Abstract:
A mobile dynamic implantable spinal apparatus comprising at least one fixed bracket secured on a correcting rod and at least one mobile carrier slidably mounted on the correcting rod. The fixed bracket and the mobile carrier each include a body and a pedicle screw or a transverse process hook articulated to the body. The distribution of the degrees of freedom between the carrier and the rod, and the pedicle screws or hooks and the carrier and the fixed bracket provide a non-rigid assembly which preserves some of the natural mobility of the vertebrae and disk, and the potential growth of the spinal column.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to spinal disorders and, more particularly, to a mobile dynamic system for treating spinal disorders. 
     2. Description of the Prior Art 
     Conventional implantable apparatuses for treating spinal disorders, such as scoliosis, typically include a pair of implantable rods for mounting on either side of the spinal column. Rigid transverse bars typically connect the rods together in spaced-apart parallel arrangement. Anchors in the form of hooks or screws are provided along each rod for anchoring same to the selected vertebrae. Once installed, the anchors are rigidly locked to the associated rod to prevent relative motion therebetween. Such an arrangement must be supplemented with bone grafts and the fusion of several vertebrae in order to prevent the apparatus from breaking due to the loads induced thereon. However, bone grafts and vertebrae fusion often cause serious complications throughout the patient&#39;s adult life. 
     Accordingly, efforts have been made to develop implantable spinal instrumentation which could sustain greater loads and, thus, eliminate the need of resorting to bone grafts and vertebrae fusion. For instance, U.S. Pat. No. 5,672,175 issued on September 30, 1997 to Martin discloses a fusionless implantable spinal instrumentation wherein the implanted rods are anchored to the spinal column with fixed central anchors and terminal dynamic anchors. Each terminal anchor is rigidly connected to a coupling member which is in turn slidably mounted to a corresponding one of the implanted rods. The coupling members can have a selected number of degree of freedom relative to the corresponding rod. 
     Although the implantable spinal instrumentation disclosed in the above mentioned patent constitutes a technological advancement, it has been found that there is a need for a new dynamic implantable instrumentation which could be used for treating spinal disorders. 
     SUMMARY OF THE INVENTION 
     It is therefore an aim of the present invention to provide a dynamic mobile implantable apparatus for treating spinal column disorders. 
     It is also an aim of the present invention to provide such a dynamic mobile implantable apparatus which allows growth of the spinal column of the patient. 
     It is a further aim of the present invention to provide a new dynamic spinal instrumentation system. 
     It is a still further aim of the present invention to provide a dynamic spinal instrumentation system which is adapted to preserve at least in part the physiological mobility of the vertebrae and the disc. 
     It is still a further aim of the present invention to provide a new dynamic anchoring assembly for connecting a spinal implantable rod with a bone. 
     It is still a further aim of the present invention to provide a dynamic cross-link for structurally connecting a pair of spinal implantable rods together. 
     Therefore, in accordance with the present invention, there is provided a mobile dynamic internal system for treating a disorder of a spinal column having a sagittal plane, comprising at least one implantable correcting rod for mounting on one side of a patient&#39;s spinal column, at least one fixed bracket rigidly mounted to said correcting rod, and at least one mobile carrier slidably mounted to said correcting rod, and first and second anchors respectively mounted to said mobile carrier and said fixed bracket for anchoring said correcting rod to the spinal column, wherein, once said dynamic internal system has been implanted, said first and second anchors still respectively have limited freedom of movement relative to said mobile carrier and said fixed bracket, thereby allowing said mobile carrier to slide along said correcting rod in response of movements of the spinal column. 
     In accordance with a further general aspect of the present invention, there is provided a mobile dynamic anchoring assembly for connecting an implantable rod with a bone, comprising a carrier adapted to be mounted to an implantable rod for sliding movement thereon and limited pivotal movement with respect thereto about an axis perpendicular to the rod, and a bone anchor articulately connected to said carrier for allowing the mobility of said carrier to be preserved once said anchor has been engaged with a bone. 
