Patent Publication Number: US-2020289169-A1

Title: Apparatus and method for percutaneously extending an existing spinal construct

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/018,891, filed Jun. 26, 2018, now U.S. Pat. No. 10,667,848, which is a continuation of U.S. application Ser. No. 15/581,865, filed Apr. 28, 2017, now U.S. Pat. No. 10,016,227, which is a continuation of U.S. application Ser. No. 15/204,196, filed Jul. 7, 2016, now U.S. Pat. No. 9,642,655, which is a continuation of U.S. application Ser. No. 14/872,287, filed Oct. 1, 2015, now U.S. Pat. No. 9,629,668, which is a continuation of U.S. application Ser. No. 14/013,234, filed Aug. 29, 2013, now U.S. Pat. No. 9,149,302, which is a divisional application of U.S. application Ser. No. 13/617,312, filed Sep. 14, 2012, now U.S. Pat. No. 8,523,906, which claims the benefit of U.S. Provisional application Ser. No. 61/568,199, filed on Dec. 8, 2011, the entire contents of these applications being incorporated by reference herein. 
    
    
     BACKGROUND 
     The present disclosure contemplates devices and instrumentation for extending an existing spinal construct, and more particularly to procedures for achieving such extension minimally invasively, and preferably percutaneously. 
     An emerging trend in spinal fixation is an increased incidence of adjacent disc degeneration subsequent to a previous fixation or fusion. This subsequent degeneration often requires fixation or fusion of additional levels of the spine. It is common in current techniques to expose the entire prior construct to access all of the existing bone fasteners to permit removal of the connecting member spanning the fasteners. The connecting member is removed and replaced with a longer member, such as a rod, to engage an additional bone fastener added at the new levels to be instrumented. 
     This exposure of the prior fixation construct disrupts the existing construct complicating and lengthening the surgical procedure for adding the additional level of fixation. Such techniques are particularly problematic for a fixation construct spanning three or more vertebral levels. As such, there is a need for a device and method that facilitates the addition of further levels of fixation. 
     Several recent advancements have been disclosed that describe the extension of existing spinal constructs with minimal disruption to the existing construct. One example is shown in co-pending commonly assigned U.S. application Ser. No. 12/797,682, entitled “Devices and Methods for Adding an Additional Level of Fixation to an Existing Construct”, filed on Jun. 10, 2010 and published as No. 2010/0318131. Other examples include U.S. Pat. No. 7,976,567, entitled “Orthopedic Revision Connector”, issued on Jul. 12, 2011 to William B. Null, et al. and U.S. Pat. No. 8,021,399, entitled “Rod Extension for Extending Fusion Construct”, issued on Sep. 20, 2011 to Stephen Ritland. While these approaches represent improvements in revision techniques and devices, it would be advantageous to not only extend an existing construct in a relatively non-disruptive manner to such construct, but to do so in a minimally invasively and, preferably percutaneous procedure. 
     SUMMARY 
     It is an object of the present invention to provide apparatus and devices for adding an additional construct to an existing spinal construct in a patient preferably minimally invasively and more preferably, percutaneously. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  is a side elevation view of a portion of a patient&#39;s spine showing instrumentation disclosed herein to extend an existing ipsilateral spinal construct. 
         FIG. 2  is an enlarged perspective view of the existing spinal construct and inline extension of  FIG. 1 . 
         FIG. 3  is a top plan view of the existing spinal construct and inline extension of  FIG. 1 . 
         FIG. 4  is a top perspective view of a rod connector in accordance with one arrangement of the disclosure for attachment to an existing spinal rod of the existing spinal construct shown in  FIG. 1 . 
         FIG. 5  is an exploded top perspective view of the rod connector of  FIG. 4 . 
         FIG. 6  is a longitudinal cross sectional view of the rod connector of  FIG. 5 . 
         FIG. 7  is a view of the rod connector of  FIG. 6  showing the hook portion having been articulated to a different angular position. 
         FIG. 8  is a further top perspective view of the rod connector of  FIG. 4  showing the rod connector in an inline engagement with an existing spinal rod. 
         FIG. 9  is a top perspective exploded view of a rod connector extension assembly comprising a rod connector introducer and the rod connector of  FIG. 4 . 
         FIG. 10  is an enlarged side elevation view of the rod connector extension assembly of  FIG. 9  showing details of the distal portion of the rod connector introducer positioned for releasable attachment to the rod connector. 
         FIG. 10 a    is a cross sectional view of  FIG. 10  as seen along viewing lines X-X of  FIG. 10 . 
         FIG. 11  is a perspective view showing the assembled rod connector extension assembly of  FIG. 9  with an inner sleeve positioned for insertion into the rod connector introducer. 
         FIG. 12  is a further perspective view of the assembled rod connector extension assembly of  FIG. 11  with the inner sleeve received within the rod connector introducer and a hook rotator positioned for insertion into the inner sleeve. 
         FIG. 12 a    is an enlarged view of the distal end of the hook rotator as encircled in  FIG. 12 . 
         FIG. 13  is a top perspective view of a portion of a patient&#39;s spine as viewed in the caudal direction showing the assembled rod connector extension assembly of  FIG. 12  disposed within an access port. 
         FIG. 14  is a top perspective view of  FIG. 13  as viewed in the cephalad direction. 
         FIG. 15  is a side elevation view of a patient&#39;s spine showing instrumentation for targeting the position of an existing spinal construct within a patient and an additional spinal implant extension assembly spaced therefrom. 
         FIG. 16  is a further view of  FIG. 15  showing dilating instruments including an access port for use in a percutaneous procedure for extending an existing spinal construct. 
         FIG. 17  is a further view of  FIG. 16  with the dilating instruments removed and the access port positioned within the patient&#39;s spine adjacent the existing spinal construct. 
         FIG. 18  is a side elevation view of the rod connector extension assembly positioned in the access port with the elongate additional rod of the rod connector being oriented in a first position generally parallel to the longitudinal axis of the access port. 
         FIG. 19  is a further view of  FIG. 18  showing the rotation of the rod connector introducer and the rod connector with the elongate additional rod being moved subcutaneously toward the additional spinal implant extension assembly. 
         FIG. 20  is a further view of  FIG. 19  showing further rotation of the rod connector introducer with the additional rod of the rod connector being introduced into a slot of the additional spinal implant extension assembly. 
