An alignment apparatus (1) for guiding a cutting element along a predetermined path in an intramedullary canal of a human bone, said apparatus comprising:-a frame (2) for guiding the cutting element along the predetermined path；-an adjustable clamp assembly (5), connected to said frame (2), for clamping the frame (2) to the bone；wherein:-the frame (2) comprises at least one tube (3, 4) with a lumen for guiding the cutting element, and which frame (2) is arranged to be inserted into the said intramedullary canal； and-the clamp assembly (5) is provided at a distal end (6) of the at least one tube (3, 4)；-the frame (2) comprises an inner tube (3) and an outer tube (4) that are coaxially positioned with respect to each other； which inner tube (3) and outer tube (4) are arranged to be inserted into said intramedullary canal；-the inner tube (3) is provided with the lumen for guiding the cutting element；-the clamp assembly (5) is configured to be actuable for clamping to the bone by a relative motion of the inner tube (3) and outer tube (4) with respect to each other；characterized in that-the clamp assembly (5) is provided on the inner tube (3) and comprises at least a first spreader (7, 8) which is embodied with two rings (9, 10； 11, 12) distant from each other that are mounted on and movable along the inner tube (3), and that are connected to each other with flexible legs (13, 14)；-a first stop (15) is provided at a distal end (6) of the inner tube (3) to prevent that the first spreader (7, 8) slides off the inner tube (3)；-a second stop (16) is embodied by a distal end (17) of the outer tube (4) which limits movement of at least one (12) of the two rings of the first spreader (7, 8)；-relative motion of the two rings (9, 10； 11, 12) of the first spreader (7, 8) causes flexing of the flexible legs (13, 14), such that an approaching motion of the two rings (9, 10； 11, 12) of the first spreader (7, 8) causes the flexible legs (13,