     In accordance with a further general aspect of the present invention, there is provided a mobile dynamic cross-link for structurally connecting a pair of implantable spinal rods together, comprising opposed first and second ends adapted to be connected to corresponding ones of a pair of implantable spinal rods, and a point of articulation between said first and second ends to prevent the implantable spinal rods from pivoting apart while allowing any other limited relative movements therebetween. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which: 
     FIG. 1 is a rear elevational view of a mobile dynamic spinal instrumentation system installed on a laterally deviated portion of a patient&#39;s spinal column in accordance with a first embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of a fixed pedicle screw bracket forming part of the mobile dynamic spinal instrumentation system of FIG. 1; 
     FIG. 3 is a cross-sectional view of a mobile pedicle screw carrier forming part of the mobile dynamic spinal instrumentation system of FIG. 1; and 
     FIG. 4 is a cross-sectional view of an articulated cross-link forming part of the mobile dynamic spinal instrumentation system illustrated in FIG.  1 . 
     FIG. 5 is a cross-sectional view of a mobile transverse process hook sub-assembly adapted to be selectively articulately connected to a mobile carrier or a fixed bracket as an alternative to the pedicle screw sub-assembly shown in FIGS.  2  and  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout the text, the term “sagittal plane” is used to designate the median longitudinal plane of the spinal column dividing the same into right and left halves in a frontal plane or a back plane of the patient&#39;s body. 
     FIG. 1 illustrates a mobile dynamic implantable instrumentation system  10  for correcting various disorders of a patient&#39;s spinal column S. For instance, the mobile dynamic implantable instrumentation system  10  can be used for treating a lateral deviation of the spinal column S, such as a scoliosis. It has been found that in patients suffering from scoliosis, that the vertebrae in the curved portion of the spinal column S may be rotated horizontally due to torsional forces acting thereon. The implantable instrumentation system  10  would, as will be seen, retain the individual vertebrae in a generally realigned position approximating their position in a normal spinal column, while advantageously preserving some of the natural mobility of the vertebrae and growth potential of the bones of the spinal column S. 
     The dynamic implantable instrumentation system  10  illustrated in FIG. 1 generally comprises a pair of spinal implantable rods  12  and  14 . Each of the rods  12  and  14  may be curved to approximate a desirable 3-dimensional curve of the portion of the spinal column in which the system  10  is to be implanted. The rods  12  and  14  are preferably made of a metal alloy, such as titanium or stainless steel. One of the rods  12  and  14  is used as a correcting rod to translate and maintain the vertebrae in a correct alignment, while the other rod acts as a stabilizer for the correcting rod. It is noted that for certain disorders, for instance, where the loads exerted on the correcting rod are less important, it might be possible to use a single rod instead of a pair of rods. 
     In the illustrated example, the rod  12  extends through a central fixed bracket  16   a  and a selected number of mobile carriers  18   a  disposed on either side of the central fixed bracket  16   a . Similarly, according to the illustrated embodiment, the rod  14  extends through a central fixed bracket  16   b  and a pair of mobile carriers  18   b  disposed on opposed sides of the central fixed bracket  16   b . It is noted that depending on the spinal disorder to be treated, the mobile carriers  18   a  and  18   b  could be placed on a same side of the fixed brackets  16   a  and  16   b  rather than on opposed sides thereof, as illustrated in FIG.  1 . Anchors, such as pedicle screws  20 , are articulated to the central fixed brackets  16   a ,  16   b  and mobile carriers  18   a ,  18   b  so as to maintain the rods  12  and  14  in a corrected position in opposition to the deformation forces of the spinal column S, while allowing some of the natural physiological movements of the vertebrae and disc. The disposition of the fixed brackets  16   a  and  16   b  relative to the mobile carriers  18   a  and  18   b  on both rods  12  and  14 , advantageously allows the patient&#39;s spinal column to grow, while the system  10  is still implanted in the patient&#39;s body. 