         FIG. 21  is a further view of  FIG. 20  showing final rotation of the rod connector introducer with the additional rod of the rod connector having been moved to a second different orientation transverse to the longitudinal axis of the access port and the distal portion of the additional rod extending through slots in the additional spinal implant extension assembly. 
         FIG. 22  is a view of  FIG. 21  with the hook rotator and inner sleeve having been removed from the rod connector introducer and a driver instrument positioned to introduce a set screw through the additional spinal implant extension assembly for securing the additional rod of the rod connector to the additional spinal implant. 
         FIG. 23  is a view of  FIG. 22  with the driver instrument removed and a driver tool positioned to introduce a set screw through the rod connector introducer for securing the rod connector to the existing spinal rod. 
         FIG. 24  is a posterior view of a portion of the patient&#39;s spine showing an additional construct extending an existing spinal construct to a further bony segment, such as the ilium. 
         FIG. 25  is a top perspective view of a first alternative arrangement of a rod connector for attachment to an existing spinal rod of an existing spinal construct of  FIG. 1 . 
         FIG. 26  is a further view of the first alternative rod connector of  FIG. 25  showing an offset parallel connection of an additional rod to an existing spinal rod. 
         FIG. 27  is a top perspective view of the first alternative rod connector of  FIG. 25  in assembly with a rod connector introducer and an additional elongate extension. 
         FIG. 28  is a top perspective view of a portion of a patient&#39;s spine showing an oval access port positioned adjacent an existing spinal rod for receipt of the rod connector in the assembly shown in  FIG. 27 . 
         FIG. 29  a top perspective view of a second alternative arrangement of a rod connector for attachment to an existing spinal rod of an existing spinal construct of  FIG. 1 . 
         FIG. 30  is a further view of the second alternative rod connector of  FIG. 29  showing an inline connection of an additional rod to an existing spinal rod. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
     Referring to  FIGS. 1 and 2 , an apparatus  10  is shown for extending an existing spinal construct  12  by adding an additional spinal construct  14  so as to increase the level of spinal fixation in a patient having previously undergone spinal fusion or other spinal surgery. The apparatus  10  generally comprises a rod connector extension assembly  16 , a spinal implant extension assembly  18  and an access port  20 . Rod connector extension assembly  16  includes a rod connector introducer  21  and a rod connector  22  comprising an elongate additional spinal rod  24  serving as a connecting element, as will be described. Spinal implant extension assembly  18  comprises an additional spinal implant  26  and an elongate extension  28  releasably coupled thereto. As illustrated, the existing spinal construct  12  as well as the additional spinal construct  14  are located ipsilaterly in the spine in this particular arrangement. As will be described in more detail below, rod connector introducer  21  comprises an elongate extension  30  releasably attached to the rod connector  22 . Each of extension  28  and access port  20  is sized and of length to be accessible outside the patient&#39;s skin. The patient&#39;s skin or fascia is depicted as a phantom line S for illustrative purposes only, with the understanding that the level of the fascia relative to the fixation location on the spine will vary from patient to patient. Spinal construct  12  is an existing spinal construct in the sense that it has been installed prior to the installation of the additional spinal construct  14  which means that existing spinal construct  12  may have been placed in a previous surgical procedure or may be placed during the same surgical procedure as, but prior to, additional spinal construct  14 . 
     Turning to  FIG. 2 , further details of the additional spinal construct  14  and the existing spinal construct  12  are described. The existing spinal construct  12  comprises at least two previously implanted bone engaging implants  34  and  36  each of which is engaged respectively to a corresponding vertebra  38  and  40 . Implants  34  and  36  are interconnected by an existing spinal rod  42  extending ipsilaterally therebetween. Existing spinal rod  42  includes an interconnecting portion  42   a  between implants  34  and  36  and an extending portion  42   b  projecting outwardly beyond implant  34 , although extending portion  42   b  may also project in the opposite direction beyond implant  36 . As shown, each of implants  34 ,  36  is a polyaxial pedicle screw having a lower threaded fastener portion  44 ,  46  for threaded engagement respectively in a pedicle of vertebra  38  and a pedicle of vertebra  40 . Each implant  34 ,  36  includes a respective upper portion defining a yoke  48 ,  50  each yoke having a respective threaded slot  52 ,  54  for receipt of the existing spinal rod  42  therein. Set screws  55  and  57  respectively secure the existing spinal rod  42  to the implants  34  and  36 . 
     The additional spinal construct  14  comprises rod connector  22  including elongate additional spinal rod  24 , and a third bone engaging implant, namely additional spinal implant  26 . Spinal implant  26 , as depicted in  FIG. 2 , is a polyaxial pedicle screw having a lower threaded portion  56  and an upper yoke portion  58  that articulates relative to threaded portion  56 . The threaded portion  56  is threadedly engaged to a third spinal segment  60  as will be described. As depicted, spinal segment  60  is another vertebral body, it being understood that such spinal segment may be segment S 1  of the sacrum. The upper yoke portion  58  defines an open ended threaded slot  62  for receipt and support therein of the distal free end  24   a  of additional spinal rod  24  and is fastened to the yoke portion  58  by a set screw  64  or other suitable fastener. While additional spinal implant  26  is described as being a pedicle screw, it should be appreciated that depending upon the application additional spinal implant  26  may include other bone engaging implants with fasteners such as hooks, or rod connectors. 
     Rod connector  22  comprises a lower first portion  66  and an upper second portion  68  articulatingly attached to the first portion  66 . The first portion  66  is attached to the existing spinal rod  42  as will be further described. The second portion  68  includes a connecting portion  70  projecting therefrom that in the arrangement described defines the elongate additional rod  24  terminating in distal free end  24   a.  As illustrated in  FIGS. 2 and 3  the additional spinal construct  14  is considered to be inline with the existing spinal construct  12 . In such an arrangement, the upper second portion  68  of the rod connector  22  is positioned above and substantially in alignment with the axis of the existing spinal rod  42 . The connecting portion  70  has a first extent  71  and a second offset extent defined by additional rod  24  with a jog  72  therebetween. Extent  71  is positioned above bone engaging implant  34  while the axis of additional spinal rod  24  is aligned generally parallel to and colinear with the axis of the existing spinal rod  42 . As such, the existing spinal rod  42  and the additional spinal rod  24  are spaced approximately the same distance from a mid-line plane through the spine of a patient. It should be appreciated that depending upon the anatomy of the patient the orientation of the additional rod  24  relative to the existing rod  42  may differ. 
