An interspinous process spacer for distraction of the vertebra including a body portion having an operative panel for increasing the height thereof and defining an internal void in which an expandable member is provided for actuating the operative panel. A self sealing percutaneous access port is provided to enlarge the expandable member and actuate the operative panel. The body portion is anchored by flanges secured to adjacent spinous process. The port allows for adding or removing fluid from the one or more chambers or envelopes of the expandable member in order to adjust the height of the body and thus the interspinous process spacing. Subsequent to initial implantation and expansion the volume of the expandable member may be increased or decreased in a non-surgical in-office procedure in which a needle is used to add or remove fluid from the expandable member via the port and tubular member.