Segmenting narrow bone structures

I am trying to segment out a scapula which has some pretty narrow sections. I tried the “Grow from Seeds” effect, but it doesn’t seem to work very well to capture the thin long cross sections. Is there a better method or is the best way to just use a threshold mask and then go in and paint through it manually?

Can you post a few screenshots, and preferably also a download link to a typical data set, so that we can see what the problems are?

If the issue is that cancellous bone regions inside are not filled then you can use “Wrap Solidify” effect (provided by SurfaceWrapSolidify extension) to fill them automatically.

Here is an example:

What is happening is that the smallest diameter of the paint brush (1%) is larger that the width of the bone profile, so I am getting a smaller than adequate segmentation area or larger adequate segmentation area depending on how I seed it.