shaft may be coated with a lubricious coating or other such treatment to facilitate sliding these may include e g teflon u00ae silicone surface energy treatments etc as noted above translation of the proximal and distal ends towards each other leads to radial expansion of portions of the expandable spacer body 14 in more detail the expandable spacer body 14 is formed of a helical body the cross section of the helical body changes to cause the expansion upon longitudinal translation referring in particular to fig3 b 3e cross sections of various helical segments 14 a 14 b 14 c 14 max 14 n are shown for a helical body having n turns of course it is noted that these elements reflect cross sections that in an actual device may be continuously changing along the helix for clarity these two dimensional cross sections are discussed here with the understanding that they refer to a three dimensional helical structure that may be continuously changing in cross section for example portions of the helical body between segments 14 b and 14 c emerge above the plane of the page and descend below the plane of the page these portions may have cross sectional shapes that are the same as or different than that of segments 14 b and 14 c in general they may be close to the same and may be shaped in a fashion intermediate to that of 14 b and 14 c in an unexpanded configuration all segments 14 a 14 n.