     Turning now to  FIGS. 4-8 , further the details of the rod connector  22  are described. The lower end of the first portion  66  of rod connector  22  comprises a pair of spaced hooks  74  and  76  each of which includes a respective projecting rod engagement member  74   a  and  76   a.  Hooks  74  and  76  are spaced from each other at a distance defining an opening  78  that allows the existing rod  42  to be received therebetween. 
     The first portion  66  of the rod connector  22  is attached to the second portion  68  by ball insert  80  which allows the first portion  66  to rotate and articulate relative to the second portion  68 , as will be described. The ball insert  80  comprises a truncated sphere having a first outer spherical surface  82  and a second outer cylindrical surface  84 , as shown in  FIG. 5 . The outer spherical surface  82  has a maximum diameter greater than the maximum diameter of the second outer cylindrical surface  84 . The second portion  68  has an interior spherical surface  86  as shown in  FIGS. 6 and 7  defining a socket for receipt of the spherical surface  82  of the ball insert  80 . Interior spherical surface of socket  86  has a diameter slightly greater than the maximum diameter of first outer spherical surface  82  of the ball insert  80 . The socket  86  has an entrance opening  88  that has a diameter less than the diameter of interior spherical surface of socket  86  and slightly greater than the maximum diameter of outer cylindrical surface  84  of the ball insert  80 . The ball insert  80  is inserted through socket opening  88  along an axis of the ball insert  80  defined by a longitudinal axis of the outer cylindrical surface  84 . As such, the ball insert  80  will pass through the socket opening  88  and into socket  86 . Once therein, ball insert  80  is rotated 90° such that the outer spherical surface  82  is in sliding facing relationship with the interior spherical surface of socket  86 . In this position, exterior threads  90  on an upper portion of the first portion  66  are threadably engaged into interior threads  92  of the ball insert  80 . The ball insert  80  may be secured to the threads  90  of the first portion  66  to prevent loosening by locking pins  94  which may be installed through clearance openings  95  on opposite sides of first portion  68 . The structure and operation of the ball insert  80  relative to socket  86  are fully described in commonly assigned U.S. application Ser. No. 11/560,587, entitled “Multi-axial Spinal Fixation System”, filed on Nov. 16, 2006 and issued as U.S. Pat. No. 8,162,990, the disclosure of which is incorporated herein by reference in its entirety. 
     As described and as shown in  FIGS. 6 and 7 , the ball insert  80  and the joined rod connector first portion  66  can jointly articulate relative to the second portion  68  about axis  96  defined by the centerline of opening  97  having interior threads  98  extending into the second portion  68  in communication with spherical socket  86 . In addition, first portion  66  can rotate relative to second portion  68  about an axis of engagement  100  defined by the centerline of exterior threads  90  of the first portion  66 . In  FIG. 6  the axis of engagement  100  and axis  96  of the second portion  68  are linearly aligned, while in  FIG. 7 , for example, the axis of engagement  100  is disposed at an angle with respect to axis  96  with first portion  66  having been articulated relative to second portion  68 . In the position shown in  FIG. 7 , the first portion  66  is in an unlocked position and may still rotate about axis of engagement  100  so as to cause hooks  74  and  76  to engage existing rod  42 , allowing greater flexibility for the attachment of the rod connector  22  to the existing rod  42 . 
     Referring to  FIGS. 5 and 6  a device for rotating the first portion  66  relative to the second portion  68  as well as for providing a provisional retention of the rod connector  22  to an existing rod  42  is described. A rotation element  102  supported by the first portion  66  comprises a rotation pin  104 , a wave spring  106  and a retention ring  108 . The rotation pin  104  comprises a head 104   a  having an internal hex socket  104   b  for receipt of the hook rotator, as will be described. Socket  104   b  may comprise other suitable socket configurations, such as a conventional Torx configuration. Rotation pin  104  further comprises a shank  104   c  having an upper outer hex surface  104   d  a distal outer cylindrical surface  104   e  and a larger intermediate cylindrical surface  104   f  between surfaces  104   d  and  104   e.  Surfaces  104   d,    104   e  and  104   f  may also include other suitable configurations. 
     To assemble the rotation element  102  to the rod connector  22 , the rotation pin  104  is inserted into opening  97  along axis  96  through threads  98  and into opening  110  interiorly of threads  90  of first portion  66 . The interior surface  112  of opening  110  comprises a complementary hex configuration for matable receipt of the hex surface  104   d  of rotation pin  104 . With such hex surfaces in engagement, rotation of the rotation pin  104  will cause rotation of the first portion  66 . Wave spring  106  is placed over intermediate cylindrical surface  104   f  and retention ring  108  is placed over distal cylindrical surface  104   e.  Retention ring  108  is secured to distal cylindrical surface  104   e  by laser welding or other conventional joining techniques. Securement of the retention ring  108  to the rotation pin  104  compresses the wave spring  106  between the retention ring  108  and an inner surface  114  adjacent, and substantially orthogonal, to interior surface  112  of opening  110  in the first portion  66 . As such, rotation element  102  is movably supported on said first portion  66  by wave spring  106  with the distal end of the retention ring 108  defining a rod engagement surface  108   a  normally biased into the opening  78  between the hooks  74  and  76  of the first portion  66 . Such biased interference of the rod engagement surface  108   a  into opening  78  allows the existing rod  42  to be received into opening  78  and provisionally held by the rod engagement members  74   a  and  76   a  upon rotation of the hooks  74  and  76  under the bias of wave spring  106  as shown in  FIG. 8 . It should be appreciated that other spring elements, such as a helical spring, may be used as alternatives to wave spring  106 . 
     While the rod connector  22  is provisionally retained to the existing rod  42  by the rod engagement members  74   a  and  76   a  under the bias of wave spring  106 , this position is an unlocked position with rotation element  102  serving as a provisional holding element. A device for locking the rod connector  22  in a locked position relative to the existing rod  42  is described with further reference to  FIGS. 5 and 6 . A locking element such as a set screw  116  has exterior threads  116   a  for threadable rotational engagement with interior threads  98  extending within the second portion  68 . The upper proximal end of the set screw  116  comprises a suitable socket, such as a Torx hexalobe socket  116   b  for receipt of a suitable tool for inserting and rotating set screw  116 . The lower distal surface  116   c  is configured to engage the upper surface of head  104   a  of rotation pin  104  during rotational insertion. Continued insertion and tightening of the set screw  116  into threads  98  will cause the rod engagement surface  108   a  at the lower end of the rotation element  102  to forcibly engage the existing rod  42 , effectively relieving the bias of wave spring  106  to thereby lock the first portion  66  to the existing rod  42 . The force against the existing rod  42  also causes the first portion  66  and thereby the ball insert  80  to move downwardly relative to second portion  68  forcing the outer spherical surface  82  at the lower half of ball insert  80  tightly against interior spherical surface of socket  86  of second portion  68 , thereby locking first portion  66  and second portion  68  securely together. 
