If you execute sql you can do whatever combinations you need:
CREATE PROCEDURE sproc_getAllForumThreads
@SortBy nvarchar(255),
@OrderType bit
AS
DECLARE @Order varchar(4), @sql varchar(1000)
IF @OrderType = 0
BEGIN
SET @Order = 'ASC'
END
ELSE
BEGIN
SET @Order = 'DESC'
END
SET @sql = 'SELECT Name,...