An apparatus for tissue separation comprises a hollow retractor expandable in at least one dimension, the retractor having upper and lower guide surface portions for contacting respective upper and lower tissue surfaces a first dilator having a distal portion configured to fit inside the upper and lower guide surface portions of the retractor so as to expand a distance between the upper and lower guide surface portions of the retractor and thereby separate the upper and lower tissue surfaces by a first distance and a second dilator having a distal portion configured to fit inside the upper and lower guide surface portions of the retractor so as to expand a distance between the upper and lower guide surface portions of the retractor and thereby render the upper and lower tissue surfaces being separated by a second distance, the second distance greater than the first distance.
