Abstract: A blade segment (4, 4a, 4b, 8, 8a, 8b) for a refiner (1) for refining fibrous material has first (20) and second (21) end edges and first (22) and second (23) side edges, the first (22) and second (23) side edges extending between the first (20) and second (21) end edges. The segment has a refining surface (5, 9) with blade bars (27) and grooves (28) on the segment front surface (25). At least one opening (14, 15) at the side edge (22, 23) extends through the whole thickness of the segment body (24) and towards the opposite side edge (22, 23). A guide element projects from the segment background surface (26) at the side edge which provides a guide surface that intensifies the feed of the material to be refined through the opening to the refining surface of the blade segment into the refining chamber of the refiner.