Abstract:
An apparatus is disclosed for connecting first and second elongated spaced apart spinal rods to one another which includes an elongated body portion, a clamp portion depending from the body portion for engaging a spinal rod, the clamp portion defining a deformable clamp body having opposed clamp arms configured for movement between a first position wherein a spinal rod is received between the opposed clamp arms of the clamp body and a second position wherein the spinal rod is securely engaged by the opposed clamp &amp;ms &amp;the clamp body, and structure operatively associated with the clamp body which h configured to effectuate movement of the opposed clamp arms of the clamp body between the first and second positions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of application Ser. No. 10/012,127, filed on Dec. 7, 2001, which is a continuation of Ser. No. 09/535,776, filed Mar. 28, 2000, now abandoned, which claims the benefit of the filing date of provisional application Ser. No. 60/126,997, filed Mar. 30, 1999, the disclosure of which herein is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE DISCLOSURE  
       [0002]     1. Field of the Disclosure  
         [0003]     The subject disclosure relates to implantable spinal stabilization systems for surgical treatment of spinal disorders, and more particularly, to an apparatus for connecting cylindrical spinal rods of a spinal stabilization system to one another across the spinous process.  
         [0004]     2. Background of the Related Art  
         [0005]     The spinal column is a complex system of bones and connective tissue which protects critical elements of the nervous system. Despite these complexities, the spine is a highly flexible structure, capable of a high degree of curvature and twist through a wide range of motion. Trauma or developmental irregularities can result is spinal pathologies which limit this range of motion.  
         [0006]     For many years, orthopedic surgeons have attempted to correct spinal irregularities and restore stability to traumatized areas of the spine through immobilization. Over the past ten years, spinal implant systems have been developed to achieve immobilization. Examples of such systems are disclosed in U.S. Pat. Nos. 5,102,412 and 5,181,917. Such systems often include spinal instrumentation having connective structures such as elongated rods which are placed on opposite sides of the portion of the spinal column intended to be immobilized. Screws and hooks are commonly utilized to facilitate segmental attachment of such connective structures to the posterior surfaces of the spinal laminae, through the pedicles, and into the vertebral bodies. These components provide the necessary stability both in tension and compression to achieve immobilization.  
         [0007]     It has been found tat when a pair of spinal rods are fastened in parallel on either side of the spinous process, the assembly can be significantly strengthened by using at least one additional rod to horizontally bridge the pair of spinal rods. An example of a cross brace assembly of this type is disclosed in U.S. Pat. No. 5,084,049. Devices such as these commonly consist of a threaded rod for providing the desired lateral support. The threaded rod is fastened to each of the spinal rods by clamps located on each end thereof. However, this configuration is bulky and can cause irritation of the patient&#39;s back muscles and other tissue which might rub against the device. A cross brace assembly that overcomes the problems associated with bulky stabilization assemblies by fitting closer to the spine, preferably in the same general plane as the cylindrical spinal rods, is disclosed in commonly assigned U.S. Pat. No. 5,989,251.  
         [0008]     It has also been found tat the distance between a pair of spinal rod located on either side of the spine can vary depending upon the anatomy of the patient and the manner in which the rods are secured to the spinous process. Thus, transverse rod connectors have been designed with adjustable bridging structures to accommodate this variability, as disclosed, for example, in U.S. Pat. Nos. 5,752,955 and 5,947,966.  
         [0009]     Most existing transverse connectors consist of rods, plates, and bars linked to the longitudinal rods by coupling mechanisms with set screws, nuts, or a combination of each. These connectors require several components and instruments to build the constructs. Each additional component or instrument required to assemble the connectors adds to the complexity of the surgical procedure. Examples of connectors constructed from multiple components are disclosed in U.S. Pat. Nos. 5,312,405, 5,334,203 and 5,498,263.  
         [0010]     It would be beneficial to provide an improved device to transversely connect spinal rods of a spinal stabilization system to one another which utilizes a minimum number of components parts and surgical instrumentation, and which has a low-profile so as to fit closely to the spine, and which may be easily adjusted during a spinal stabilization procedure.  
