Abstract:
A low-profile rod connector is disclosed that includes two substantially conical surfaces that allows two rods to be secured together. The device is easily manipulated and occupies very little space. The connector allows for the rods to be oriented at a number of different positions prior to securing the rods in a final orientation. Medical implants utilizing the present invention include surgical implants for spine stabilization. One particular application comprises securing the shaft of a pedicle screw to a spinal rod. In such application, since the connector is relatively small, displacement and disruption to nearby tissue is minimized. The connector also has application to external fixation systems which are conducted exterior of the skin surface, as well as other mechanical devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Priority is claimed from U.S. Provisional Patent Application No. 60/359,246 filed Feb. 20, 2002 entitled “PEDICLE SCREW CONNECTOR APPARATUS AND METHOD,” which is incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   This invention relates generally to securement devices and, more particularly, to a coupling and locking mechanism that is used to secure two rods together, or to secure a rod to one or more pedicle screws. 
   BACKGROUND OF THE INVENTION 
   Spinal fusion surgery is a method of placing bone graft material between two mobile segments of the spine to knit them together as one unit and eliminate motion between the segments. Fusion surgery can be performed with or without the use of spinal instrumentation for internal fixation. Internal fixation instruments are used to provide stability to decrease motion between segments of the spine and to allow the bone fusion to knit together. They act as an internal splint. Internal fixation devices may be attached with hooks, wires or bone screws. When bone screws orpedicle screws are employed they are screwed into the pedicles of a vertebra and connected to rods or plates to stabilize movement between the vertebrae to which they are connected. Thus, pedicle screws are implants used in the thoracic and lumbar spine to help surgeons stabilize the spine. “Headless” pedicle screws are used for several reasons, including the fact that headless screw design has been known to make it easier for surgeons to implant pedicle screws while avoiding the facet joint. In addition, pedicle screws can be implanted at each spinal level. 
   One such headless pedicle screw is the screw associated with TSRH-3D™ manufactured by Medtronic Sofamor Danek. More particularly, the present invention is capable of working in conjunction with “bolt 88” disclosed in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson. The present invention is a replacement for the clamp found in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson, the disclosures of which are specifically incorporated into this specification by reference. Details of the TSRH spinal implant system are disclosed in the “Surgical Technique Manual” provided by Danek Medical, Inc., published in 1990, which disclosure is also incorporated herein by reference. 
   The use of fixation devices for the treatment of vertebrae deformities and injuries is well known in the art. Various fixation devices are used in medical treatment to correct curvatures and deformities, treat trauma and remedy various abnormal spinal conditions. Treatment of these conditions generally requires the implantation of various component pieces such as support rods, crosslinks, caudal facing hooks, cranial facing hooks and like components, which form a spinal implant system. 
   It is necessary in spinal implant systems to properly anchor the system to bone to provide necessary support of the implant. Bone screws are commonly used for anchoring spinal implant systems. There are, however, several problems with the use of fixed screws for anchoring spinal implants. The exact final position of a bone screw is difficult, if not impossible, to predict prior to the exposure of the patient&#39;s bone. This unpredictability results from the uncertainty of exact bone formation and shape within an individual patient. Additionally, it can be difficult to predetermine the structure of the bone, i.e. whether the bone is soft or even osteoporotic. Even if the final position of the screw can be predetermined, the necessary shape and position of a spinal rod implant may create unwanted stress upon the bone screw or the bone itself. This is especially true where a plurality of screws is required along the spinal column for securement of an implant. The alignment of the rod with several screws along the vertebrae compounds this problem and makes undesired stress much more probable. Moreover, this misalignment may influence the extent and speed of correction of the spinal defect. 
   With regard to the size of a bone screw and connector, a low profile arrangement provides less disruption of the tissues in the vicinity of the spine. Nonetheless, it is common in the insertion of spinal implants to necessarily remove portions of vertebral bone to allow proper insertion of a bone screw. Moreover, current systems in use may result in long-term muscular displacement that may lead to a patient&#39;s pain or discomfort. Thus, a low profile bone screw and connector offers advantages, including less post-operative pain and discomfort for the patient. 
   Increased complexity of the installation procedure is undesirable because it increases a patient&#39;s time in surgery. Increased operating time is known to increase the risk of many complications associated with surgery. The additional time necessary to remove, or even temporarily dislocate, bone or muscular tissue also increases operating time, and thus the risk of complications. 
   In view of the above, there is a long felt but unsolved need for a method and system that avoids the above-mentioned deficiencies of the prior art and that provides an effective system that is relatively simple to employ and requires minimal displacement or removal of bodily tissue. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a low-profile connector device is provided for attaching two cylindrical objects or rods together, such as a spinal rod implant and the shaft of a pedicle screw used in spinal stabilization surgeries. The present invention is a variable angle connector that allows single point clamping. More particularly, after the rods are inserted into the receptacles of the connector, they may be moved longitudinally within the receptacles, and they may be rotated within the receptacles. Furthermore, in at least one embodiment of the present invention, approximately 60 degrees of rotational freedom exists for adjusting the connector to accommodate the position of the rods, thus allowing for motion to manipulate the assembly and to adjust the location of the connector and rods to their pre-final position. Subsequently, a single tightening screw is advanced within the connector to secure all degrees of freedom. The action of the tightening screw on the connector creates forces within the connector that secure and fixedly interconnect both of the rods within the connector, thus setting the connector and the rods in an interlocked final position. 
