Patent Publication Number: US-2022233216-A1

Title: Modular apparatus for extending an existing spinal construct

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 63/142,138, filed Jan. 27, 2021, the entire contents of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure contemplates a spinal surgery construct, and more particularly a modular apparatus for extending an existing spinal construct, and procedures for achieving such modular extension. 
     BACKGROUND OF THE INVENTION 
     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 commonly assigned U.S. Pat. No. 8,657,826, entitled “Apparatus and Devices for Percutaneously Extending an Existing Construct”, issued to McLean et al. on Feb. 25, 2014 (the &#39;826 Patent). The device disclosed in the &#39;826 Patent includes a rod connector comprising a lower portion having a pair of spaced hooks for engaging an existing spinal rod and an upper portion defining a yoke receiving an additional rod to extend the existing construct. Another example includes commonly assigned U.S. Pat. No. 8,523,906, entitled “Apparatus and Devices for Percutaneously Extending an Existing Construct”, issued to McLean et al. on Sep. 3, 2013 (the &#39;906 Patent). The device disclosed in the &#39;906 Patent includes a rod connector comprising a lower portion having a pair of spaced hooks for engaging an existing spinal rod and an upper portion having an integral additional rod to extend the existing construct. The entire contents of the &#39;826 Patent and the &#39;906 Patent are incorporated herein by reference. 
     A further trend in spinal construct extension technology is the evolution of modularity. Modularity allows a portion of the extension construct to be attached to an existing spinal structure with a separate modular portion configured to include a spinal rod extension attached to the first portion. This permits greater flexibility in supplying and choosing spinal implants and fixation components that are properly sized and dimensioned for a particular anatomy. One known example is described in U.S. Pat. No. 10,307,185, entitled “Revision Connectors, Systems, and Methods Thereof”, issued to Patrick Murray on Jun. 4, 2019 and assigned on its face to Globus Medical, Inc. While this approach represents an improvement in revision techniques and devices, it would be advantageous to provide a cost-effective modular revision system that is simple and easy for a surgeon to use. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved modular rod extender for extending a rod in an existing spinal construct. 
     It is another object of the invention to provide an improved modular apparatus for extending a rod in an existing spinal construct that includes a rod connector attachable to the existing rod and a modular rod extender that has a modular attachment feature at one end for attachment to the rod connector and an extension rod extending from the other opposite end. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a modular apparatus for extending an existing ipsilateral spinal construct comprising a rod connector and a modular rod extender in accordance with an embodiment of the invention. 
         FIG. 2  is an exploded perspective of the modular apparatus of  FIG. 1 . 
         FIG. 3  is a longitudinal cross-sectional view of the exploded view of the modular apparatus as seen along viewing lines III-III of  FIG. 2 . 
         FIG. 4  is an enlarged cross-sectional view of the modular apparatus as seen along viewing lines IV-IV of  FIG. 1 . 
         FIG. 5  is a perspective view of the modular rod extender of the modular apparatus of  FIG. 1 . 
         FIG. 6  is a longitudinal cross-sectional view of the modular rod extender of  FIG. 5 . 
         FIG. 7  is an exploded perspective view of the modular rod extender of  FIG. 5 . 
         FIG. 8  is a longitudinal cross-sectional view of the exploded view of the modular rod extender of  FIG. 7 . 
         FIG. 9  is a top perspective view of the extender body of the modular rod extender of  FIG. 5 . 
         FIG. 10  is the view of  FIG. 9  with a portion removed to reveal inner structural details of the extender body. 
         FIG. 11  is a top plan view of the extender body of  FIG. 9 . 
         FIG. 12  is a top perspective view of a modular rod extender in accordance with a second embodiment having an offset extension rod. 
         FIG. 13  is an exploded view of the alternative modular rod extender of  FIG. 12 . 
         FIG. 14  a top perspective view of the modular rod extender of  FIG. 12  having an offset extension rod attached to a lateral rod connector in accordance with a third embodiment. 
         FIG. 15  is an exploded view of the offset modular rod extender and lateral rod connector of  FIG. 14 . 
