A para-spinal retractor for use during surgery which includes a planar ellipsoidal ring and a plurality of retractor blades which mount in the ring. The ring has a series of generally rectangular openings on either side of the major axis, and the blades have upturned rectangular cross-sections to slidably...http://www.google.com.au/patents/US4817587?utm_source=gb-gplus-sharePatent US4817587 - Ring para-spinal retractor
