Abstract:
An orthopaedic implant for implanting between adjacent vertebrae and a spine, includes a generally annular bag; and a hardened polymer with the bag. The method of fusing adjacent vertebrae in a spine includes the steps of forming an access hole in an annulus of a disc between the adjacent vertebrae; removing the nucleus within the disc to form a cavity surrounded by the annulus; placing a generally annular bag within the cavity; filling the bag with a polymer; injecting bone particles into the cavity surrounded by the annular bag; and hardening the polymer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to orthopaedic implants, and, more particularly, to spinal fusion devices. 
     2. Description of the Related Art 
     Spinal fusion typically involves fusion between two adjacent vertebrae by removing a disc between two adjacent vertebrae and placing a cage between the vertebrae. The patient may be cut both on the anterior and posterior sides (stomach and back) and the disc removed from between the two adjacent vertebrae. The disc includes an annulus which surrounds a nucleus. The annulus is torn, cut or otherwise removed from between the vertebrae and the softer nucleus also removed. A cage is placed between the vertebrae where the disc is removed and a bone graft including bone particles is packed within the cage and extends between the end plates of the adjacent vertebrae. Rods may also be placed on the posterior side of the spine, with screws attached to a respective rod and extending into a respective vertebrae. 
     SUMMARY OF THE INVENTION 
     The present invention provides an orthopaedic implant including a bag which is placed within a cavity surrounded by an annulus of a disc and which includes a central cavity. The bag is filled with a polymer, and the central cavity defined by the bag is filled with a bone particle and polymer matrix. 
     The invention comprises, in one form thereof, an orthopaedic implant for implanting between adjacent vertebrae in a spine, including a generally annular bag; and a hardened polymer within the bag. 
     The invention comprises, in another form thereof, a method of fusing adjacent vertebrae in a spine, including the steps of forming an access hole in an annulus of a disc between the adjacent vertebrae; removing the nucleus within the disc to form a cavity surrounded by the annulus; placing a generally annular bag within the cavity; filling the bag with a polymer; injecting bone particles into the cavity surrounded by the annular bag and hardening the polymer. 
     An advantage of the present invention is that an orthopaedic implant may be implanted between adjacent vertebrae in a spine in a minimal evasive surgery technique. 
     Another advantage is that the ligaments and tendons surrounding the spine may be properly tensioned. 
     Yet another advantage is that the patient may begin loading the implant soon after surgery. 
     A still further advantage is that the implant may be implanted from a single posterior incision location, or may be implanted from a posterior and/or anterior incision location. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a fragmentary, sectional view of a vertebrae and disc, illustrating an orientation and size of an incision made relative thereto; 
     FIG. 2 is a perspective view illustrating evacuation of a nucleus within a disc; 
     FIG. 3 is a perspective view illustrating placement of an annular bag within a disc; 
     FIG. 4 is a perspective view of the bag in a relaxed state after being placed within the disc; 
     FIG. 5 is a side, sectional view of the bag while being filled with a polymer to a first predetermined amount; 
     FIG. 6 is a side, sectional view illustrating a bone particle and polymer matrix being injected into a cavity surrounded by the bag; 
     FIG. 7 is a side, sectional view illustrating the bag being filled to a second predetermined amount after injection of bone particles; 
     FIG. 8 is a fragmentary, sectional view with the orthopaedic implant implanted within a disc and the incision being closed; 
     FIG. 9 is a perspective view of the bag shown in FIGS. 4-9; and 
     FIG. 10 is a side, sectional view of the bag shown in FIGS.  4 - 10 . 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, an embodiment of the method of the present invention for fusing adjacent vertebrae in a spine will be described hereinafter. The spine includes a plurality of adjacent vertebrae  10 , which each adjacent pair of vertebrae  10  being separated by a disc  12 . A disc  12  may become damaged because of a number of reasons, thus requiring the fusion of adjacent vertebrae. 
     FIG. 1 illustrates a fragmentary, sectional view of a spine as viewed in a direction parallel to the spine of a patient. Disc  12  is assumed to be damaged to an extent requiring fusion between adjacent vertebrae  10 . Referring to FIG. 2., each vertebrae  10  includes oppositely facing end plates  24  on each longitudinal end thereof. Each disc  12  is interposed between a pair of adjacent vertebrae, and includes an annulus  26  surrounding a nucleus  28 . 
