MSK Growth, Injury and Repair Flashcards
Define osteogenesis/ossification
Process of bone formation
When does bone development continue until?
Adult life (repair of fractures/remodelling)
What are the three types of bone cells?
Osteoclasts = breakdown bone and resorb it Osteoblast = produce bone Osteocytes = mature bone cells
What are the two types of ossification?
Intramembranous = mesenchyme –> bone (flat bones, irreg bones)
Endochondral = hyaline cartilage model –> bone (long bones)
What is interstitial growth?
Increase in length of the bone occurs at epiphyseal plate by mitosis
Chondrocytes next to diaphysis age and degenerate
Osteoblasts move in and ossify the matrix –> bone
(happens in early adulthood)
What is appositional growth?
Increase in bone width
Happens past adulthood in response to increased muscle activity/wt
Osteoblasts in periosteum form compact bone around external bone surface
Describe the long bone anatomy
Consists of:
Diaphysis - shaft
Epiphysis - ends
Metaphysis - flares at end of diaphysis
Physis - eipiphyseal growth plates (physis also on the lesser and greater trochanters)
Medullary canal (w. huge haematogenic potential)
What sort of movement does cortical bone resist?
Bending/torsion
What does cancellous bone resist?
Absorbs/resists compression
What does the cancellous bone contain?
Red bone marrow
How is cortical bone laid down?
Circumferentially
Which of cortical bone and trabecular bone is more active?
Trabecular
Define bone fracture
Break in structural continuity of the bone (crack, break, split, buckle, crumpling)
Why do bones fail?
Normal bones req. high energy injuries or repetitive stress (–> stress fracture)
Abnormal bones (osteoporosis, osteomalacia, metastatic tumours) may only req. a little bit of energy
Describe the process of fracture repair
Stage 1 - INFLAMMATION
Blood cells accumulate, pro-inflammatory cytokines released –> recruitment of platelets, monocytes, PMNs, neutrophils, macrophages etc. –> haematoma formation
Bone necrosis at fracture ends –> byproducts of cell death
Fibroblast replication in these areas
Osteogenic induction of muscle/soft tissue cells
Angiogenesis (low O2 in middle of fracture & macrophages produce angiogenic factors)
CAREFUL not to lose haematoma
Stage 2 - SOFT CALLUS FORMATION Pain and swelling subside Bony fragments become united by cartilage/fibrous tissue Stability by angulation can still occur Continued inc. in vascularity
Stage 3 - HARD CALLUS FORMATION
Conversion of cartilage –> woven bone (bone grows in from edges until it meets in middle)
Obvious callus on XRay
STAGE 4 - BONE REMODELLING
Conversion of woven bone –> lamellar bone
Medullary canal reconstituted
Bone responds to loading characteristics (Wolff’s law)
Why must you not give NSAIDs to patients straight after they fracture their bone?
Stop inflammatory process that is necessary for clot formation
Distinguish between primary bone healing and secondary bone healing
Primary = cortical bone directly tries to form bone without formation of a callus
Secondary = as above with callus formation
What is Wolff’s Law?
Bone in a healthy person will adapt to the loads under which it is placed
Finish the sentence:
Degree of instability is best expressed as …
A magnitude of strain
What happens if the amount of strain on the fracture is not right?
Too much - fracture won’t heal
Too little - won’t be enough mechanical induction of tissue differentiation
What is delayed union?
Failure to heal in expected time
What are the reasons for delayed union?
High energy injury Infection Distraction (osteogenic jumping) Steroids Immune supressors Warfarin NSAIDs Ciprofloxacin Smoking
What is non-union?
Failure to heal
What are the reasons for non-union?
Instability (xs osteoclasis) Failure calcification fibrocartilage (too much movement) Abundant callus formation Pain and tenderness Sclerosis Persistent fracture line
