An implantable spacer for placement between adjacent spinousprocesses in a spinal motion segment is provided. The spacer includes a bodydefining a longitudinal passageway. A first arm and a second arm are connectedto the body. Each arm has a pair of extensions and a saddle defining areceiving portion configured for seating a spinous process of a scolioticspine ora spine with misaligned spinous processes. Each arm has a proximal camingsurface and is capable of rotation with respect to the body. An actuatorassemblyis disposed inside the passageway and connected to the body. Whenadvanced, a threaded shaft of the actuator assembly contacts the camingsurfacesof arms to rotate them from an undeployed to a deployed configuration. In thedeployed configuration, the distracted adjacent spinous processes are seatedinthe superior and inferior arms of the spacer. Variations adapted for scolioticcurves are provided.