     An incision  14  is made in the back  16  of the patient using a scalpel  18  or other appropriate cutting instrument. Incision  14  may be held open using suitable instrumentation  20 . Incision  14  is made at an angle approximately as shown to disc  12 , thereby avoiding an area  22  where the spinal cord is located. After incision  14  is made, an access hole  30  is formed in an annulus  26  of a selected disc  12  by known methods such as a drill bit or scalpel. Since incision  14  is formed in the back  16  of the patient, access hole  30  generally is formed in the posterior side of disc  12 . 
     After formation of access hole  30 , the nucleus  28  is evacuated from within disc  12  (FIG.  3 ). A vacuum tube  34  or the like may be used to remove nucleus  28 . Removal of nucleus  28  causes the formation of a cavity  42  within disc  12  surrounded by annulus  26 . Vacuum tube  34  is removed from cavity  42  and incision  14  after evacuation of nucleus  28 . 
     A flexible bag  44  having a generally annular shape when in a relaxed state is then inserted within cavity  42  (FIG.  4 ). More particularly, bag  44  is folded and inserted within a pre-load tube  46 . Pre-load tube  46  has an outside diameter which is slightly smaller than the inside diameter of access hole  30  formed in annulus  26 . Pre-load tube  46 , with bag  44  loaded therein, is inserted into incision  14  and access hole  30  such that an end  48  of pre-load tube  46  extends through access hole  30  and into cavity  42 . Bag  44  is then slid out of pre-load tube  46  and into cavity  42  as indicated by arrows  50 . Bag  44  may be ejected from pre-load tube  46  in any suitable manner, such as by utilizing a plunger (not shown) disposed within pre-load tube  46  having an outside diameter which is slightly smaller than the inside diameter of pre-load tube  46 . 
     Bag  44  is selected with a size and shape to generally fill the perimeter of cavity  42  when disposed therein (FIG.  5 ). A first fill hose  52  and a second fill hose  54  are each attached to bag  44  (FIGS.  5 - 11 ). First fill hose  52  extends through bag  44  and terminates in a portion of cavity  42  surrounded by bag  44  (FIG.  6 ). On the other hand, second fill hose  54  extends into and terminates within bag  44 . A high strength polymer is injected within bag  44  through second fill hose  54 , as indicated by arrows  56 . During this first fill stage of bag  44 , the polymer  58  is injected to substantially fill bag  44  to a first predetermined amount without expanding or deforming bag  44 . In the embodiment shown, bag  44  is porous and polymer  58  is in the form of a bioresorbable and curable polymer, some of which passes through bag  44 . The curing can be effected by the application of energy such as thermal energy, light energy, or X-ray energy, or the addition of a chemical catalyst. During the first fill stage of bag  44  shown in FIG. 6, polymer  58  preferably remains in an uncured state. 
     A bone graft in the form of bone particles  60  is then injected through first fill hose  52  into the portion of cavity  42  surrounded by bag  44  (FIG.  7 ), as indicated by arrows  62 . It should be understood that a bone substitute material can also be used. In the embodiment shown, bone particles  60  are suspended within a liquid such as synthetic bone substitute. The bone particle and suspension liquid is injected through first fill hose  52  and into cavity  42  until the portion of cavity  42  surrounded by bag  44  is substantially filled as shown in FIG.  7 . Thereafter, bone particles  60  are retained within cavity  42  and additional polymer  58  is injected into bag  44  (FIG.  8 ). Polymer  58  is injected into bag  44  to a second predetermined amount causing expansion of bag  44 . Bag  44  expands in an axial direction (relative to disc  12 ) and contacts end plates  24 . Additionally, bag  44  expands in a radially inward direction causing radial compression and axial expansion of bone particles  60  within cavity  42 . The ligaments and tendons surrounding vertebrae  10  may thus be retensioned by axially expanding bone particles  60  therebetween. Additionally, the fusion area is provided with a large contact area since substantially all of the area contacted by bone particles  60  and bag  44  forms a load bearing member. The polymer compound  58  within bag  44 , as well as the polymer surrounding and carrying bone particles  60  may be cured to a load bearing state in a relatively fast manner. For example, the polymer compound may be cured with X-ray energy or a chemical catalyst. Thus, in addition to being minimally evasive, the patient is able to quickly load the spine through sitting, standing, etc. after curing of the polymer within orthopaedic implant  8 . First fill hose  52  and second fill hose  54  are cut from orthopaedic implant  8 , as indicated in FIG. 9, and incision  14  is closed using suitable closure techniques. 
     From the foregoing description, it can be seen that the present invention provides an orthopaedic implant  8  which may be easily implanted within a disc  12  with minimal evasive surgical procedures. The curing of the polymer within the bag between the adjacent vertebrae  10  occurs quickly and provides a large surface area for transfer of loads and a stable structure for the regrowth of bone between the vertebrae. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.