- Blast injuries
- Crush injuries
- Combination of injuries
- Pathological fractures
How can falls cause fractures?
- Lead to transfer of energy into patient’s body
- The higher the fall is from, the greater energy transfer
- What part of the body the patient falls on determines the injuries
- Can also cause compression of spinal cord
How can twisting cause fracture? What kind of fracture can it cause? What do we need to try and overcome?
- Twisting transmits torsional forces through the patient
- Can lead to spiral fractures
- When treating this, we need to try and overcome the natural property of bone to try and twist back as this can displace the fracture?
How can blunt trauma cause fractures?
- Can cause bone to bend
- Resulting in transverse and wedge fractures
- Size of patient has a large impact of a blunt force e.g baby vs hench man getting run over
How can penetrating trauma cause fractures? What kind of fracture? What should you look for?
- Involves soft tissue more than bone
- Certain penetrating injuries can cause comminuted fractures e.g gun shot wounds
- Always look for several entry holes and exit wounds
How do blast injuries cause fractures?
- Primary injury from the blast wave which damages hollow viscera where there is a pressure difference or air-fluid level
- There is potential for secondary injury from projectiles (penetrating trauma)
- Tertiary injury from falls
- Quaternary injury from fire burns or building collapse (blunt trauma or crush injuries)
How do crush injuries cause fracture?
- Usually involve a limb
- Can be more severe if pelvis or thorax is involved
- Continual load is applied and severely damage the soft tissue and bone
- Soft tissue injuries continue for hours after initial insult
How do combination injuries cause fractures?
- Combination of the injuries mentioned before
- Often occurs in sports injuries
What are pathological fractures? What can cause them?
- Normal force is applied to bone, causing it to break
- Osteoporosis is associated with fragility of hip, spine and wrist fractures
- Malignancies can also cause fractures by causing lytic lesions - can be primary or secondary (metastasis)
- Osteomalacia, and Paget’s syndrome are also associated with fractures
- Stress fractures count as pathological fractures (repetitive but normal-sized force causes a fracture as bone does not have time to release absorbed energy before the stress is reapplied.
What causes stress fractures?
Repetitive but normal-sized force is applied. Bone does not have enough time to release the absorbed energy before the stress is reapplied
What key points about MOI of fractures?
- The type of force applied to bone determines the mode of failure and therefore fracture pattern
- Traumatic fractures are where an abnormal load is applied to a normal bone
- Pathological fractures are where a normal load is applied to an abnormal bone
How can fractures heal?
-Occurs via primary or secondary mechanisms
What is secondary fracture healing? What does it result in?
-Physiological healing, resulting in formation of callus
What is primary fracture healing?
-When the bone heals without callus formation due to surgical intervention
What is secondary healing? How long does it take to produce the section of remodelled bone? How many stages are there? What are the stages?
What two ossifications are involved?
- Physiological healing with callus formation
- Can take months to years
- 4 stages
- Stage 1: Haematoma formation (days 1-5)
- Stage 2: Fibrocartilaginous (soft) callus formation (days 5-15)
- Stage 3: Bony hard callus formation (days 11-28)
- Stage 4: Bony remodelling (day 18 and years after insult)
- Ossifications: Endochondral ossification and intramembranous ossification
What can cause delayed or failed healing?
- Infection
- Tumour
- Disrupted vascular supply
What is a haematoma formation? (days 1-5) When does it occur? What has ruptured? What does this cause?
What are the first cells on the scene? Why? What happens next? What cells are attracted? What other cytokines are produced and why?
Is the initial acute inflammatory response short-lived or long-lasting?
- Localised bleeding outside of blood vessels
- Begins immediately after fracture is sustained
- The nutrient vessels in the fibrous superficial layer of the periosteum are ruptured, forming a hematoma around the fracture site
- Platelets are the first cells on the scene to cause clotting
- Platelets, damaged bone and periosteum secrete pro-inflammatory cytokines such as TNF-A, BMP, IL1,6,11,23
- These cytokines attract macrophages, monocytes and lymphocytes which begin to remove damaged tissue and secrete cytokines like VEGF to promote healing and angiogenesis
- The initial acute inflammatory response short-lived
What are the pro-inflammatory mediators produced by platelets and damaged bone and periosteum?
What do the macrophages and monocytes produce?
- TNF-a, BMP, IL-1,6,11,23 which attract macrophages, monocytes
- VEGF for healing and angiogenesis
What are the steps in fibrocartilaginous callus formation? What happens within the hematoma?
What does the BMP do? What types of cells are produced and what do they do?
What does it result in?
What happens to the periosteum?
- The release of VEGF promotes angiogenesis
- Within haematoma, fibrin rich granulation begins to develop
- The BMP recruit mesenchymal stem cells which differentiate to fibroblasts
- Fibroblasts lay down a matrix to bridge the fracture
- Later, the mesenchymal stem cells differentiate into chondroblasts and osteoblasts
- The chondroblasts and osteoblasts lay down are cartilaginous matrix and osteoid at the fracture site
- The result is a fibrocartilaginous network that spans the fracture site
- At the same time, adjacent to the periosteum, a layer of woven bone is laid down by osteoprogenitor cells
What is bony callous formation (days 11-28)? What kind of ossification does the cartilaginous callus undergo?
What does the expression of RANK-L induce?
What does this lead to?
What happens superiosteally?
- The cartilaginous callus undergoes endochondral ossification
- RANK-L is expressed, stimulating further differentiation of chondroblasts, chrondroclasts, osteoblasts and osteoclasts
- As a result, the cartilagenous callus is resorbed and calcifies
- Subperiosteally, woven bone continues to be laid down
- The newly formed blood vessels continue to proliferate, allowing further migration of mesenchymal stem cells into the area
- At the end of this phase, a hard calcified callus of immature woven bone forms
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