Abstract:
A surgical speed wrench useful in installing spinal implant devices is provided with a thin profile and means for holding a part to be installed with a threaded fastener. The thin profile is achieved by a socket formed directly in a torque transmitting gear. The threaded fastener head is received directly in the socket and no other tool or adapter is required which would increase the profile. The holding means includes two extending arms terminating in spherical members which biasly engage a bore in the part to be installed. With the part thus held, the threaded fastener is received in the wrench socket and may be started and driven without the surgeon using his or her fingers or other instruments.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to surgical instruments, and more particularly to a surgical wrench for simultaneously driving a bolt and holding in place a part through which the bolt is driven, until the bolt has been tightened. 
     Although not part of the present invention, a basic understanding of surgical implants that may be installed using the present invention is important to the understanding of the invention. The Vermont Spinal Fixator (VSF) is one such device. FIG. 7 illustrates a Vermont Spinal Fixator device 10 in place on a spinal column. FIG. 8 is an exploded view showing the relationship of the various components of the VSF. The fixator device is designed to rigidly fix together two spinal vertebrae surrounding a fractured vertebrae and, thus, fuse the spine around the fractured vertebrae. The Vermont Spinal Fixator is disclosed in detail in Krag et al., An Internal Fixator for Posterior Application to Short Segments of the Thoracic, Lumbar, or Lumbosacral Spine, Clinical Orthopaedics and Related Research, 203: 75-98, (Feb. 1986), incorporated by reference herein. 
     In order to implant the fixator device 10, holes are drilled in the appropriate vertebrae through surface A overlying the pedicle on either side of each vertebrae. After the holes are drilled, pedicle screws 12 are screwed into the pedicle using a shaft handle which is attached to flats 16 provided on the top of each screw 12. Once the pedicle screws 12 are in place in each of the four pedicles, an articulating clamp 18 is attached to each pedicle screw 12 with a clamp bolt 20. 
     After the articulating clamps 18 are in place, the clamp bolts 20 are initially left somewhat loose to allow for the assembly of connecting rods 22 between the two pedicle screws 12 on both sides of the fractured vertebra. After the fractured spine has been appropriately aligned, the clamp bolts 20 are tightened to permanently fix the spine and isolate the fractured vertebra. 
     In the past, surgeons have had difficulty in starting the clamp bolts 20 in threaded holes 14 provided in each pedicle screw 12. Part of the reason for the difficulty is that the clamp bolt 20 passes through articulating clamp 18, which must be held in place while the bolt is started. In addition, the space between the spinous process B and the installed pedicle screw is limited and the incision made for this procedure is relatively small. There is generally not room for the surgeon to reach into the incision and start the bolt 20 with his fingers while holding the articulating clamp 18 in place. Additionally, the components are small and relatively slippery during the operation, rendering their manipulation by hand difficult even if sufficient room was available. The limited space between spinous process B and pedicle screw 12 makes the use of known wrenches problematic. 
     In the past, surgeons have attempted to hold the articulating clamp in place with forceps while spinning the head of the bold with another instrument. Although workable, this method is slow, cumbersome and technically very difficult. 
     Low profile wrenches for use in surgical procedures are known, such as the &#34;Twin Cities Spinal Wrench&#34; by the Twin City Surgical Company designed for use in installing threaded nuts on threaded Harrington compression rods. This wrench utilizes a flat meshing gear train for transmitting torque to an end gear having a open-end wrench configuration for receiving nuts to be torqued. 
     U.S. Pat. No. 4,374,480 to Diaz discloses an extension tool for torquing screw fasteners located in restricted access areas. The Diaz extension tool is provided with a flat meshing gear train wherein the gears are supported by being disposed in close fitting circular recesses instead of on shafts, in order to reduce the thickness of the tool. The first and last gears are provided with multifaceted recesses for receiving commercially available torquing tools. 
     These wrenches are illustrative of the prior art, which, in general, does not provide a device suitable for the task of installing parts fixed by threaded fasteners such as articulating clamps and clamp bolts in surgical implants such as the VSF. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a surgical wrench having a profile which allows access to the limited space available in the installation of spinal fixation implants. A feature of present invention which assists in achieving this object is a drive means that includes a socket formed directly in a driven gear. This design decreases the overall profile of the wrench by eliminating the need for a socket tool or other adapter because the bolt to be driven is received directly in the gear which applies the torque. 