   In a first aspect of the invention, a connector is presented for securing two rods. The connector comprises a body including a first substantially conical surface having a slit and opposing joining sections adjacent the slit. In addition, the connector includes first and second receptacles for receiving first and second rods, respectively. The connector also includes a second substantially conical surface that is operatively associated with the first substantially conical surface. Finally, the connector includes means for urging the joining sections toward each other. Tension force is created within the connector upon urging the opposing joining sections in closer proximity because narrowing the slit reduces the diameter of the first substantially conical surface, which in turn pushes down on the second substantially conical surface. The tension force causes the two rods to be secured within the connector&#39;s receptacles because the receptacles create constricting or compressive forces around the rods. As an example of use in spinal surgery, one rod may take the form of a shaft of a pedicle screw, while the other rod is a stabilization rod that bridges a problematic spinal disc. The connector may be of unitary or one-piece construction, or it may be formed of a plurality of parts, such as two-part construction. In a preferred embodiment, the receptacles are formed of bands that are interconnected. 
   In a second aspect of the invention, a two-member connector is presented for securing two rods. Here, the connector includes a first member having a first receptacle for one of the rods, a first substantially conical surface having a slit and opposing joining sections adjacent the slit. The connector also has a second member that includes a second receptacle for a second rod, and a second conical surface for contacting the first conical surface. Finally, the connector includes means for forcing the joining sections toward each other, wherein the two rods are secured within the connector upon forcing the joining sections toward each other. 
   In yet a separate aspect of the invention, a connector for securing two rods is presented. The connector includes a first member having an interior substantially conical surface having a slit and adjacent opposing joining sections. The first member also has a first rod band at least partially disposed through a center opening in the first member. In addition, the connector has a second member including an exterior substantially conical surface and a second rod band that is also at least partially disposed through a central opening in the second member. Means for interconnecting the first rod band to the second rod band are provided, such as by threading the two bands together. In addition, means for forcing the opposing joining sections toward each other are also provided, such as by using a threaded tightening screw. 
   In yet a separate aspect of the invention, an end connector is provided that utilizes an end position on the end of a rod to form at least a portion of the connector of the present invention. The end connector includes two substantially conical surface members where one of the conical surfaces is formed as an integral part of the end of the rod. Among other things, this aspect of the invention allows for further controlling the eccentricity of the connector, as well as reducing the size of the connector because a second receptacle or rod band is not necessary given that the rod is already connected to the end connector. The end connector functions in a manner similar to the other connectors described herein. More particularly, a slit along the first substantially conical surface is narrowed by using a tightening screw to pull the two opposing joining sections of the slit toward each other. This ultimately results in creating a compression force around the rod band that holds the pedicle screw, thereby securing the pedicle screw to the rod. 
   In yet a separate aspect of the invention, a connector is provided that includes a plurality of pieces, and more particularly, a connector having four pieces is described. The four-piece connector includes first and second rod receiving members, and first and second substantially conical surface members. One of the conical surface members includes a slit and opposing joining sections adjacent the slit. Means for urging the joining sections toward each other is also provided, such as a tightening screw. The rod receiving members force the rods inserted therein to impinge upon the conical surface members, thereby securing the rods within the connector. 
   In yet a separate aspect of the present invention, a method of securing a pedicle screw to a stabilizing rod is presented. The method includes several steps, including inserting the exposed shaft of the pedicle screw and the rod into a connector having a first substantially conical surface that has a slit and opposing joining sections adjacent the slit. The connector also has first and second receptacles for receiving the rod and the shaft of the pedicle screw. In addition, the connector includes a second substantially conical surface that at least partially contacts the first substantially conical surface. Additional steps include inserting a tightening screw into the openings of the joining sections, and tightening the tightening screw to force the joining sections together and thus constricting the first substantially conical surface of the first member. The tightening step decreases the diameter of the first substantially conical surface, which pushes against the second substantially conical surface and thereby creates a constricting force around the rod and the shaft of the pedicle screw through the receptacles. 
   In a separate aspect of the invention, a projection or surface texturing may be provided within a receptacle or rod band of the connector, and also potentially provided on the shaft of the screw or the rod to provide additional stability to the assembly. 
   Based on the foregoing summary, a number of worthwhile aspects of the present invention can be readily identified. The minimal size of the connector device allows attachment of the device to human bone without significant displacement of human tissue. Therefore, the complexity of surgery and the following pain and discomfort of the patient may be minimized. The nature of the device, combined with its small size and profile, may allow a surgeon to attach the securement device to a secure portion of the human body without the need to remove bony processes which may be necessary to accommodate a larger attachment device. The simplicity of the elements, and the assembly process thereof reduces the training and experience or surgeons necessary to achieve desired results, and, may reduce the patient&#39;s time in surgery, thus reducing the risk and probability of surgical complications. Finally, a number of embodiments of the present invention may be used in combination to allow a surgeon great latitude in the selection of materials used. The surgeon may select from different embodiments of the connector to best fit the surgical implant parameters. With these choices, the surgeon may then best determine which embodiments of which elements to select to minimize removal or displacement of bodily tissue or bone, and thereby reduce both the patient&#39;s risk of surgical complications and post-surgical pain and discomfort. 
   A significant feature of the present invention is the ability to provide a construct used to stabilize the spine or a portion thereof. This is a very low profile configuration (as compared to existing devices) that minimizes the length of the incision that is necessary to perform the surgery. Furthermore, a mechanical advantage is gained by the interaction of the components as previously described. Specifically, strength of the final connection is not simply attributable to the tightening of the tightening screw, but is also attributable, in part, to the placement of the spinal rod or screw shaft within the receptacles of the connector, and the wedge like interaction of the conical surfaces of the connector. 
   Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation view of a first embodiment of the present invention; 
       FIG. 2A  is a is a top view of a first member of a two-piece connector; 
       FIG. 2B  is a bottom view of the first member shown in  FIG. 2A ; 
       FIG. 2C  is a side elevation view of the first member shown in  FIG. 2A ; 
       FIG. 2D  is a second side elevation view of the first member shown in  FIG. 2A ; 
       FIG. 3A  is a side elevation view of a second member of a two-piece connector; 
       FIG. 3B  is a bottom view of the second member shown in  FIG. 3A ; 
       FIG. 3C  is a second side elevation view of the second member shown in  FIG. 3A ; 
       FIG. 4  is a plan view of two connectors used to connect pedicle screws to a stabilizing rod; 
       FIG. 5  is a side view of the apparatus depicted in  FIG. 4 ; 
       FIG. 6  is a pedicle screw known in the prior art; 
       FIG. 7  is a plan view of two connectors, including an end connector formed as an integral part of a rod, wherein the connectors are used to connect pedicle screws to a stabilizing rod; 
       FIG. 8  is a perspective view of an end connector formed as an integral part of a rod; 
       FIG. 9  is a perspective view of a two-piece end connector formed as an integral part of a rod; 
       FIG. 10  is a different a perspective view than that of  FIG. 9  of a two-piece end connector formed as an integral part of a rod; 
       FIG. 11  is a different perspective view than that of  FIG. 8  of an end connector formed as an integral part of a rod; 
       FIG. 12  is a different perspective view than that of  FIGS. 8  or  11  of an end connector formed as an integral part of a rod; 
       FIG. 13  is a side elevation view of two connectors of the present invention used to bridge a problematic vertebral disc; 
       FIG. 14  is a plan view of an incision showing implantation of two connectors and a rod; 
       FIG. 15  is an elevation view of an exploded four-piece connector of the present invention; 
       FIG. 16  is a top view of a component of the four-piece connector shown in  FIG. 15 ; 
       FIG. 17A  is a bottom view of a separate component of the four-piece connector shown in  FIG. 15 ; 
       FIG. 17B  is a top view of the component shown in  FIG. 17A ; 
       FIG. 18A  is a top view component of a separate embodiment of a multi-piece connector; 
       FIG. 18B  is a cross-section along line  18 B- 18 B as shown in  FIG. 18A ; 
       FIG. 18C  is second cross-section along line  18 C- 18 C as shown in  FIG. 18A ; 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a first embodiment of the connector of the present invention is shown. The connector  10  includes a first rod band  45  and a second rod band  105 . In addition, the connector includes substantially conical surfaces within the interior of the connector. Finally, the connector includes a slit and a means for drawing together the adjacent joining sections of the slit, thereby decreasing the diameter of the upper conical surface that in turn forces the lower conical surface downwards, thereby tightening the bands  45  and  105 . The bands may be tightened around two rods, such as a vertebrae stabilizing rod and the shank of a pedicle screw. Various embodiments of the invention will be described below. 
   Referring now to  FIGS. 2A-3C , a first embodiment of the connector  10  of the present invention is shown, wherein the connector is formed of two pieces. However it is to be understood that the present invention may be of unitary construction, or it may be constructed of a plurality of pieces, such as three or four pieces, as will be discussed below. 
   In a first embodiment, connector  10  utilizes two-piece construction, wherein the first piece is first member  35 . First member  35  shown in  FIGS. 2A-2D  includes a first body  40 , first rod band  45 , first band fitting  50 , slit  55 , opposing joining sections  60   a  and  60   b , openings  65   a  and  65   b , interior substantially conical surface  70 , and center body opening  75 . As can be seen in the figures, the various substantially conical surfaces may be truncated, thereby allowing for passage of other structure, such as the band fittings. Accordingly, as used herein, the term “substantially conical surface” includes a substantially truncated conical surface. First body  40  is preferably circular, although its exterior surface may be other shapes, such as square, rectangular, or a multi-side polyhedron. One end of first rod band  45  is connected to first body  40 . First rod band  45  forms a loop along its length, thereby creating an opening or a first rod position  80 . As first rod band  45  curves, it is disposed through center body opening  75  and extends below interior substantially conical surface  70 . At the end of the portion of first rod band  45  that is disposed through center body opening  75  is first band fitting  50 . First band fitting  50  is preferably an interconnection device that allows first member  35  to be interconnected to the second piece of connector  10 , as will be discussed below. First band fitting  50  includes interconnection means, such as threads, a hook, or a socket, that receives, or is received in, the second piece of connector  10 . Joining sections  60   a  and  60   b  are adapted to provide means for pulling joining section  60   a  toward joining section  60   b . Preferably, joining sections  60   a  and  60   b  include openings  65   a  and  65   b , respectively, that receivingly accept a tightening screw  85 . When connector  10  is installed, as will be discussed below, tightening screw  85  is placed through openings  65   a  and  65   b  and is tightened to bring joining section  60   a  closer to joining section  60   b . More particularly, due to the presence of slit  55  in first body  40  between joining sections  60   a  and  60   b , tightening screw  85  is used to pull joining section  60   a  toward joining section  60   b.    
