A device for placement between two adjacent spinous processes of a spinal column to treat a spinal condition, and a method for performing a procedure on a spine of a patient, are provided. The device may include a first member, a second member mounted onto the first member, and a locking plug configured to restrict movement of the second member relative to the first member. The method may include positioning a portion of a first member between two adjacent spinous processes of the spine, advancing a second member along a length of the first member, and restricting the second member from moving relative to the first member.