     A further object of the invention is to provide means for holding a part in place while a threaded fastener is driven therethrough. In this regard, the present invention provides a holding means comprising two adjacent arms that biasly engage the part to be held in a position that allows the threaded fastener to be engaged at the same time by the wrench. This feature prevents the need for separately holding the part to be installed while the threaded fastener is started. 
     Thus, according to the present invention an apparatus for installing a first part on a second part utilizing a threaded fastener passing through the first part and engaging the second part generally comprises a body, a driven gear mounted in the body with the driven gear having a drive means for directly engaging the threaded fastener without an adapter or other intermediate tool. In a preferred embodiment, the drive means includes a socket formed directly in the driven gear and configured to receive a hex-head threaded fastener. A drive gear and at least one intermediate gear are provided to transfer externally applied torque to the driven gear. 
     A means for holding the first part adjacent to the body with the threaded fastener passing through the first part and engaging the drive means is provided. In a preferred embodiment the holding means includes two adjacent arms, extending from one side of the body in the direction of the drive means, with the arms adapted to biasly engage the first part therebetween. To assist in engaging the first part, the arms may be provided with spherical members cooperating with an the connecting rod bore in the first part. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be better understood if reference is made to the accompanying drawing, in which: 
     FIG. 1 is a top plan view of one embodiment of the wrench according to the present invention; 
     FIG. 2 is a side elevation of the wrench shown in FIG. 1; 
     FIG. 3 is a top plan view of the wrench shown in FIG. 1 with the cover plate removed to reveal the gear train; 
     FIG. 4 is a cross-sectional view of the wrench shown in FIG. 1, with an articulating clamp and clamp bolt installed thereon; 
     FIG. 5 is a top plan view of an alternative embodiment of the wrench according to the present invention; 
     FIG. 6 is a partial cross-sectional side elevation view of the wrench of FIG. 5; 
     FIG. 7 is a dorsal plan view of a Vermont Spinal Fixator implant in place on a spine; and 
     FIG. 8 is an exploded view illustrating the components of the Vermont Spinal Fixator implant and their relationship to a vertebra. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, wrench 100 according to one embodiment of the present invention is provided with a cover plate 24 and base plate 26 which supports the various other components of the wrench. Wheel 27 is screwed on to shaft 25 in order to fasten together cover plate 24 and base plate 26. As can be seen in FIG. 4, shaft 25 fits into base plate 26 and wheel 27 is rotatably retained by collar 30, which fits into cover plate 24. Shaft 25 and collar 30 can be permanently secured in base plate 26 and cover plate 24, respectively, by welding. 
     Extending from cover plate 24 are two arms 32 and 34 which terminate in engaging members 36 and 38, respectively. Engaging members 36 and 38, shown as balls in FIGS. 1, 2 and 4 cooperate with the connecting rod receiving bore 19 of the articulating clamp 18 to firmly grasp the articulating clamp due to a biasing force applied by arms 32 and 34. As illustrated in FIG. 4, when grasped between arms 32 and 34, articulating clamp 18 is disposed with hole 14, which receives clamp bolt 20, aligned with socket 40. Socket 40 receives and engages the head of bolt 20 for the application of torque by the wrench. 
     The drive train of wrench 100 comprises a number of spur gears that transmit torque from wheel 28 to socket gear 42. As shown in FIGS. 3 and 4, wheel 28 is fixed to drive gear 44 by shaft 48. Drive gear 44 cooperates with gear 52; thus, from drive gear 44 torque is transmitted forward by the cooperating engagement of gears 52-58. Gear 58 engages and drives socket gear 42. Gears 52, 53 and 55-58 are all similarly mounted on shaft pins 60, 61 and 63-66, which fit into base plate 26 and can be permanently secured by welding. As can be seen in FIG. 4, the thickness of the spur gears is only slightly greater than half of the height of the space provided between base plate 26 and cover plate 30. This allows the spur gears to slide on the shaft pins to provide a clearance for cleaning behind the gears. The thickness of the gears ensures that each gear always contacts at least a portion of the neighboring gears. 
     To provide a shape more conducive to manipulation in the surgical area, gears 56-58 are approximately one half of the diameter of gears 52-55. In a preferred embodiment gears 52-55 have a pitch radius of about 1/2 inch. It is also preferred that the gear ratio between wheel 28 and socket gear 42 is 1:1. Of course, the ratio could be varied to increase the torque applied by socket gear 42 or to increase the speed of operation, without departing from the teachings of the invention. 