   Referring now to  FIGS. 3A through 3C , the second member  90  of connector  10  is illustrated. Second member  90  includes a second body  100 , second rod band  105 , second rod band fitting  110 , exterior substantially conical surface  115 , and second central body opening  120 . Second body  100  is preferably circular, although its exterior surface may be other shapes, such as square, rectangular, or a multi-side polyhedron, as long as the upper exterior surface is substantially conical, that is, exterior substantially conical surface  115 . One end of second rod band  105  is interconnected to body  100 . Second rod band  105  forms a loop along its length, thereby creating an opening or a second rod position  125 . As second rod band  105  curves, it is disposed through or in the vicinity of center body opening  120 . At the end of second rod band  105  is second band fitting  110 . Similar to first band fitting  50 , second band fitting  110  is preferably an interconnection device that allows first member  35  to be interconnected to second member  90 . More particularly, first rod band  45  is connected to second rod band  105 . Accordingly, second band fitting  110  must mate with first band fitting  50 . Preferably, the interconnection means includes threads, a hook, or a socket, an expansion fitting or some type of connection that interconnects first band fitting  50  with second band fitting  110 . For example, preferably first band fitting  50  may be fitted with male threads and second band fitting  110  with matching female threads. Alternately, first band fitting  50  may be fitted with a T-shaped interlocking fitting (not shown) that can be pushed into an opening in second band fitting  110  and turned 90 degrees to lock the two pieces together. Rotational freedom between rods is provided when using a threaded connection between the first rod band  45  and second rod band  105  because the threads can be partially released with the rods situated within the connector to adjust the connector to accommodate the position of the first rod (or pedicle screw shaft) relative to the second rod (or spinal stabilization rod). At least approximately 60 degrees of rotational freedom exists for moving and adjusting the rods/screw  20  and  15  relative to one another, thus allowing for motion to manipulate the assembly and to adjust the location of the connector  10  and rods/screw  20 ,  15  to their pre-final position. Subsequently, the tightening screw  85  can be used to interlock the rods/screws  20 ,  15  within the connector  10 . If properly configured, this rotational adjustability would also be available if a socket type of fitting were used to make the connection between first band fitting  50  and second band fitting  110 . 
   Referring now to  FIG. 2D , the dimensions of first member  35  may be reduced, and therefore optimized, by reducing the size of its various components. For example, rounded corners may be incorporated into first body  40  to further reduce its size. In addition, the height of dimension “d 1 ” may be adjusted to reduce the overall size of first body  40 , and therefore, of first member  35 . The typical diameter of a pedicle screw  15  is 5 mm, and the distance between pedicle screw  15  and tightening screw  85  is about 4 mm, although this dimension will vary depending upon the size and the configuration of the connector used. The angle θ of interior substantially conical surface  70  is preferably between 15 and 75 degrees, and more preferably, between 20 and 60 degrees, and more preferably yet, between 25 and 50 degrees, and still more preferably yet, between about 30 to 45 degrees, with one preferred embodiment having an angle θ of about 30 degrees. Exterior substantially conical surface  115  is formed at an angle θ similar to that of interior substantially conical surface  70 . Slit  55  is preferably formed by an open arc φ in the substantially conical surface in which it is disposed. The open arc φ is preferably between about 5 to 50 degrees, and more preferably, between about 10 to 40 degrees, and more preferably yet, between about 15 to 35 degrees, with one preferred embodiment having an angle φ of about 30 degrees. 
   Similarly, the dimensions of second member  90  may also be reduced, and therefore optimized, by reducing the size of its various components. For example, the height of dimension “d 2 ” of second body  100  may be adjusted to reduce the overall size of second member  90 . Rounded corners may be incorporated into second body  100  to further reduce its size. In addition, exterior substantially conical surface  115  may be reduced in size by reducing its height “d 3 ” depending upon the specific application. Thus, a separate aspect of the present invention is the ability to optimize the dimensions of the connector&#39;s components, by considering the specific application at hand. Optimization techniques are applied, such as finite element analysis, to calculate the anticipated stress and strain on the various structures of the connector. Thereafter, the size of the connector can be reduced to provide the minimum profile necessary to withstand the anticipated stresses, while still maintaining a satisfactory factor of safety against structural failure for the given mode of use. 
   Connector  10  is assembled by operatively associating first member  35  with second member  90 . Depending on the type of interconnection used between first member  35  and second member  90 , and also depending upon the special constraints of the patient&#39;s particular surgical condition, first member  35  may be joined to second member  90  either before or after each member is attached to a rod or screw. In the first embodiment depicted in  FIGS. 2A-3C , first band fitting  50  possesses male threads and second band fitting  110  possesses female threads. As such, first band fitting  50  is threaded into second band fitting  110 , thereby connecting first member  35  to second member  90  to form connector  10 . Since the threading action is not possible after insertion of a pedicle screw  15  into the patient&#39;s bone and insertion of the shank of the pedicle screw  15  into first member  35 , first member  35  is preferably threaded to the second member  90  prior to inserting the shank of the pedicle screw  15  into connector  10 . However, as noted above, connector  10  may be formed of one piece. 
   Unitary or one-piece connector construction is possible by manufacturing connector  10  such that first member  35  is interlocked with second member  90 . For example, a one-piece connector  10  may be formed by welding first rod band  45  of first member  35  to second rod band  105  of second member  90 . Other means for interconnecting first member  35  to second member  90  to form connector  10  are considered within the scope of the invention, such as by chemically bonding the components together, casting them as one unit, or otherwise providing a structural mechanism for interlocking the pieces together. A unitary construction would limit rotational freedom between rods, although each rod may be rotated within each receptacle or rod band before securing the rods using the tightening screw or other similar means for creating the interlocking tension and constricting forces within the connector. Alternately, a unitary construction could be used that provides rotational adjustability, such as by utilizing a permanently interlocked rotatable socket type of fitting (not shown) that is engaged during manufacture of the device. 
   Referring now to  FIG. 2C , in a separate aspect of the invention, projections or surface texturing  130  maybe added to a portion of the interior surface of first rod band  45 . Similarly, as shown in  FIG. 3C , projections or surface texturing  130  may be added to a portion of the interior surface of second rod band  105 . Preferably, surface texturing may take the form of ridges and grooves or arcuate shaped projections. Such a configuration of texturing allows first rod band  45  and second rod band  105  to tighten around rods  20  or screws  15  held within their respective interior regions, namely first rod position  80  and second rod position  125 . These ridges and grooves are preferably positioned to provide a mating surface with the exterior surface of a rod  20  or screw  15 , which may also have surface texturing  130 , and which is placed within first rod position  80  and second rod position  125 . Surface texturing  130 , therefore, would tend to aid in preventing longitudinal motion of a rod  20  or screw  15  within first rod position  80  and/or second rod position  125 . Surface texturing  130 , however, is considered optional, and is not necessary for the proper functioning of connector  10 . 