     Referring still to  FIGS. 4 through 7  further details of the rod connector  22  are described. Projecting outwardly from second portion  68  is a connecting element  70 . In this arrangement, connecting element  70  includes first extent  71  and elongated additional rod  24  terminating in distal end  24   a.  Connecting element  70  includes a jog  72  between first extent  71  and additional rod  24  causing the additional rod  24  to be offset relative to the first extent  71  so as to accommodate spinal anatomy. It should be appreciated that the height of jog  72  may be varied to provide different offset dimensions between additional rod  24  and first extent  71 . In some arrangements, jog  72  may be eliminated such that first extent  71  is colinear with additional rod  24 . In addition, first extent  71  and/or additional rod  24  may be curved so as to accommodate different spinal anatomical conditions. In the arrangement shown, additional spinal rod  24  defines a longitudinal axis  24   b  that extends transverse to axis  96  of the second portion  68  of rod connector  22 . In one application, for example, axis  24   b  may be disposed at an angle of approximately 90° with respect to axis  96 , shown in  FIGS. 5 and 6 . In the arrangement shown, rod connector  22  is formed as a one-piece structure. Connecting element  70  including elongated additional rod  24  may be otherwise integrally attached to second portion  68  by any suitable fastening means, including without limitation, welding, brazing and screws. 
     Turning now to  FIGS. 9-12 , details of the free hand rod connector introducer  21  are described. Rod connector introducer  21  comprises an elongate hollow extension  30  and a handle  118  interconnected to extension by an offset bracket  120 . Handle  118  may be selectively moved to different angular orientations by releasing and interlocking projection  122  into multiple grooves  120   a,    120   b  and  120   c  in bracket  120 . Three positions are shown, namely 0°, 45° and 90° with handle  118  being in the 0° position shown in  FIG. 9  and in the 45° position as shown in  FIG. 12 . Other angular orientations may also be provided. Hollow extension  30  comprises an elongate outer sleeve  124  having a proximal end  124   a  and a distal end  124   b  with a lumen  124   c  extending fully longitudinally therethrough. Proximal end  124   a  is suitably attached to bracket  120  and distal end  124   b  is configured to secure releasably to the second portion  68  of the rod connector  22 . 
     As illustrated in further detail in FIG. 10 , the rod connector securement structure at the distal end  124   b  of sleeve  124  comprises a projecting attachment pin  126  and a skirt member  128  disposed diametrically opposite pin  126 . Attachment pin  126  is of generally oval shaped configuration and comprises a flexible latch  126   a  projecting from a side surface of pin  126 . Skirt member  128  projects axially downwardly from distal end  124   b  and has a concave inner surface configured to correspond to the outer curved surface  68   a  at one end of second portion  68 . Attachment pin  126  is configured to be received in a complementary oval shaped hole  130  formed in an upper surface of second portion  68  of rod connector  22  (see  FIGS. 7-8 ) with flexible latch  126   a  being releasably attached to a ledge  130   a  formed in a side wall of hole  130  in a snap-fit manner as shown in  FIG. 10   a.  With attachment pin  126  received in hole  130  and skirt member  128  extending in close proximity around a portion of curved surface  68   a,  the outer sleeve  124  is substantially prevented from rotating relative to both the second portion  68  of rod connector  22  and elongate additional rod  24  which is integral with second portion  68 . While attachment pin  126  and skirt member  128  are effective in releasably securing the outer sleeve  124  to the rod connector second portion  68 , it should be appreciated that other releasable securement structure, such as screw threads, may be used. 
     Referring now to FIG. 11 , rod connector introducer  21  is shown preliminarily attached to rod connector  22 . To provide a more secure attachment, an inner elongate hollow sleeve  134  is included. Inner sleeve  134  has a proximal end  134   a  and a distal end with a lumen  134   c  extending fully longitudinally therethrough. Proximal end  134   a  terminates in a flange  134   d having a hex surface for engagement with a wrench or other suitable tool. Distal end  134   b  comprises external threads  134   e  for threadable attachment with the interior threads  98  in the second portion  68  of rod connector  22 . After outer sleeve  124  is preliminarily attached to rod connector  22 , inner sleeve  134  is inserted through lumen  124   c  of sleeve  124  with threads  134   e  of the inner sleeve threadably engaging threads  98  in the second portion  68  of rod connector  22 . Continued tightening of inner sleeve  134  causes flange  134   d  to engage an upper surface of distal end  124   a  of outer sleeve  124  thereby compressing the outer sleeve  124  between flange  134   d  and rod connector  22  for secure attachment thereto. 
     With extension  30  suitably releasably secured to rod connector  22 , a hook rotator  136 is inserted into the lumen  134   c  in the inner sleeve  134 , as shown in  FIG. 12  to complete the rod connector extension assembly  16 . Hook rotator  136  comprises an elongate shaft  136   a  having a proximal end  136   b  and a distal end  136   c.  Proximal end  136   b  includes a tool attachment surface  136   d  having a hex or other suitable configuration for engagement with a hand wrench  135  (see  FIG. 21 ). Distal end  136   c  comprises an engagement surface  136   e  having a complementary mating configuration, such as hex configuration, for engagement with the socket  104   b  of rotation pin  104 . As described above with reference to  FIG. 5  rotation of the rotation pin  104  causes rotation of rod connector first portion  66  and hooks  74  and  76  projecting therefrom. 
