gure Q1 below). The wrist is a joint with three axes of rotation. The loading going through the wrist can vary depending on what the person is carrying and could be several times body weight. The loading is distributed between the radius and ulna with 87.5 % loading on the radius bone and 12.5 % loading on the ulna bone. The plate is designed to bridge the joint using titanium alloy screws fixed to the bone so that it can compress the bone and restrict movement and rotation in 3 axes while the bones heal and fuse together. The plate will experience tensile and bending stresses as shown. Assume bone size and shape does not change (i.e. no human variability).
Q1: A compression bone plate made from Titanium alloy (Ti-6Al-4V) has been designed to fuse
the wrist joint. This means securing the 3rd metacarpal bone (middle finger) to the radius bone
via screws to pre-tension the plate and as a result compress the bone to encourage bone healing
and prevent any movement of the wrist (see figure Q1 below). The wrist is a joint with three axes
of rotation. The loading going through the wrist can vary depending on what the person is
carrying and could be several times body weight. The loading is distributed between the radius
and ulna with 87.5 % loading on the radius bone and 12.5 % loading on the ulna bone. The plate
is designed to bridge the joint using titanium alloy screws fixed to the bone so that it can
compress the bone and restrict movement and rotation in 3 axes while the bones heal and fuse
together. The plate will experience tensile and bending stresses as shown. Assume bone size
and shape does not change (i.e. no human variability).
a) Assume the plate is in tension only and flat, this is the case immediately after
surgery when the wrist position is fixed with a splint and does not bend. Discuss
your approach to FE modelling the plate. Include the rationale for your boundary
conditions, mesh density, lines of symmetry (where necessary), 2D vs 3D modelling,
element types etc.
b) Discuss your approach to optimising the design. Use sketching and annotations to
help you illustrate.
c) How will your model and analysis be validated? Include the different validation steps
you would use.
d) Now assume the pre-tensioned plate is undergoing all three loading conditions
(bending in two directions and torsion), which is time when the patient can start
using their wrist. You will need to consider the bone curvature. How will this change
your approach outlined above? What would you do differently?
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