Limbs and back week 1 Flashcards
Describe the blood supply to bone
vessels enter through epiphyses and periosteum
main supply from the nutrient artery somewhere in the middle of the shaft
Nutrient artery enters through the nutrient foramen
Describe Volkmann’s canals
carry arteries into the cortex from the inside of the bone
these branch into small vessels of the central canals of osteons
How are the collagen fibres arranged in osteons?
In different directions from layer to layer - this gives strength
How is calcium obtained in the body?
mainly from dairy products in the diet
it is absorbed by the duodenum of the small intestine
What are the two major hormones that regulate calcium absorption?
vitamin D and parathyroid hormone (PTH)
Describe PTH
parathyroid hormone
most important regulator of calcium metabolism
secreted by chief cells of the parathyroid gland
secretion of PTH is increased on response to hypocalaemia and hyperphoshphataemia
Describe the role of PTH
mainly acts on the bones and the kidneys
stimulates osteoclasts and increases bone resorption - increases serum concentrations of calcium and phosphorus
Stimulates the 1-alpha hydroxylase activity in the kidney, resulting in increased 1,25dihydroxyvitamin D production
Increases calcium reabsorption in the distal renal tubules
Increases phosphorus excretion by the kidney
What is the overall effect of PTH?
hypercalcaemia
hypophosphataemia
high urinary phosphorus
How is the secretion of PTH regulated?
calcium has a negative feedback effect in the parathyroid gland through calcium-detecting sensors
Describe vitamin D
essential in the homeostasis of calcium and phosphorus
mainly synthesised in the skin but also through diet
Active form is called 1,25dihydroxyvitamin or calcitriol
Describe the actions of vitamin D
a required factor for the bone resorption process
reabsorption of calcium and phosphorus from the renal tubules
Suppresses PTH secretion
Describe calcitonin
calcitonin lowers serum calcium but normally only when it is pathologically elevated
its exact physiological action is unknown but it has an inhibitory effect on osteoclasts
Where is calcitonin secreted from?
specialised parafollicular cells of the thyroid in response to high calcium levels
Describe fibroblast growth factor 23
mainly secreted by osteocytes in response to hyperphosphataemia
increases phosphorus clearance in the kidney
inhibits the 1 -alpha hydroxalase enzyme so prevents the production of calcitriol.
Describe bone healing
immediately after the fracture there will be a haemorrhage within the bone due to ruptured vessels in the marrow cavity, and also around the bone related to the periosteum
A haematoma at the fracture site facilitates repair by providing a foundation for the growth of cells
Deviated bone fragments and soft tissue damage is removed in the initial phase of repair, along with organisation of the haemoatoma
The capillaries will be accompanied by fibroblasts and osteoblasts - bone is deposited in an irregularly woven patten
the mass of new bone is called callus bone
within the medullary cavity - internal callus
at the periosteum - external callus
Woven bone is subsequently replaced by more orderly lamellar bone
lamellar bone is gradually remodelled according to the direction of mechanical stress
What slows fracture healing?
if bone ends are mobile
infection
badly misaligned
avascular
describe osteoporosis fractures
most likely to occur in the thoracic region of the spine
due to thinning of bone they can collapse
compression fracture - vertebral wedging
pain, increased kyphosis, immobility
What is the management of vertebral fractures?
conservative
analgesics for pain
physiotherapy - increase mobility, weight bearing exercise
What is osteoporosis?
a disease in which there is a reduction in bone mass in the presence of normal mineralisation
What causes the bone to thin in osteoporosis?
a loss of coupling where bone resorption is greater than bone reformation
How might osteoporosis present?
fragility fracture
loss of height
stooping deformity
What are risk factors for osteoporosis?
increasing age female steroid therapy cushing's syndrome immobility alcoholism diabetes liver disease smoking
How is osteoporosis prevented and treated?
vertebral osteoporosis is reduced in women treated with hormone replacement therapy
biphosphonate drugs inhibit bone resorption and are more effective at preventing hip fractures
regular weight bearing exercise
dietary calcium intake
Describe typical vertebrae
increase in size distally
pedicle and laminae connect to create vertebral arch
successive vertebrae stack on top of each other to form the vertebral canal
vertebral body anterior to spinous proces
At what level does the spinal cord end at?
L1 to L2
What is kyphosis?
inward curve (naturally in lumbar and cervical spine)
What is lordosis?
outward curve (thoracic spine)
What is the facet orientation at the atlanto-occipital joint?
convex(occipital) , concave (atlas)
What movement is allowed at the atlanto-occiptial joint?
flexion / extension
what is the facet orientation at the atlanto-axial joint?
almost transverse
What movement is allowed at the atlanto-axial joint?
rotation
What is the facet orientation in the cervical spine (C2-C7)?
oblique
What movement is allowed in the cervical spine?
flexion / extension
What is the facet orientation in the thoracic spine?
almost coronal
What movement is allowed in the thoracic spine?
limited rotation
What is the facet orientation in the lumbar spine?
almost saggital
What movement is allowed in the lumbar spine?
flexion / extension
Describe the ligaments in the vertebrae
C1 and C2 alar ligament and transverse ligament of dens. Holds dense of C2 against anterior arch of C1
around most vertebral bodies - anterior longitudinal ligament (broad), posterior longitudinal ligament (thin)
Around most laminae and posterior processes - supraspinous ligament, interspinous ligament, ligaments flavour (between laminae)
describe IV disks
intervertebral disks
separate bodies
increase in size distally
important in absorption and dissipation of force
joint movement
disk is weakest posteriolaterally - annulation fibrosis
blood pumped through mechanical movement
what do IV disks contain?
phospholipase prostaglandins nitric oxide metalloproteinases inflammatory agents
Describe concentric movement
muscle tension sufficient to overcome the load - muscle shortens as in contracts
Describe eccentric movement
insufficient muscle tension to overcome the force - fibres lengthen as they contract
Give examples of conditions that cause a loss of mineralisation
osteomalacia, rickets
Give examples of conditions that cause a loss of bone mass
osteoporosis, osteogenesis imperfecta
Give examples of conditions that cause a high bone turnover
pagets
hyperparathyroidism
thyrotoxicosis
Give examples of conditions that cause low bone turnover
hypophostatasia
Describe osteomalacia / rickets
poorly mineralised osteoid
severe / long standing vitamin D deficiency
reduced availability of calcium and phosphate
Describe paget’s disease
rapid bone turnover both resorption and formation increased disorganised structure reduced bone strength risk of fracture linked to osteosarcoma tumour suppressor gene
describe corticosteroid induced osteoporosis
increased osteoclastic activity
decreased osteoblastic activity
impaired collagen formation
increased bone turnover and poor bone formation and healing
Describe osteopetrosis
failure of remodelling - decreased turnover
unregulated osteoblastic activity though not necessarily increased
impaired osteoclastic activity
dense but weak bones
Describe fluorosis
defective mineralisation
fluoride replaces calcium in the matrix
Describe primary hyperparathyroidism
unregulated PTH secretion hypercalcaemia loss phosphate markedly increased bone turnover may retain bone mass but often osteoporosis
Describe osteogenesis imperfecta
genetic bone disorder defect / deficiency in collagen I various types recurrent childhood fractures deformities low muscle tone bluish sclerae
Describe the causes of Rickets
nutritional congenital rickets of prematurity neoplastic rickets hypophosphataemia rickets drug - induced rickets renal causes - renal osteodystrphy, falcon syndrome tumour induced osteomalacia
