Patent Publication Number: US-8992578-B2

Title: Anchoring systems and methods for correcting spinal deformities

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/963,290 filed on Dec. 8, 2010 and entitled “Anchoring Systems and Methods for Correcting Spinal Deformities,” which is a continuation of U.S. patent application Ser. No. 10/709,795 now U.S. Pat. No. 7,901,435) filed on May 28, 2004 and entitled “Anchoring Systems and Methods for Correcting Spinal Deformities,” which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to non-fusion methods and devices for correcting spinal deformities. 
     BACKGROUND OF THE INVENTION 
     Spinal deformities, which include rotation, angulation, and/or curvature of the spine, can result from various disorders, including, for example, scoliosis (abnormal curvature in the coronal plane of the spine), kyphosis (backward curvature of the spine), and spondylolisthesis (forward displacement of a lumbar vertebra). Early techniques for correcting such deformities utilized external devices that apply force to the spine in an attempt to reposition the vertebrae. These devices, however, resulted in severe restriction and in some cases immobility of the patient. Thus, to avoid this need, several rod-based techniques were developed to span across multiple vertebrae and force the vertebrae into a desired orientation. 
     In rod-based techniques, one or more rods are attached to the vertebrae at several fixation sites to progressively correct the spinal deformity. The rods are typically pre-curved to a desired adjusted spinal curvature. Wires can also be used to pull individual vertebra toward the rod. Once the spine has been substantially corrected, the procedure typically requires fusion of the instrumented spinal segments. 
     While several different rod-based systems have been developed, they tend to be cumbersome, requiring complicated surgical procedures with long operating times to achieve correction. Further, intraoperative adjustment of rod-based systems can be difficult and may result in loss of mechanical properties due to multiple bending operations. Lastly, the rigidity and permanence of rigid rod-based systems does not allow growth of the spine and generally requires fusion of many spine levels, drastically reducing the flexibility of the spine. 
     Accordingly, there remains a need for improved methods and devices for correcting spinal deformities. 
     SUMMARY OF THE INVENTION 
     The present invention provides various embodiments of spinal anchoring methods and devices for correcting spinal deformities. In one exemplary embodiment, a spinal anchoring device is provided having a bone-engaging member that is adapted to engage bone, and a receiver member that is movably coupled to the bone-engaging member and that is adapted to seat a spinal fixation element. The anchoring device can also include a fastening element, such as a set screw, that is adapted to mate to the receiver member to lock a fixation element in a fixed position relative to the receiver member while allowing the receiver member to move freely relative to the bone-engaging member. 
     The receiver member can have a variety of configurations, but in one exemplary embodiment the receiver member includes a recess formed in a proximal portion thereof that is adapted to seat a spinal fixation element. The recess is preferably spaced apart and separate from the cavity in the distal portion of the receiver member. The receiver member can also include a distal portion that is movably mated to the bone-engaging member, and a proximal portion having a recess formed therein for seating a spinal fixation element. 
     Movement of the receiver member relative to the bone-engaging member can vary, and in one embodiment the bone-engaging member can be pivotally coupled to the receiver member such that the receiver member pivots along an axis relative to the bone-engaging member. By way of non-limiting example, a pin member can extend through a distal end of the receiver member and through a proximal end of the bone-engaging member for pivotally mating the receiver member and the bone-engaging member. In another embodiment, the bone-engaging member can be polyaxially coupled to the receiver member. By way of non-limiting example, the bone-engaging member can include a spherical head formed on a proximal end thereof, and the receiver member can include a cavity formed in a distal portion thereof that is adapted to polyaxially seat the spherical head of the bone-engaging member. In other aspects, portions of the receiver member and/or the bone-engaging member can optionally include a surface coating, such as titanium oxide, nitride, or a cobalt-chrome alloy, that is adapted to facilitate movement of the receiver member relative to the bone-engaging member. 
     In another embodiment of the present invention, a spinal anchoring system is provided having a spinal fixation element, a spinal anchoring device having a bone-engaging member and a receiver member freely movably coupled to the bone-engaging member and configured to receive the spinal fixation element, and a fastening element that is receivable within the receiver member of the spinal anchoring device and that is configured to lock the spinal fixation element to the spinal anchoring device. The spinal fixation element can have a variety of configurations, and suitable spinal fixation elements include, for example, cables, tethers, rigid spinal rods, or flexible spinal rods. The spinal fixation can also be formed from a variety of materials include, for example, stainless steel, titanium, non-absorbable polymers, absorbable polymers, and combinations thereof. 