     
    
    
     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. 1-2  a modular apparatus  10  is shown for extending an existing spinal construct that includes an existing spinal rod  12  (shown in phantom) so as to increase the level of spinal fixation in a patient having previously undergone spinal fusion or other spinal surgery. The modular apparatus  10  generally comprises a rod connector  14 , a modular rod extender  16  and a locking element is. In one arrangement, locking element  18  is a set screw that has external threads  18   a . In use, the existing spinal rod  12  and the modular rod extender  16  are typically located ipsilaterally in the spine. Spinal rod  12  is an existing spinal construct in the sense that it has been installed prior to the installation of the modular apparatus  10 , which means that existing spinal rod  12  may have been placed in a previous surgical procedure or may be placed during the same surgical procedure as, but prior to, modular apparatus  10 . As will become more evident, modular apparatus  10  is an enhancement over the rod connector shown and described in the above referenced, commonly assigned &#39;906 Patent which comprises a lower portion that is attachable to an existing spinal rod and an upper portion with an integral additional spinal rod that is pre-attached polyaxially to the lower portion. As will be described, rod connector  14  and modular rod extender  16  are separate components that are attached in a modular fashion, for example during a surgical procedure, to form the modular apparatus  10 . 
     Turning now also to  FIGS. 3-4 , details of rod connector  14  are described. Rod connector  14  comprises an attachment portion  20  that includes, in one arrangement, a pair of spaced hooks  22  and  24  each of which includes a respective projecting rod engagement member  22   a  and  24   a . Hooks  22  and  24  are spaced from each other at a distance defining an opening  26  that allows the existing rod  12  to be received therebetween. A threaded opening  28  is formed into attachment portion  20  opposite hooks  22  and  24 , with threaded opening  28  being in communication with rod receiving opening  26 . An elongate post  30  has a lower threaded portion  30   a  and an upper head  30   b  having an outer surface formed as a truncated sphere. Head  30   b  may have annular ridges  30   c  as seen in  FIGS. 2 and 4 , or a suitable serrated surface to assist in the securement of post  30  to modular rod extender  16 , as will be described. A socket  30   d  may be included to extend into upper head  30   b , socket  30   d  being in a suitable configuration such as a hexalobe to receive a tool for attaching rod connector  14  to existing spinal rod  12  and for securing rod connector  14  thereto. Threaded portion  30   a  is threadably received in threaded opening  28  of attachment portion  20  to form rod connector  14 . 
     Turning in addition to  FIGS. 5-11 , further details of modular rod extender  16  are described. Modular rod extender  16  comprises an extender body  32  and an extension rod  34  attached thereto. Extender body  32  comprises a modular attachment feature  36  at one end  32   a  and a rod attachment feature  38  at an opposite end  32   b . Modular attachment feature  36  comprises a central bore  40  formed through a top surface  32   c  and a bottom surface  32   d  of extender body  32 , a socket collar  42 , a crown  44  and a retention insert  46 . Central bore  40  extends along an axis  41  as shown in  FIG. 6  and has internal threads  40   a  in an upper portion adjacent top surface  32   c . Extension rod  34  is elongate and serves to provide an additional rod to extend the existing construct from existing spinal rod  12  to another spinal level where it may be attached to a further pedicle screw or other suitable bone anchor. Extension rod  34  is attached to extender body  32  by rod attachment feature  38  as shown in  FIGS. 5-6 , which may include external threads  34   a  threadably engaging internal threads  38   a  formed into extender body  32  at end  32   b . Extension rod  34  may be welded to extender body  32  subsequent to threaded engagement thereto to further secure the connection. Alternatively, extender body  32  and extension rod  34  may be formed as an integral, one-piece member. As shown in  FIGS. 5-6 , extender body  32  and extension rod  34  form an in-line modular rod extender  16  wherein the longitudinal axis of extension rod  34  is axially aligned with extender body  32  and, particularly with central bore  40 . 
     Referring now to  FIGS. 4 and 7-8 , further details of central bore  40  forming a portion of modular attachment feature  36  are described. The lower portion of central bore  40  adjacent bottom surface  32   d  is formed to have a lower opening  48  and a lower interior cavity  50 , lower interior cavity  50  communicating with lower opening  48  and central bore  40 . Lower opening  48  has a diameter greater that the maximum diameter of spherical outer surface of post head  30   b  such that post  30  may be bottom loaded through lower opening  48 . An outwardly downwardly flared chamfer  48   a  may be formed at the bottom of lower opening  48 . Lower interior cavity  50  has a first region  52 , a second region  54  and a third region  56 . First region  52  communicates with lower opening  48  and preferably has a first partially spherical internal surface  52   a  having a first radius of curvature. First region  52  has a portion that is diametrically wider than the diameter of opening  48 . Second region  54  communicates with first region  52  and preferably has a second partially spherical internal surface  54   a  having a second radius of curvature. The second radius of curvature of second internal surface  54   a  is in one arrangement less than the first radius of curvature of first internal surface  52   a . Second region  54  has a portion that is diametrically wider than the widest diameter of region  52 . Third region  56  communicates with second region  54  and preferably has a cylindrical internal surface  56   a . Third region  56  is substantially as wide as the widest portion of second region  54  and greater than the diameter defining central bore  40 . A ledge  55  extends radially interiorly within extender body  32 , ledge  55  having an upper contact surface  57  and a lower surface defining an interior stop surface  58 . Third region  56  terminates interiorly of lower interior cavity  50  at interior stop surface  58  that extends transversely relative to cylindrical internal surface  56   a . Formation of the second region  54  and third region  56  allows for expansion of socket collar  42 , as will be described. 
