A patella resection assembly comprising: a patella resection guide having a first arm having a first bone-gripping member and a flat and planar saw guide surface, a second arm having a second bone gripping member, a connecting member connecting the first arm and the second arm, the connecting member having a slot and the first bone gripping member and the second bone gripping member facing each other, a stylus pivotably mounted to the first arm and the second arm and having a free end received in the slot in the connecting member, the stylus including an elongate member having a first longitudinal edge lying in a plane between the first bone-gripping member and the second bone-gripping member, in which the plane of the saw guide surface is perpendicular to the plane of the longitudinal edge of the stylus, and the distance between the longitudinal edge of the elongate member of the stylus and the plane of the saw guide surface defines the amount of bone to be resected from the patella, in which the first arm and second arm of the patella resection guide are movable to a variety of positions with different distances between the first bone-gripping member and the second bone-gripping member while the stylus is in place connected to the first arm and second arm and with the free end of the stylus within the slot in the connecting member, characterised in that the stylus includes a cross-member having a central portion connected to the elongate member and two end portions (114, 116) pivotably connected to the central portion, the end portions including mounting members (122, 124) for pivotally and removably mounting the stylus to the first arm and second arm of the resection guide. a patella resection guide having a first arm having a first bone-gripping member and a flat and planar saw guide surface, a second arm having a second bone gripping member, a connecting member connecting the first arm and the second arm, the connecting member having a slot and the first bone gripping member and the second bone gripping member facing each other, a stylus pivotably mounted to the first arm and the second arm and having a free end received in the slot in the connecting member, the stylus including an elongate member having a first longitudinal edge lying in a plane between the first bone-gripping member and the second bone-gripping member, in which the plane of the saw guide surface is perpendicular to the plane of the longitudinal edge of the stylus, and the distance between the longitudinal edge of the elongate member of the stylus and the plane of the saw guide surface defines the amount of bone to be resected from the patella, in which the first arm and second arm of the patella resection guide are movable to a variety of positions with different distances between the first bone-gripping member and the second bone-gripping member while the stylus is in place connected to the first arm and second arm and with the free end of the stylus within the slot in the connecting member, characterised in that the stylus includes a cross-member having a central portion connected to the elongate member and two end portions (114, 116) pivotably connected to the central portion, the end portions including mounting members (122, 124) for pivotally and removably mounting the stylus to the first arm and second arm of the resection guide.