Fracture Healing Flashcards
what does an osteoblast do?
- make bone matrix (aka osteoid)
- initiates mineralization of said matrix
- initiate resoprtion of this matrix via osteoclasts
bonus: help with calcium homeostasis and detection of use/damage to bone
what are osteocytes?
osteoblasts that have been surrounded by mineralized bone matrix
they sit in spaces called lacunae and extend long cytoplasm through canaliculi tunnels in bones to touch other osteocytes/blasts
what purpose do these canaliculi serve?
- facilitate Ca++ shifting (w/o bone structure change)
- detect changes in stress/strain/micro cracks in bone
- signal to osteoblasts –> initiate bone formation or resorption
what are osteoclasts?
multinucleate cells that do the bone resorbing
need access to mineralized surface of bone to do their work (they can’t bind to unmineralized bone)
how to osteoclasts resorb bone?
cell brush border needs to contact with mineralized bone
brush border secretes H+ ions = dissolves mineral and proteinases that cleave collagen within the matrix
what protects the surface of the bone from osteoclasts?
surface has continuous layer of osteoblasts as well as a thin layer of unmineralized bone mineral matrix
what gives bone its strength and flexibility?
- collagen content
- lamellar arrangement
what are the two developmental bone formation pathways? what’s the main difference?
intramembranous ossification
endochondral ossification
intramembranous - bone tissue formed directly
endochondral - hyaline cartilage template first, then bone
what is bone modelling? what are the two types and what differences between these types?
bone modelling = process by which primary (new) bone is formed by osteoblasts or resorbed by osteoclasts on a given bone envelope
types:
1. formation modelling = done by osteoblasts (bone deposited where it wasn’t before); stimulated by increase in bone strain
2. resorptive modelling = done by osteoclasts (bone removed to alter shape of primary bone); stimulated by decrease in bone strain
define Wolff’s Law
a principle describing how bone remodels in response to its mechanical environment: “bone adapts to the load under which it is placed”
explain Wolff’s Law
If the stresses in a region of bone increase, osteogenesis is
stimulated and the bone becomes stiffer and stronger.
If the stresses in a region of bone decrease, osteoclasts are stimulated to make the bone less stiff and strong.
= biofeedback system
* energy expenditure maintaining the bone is balanced against the strength of the bone needed for load-bearing, which makes for optimal bone structure
strength vs stiffness of bones
strength = ultimate load a material can stand before catastrophic failure
stiffness = rate at which material deforms when load is applied
how do you interpret a load-displacement curve?
elastic modulus / stiffness= slope of ascending linear portion of curve
* steeper slope = stiffer material
* here, displacement is elastic because material can return to original state
yield point = load exceeds ability for material to recover = material is permanently deformed
* permanent deformation = plastic deformation
ultimate point of failure = where material can withstand no more load –> material fails
total area under curve = toughness
* total energy absorbed during loading process
what type of material is bone?
viscoelastic
ability of bone to handle particular load depends on rate that load is applied to it
how to describe the behaviour of bone as material?
anisotropic
mechanical behaviour of material varies depending on direction in which the force is applied
