This invention is in the field of surgical staplers and staple guns for implanting surgical staples. More particularly, this invention concerns the mechanism for controlling the staple during descent and closure and for causing release and separation of the closed staple from the stapler.
Numerous prior art staplers have been developed, each using a staple having an initial open state followed by closure to a formed or closed configuration. In these staplers, typically each staple is positioned upon an anvil which supports the staple's crossarm or crossbar with the staple's sharply pointed legs extending generally downward. Force from the former bends the staple until a rectangular or other generally closed polyganic configuration is achieved. For all these staplers the final step following closure is release or stripping of the staple from the stapler. In many staplers the release is not reliable or not quick or not smooth or combinations of the above. When a complete clean release fails to occur the staple which is closed in the incision remains attached to stapler. The surgeon must then either manipulate the stapler in different directions trying to separate the staple either from the stapler or from the wound, or he may pull on the trigger again, which is likely to force a second staple onto the stuck one causing a worse jam or hang-up of the device.
Where the staple remains engaged in the stapler, the surgeon will, because the tissue is soft, usually be able to manipulate the stapler until the staple pulls free of the tissue; however, the staple hang-up scenario described above is an inconvenience at best and may be a critical delay in the wound or incision closure process. From a commercial consideration many surgeons refuse to use staplers which have a reputation for unreliable closure and/or release.
The reasons for failure of staplers to reliably release are many, obviously depending on the individual stapler. In the typical case a former element presses with substantial force that bends a staple about an anvil element. The formed staple then tends to adhere to the former because the latter maintains the staple closed against spring-back force of the staple trying to open. The staple also tends to adhere to the anvil because of being bent tightly around the anvil lip. Finally staples may jam in passageways due to dimensional tolerance that are either too tight or too loose. Attempts to release or strip the staple must overcome the frictional forces created between the former and/or the anvil with this closed staple.
The focus herein is primarily on staplers of the type described in U.S. Pat. Nos. 4,582,237 and 4,669,647 which patents are incorporated by reference into this specification. In these particular prior art patents the staplers have a "moving anvil" which is caused to descend while it carries an open staple to a position below the housing where more visible closure occurs. Some other relevant prior art staplers have "fixed" anvils situated at one predetermined elevation. Stripping of the formed staple in these various prior art devices occurs during the final downward movement of the former at which time one or more of the above-described frictional forces must be overcome by a stripping element on the former. Typically the anvil remains at its originally fixed or descended elevation with the closed staple thereon, or more specifically, with the anvil's lip extending beneath the central part of the staple's crossarm. The former is then caused to descend slightly further with a bevelled edge of the former camming the staple's crossarm transversely off the anvil's lip.
The above type of stripping mechanism, while appearing seemingly simple, has been found unreliable to produce a reliable and clean release of the closed staple. In part the frictional forces interfere with smooth operation. Attempts at solutions included tightening dimensional tolerances which resulted in substantial cost increases, or seeking to reduce friction by a less tightly closed staple which was equally unsatisfactory.
Also, in relevant prior art staplers other unsatisfactory features include a tendency of the staple's crossarm to bow upward during closure, and/or a tendency for the staple to move from its proper position orientation during descent.
The stapler of the new invention provides significant improvements in all these areas as described below. The present invention approaches the stripping problem from a totally different point of view, thus providing a stripping mechanism that has numerous advantages over the prior-disclosed stripper, along with improvements in the other features discussed above.