this is one problem for wenger. his choice of mertesacker and koscielny as central defenders is so predictable that other managers build their tactics around it.
he needs to find a defender to play with vermaelen and rotate the two defences. one set of defenders should be designed to defend against fast teams and another to defend against tall teams. eg chelsea is fast but small and likes to counterattack so you don't need a giant, whereas west ham is tall but slower and exactly the kind of team where you need the bfg.
same goes for sagna who gets caught upfield playing winger - which is great for attacking but lousy when the other team turns over possession.
but the basic truth is, arsenal cannot afford the loss of ramsey. he's the extra man in attack and defence and he makes the runs that ozil targets. we've been much, much worse while he's been injured.