     In other embodiments the present invention provides a method for correcting spinal deformities that includes the step of implanting a plurality of anchoring devices into adjacent vertebrae in a spinal column. Each anchoring device preferably includes a bone-engaging member that is fixedly attached to the vertebra and a receiver member that is freely movable relative to the bone-engaging member and the vertebra. A spinal fixation element is then coupled to the receiver member on each anchoring device such that the fixation element extends between each of the adjacent vertebrae. Once properly positioned, the spinal fixation element is locked to the receiver member on each anchoring device to maintain the adjacent vertebrae at a fixed distance relative to one another while allowing free movement of each vertebrae in the fixed position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a side view of one embodiment of a spinal anchoring device in accordance with the present invention; 
         FIG. 1B  is another side view of the spinal anchoring device shown in  FIG. 1A ; 
         FIG. 1C  is a cross-sectional view of the spinal anchoring device shown in  FIG. 1A  taken across line A-A; 
         FIG. 1D  is an enlarged view of a proximal portion of the spinal anchoring device shown in  FIG. 1C ; 
         FIG. 1E  is an enlarged view of a proximal portion of another embodiment of a spinal anchoring device; 
         FIG. 2  is a side, partially cross-sectional view illustration of two spinal anchoring devices, as shown in  FIG. 1A , implanted in adjacent vertebrae in accordance with one embodiment of a method for correcting spinal deformities; 
         FIG. 3A  is a side view illustration of two spinal anchoring devices having receiver members coupled to a spinal fixation rod and having bone-engaging members implanted in adjacent vertebrae in accordance with another embodiment of a method for correcting spinal deformities; and 
         FIG. 3B  illustrates the spinal anchoring devices shown in  FIG. 3A  with the receiver members pivoted relative to the bone-engaging members to allow for movement of the vertebrae. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention generally provides spinal anchoring methods and devices that are effective to correct spinal deformities while allowing some flexibility to the spine. In particular, the methods and devices allow a spinal fixation element to mate to several adjacent vertebrae to maintain the vertebrae at a fixed distance relative to one another, yet to allow the orientation of each vertebrae in that fixed position to adjust as the orientation of the patient&#39;s spine changes, e.g., due to movement and/or growth. While various techniques can be used to provide for such a configuration, an exemplary anchoring device in accordance with one embodiment of the present invention generally includes a bone-engaging member that is adapted to be implanted in a vertebra, and a receiver member that is movably coupled to the bone-engaging member and that is effective to mate to a spinal fixation element. In use, when several anchoring devices are implanted within adjacent vertebrae in a patient&#39;s spine and a spinal fixation element is fixedly mated to each anchoring device, the spinal fixation element is effective to maintain the adjacent vertebrae at a desired fixed distance relative to one another. Each vertebra can, however, change orientations in that fixed position relative to the spinal fixation element because the bone-engaging member implanted therein is movably attached to the receiver member mated thereto and mated to the spinal fixation element. As a result, the spinal anchoring devices allow movement of the patient&#39;s spine. Such a technique can be advantageous for shortening and/or halting growth of the patient&#39;s spine, however the methods and devices can be used in a variety of other spinal applications. By way of non-limiting example, the device can be used for posterior dynamization to function as a decompressive device for stenosis and/or an adjunct to an intervertebral disc to unload the facets of the vertebra. 
       FIGS. 1A-1D  illustrate one exemplary embodiment of a spinal anchoring device  10  that includes a receiver member  12  that is polyaxially coupled to a bone-engaging member  14 . While the bone-engaging member  14  can have a variety of configurations, in this embodiment the bone-engaging member  14  is in the form of a polyaxial screw having a threaded shank  14   b  and a substantially spherical head  14   a . The proximal end of the head  14   a , in the illustrated embodiment, may be truncated to form a flattened proximal surface  14   c  that facilitates polyaxial movement of the bone engaging member  14  relative to the receiver member  12 , as will be discussed in more detail below. The head  14   a  can also include a driver-receiving element formed in the flattened proximal end  14   c  for mating with a driver device. The driver-receiving element can be, for example, a socket  14   d  ( FIGS. 1C-1D ) formed within the proximal end  14   c  of the head  14   a  for receiving a driver tool which can be used to thread the bone-engaging member  14  into bone. A person skilled in the art will appreciate that virtually any device that is effective to mate to bone can be used in place of bone-engaging member  14 , including, for example, screws, hooks, bolts, plates, etc., as long as the bone-engaging member  14  is movably coupled to the receiver member  12 . 
