The knee prosthesis with rotary plate comprises a metal base and a tibia plate which are equipped with guide means defining a center of rotation which may be offset from that of the tibia bone axis, so as to allow the tibia plate to slide in rotation over the said base, the said guide means being positioned a certain distance away from the center of rotation. The protective covering includes a main sleeve portion which is inserted over the electronic device and which contains apertures therein to allow continued access to portions of the electronic device. Both seal elements are held in place by a seat member which is accommodated in a recess provided on the inside surface of the seat housing or valve body. The strips can have different radiopacities, or can be splittablepeelable. The spool may be provided with at least one land adapted to connect and disconnect two flow passages, and the first ends of the two passages are spaced apart in a direction parallel to the axis of the bore by a smaller distance than the spacing between the second ends of the passages.