In some people, the top of the arm bone needs to be replaced, but the socket is still in good shape. In others, the bone in the socket is too worn out and not strong enough to hold a new lining. In these cases an operation called a hemiarthroplasty may be the best option. Hemi means partial.
As seen before, the surgeon exposes the joint, prepares the top of the arm bone and inserts a metal stem with a ball on the end. If the socket is worn out, the surgeon smooths and reshapes it. The arm bone is then put back in place.