Interspinous spacer with relatively few components and methods and systems

An interspinous spacer, comprising:

• a first arm comprising a body and two receiving extensions extending distally from the body, the body comprising a bridge extending between the two receiving extensions, two walls extending proximally from the bridge, and a latch extending distally from a proximal end of a one of the two walls of the body of the first arm and extending between the two walls of the body of the first arm;
• and
• a second arm comprising a body and two receiving extensions extending distally from the body, the body comprising a bridge extending between the two receiving extensions, two walls extending proximally from the bridge, and a lip extending from a proximal end of a one of the two walls of the body of the second arm and extending between the two walls of the body of the second arm;
• wherein the first arm and the second arm are coupled together by interleaving the two walls of the first and second arms, wherein the first arm and second arm, when coupled together, are rotatable from an implantation position with the two receiving extensions of both the first arm and second arm extending in a same direction to a deployed position with the two receiving extensions of the first arm extending in an opposite direction from the two receiving extensions of the second arm, wherein, in the deployed position, the latch of the body of the first arm is configured to engage the lip of the body of the second arm when the first arm and the second arm are pulled away from each other to prevent or hinder decoupling of the first arm from the second arm.