An improved spinous process fixation implant assembly 50 includes a spinous process fixation implant 100 and an interspinous spacer implant 200. The spinous process fixation implant 100 includes elongated first and second components 110, 120, that are arranged opposite and parallel to each other. First and second spinous processes 90a, 90b of first and second adjacent vertebrae 80a, 80b are clamped between the first and second components 110, 120, respectively, and are separated by the interspinous spacer implant 200. The interspinous spacer implant 200 may be inserted between the spinous processes of adjacent vertebrae from two different directions.