A device 200 comprises a body 201 having a first opening, the first opening including a passage penetrating completely through the body from a first face 201a of the body 201 to a second face opposite the first face 201a, and a slot 205 extending from the passage to a side edge of the body 201, the slot 205 having a height that is less than a height of the first opening； and a leg positioning element 204, 206 which comprises an arm 207 adapted to slidably fit in the first opening for sliding along a first direction normal to the first face； a support 208 adapted to support a first portion of a limb of a patient； and a neck portion 207n connecting the support to an end of the arm 207, the neck portion 207n adapted to slidably fit in the passage, to permit removal of the leg positioning element 204, 206 from the body 201 through the passage in a second direction parallel to the first face.