     Due to the limited space between the pedicle screw 12 and spinous process B, there is not sufficient room for a standard type socket tool to grip the head of clamping bolt 20 in order to start the bolt in the pedicle screw 12. Therefore, the present invention provides socket gear 42 with socket 40 formed directly therein. Socket gear 42 is mounted on shaft pin 68, which is shaped with a head that is received in a further circular recess 70 within socket 40, in order to avoid interference with the head of bolt 20 when received in socket 68. In this manner, the overall profile of the wrench is significantly reduced to allow the wrench, with articulating clamp 18 and clamp bolt 20 attached, to fit into a limited space, such as that between the spinous process B and installed pedicle screw 12. With wrench 100, a profile (P as shown in FIG. 2) of approximately 3/8 inch or less is possible. 
     It is possible to further reduce the profile of wrench 100 by utilizing an alternative drive means such as a plastic pulley and belt system. With such a drive means the outside configuration of the wrench would remain substantially unchanged. A socket pulley, configured substantially as is socket gear 42, described above, would be utilized in connection with a drive pulley rotated by wheel 28. 
     FIGS. 5 and 6 illustrate wrench 200 according to an alternative embodiment of the present invention. Shaft 80 is supported within casing 82 by bearing 84 at one end and cylindrical bushing 86 at the other. Bearing 84 is fixed to shaft 80 and rides on casing 82. Cylindrical bushing 86 has external screw threads 88 which mate with internal threads in casing 82. Bushing 86 is thus fixed to casing 82 and shaft 80 rides within a cylindrical bore through the bushing. Spring 90 acts between pin 92 and bushing 86 to bias shaft 80 and bevel gear 94, mounted the shaft, against cooperating bevel gear 96. Bushing 86 is provided with thumb wheel 98 to facilitate tightening of the screw threads. Thumb wheel 100 is provided for rotating shaft 80. 
     Bevel gear 96 is formed integrally with socket 104 and rides on shaft pin 102. In a preferred embodiment, socket 104 is designed to receive a hex-head threaded fastener. Arms 32 and 34 function as shown and described in FIGS. 1 and 2. Engaging members 36 and 38 have flattened sides in FIGS. 6 and 7; however, they cooperate with articulating clamp bore 19 as previously described. 
     The use of both wrench 100 and 200 is generally the same. The surgeon places clamp bolt 20 through hole 17 in articulating clamp 18. Articulating clamp 18 is then forced between engaging members 36 and 38 which are biased together by arms 32 and 34. The biasing force of arms 32 and 34 is sufficient to firmly hold articulating clamp 18 in place, however not so great that the wrench may not be easily removed once clamp bolt 20 is secured in the pedicle screw 12. 
     With the articulating clamp and clamp bolt installed on the wrench as shown in FIG. 4, the surgeon may simply align clamp bolt 20 with threaded hole 14 in pedicle screw 12 and drive the bolt into threaded hole 14 by rotation of wheel 28 or 100. This arrangement insures that clamp bolt 20 is held firmly in socket 40 or 104 as it is driven into the pedicle screw. There is no necessity for the surgeon to place his fingers actually in the incision around the pedicle screw in order to guarantee proper starting of clamp bolt 20. 
     Depending on a number of factors, including the patient&#39;s size and the particular vertebra involved, initially there may not be sufficient room to fit even the wrench according to the present invention between the pedicle screw and spinous process, with the articulating clamp and clamp bolt attached. This interference may be avoided by rotating the pedicle screw a small amount, approximately one quarter (1/4) of one rotation or less, in a direction which positions the face of the pedicle screw receiving the clamp bolt slightly caudally. 45° will generally be an appropriate rotation, although, depending on the particular case, rotation may be between about 20°-80°. This will provide adequate clearance for the initial installation of the clamp bolt. Once the clamp bolt has been screwed in a short distance, the pedicle screw may be finally positioned without interference between the wrench and the spinous process. Clamp bolt 20 then may be tightened as required and the wrench subsequently removed. 
     The detailed description of the preferred embodiments contained herein is intended to in no way limit the scope of the invention. As will be apparent to a person of ordinary skill in the art, various modifications and adaptions of the structure above described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.