     As seen in FIG. 2, each fixed bracket  16   a ,  16   b  is provided in the form of a C-shaped clamp collar  22  having an intermediate curved rod engaging portion  23  and opposed first and second ends  24  and  26  extending in parallel and defining a circumferential gap  28  therebetween. A pin  30  extends through a pair of registered through bores  32  and  34  respectively defined in the first and second ends  24  and  26  of the clamp collar  22 . A plurality of axially extending splines  36  are circumferentially distributed on a tapering enlarged bottom portion of the pin  30  to mate with corresponding splines (not shown) formed in the side wall of the through bore  34 . This prevents the pin  30  from rotating about a longitudinal axis thereof relative to the clamp collar  22 . The pin  30  has a threaded portion  38  upon which a self-breaking and self-aligning nut  40  can be threadably engaged to press the first and second ends  24  and  26  together and, thus, fixedly secure the clamp collar  22  to one of the rods  12  and  14  with the pin  30  extending generally perpendicularly to a longitudinal axis of the associated rod  12 ,  14  and being spaced laterally therefrom. The self-breaking and self aligning nut  40  is provided with an annular weak region  42  which is adapted to break at a predetermined tightening torque. A weak region  44  is also defined in the threaded portion of the pin  30  to facilitate removal of the extra-length thereof once the self-breaking and self-aligning nut  40  has been broken while being tightened to transmit the desired clamping force to the clamp collar  22 . The extra-length of the pin  30 , i.e. the portion of the pin  30  between the weak region  44  and the free distal end of the threaded portion  38 , is used to facilitate the engagement of the pin  30  within the through bores  32  and  34 . 
     The pin  30  is provided at one end thereof opposite the threaded portion  38  with a ball formation  46  adapted to be received in a socket  48  defined in the head of each pedicle screw  20  to permanently permit limited relative movements between the collar clamp  22  and the associated pedicle screw  20  in three degrees of freedom. Axial removal of the ball formation  46  from the socket  48  is prevented by a hollow retaining cap  50  threadably engaged in the socket  48  and through the central portion of which the pin  30  extends outwardly. 
     The retaining cap  50  has a top annular flange  52  which is adapted to bear against the underlying top surface of the head of the associated pedicle screw  20  and from which a segment of a sphere  54  projects integrally upwardly. A semi-spherical recess  56  is defined in the bottom surface of the second end  26  of the clamp collar  22  to receive the sphere segment  54  therein and define a gap  58  therewith for allowing relative constricted angular movement between the pedicle screw  20  and the clamp collar  22 . In one embodiment of the present invention, the angular movement of the pedicle screw  20  relative to the pin  30  is limited to approximately 28 degrees. 
     By directly articulating the pedicle screw  20  to the pin  30 , the number of pieces to be assembled can be minimized in that the nut  40  cooperates with the pin  30  to retain the clamp collar  22  in secure engagement with one of the rods  12  and  14 , while at the same time holding the pedicle screw  20  and the clamp collar  22  together. 
     As opposed to conventional orthopedic implantable systems wherein the anchors are locked in position relative to the associated fixation means after the rods have been fitted therethrough, the pedicle screw  20 , illustrated in FIG. 2, is permanently articulated to the clamp collar  22 . This greatly contributes to reduce the loads transmitted to the system  10  and, thus, eliminates the need of resorting to bone graft and spinal fusion to supplement the support offered by the system  10 . 
     As seen in FIG. 3, each mobile carrier  18   a ,  18   b  includes a generally cylindrical body  60  defining a pair of opposed registered oblong holes or circumferentially extending slots  62  which communicate with a socket  64 . A roller  66  having a transversal through bore  68  is received in the socket  64 . The roller  66  is free to rotate about a longitudinal axis thereof within the socket  64 . The roller  66  is retained captive within the socket  64  by means of a cap  70  securely engaged over an open end of the body  60 . A polished bushing  72  is mounted to the inner side of the cap  70  to prevent axial movement of the roller  66  within the socket  64 . The bushing  72  has an integral central pin projection  74  extending perpendicularly from one side thereof. The pin projection  74  is pressure fitted in a corresponding bore defined in the cap  70  for retaining the bushing  72  in position on the inner side of the cap  70 . 
