An interspinous process implant, comprising: a) an elongated body dimensioned and configured for percutaneous interspinous process implantation, defining a longitudinal axis, an interior cavity and opposed proximal and distal end portions (112, 113); b) a pair of laterally opposed engagement members (220a, 220b) mounted for movement between a first position stowed within the interior cavity of the body and a second position deployed from the interior cavity of the body to engage the spinous process, each engagement member (220a, 220b) including a central hub defining a common hub axis extending perpendicular to the longitudinal axis of the body; and c) an elongated drive shaft, characterized in that: the central hub of each engagement member (220a, 220b) has an inwardly extending crank pin (230a, 230b), wherein the inwardly extending crank pins (230a, 230b) of the two central hubs are radially offset from the hub axis and circumferentially spaced apart from one another about the hub axis, and the elongated drive shaft is mounted for axial movement within the interior cavity of the body along the longitudinal axis thereof and includes a distal actuation portion having upper and lower yokes (316a, 316b) positioned to cooperate with the circumferentially spaced apart inwardly extending crank pins (230a, 230b) of the two central hubs of the engagement members (220a, 220b), whereby axial movement of the drive shaft causes the two crank pins (230a, 230b) to translate through respective arcuate paths about the hub axis, causing corresponding rotational movement of the laterally opposed engagement members (220a, 220b) about the hub axis. a) an elongated body dimensioned and configured for percutaneous interspinous process implantation, defining a longitudinal axis, an interior cavity and opposed proximal and distal end portions (112, 113); b) a pair of laterally opposed engagement members (220a, 220b) mounted for movement between a first position stowed within the interior cavity of the body and a second position deployed from the interior cavity of the body to engage the spinous process, each engagement member (220a, 220b) including a central hub defining a common hub axis extending perpendicular to the longitudinal axis of the body; and c) an elongated drive shaft, characterized in that: the central hub of each engagement member (220a, 220b) has an inwardly extending crank pin (230a, 230b), wherein the inwardly extending crank pins (230a, 230b) of the two central hubs are radially offset from the hub axis and circumferentially spaced apart from one another about the hub axis, and the elongated drive shaft is mounted for axial movement within the interior cavity of the body along the longitudinal axis thereof and includes a distal actuation portion having upper and lower yokes (316a, 316b) positioned to cooperate with the circumferentially spaced apart inwardly extending crank pins (230a, 230b) of the two central hubs of the engagement members (220a, 220b), whereby axial movement of the drive shaft causes the two crank pins (230a, 230b) to translate through respective arcuate paths about the hub axis, causing corresponding rotational movement of the laterally opposed engagement members (220a, 220b) about the hub axis. the central hub of each engagement member (220a, 220b) has an inwardly extending crank pin (230a, 230b), wherein the inwardly extending crank pins (230a, 230b) of the two central hubs are radially offset from the hub axis and circumferentially spaced apart from one another about the hub axis, and the elongated drive shaft is mounted for axial movement within the interior cavity of the body along the longitudinal axis thereof and includes a distal actuation portion having upper and lower yokes (316a, 316b) positioned to cooperate with the circumferentially spaced apart inwardly extending crank pins (230a, 230b) of the two central hubs of the engagement members (220a, 220b), whereby axial movement of the drive shaft causes the two crank pins (230a, 230b) to translate through respective arcuate paths about the hub axis, causing corresponding rotational movement of the laterally opposed engagement members (220a, 220b) about the hub axis.