   Referring now to  FIGS. 4 and 5 , in a separate aspect of the invention, a plurality of connectors  10  may be used along a length of rod  20 . The adjustable nature of the connector  10  allows the connector to be moved along the length of rod  20  prior to advancing tightening screw  85  and interlocking the connector  10  to the rod  20 . As shown in  FIG. 6 , a pedicle screw of the prior art is illustrated. Such a pedicle screw includes a smooth shaft or shanked portion  19  that can easily be grasped by the connector  10  of the present invention. 
   In a separate aspect of the present invention, a connector having two conical surfaces may be adapted to the end of a rod  20 , as shown in  FIGS. 7-12 . More particularly, rod  20  is manufactured with a conical surface forming an end of rod  20 . For example, in the case of the embodiment referred to as connector  10 , rod  20  may be manufactured with second member  90 ′ pre-formed at the end of rod  20 . Referring to  FIG. 7 , a connector  10 ′ is shown at the end  25  of rod  20 . In addition, a second connector  10  is shown at an interior rod location  30 . Thus, the connector of the present invention may be formed as an integral part of rod  20 , that is, connecter  10 , or it may be a separate device that is adjustable along the length of the rod  20 , as in the case of connector  10 . 
   Referring now to  FIGS. 8-12 , the separate embodiment of the connector  10 ′ formed as an integral part of rod  20  is illustrated. In this embodiment, rod  20  is continuous with end connector  10 ′. In an illustrative example of end connector  10 ′, a two-piece connector  10 ′ is shown that includes a first member  35  that is consistent in characteristics to the first member  35  of previously discussed for connector  10 . However, connector  10 ′ features a second member  90 ′ that is formed at the end of rod  20 . Here, rod  20  includes an exterior substantially conical surface  115 . When assembled by threading or otherwise connecting first member  35  to second member  90 ′, the exterior conical surface  115  of second member  90 ′ comes in close proximity of interior substantially conical surface  70  of first member  35 . 
   In use, the present embodiment functions similarly to the other embodiments described herein in terms of how the conical surfaces of the connector create interlocking forces. In the present embodiment, first member  35  is interlocked with rod  20  at second member  90 ′, such as by threading. After a pedicle screw  15  is inserted into a vertebra, first rod band  45  of first member  35  is slipped over the exterior of pedicle screw  45 . If necessary, the threads between the first member  35  and second member  90 ′ can be partially released (or not fully tightened) to provide rotational adjustability to the connector  10 ′ to accommodate the location of pedicle screw  15  and rod  20 . Tightening screw  85  is then tightened to urge joining section  60   a  toward joining section  60   b  of first member  35 . This action decreases the diameter of interior substantially conical surface  70 , forcing exterior conical surface member  90 ′ to move longitudinally from a first position to a second position relative to first member  35 , thereby placing the first rod band  45  in a state of compression around pedicle screw  15 , and therefore, interlocking the rod  20  to the pedicle screw  15 . 
   Referring now to  FIG. 13 , an example of use in spinal surgery is illustrated. Here, a problematic spinal disc D is initially identified by a physician. During surgery, an incision is made through the skin and muscle overlying the implant location of the spine. Then a first pedicle screw is inserted in vertebra V 1  and a second pedicle screw is inserted into vertebra V 2 . The surgeon then uses an adjustable connector, such as connector  10  and/or a rod  20  having an end connector  10 ′. If not of unitary construction, and if not already assembled, connector  10  is assembled by connecting first member  35  to second member  90 . Specifically, for a two-piece connector, first member  35  is connected to second member  90  by preferably threading first band fitting  50  into second band fitting  110 . Subsequently, the smooth shanked portion  19  of pedicle screw  15 , as depicted in  FIG. 6 , is inserted through first rod position  80  of first rod band  45 , as depicted in  FIG. 2 . If connector  10  is used (as opposed to end connector  10 ′), a rod  20  is then inserted through second rod position  125  of second rod band  105 . After inserting the rod and shanked portion  19  of pedicle screws  15  into the connectors, tightening screw  85  is then threaded through openings  65   a ,  65   b  of joining sections  60   a ,  60   b . Tightening screw  85  is advanced within openings  65   a ,  65   b , whereby the rod  20  and connectors  10  and/or  10 ′ are then interlocked together by urging joining sections  60   a  and  60   b  toward each other. Note that other means of bringing together joining sections  60   a  and  60   b  are also contemplated, such as by the surgeon using a separate tool, such as pliers, followed by the placement of a permanent clip (not shown) that holds the joining sections together in their desired location. Regardless of the means used for bringing together the joining sections  60   a  and  60   b , the movement of urging joining section  60   a  toward joining section  60   b  reduces the diameter of interior substantially conical surface  70 . This reduction in diameter progressively forces exterior substantially conical surface  115  to move away from interior substantially conical surface  70 . That is, the reduction in diameter of the interior substantially conical surface  70  tends to longitudinally drive exterior surface member  90 ′ from a first position to a second position relative to first member  35 . Since first rod band  45  is joined to second rod band  105  at first band fitting  50  and second band fitting  110 , tension is created in first rod band  45  and second rod band  105 , thereby tightening first rod band  45  around the pedicle screw  15  held within first rod position  80 , and also tightening second rod band  105  around the rod  20  held within second rod position  125 . The tension created in first rod band  45  and second rod band  105  creates a compression force around the shaft of pedicle screw  15  and the circumference of rod  20 . Continued advancement of tightening screw  85  is performed until a sufficient tension is developed in first rod band  45  and second rod band  105  to securely hold and lock in place connector  10  with the screw  15  held in first rod position  80  and rod  20  held in the second rod position  125 . This procedure is repeated for attaching a different connector to the other end of rod  20 . 