     A flat base projection  76  extends integrally axially from one end of the body  60  opposite the open end thereof. The base projection  76  has a bore  78  which communicates with a semi-spherical recess  80  defined in the underside surface of the base projection  76 . A pin  82 , similar to pin  30  illustrated in FIG. 2, extends through the bore  78  and the semi-spherical recess  80 . A self-breaking and self-aligning nut  84  is threadably engaged on the pin  82  to couple the same to the base projection  76  of the body  60 . A series of axially extending splines  77  are circumferentially distributed on an enlarged tapering portion of the pin  82  to mate with corresponding splines (not shown) formed on the side wall of the bore  78  in order to prevent the pin  82  from rotating about a longitudinal axis thereof relative to the base projection  76 . The pin  82  is provided at one end thereof with a ball formation  86  adapted to be received in a socket  88  defined in the head of each pedicle screw  20 , as explained hereinbefore with respect to the clamp collar  22 . The ball formation  86  is retained captive in the socket  88  by means of a hollow retaining cap  90  similar to the retaining cap  50  illustrated in FIG.  2 . The ball formation  86 , the socket  88  and the retaining cap  90  form a ball and socket joint allowing the associated pedicle screw  20  to move in three degrees of freedom relative to the pin  82  and, thus, the body  60  of the mobile carrier  18   a ,  18   b.    
     The body  60  is adapted to be mounted on rods  12  or  14  with the rod slidably received in the through bore  68  of the roller  66  and extending outwardly of the body  60  through the registered slots  62  thereof. Accordingly, the mobile carriers  18   a  and  18   b  can slide along the associated rods  12  and  14  and pivot relative thereto in a plane parallel to the sagittal plane of the spinal column S. The pivotal movement of the body  60  of each mobile carrier  18   a ,  18   b  relative to the rods  12  and  14  is limited by the spinal mobility. 
     The mobile carriers  18   a  have two degrees of freedom relative to the rod  12  and, likewise, the mobile carriers  18   b  have two degrees of freedom relative to the rod  14 . The tilting capability of the mobile carriers  18   a  and  18   b  relative to the rods  12  and  14  along with the freedom of movements of the pedicle screws  20  relative to the body  60  of the mobile carriers  18   a  and  18   b  provide the required flexibility to ensure the translational mobility of the mobile carriers  18   a  and  18   b  along the rods  12  and  14 . It is important that the mobile carriers  18   a  and  18   b  remain slidable on the rods  12  and  14  in order to permit spinal growth and some of the natural movement of the vertebrae and disc. The above described distribution of the degrees of freedom between the mobile carriers  18   a  and  18   b  and the rods  12  and  14 , and the mobile carriers  18   a  and  18   b  and the pedicle screws  20  ensures that the mobile carriers  18   a  and  18   b  will not become locked against translational movement along the rods  12  and  14  once installed thereon. 
     As seen in FIG. 1, optional stoppers  92  can be fixedly secured to the ends of the rods  12  and  14  to prevent the mobile carriers  18   a  and  18   b  from sliding off the rods  12  and  14 . An optional cross-link  94  can be installed between the rods  12  and  14  to prevent the same from pivoting apart, while allowing any other possible relative movements therebetween. 
     As seen in FIG. 4, the cross-link  94  includes a first segment  96  having a proximal end defining a socket  98  for receiving a ball  100  integrally formed at a proximal end of a second segment  102 . The ball  100  is freely rotatable in all directions within the socket  98 , thereby providing an articulation between the first and second segments  96  and  102 . 
