An active cannula or sleeve which does more than merely maintain a channel or passage is usable to create and/or enlarge a channel or passage, to position a scope or instrument, to move or locate tissue, etc. The cannula can vary in size or shape as needed, intraoperatively. Because a cannula of the...http://www.google.com.au/patents/US5514153?utm_source=gb-gplus-sharePatent US5514153 - Method of dissecting tissue layers
