A uniplanar bone screw (10, 1000) for adjusting a position of a rod (12, 1012), comprising: a main body (14, 1014) having a shaft (22, 1022) with a threaded part; a rocker (16, 1016) coupled to and moveable relative to the main body (14, 1014), wherein the rocker (16, 1016) is configured to at least partially receive the rod (12, 1012); and a rod-securing element (18, 1018) configured to secure the rod (12, 1012) between the rocker (16, 1016) and the rod-securing element (18, 1018) and relative to the main body (14, 1014), wherein the rod-securing element (18, 1018) includes a fulcrum (85, 1085) serving as an axis of rotation about which the rod (12, 1012) rotates; the fulcrum (85, 1085) of the rod-securing element (18, 1018) directly abuts the rod (12, 1012); the main body (14, 1014) includes a screw head (24, 1024) coupled to the shaft (22, 1022) the screw head (24, 1024) includes a slot configured to at least partially receive the rod (12, 1012) and the rocker (16, 1016); and the slot includes a first interior sidewall and a second interior sidewall and a bottom surface that extends from the first interior sidewall to the second interior sidewall; characterised in that: the bottom surface of the slot is one of: (i) substantially curved in a first direction and in a second direction, and (ii) substantially flat in a first direction and substantially curved in a second direction, and the second direction is parallel to the axis of rotation and is substantially perpendicular to the first direction. a main body (14, 1014) having a shaft (22, 1022) with a threaded part; a rocker (16, 1016) coupled to and moveable relative to the main body (14, 1014), wherein the rocker (16, 1016) is configured to at least partially receive the rod (12, 1012); and a rod-securing element (18, 1018) configured to secure the rod (12, 1012) between the rocker (16, 1016) and the rod-securing element (18, 1018) and relative to the main body (14, 1014), wherein the rod-securing element (18, 1018) includes a fulcrum (85, 1085) serving as an axis of rotation about which the rod (12, 1012) rotates; the fulcrum (85, 1085) of the rod-securing element (18, 1018) directly abuts the rod (12, 1012); the main body (14, 1014) includes a screw head (24, 1024) coupled to the shaft (22, 1022) the screw head (24, 1024) includes a slot configured to at least partially receive the rod (12, 1012) and the rocker (16, 1016); and the slot includes a first interior sidewall and a second interior sidewall and a bottom surface that extends from the first interior sidewall to the second interior sidewall; characterised in that: the bottom surface of the slot is one of: (i) substantially curved in a first direction and in a second direction, and (ii) substantially flat in a first direction and substantially curved in a second direction, and the second direction is parallel to the axis of rotation and is substantially perpendicular to the first direction. the bottom surface of the slot is one of: (i) substantially curved in a first direction and in a second direction, and (ii) substantially flat in a first direction and substantially curved in a second direction, and (i) substantially curved in a first direction and in a second direction, and (ii) substantially flat in a first direction and substantially curved in a second direction, and the second direction is parallel to the axis of rotation and is substantially perpendicular to the first direction.