Abstract:
A laparoscopic scissors, comprising a pair of blades connected at a pivot, each of the blades having a length, a tip portion, a body portion, an outer surface, an inner surface and a cutting edge is provided. The tip portion may have a first body thickness and the body portion may have a second body thickness different from the first body thickness. During the cutting operation, the blades progressively move over each other to provide a point contact along the cutting edges. In another aspect of the invention, a process of manufacturing the pair of scissors of the invention is disclosed, comprising the steps of forming the blades into a desired shape with wire EDM processes from a pre-hardened block of material, and sharpening the cutting edges of the blades.

Description:
This application is a continuation of currently-pending U.S. patent application Ser. No. 10/976,505, filed on Oct. 29, 2004, entitled “Multiple-Angle Scissor Blade,” which is a non-provisional application claiming the priority of provisional application Ser. No. 60/517,729, filed on Nov. 5, 2003, entitled “Multiple-Angle Scissor Blade,” both of which are fully incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to laparoscopic scissors and, more particular, to laparoscopic scissors having multiple cutting angles and multiple thicknesses. 
     2. Discussion of Related Art 
     During surgery, surgeons will typically need to cut into a multitude of objects such as tissues, suture and metal staples. A goal in the design of scissors and, in particular, in the design of scissors&#39; blades is to optimize its effectiveness in cutting through different objects. For cutting through soft tissues, a large angle ground into the blade is most effective. That is, when sharp edges shear against each other, any tissue which comes between the blades of the scissors will get cut. The large angle on each blade is effective when cutting soft material because the blades can stay thin and razor sharp throughout the cut. A thin and sharp edge is optimal for soft materials because there is less resistance throughout the cut. 
     In contrast, when cutting through something hard such as a metal staple, the fine edge of a typical scissors&#39; blade may not be as effective as when cutting soft tissue. A very fine and sharp edge may deform when required to cut a hard object. That is, a blade having a very large angle ground into it will deform if used to cut hard objects. To prevent the blades from deforming, the blades have to be designed to be thicker at and behind the point of cutting so that the blade edges do not deform. Having a small angle on the cutting edge of a scissor blade like this would help when cutting through hard materials such as staples or hard objects. Accordingly, because tissue and staples are typically cut with the same instrument, there is a need in the art for a laparoscopic scissors having both a large angle cutting edge and a small angle cutting edge on the same device. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a pair of laparoscopic scissors, comprising a pair of blades connected at a pivot, each of the blades having a length, a tip portion, a body portion, an outer surface, an inner surface and a cutting edge, the cutting edge forming an angle with the outer surface along the length of the blade such that tension during a cutting operation at the tip portion is about the same as tension at the body portion during the cutting operation. In one aspect of the invention, the angle formed is continuously changing over the length of the blade. In another aspect, the angle at the tip portion is greater than at the body portion, and the angle progressively decreases from the tip portion to the body portion. The tip portion may have a first body thickness and the body portion may have a second body thickness different from the first body thickness. In yet another aspect, the blade may comprise a proximal portion proximal to the body portion having a third body thickness, wherein the second body thickness is thicker than the first and third body thicknesses. 
     The cutting operation may include cutting at least one of a body tissue, a suture and a surgical staple. During the cutting operation, the blades progressively move over each other to provide a point contact along the cutting edges. It is appreciated that the blades may be thickened in a number of locations and combinations including: (1) one blade could be thicker than the other to force the opposing blade to flex; (2) both blades could be thicker at the body or throat sections to give more strength when cutting staples; (3) each blade could be thickened on one side or the other to stiffen certain locations; and (4) the tips of each blade could be thicker than the body or throat sections to provide increased tension at the tips. 
     In another aspect of the invention, a process of manufacturing the pair of scissors of the invention is disclosed, comprising the steps of form grinding the blades into a desired shape from a pre-hardened block of material, and sharpening the cutting edges of the blades. It is appreciated that the blades of the invention may also be formed through other processes including Wire EDM (Electrical Discharge Machining), laser cutting, waterjet cutting, machining, cast or metal injection molding, and other independent profile manufacturing process. The manufacturing process of the invention is beneficial in that each profile can be accurately controlled, and the parts will be exact every time. Additionally, there is no heat-treating step afterwards because it was done prior to grinding and cutting. Another feature of the manufacturing process of the invention is that the parts can be made with any number of multiple thickness sections in the profile. 
