Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2001-04-20
2003-07-15
Maust, Timothy L. (Department: 3751)
Surgery
Instruments
Orthopedic instrumentation
C606S060000, C606S075000, C606S08600R, C606S104000, C411S378000
Reexamination Certificate
active
06592587
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an apparatus and process for fastening at least two objects together. More specifically, the present invention relates to an apparatus and process for fastening at least two objects together in a desired alignment. The apparatus and process of the present invention is also particularly beneficial when used in the treatment of orthopaedic injuries requiring surgical intervention.
BACKGROUND ART
Screws, nails, pins and other securing members are widely used, alone or in combination with adhesives, cements, or the like, for fastening objects together. In the fields of carpentry, mechanics and orthopaedic surgery, to name a few, there are numerous circumstances in which it is desirable and/or crucial for objects to be so fastened in a particular and/or specific alignment. Indeed, orthopaedic procedures, such as the fixation of a ligament to a bone or the fastening of one portion of bone to another, provide clear examples of such circumstances.
Fastening one object to another with a screw can be a fairly straightforward process. However, ensuring that such objects are fastened in a specific alignment can be troublesome. There are at least two main reasons for this. First, the leading end of a screw is invariably a sharp, pointed surface designed to be capable of penetrating an object into which it is to be screwed. In the absence of some very specific means for guiding the screw, it is difficult to determine the exact angle at which the screw enters the object, and therefore, it not possible or at least difficult to ensure that such ail angle is the correct one for fastening the objects together in the required alignment.
Secondly, as the screw passes from the first object into the second, until the latter has been adequately penetrated, the screw will tend to push it relatively away from the former. While the screw will be able to hold the objects together, it will not necessarily cause them to abut one another as is generally desired. In addition, the screw may enter the second object at a different angle (albeit minimally different) to that which it entered the first, and thereby prevent the possibility of having the objects fastened together in the required specific alignment. Naturally, the screw can be withdrawn and re-screwed again. However, on the second occasion, and each occasion thereafter, the screw hole within the second object, if not the one within the first object also, will tend to enlarge. As a consequence, the screw may not be able to adequately engage with the objects, and may move around in the enlarged hole/s; it may even be more prone to setting itself free over short periods of time. These complications may be undesirable in most circumstances where at least two objects have been fastened together. The complications would be particularly undesirable, and could, in fact, be associated with significant morbidity, when arising following an orthopaedic procedure to fasten together two or more portions of bone surrounding a fracture site.
The first of these difficulties has, in many respects, been overcome in the prior art with the use of cannulated screws. Each such cannulated screw has a lumen, machined or otherwise formed about its longitudinal axis, which is capable of receiving a guidewire for guiding the screw in the appropriate direction.
The use of cannulated screws in orthopaedic surgery is well known. Generally, a guidewire is passed through the bone at the most appropriate angle for the screw. Once the guidewire is in position, the lumen of the screw is passed over the guidewire, such that the screw attains the correct orientation for advancement into the bone. The screw is then advanced the required distance, and the guidewire removed.
While cannulated screws provide a mechanism for guiding screws in the appropriate direction, such screws also create a number of new problems, which are yet to have been adequately addressed. Cannulated screws are more expensive and generally more complicated to manufacture. Lacking a central core, they are also generally weaker and more prone to breakage under pressure and fatigue loading. This is particularly relevant with resorbable screws, which already have a reduced strength compared to normal orthopaedic, screws. Further, the depth of the screw thread is limited by the wall thickness of the screw extending from the outer edge of the lumen to the outer edge of the screw's shank. Each of these problems is exaggerated in screws with very small diameters, such as those used in orthopaedic procedures involving, for example, the phalanges. To these problems should also be added the fact that the tools, which are used to drive the cannulated screws into place, such as screw drivers and Allen Keys, must, themselves, also be cannulated. This, of course, further adds to the cost of using cannulated screws and also weakens the drivers.
Kirschner wires (or “K-wires”) have also been used as guiding means for cannulated screws in orthopaedic surgery. A K-wire typically has a drilling trocar tip and is capable of drilling into the bones into which the K-wire is to guide the screw. The K-wire is then normally adapted to hold in place by virtue of a friction fit. However, K-wires have limited grip and are often unable to adequately hold the portions of bone together.
Another example of a screw designed to deal with the relative separation of objects upon advancement of a screw is the Herbert screw. The Herbert screw has a thread, the pitch of which varies along its length such that the pitch is greater at the leading end of the screw than it is near the head of the screw. Herbert screws can be cannulated and, if so, have the problems of normal cannulated screws as described above. Once the leading end of the Herbert screw has penetrated the second object, the latter will be drawn relatively toward the former. This is because in order to make a full turn of the thread where the pitch is greater (ie at the leading end of the screw), the screw must be turned a greater distance than to make a full turn of the thread where the pitch is lesser (ie near the head of the screw). Rotating the screw enough for a full turn of the thread near the head of the screw may cause the second object to be pushed relatively away from the first a distance equal to the pitch near the head of the screw. At the same time, however, such rotation will only lead to a partial turn of the thread at the leading end of the screw. The next, even slight, turn of the screw will be adequate to complete a full turn of the thread at the leading edge of the screw, but only just begin the next turn of the thread near the head of the screw. Consequently, the second object is drawn relatively toward the first by a distance equal to the difference between the pitch at the leading end and the pitch near the head of the screw. The objects are, therefore, drawn relatively together rather than pushed relatively apart. A problem can arise, however, when the relative motion of the two objects is fixed in amplitude as there is a risk of overtightening and therefore thread stripping on the distal object.
Unfortunately, the design of the Herbert screw does not overcome the difficulty of ensuring that the screw enters the objects at the correct angle for their desired alignment.
The present invention addresses the problems of the prior art and is adapted to substantially increase the ease of use and functionality of appropriate apparatus for securing at least two objects together.
DESCRIPTION OF THE INVENTION
In a first aspect, the present invention is a securing member when used in conjunction with a guiding means for fastening at least two objects together, the securing member having a head, a shank, and an end region distal the head, wherein the end region is engageable with the guiding means.
In a second aspect, the present invention is a guiding means when used in conjunction with a securing member for fastening two objects together, the guiding means comprising at least an elongate member, wherein at least
Australian Surgical Design and Manufacture PTY Limited
Berkowitz Marvin C.
Kontos Lina R
Maust Timothy L.
Nath Gary M.
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