     The receiver member  12  can also have a variety of configurations, however, in the illustrated embodiment the receiver member  12  is generally U-shaped and includes a proximal portion  12   a  having opposed side walls or legs  13   a ,  13   b  that are substantially parallel to one another and that define a recess  16  therebetween for seating a spinal fixation element  18 . The spinal fixation element  18  can have a variety of configurations, and, by way of non-limiting example, it can be rigid, semi-rigid, bendable, flexible, etc. Suitable spinal fixation elements for use with the present invention include, by way of non-limiting example, rods, tethers, cables, plates, etc. The spinal fixation element  18  can also be formed from a variety of materials including, for example, stainless steel, titanium, non-absorbable polymers, absorbable polymers, and combinations thereof. In certain applications, it may be desirable to provide a fixation element that is flexible to allow for bending, yet that is rigid in tension such that the fixation element can not stretch or lengthen. This is particularly useful in applications where it is necessary to prevent growth of the spine while allowing normal flexibility. 
     Still referring to  FIGS. 1A-1D , the receiver member  12  also includes a distal portion  12   b  that is adapted to movably couple to the bone-engaging member  14 . In particular, the distal portion  12   b  may include a seat  19  that is preferably effective to receive the head  14   a  of the bone-engaging member  14  such that the bone-engaging member  14  is polyaxially movable relative to the receiver member  12 . In the illustrated embodiment, the seat  19  is defined by at least a portion of the walls of a substantially spherical cavity  20  formed in the distal portion  12   b . The seat  19  is preferably complementary in shape to the head  14   a . For example, in the illustrated embodiment, the seat  19  and the head  14   a  are spherical in shape. One skilled in the art will appreciate, however, that the seat  19  and head  14   a  need not be spherical in shape or complementary in shape; the seat  19  and head  14   a  may have any shape(s) sufficient to allow polyaxial motion of the bone engaging member  14  relative to the receiver member  12 . As discussed above, in certain embodiments the proximal end of the head  14   a  may be truncated to facilitate polyaxial motion. As shown in  FIG. 1C , for example, the gap  17  between the fixation element  18  and the flattened proximal surface  14   c  provides an increased range of polyaxial motion to the head  14   a  within the cavity  20 . 
     In the illustrated embodiment, the cavity  20 , and thus the seat  19 , is spaced apart from the recess  16  in the proximal portion  12   a  of the receiver member  12  to inhibit contact between the head  14   a  and the spinal fixation element  18 , thus allowing polyaxial movement of the spherical head  14   a  of the bone-engaging member  14  without interference from the spinal fixation element  18  disposed in the recess  16 . The spacing between the recess  16  in the proximal portion  12   a  and the cavity  20  in the distal portion  12   b  can be achieved using a variety of techniques, but in the illustrated embodiment the legs  13   a ,  13   b  each include a protrusion or ridge  22   a ,  22   b  formed therein that separates the recess  16  and the cavity  20 , as shown in  FIGS. 1C-1D . The ridges  22   a ,  22   b  together define an opening  22   c  having a diameter D o  that is less than both the diameter D r  of the spinal fixation element  18  and the diameter D b  of the spherical head  14   a  of the bone-engaging member  14  to prevent passage of the fixation element  18  and the head  14   a  therethrough, thus separating the two components. 
     Since the diameter D o  of the opening  22   c  is preferably smaller than the diameter D b  of the head  14   a  of the bone-engaging member  14 , the device  10  can be adapted to allow the bone-engaging member  14  to be inserted through the proximal portion  12   a  of the receiver member  12  to seat the head  14   a  in the spherical cavity  20 . This can be achieved, for example, by expanding or pulling apart the legs  13   a ,  13   b  to increase the diameter D o  of the opening  22   c , thereby allowing the spherical head  14   a  to pass therethrough. The head  14   a  can then seated within the cavity  22  and the legs  13   a ,  13   b  can return to their original state. The spinal fixation element  18  can then be seated in the recess  16  in the proximal portion  12   a  of the receiver member  12  and the ridges  22   a ,  22   b  will prevent the fixation element  18  from passing therethrough into the cavity  22 . The legs  13   a ,  13   b  can thereafter be locked in a fixed position relative to one another using a locking mechanism that mates to the legs. Exemplary locking mechanisms will be described in more detail below. 
