1. Field of the Invention
The present invention pertains to an instrument for cutting elongated steel pins or rods insertable in the medullary cavity in repairing human and animal bone fractures. The instrument includes mechanical screw and hydraulic force multiplying mechanism for severing pins to a predetermined length prior to or after the pins have been inserted in the bone.
2. Background Art
In the performance of orthopedic surgery in both human and veterinary medicine, it is known to provide for repairing fractured bones by inserting steel pins of various cross-sectional shapes in the medullary cavity of the bone to support the bone sections on opposte sides of the fracture. Since the repair of some bone fractures requires the insertion of intramedullary support pins of varying lengths, it may be necessary to cut the pin during the surgical procedure once the required length of the pin has been determined. Quite often in the performance of a surgical procedure, a pin of more than sufficient length is inserted into the medullary cavity and then cut to the desired length prior to completion of the procedure.
Since intramedullary pins and the like are preferably formed of stainless steel, the procedure for cutting the pin after it has been inserted in the bone becomes difficult due to the strength and hardness of the pin material. Heretofore, various tools such as saws and pivoting jaw type cutters have been used to cut intramedullary pins to the required length both before and during the surgical procedure. The use of these devices has been generally unsatisfactory in that they are cumbersome and difficult to manipulate properly. Known techniques for cutting intramedullary pins, particularly when they have already been inserted into the bone, are generally unsatisfactory since it is usually required that the bone and associated portion of the patient's body be carefully maintained in a particular position without any forces exerted thereon during the procedure to avoid further damage to the fractured bone or other parts of the patient's body.
Accordingly, there has been a serious need for an instrument of a type particularly adapted for cutting intramedullary pins wherein the cutting operation may be performed before as well as after the pin has been inserted into the medullary cavity or the like. It is particularly desirable that the instrument be as compact and as easily handled as possible in the vicinity of the operating table by the person performing the surgery. It is also important that the instrument be applied to cut the pin without exerting any substantial forces on the portion of the pin already inserted into the bone so as to avoid further damage to the bone or other areas of the patient's body. Furthermore, the hardness of stainless steel intramedullary pins requires that an instrument be used which is capable of exerting substantial cutting forces without requiring an operating force greater than that which the average person using the instrument may easily exert.
It has been further determined that it is often desirable in the environment of a surgical operating room to provide instruments instruments which may be suitably manually actuated thereby eliminating the need for instruments requiring electrical or other sources of power which can be hazardous as well as inconvenient to use. These and other desiderata in the art of instruments for cutting intramedullary pins and similar members used in surgical procedures have been met by the apparatus of the present invention.