Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-06-02
2003-01-14
Reip, David O. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S077000
Reexamination Certificate
active
06506192
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention generally relates to threaded devices used to facilitate bone fracture or osteotomy fixation in human surgery and more specifically relates to threaded devices made of allograft bone.
2. Description of the Prior Art
The prior art contains many references directed to fastener drivers which drive screws having a Phillips head, standard slot head or other heads having various shaped slots or recesses which receive the torque from the driver end. See for example the prior art shown in U.S. Pat. No. 5,367,926. There are other examples of prior art fastener drivers having female driver ends which receive and drive fasteners having a male torque receiving end. Typical driver screw fasteners and screws of such a construction are shown in U.S. Pat. Nos. 755,804; 1,300,275; 4,724,731; 5,012,624; 5,443,482 and 5,730,744. Wrenches having a female driving end which drive caps or nuts are shown by U.S. Pat. Nos. 1,336,794 and 4,823,650.
Several patents such as U.S. Pat. Nos. 172,351 and 173,356 show screws having a head formed with a wedge shaped groove or slot which receives the angular notch of a driver head to transmit torque and drive the screw. While most screws have a uniform diameter shank, U.S. Pat. Nos. 4,463,753 and 5,403,136 disclose bone screws which have a tapered shank which cause compression of the bone between the distal end of the screw and the taper.
Millions of people suffer from a variety of musculoskeletal disorders or traumatic occurrences necessitating the use of devices to reduce osteotomies or fractures. Many different means have been developed to facilitate fixation and healing of the traumatized bone tissue. In the past, metallic pins and screws have been used to establish initial mechanical stability of the trauma site, and to facilitate permanent, mechanically stabile fracture or osteotomy healing.
The most significant difficulties with screws and pins currently used to facilitate fixation include the residual presence of “hardware” that may migrate, include adverse tissue reaction to the presence of foreign particulate debris, and otherwise compromise the functionality of the fixation. Some recently offered products feature bioresorbable material technology which allows for gradual absorption of the screws and pins. Unfortunately, these materials may fall short of expected performance due to incomplete osseointegration of patient bone. Allograft bone offers a suitably strong, biocompatible, and bioresorbable material that addresses these deficiencies.
Screws made completely of allograft bone have been described in F. Albee,
Bone Graft Surgery in Disease, Injury and Deformity
p. 22 (1940); and F. Albee,
The Improved Albee Bone Mill
, American Journal of Surgery p. 657 (March 1938). These screws offer the advantage of the biointegration of allograft bone tissue. However, the conventional slotted or rectangular head designs commonly used in metal screws when used with allograft bone screws, result in premature failure of the screws during intraoperative insertion due to excessively high shear forces applied to the head and the transition between the head and threaded portion of the screw. This shearing is due to several factors. First, and foremost, while bone is quite strong in compressive loading, it is relatively weak in tension and shear. Since the torque applied to a screw induces shear stresses, the design of a screw made of allograft bone tissue must be as robust as necessary with respect to torque loading.
Additional screws and fasteners of various construction which have been made of allograft bone are additionally shown in U.S. Pat. No. 5,968,047.
There are several problems with screws presently used in the prior art. As can be appreciated, the screws are small with a round or cylindrical head and are difficult to place in the driver or area to be fastened because of the nature of the surgery, namely that the same are used in circumstances where fluid such as blood is present, thus, presenting a slippery condition for handling and use.
In addition, the use of a cylindrical barrel or round head on the screw is not the most efficient way of transmitting torque to the screw when the same is screwed into the bone and the present invention allows a maximum torque to be applied over the driver head portion of the screw allowing the same to be more easily inserted.
SUMMARY OF THE INVENTION
In response to the needs still left unresolved by the prior art devices, the present invention contemplates allograft bone screws made of cortical and cancellous bone with both a unique head design and a bone formation treatment which solves the deficiencies of the prior art prostheses.
The inventive screw design offers two unique features which fulfill the potential of allograft bone as an ideal material for screws used in fracture and osteotomy reduction. The first unique feature is a drive head having a rectangular shaped body with a wedge end which mates with a specialized driver used to apply torque to the screw. The second unique feature is an outwardly tapering shank portion adjacent the rectangular shaped body which provides an undercut for the head providing a tight engagement of the screw in the bone bore. This drive head accomplishes two desirable functions. The first function is that it avoids localized tensile stresses inherent in standard drive designs that would lead to mechanical failure of an allograft bone screw and the second function is the ability of this body to place an increased torque on the screw thread that also avoids mechanical failure of the screw.
It is an object of the invention to provide a flat surface abutting the drive head allowing the tapered section of the screw to be easily cut flush along the bore surface.
Thus the present screw design is both easy to use and offers the ideal physiological response of patient tissue to allograft bone tissue.
In the operation of the invention, a method is provided for implanting a bone screw into two separate bone sections. The approach includes the steps of drilling a first tapped bore drill through both pieces of bone. The first bone piece bore is then overdrilled to a larger diameter and countersunk. The bone screw head is then mounted in a rectangular or square chamber having a rear V shaped notch formed in the driver head. The bone screw is then driven or screwed into the prepared bone bore until the undercut of the bone screw engages the countersink. The rectangular portion of the bone screw extending outward past the surface of the outer bone piece is then cut off so that the head of the bone screw is flush with the fastened bone piece surface.
These and other objects, advantages, and novel features of the present invention will become apparent when considered with the teachings contained in the detailed disclosure along with the accompanying drawings.
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F. Albee,Bone Graft Survey in Disease, Injury and Deformity,p. 22 (1940).
F. Albee,The Improved Albee Bone Mill,American Journal of Surgery, p. 657 (Mar., 1938).
Ferrara, Jr. Raymond G.
Gertzman Arthur A.
Haines Timothy G.
Gipple & Hale
Hale John S.
Musculoskeletal Transplant Foundation
Reip David O.
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