Abstract:
A spinal rod insertion instrument includes a hollow, monolithic body having a proximal end and a distal end. The body defines a passageway that extends along a first axis between the proximal and distal ends. The distal end includes first and second arms defining a slot therebetween. The first and second arms are configured to releasably retain a spinal rod therebetween. Also provided is a method of securing a spinal rod to a coupling element attached with a pedicle screw.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/781,985 filed Mar. 14, 2013, the disclosure of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an instrument for urging an orthopedic rod into a recess in an orthopedic device and more particularly, to an instrument for securing a spinal rod to a coupling element. 
         [0003]    Surgical techniques commonly referred to as spinal fixation use surgical implants and/or mechanical immobilization to fuse two or more vertebral bodies of the spinal column. Spinal fixation may also be used to alter the alignment of adjacent vertebral bodies relative to one another so as to change the overall alignment of the spinal column. Such techniques have been used effectively to treat many spinal column disorders and, in many cases, to relieve pain. 
         [0004]    One spinal fixation technique involves immobilizing the spine using orthopedic stabilizing rods, commonly referred to as spine rods, which are positioned generally parallel to the spine. This may be accomplished by exposing the spine posteriorly and fastening bone screws to the pedicles of vertebral bodies. The pedicle screws are generally placed two per vertebra and serve as anchor points for the spine rods. Coupling elements or implants adapted for receiving a spine rod therethrough are then used to join the spine rods to the pedicle screws. A set screw or fastener then fastens the spine rod into a seat in a coupling element. 
         [0005]    Instruments are utilized for inserting a spine rod into position within an orthopedic device such as a coupling element. Surgeons have encountered considerable difficulty when attempting to use these instruments to insert a spine rod into the seat of the coupling element and then inserting a fastener to secure the rod to the coupling element. Many of these instruments require initial insertion of the rod into the coupling element and then alignment of the instrument with the construct to ensure proper positioning of the rod. A separate instrument is typically used to insert and secure the fastener to the coupling element. Many of the current instruments are difficult to use since they require two hands, one hand to hold the instrument while it clamps the implant and one hand to operate different alignment means to properly position the rod in the implant. An entirely second instrument is often then required for inserting the fastener. 
         [0006]    There remains a need for improved instruments for urging or persuading spinal rods into position in orthopedic devices and for securing the rods in place. Moreover, there is a need for an instrument that manipulates and positions the rod and facilitates anchoring of a subsequent fastener to hold the rod in its implanted position. 
       SUMMARY OF THE INVENTION 
       [0007]    A first aspect of the present invention is s rod insertion instrument including a body having a proximal end and a distal end, and a slot separating a portion of the distal end into first and second arms, wherein the first and second arms are configured to releasably retain a rod therebetween. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a front view of a rod insertion instrument in accordance with an embodiment of the present invention. 
           [0009]      FIG. 2  is a front view of the distal end of the rod insertion instrument shown in  FIG. 1 . 
           [0010]      FIG. 3  is a perspective view of the distal end of the rod insertion instrument shown in  FIG. 1  engaged with a rod. 
           [0011]      FIG. 4  is a front view of the distal end of the rod insertion instrument shown in  FIG. 1  engaged with a rod. 
           [0012]      FIG. 5  is a front view of the rod insertion instrument shown in  FIG. 1  engaged with a rod and a coupling element attached to a screw. 
           [0013]      FIG. 6  is an enlarged front sectional view of the construct shown in  FIG. 5 . 
           [0014]      FIG. 7  is an enlarged side view of the construct shown in  FIG. 5 . 
           [0015]      FIG. 8  is an enlarged front sectional view of the construct shown in  FIG. 5  with a fastener and a driving tool. 
           [0016]      FIG. 9  is a front view of the construct shown in  FIG. 5  with a driving tool. 
           [0017]      FIG. 10  is a perspective view of a rod insertion instrument in accordance with another embodiment of the present invention. 