     These and other features of the invention will become more apparent with a discussion of the various embodiments in reference to the associated drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included in and constitute a part of this specification, illustrate the embodiments of the invention and, together with the description, explain the features, advantages and principles of the invention. In the drawings: 
         FIG. 1  illustrates a multiple-angle scissor blade in accordance with a first embodiment of the invention where the angle is continuously changing; 
         FIG. 2  illustrates a multiple-angle scissor blade in accordance with another embodiment of the invention where an angle is held constant in each section of the blade; 
         FIG. 3  illustrates a side view of a blade having multiple thicknesses in accordance with another embodiment of the invention; 
         FIG. 4  illustrates a profile of a blade formed from grinding in accordance with a manufacturing process of the invention; 
         FIG. 5  illustrates a top view of a blade formed from another independent profile manufacturing process in accordance with an embodiment of the invention; and 
         FIG. 6  shows pair of scissors and illustrating the cutting edges and throat portion in accordance with an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The following description refers to the accompanying drawings that illustrate the embodiments of the invention. Other embodiments are possible and modifications may be made to the embodiments without departing from the spirit and scope of the invention. Thus, the following description is not meant to limit the invention. 
     Referring now to the drawings, and in particular to  FIG. 1 , there is shown an exemplary blade  10  of a scissors in accordance with the first embodiment of the invention. The blade  10  includes a tip portion  12 , a body or throat portion  14 , an outer surface  16 , an inner surface  18 , a cutting edge  22  and a pivot area  20 . The cutting edge  22  forms an angle with the outer surface  16  along the length of the blade  10  such that tension at the tip portion  12  is about the same as tension at the body or throat portion  14 . The function and effectiveness of the scissor blades depend heavily on the tension and angle the cutting surfaces are to each other. The blades are designed such that the tension when cutting is about the same throughout the length of the blades, e.g., at the tip and at the body or throat portion. In contrast, the conventional scissors have uniform blade thicknesses where tension at the tip is less than tension at the body portion because it is further away from the pivot. As a result, the conventional scissors blades may deform when cutting through harder and denser objects. 
     A novel feature of the invention is that an angle a formed between the cutting edge  22  and the outer surface  16  at the tip portion  12  is different from an angle β formed between the cutting edge  22  and the outer surface  16  at the body or throat portion  14 . That is, the angle formed between the cutting edge  22  and the outer surface  16  may be continuously changing over the length of the blade  10 . In one aspect, the angle α is greater than the angle β. With this aspect, the edge of the blade would start at a very large angle α at the tip portion  12  and as it proceeds back along the edge toward the back of the blade, the angle starts to reduce until it is much smaller at the body or throat portion  14  of the blade. An advantage of the multiple-angle scissor blade  10  of the invention is the angles that most effectively cut different materials are all included on the same blade. Surgeons typically “snip” at tissue with the tip of the blades. Thus, grinding a large angle edge near the tip portion  12  of blade  10  would be most effective. Surgeons typically cut suture, which is a little harder than tissue, somewhere in the middle of the blades. Thus, grinding a smaller angle near the mid-portion of blade  10  would be optimal for suture. When cutting through very hard staples, surgeons will typically take a bite and force the staple somewhere between the center and the throat of the blades as illustrated in  FIG. 6 . Thus, grinding a very small angle into the blade near the throat portion  14  would be optimal for cutting hard materials. Also, the most leverage is available at the throat section, making the cut easier. 
     It is further appreciated that the blades may be of any shape. In one aspect, the blades define a slight curve towards one another, which provides sharper cutting due to a single point cutting action. The tip portion  12  may also be provided by an outer edge  26 . The tapered tip portion  12  allows insertion of the scissor blades into a cavity in the body of a patient. Additionally, the tip is rounded at its outer edge  26  to avoid inadvertent puncturing or abrasion by the tip during use. 
