Please help with cutting and rotating an object

So I have a project I’m working on and want to be able to cut a small semicircular region out of an object and then rotate it. You can see in this image of a bone (what I"m working with specifically the arc. Basically I’d like it to be as if I’d taken a saw to the original object along that arc so I end up with to components. The original bone with an arc cut out, and the bit of bone that was removed. I then want to rotate that bit of bone in place about 25%. This is basically simulating a TPLO procedure which you can look up if my explanation doesn’t make sense. I thought something along the lines of the Boolean procedure might work but can’t get it to quite shape up… I’m new to Sketchup so any suggestions would be appreciated!

I’m a woodworker, so cutting bone is a little outside my area, but I have some suggestions.
First, I assume you’ve made the bone a component. So, double-click on the bone to open the component for editing. Then double-click on the arc you wish to extract. If that highlights more than the arc, then you have other problems and need to back up, but let’s assume the arc gets highlighted. Cut the arc from the component (control-X on a PC, command-X on a Mac). Click away from the bone component to close it. Then go to Edit>paste in place. This will put the arc piece back where you left it; click on the arc and move it away from the bone; make the arc piece a component. Now you can rotate it to your heart’s content.
That’s the basic procedure I would follow, but you may encounter problems. If you simply drew the arc line on the surface of the bone, you will be left with some missing curved faces when you cut it from the bone component. Unless the arc piece is simply sawed away from the bone in a straight line, you’ll probably need to use a plug-in like Curviloft to generate all the needed faces for the arc piece as well as on the bone.
Hope this makes some sense, and I hope it helps.