TUTORIAL: 3D Scan to Prosthetic Socket

This is a tutorial for the Hospital and Rehabilitation Center for Disabled Children in Nepal on how to cleanup their scan data for use in creating prosthetic legs.

Please view this tutorial on a desktop browser to see the embedded .WEBM videos.

Start by downloading Autodesk Meshmixer; a free mesh editing software.

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You will need some scan data. I have provided a scan of the mannequin I used to develop my 3D printed prosthetic design. Click the image to the right to download it.
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To open the file in Meshmixer, Press the “Import” button and select the file. “Import” lets you bring in objects of other file types (.OBJ, .STL, etc.) while “Open” opens Meshmixer files (*.mix).
Once you open the file in Meshmixer you will need to know these controls:
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Next, let’s make sure our units are correct. I used a Structure Core scanner to scan this mannequin. The Structure Core scans in Meters, but the file is in Millimeters.
  1. Go to Analysis -> Units/Dimensions.
  2. Change the Units of one of the drop down menus to “M” for “Meters”.
  3. Keep the unit numbers the same – so .911 mm becomes .911 meters.
  4. Next, select the same drop down and set it to mm. Say “Convert XYZ”. Now .911 meters becomes 911 mm.
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The scan will come in at a weird angle with some extra stuff we don’t need.
  1. To fix this, we will first press the “Select” button (Shortcut: “S”) on the left-hand main menu. Click and drag with your left mouse button on any empty spot in the 3D window to draw a lasso around the extra bits that we do not need.
  2. Press “X”, “Delete” to remove the extra parts.
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Next, we need to align the scan.
  1. Go to the Edit main menu.
  2. Select “Align”.
  3. You will see a ghosted transparent model and a solid model. The ghost model is where your model is now. The solid model is where it will move to.
  4. Make sure that the “Source” is set to “Surface Point” and the Destination is set to “World Origin/Y-Up”. Make sure “Transformation” is set to “Translate and Rotate”.
    1. For more explanation see the image to the right.
  5. Click on the very bottom of the residual limb on the transparent model, as close as you can to its center. We want this to be in the center of our scene.
  6. Try moving the point along the original model’s surface to see how the final result looks. Once you are satisfied, press accept.
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Once you hit accept, we will still have the “Edit” main menu open. Press Escape on your keyboard to close it. You can use Escape at any time to cancel the operation or menu you have open.
Ctrl-Z on the keyboard is undo.
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Next we need to separate the residual limb from the rest of the scan.
  1. Open the Select tool (Shortcut: “S”).
  2. Draw a lasso around the residual limb that we want to keep.
  3. Go to Edit submenu -> Separate (Shortcut: “Y”).
This will move the residual limb into a different object.
Different objects in Meshmixer can be shown and hidden separately. This allows us to keep the rest of the scan in the scene just in case, but hide it so that we can work on just the area we are interested in.
To view all the objects in the scene, go to View -> Show Object Browser. If the Object Browser is already open, this menu item will show “Hide Object Browser”.
For more details about the Object Browser, see the image to the right. This is a very powerful tool!
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Next, this scan has some issues with extra geometry inside of it. Using the select tool, double click on any extra remaining geometry. This will select all connected geometry pieces. Press X or Delete to remove the excess geometry.
NOTE: If your brush does not select the geometry after you double click, make the brush smaller and trying again.
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Now, go to the Select tool and make your brush relatively small. Double-click around the top of the residual limb to select the open loop of faces.
Then, go to the Edit submenu -> Modify -> Smooth Boundaries. This will smooth your selection so the top of the socket is not jagged and sharp.
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If you have an area of your mesh that has a hole in it, you can use this technique to fill that hole.
  1. Activate the Select tool.
  2. Double-click the area around the hole that you want to fill.
  3. Go to the Edit submenu and select “Erase and Fill” (Shortcut: “F”).
  4. Adjust the settings to your liking.
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Finally, to thicken the residual limb mesh and turn it into a socket:

  1. Press Ctrl-A on your keyboard to select everything in the Object.
  2. Then, go to the Edit submenu -> Offset command (Shortcut: “Ctrl-D”).
  3. Set the thickness of the socket that you would like; 5mm is typical. Make sure “Connected” is checked on.
  4. Press “Accept”.

NOTE: If you forgot to set your units properly in step three Meshmixer will freeze when you try to offset your model.

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That’s it! I hope this was helpful and if you have any questions drop a comment below and I’ll get back to you ASAP! Thanks for reading!