       SUMMARY OF THE DISCLOSURE  
       [0011]     The subject disclosure is directed to an apparatus for connecting two conventional spinal rods of a spinal stabilization system to one another in such a manner so as to provide an adjustable low-profile rigid linkage therebetween. In accordance with a preferred embodiment of the subject disclosure, the apparatus includes an elongated body portion and a clamp portion depending from the body portion for engaging a spinal rod.  
         [0012]     Preferably, the clamp portion defines a deflectable clamp body having opposed clamp arms configured for movement between a first position wherein a spinal rod is received between the opposed clamp arms of the clamp body and a second position wherein the spinal rod is securely engaged by the opposed clamp arms of the clamp body. In addition, structural means are operatively associated with the clamp body to effectuate the movement of the opposed clamp arms of the clamp body between the first and second positions.  
         [0013]     In accordance with one aspect of the disclosure, the structural means for moving the opposed clamp arms between the first and second positions comprises a cam lug configured for reception within a bore formed in the clamp body and adapted for axial rotation within the bore. The cam lug has a generally cylindrical body with camming surfaces formed thereon, and the reception bore is defined at least in part by interior walls. In operation, the camming surfaces of the cam lug are adapted and configured for bearing against the interior walls of the reception bore upon rotation of the cam lug within the reception bore.  
         [0014]     In accordance with another aspect of the subject disclosure, the structural means for moving the opposed clamp arms between the first and second positions comprises an engagement tab projecting outwardly from an exterior surface of the clamp body, and a recess formed within the clamp body spaced from the engagement tab. In operation, the engagement tab is grasped with a tool and pulled outwardly to enlarge a gap between the opposed clamp arms.  
         [0015]     In accordance with one aspect of the subject disclosure the elongated body portion has a predetermined span length for extending between a pair of elongated spinal rods disposed in parallel relationship. Alternatively, the elongated body portion has a span length that is selectively variable for extending between a pair of elongated spinal rods disposed in parallel relationship. Accordingly, the elongated body portion includes means for selectively adjusting the length of the body portion.  
         [0016]     In accordance with one aspect of the subject disclosure, the means for selectively adjusting the length of the body portion includes a first body portion having an axial bore defined therein and a second body portion having an axial shaft for reception within the axial bore of the first body portion, and a locking ring for radially compressing the first body portion against the second body portion when the axial shaft is disposed within the axial bore. In accordance with another aspect of the subject disclosure, the means for selectively adjusting the length of the body portion includes a first body portion having a threaded bore defined therein and a second body portion having an threaded shaft for reception within the threaded bore of the first body portion.  
         [0017]     These and other unique features of the apparatus disclosed herein and the method of installing the same will become more readily apparent from the following description of the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     So that those having ordinary skill in the art to which the disclosed apparatus appertains will more readily understand how to construct and use the same, reference may be had to the drawings wherein:  
         [0019]      FIG. 1  is a perspective view of a spinal stabilization system for immobilizing a region of the spinal column which includes variable and fixed length rod connecting apparatus constructed in accordance with preferred embodiments of the subject disclosure, and a set of bone screws with linear locking mechanisms;  
         [0020]      FIG. 1A  a perspective view of another spinal stabilization system for immobilizing a region of the spinal column which includes a set of bone screws with top-loading rotatable locking mechanisms;  
         [0021]      FIG. 2  is a top plan view of the spinal stabilization system of  FIG. 1  implanted on the posterior side of the spinal column;  
         [0022]      FIG. 3  is a perspective view of the variable length rod connecting apparatus of the subject disclosure with the parts thereof separated for ease of illustration;  
         [0023]      FIG. 4  is a perspective view of the fixed length rod connecting apparatus of the subject disclosure;  
         [0024]      FIG. 5  is a cross-sectional view taken along line  5 - 5  of  FIG. 1  illustrating the clamping portion of the rod connecting apparatus of  FIG. 3  in fastened condition;  
         [0025]      FIG. 6  is a perspective view of the cam lug of the subject disclosure which facilitates movement of the clamping portion of the rod connecting apparatus of  FIGS. 3 and 4  between first and second positions;  
         [0026]      FIG. 7  is a top plan view of the cam lug illustrated in  FIG. 6  showing the opposed lateral cam surfaces thereof;  
