Abstract: A multi-axial screw assembly comprises a bone anchoring member, a receiver, a crown and a snap ring. The receiver member has an aperture extending along a central axis of the receiver member. The aperture receives the bone anchoring member. The receiver member has a cutout on an interior wall of the receiver member. The cutout has an angled wall surface. The angled wall surface extends along the central axis of the receiver. The crown is configured to be received within the receiver member along the central axis of the receiver member. The crown has a groove around the circumference of the crown. The snap ring is configured to be received in the groove of the crown and in the cutout in the receiver member. The snap ring exerts an axial force on the crown when the snap ring abuts the angled wall surface of the receiver member.

Abstract: A work station chair (10) is enabled to shift in response to a person leaning forward in the chair (10) when in a working mode and leaning back in a rest position. The chair includes a seat (18), a backrest (24) and supportive structure. The seat (18) is resiliently supported on the supportive structure (22) and moveably along an arc track (30) which is mounted on the supportive structure and has a radius generated from the ankle of the person sitting on the chair. The backrest (20) is resiliently supported on the seat (18) and moveable along an arc track (64) which is mounted to the seat (18) and has a radius generated from H-point that is a natural pivot point of the torso and thigh lines of the person. The chair (10) provides a combined tilting movement of the person's body about the ankle point and the H-point when the person shifts his or her gravity to reduce adverse static postural loads and forces which are responsible for the fatigue and biomechanical dysfunction.

Abstract: A chair comprises a base with a fixed stem extending vertically from the base and a track member mounted to the top of the stem. The track member is a segment of a circle, the center of which is forward of the chair and coincident with either the knee or ankle of the person utilizing the chair. A carriage having wings which are concentric with the track slides in the track. A seat is mounted on the carriage. The disclosure also relates to a backrest for a chair which pivots around an axis coincident with the H point axis relative to the chair, and to a chair which can shift in response to a person sitting on the chair, the chair also comprising a backrest which pivots around the H point.

Abstract: A chair adapted to passively adjust itself to be in equilibrium with the user's body in relation to changes in the center of gravity and thigh inclination. The chair includes a post from which is provided, in one embodiment, a convex track on which a carriage is allowed to travel, and a seat pan is pivoted on the carriage for angle adjustment relative to the carriage. In another embodiment, a first concave track is provided on the top of the post with a carriage slidable in the concave track and a seat pan mounted for travel in a track on the carriage wherein the second concave track has a smaller radius than the first track.