fracures through the ages lecture - (osteoporosis etc.) Flashcards
effect of age on trabeculae
thick, high density trabeculae when young, but as get older they get thinner and become more fragile
composition of bone
matrix (organic: type 1 collagen, mucopolysaccharides, non-collagenous proteins; inorganic (hydroxyapatite: calcium, phosphorus) and cells (osteoprogenitor, osteocyte, osteoblast, osteoclast)
function of inorganic bone
Ca2+ reservoir
what can bone cells (10% of bone) respond to
hormones and other EC signals
normal bone turnover
amount reabsorbed by osteoclasts = amount laid down by osteoblasts
reason for bone turnover
replenished as otherwise more susceptible to fracture
what happens to bone turnover in osteoporosis
osteoclasts predominate, so more bone reabsorbed than is laid down (increase risk of fracture)
what measures bone density to give likelihood of fracture, and consequence
DEXA scan (score compares to same ethnicity but peak bone mass age), but doesn’t give information on health of bone (e.g. strength of trabeculae)
what measures bone density to give likelihood of fracture, and consequence
DEXA scan, but doesn’t give information on health of bone (e.g. strength of trabeculae)
how do bisphosphonates work, and consequence
kill osteoclasts (half life of 7 years) to prevent bone reabsorption, but no turnover of bone so bone may get microcracks, causing atypical fractures e.g. of shaft cortex which can’t heal due to long bisphosophonate half-life
who are more susceptible to osteoporosis
post-menopausal women (less protective effect of oestrogen), amputees (Wolff’s law - socket means it don’t load bone properly, and lost muscle insertion and pulling)
treatment for osteoporosis in amputees
not bisphosphonates as local, so exercise etc. to increase bone loading locally
alternative to bisphosphonates which is more specific
demosumab, which binds to RANKL to prevent upregulation of osteoclasts
fracture location with high mortality
neck of femur (generally associated with other medical problems in elderly)
why is exercise good for osteoporosis
Wolff’s law, as it stimulates bone lay-down (e.g. loaded deep flexion)
when is Ca2+ at maximum capacity, and consequence of Ca2+ on osteoporosis
when children (hence drinking milk etc.), and this affects osteoporosis later on (e.g. bone cleaved when need Ca2+, so higher risk of osteoporosis if less Ca2+ reservoir when child)
3 major signalling molecules of calcium homeostasis
vitamin D (increase Ca2+), PTH (increase Ca2+) and calcitonin (decrease Ca2+)
2 ways fractures heal
surgical, callous
describe surgical fracture healing
if two broken bones held directly together using plate or rod, bone can directly join across
describe 4 stages of callous fracture healing
week 1: blod pouring in to fracture to form haematoma, contained by soft tissue either side -> week 2-3: soft callus as cartilage laid down to improve stability -> week 4-16: cartilage becomes calcified to turn into woven (disorganised) bone so less strong -> week 17+: Wolff’s law as disorganised bone gets loaded, so forms cortical and trabeculae bone (excess bone reabsorbed by osteoclasts)
age at which bone fracture is fastest
when baby/young child
injuries causing different fracture patterns: spiral
twisting torsional injury
injuries causing different fracture patterns: oblique diagonal
compression injury
injuries causing different fracture patterns: butterfly fragment
direct hit injury