         [0027]      FIG. 8  is a perspective view of the variable length rod connecting apparatus of  FIG. 3  prior to installation between a pair of parallel I spinal rod;  
         [0028]      FIG. 9  is a perspective view of the variable length rod connective apparatus shown in  FIG. 8 , with the clamping portions thereof engaged to the spinal rods in a frictionally engaged condition;  
         [0029]      FIG. 10  corresponds to the operative step shown in  FIG. 9  and illustrates the relative movement of the arms of the clamping portion between an initial position and a frictionally engaged position with respect to a spinal rod extending therethrough prior to being moved into a tightly secured position about the periphery of the spinal rod;  
         [0030]      FIG. 11  is a perspective view of the variable length rod connecting apparatus shown in  FIGS. 7 and 8 , with the locking collet moved into a locked position to maintain the length of the connector using a surgical instrument;  
         [0031]      FIG. 12  is a perspective view of the variable length rod connecting apparatus shown in  FIGS. 7 and 8 , illustrating the positioning of the cam lugs into the reception areas of the clamping portions;  
         [0032]      FIG. 13  is a perspective view of the variable length rod connecting apparatus shown in  FIG. 12 , illustrating the rotation of the cam lugs to facilitate movement of the clamping portions into a securely fastened position to fixedly connect the apparatus to the spinal rods;  
         [0033]      FIG. 14  is a perspective view of another variable length rod connecting apparatus constructed in accordance with a preferred embodiment of the subject disclosure with the parts thereof separated for ease of illustration;  
         [0034]      FIG. 15  is a perspective view of still another variable length rod connecting apparatus constructed in accordance with a preferred embodiment of the subject disclosure with the parts thereof separated for ease of illustration; and  
         [0035]      FIG. 16  is a perspective view of a kit containing various components and tools constructed in accordance with the subject disclosure. 
     
    
       [0036]     These and other features of the apparatus disclosed herein will become more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]     Referring now to the drawings wherein like reference numerals identify similar structural elements of the subject apparatus, there is illustrated in  FIGS. 1 and 2  a spinal stabilization system constructed in accordance with a preferred embodiment of the subject disclosure and designated generally by reference numeral  10 .  
         [0038]     Referring to  FIG. 1 , spinal stabilization system  10  includes a pair of elongated spinal rods  12  and  14 . The spinal rods are adapted for parallel deployment on either side of the spinous process, as illustrated in  FIG. 2 . Spinal rods  12  and  14  are of a conventional type, constructed from a bio-compatible material and having a circular cross-section with a smooth outer surface finish. Spinal rods  12  and  14  are segmentally secured to the bones of the spinous process by a variety of structural components including, for example, bone screws  18 .  
         [0039]     Bone screws  18  have linear locking mechanisms of the type disclosed in commonly assigned U.S. Pat. No. 5,989,251, the disclosure of which is herein incorporated by reference in its entirety. An alternative spinal stabilization system designated generally by reference numeral  1   a  is illustrated in  FIG. 1A . Spinal stabilization system  10   a  includes bone screws  18   a  that have top-loading rotatable locking mechanisms of the type disclosed in commonly assigned U.S. application Ser. No. 09/487,942, the entirety.  
         [0040]     It has been found that when a pair of spinal rods are fastened to one another in parallel relationship on either side of the spinous process, as illustrated in  FIGS. 1 and 2 , the stabilization system can be significantly strengthened. Thus, the spinal rods  12  and  14  of stabilization system  10  are connected to one another by a plurality of rod linking devices constructed in accordance with a preferred embodiment of the subject disclosure.  FIGS. 1 and 2  illustrate two embodiments of the rod linking device of the subject disclosure constructed from high-strength, low-weight, corrosion resistant, bio-compatible metal alloy, such as, for example, titanium or stainless steel.  
         [0041]     The first embodiment is a variable length rod linking device designated generally by reference numeral  20 . (See  FIG. 3 ). The second embodiment has a fixed length and is designated by reference numeral  60 . (See  FIG. 4 ). Rod linking device  20  is adapted and configured to be selectively adjusted during a spinal stabilization procedure to bridge the gap that exists between spinal rod  12  and  14 . In contrast, rod linking device  60  has a predetermined span length and is configured to bridge a fixed gap between spinal rods  12  and  14 . As discussed in greater detail hereinbelow, rod linking devices  20  and  60 , also referred to herein as transverse rod connectors  20  and  60 , both have a unique rod engaging system in the form of a generally unshaped deflectable clamping portion or hook.  
