Prosthesis for arthrodesis, wherein the prosthesis (1 a; 1 b; 1 c) comprises two prosthesis members (2a, 3a; 2b, 3b; 2c, 3c) which each is configured for attachment thereof to at least one of the bones at the joint, wherein one of the prosthesis members (2a; 2b; 2c) comprises a first attachment member (4a; 4b; 4c) which is configured for attachment to at least one of the bones at the joint and the other prosthesis member (3a; 3b; 3c) a second attachment member (5a; 5b; 5c) which is configured for attachment to at least one other bone at the joint, and wherein said one prosthesis member (2a; 2b; 2c) comprises a locking member (33a; 33b; 33c) and said other prosthesis member (3a; 3b; 3c) a lockable member (34a; 34b; 34c), wherein the locking member (33a; 33b; 33c) is configured with an attachment portion (16a; 16b; 16c) which is insertable into a hole (8a; 8b; 8c) in said first attachment member (4a; 4b; 4c) for attachment or location of the locking member therein, wherein except for the attachment portion (16a; 16b; 16c) the locking member (33a; 33b; 33c) is also configured with a locking portion (37a; 37b; 37c) which is connected to the attachment portion and configured for fixation or attachment of the lockable member (34a; 34b; 34c) thereto, characterized in that the attachment portion (16a; 16b; 16c) is configured with a hole (38a; 38b; 38c) which extends through said attachment portion and in the longitudinal direction thereof for insertion therein of a partly threaded attachment means (39a; 39b; 39c) for tightening or securing by screwing the locking member (33a; 33b; 33c) to the first attachment member (4a; 4b; 4c) by bringing said attachment means to cooperate with the threaded portion (14a; 14b; 14c) of the hole (8a; 8b; 8c) in said first attachment member, that the locking portion (37a; 37b; 37c) of the locking member (33a; 33b; 33c) is substantially U-shaped and comprises two shanks (40a; 40b; 40c) with two holes (41 a, 42a; 41 b, 42b; 41 c, 42c) provided in each shank opposite each other and substantially in line in the longitudinal direction of the locking portion (37a; 37b; 37c), whereby one hole (41a; 41b; 41c) is configured for a locking means (43a; 43b; 43c) for fixation or attachment of the lockable member (34a; 34b; 34c) to the locking member (33a; 33b; 33c) and whereby the other hole (42a; 42b; 42c) is configured for an axis (44a; 44b; 44c) about which the lockable member can pivot for adjustable setting thereof relative to the locking member, μ that the lockable member (34a; 34b; 34c) comprises a lockable portion (45a; 45b; 45c) which is configured for insertion between the shanks (40a; 40b; 40c) of the locking portion (37a; 37b; 37c) of the locking member (33a; 33b; 33c), that the lockable portion (45a; 45b; 45c) is configured with a curved long-hole (46a; 46b; 46c), which extends transversely therethrough, for said locking means (43a; 43b; 43c) and with a hole (47a; 47b; 47c), also extending transversely through said lockable portion, for the axis (44a; 44b; 44c) about which the lockable member (34a; 34b; 34c) can pivot for adjustable setting thereof relative to the locking member, that at insertion of the lockable portion (45a; 45b; 45c) between the shanks (40a; 40b; 40c) of the locking portion (37a; 37b; 37c) of the locking member (33a; 33b; 33c), portions of the long-hole (46a; 46b; 46c) are brought in line with the holes (41a; 41b; 41c) for the locking means (43a; 43b; 43c) in said shanks to allow the locking means (43a; 43b; 43c) to pass through the long-hole (46a; 46b; 46c) and the holes (41a; 41b; 41c) for fixation or attachment of the lockable portion to the locking portion of the locking member and the hole (47a; 47b; 47c) for the pivoting axis (44a; 44b; 44c) is brought in line with the holes (42a; 42b; 42c) for said pivoting axis (44a; 44b; 44c) in said shanks, and that the long-hole (46a; 46b; 46c) in the lockable portion (45a; 45b; 45c) of the lockable member (34a; 34b; 34c) is configured with a plurality of fixed positions corresponding to different angular positions of the lockable member relative to the locking member (33a; 33b; 33c) for fixation of the lockable member in any of said angular positions.