     Hook rotator  136  includes at its proximal end a connection portion  136   f  and a ring  136   g.  Ring  136   g  is pinned to connection portion  136   f  to prevent relative rotation therebetween but is spring biased to allow axial translation when ring  136   g  is depressed distally. Ring  136   g  includes an internal hex surface that engages the hex surface of the tool attachment surface  136   d  when ring  136   g  is biased normally upwardly, thus preventing rotation. When ring  136   g  is depressed distally downwardly by a suitable tool such as by hand wrench  135 , the internal hex surface of ring  136   g  disengages from the external hex surface of tool attachment surface  136   d,  thereby allowing rotation of the shaft  136   a  relative to connection portion  136   f.  Such disengagement allows the tool attachment surface  136   d  to engage a complementary hex surface (not shown) within the hand wrench  135  such that rotation of the hand wrench  135  rotates the elongate shaft  136   a.  Upon rotation of the shaft  136   a  by hand wrench  135  from outside the patient, the first portion  66  of the rod connector  22  and thereby hooks  74  and  76  are also rotated in a manner to effect connection of the rod connector  22  to existing rod  42 , as will be described. 
     As hook rotator  136  is inserted into the lumen  134   c  of inner sleeve  134  engagement surface  136   e  is properly seated within the socket  104   b  of rotation pin  104 . If proper seating is not achieved a marker or other suitable indicator may extend from the proximal end of elongate shaft  136   a  to inform the surgeon that engagement surface  136   e  is not properly inserted into socket  104   b  . The first portion  66  with hooks  74  and  76  may be rotated manually until proper seating is achieved. Upon such proper seating, connection portion  136   f  of hook rotator  136  is releasably attached to the bracket  120  at bracket portion  120   d  by a flexible portion  136   h,  as shown in  FIG. 12  to hold connection portion  136   f  fixed relative to extension  30 . As such, rotation of elongate shaft  136   a  relative to connection portion  136   f  also rotates shaft  136   a  relative to extension  30  and the rod connector  22  attached thereto. With the rod connector extension assembly  16  thus being assembled, longitudinal axis  24   b  of the elongate additional rod  24  projects outwardly from extension  30  and transverse to axis  96  of the second connector portion  68 . In the arrangement shown, the angle between longitudinal axis  24   b  and axis  96  is substantially 90° . While a 90° angle is suitable, it should be appreciated that other angles may be contemplated. 
     In a preferred arrangement of rod connector extension assembly  16 , hook rotator  136  is formed at its distal tip  136   i  as illustrated in  FIG. 12 a    to have a curved configuration defining a ball hex shape. Thus, while the complementary mating configuration of engagement surface  136   e  is constructed to engage socket  104   b  and substantially prevents rotation unless shaft  136   a  is rotated, the ball hex shape will allow some articulation of the rod connector first portion  66  relative to second portion  68 , as illustrated in  FIG. 7 , even when engagement surface  136   e  is seated within the socket  104   b  of rotation pin  104 . With the rod connector first portion  66  being disposed at an angle with respect to rod connector second portion  68 , first portion  66  may still be rotated about axis of engagement  100  by hook rotator  136 . It should be understood that the distal tip  136   i  of rotator hook  136  may also be formed to be relatively flat such that when the complementary mating configuration of engagement surface  136   e  engages socket  104   b  there will be substantially no articulation of the first portion  66 , with such first portion  66  being held generally fixed relative to the rod connector introducer  21  by the hook rotator  136 . 
     Turning now to  FIGS. 13-14 , details of the access port  20  are described. Access port  20  comprises an elongate sleeve  20   a  having a proximal end  20   b  and a distal end  20   c  for placement into the patient adjacent the existing spinal construct  12 . The access port  20  is of length such that the proximal end  20   b  projects out from the patient&#39;s skin S when the distal end  20   c  is positioned adjacent existing construct  12 . Sleeve  20   a  includes a perimetric sidewall  20   d  and a lumen  20   e  extending lengthwise therethrough. Lumen  20   e  is sized to receive the rod connector introducer  21  with the rod connector  22  secured thereto for attachment of the rod connector  22  to the existing spinal rod  42 . Sleeve  20   a  has a slot  20   f  extending axially for a length through the sidewall  20   d  such that the slot  20   f  extends outside the patient when the distal end of the access port  20  is positioned adjacent existing construct  12 . In the arrangement shown, slot  20   f  is arranged to face the additional spinal implant  26  to be implanted and extends axially fully through both the proximal end  20   b  and the distal end  20   c.  Slot  20   f  is sized and configured to receive therethrough the rod connector introducer  21  and the connecting portion  70  of rod connector  22  with the elongate additional rod  24  projecting therefrom. Slot  20   g  is formed diametrically opposite slot  20   f,  as shown in  FIG. 14 , slot  20   g  extending through distal end  20   c  and extending axially through perimetric sidewall  20   d  for a length that extends outside skin S of the patient. Slot  20   g  is sized and configured to receive therethrough at least a portion of the rod connector  22  and rod connector introducer  21  to accommodate rotation of the rod connector introducer  21 , as will be described. A bracket  138  may be utilized to fix the access port  20  to an operating table in a conventional manner so as to maintain the access port  20  in place throughout the surgical procedure. While access port  20  is described in this arrangement as being generally tubular, it should be appreciated that access port may include other suitable structures such as by a pair of opposed blades defining a lumen therebetween, wherein the blades may be coupled at their proximal ends by a suitable ring or other coupling member. 
     Having described the devices and instruments for extending an existing spinal rod construct in a patient, the procedures for such extension are now described with particular reference to  FIGS. 15-23 . The first procedure relates to percutaneously extending an existing spinal construct  12  as shown in  FIG. 15  with an inline ipsilateral additional construct  14  as described above. The engagement of the additional spinal implant  26  as a component of the additional spinal rod construct  14  is described. Spinal implant extension assembly  18  comprises an elongate extension  28  which includes a hollow sleeve  140  releasably secured to the additional spinal implant  26 . Spinal implant  26  is described as noted above with reference to FIG. 2  as being a polyaxial pedicle screw in this arrangement. Sleeve  140  has a pair of opposing slots  142  extending axially through the sleeve diametrically apart. The slots  142  are aligned and in communication with the slot  62  in the upper yoke portion  58  (see  FIG. 2 ) of the spinal implant  26 . The additional spinal implant  26  is percutaneously attached to the pedicle of the third spinal segment  60 , which may be a segment of the sacrum  51  or another vertebral body. Additional spinal implant  26  is introduced through a small percutaneous incision  144  made through the skin S of the patient. The incision  144  is approximately 10-30 mm in length. The dilation of incision  144  and the percutaneous attachment of spinal implant  26  to a spinal segment such as vertebral body  60  is fully described in commonly assigned U.S. patent application Ser. No. 12/818,965, entitled “System for Percutaneously Fixing a Connecting Rod to a Spine”, filed on June  18 ,  2010 , and issued as U.S. Pat. No. 8,142,437, (the &#39;437 Patent), the disclosure of which is incorporated herein by reference in its entirety. Once spinal implant  26  is attached to the vertebral body  60 , the sleeve  140  as well as slots  142  project out from the patient through dilated incision  144  with the slots  142  being rotatably manipulable upon rotation of sleeve  140  to be aligned with slot  20   f  of access port  20  as will be described with reference to  FIG. 16 . 