         [0042]     Referring now to  FIG. 3 , there is illustrated the variable length rod linking device  20  of the subject disclosure. Rod connector  20  includes first and second body portions  12  and  24 . The distal section  22   d  of the first body portion  22  has a slight outward taper so that the outer diameter of the distal section  22   d  is slightly greater than that of the main section of the first body portion  22 . In addition, an axial reception bore  26  is defined in the first body portion  22  for receiving the second body portion  24 . An annular locking collet  28  is operatively associated with the first body portion  22  for securely retaining the second body portion  24  within the axial reception bore  26 . More particularly, the distal section  22   d  of the first body portion  22  has a pair of diametrically opposed compression slots  30   a  and  30   b  defined therein, which extend from the free distal end of body portion  22  to a location intermediate its length, to facilitate radial compression of the distal end section  22   d  of body portion  22  against the second body portion  24  when it is disposed within axial bore  26 .  
         [0043]     Annular locking collet  28  is coaxially positioned on body portion  22  and is configured for axial movement along the length thereof, between an annular blocking flange  34  disposed intermediate the length of body potion  22  and a pair of diametrically opposed blocking ribs  36   a  and  36   b  disposed at the free distal end of body portion  22 . In use, movement of the locking collet  28  between an initial position adjacent annular blocking flange  34  and a final position adjacent blocking ribs  36   a  and  36   b  causes radial compression of the distal end section  22   d  of body portion  22 , as the locking collet  28  moves relative to the outwardly tapered distal section  22   d  of body portion  22 .  
         [0044]     As best seen in  FIG. 3 , blocking ribs  36   a  and  36   b  are dimensioned and configured to facilitate the mounting of locking collet  28  on body portion  22  during assembly of the connector  20 . More specifically, during assembly, locking collet  28  is slid over blocking ribs  36   a  and  36   b  for positioning within the area defined between the blocking ribs and annular blocking flange  34 . Manipulation of locking collet  28  is aided by the provision of tab  28   a . Also shown in  FIG. 3  is a location guide hole  38  disposed between the free distal end of body portion  22  and the annular blocking flange  34 . The hole  38  enables a surgeon to locate the position of the collet  28  during locking to ensure collet  28  is moved sufficiently axially to the final locking position.  
         [0045]     The second body portion  24  of rod connector  20  is defined by an axial shaft having a uniform outer diameter along substantially the entire length thereof The outer diameter of the axial shaft is about approximately equal to the inner diameter of the axial bore  26  defined within the first body portion  22 , so that an interference fit exists therebetween when the two components are telescopically connected to one another during assembly. A retaining ring  24   a  is provided to retain first and second body portions  24  and  22  together, when assembled, as a lip (not shown) on first body portion  22  engages the larger diameter retaining ring  24   a.    
         [0046]     With continuing reference to  FIG. 3  in conjunction with  FIGS. 5 through 7 , rod connector  20  includes a unique rod engaging system for securely fastening the transverse connector to spinal rods  12  and  14  during a spinal stabilization procedure with imparting undue stress upon the spine. This system consists of deflectable rod clamps  42  and  44  which depends from the first and second body portion  22  and  24 , respectively, for securely engaging spinal rods  12  and  14 , respectively. Rod clamp  42  depending from body portion  22  includes a first and second clamp arms  42   a  and  42   b  between which is defined a gap or channel  43   a  for accommodating spinal rod  12 . Similarly, rod clamp  44  which depends from body portion  24  includes first and second opposed clamp arms  44   a  and  44   b  between which is defined a gap or channel  43   b . Each rod clamp  42 ,  44  has a respective reception port  46 ,  48  for receiving a camming lug  50 . The camming lug  50  is configured to effectuate movement of a clamp  42 ,  44  from an initial position wherein the clamp Is frictionally engaged with a spinal rod to a final position wherein the clamp is tightly compressed about the periphery of the spinal rod, as shown in  FIG. 5 .  
