Forces acting on bone

Question 1

Describe compression force

Answer 1

Acts on long axis of bone
One end of bone must be in fixed position while other end is forced towards fixed end
Creates impacted or compression fracture

Question 2

Describe tension force

Answer 2

Force that pulls apart both axial ends
One end of bone must be in fixed position while other end is forced away from fixed end
Creates separation or avulsion fracture

Question 3

Describe torsion force

Answer 3

Force that tries to twist bone along its long axis
Usually result of one end of bone being placed in fixed position while other end is forced to rotate
Generally result in short or long spiral fractures

Question 4

Describe shear force

Answer 4

Unaligned forces pushing one part of body in one direction & another part in opposite direction
Produces fracture parallel to direction of applied force
Bone is weakest under shear stress

Question 5

Describe bending force

Answer 5

Combination of compression & tension

Question 6

Relate biomechanical strength of typical long bone to its anatomical structure

Answer 6

Bone mass distributed to where its needed & removed where not needed
The further bone mass is from centre the more difficult it is to bend
Bone is malleable so requires lot of force to break

Question 7

Explain how bone fatigue occurs

Answer 7

Develops when bone microdamage occurs faster than bone remodeling
Often manifests as stress fracture

Question 8

Explain Wolff’s law

Answer 8

Natural healthy bones will adapt & change to stress that its subjected to
e.g. if bones are subjected to heavier loads they will reconstruct themselves to accommodate that weight

Question 9

List factors that lead to bone remodeling & adaptation

Answer 9

Nutritional status
Humoral factors
Biomechanical stress
Physical activity

Question 10

Describe balance between bone resorption & deposition

Answer 10

Balance requires equal activity of osteoblasts & osteoclasts
Dynamic process
Important to maintain bone strength

Excessive resorption causes bones to weaken & become brittle (prone to fracture)

Osteoclasts lower pH by pumping protons into extracellular space causing bone mineral to dissolve
Also produce minerals that break down bone matrix

Osteoblasts then lay down new bone mineral

Bone formation takes longer than bone resorption