//This could be used to grab the post into $output.

parse_str($_POST[item_order_str], $output);

//Now, as $output has multi dimensional associative array. Now, foreach would work with item_order:

    foreach ($output as $item_order)
    {
            foreach($item_order as $position => $values)
            {
            print "Item from $values moved to => $position\n"; //or add your sql statements

            }

    }