   Now referring to  FIG. 14 , an incision is shown with the connector  10 ,  10 ′ or  200  (as discussed below) used at either end of rod  20 . As can be seen, both the top of the pedicle screw  15  and the top of the tightening screw  85  are accessible from the top of the incision. Therefore, using the present invention, a surgeon can make an incision that is only slightly longer than the rod to be implanted. This provides access to the surgical site for installation of the pedicle screws  15 , connectors  10 ,  10 ′, or  200  and the rod  20 . Given that both the top of the pedicle screw  15 , and the top of the tightening screws  85  are accessible, the surgeon can perform the installation of the screws  15 , rod  20 , and connectors  10 ,  10 ′ or  200  in a minimally invasive manner. That is, excessive retraction of the incision is not necessary to gain access to the surgical site to place the implant. Furthermore, excessive retraction of tissue is also not necessary to attach, connect, and tighten the various components. In a separate aspect of the invention, pedicle screws  15  may be equipped with leaders (not shown), preferably flexible leaders, that allow the connectors  10 ,  10 ′, or  200  and the rod  20  to be assembled above the top of the incision, and then slipped over the flexible leaders onto the smooth shanked portion  19  of pedicle screws  15 , at which point the tightening screws  85  may be adjusted to secure the connectors  10 , 10 ′, or  200 , to the pedicle screws  15  and rod  20 . Thereafter, the flexible leaders may be removed and the incision closed. Thus, the present invention offers a minimally invasive method for performing spinal stabilization surgery. 
   In a separate embodiment, the connector is formed using more than two pieces. More particularly, the connector may be formed of three pieces, or alternately, of four pieces. Referring now to  FIGS. 15-17B , connector  200 , comprising four pieces, is presented.  FIG. 15  shows an exploded view of a four-piece connector having conical surfaces. Connector  200  is comprised of two rod receiving members and two conical surface members. First rod receiving member  205  is shown at the top of  FIG. 15 . First rod receiving member  205  includes means for interconnecting first rod receiving member  205  to a second rod receiving member  230 . Preferably, the means for connecting these two components comprises threads, although a hook or socket-type of interlocking means is also within the scope of the invention, as is any means for connecting the two members together. Using threaded connections to connect first rod receiving member  205  to second rod receiving member  230  provides rotational adjustability to connector  200  to accommodate the position of the two rods, such as pedicle screw  15  and rod  20 . Adjustability is attained by partially releasing the tightened threads. As shown in  FIG. 15 , first rod receiving member  205  includes first interlocking portion  210  and first rod receiving portion  215 . First interlocking portion  210  is preferably circular in cross section, and includes male threads  220 . First rod receiving portion  215  is preferably rectangular or square in cross section, and includes first rod opening  225 . First rod opening  225  is sized to receive a rod  20  or the smooth shaft  19  of a pedicle screw  15 . 
   Still referring to  FIG. 15 , second rod receiving member  230  is shown at the bottom of the figure. Second rod receiving member  230  includes a second interlocking portion  235  and a second rod receiving portion  240 . Second interlocking portion  235  is preferably circular in cross section, and includes female threads  245  that interlock with male threads  220  of first rod receiving member  205 . Second rod receiving portion  240  is preferably rectangular or square in cross section, and includes second rod opening  250 . Second rod opening  250  is sized to receive a rod  20  or the smooth shaft  19  of a pedicle screw  15 . First rod opening  225  and second rod opening  250  are depicted in the figures to be circular; however, within this embodiment, rods of alternate shapes may be used, such as multiple-sided rods (not shown), or semicircular shafts that also have one flat side (also not shown). 
   The third and fourth components of connector  200  include two conical surface members. Referring now to  FIGS. 15-17B , first conical surface member  255  is depicted in top and side elevation views, respectively. First conical surface member  255  includes a first central opening  260 , opposing joining sections  60   a ,  60   b , slit  55 , and grooves  265   a ,  265   b . First central opening  260  receivingly accepts first rod receiving member  205 . More particularly, first central opening  260  includes a first circular opening  270  that passes through first conical surface member  255  at a position interior to slit  55 . In addition, a recessed rectangular or square shaped recess  275  with flange  280  is cutout within the central area of first conical surface member  255 . As such, first interlocking portion  210  of first rod receiving member  205  passes through first circular opening  270  when connector  200  is assembled. However, flange  280  of recess  275  prevents first rod receiving portion  215  of first rod receiving member  205  from passing through first central opening  260 . Rather, flange  280  of recess  275  retains first rod receiving portion  215  of first rod receiving member  205 . In addition, optional grooves  265   a ,  265   b  serve to cradle rod  20  when it is inserted into first rod opening  225  of first rod receiving member  205 . Preferably, joining sections  60   a  and  60   b  include openings  65   a  and  65   b , respectively, that receivingly accept a tightening screw  85 . First conical surface member  255  also includes an interior substantially conical surface  285  located on the underside of first conical surface member  255 , or situated on the surface of first conical surface member  255  opposite the location of grooves  265   a ,  265   b . Interior substantially conical surface  285  of first conical surface member  255  contacts the second conical surface member  290 , as described below. 
