Proximal anchors for bone fixation system

Abstract

Disclosed is a bone fixation device of the type useful for connecting soft tissue or tendon to bone or for connecting two or more bones or bone fragments together. The device comprises an elongate body having a distal anchor thereon. An axially moveable proximal anchor is carried by the proximal end of the fixation device, to accommodate different bone dimensions and permit appropriate tensioning of the fixation device.

Description

[0001] The present application is a continuation of U.S. patent application Ser. No. 10 / 745,360, filed Dec. 23, 2003, which is a continuation of U.S. patent application Ser. No. 09 / 990,587, filed Nov. 19, 2001, now U.S. Pat. No. 6,685,706, the entire contents of these applications are hereby incorporated by reference herein.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to bone fixation devices, and, more particularly, to an improved proximal anchor for a bone fixation device. [0004] 2. Description of the Related Art [0005] Bones which have been fractured, either by accident or severed by surgical procedure, must be kept together for lengthy periods of time in order to permit the recalcification and bonding of the severed parts. Accordingly, adjoining parts of a severed or fractured bone are typically clamped together or attached to one another by means of a pin or a screw driven through the rejoined parts. Movement of the pertinent...

AI Technical Summary

Benefits of technology

[0016] Another aspect of the present invention is a bone fixation device, for securing a first bone fragment to a second bone fragment. The bone fixation device comprises an elongate pin, having a proximal end, a distal end and a first retention structure. The bone fixation device also includes at least one distal anchor carried by the elongate pin and a proximal anchor, axially moveable with respect to the elongate pin and comprising a second retention structure. At least a portion of the second retention structure is moveable between a first position and a second position. The second position is located closer to a longitudinal axis of the elongate pin as compared to the first position so as to engage at least a portion of the first retention portion and prevent proximal movement of the proximal anchor with respect to the elongate pin while the first position allows distal movement of the proximal anchor with respect to the elongate pin.

Problems solved by technology

The leading end portion of the implant typically includes means to positively grip the femoral head bone (external threads, expanding arms, etc.), but the inclusion of such gripping means can introduce several significant problems.

First, implants with sharp edges on the leading end portion, such as the externally threaded implants, exhibit a tendency to migrate proximally towards the hip joint bearing surface after implantation.

This can occur when the proximal cortical bone has insufficient integrity to resist distal movement of the screw head.

Such proximal migration under physiological loading, which is also referred to as femoral head cut-out, can lead to significant damage to the adjacent hip joint.

Also, the externally threaded implants can generate large stress concentrations in the bone during implantation which can lead to stripping of the threads formed in the bone and thus a weakened grip.

As a result, all fatigue loading is concentrated at the attached ends of the arms and undesirably large bending moments are realized at the points of attachment.

In addition, conventional threaded implants generally exhibit insufficient holding power under tension, such that the threads can be stripped out of the femoral head either by overtightening during the implantation procedure or during post operative loading by the patient's weight.

Notwithstanding the common use of the K-wire to achieve shear-force stabilization of bone fractures, K-wire fixation is attended by certain known risks.

Another potential complication involving the use of K-wires is in vivo migration.

Axial migration of K-wires has been reported to range from 0 mm to 20 mm, which can both increase the difficulty of pin removal as well as inflict trauma to adjacent tissue.

In addition to the undesirable appearance, percutaneously extending K-wires can be disrupted or cause damage to adjacent structures such as tendons if the K-wire comes into contact with external objects.

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