     Rod engaging members  104   a  and  104   b  are provided at respective distal ends of the first and second segments  96  and  102 . According to the illustrated embodiment, the rod engaging member  104   a  and  104   b  are provided in the form of hooks  106   a  and  106   b  having respective tubular projections  108   a  and  108   b  extending from one end thereof for selectively receiving a locking bolt  110  or a sliding bolt  112  depending whether it is desired to fixedly secure or slidably mount the cross-link  94  to the rods  12  and  14 . For illustration purposes, the hook  106   a  is used in connection with a locking bolt  110 , whereas the hook  106   b  is used in connection with a sliding bolt  112 . In practice either a pair of sliding bolts  112  or a pair of locking bolts  110  could be simultaneously used or a combination of the two. 
     As seen in FIG. 4, the locking bolt  110  is threadably engaged within a threaded bore  114   a  defined in one end of the hook  106   a  opposite the tubular projection  108   a  thereof so as to wedge the rod  12  and lock the cross-link  94  in position thereon. Similarly, the sliding bolt  112  extends through the tubular projection  108   b  of the hook  106   b  to threadably engage a threaded bore  114   b  defined in the end of the hook  106   b  opposite the tubular projection  108   b . However, the sliding bolt  112  only closes the mouth of the hook  106   b  without engaging the rod  14 , thereby allowing the cross-link  94  to slide thereon. 
     A bushing  116  is fitted in the tubular projection  108   a  of the hook  106   a  about the locking bolt  110 . Likewise, a bushing  118  is fitted in the tubular projection  108   b  of the hook  106   b  about the sliding bolt  112 . 
     The mobile dynamic implantable instrumentation system  10  thus provides an implant which is adapted to be used without bone grafts and fusion, thereby preserving growth potential of the spinal column and bone as well as some of the natural mobility of the vertebrae and the disc thereof. 
     It is pointed out that according to a further embodiment of the present invention, the number of degrees of freedom between the pedicle screws  20  and the associated brackets  16   a  and  16   b  and the associated mobile carriers  18   a  and  18   b  could be limited to two. 
     As an alternative to the pedicle screws  20 , a transverse process hook  120  (see FIG. 5) can be articulately mounted to each of the fixed brackets  16   a ,  16   b  and the mobile carriers  18   a  and  18   b . The process hook  120  includes a pin  122  (similar to pin  30 ) having a ball formation  123  at one end thereof. The ball formation  123  is adapted to be trapped in a socket  124  defined in a cylindrical head portion  126  of a fixed arcuate gripping arm  128 , thereby allowing limited relative movement between the pin  122  and the gripping arm  128 . A cap  127  is threadably engaged on the head portion  126  to retain the ball formation  123  in the socket  124 . A mobile gripping arm  130  is pivotally mounted to the fixed gripping arm  128  by means of a pivot pin  132  extending in a normal direction relative to the plane of the fixed gripping arm  128 . A locking ring  134  is adapted to be threadably engaged on the cylindrical head portion  126  to push, via an integral depending tongue  136 , on the mobile gripping arm  130  so as to cause the same to pivot towards the fixed gripping arm  128 . In this way, the gripping arms  128  and  130  can be closed about a selected transverse process of a vertebrae in order to anchor an implantable spinal rod on one side of a spinal column. The opening of the gripping arms  128  and  130  is prevented from opening by the presence of the depending tongue  136  which acts as a stopper. A number of longitudinally extending bendable tabs  138  are distributed along an upper portion of the locking ring  134 . Loosening of the locking ring  134  on the head portion  126  can be prevented by pressing a pair of diametrically opposed tabs  138  inwardly against corresponding diametrically opposed flattened portions  140  defined on the periphery of the cap  127 . The threads of the cap  127  and the threads of the locking ring  134  are preferably opposite to prevent the latter from unlocking in the event that the cap  127  becomes loose on the head portion  126 . 
     The process hook  120  can be readily installed on a fixed bracket  16   a ,  16   b  or a mobile carrier  18   a ,  18   b  by threadably engaging a nut, similar to nut  40 , on the upper threaded portion of the pin  122 , as described with respect to the pedicle screws  20  illustrated in FIGS. 2 and 3.