   Still referring to  FIGS. 15-17B , second conical surface member  290  includes exterior conical surface  295 , second central opening  300 , and grooves  305   a ,  305   b . Second central opening  300  includes a second circular opening  310  that passes through second conical surface member  290 . A recessed rectangular or square shaped recess  315  with flange  320  is cutout within the central area of second conical surface member  290 . As such, second interlocking portion  235  of second rod receiving member  230  passes through second circular opening  310  of second central opening  300  when connector  200  is assembled. However, flange  320  of recess  315  prevents second rod receiving portion  240  of second rod receiving member  230  from passing through second central opening  300 . Rather, flange  320  of recess  315  retains second rod receiving portion  240  of second rod receiving member  230 . In addition, optional grooves  305   a ,  305   b  serve to cradle rod  20  when it is inserted into second rod opening  250  of second rod receiving member  230 . 
   Connector  200  is assembled by passing first rod receiving member  205  through first conical surface member  255 , and by passing second rod receiving member  230  through second conical surface member  290 , and subsequently interconnecting male threads  220  of first rod receiving member  205  with female threads  245  of second rod receiving member  230 . First conical surface member  255  is aligned with second conical surface member  290  such that interior substantially conical surface  285  of first conical surface member  255  contacts exterior substantially conical surface  295  of second conical surface member  290 . Following assembly of connector  200 , a rod  20  or pedicle screw  15  is passed through first rod opening  225  of first rod receiving member  205 , and through second rod opening  250  of second rod receiving member  230 . Tightening screw  85  is then placed within openings  65   a,    65   b  of joining sections  60   a ,  60   b  and is tightened. As with connector  10  of a previously discussed embodiment, the action of advancing tightening screw  85  forces together joining section  60   a  with joining section  60   b  of first conical surface member  255 . The movement of advancing joining section  60   a  toward joining section  60   b  reduces the diameter of interior substantially conical surface  285 . This reduction in diameter progressively forces exterior substantially conical surface  295 , and therefore, second conical surface member  290 , to shift relative to interior substantially conical surface  285  of first conical surface member  255 . Force is then applied to rods  20  or pedicle screw  15  by grooves  265   a ,  265   b  and  305   a ,  305   b  of first conical surface member  255  and second conical surface member  290 , respectively. Tightening screw  85  is advanced as necessary to develop sufficient force on rod  20  or pedicle screw  15  to secure and interlock the rod  20  or pedicle screw  15  in a desired final position. 
   Referring now to  FIGS. 16 and 17A , in a separate aspect of the invention, surface texturing  130  may be added to a portion of optional grooves  265   a  and/or  265   b . Similarly, as shown in  FIG. 8   a , surface texturing  130  may be added to a portion of optional grooves  305   a  and/or  305   b . Preferably, surface texturing may take the form of ridges and grooves, with the ridges and valleys of the grooves preferably aligned perpendicular to the longitudinal axis of grooves  265   a ,  265   b  or  305   a ,  305   b . The ridges and grooves of texturing  130  are preferably positioned to provide a mating surface with the exterior surface of a rod  20  or screw  15 , which may also have texturing  130 , and which is placed in contact with grooves  265   a ,  265   b  and/or  305   a ,  305   b . Surface texturing  130 , therefore, would tend to aid in preventing longitudinal motion of a rod  20  or screw  15  after connector  200  is tightened using tightening screw  85 . Surface texturing  130 , however, is considered optional, and is not necessary for the proper functioning of connector  200 . 
   Referring now to  FIGS. 18A-18C , in still a separate embodiment, a connector may be configured such that tightening screw  85  is aligned perpendicular to ipsilateral rod  20 . More particularly,  FIG. 18A  depicts a top view of first conical surface member  255 ′. However, unlike first conical surface member  255  of connector  200 , first conical surface member  255 ′ is configured such that the longitudinal axis of tightening screw  85  is perpendicular to rod  20 . First conical surface member  255 ′ includes a first body  505 , a first central opening  260 ′, body joining sections  510   a ,  510   b , section openings  515   a ,  515   b , slit  520 , and grooves  265   a ′ and  265   b ′. First central opening  260 ′ receivingly accepts first rod receiving member  205 , in a manner similar to that previously described for connector  200 . Tightening screw  85  is inserted into section openings  515   a  and  515   b . Upon advancing tightening screw  85 , body joining section  510   a  is drawn toward body section  510   b . The interaction of the conical surfaces tighten and secure the connector in a manner similar to that described above. In addition, groove  265   b ′ is formed by cradle wings  525   a  and  525   b  when body joining sections  510   a  and  510   b  are drawn toward each other. Thus, it can be appreciated that various configurations and orientations are possible for the tightening screw  85  relative to the rod(s)  20  and/or pedicle screw  15 . 
   In yet a separate embodiment, a connector is formed using three portions. As described in detail above, a two piece connector, connector  10 , may be formed using a first member  35  operatively associated with a second member  90 . Alternately, a four piece connector, connector  200 , is formed using two rod receiving members  205  and  230 , and two conical surface members  255  and  290 . A three piece connector is formed by combining portions of connector  10  with portions of connector  200 . In one separate aspect of this embodiment, a connector is formed by combining first member  35  in combination with second rod receiving member  230  and second conical surface member  290 . Alternately, in a second and separate aspect of this embodiment, a connector is formed by combining first rod receiving member  205  with first conical surface member  255 , in combination with second member  90 . Unitary connectors, two-piece connectors, three-piece connectors, and four-piece or more connectors allow a surgeon to customize the assembly to suit the particular patient&#39;s needs. As with connectors  10  and  200  described above, three-piece connectors are secured to the smooth shaft  19  of the pedicle crew  15  and the rod  20  by utilizing a tightening screw  85  to draw joining sections  60   a  and  60   b  together, thereby creating tension in the three-piece connector when the conical surfaces are forcibly adjusted relative to each other, wherein the tension thus created serves to grasp and secure the pedicle screw  15  and rod  20  together via the connector. 
