DoITPoMS

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Questions

Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

  1. Bone is a composite of a mineral which can be approximated to hydroxyapatite, and which protein?

    a Keratin
    b Elastin
    c Collagen
    d Skelatin

  2. Which component of the hip implant is often made from ultra high molecular weight polyethylene?

    a Acetabular cup
    b Femoral head
    c Femoral stem
    d Bone cement

  3. A titanium alloy is often used for the femoral stem component of the hip implant. Which other metals are present in this alloy?

    a Aluminium and Vanadium
    b Aluminium and Chromium
    c Chromium and Molybdenum
    d Cobalt and chromium

  4. Fracture of bone occurs most easily:

    a In the transverse direction, perpendicular to the long axes of the osteons
    b Along the cement line, parallel to the long axes of the osteons
    c Between different lamellae in the same osteon
    d Parallel to the collagen fibres

Deeper questions

The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

  1. Which of these statement(s) is/are true?

    Yes No a Bone is stronger in compression than tension
    Yes No b Cortical bone has a J-shaped stress-strain curve
    Yes No c Tensile and compressive strength are higher in the longitudinal direction - parallel to osteon alignment.
    Yes No d The bone mineral forms a continuous matrix in the bone material.

  2. Which of these statement(s) is/are true?

    Yes No a Titanium has a Young's Modulus of around half that of stainless steel
    Yes No b Increasing the porosity of the titanium or titanium alloys will increase its Young's Modulus.
    Yes No c Uncemented implants have roughened surfaces to encourage bone growth.
    Yes No d Metal femoral heads have much lower wear rates than ceramic ones when used with a polyethylene acetabular cup.
    Yes No e Metal-on-metal implants can lead to elevated levels of metal ions in the bloodstream.

  3. Hydroxyapatite has a density of 3.16 Mg m-3 and collagen's density is 1.33 Mg m-3. Using the weight percentages for dry bone given, calculate the volume fractions of bone mineral and collagen in cortical bone.
    Use these volume fractions and the Young's Moduli of these components to calculate a value for the Young's modulus of dry cortical bone.
    Explain any difference between this and the value quoted in the TLP.

  4. In this diagram of the top of a femur, the thickness of the cortical bone in the main shaft of the femur is marked.
    This thickness is roughly 1 cm, with the marrow space located in the centre.
    Using this diagram, make estimates of the maximum stress generated in the femur when
    (A) standing still
    (B) walking down stairs
    human femur
    (S. Blatcher, PhD Thesis, Queen Mary College, London, 1995)


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