It is very rare to get any nerve pain following subacromial decompression in relation to the shoulder surgery itself. What probably happened is that the outstretched arm position adopted during the surgery stretched the nerves that go from the neck to the arm. This causes a problem of irritated nerve root. The pain in your hand should be accompanied by either/or tingling or numbness. Usually this problem settles but in my experience anywhere between 3m and 1 year. If it does not settle the MRI of the neck is needed to check for a structural compression of a nerve root.