     Using fluoroscopy or other suitable imaging techniques, the existing spinal rod  42  is initially targeted so as to establish the position of the existing rod  42  in the patient. In this instance, the interconnecting portion  42   a  of existing rod  42  is targeted rather than extending portion  42   b  projecting outwardly beyond implant  34 . A small percutaneous incision  146  is made through the skin S of the patient, the incision  146  being approximately  10 - 30  mm in length, although other suitable dimensions may be used. A targeting rod  148  is placed through the incised puncture and pushed through the tissue of the patient down to the existing spinal rod  42 . Once the access path has been created and the position of the existing rod  42  established a series of sequentially increasing dilating instruments are inserted over the targeting rod  148 . As depicted in  FIG. 16 , the dilating instruments include dilating cannulas  150 ,  152  and  154  of increasing diameter. The number of dilating cannulas may vary depending upon the procedure and the desired extent the incision  146  is to be expanded upon dilation. In addition, the dilating cannulas may include features that maintain the lateral position of such cannulas relative to existing rod  42  during insertion. Access port  20  is then finally placed over the last dilating cannula  154  with the opposing slots  20   f  and  20   g  communicating with existing rod  42  such that the distal end  20   c  of access port  20  straddles but does not attach to existing rod  42 , as shown in  FIG. 16 . The dilating instruments are then removed as illustrated in  FIG. 17  leaving the access port  20  in place. The central longitudinal axis of the access port  20  is generally aligned with and perpendicular to the longitudinal axis of existing rod  40 . Bracket  138  may be utilized to fix the access port  20  to the operating table so as to maintain access port  20  fixed in place throughout the surgical procedure. The proximal end  20   b  of the access port  20  as well as slot  20   f  project out from the patient&#39;s skin, S, with access port slot  20   f  being generally aligned with and in facing relation to slots  142  of sleeve  140  in spinal implant extension assembly  18 . Although also shown as extending outwardly of the patient&#39;s skin, S, slot  20   g  may be of length to lie below the patient&#39;s skin, S. 
     By reference to  FIG. 18  as well as to  FIG. 1 , the introduction of the rod connector  22  through manipulation of the rod connector extension assembly  16  is explained. The handle  118  may be in the 45° position for this stage of the procedure. With access port  20  fixed in place a surgeon grasps handle  118  and initially orients the extension  30  of rod connector introducer  21  generally parallel to the spine of the patient such that the axis  24   b  elongate additional rod  24  is oriented in a first position generally parallel to the longitudinal axis of access port  20 . In this position, the additional rod  24  is within the lumen  20   e  of access port  20  with the connecting portion  70  of rod connector  22  extending through and projecting outwardly from slot  20   f  of access port  20 . Through manipulation of rod connector introducer  21  the additional rod  24  is moved in this first orientation until the rod connector  22  is below the skin S of the patient. At this point, the rod connector introducer  21 , with the access port slot  20   f  serving as a guide, is rotated so that additional rod  24  is rotated clockwise as viewed in  FIG. 19  in a direction indicated by arrow, R.from its first orientation out from access slot  20   f  and toward sleeve  140  of spinal implant extension assembly  18 . During such movement, the distal end  24   a  of additional rod  24  is subcutaneously moved through tissue of the patient beneath the skin S of the patient toward the sleeve  140  of spinal implant extension assembly  18 . 
     Continued rotation of handle  118  in the direction R further rotates rod connector introducer  21  until the distal end  24   a  of additional rod  24  approximates sleeve  140 . With fluoroscopy the distal end  24   a  of additional rod  24  is guided into slot  142  that is in facing relationship with access port slot  20   f,  as shown in  FIG. 20  for ultimate reduction into slot  62  of additional spinal implant  26 . It should be appreciated that the additional rod distal end  24   a  may be directly received within slot  62  of additional spinal implant  26 . During this portion of the rotation of rod connector introducer  21 , the rod connector  22  as well as the distal end  124   b  of the rod connector introducer extension  30  may project outwardly from the opposite access port slot  20   g  to accommodate the rotation of rod connector introducer  21 . 
     Upon final rotation of rod connector introducer  21  by handle  118  as shown in  FIG. 21  the distal end  24   a  of additional rod  24  extends through both slots  142  of sleeve  140  and is either situated in slot  62  of additional spinal implant  26 ( FIG. 2 ) or closely thereto. In this position the additional rod  24  has been moved to a second different orientation such that the axis  24   b  is transverse, and substantially perpendicular, to the longitudinal axis of access port  20 . Also with the aid of fluoroscopy, the rod connector  22  at this point receives the existing spinal rod  42  within the opening  78  between hooks  74  and  76  of rod connector first portion  66 . As described above, with first portion  66  capable of articulating while being held against rotation by the hook rotator  136 , proper receipt of existing spinal rod  42  within opening  78  is achieved even if the longitudinal axis of rod connector introducer  21  is not precisely perpendicular to the axis of existing rod  42  thus allowing for potential irregularities of the spine. In this position, existing spinal rod  42  is in an unlocked position with respect to rod connector  22 . Prior to rotation of rod connector hooks  74  and  76  to engage existing rod  42  for locking, the surgeon may, if necessary, reduce the additional rod  24  into slot  62  of additional spinal implant  26 . Such reduction may be achieved by connecting a rod persuader (not shown) to a rod persuader coupling member  156  disposed at the proximal and of sleeve  140 . The rod persuader including its structure and cooperation with rod persuader coupling member  156  is fully described in the &#39;437 Patent, the disclosure of which is incorporated herein by reference in its entirety. 
