A device (100, 400, 500, 530, 540, 550, 600, 700) comprising: (a) a base having a length defining a direction of elongation of said base; (b) a first arm (14 a) pivotally connected to said base, said first arm having a length defining a direction of elongation of said first arm; (c) a second arm (14 b) pivotally connected to said base, said second arm having a length defining a direction of elongation of said second arm; and (d) a worm gear configuration comprising: (i) a worm element mounted within said base so as to be rotatable about a central axis of said worm element, said worm element comprising first and second worms (18 a, 18 b) rigidly interconnected by a shaft, and (ii) first and second sets of gear teeth (20 a, 20 b) associated respectively with said first and second arms (14 a, 14 b), said first set of gear teeth (14 a) being deployed to engage, and be driven by, said first worm (18 a), and said second set of gear teeth (14 b) being deployed to engage, and be driven by, said second worm (18 b), such that, when said worm element is rotated about its central axis, said first and second arms are driven through a range of pivotal motion relative to said base so as to change an angle of inclination between said respective directions of elongation of said first and second arms and said direction of elongation of said base, wherein the device is at least part of an orthopedic implant, and characterized in that said worm element is formed with an internal channel extending through said first worm (18 a) and along at least part of said shaft, and wherein said shaft is provided with lateral openings interconnecting with said internal channel so as to define a continuous filling channel extending through said first worm, along said shaft and laterally outwards for introducing biocompatible material into said orthopedic implant. (a) a base having a length defining a direction of elongation of said base; (b) a first arm (14 a) pivotally connected to said base, said first arm having a length defining a direction of elongation of said first arm; (c) a second arm (14 b) pivotally connected to said base, said second arm having a length defining a direction of elongation of said second arm; and (d) a worm gear configuration comprising: (i) a worm element mounted within said base so as to be rotatable about a central axis of said worm element, said worm element comprising first and second worms (18 a, 18 b) rigidly interconnected by a shaft, and (ii) first and second sets of gear teeth (20 a, 20 b) associated respectively with said first and second arms (14 a, 14 b), said first set of gear teeth (14 a) being deployed to engage, and be driven by, said first worm (18 a), and said second set of gear teeth (14 b) being deployed to engage, and be driven by, said second worm (18 b), (i) a worm element mounted within said base so as to be rotatable about a central axis of said worm element, said worm element comprising first and second worms (18 a, 18 b) rigidly interconnected by a shaft, and (ii) first and second sets of gear teeth (20 a, 20 b) associated respectively with said first and second arms (14 a, 14 b), said first set of gear teeth (14 a) being deployed to engage, and be driven by, said first worm (18 a), and said second set of gear teeth (14 b) being deployed to engage, and be driven by, said second worm (18 b),