I am trying to forward old posts on my site using .htaccess RewriteRule to new addresses.
First rule is
RewriteCond %{QUERY_STRING} id=16
RewriteRule ^current_article\.php$ /article/basics-of-electrosurgery [L,R=301]
which rewrites http://www.megadyne.com/current_article.php?id=16 to http://www.megadyne.com/article/basics-of-electrosurgery
Second rule is
RewriteRule ^article/([A-Za-z0-9-]+)/?$ articles.php?id=$1 [NC]
which rewrites http://www.megadyne.com/article/basics-of-electrosurgery to http://www.megadyne.com/articles.php?id=basics-of-electrosurgery
All works fine except the final result is http://www.megadyne.com/article/basics-of-electrosurgery?id=16 and I don't want it to append the final variable "?id=16" to the address.
You need a ? at the end of your first rule, and should probably add some boundaries to the query string match:
RewriteCond %{QUERY_STRING} (^|&)id=16($|&)
RewriteRule ^current_article\.php$ /article/basics-of-electrosurgery? [L,R=301]
When there's a query string in the request, it automatically gets appended to the end of the rule's target unless you are creating a query string in the target. So here, you're creating an empty query string, and without the QSA flag, the existing query string won't get appended.