     In another embodiment of the invention as illustrated in  FIG. 2 , multiple sections of different angles may be grinded in the blade  10   b  of the scissors. For example, the cutting edge  22   b  of the blade  10   b  may start out forming a very large angle α with the outer surface  16   b  at the tip portion  12   b.  This angle a could be held constant for a given length. The angle α could then transition into a smaller angle β, which then could be held constant for a next given length. There could be as many sections along the blade as desired to obtain the various angles needed. For example, the angle α may be held constant over the tip portion  12   b  and the angle β may be held constant over the throat portion  14   b  with an angle transition portion  24   b  formed between the tip portion  12   b  and the throat portion  14   b  as illustrated in  FIG. 2 . 
     Another method for keeping the tension tight at the tips of the blades is to vary the thicknesses of the scissors blades. Referring to  FIG. 3 , there is shown a side view of a blade  30  having a tip portion  32 , a mid-portion  34  and proximal portion  36 . In this embodiment of the invention, the mid-portion  34  is thicker than the tip portion  32  and the proximal portion  36 . That is, when the blades slide over each other during a cutting stroke, the blades flex so that only one point is actually touching. This flexure and the tension between the blades can be controlled and “forced” to different areas by varying the thickness of the blades. By providing a scissors with the blades having multiple thicknesses, the tension of each blade can be controlled and the flexure can be forced into certain areas on the blade. A thicker blade is also stronger in that section. When cutting through hard materials such as staples, a thicker, stronger blade is always beneficial. 
     It is appreciated that the scissors blades can be thickened in a number of locations and combinations such as: 
     (1) One blade could be thicker than the other to force the opposing blade to flex; 
     (2) Both blades could be thicker at the throat section to give more strength when cutting staples; 
     (3) Individual blades could be thickened on one side or the other to stiffen certain locations; and 
     (4) The tips of the blades could be thicker than the throat section to provide increased tension at the tips. 
     In another aspect of the invention, it is appreciated that the scissors can be manufactured in a number of different ways. The most common method is to stamp and form the blades from a predetermined thick material, and then grind a razor edge into them. This method is relatively inexpensive, but if the blades need to be heat treated after forming, the parts can twist and distort thereby reducing or eliminating the tension between the blades. Thus, another process may be required to bring the parts back into specification so the proper blade tension may be realized. 
     Since the blade tension is the most critical aspect of a scissors, it needs to be controlled from the beginning. A block of material that is heat treated to the required hardness can be manufactured prior to manufacturing the blades. A form-grinding machine can grind one profile into the blade such as the cutting profile  40  illustrated in  FIG. 4 . Form grinding is the process of taking a diamond impregnated grinding stone that has a particular shape cut into it, and shaving away the pre-hardened material until a block has the desired profile. 
     The profile as shown in  FIG. 4  is not limited to grinding and may be cut with Wire EDM (Electrical Discharge Machining). Wire EDM is a metal removal technique using a controlled electrical current or spark erosion. The EDM machine moves a wire through the part eroding material away. With Wire EDM, there is always a gap between the part and the wire so there is no contact and virtually no deflecting force applied to the part, which ensures greater accuracy and tight tolerances of the finished part. The parts can also be formed by machining, cast injection molding or metal injection molding. The molded or cast part or block can then be further processed by EDM, laser cutting, waterjet cutting, or other manufacturing process to produce the finished parts. Waterjet cutting is a process of directing a fine, very high-pressure water stream to a material to cut or form a part. The waterjet stream may include fine metal particles to facilitate cutting. With the process of the invention, the profile can be accurately controlled, and the parts can be accurately produced every time. Additionally, there is no heat-treating step afterwards because it was done prior to grinding and cutting. The final step would be the edge sharpening. Another advantage of the independent profile manufacturing process is that the parts can be made with any number of multiple thickness sections in either profile as illustrated in  FIG. 3 . To do this with a traditional stamping process would be difficult as well as expensive, if possible at all. 
     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiments may have been set forth only for the purposes of examples and that they should not be taken as limiting the invention.