           [0018]      FIG. 11  is an enlarged side view of the distal end of the rod insertion instrument shown in  FIG. 10 . 
           [0019]      FIG. 12  is a side view of the rod insertion instrument shown in  FIG. 10 . 
           [0020]      FIG. 13  is a top view of the rod insertion instrument shown in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    A rod insertion instrument  100  in accordance with an embodiment with the present invention is shown in  FIGS. 1-9 . Instrument  100  is configured for use in inserting a rod  70  into a coupling element  80  connected with a screw  90 , shown more clearly in  FIGS. 5-9 . Screw  90  is typically a pedicle screw and is at least initially polyaxially connected with coupling element  80 . 
         [0022]    Instrument  100  is a generally hollow cylindrical body having a proximal end  10  and a distal end  12 , which is separated by a slot  20  into a first arm  30  and a second arm  40 . A distal end of slot  20  forms a rod capture mechanism  22 , which is a portion of slot  20  configured to accept and temporarily retain rod  70 . 
         [0023]    Slot  20  extends axially along instrument  100  from distal end  12  toward proximal end  10 . Slot  20  is open at distal end  12 , thus forming arms  30  and  40  as portions of distal end  12  of instrument  100 . Rod capture mechanism  22  is a contoured portion of slot  20  configured with lead-in chamfers  31 ,  41  on first and second arms  30 ,  40  that allows for easy engagement and locking with rod  70 . Adjacent to chamfers  32 ,  42  are protrusions  34 ,  44  on each arm  30 ,  40 , which open proximally into a retaining aperture  24  of slot  20 . Retaining aperture  24  leads proximally into a channel  26 , which leads proximally into slot end  28 . 
         [0024]    As slot  20  separates arms  30  and  40  in a hollow cylindrical body, slot  20  of course defines portions on either side of the cylindrical body. Reference to any portion of slot  20  is meant to reference both aspects thereof on either side of the cylindrical body, which aspects are preferably substantially identically dimensioned. It is contemplated that the opposing portions of the slot could be differently dimensioned to alter the movement or forces applied by the arms. 
         [0025]    Arms  30  and  40  are moveable towards and away from each other due to the elasticity of the material of which instrument  100  is constructed and due to the configuration of slot  20 . The moveable nature of arms  30  and  40  is configured in a way that allows rod  70  to be loaded into retaining aperture  24  and so that rod  70  can be releasably retained and secured within retaining aperture  24  through an interference fit in which the lateral spring forces of arms  30  and  40  with respect to the body of instrument  100  maintain a grasp on rod  70 . This is enhanced by retaining aperture  24  being configured to substantially match an outer contour of rod  70 . 
         [0026]    The following relative dimensions are with respect to instrument  100  in its resting state as depicted in  FIGS. 1 and 2 . As shown in  FIG. 2 , chamfers  32  and  42  are contoured to have a dimension D1 therebetween at distal end  12  that is larger than the diameter of rod  70  with which instrument  100  is configured for use, and also larger than a dimension D2 between adjacent protrusions  34 ,  44 . This allows for rod  70  when contacting chamfers  32 ,  42  to be led toward retaining aperture  24 . Protrusions  34  and  44  are separated by distance D2 that is smaller than the diameter of rod  70 , which provides an interference or press fit once rod  70  passes protrusions  34  and  44  and is disposed within retaining aperture  24 . Retaining aperture  24  has an edge that is circular and closely matches the circumference of rod  70 . The diameter D3 of aperture  24  is larger than dimension D2 between protrusions  34 ,  44 . 
         [0027]    As shown in  FIG. 6 , the inner portion of distal end  12  defines a main bore  14  and a distal bore  16  of a slightly larger inner diameter than that of main bore  14 . A shoulder  18  is configured as an annular seat at the junction of main bore  14  and distal bore  16 . Coupling element  80  is cylindrically configured and has an outer diameter similar to or slightly less than the inner diameter of distal bore  16  and larger than the inner diameter of main bore  14 . In this way, instrument  100  can be inserted over coupling element  80  up to shoulder  18 , as shown in  FIG. 6 . Shoulder  18  will contact an upper portion of coupling element  80  to stop insertion thereof. Other features can be disposed on the inner portion of distal end  12  at distal bore  16 , such as protrusions or notches, to interact with cooperating protrusions or notches on coupling element  80  to enhance the grip of instrument  100  on coupling element  80 . 