         [0047]     Referring to  FIGS. 6 and 7 , camming lug  50  includes a main body portion  52 , illustratively generally elliptical in cross section, with enlarged radially outwardly projecting curved lateral camming surfaces  52   a  and  52   b  for interacting with the interior walls of reception ports  46 ,  48 . Camming lug  50  further includes a central aperture  54  for receiving an appropriate tool or implement designed to facilitate axial rotation of camming lug  50  within reception ports  46 ,  48  during a spinal stabilization procedure (see  FIG. 13 ). Advantageously, the rotational forces imparted upon camming lug  50  during assembly do not impose undue stress on the patient&#39;s spine during a stabilization procedure. A retention flange  56  is provided at the lower end of the main body portion  52  of camming lug  50  for cooperating with retention channels  46   a ,  48   a  formed in reception portions  46 ,  48 , respectively. This interaction is intended to inhibit the displacement of the camming lugs from the reception ports during shipment, as well as during a surgical procedure.  
         [0048]     In use, rotation of the camming lug  50  within reception ports  46 ,  48  causes the lateral camming surfaces  52   a ,  52   b  to bear against the walls of reception ports  46 ,  48 , urging the walls to expand radially outwardly. In what can best be described as a scissors-like action, the outward expansion of the port walls causes the clamp arms  42   a ,  42   b  and  44   a ,  44   b  to move inwardly toward one another so as to reduce the size or diameter of the gaps or channels  43   a ,  43   b  defined therebetween, respectively. As a result, spinal rods  12  and  14  are compressed tightly between clamp arms  42   a ,  42   b  and  44   a ,  44   b , as illustrated, for example, in  FIG. 5 . It should be recognized that the amount of outward deflection of the walls of the reception bore caused by rotating the canning lugs, and the resultant inward compression of the clamp arms is relatively small, as the arms must only move a sufficient distance so as to clamp about the spinal rod after having already achieved a frictional engagement therewith upon initial assembly.  
         [0049]     Referring now to  FIGS. 8 through 13 , there is illustrated, in sequential order, one embodiment of the operative steps associated with mounting the rod linking device  20  of the subject disclosure to a pair of parallel spinal rods  12  and  14  during a spinal stabilization procedure. As illustrated in  FIG. 8 , initially the rod linking device  20  is moved into approximation with spinal rods  12  and  14  with the body portions  22  and  24  telescopically mated to one another, i.e., body portion  24  is disposed within the axial reception bore  26  of body portion  22 . At such a time, locking collet  28  is positioned intermediate the distal end section  22  of body portion  22 , proximal of compression slots  30   a  and  30   b , and the outwardly tapered portion of the distal section  22   d.    
         [0050]     Then, as illustrated in  FIG. 9 , the rod clamps  42 ,  44  are brought into engagement with spinal rods  12  and  14 , respectively. At such a time, the rod clamps are not securely fastened to the spinal rods and may moved along the length of the spinal rods or be removed from the rods by the surgeon for repositioning if such action becomes necessary.  FIG. 10  illustrates the engagement of a rod clamp with a spinal rod, whereby the “broken lines” illustrate the clamp in a non-engaged position and the “solid lines” illustrate the rod clamp in a frictionally engaged position.  
         [0051]     Referring to  FIG. 11 , after rod clamps  42  and  44  are engaged to spinal rod  12  and  14 , respectively, the length of rod linking device  20  is set. This is accomplished by moving locking collet  28  from its initial location adjacent blocking flange  34  toward the blocking ribs  36   a  and  36   b . This movement is accomplished by an appropriate tool, such as surgical pliers  70  or a similar surgical instrument. As the collect  28  translates in the direction of arrow “A”, it moves against the tapered surfaces of the distal end section  22   d  of body portion  22 , causing the distal end section  22   d  of body portion  22  to radially compress against the cylindrical outer surface of body portion  24  disposed within axial bore  26 . When locking collet  28  is moved past location guide hole  38 , the user is informed that it is in the locked position.  
