An alignment apparatus for guiding a cutting element along a predetermined path in an intramedullary canal of a human bone, said apparatus comprising: - a frame for guiding the cutting element along the predetermined path; - an adjustable clamp assembly, connected to said frame, for clamping the frame to the bone; wherein: - the frame comprises at least one tube (3, 4) with a lumen for guiding the cutting element, and which frame is arranged to be inserted into the said intramedullary canal; and - the clamp assembly is provided at a distal end of the at least one tube (3, 4); - the frame comprises an inner tube and an outer tube that are coaxially positioned with respect to each other; which inner tube and outer tube are arranged to be inserted into said intramedullary canal; - the inner tube is provided with the lumen for guiding the cutting element; - the clamp assembly is configured to be actuable for clamping to the bone by a relative motion of the inner tube and outer tube with respect to each other; characterized in that - the clamp assembly is provided on the inner tube 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, and that are connected to each other with flexible legs (13, 14); - a first stop is provided at a distal end of the inner tube to prevent that the first spreader (7, 8) slides off the inner tube; - a second stop is embodied by a distal end of the outer tube which limits movement of at least one 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) will cause 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) will cause the flexible legs (13, 14) to flex out and engage the intramedullary canal so as to act as a clamp within said intramedullary canal. - a frame for guiding the cutting element along the predetermined path; - an adjustable clamp assembly, connected to said frame, for clamping the frame to the bone; - the frame comprises at least one tube (3, 4) with a lumen for guiding the cutting element, and which frame is arranged to be inserted into the said intramedullary canal; and - the clamp assembly is provided at a distal end of the at least one tube (3, 4); - the frame comprises an inner tube and an outer tube that are coaxially positioned with respect to each other; which inner tube and outer tube are arranged to be inserted into said intramedullary canal; - the inner tube is provided with the lumen for guiding the cutting element; - the clamp assembly is configured to be actuable for clamping to the bone by a relative motion of the inner tube and outer tube with respect to each other; - the clamp assembly is provided on the inner tube 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, and that are connected to each other with flexible legs (13, 14); - a first stop is provided at a distal end of the inner tube to prevent that the first spreader (7, 8) slides off the inner tube; - a second stop is embodied by a distal end of the outer tube which limits movement of at least one 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) will cause 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) will cause the flexible legs (13, 14) to flex out and engage the intramedullary canal so as to act as a clamp within said intramedullary canal.