     In other embodiments (not shown), rather than having ridges  22   a ,  22   b  formed on the legs  13   a ,  13   b  of the receiver member  12 , the receiver member  12  can include an insert that is adapted to be disposed therein after the spherical head  14   a  is positioned within the cavity  22  in the distal portion  12   b  to separate the spherical head  14   a  from the fixation element  18 . The insert can have any shape and size, but it is preferably adapted to complete the substantially spherical cavity  20  in the distal portion  12   b  of the receiver member  12 , and to seat a spinal fixation element  18  extending through the receiver member  12 . The insert can also be configured to merely sit within the receiver member  12 , or it can be adapted to mate to the receiver member  12 , e.g., using threads, a snap-fit, or some other engagement technique known in the art, such that the insert is retained at a desired location in the receiver member  12 . In use, the insert will allow the bone-engaging member  14  to rotate freely within the cavity  20  in the distal portion  12   b  of the receiver member  12  because the insert does not bear against the spherical head  14   a  of the bone-engaging member  12 . The insert will also allow the spinal fixation element  18  to be locked within the receiver member  12  using techniques which will be discussed in more detailed below. A person skilled in the art will appreciate that a variety of other techniques can be used to allow the bone-engaging member  14  to be assembled and disassembled from the receiver member  12 . By way of non-limiting example, the proximal and distal portions  12   a ,  12   b  of the receiver member  12  can be separate components that are matable to one another, e.g., using threads or other mating techniques known in the art. Such a configuration allows the head  14   a  of the bone-engaging member  14  to be seated within the cavity  20  in the distal portion  12   b  prior to mating the proximal and distal portions  12   a ,  12   b  of the receiver member  12  to one another. Other techniques not shown or described herein can also be used as long as the bone-engaging member  14  and the receiver member  12  are at least partially freely movable relative to one another. For example, in certain embodiments, the head  14   a  of the bone engaging member  14  may be inserted through the distal end of the receiver member  12 . In such embodiments, the opening  12   c  may not be necessary and thus, as shown in  FIG. 1E  by way of non-limiting example, the cavity  20 ″ and the recess  16 ″ may be completely separated within the receiver member  12 ″. 
     As previously indicated, the device  10  can also include a fastening element that is effective to lock the spinal fixation element  18  to the receiver member  12 , and more preferably that is effective to lock the spinal fixation element  18  within the recess  16  in the receiver member  12  such that the spinal fixation element  18  cannot move relative to the receiver  12 . The fastening element can have a variety of configurations, and it can be adapted to mate to inner and/or outer portions of the legs  13   a ,  13   b  on the receiver member.  FIGS. 1B-1D  illustrate one embodiment of a fastening element that is in the form of a threaded set screw  24  that is adapted to mate with corresponding threads formed within the receiver member  12 , i.e., on the legs  13   a ,  13   b . A person skilled in the art will appreciate that a variety of fastening elements known in the art can be used with the various spinal anchoring devices of the present invention and that the illustrated set screw  24  is merely one exemplary embodiment of a fastening element. 