     With continued reference to  FIG. 21  as well as to  FIGS. 5-6 , the engagement of the rod connector  22  to the existing spinal rod  42  is described. Hand wrench  135  is used to suitably depress ring  136   g  for attachment to tool attachment surface  136   d  as described above and is rotated either by hand or an appropriate tool. Rotation of wrench  135  rotates hook rotator shaft  136   a  as well as engagement surface  136   e  which is engaged within socket  104   b  of rotation pin  104 . Upon such rotation of the shaft  136   a,  the rotation pin  104  rotates the first portion  66  of the rod connector  22  about the axis of engagement  100  in a manner to facilitate alignment of opening  78  relative to existing rod  42 . Hooks  74  and  76  and the respective rod engagement member  74   a  and  76   a  are then rotated in a manner to engage the existing rod  42 . As the hooks  74  and  76  are rotated, the engagement surface  108   a  at the distal end of rotation element  102  engages the existing rod  42  under the bias of wave spring  106  pushing the head  104   a  of the rotation pin  104  slightly upwardly into opening  97  of first portion  66 . During such rotation the existing rod  42  is thereby received between the rod engagement member  74   a  and  76   a  and rotation pin engagement surface  108   a  in a snap-fitting movement that provides a tactile and potentially an audio indication to the surgeon that the existing rod  42  is properly seated in the rod connector  22  in a provisional engagement whereby the rod connector  22  is held on but not locked to the existing rod  42 . Rod connector first portion  66  is rotated approximately 60° with respect to second portion  68  to establish such provisional engagement. It should be understood that first portion  66  may be rotated relative to second portion  68  at other angles which may be less than 60° or up to approximately 90°. 
     Once the rod connector  22  has been rotated to the provisional engagement position, the distal end  24   a  of additional rod  24  may then be secured to additional spinal implant  26  as described with reference to  FIG. 22 . Set screw  64  is suitably attached to a driver instrument  158  and sized and configured to introduce the set screw  64  with instrument  158  attached thereto into and through hollow sleeve  140  until set screw  64  engages the threads in the slot  62  of the upper yoke portion  58 . Set screw  64  is tightened by rotation of instrument  158  to secure the additional rod  24  to the additional spinal implant  26 . Instrument  158  is then detached from set screw  64  and removed from sleeve  140 . 
     Turning now to  FIG. 23  as well as to  FIGS. 5-6 and 11 , locking of the rod connector  22  to additional rod  42  is described. After removing hook rotator  136  and inner sleeve  134  from rod connector introducer  21 , set screw  116  is suitably attached to a driver tool  160  with the distal tip of tool  160  in engagement with socket  116   b  of set screw  116 . Tool  160  with set screw  116  attached thereto is sized and configured to be received within lumen  124   c  of outer sleeve  124  of rod connector introducer  21  until set screw  116  engages the threads  98  in rod connector second portion  68 . As noted above, the lower distal surface  116   c  of set screw  116  engages the upper surface of head  104   a  of rotation pin  104  during rotational insertion of set screw  116 . Continued insertion and tightening of the set screw  116  into threads  98  will push the rotation pin  104  downwardly causing the rod engagement surface  108   a  at the lower end of the rotation element  102  to forcibly engage the existing rod  42 . The force against the existing rod  42  also causes the first portion  66  and thereby the ball insert  80  to move downwardly relative to second portion  68  forcing the outer spherical surface  82  of ball insert  80  tightly against interior spherical surface of socket  86  of second portion  68 , thereby locking first portion  66  and second portion  68  securely together. 
     With rod connector  22  properly secured to existing spinal rod  42 , tool  160  is detached from set screw  116  and removed from rod connector introducer  21 . Spinal implant extension assembly  18 , rod connector introducer  21  and access port  20  are also then removed from the patient. To facilitate removal of rod connector introducer  21  from rod connector  22 , handle  118  may be adjustably moved to a position generally parallel to the longitudinal axis of outer sleeve  124  as shown, for example in  FIG. 9 . With the removal of the instruments the inline ipsilateral extension of the existing spinal construct  12  by additional spinal construct  14  as shown in  FIG. 2  is complete and the incisions  144  and  146  maybe appropriately sutured. In the percutaneous procedure described, the rod connector  22  is inserted through the access port  20  and rotated for attachment to the existing rod  42  in a top loading procedure without disturbing the existing implants  34  and  36  or the previous connections to the existing rod  42 . Such top loading allows a surgeon to insert the rod connector  22  by manipulating the rod connector by rotation and connect it to the existing rod  42  from above the spine facilitating the percutaneous procedure. 
     In the procedure just described, rod connector  22  is attached to existing spinal rod  42  by targeting the interconnecting extent  42   a  between two existing bone engaging implants  34  and  36 , each of which is engaged respectively to a corresponding vertebra  38  and  40 . The elongate additional rod  24  projecting from rod connector  22  may be attached to additional spinal implant  26  in either the caudal or cephalad direction. Using the same technique described herein, it should be understood that rod connector  22  may also be used to attach an existing spinal construct to other bony segments, not only within the spine, such as vertebral bodies or the sacrum, but outside the spine, such as the ilium. Such an arrangement is contemplated, for example as shown in  FIG. 24  where bone engaging implant  36  is attached to vertebral body L 5  and bone engaging implant  34  is attached to segment Si of the sacrum and these implants are interconnected by existing spinal rod  42  with extending portion  42   b  projecting in the caudal direction. With extending portion  42   b  having sufficient extent, extending portion  42   b  may be targeted for receipt of and connection to rod connector  22 , as described above. A third bone engaging implant  162  such as an iliac screw similar to spinal implant  26  may be percutaneously secured to the ilium through a separate spaced incision with a releasable bone implant extension assembly similar to spinal implant extension assembly  18 , as described in the &#39;437 Patent. Rod connector  22  may then be inserted with additional rod  24  passed subcutaneously from existing rod  42  to the iliac screw  162  in a manner as described hereinabove to form the additional construct extending from segment Si of the sacrum to the ilium. Rod connector  22  may be configured with or without jog  72  and curved if desired to accommodate the anatomical conditions. 
     Having described a particular arrangement of rod connector  22  wherein additional rod  24  is integrally attached thereto, two alternative arrangements are described wherein a rod connector is configured to receive an additional rod rather than such additional rod being integrally attached. The first alternative arrangement is shown and described with reference to  FIGS. 25 and 26 . Rod connector  200  comprises a first portion  66  articulatingly attached to a second portion  68 , first portion  66  and second portion  68  having structure identical to first and second portions  66  and  68  respectively of rod connector  22 . Rod connector  200  further includes a connecting portion  202  projecting outwardly from second portion  68  and terminating in an additional rod support  204 . Support  204  comprises a yoke  206  having a pair of opposing upstanding arms  206   a  and  206   b  defining an open ended slot  208  having internal threads  210 . The slot  208  is sized and configured to receive and support therein an additional spinal rod  212  which is fastened to the yoke  206  by a set screw  214  or other suitable fastener. As shown in  FIG. 26 , rod connector  200  is configured to be attached to the existing spinal rod, such as rod  42  and to receive and support additional rod  212  in an orientation that may be generally parallel to existing rod  42 . As such, the axis of additional rod  212  is laterally offset with respect to the axis of existing rod  42 . It should be appreciated that depending upon the anatomy of the patient the orientation of the additional rod  212  relative to the existing rod  42  may not necessarily be parallel. 
