Abstract: An instrument including a cutter (2) mountable on a cutter 32 spindle (1) and shaped in such a way that it also acts as a test cup 33 engageable by a test head of a femoral prosthesis. The cutter (2) may be attached to the pelvis (34) by means of nails (29), and the cutter position is detected by sighting means (32) on the cutter spindle (1). The sighting means (32) are then used to arrange the final cup in the same position as the cutter (2) so that the position of the final cup may be selected in such a way that the risk of joint dislocation is reduced.

Abstract: The prosthesis of the invention comprises a shaft (1) with its upper end (3) linked to a neck (2) connecting it to a spherical joint head. The shaft (1) comprises a proximal area (H1, H2) with a reversed spiral double twist, over a length substantially equal to one third or half of the length (H) of the shaft (1). The proximal segment (H2) of the proximal area and the distal area (H3) are generally rectilinear in the antero-posterior plane, while the distal segment (H1) of the proximal area is curved with the center offset frontwards. The invention provides a prosthesis that fits more effectively in the medullary channel and does not need cement to fix it.