Any question answered...

Just to point out we're in to deep unqualified territory here. I'm not medically or veterinarly veterinarially trained as a vet so I really am guessing here, but I used to work in catering (again, no official qualifications) and used to see the bones that would come out of various joints of meat.

It looks like a scapula.

Human scapula are less symmetrical. A lot less symmetrical.

Something that size is quite big, a google search for 15cm scapula brings up pictures of deer.

People buy joints of venison and probably (stupidly, if they want their gardens to be ravaged by foxes) dispose of said bones in a compost bin.

Occam's razor, QED, etc.