     By reference to  FIGS. 27 and 28  a minimally invasive technique for attaching rod connector  200  to a spinal rod in an existing spinal construct is described. A rod connector introducer  21  as described above may be releasably attached to second portion  68  of rod connector  200 . An elongate extension  28  as described above with respect to spinal implant extension assembly  18  includes a hollow sleeve  140  that is releasably secured to the additional rod support  204  in the same manner as attached to additional spinal implant  26 . To attach rod connector  200  to existing spinal rod such as rod  42 , either the interconnecting portion  42   a  between two existing bone implants or the extending portion  42   b  projecting beyond one of the two existing bone implants may be targeted for attachment.  FIG. 28  illustrates the targeting of the interconnecting portion  42   a  for connection. Using fluoroscopy or other suitable imaging techniques as described above, a small incision  216  is initially formed through the skin S. The incision  216  is enlarged radially and laterally with a series of sequentially increasing dilating instruments with the ultimate insertion of an oval access port  218 . Oval access port  218  is sized and configured to receive the assembly  220  comprising rod connector  200 , rod connector introducer  21  and the elongate extension  28 . A hook rotator, such as hook rotator  136 , may be inserted through rod connector introducer  21  to engage the rotation element  104  in rod connector  200  so as to restrain the hooks  74  and  76  from rotation, as set forth above. The assembly  220  is introduced into oval access port  216  with the rod connector  200  in an orientation that is maintained beneath the skin until the interconnecting portion  42   a  of existing spinal rod  42  is received within the opening  78  between hooks  74  and  76 , as described above. Rotation of the hooks  74  and  76  about axis of engagement  100  and connection of the rod connector  200  to the interconnecting portion  42   a  of existing rod  42  proceeds thereafter as described above. 
     In the attachment of rod connector  200  by the procedure shown in  FIG. 28 , the yoke  206  and therefore the additional rod  212  are located laterally farther away from the midline of the patient than the existing spinal rod  42 . In a variation, the rod connector  200  may be attached with the yoke  206  located interiorly of the existing spinal construct  12  such that the additional rod  212  lies closer to the midline of the patient. Once the rod connector  200  is properly secured to the existing rod  42 , the rod connector introducer  21  with the hook rotator  136  and access port  218  are removed and the elongate extension  28  is maintained. A third bone engaging implant such as an iliac screw similar to spinal implant  162  in  FIG. 24  may be percutaneously secured to the ilium through a separate spaced incision with a releasable bone implant extension assembly similar to spinal implant extension assembly  18 , as described in the &#39;437 Patent. An additional rod may now be used to percutaneously interconnect yoke  206  of rod connector  200  with the third bone engaging implant by passing the additional rod subcutaneously beneath the skin of the patient using the extensions attached to yoke  206  and the third bone implant as guides in a manner as fully described in the &#39;437 Patent. It should be appreciated that an additional rod may also be percutaneously placed between the yoke  206  of rod connector  200  and other bony segments within the spine, such as vertebral bodies or the sacrum, either in a caudal or cephalad direction. 
     Turning now to  FIGS. 29 and 30  the second alternative arrangement is shown and described. Rod connector  300  comprises a first portion  66  articulatingly attached to a second portion  68 , first portion  66  and second portion  68  having structure identical to first and second portions  66  and  68  respectively of rod connector  22 . Rod connector  300  further includes a connecting portion  302  projecting outwardly from second portion  68  and terminating in an additional rod support  304 . Support  304  comprises a yoke  306  having a pair of opposing upstanding arms  306   a  and  306   b  defining an open ended slot  308  having internal threads  310 . The slot  308  is sized and configured to receive and support therein an additional spinal rod  312  which is fastened to the yoke  306  by a set screw  314  or other suitable fastener. As shown in  FIG. 30 , rod connector  300  is configured to be attached to the existing spinal rod, such as rod  42  and to receive and support additional rod  312  in an orientation generally inline with existing rod  42 . As such, the axis of additional rod  312  is generally parallel to and colinear with the axis of existing rod  42 . Such an arrangement is contemplated where an existing spinal construct exists, for example, between bone implants attached to vertebral bodies L 4  and L 5  and extension is desired generally inline to sacral segment, Si in the caudad direction or to vertebral body L 3  in the opposite cephalad direction. In either case, the extending portion  42   b  of the existing rod  42  is targeted for connection by the rod connector  300 . It should be appreciated that depending upon the anatomy of the patient the orientation of the additional rod  312  relative to the existing rod  42  may not necessarily be precisely inline and colinear. 
     To attach rod connector  300  to existing spinal rod such as rod  42  that interconnects two existing bone engaging implants, the extending portion  42   b  projecting beyond one of the two existing bone implants is targeted. The attachment of rod connector  300  through an oval access port such as access port  218  within dilated incision similar to incision  216 , proceeds in a similar manner as described with respect to rod connector  200 . A third bone engaging implant such as a pedicle screw similar to spinal implant  26 , may be percutaneously secured to the sacrum or additional vertebral body through a separate spaced incision approximately  10 - 30  mm in length with a releasable bone implant extension assembly similar to spinal implant extension assembly  18 , as described in the &#39;437 Patent. An additional rod may now be used to percutaneously interconnect yoke  306  of rod connector  300  with the third bone engaging implant by passing the additional rod subcutaneously beneath the skin of the patient using the extensions attached to yoke  306  and the third bone implant as guides in a manner as fully described in the &#39;437 Patent. 
     While the existing spinal construct  12  has been described herein as being extended by a single level, it should be appreciated that the extension may comprise two or more levels with the devices and instruments as described herein. In addition, while the devices and instruments described herein provide surgeons the ability to extend existing spinal constructs at least minimally invasively and more preferably, percutaneously, it should be understood that a surgeon may also use the described devices and instruments in an open procedure if that is the surgeon&#39;s surgical preference. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.