PDO and "ORDER BY" clausel with parameters

Hello!

I would like to know how I should bind a value to a parameter in a
"ORDER BY" clauses (the safe way).
I tried:

$sortfield = 'timestamp';
$sortorder = 'DESC';
$sql = "
SELECT newsid, title, timestamp
FROM news
ORDER BY :sortfield :sortorder
LIMIT 10
";
$newsitems = $dbh->prepare($sql);
$newsitems->bindparam(':sortfield', $sortfield, PDO::PARAM_STR);
$newsitems->bindparam(':sortorder', $sortorder, PDO::PARAM_STR);
$newsitems->execute();
[...]

But this will fail, because the query will look like

SELECT newsid, title, timestamp
FROM news
ORDER BY 'timestamp' 'DESC'
LIMIT 10

Is there a way to do it with PDO (I like the way PDO will secure the
values) or do I need to do it by myself?


Thanks!

--
Igor