Bone-implant assembly in AnyBody

Main Forum
1

Hi!
I want to try my own hip-implant model in AnyBody, and I learnt that it can be done as shown in the THA-KneeBendDemo. But, as my implant geometry is different from the geometry shown, the bone-implant assembly needs to be created freshly. How to do that in AnyBody? If I have my own bone-implant assembly, can I feed it to replace the existing femur part of the human model?

2

Dear Sumanta,

It is possible to scale and morph the generic AnyBody model into your subject. And the details depend on the level of accuracy you want to achieve. But, in general, I would use the following procedure:

  1. Scale the model using the anthropometric parameters of the patient
    2a. Replace the generic femur by the subject-specific scaling using a pre-op STL (if you have it).
    2b. If you don’t have the geometry - it is possible to do partial morphing of the femur or a linear scaling to get the joint-to-joint length right.
  2. Position the implant (meaning adjust the hip joint centre) according to the surgical plan.
  3. Account for change in muscle attachments/volumes/etc.

You can read the tutorials to learn about the subject-specific scaling and morphing.

Kind regards,
Pavel

3

Dear Mr. Pavel,
Thank you for the assistance. I am going through the subject-specific scaling and morphing tutorials to apply the scaling law to the body. But, when I am placing the implant in the model, to think of it physically, I need to cut the neck part of the femur and remove some amount of bone material so that a matching cavity is formed. This I used to do using Boolean operations in softwares like Mimics and Simpleware. How to achieve that in AMS?

4

AnyBody is a rigid-body dynamics system. So the cavity itself does not matter so much if you reconstruct the joint location correctly. The purpose of scaling is to get the correct muscle attachment locations. Once you achieve that - you could replace the drawing by the resected target bone surface with resection + the implant surface. You could use one of the morphing transformations to align geometries to be in the same reference frame.

AnyBody does not have a capability to perform boolean operations on STLs - only morphing is possible. So it will have to be outside using Mimics or something else.

Kind regards,
Pavel