         [0052]     Referring to  FIG. 12 , once the appropriate span length of rod linking device  20  has been set, camming lugs  50  are inserted into the reception ports  46  and  48  of deflectable rod clamp  42  and  44 . At such a time, the camming surfaces  50   a  and  50   b  of the camming lugs are not bearing against the walls of the reception ports within which they are disposed. Consequently, the position of the rod clamps can still be adjusted if such action is necessary. It is contemplated in a preferred embodiment that the system is shipped and utilized with the camming lugs  50  already in reception ports  46  and  48 . Thus, in this embodiment, in the steps shown in  FIGS. 8, 9  and  11  the camming lugs would already be in place, saving the surgeon the additional step of inserting the individual camming lugs  50  in reception ports  46 ,  48 .  
         [0053]     Alternatively, it is envisioned that the rod linking devices of the subject disclosure could be shipped with the camming lugs  50  already positioned within the reception ports  46 ,  48  so as to reduce the number of steps required to secure the spinal rods  12 ,  14  to one another during a spinal stabilization procedure. Thus, the operative step illustrated in  FIG. 12  would become unnecessary.  
         [0054]     In either instance, to securely fasten the rod clamps  42 ,  44  to spinal rods  12 ,  14 , camming lugs  50  are axially rotated in a clock-wise direction within reception ports  46 ,  48  using an appropriate surgical tool or implement, such as for example, lug driver  75 . This axial rotation causes the outwardly projecting camming surfaces  52   a ,  52   b  to bear against the interior walls of the reception ports  46 ,  48 , urging them to move radially outwardly. As a result, an equal and opposite scissors-like movement of the opposed clamp arms occurs, causing the opposed clamp arms of each rod clamp  42 , 44  to tightly engage the outer periphery of the spinal rods  12 ,  14 , as best seen, for example, in  FIG. 5 , without imparting undue stress on the spine. Once tightly engaged about the spinal rods, the rod clamps  42 ,  44  are essentially immobilized.  
         [0055]     While the operative steps involved in mounting and securing rod linking device  20  to a pair of spinal rods has been described with respect to a sequential order, it will be readily apparent to those having ordinary skill in the art to which the subject disclosure appertains that the order or sequence of the operative steps can be altered or modified. For example, in an alternative and preferred embodiment, the rod clamps can be secured to the spinal rods prior to setting the desired length of the linking device. In this preferred version, the camming lugs  50  are rotated to the clamps  42  and  44  on the spinal rods and then the locking collet  28  is moved axially to its final locking position.  
         [0056]     Referring to  FIG. 4 , the rod linking device  60  of the subject disclosure has a predetermined span length configured to extend a fixed distance across the spinous process between a pair of parallel spinal rods  12  and  14 , as illustrated in  FIGS. 1 and 2 . Rod linking device  60  includes a main body portion  62  defining a longitudinal axis. Body portion  62  has a low profile construction for fining closely to the spine, so as to reduce any bulkiness associated with spinal stabilization system  10 . Deflectable rod clamps  72  and  74  depend from the opposed ends of the main body portion  62  for securely engaging spinal rods  12  and  14 , respectively. Rod clamps  72 ,  74  are substantially identical to rod clamps  42 , 44  of rod connector  20  and include reception ports  76 ,  78 , respectively for receiving camming lugs  50 . As in the previous embodiment, camming lugs  50  are configured to effectuate movement of the opposed clamp arms of rod clamps  72 ,  74  from an initial position in frictional engagement with the spinal rods to a final position tightly secured about the periphery of the spinal rods.  
         [0057]     Rod linking device  60  is preferably provided in several different span lengths ranging from about 16 mm in length to about 24 mm in length, in about 2 mm increments. Additional lengths with varying increments are also contemplated. Referring to  FIG. 16 , in accordance with the subject disclosure a kit  100  is provided defined by a packing enclosure  110  containing, among other things, a plurality of rod linking devices  60   a - 60   c , each of which has a different preset span length for bridging the gap between a pair of elongated spinal rods. For example, the kit  100  could include a rod connector  60   a  having a span length of about 16 mm, a rod connector  60   b  having a span length of about 18 mm, and rod connector  60   c  having a span length of about 20 mm.  