     Referring again to  FIGS. 4 and 7-8 , details of socket collar  42  are described. Collar  42  comprises a ring  60  of generally circular configuration having a generally circular central opening  62 . Ring  60  includes a top surface  60   a  and a bottom surface  60   b  that in one arrangement are substantially parallel. Opening  62  preferably has a partially spherical internal surface  64  having a radius of curvature, R 1 . The radius of curvature of internal partially spherical surface  64  is in one arrangement substantially the same as the radius of curvature of the outer spherical surface  30   b  of post  30 . Ring  60  has an outer surface  66  that preferably includes a partially spherical external surface that has a radius of curvature, R 2  that is greater than the radius of curvature, R 1  of internal surface  64 . The radius of curvature of external partially spherical surface  66  is in one arrangement substantially the same as the radius of curvature of first partially spherical surface  52   a  in the lower interior cavity  50  at the lower portion of central bore  40 . As such, socket collar  42  cannot pass through the lower portion of central bore  40 . In a preferred arrangement, ring  60  is split as defined by a gap  68  as shown in  FIG. 7  that extends angularly through ring  60 . Gap  68  allows a certain amount of radial expansion and contraction of ring  60 . In the unexpanded condition of socket collar  42 , opening  62  has a dimension that is less than the maximum diameter of head  30   b  of post  30  such that head  30   b  may not pass therethrough unless socket collar  42  is expanded. Further details of socket collar  42  and its function are set forth in commonly assigned U.S. patent application Ser. No. 16/843,160, issued as U.S. Pat. No. 11,219,470, entitled “Modular Tensioned Spinal Screw”, filed by Eugene Avidano on Apr. 8, 2020, the entire contents of the &#39;160 application being incorporated herein by reference. 
     Referring yet again to  FIGS. 4 and 7-8 , further the details of crown  44  are described. Crown  44  is of generally cylindrical configuration having an upper end  44   a  and an opposite lower end  44   b  with a bore  44   c  extending therethrough. As best seen in  FIG. 7 , crown  44  includes a pair of lobes  70  that project outwardly radially oppositely from crown  44  and provide crown alignment, as will be described. Exteriorly between lobes  70  crown  44  includes a generally cylindrical body  72  having a diameter slightly smaller than the diameter defining central bore  40 . A lower interior surface  74  at the lower end  44   b  of crown  44  is formed to have a partially spherical concave surface having a radius of curvature that in one arrangement is substantially the same as the radius of curvature of the outer spherical surface of past head  30   b.    
     Referring still further to  FIGS. 4 and 7-8 , additional details of retention insert  46  are described. Retention insert  46  is generally cylindrical having a central opening  46   a  extending therethrough. In one arrangement, retention insert  46  has internal threads  46   b  in central opening  46   a  and external threads  46   c  extending on an outer surface of retention insert  46 . Internal threads  46   b  are configured to threadably receive external threads  18   a  of locking element  18  while external threads  46   c  on retention insert  46  are configured for threadable receipt into internal threads  40   a  of central bore  40 , as will be described. 
     Turning now to  FIGS. 9-11 , additional details of extender body  32  are described. As shown particularly in  FIGS. 10 and 11 , central bore  40  has a pair of opposing cutouts  40   b  formed into an interior surface  40   c  that has a diameter defining central bore  40 . Cutouts  40   b  are configured to receive respective lobes  70  of crown  44  in assembly, as will be described. Top surface  32   c  may be formed to include an opening  76  that is configured to receive a portion of an insertion instrument that is used to introduce modular rod extender  16  to the surgical site. In one arrangement, opening  76  may have an oval shape so as to provide suitable alignment between the insertion instrument and modular rod extender  16 . Opening  76  may be formed to extend partially into extender body  32  through top surface  32   c  (see  FIG. 6 ). Alternatively, opening  76  may be formed to extend fully through extender body  32 . 