   The various embodiments of the present invention use substantially conical surfaces within the connector devices. The conical surfaces may include coatings to alter the frictional characteristics of the conical surfaces. In addition, the conical surfaces may include structural modifications such as projections to reduce friction. For example, one or both of the conical surfaces may include elongated projections that run from the center of the conical surfaces to the edge of the conical surfaces. Such features would reduce the surface area that is in contact between the two conical surfaces and thereby reduce the friction created when advancing the tightening screw or the means for bringing the opposing joining sections closer to one another. Accordingly, the conical surfaces are operatively associated with each other, but are not necessarily fully in contact with each other. Indeed, a conical surface can essentially be formed by a discontinuous ridge pattern, taking the analogous form of the ribs of an umbrella or an inverted umbrella, with or without a recessed surface between the ribs. In various embodiments, spherical surfaces or spherical-like surfaces may be used within the connector. For example, the conical surfaces noted herein may be substituted with surfaces similar to that of a ball. Alternately, the conical surfaces noted herein may be substituted with undulating surfaces similar to that of a golf ball, with the individual dimpled surfaces projected outward, inward, or both. 
   In yet a separate aspect of the invention, the connector  10 ,  10 ′ or  200  may be placed or integrally formed at the end of a rod as previously discussed, and a separate but similar connector may be placed at the other end of a different rod, with the two rods joined together in the middle by telescoping means. The telescoping means may take the form of a outer and an inner sleeve with or without a locking pin, or the telescoping means make take the form of a clamp-type of device that utilizes an outer structure to clamp around an inner rod member. This aspect of the invention allows the length of the rod to be customized at the surgical site by the surgeon. 
   In a separate aspect of the invention, pedicle screws  15  may be equipped with the same size head opening  17  as the head opening  87  of tightening screw  85 . More particularly, as previously discussed, in a preferred embodiment, headless pedicle screws are used, such as those associated with the TSRH-3d™ spinal instrumentation manufactured by Sofamor Danek. These headless screws utilize a multi-faceted opening  17  in the head of the screw  15  to receive the tip of a tool to drive the screw  15  into the bone. The head opening  87  of tightening screw  85  can be sized to exactly match the head opening  17  of the pedicle screw  15 . This offers the surgeon the ability to utilize the same tool to install pedicle screw  15  and tighten tightening screw  85 . 
   In yet a further aspect of the invention, the head opening  17  of pedicle screw  15  may be color coded (not shown) to indicate that it is a pedicle screw  15  as opposed to the tightening screw  85 . For example, head opening  17  of pedicle screw  15  may be the color white, while the head opening  87  of tightening screw  85  may be the color green. Obviously, any variation of colors could be used. 
   In yet a separate aspect of the present invention, different size openings may preferably be used in the head opening  17  of pedicle screw  15  and the head opening  87  of tightening screw  85 . More particularly, the use of different size or shaped openings in head openings  17  of pedicle screws  15  as compared to head openings  87  in tightening screws  85  may aid in preventing confusion during surgery. That is, head openings  87  of tightening screws  85  that require a different tool to tighten than the pedicle screw  15  may assist the surgeon in not over-tightening one screw when he or she believes they are tightening the other. 
   Further structural aids or devices may also be employed to assist with installation of the various aspects of the present invention. For example, a torque wrench (not shown) may be used to provide the proper torque to tightening screw  85  to ensure it is not over-tightened during installation. Alternately, the head opening  87  of tightening screw  85 , or head opening  17  of pedicle screw  15  may be designed to slip or create an audible clicking noise once a specified torque is reached, thereby preventing over-tightening. 
   The present invention has the distinct advantage of offering a very low profile device for securing two rods together, or one rod and one screw, such as a stabilizing rod and the shank of a pedicle screw. Given that the present invention offers the advantage of being very low profile, a surgeon is able to implant a stabilizing device for the spine with minimal disruption to neighboring tissue. As a result, the patient undergoes less pain, and less recovery time, and medical costs are consequently also reduced. 
   The structures of the present invention are made from one or more materials that possesses the appropriate strength characteristics necessary to withstand loading from the human body when used in medical applications. Preferably, materials include ceramics, plastics, metals, or carbon fiber composites. More preferably, the materials are made from titanium or stainless steel. 
   Devices disclosed herein can also be made of thermal memory materials or materials that possess different elastic properties at varying temperatures. In this aspect of the invention, the subject component(s) may be heated or cooled to a desired temperature, implanted, then subsequently allowed to cool or warm to the temperature of the ambient conditions that will exist during the usage period for the subject device, namely, normal body temperature. 
   It is to be understood that the present invention has application to medical devices other than spinal implants. For example, the present invention can be used in external fixator systems. Specifically, connectors are used to secure rods to screws that project outside of the skin surface. The present invention offers a low-profile system of connecting two rods, or a rod to the shaft of a screw. In addition, the present invention may be used to secure various orthodontic appliances. For example, it maybe used to secure arch wires to brackets. Alternately, it may be used in various orthodontic headgear apparatus. 
   Furthermore, it is understood that the present invention has application outside the medical field. The securing mechanism of the present invention is not limited to medical implants. The present invention could be used to secure any two wires, screws, rods, or a combination of these such devices, such as in linking mechanisms, and has application to any type of mechanical device with static or moving parts. Other applications, by no means exhaustive, may include connecting legs of a tripod to a base and mounting track lighting fixtures. One of skill in various of the construction arts will appreciate how to make and use the present invention in view of the guidance provided herein (with respect to a surgical application) and in view of the Figures set forth herein. 
   While various embodiments of the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention, as set forth in the following claims.