0624 - Fracture Healing Flashcards
What are the two primary forms of bone? Outline each.
Woven and Lamellar bone
Woven - Immature, randomly arranged collagen (Type 1) in osteoid. Seen in rapid osteoid production (foetal bone, healing fracture).
Lamellar - Regular parallel bands of collagen arranged in sheets. Can be compact or cancellous. Most healthy adult bone, stronger and more resilient than woven bone.
Woven is eventually remodelled to form lamellar.
What are the three main bone cells? What is the function of each?
Osteoblasts - Make osteoid and mediate mineralisation.
Osteocytes - Inactive osteoblasts trapped within formed bone.
Osteoclasts - Capable of eroding bone and remodelling bone. Monocyte derived.
How are osteoclasts activated?
RANK-Ligand and RANK
RANK activation causes osteoclast activation. RANKL inhibitors important for treating Paget’s and metastatic disease - strengthens bone and decreases risk of fracture.
What are the broad components of bone?
Cells and ECM
Cells - Osteoblasts/cytes/clasts
ECM - Osteoid (type I collagen), calcium hydroxyapatite, and non-fibrillar proteins (osteopontin, osteonectin)
What are the two types of bone development
Endochondral ossification - Form bone from a cartilage matrix - how bones grow in length, making cartilage that turns into bone. Via hypertrophy of chondroblasts.
Intramembranous ossification - Primitive mesenchymal matrix (laid by periosteum) which then forms bone by mesenchymal preosteoblasts differentiating directly into osteoblasts (without a cartilage matrix) - how bones grow in width and in foetus.
Define Fracture
A discontinuity in the bone
What are the types of fracture? (5)
Comminuted - Multiple fragments
Transverse - straight across
Oblique - Oblique line
Spiral - around the bone
Segmental - 2 or more fractures in one bone.
What is the difference between a Linear and a Comminuted fracture?
Linear - Oblique or transverse line of fracture.
Comminuted - more complex, may involve shattered bones.
What is the difference between Complete and incomplete fracture?
Complete - the fracture line proceeds across the entire plane of the bone.
Incomplete - there is an element of continuity that is contiguous with the fracture line.
What is the difference between displaced and non-displaced fractures?
Displaced - edges are no longer opposed, possible laceration of vessels/nerves in vicinity.
Non-displaced - edges are opposed allowing for better healing.
What is the difference between Open vs Closed fractures?
Open - through the skin
Closed - contained within.
What are the three causes of fracture?
Trauma - mechanical force
Pathological - Bone weakened by another primary process (low-impact)
Stress - repeated, chronic, comparatively low stress.
What are the two types of fracture healing?
Primary and secondary.
No different to any other tissue (requires lots of granulation tissue) except that bone needs to form too.
Describe primary fracture healing
Occurs with reduction and/or rigid internal fixation (oppose the ends or fix it in place).
Minimal periosteal response, so no callus formation. Attempt by cortex to re-establish new Haversian systems (normal bone homeostasis)
Describe secondary fracture healing
Occurs in majority of fractures. There is a periosteal reaction, forming a callous.
Involves both endochondral and intramembranous ossification.
Need rigid fixation to minimise the callous.
What are the temporal stages of fracture healing (brief)
Inflammatory - Haematoma formation, inflammation, granulation tissue formation
Reparative - Soft callous, becoming hard callous
Remodeling - Reshaping bone to normal contour.
Outline the 6 physiological stages of fracture healing.
1 - Haematoma - Stimulated by bone necrosis and hyposia, phagocytes and lysosomes clear debris, fibrin mesh forms scaffold, and new capillaries grow in from periosteum.
2 - Cellular/Granulation - Formation of granulation tissue (new CT and angiogenesis)
3 - Soft Callus - Influx of fibroblasts and osteoblasts form periosteum, produce a fibrocartilagenous (soft) callus of woven bone. Lasts for 3 weeks
4 - Hard Callus - Connects bone filament to woven bone. Gains strength, but without immobilisation, cartilage will form instead of bone.
5 - Ossification (mineralisation) - Starts by 2-3 weeks, lasts 3 months. Requires immobilisation, allowing bone ends to cross over and develop new Haversian system.
6 - Remodeling - Hard callus is remodeled to compact bone. May take months-years.
What are the broad causes of non-healing fractures?
Local - Poor blood supply, poor immobilisation, infection, soft tissue injury, bone death
Systemic - Malnutrition (reduces osteochondral cells, decreases callous formation), smoking (inhibits osteoblasts, nicotine vasoconstriction), Diabetes (collagen defects, microvascular disease), anti-inflammatory medications (cause temporary reduction in bone healing).
