Bones 2 Flashcards
What do bones tell you about someones past?
Trauma
Disease - : OA, scoliosis, leprosy, syphilis
Physical activity
Diet (rickets)
Genetics
How does HRT affect bone and also what are the potential side effects?
Reduces loss in bone mineral density
Increases chance of breast cancer, coronary heart disease and stroke.
Which bone cell type is mechanosensitive?
Osteocytes
What are osteocytes sensitive to?
•Sensitive to
–Strain magnitude
–Strain rate
–Number of cycles (Static loads ignored)
–Load distribution
What is the role of sclerostin (produced by osteocytes?)
Sclerostin is expressed in osteocytes and some chondrocytes and it inhibits bone formation by osteoblasts
Sclerostin is essentially a glycoprotein that tells osteoblasts to chill out.
Sclerostin is inhibited by mechanical loading, parathyroid hormone and cytokines including prostaglandin E2. (all the times when we need osteoblasts to start replacing bone)
Which signalling pathway does sclerostin inhibit?
Wnt signalling pathway
What type of excersie maximises bone formation?
Exercise that features increased strain rates
What is meant by the refractory period of bone cells?
After stimulation won’t respond to further stimulation for some time.
Recovery periods restore mechanosensitivity of cells & enhance osteogenic potential
What is Wolffs law?
Bone in a healthy person or animal will adapt to the loads under which it is placed. If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading.
The inverse is true as well: if the loading on a bone decreases, the bone will become less dense and weaker due to the lack of the stimulus required for continued remodeling.
What are the different methods of bone imaging, and what is the colour of bone in each one?
DXA - dual energy X-Ray absorptiometry
Radiograph
CT
MRI (bone is black - the signal is from surrounding fat and water tissues)
HRpQCT - High Resolution Peripheral Quantitive Peripheral Computed tomography
Microscopy
Where is the bone stress located during axial loading and bending?
Axial loading - Stress unifrmly distributed
Bending - Focused at outer margins
What is meant by CSMI?
The cross-sectional moment of inertia (CSMI) is a measure of the distribution of material around a given axis, and it is proportional to its rigidity in bending.
The image shows that as the bone material moves further away from the centre then the CSMI and the section modulus actually increase - even when the bone mineral density stays the same.
When bone bending ability is measured in vivo - what directions is bend measured in?
AP
Torsion angle
ML Bending angle
•Significant increases in AnteroPosterior (AP) bending are seen as speed increased.
How do bones grow axially?
–Periosteal apposition (growth on the outside of cortex)
–Endocortical resorption (erosion on the inside of cortex)
Not symmetrical - strong and light
Which axis is most bone deposited over time?
Anterior - posterior axis
How does one change after menopause?
There is a loss in bone mass
Increase in periosteal and medullary diameters
Increase in CSMI and section modulus - although bone is lost - there is an increase in the efficiency of the bone
How did the skeletons of the long bow archers on ary Rose differ?
Robust humeri
Non-fusion in the scapula
Give examples of bone problems which matched occupations?
Tennis elbow
Housemaids knee
Clay - shovelers fracture
What examples of lack of loading leads to bone loss?
Bed rest
Spinal cord injury
Space flight
What hip gemoetry is associated with osteoporosis hip fracture?
Longer hip axis length
Increased neck shaft angle - ‘steeper’?
‘Decreased femoral neck width and increased length’ - I think?
https://www.sciencedirect.com/science/article/pii/S2214031X17300372
Fajar et al
‘There is strong evidence that elevated hip axis length, femoral neck angle and neck width are the risk factor for femoral neck fractures.’
What hip geometry is assocaited with osteoarthritis of the hip?
Hip Dysplasia
Cam/Pincer impingement
steeper neck shaft angle
Acetabular coverage
Other measurements of the hip include:
- Alpha angle
- CE angle
- Acetabular depth
- Extrusion index
•Femoral head /
neck ratio
How do we compare bone shapes?
Statistical shape modelling - gives us mode scores which can be used to predict fracture risk
•Mode 2 (shown)
–P = 0.019
–(Fracture vs. Control)
•Long thin neck, steep angle
–More likely to fracture
•Short stumpy neck
–Less likely to fracture
•Combination better than BMD alone
Further studies include: extended models, 3D models from CT, combination of shape and bone mineral
Osteoarthritis - can use kellgren and Lawrence grading although this is very subjuctive. Uses information such as loss of cartilage, cysts, ostephyte growth, sclerosis, femoral head deformation.
Bone resorption is greater in older people becuase resorption is greater than formation
Bone is still however responsive to exercise
Hip hop study showed that there was increase in Bone mass in both legs even though they were only exercising on one leg. Greater increase in the exercise leg.
What are the key exercise guidlines for people with osteoporosis?
Weight bearing and impact exercise
Using exercise to improve balance and prevent falls
Increasing back muscle strength for posture and pain management