     The components of rod connector  14  and modular rod extender  16  may comprise any suitable biocompatible material, including but not limited to titanium, cobalt chrome and PEEK. 
     Having described details of the components of modular apparatus  10 , the assembly of the components to form modular rod extender  16  is now described with particular reference to  FIGS. 4 and 6-8 . Socket collar  42 , crown  44  and retention insert  46  are sequentially introduced into central bore  40  of extender body  32  in a top-loading process. Socket collar  42 , introduced initially, is rotated 90° so that top surface  60   a  and bottom surface  60   b  of socket collar  42  respectively face internal threads  40   a  within central bore  40 . In this manner socket collar  42 , with slight contraction if necessary, is capable of passing through central bore  40  until socket collar  42  reaches the wider lower interior cavity  50  adjacent bottom surface  32   d  of extender body  32 . Socket collar  42  is then rotated 90° within lower interior cavity  50  to the position shown in  FIG. 4  wherein socket collar  42  rests floatingly on first partially spherical internal surface  52   a  of lower interior cavity region  52 . Crown  44  is then introduced into inner central bore  40  in a top-loading process whereby lobes  70  are oriented in alignment with cutouts  40   b , as shown in  FIGS. 10 and 11 . In this orientation, crown  44  is in a fixed alignment with extender body  32  and will be prevented from rotation and thereby remain in a fixed position during modular attachment of rod extender  16  to rod connector  14 , as will be described. In certain instances, crown  44  may be formed of a softer material such as commercially pure titanium (CP Ti). This would allow crown  44  to lock against head  30   b  of rod connector post  30  during use, as will be described. 
     Retention insert  46  is then introduced into central bore  40  by threading external threads  46   c  into internal threads  40   a  of central bore  40 . Upon reaching the proper position within central bore  40  when retention insert  46  bottoms out on upper contact surface  57  of ledge  55 , insert  46  is secured therein by a suitable process, such as by welding. As so secured, retention insert  46  is fixed in position relative to central bore  40  and covers lobes  70  of crown  44 , effectively retaining socket collar  42  and crown  44  within central bore  40 . With retention insert  46  secured in such a fixed position and with socket collar  42  being prevented from passing out through the bottom of central bore  40 , both socket collar  42  and crown  44  may move up and down to a degree within central bore  40  until post  30  is modularly received. It should be appreciated that retention insert  46  may also be formed, for example, as a bushing that is welded in place, thereby potentially eliminating the need for external threads  46   c  and internal threads  40   a  within central bore  40 . 
     In use for spinal surgery, a kit may be provided comprising a plurality of rod connectors  14  and a plurality of modular rod extenders  16 . The rod connectors  14  may be modular and configured to each have a different rod receiving opening  26  to accommodate existing spinal rods  12  of different diameter. The modular rod extenders  16  may have extension rods  34  of different lengths and different diameters to accommodate different surgical procedures or patient anatomies. However, the heads  30   b  of each rod connector post  30  are commonly formed to have a spherical surface having the same size and configuration such that any selected modular rod extender  16  may be attached to a selected rod connector  14 . It should therefore be appreciated that the subject modular apparatus  10  provides flexibility and options for the surgeon in selecting appropriate spinal fixation implants depending upon surgical circumstances and anatomies in a cost-effective manner. 
     After selection of a suitable rod connector  14  and a suitable modular rod extender  16 , the chosen rod connector  14  is placed on the existing spinal rod  12  by introducing the existing spinal rod  12  into rod receiving opening  26 . Rod connector  14  is rotated such that hooks  22  and  24  straddle existing spinal rod  12 . Such placement and rotation of rod connector  14  may be achieved by a suitable instrument. Rod connector  14  may be slid axially along existing spinal rod  12  to a position determined to be appropriate by the surgeon. Post  30  is then tightened against existing spinal rod  12  by a tool engaged with socket  30   d  to cause rod engagement members  22   a  and  24   a  to engage and securely lock the chosen rod connector  14  onto the existing spinal rod  12 . A chosen modular rod extender  16  may then be pushed by an appropriate instrument on to the spherical outer surface of head  30   b  of post  30  to form the assembled modular apparatus as shown in  FIG. 1 , prior to placement of locking element  18 . In some circumstances, locking element  18  may be pre-attached to modular rod extender  16  before modular attachment to rod connector  14 . Upon downward movement of modular rod extender  16  onto head  30   b , head  30   b  moves socket  42  axially upwardly into the wider regions  54  and  56  of lower interior cavity  50  of central bore  40  since head  30   b  cannot pass through socket collar opening  62  in the relaxed unexpanded condition. Upon further relative movement of head  30   b  upwardly socket collar top surface  60   a  will ultimately contact interior stop surface  58  within lower interior cavity  50 . Continued movement of modular rod extender  16  downwardly will then push head  30  into and through socket collar opening  62  to expand the socket collar  20  radially via the gap  68 . 
