Patent Application
20060149263
The invention relates generally to bone screws used in orthopedic surgeries. More particularly, the invention relates to a self-drilling bone screw.
Bone screws are widely used in orthopedic surgical procedures such as spinal surgeries. Typically, bone screws are used to secure structures, such as spinal plates and spinal rod connectors, to various bone portions to stabilize the bone portions relative to others. For example, cervical plates are typically secured to vertebrae with bone screws for stabilization of the cervical spine. Likewise, occipital plates are typically secured to the back of the skull with bone screws for attaching spinal rods.
To attach a bone screw to the bone, the dense outer layers of the bone, or cortical bone, are typically penetrated. The softer inner portions of the bone, or cancellous bone, are typically at least partially penetrated. Various procedures are used to install bone screws. Some include drilling a pilot hole in the bone and tapping the pilot hole to form an internal screw thread before a bone screw is driven into the pre-drilled and pre-tapped pilot hole. Others include driving self-tapping screws into pre-drilled pilot holes. Still others include driving self-drilling screws directly into the bone without pre-drilling or pre-tapping.
In surgical operations, it is generally desirable to minimize the length of time when the surgical wounds remain open and to ensure the quality of the operations. Consistent with this goal, there is therefore a need for bone screws that can be accurately, quickly and securely fastened to bones.
In one embodiment of the invention, a bone screw has a screw body centered on a longitudinal axis and having proximal and distal ends; a head portion at the proximal end; and a drill point at the distal end. At least a portion of the screw body has an external thread winding about the longitudinal axis. The drill point has two blades. Each blade has a cutting lip and a primary relief surface trailing from the cutting lip and having a trailing edge opposite the cutting lip across the relief surface. The two blades define a flute between them with the first blade leading the second blade. When viewed from the distal end along the longitudinal axis, the cutting lip of each blade is at an obtuse angle from trailing edge of the primary relief surface of the opposite blade across the flute between the two blades. The primary relief surface can have a lip relief angle of about 30°. The point angle of the drill point can be about 100°.
In another embodiment of the invention, a bone screw includes a screw body centered on a longitudinal axis and having two ends; a head portion at one end of the screw body; and a drill point at the other end of the screw body. At least a portion of the screw body has an external thread winding about the longitudinal axis. The drill point having two and only two blades, each having a cutting lip and a primary relief surface trailing from the cutting lip. The two blades defining a flute between them. The flute having an opening on a side wall of the screw body. The opening spans an obtuse angle, such as about 120°, about the longitudinal axis.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Referring to
With additional reference to
Referring further to
The blade 141a has a cutting lip 142a, a primary relief surface 144a trailing from the cutting lip 142a and having a trailing edge 146a, and a secondary relief surface 148a trailing from the trailing edge 146a and having a trailing edge 149a. Likewise the blade 141b has a cutting lip 142b, a primary relief surface 144b trailing from the cutting lip 142b and having a trailing edge 146b, and a secondary relief surface 148b trailing from the trailing edge 146b and having a trailing edge 149b. The blades 141a and 141b are approximately 180° apart about the longitudinal axis 112. The blades 141a and 141b can have different dimensions and appearances due to the intersection between the blades 141a and 141b and the helical external thread 120 and other features near the tip of the screw body 110 but are otherwise symmetrical with each other according to a two-fold symmetry about the longitudinal axis 112. For example, a recess 147 appears on the secondary relief surface 148b of the blade 141b as a result of the secondary relief surface intersecting two adjacent windings of the external thread 120 near the bottom of the trough between the windings.
The blades 141a and 141b form two flutes 150a and 150b between and on either side of the blades 141a and 141b. As best shown in
The drill point 140 has a point angle a of about 100° in this illustrative embodiment of the invention. Other angles can be used, such as from about 90° to about 110°.
The cutting lips 142a and 142b lie in respective virtual planes that are parallel to, but offset from, the longitudinal axis 112 and offset from each other. In the embodiment shown in of about 13 to 380 μm. The blades 141a and 141b overlap each other when viewed in the direction parallel to the planes passing through the cutting lips 142a and 142b. That is, a plane 180 passing through the longitudinal axis 112 and parallel to the cutting lips 142a and 142b intersects both blades 141a and 141b.
A web 160 connects the two blades 141a and 141b. The web 160 is formed by the drill tip material remaining after the flutes 150a and 150b are cut and has a finite width, providing mechanical strength to the tip of the drill point. The tip of the web 160 in this illustrative embodiment is cone-shaped but can be any other shape suited for a particular application. For example, a chisel edge can be formed at the tip.
The primary lip relief surfaces 144a and 144b have a lip-relief angle of about 30° in the illustrative embodiment of the invention, but can be other suitable angles as well, such as from about 25° to about 35°. The secondary lip relief surfaces 148a and 148b are inclined further relative to the plane perpendicular to the longitudinal axis 112 than the primary lip relief surfaces by about 20° or other suitable angle.
Referring more particularly to
Referring again to
The external thread 120, as illustrated in detail in
The bone screws can be made of any material for implantation, including biocompatible materials such as titanium and stainless steel.
The bone screws according to the embodiments disclosed above provide more aggressive cutting than conventional bone screws and thus is more easily driven into bones without the need for pre-drilling of pilot holes or pre-tapping. The features of the bone screws according to the invention also facilitate secure engagement of the bone screws to bone.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