         [0028]    As shown in  FIGS. 6-8 , each arm  30 ,  40  includes a window  36 ,  46  that faces the other and is located at the distal end  12  of instrument. Windows  36 ,  46  are configured to allow a surgeon to view the components disposed within instrument  100 . Particularly, visualization of proper placement of instrument  100  over coupling element  80  and of fastener  95  entering coupling element  80  is available through windows  36 ,  46  under fluoroscopy to determine proper placement of fastener  95 . As such, the placement and configuration of windows can be widely varied and selected to facilitate this viewing purpose. In instrument  100 , windows  36 ,  46  are circularly configured and are centrally located on each arm  30 ,  40 . Additional windows may be provided as desired, and either or both arms may not include a window. In other embodiments, slot  20  may be configured to include a portion that acts as a window. 
         [0029]    Proximal end  10  of instrument  100  includes ribs  11  on its external surface to provide an ergonomic, non-slip gripping surface for the surgeon. Other similar types of gripping surfaces can also or alternatively be used. 
         [0030]    A second embodiment of a rod insertion instrument  100   a  is shown in  FIGS. 10-13 . Instrument  100   a  is similarly configured to instrument  100 , but includes a relatively larger vertical rectangular window  36   a  in arm  30   a  at distal end  12   a . A similarly configured window  46   a  is disposed in arm  40   a . These windows provide a greater open area through which to view the components within instrument  100   a  through fluoroscopy during use. 
         [0031]    In use, rod  70  can be loaded into retaining aperture  24  of instrument  100  prior to a surgical procedure. This can be done away from the patient on a preparation table, which eliminates a step that would otherwise have to be carried out during the actual surgical procedure. Rod  70  is placed into slot  20  between lead-in chamfers  32 ,  42  and press fit past protrusions  34 ,  44  into retaining aperture  24 . During this step, arms  30  and  40  are allowed to elastically flex away from each other and to snap back into place once rod  70  is disposed within retaining aperture  24 . This “snap” can provide a tactile and, in some cases, audible feedback to the surgeon to indicate that rod  70  is in place. Also during this step, slot end  28  is configured to permit channel  26  to widen and return to its resting state without stressing any proximal portion of instrument  100 . Thus, instrument  100  can be sterilized and reused many times before needing replacement. Rod  70  can be loaded into instrument  100  either by manipulating instrument  100  against rod  70 , manipulating rod  70  and placing it into a stationary instrument  100 , or a combination of both. 
         [0032]    With rod  70  disposed within retaining aperture  24  of instrument  100 , instrument  100  can be located over coupling element  80 , which is connected to the patient via screw  90 . Distal end  12  of instrument is placed onto coupling element  80  until coupling element  80  contacts shoulder  18 . As instrument  100  is located and moved into this position, captured rod  70  is automatically aligned within a U-shaped channel  81  of coupling element  80 . 
         [0033]    At this point, instrument is held in place to maintain rod  70  in this desired location while rod  70  is secured in place via a fastener  95 . Insertion of fastener  95  is also facilitated by the construction of instrument  100 , eliminating the need for the surgeon to switch to using an extra instrument at this point in the surgical procedure. A driving tool  92 , such as a split hex-head tool, is of a dimension such that it can be inserted through instrument to gain access to coupling element  80 . The inner diameter of main bore  14  of instrument is preferably at least slightly larger than the outer diameter of tool  92  and of fastener  95  to facilitate proper guidance of fastener  95  into coupling element  80  during insertion. Fastener  95  is preferably removably loaded onto the end of tool  92  and inserted through instrument  100  to a position adjacent coupling element  80 . Fastener  95  is externally threaded to engage with internal threads of U-shaped channel  81  of coupling element  80 . Of course, often embodiments may include an externally threaded coupling element and an internally threaded fastener. 