     Once the spherical head  30   b  of post passes through collar opening  62  an audible click may be heard together with a tactile feel as socket collar  42  returns to its non-stressed radius. At this point, socket collar  42  will be disposed below the maximum diameter of post head  30   b , as shown in  FIG. 4 . In such assembled but unlocked configuration, rod extender  16  may be moved polyaxially and rotationally on post head  30   b  relative to rod connector  14 . It should also be appreciated that while a chosen rod connector  14  may be initially separately placed on and secured to an existing spinal rod  12  as described, where appropriate access to socket  30   d  of post  30  through central bore  40  is provided, the chosen rod connector  14  and the chosen modular rod extender  16  may be pre-attached and jointly placed on existing spinal rod  12 . 
     To tighten modular rod extender  16  to rod connector  14 , locking element  18  may then be threaded into internal threads  46   b  of retention insert  46 . Locking element  18  includes an interior socket  18   b  (see  FIGS. 1 and 2 ) formed to have a hexalobe shape or other suitable configuration for receipt of a driver instrument (not shown) for threading locking element  18  into internal threads  46   b  of retention insert  46 . Upon tightening, locking element  18  will engage upper end  44   a  of crown  44 . Continued tightening will push crown  44  further downward within central bore  40  causing lower concave surface  74  of crown  44  to forcibly engage head  30   b  of post  30 . This in turn moves post head  30   b  further downward as extender body  32  moves relatively upward. Such relative movement causes the bottom of post head  30   b  to forcibly engage socket collar  42  and wedge socket collar  42  rigidly against first partially spherical internal surface  52   a  at the lower end of central bore  40 . Upon complete tightening of locking element  18 , modular rod extender  16  and rod connector  14  are securely coupled, thereby preventing relative movement therebetween. Annular ridges  30   c  on post head  30   b  enhance the security of the connection between post head  30   b  and socket collar  42 . 
     Having described a particular arrangement of modular apparatus  10  wherein modular rod extender  16  has an extension rod  34  in-line with modular attachment feature  36 , two alternative embodiments are now described. The first alternative arrangement is shown and described with reference to  FIGS. 12 and 13 . A modular rod extender  116  comprises elongate extension rod  34  attached to a curved extender body  132  by rod attachment feature  38 . Curved extender body  132  is substantially the same in all respects as modular extender body  32 , including modular attachment feature  36 , except that it is curved in a plane transverse to the direction of central bore  40 . Such curvature results in a lateral offset orientation of the longitudinal axis of extension rod  34  relative to central bore  40 . The curvature of curved extender body  132  may be formed in a manner to allow extension rod  34  to be positioned closer to the midline axis of the patient&#39;s spine or in an opposite manner to allow extension rod  34  to be positioned farther away from the patient&#39;s midline axis. Such a curved extender body  132  is configured to provide a lower profile extension of an existing spinal construct. 
     Turning now to  FIGS. 14 and 15  the second alternative arrangement is shown and described. In this embodiment modular rod extender  116 , as described with reference to  FIGS. 12 and 13 , is modularly attachable to a lateral rod connector  114 . Lateral rod connector  114  has a side opening  126  for lateral receipt of an existing spinal rod  12 . Lateral rod connector  114  may be suitably attached to existing spinal rod  12  by a fastening element (not shown) threadably engaging threaded opening  118 . Lateral rod connector  114  includes an elongate post  130  similar to post  30  of rod connector  14 . Post  130  has an upper head  130   b  having an outer surface formed as a truncated sphere, which may include annular ridges  130   c  or other suitable high friction surface. Post head  130   b  is received in modular attachment feature  36  of modular rod extender  116  in the same manner as post  30  of rod connector  14  is received in modular rod extender  16 , as described above. Initial attachment is unlocked and allows polyaxial and rotational movement of modular rod extender  116  on post head  130   b , relative to lateral rod connector  114 . Modular rod extender  116  may be subsequently locked in a desired orientation to lateral connector  114  by advancing locking element  18  into threads  40   a  central bore  40 . This arrangement is configured to allow not only for a lower profile extension of existing spinal rod  12 , but also a substantial co-axial orientation of extension rod  34  relative to an existing spinal rod  12 , while potentially passing around existing spinal constructs. 
     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.