       FIG. 2  illustrates the spinal anchoring device  10  shown in  FIGS. 1A-1D  in use. In the illustrated embodiment, two spinal anchoring devices  10 ,  10 ′ are implanted in adjacent vertebrae  50 ,  52 , however any number of spinal anchoring devices can be used and the number will vary depending on the nature of the procedure being performed. The devices  10 ,  10 ′ are implanted in the vertebrae  50 ,  52  by inserting the bone-engaging member  14 ,  14 ′ of each device  10 ,  10 ′ through the receiver member  12 ,  12 ′ and then threading the bone-engaging member  14 ,  14 ′ into the vertebra. As previously mentioned, this can be achieved using a driver tool that is adapted to engage a driver-receiving element, such as socket  14   d ,  14   d ′, in the spherical head  14   a ,  14   a ′ on each bone-engaging member  14 ,  14 ′. Once the bone-engaging members  14 ,  14 ″ are implanted in the adjacent vertebrae  50 ,  52 , a spinal fixation element, such as spinal rod  18 , is positioned within the receiver member  12 ,  12 ′ of each device  10 ,  10 ′. Since the devices  10 ,  10 ′ are preferably used to correct a spinal deformity, the position of each vertebra will likely need to be adjusted to correct the deformity in order to seat the rod  18  within each receiver member  12 ,  12 ′. Once properly positioned, the rod  18  can be locked to each receiver member  12 ,  12 ′ preferably by inserting a locking mechanism, such as a set screw, into the head of each receiver member  12 ,  12 ′, thereby maintaining the vertebrae  50 ,  52  at a fixed distance apart from one another. Since each bone-engaging member  14 ,  14 ′ is polyaxially movable relative to each receiver member  12 ,  12 ′, each vertebrae  50 ,  52  is free to move in that fixed position relative to the receiver member  12 ,  12 ′ coupled thereto, thus allowing for movement of the spine. 
       FIGS. 3A-3B  illustrate yet another embodiment of a spinal anchoring device  100 . While the drawings illustrate two devices  100 ,  100 ′ implanted in adjacent vertebrae  150 ,  152 , the devices  100 ,  100 ′ are substantially similar and those only one device  100  will be described. As shown, the device  100  is similar to device  10  in that it includes a receiver member  112  having a proximal portion  112   a  for seating a spinal fixation element  118 , and a distal portion adapted to couple to a bone-engaging member  114 . In this embodiment, however, rather than allowing polyaxial movement of the receiver member  112  relative to the bone-engaging member  114 , the receiver member  112  pivots along an axis, indicated by point A, relative to the bone-engaging member  114 . Pivotal movement can be achieved using a variety of techniques, and in one exemplary embodiment a bearing element can be formed between the components  112 ,  114 . The bearing element can be, for example, a pin member  120  that extends through the distal portion  112   b  of the receiver member  112  and through a portion of the bone-engaging member  114 . Since the bone-engaging member  114  is not polyaxial, the bone-engaging member  114  may or may not include a head formed thereon, and thus the pin member  120  can extend through a head of the bone-engaging member  114 , or it can extend directly through a portion of the shaft  114   b  of the bone-engaging member  114 . A person skilled in the art will appreciate that a variety of other techniques can be used to provide a receiver member  112  that is pivotally coupled to a bone-engaging member  114 . 
     In use, several devices  100  can be implanted in adjacent vertebrae to maintain the vertebrae in a fixed position relative to one another, yet to allow pivotal movement of each vertebrae in that fixed position, e.g., to allow the patient&#39;s spine to flex. As shown in  FIGS. 4A-4B , two devices  100 ,  100 ′ are implanted in adjacent vertebra  150 ,  152 . In  FIG. 4A , the vertebrae  150 ,  152  are maintained in a first, fixed position by locking spinal rod  118  to the receiver member  112 ,  112 ′ of each device  100 ,  100 ′. In  FIG. 4B , the vertebrae  150 ,  152  have pivoted within that fixed position due to flexion of the patient&#39;s spine, and thus each bone-engaging member  114 ,  114 ′ has pivoted along axis A relative to the receiver member  112 ,  112 ′ coupled thereto, and relative to the spinal fixation element  18  mated to each receiver member  112 ,  112 ′. Such a configuration can be useful in applications where movement along a single plane, such as the patient&#39;s coronal plane, is desired while preventing axial rotation of the vertebrae  150 ,  152 . 
     The spinal anchoring devices in accordance with various embodiments of the present invention can be formed from a variety of materials, including, for example, stainless steel, titanium, cobalt-chrome alloys, etc. In other embodiments, the spinal anchoring devices can include features to facilitate movement of the bone-engaging member relative to the receiver member. For example, referring to the device  10  shown in  FIGS. 1A-1D , portions of the bone-engaging member  14  and the receiver member  12  that come into contact with one another, e.g., the spherical head  14   a  of the bone-engaging member  14  and/or the cavity  20  in the receiver member  12 , can include a surface coating thereon or therein. The surface coating can be formed from a material that allows free movement of the components  12 ,  14 , and that is preferably wear-resistant. By way of non-limiting example, suitable materials include titanium oxide, nitride, and a cobalt-chrome alloy. 
     One of ordinary skill in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.