         [0034]    Instrument  100  acts as a guide for at least the provisional tightening of fastener  95 . As fastener  95  is threaded into coupling element  80  under the manipulation of tool  92 , rod  70  is secured in place with respect to screw  90 , coupling element  80 , and fastener  95 . During any or all of these processes for inserting rod  70  and fastener  95 , visualization of proper placement of instrument  100  and the other components with respect to coupling element  80  can be gained under fluoroscopy. Windows  36 ,  46  may enhance the ability of the surgeon to view the components within instrument  100  during this viewing. 
         [0035]    With fastener  95  at least provisionally secured or even fully secured, tool  92  is removed from instrument  100 . It is noted that while fastener  95  is threaded into coupling element  80 , the load distributed by fastener  95  to coupling element  80  during provisional tightening will cause arms  30  and  40  of instrument  100  to splay outward. This lessens or removes the forces of arms  30  and  40  on rod  70  to facilitate a release of rod  70  from the grip of instrument  100 . Instrument  100  is then pulled proximally by the surgeon to remove it from coupling element  80  and rod  70 . As fastener  95  is sometimes secured very tightly to the end of tool  92 , removal of instrument  100  can also assist in removing tool  92  from fastener  95  as well. During removal of instrument  95 , the spring forces that allow arms  30 ,  40  to snap over rod  70  operate similarly to allow rod  70  to slide out of retaining aperture  24  so that instrument  100  is released from the implanted construct. Instrument  100  is then removed from the surgical site. 
         [0036]    Tool  92  can then be used to continue tightening fastener  95  with respect to coupling element  80 , if desired. Instrument  100  can be located over another coupling element  80  disposed within the patient to aid in aligning rod  70  with U-shaped channel  81  of that coupling element. Nonetheless, instrument  100  offers the surgeon the ability to manipulate rod  70  into other coupling elements  80 , and can facilitate insertion and at least provisional tightening of fasteners  95  at these subsequent locations. As a result, there is no need for the surgeon to switch to a separate instrument for guidance of fastener  95  into coupling element  80 , either during the initial connection of rod  70  with coupling element or during subsequent couplings. Instrument  100  is therefore configured to not only capture and retain a rod in preparation for rod insertion, but can also serve as a guide for insertion of a fastener and subsequent provisional and final tightening. 
         [0037]    While instrument  100  is configured for use with rod  70  of a particular diameter, it is contemplated that a kit of different instruments could be provided with retaining apertures  24  of relative sizes. Other dimensions of instrument  100  and slot  20  can vary accordingly to accommodate many differently sized rods. Other cross-sectional configurations of rods can also be accommodated by matching such cross-section with the configuration of retaining aperture  24 . The diameters of main and distal bores  14 ,  16  within instrument  100  can also be varied to coordinate with different sizes of coupling elements  80 . In this way, a universal kit of instruments can be provided, each configured with the novel aspects of the present invention, so that an appropriately dimensioned instrument can be selected and used by a surgeon during any one of a number of different surgical procedures. The configuration of the instruments allow for sterilization and reuse, resulting in an instrument and a kit having a long life. 
         [0038]    One particular embodiment of instrument  100  is configured for use with a rod having a 3.5 mm diameter. With reference to  FIG. 2 , diameter D3 of retaining aperture  24  is also approximately 3.5 mm. Dimension D2 is approximately 3.0 mm. An outer diameter of instrument  100  at distal end  12  is approximately 11.1 mm, with other more proximal portions of the outer diameter being approximately 14.0 mm to facilitate gripping by the surgeon. This allows instrument  100  to be a low-profile construction to reduce the size and configuration of the instrument for wider applicability to surgical procedures among many patients. 
         [0039]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.