| abstract |
A Top-Loading Multi-axial, double locking bone anchor apparatus is disclosed. The apparatus includes a receiver member, internal threaded ring member, an internal 'saddle' member, a bi-polar member, a bone anchor and a double-locking compression retaining member comprising of two components; one external 'nut-like' fastener and, one internal 'setscrew-like' fastener; both fasteners comprising one single double- locking compression retaining member. The 'nut-like' fastener only interfaces with the internal 'saddle' member and the receiver member. The 'setscrew-like' fastener only interfaces with the elongated member. When installed, the opposing forces created by both fasteners create a 'locking' force within the double-locking compression retaining member thus restricting the involuntary 'loosening' of the double-locking compression retainer member. The receiver member defines an upper opening and a lower opening, which may form part of the same opening, a channel, and external threaded portion located at the bottom. The internal 'saddle' member, bi-polar member and bone anchor are loaded into the lower opening of the receiver member thru the bottom of the receiver member, and internal threaded ring member fits around the bone anchor and over the outer lower threaded portion in the receiver member to retain the internal 'saddle' member, bi-polar and the bone anchor member. The bone anchor is capable of multi-axial as well as multi-polar positioning with respect to the receiver member. An elongated member is placed in the channel of the receiver member, contacting the internal 'saddle' member, and the double-locking compression retaining member is applied via the upper opening. The external component of the double-locking compression retaining member presses down on the internal 'saddle' member and locks the bone anchor member between bi-polar member and the internal 'saddle' member: the internal threaded retaining member retains this assembly. The internal component of the double-locking compression retaining member presses down and locks the elongated member between the internal 'saddle' member and itself; the two opposing forces create a 'locking' that resists the involuntary loosening of the double-locking compression retaining member assembly. |