Bones 2

Question 1

What do bones tell you about someones past?

Answer 1

Trauma

Disease - : OA, scoliosis, leprosy, syphilis

Physical activity

Diet (rickets)

Genetics

Question 2

How does HRT affect bone and also what are the potential side effects?

Answer 2

Reduces loss in bone mineral density

Increases chance of breast cancer, coronary heart disease and stroke.

Question 3

Which bone cell type is mechanosensitive?

Answer 3

Osteocytes

Question 4

What are osteocytes sensitive to?

Answer 4

•Sensitive to

–Strain magnitude

–Strain rate

–Number of cycles (Static loads ignored)

–Load distribution

Question 5

What is the role of sclerostin (produced by osteocytes?)

Answer 5

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)

Question 6

Which signalling pathway does sclerostin inhibit?

Answer 6

Wnt signalling pathway

Question 7

What type of excersie maximises bone formation?

Answer 7

Exercise that features increased strain rates

Question 8

What is meant by the refractory period of bone cells?

Answer 8

After stimulation won’t respond to further stimulation for some time.

Recovery periods restore mechanosensitivity of cells & enhance osteogenic potential

Question 9

What is Wolffs law?

Answer 9

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.

Question 10

What are the different methods of bone imaging, and what is the colour of bone in each one?

Answer 10

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

Question 11

Where is the bone stress located during axial loading and bending?

Answer 11

Axial loading - Stress unifrmly distributed

Bending - Focused at outer margins

Question 12

What is meant by CSMI?

Answer 12

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.

Question 13

When bone bending ability is measured in vivo - what directions is bend measured in?

Answer 13

AP

Torsion angle

ML Bending angle

•Significant increases in AnteroPosterior (AP) bending are seen as speed increased.

Question 14

How do bones grow axially?

Answer 14

–Periosteal apposition (growth on the outside of cortex)

–Endocortical resorption (erosion on the inside of cortex)

Not symmetrical - strong and light

Question 15

Which axis is most bone deposited over time?

Answer 15

Anterior - posterior axis

Question 16

How does one change after menopause?

Answer 16

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

Question 17

How did the skeletons of the long bow archers on ary Rose differ?

Answer 17

Robust humeri

Non-fusion in the scapula

Question 18

Give examples of bone problems which matched occupations?

Answer 18

Tennis elbow

Housemaids knee

Clay - shovelers fracture

Question 19

What examples of lack of loading leads to bone loss?

Answer 19

Bed rest

Spinal cord injury

Space flight

Question 20

What hip gemoetry is associated with osteoporosis hip fracture?

Answer 20

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.’

Question 21

What hip geometry is assocaited with osteoarthritis of the hip?

Answer 21

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

Question 22

How do we compare bone shapes?

Answer 22

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.

Question 23

Bone resorption is greater in older people becuase resorption is greater than formation

Answer 23

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.

Question 24

What are the key exercise guidlines for people with osteoporosis?

Answer 24

Weight bearing and impact exercise

Using exercise to improve balance and prevent falls

Increasing back muscle strength for posture and pain management