A novel implantable spacer for placement between adjacent spinous processesin a spinal motion segment is provided. The spacer includes a body defining a longitudinalpassageway. A first arm and a second arm are connected to the body. Each arm hasa pair of extensions and a saddle defining a U-shaped configuration for seatinga spinous process therein. Each arm has a proximal camming surface and is capableof rotation with respect to the body. An actuator assembly is disposed insidethe longitudinal passageway and connected to the body. When advanced, the actuatorassembly contacts the camming surfaces of the arms to rotate them from an undeployedconfiguration to a deployed configuration. In the deployed configuration,the distracted adjacent spinous processes are seated in the U-shaped portionof the arms providing sufficient distraction to open the neural foramen to relievepain. An insertion instrument is provided for implanting the interpsinous processspacer. The system is configured for quick implantation through a small percutaneousincision employing minimally invasive techniques.