         [0058]     Preferably, the rod connectors  60   a - 60   c  would be packaged with camming lugs  50  already installed in the reception ports of the of clamps of each connector. Alternatively, a plurality of camming lugs  50  could be provided in the package separate from the connectors. The kit would also include an lug driver  75  for securing the camming lugs  50  within the reception ports of the linking devices. It is envisioned that kit  100  could also contain a plurality of variable length rod linking devices  20   a - 20   c  and an appropriate surgical instrument  70  for moving the locking collet  28  along the length of the body portion, as described hereinabove with respect to  FIG. 11 .  
         [0059]     Referring to  FIG. 14 , there is illustrated another rod linking device constructed in accordance with a preferred embodiment of the subject disclosure designated generally by reference number  80 . Rod linking device  80  is a variable length connector that includes first and second telescopically associated body portions  82  and  84  that are substantially similar to the first and second body portion  22  and  24  of rod linking device  20 , which is described hereinabove and illustrated in  FIG. 3 . The first and second body portions  82 ,  84  of rod linking device  80  differ from those of rod linking device  20  in that the rod clamps  92 ,  94  thereof do not employ camming lugs  50  to effectuate movement of the opposed clamp arms  92   a ,  92   b  and  94   a ,  94   b  into a tightly engaged position about the periphery of the spinal rods. Instead, the gaps  93   a ,  93   b  defined between the opposed arms of each rod clamp  92 ,  94  are dimensioned and configured to tightly engage the periphery of the spinal rods without using a camming lug.  
         [0060]     To engage a rod clamp  92 ,  94  to a spinal rod, the gap  93   a ,  93   b  between the opposed clamp arms thereof of is radially expanded to allow the rod to enter the gap. This is accomplished by gripping a tab  96 ,  98  projecting outwardly from the leading edge of each rod clamp  92 ,  94  with an appropriate surgical instrument or tool (not shown), and drawing the outer clamp arm  92   a ,  94   a  away from the inner clamp arm  92   b ,  94   b . The deflection of the rod clamp  92 ,  94  and resultant radial expansion of the gap  93   a ,  93   b  is aided by the provision of cross-slots  95 ,  97  formed in rod clamps  92 ,  94  which provide areas within which the upper portion of the outer clamp arms  92   a ,  94   a  can effectively translate during the radial expansion of the gaps  93   a ,  93   b . Once a spinal rod is situated within the gap  93   a ,  93   b , the tab  96 ,  98  is released by the surgeon, allowing the outer clamp arm  92   a ,  94   a  to return to its normal position. Thereupon, the inner diameter of the gap  93   a ,  93   b  is substantially equal to the outer diameter of the spinal rod and the rod connector  80  is essentially immobilized.  
         [0061]     Referring to  FIG. 15 , there is illustrated yet another rod linking device constructed in accordance with a preferred embodiment of the subject disclosure designated generally by reference number  120 . Rod linking device  120  is also a variable length rod connector in that the span length thereof may be selectively and easily adjusted by a surgeon during a spinal stabilization procedure to accommodate different anatomical conditions. Rod linking device  120  includes a first body portion  122  which has an internally threaded axial bore  126  extending therethrough for receiving a corresponding threaded shaft which defines the second body portion  124 . During assembly, the second body portion  124  is threadably secured within the internal bore  126  of the first body portion  122  to set the desired span length of rod linking device  120 .  
         [0062]     The body portions  122  and  124  of rod linking device  120  include deflectable rod clamps  142  and  144 , respectively for securing engaging spinal rods rod during a surgical procedure. In contrast to the rod clamps of rod connectors  20 ,  60  and  80 , described hereinabove, rod clamps  142 ,  144  do not include additional structures to facilitate movement of the opposed clamp arms  142   a ,  142   b  and  144   a ,  144   b  into a securely engaged position. Instead, the opposed clamp arms of rod clamps  142 ,  144  are simply snap-fit onto the spinal rods during a surgical procedure, so that the opposed clamp arms of the rod clamps are tightly engaged about the periphery of the spinal rods.  
         [0063]     Although the apparatus disclosed herein has been described with respect to preferred embodiments, it is apparent that modifications and changes can be made thereto without departing from the spirit and scope of the invention as defined by the claims. For example, while each embodiment of the subject rod linking device has been described in conjunction with a particular type of deflectable rod clamping mechanism, it is envisioned and well within the scope of the subject disclosure that the various rod clamping mechanisms disclosed herein are easily interchangeable with respect to one another.