Abstract:
A growing rod for mounting between attachment mechanisms that are secured to anatomical structures of a patient having scoliosis. The growing rod includes an outer housing and an inner housing disposed within the outer housing. The inner housing includes a magnet assembly including a magnet having a first pole and a second pole and a gear reduction mechanism coupled to the magnet. A first rod is secured to the inner housing and a second rod is secured to the outer housing. The gear reduction mechanism reduces an output rotation of the magnet to rotate a driver that operates to move the inner housing along a longitudinal axis with respect to the outer housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present disclosure is a continuation of U.S. patent application Ser. No. 13/302,187, filed Nov. 22, 2011, entitled “Non-Fusion Scoliosis Expandable Spinal Rod,” which claims priority to which claims priority to U.S. Patent Application Ser. No. 61/416,266, filed Nov. 22, 2010, entitled “Non-Fusion Scoliosis Expandable Spinal Rod,” which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE DISCLOSURE 
       [0002]    Scoliosis is a medical condition where an individual&#39;s spine curves off of its anatomical shape, typically in an “S” or “C” shape, and may also be rotated about a vertical axis or a longitudinal axis of the spine. Scoliosis can be a particularly painful and dangerous condition for young persons including infants, juveniles and adolescents, who are not fully grown. Young persons with scoliosis may be treated in various manners depending upon age, severity of the curve and the likelihood of progression of the condition. Conventional options for scoliosis include observation, bracing and surgery. 
         [0003]    Surgery is typically indicated for juvenile scoliosis when there is a high likelihood of progression, the curve is causing significant pain and/or the curve is impacting physiological functions, such as breathing. Surgical intervention typically results in fusion of the impacted portion of the spine, which is ideally delayed until the patient is skeletally mature. However, certain severe cases of juvenile scoliosis require surgical intervention prior to skeletal maturity to prevent progression of the curve and/or to stabilize the spine. Multiple surgeries in such cases are common to gradually correct the curvature and/or modify the surgical construct to permit growth or to gradually move the curved or twisted spine. 
       SUMMARY 
       [0004]    The present disclosure relates generally to orthopedics. More specifically, the disclosure relates to a non-fusion scoliosis construct including a magnetically actuated growing rod that permits extension of the rod, growth of the construct and extension or correction of a patient&#39;s spine without significantly invasive surgical intervention. The device includes an actively expandable rod that is mounted to a patient&#39;s spine or ribs using hooks, screws and/or other fastening mechanisms to be fixed to the posterior of the patient&#39;s spine or to nearly any other portion of the patient&#39;s spine that permits correction of an undesirable spinal curvature. The system is preferably magnetically activated from outside of the patient&#39;s body utilizing a magnetic field without further surgery for expansion. 
         [0005]    In accordance with some implementations, there is provided a growing rod for mounting between attachment mechanisms that are secured to anatomical structures of a patient having scoliosis. The growing rod may include an outer housing, an inner housing disposed within the outer housing, and a magnet assembly rotably mounted within the inner housing. The magnet assembly may include a magnet having a first pole and a second pole. A gear reduction mechanism may be coupled to the magnet within the inner housing. The gear reduction mechanism reduces an output rotation of the magnet to rotate a driver that operates to move the inner housing along a longitudinal axis with respect to the outer housing. The growing rod may include an interchangeable first rod attached to the inner housing and an interchangeable second rod attached to the outer housing. 
         [0006]    In accordance with some implementations, there is provided a drive mechanism for a growing rod. The drive mechanism may include an inner housing comprising a magnet assembly including a magnet having a first pole and a second pole and a gear reduction mechanism coupled to the magnet, the gear reduction mechanism reducing an output rotation of the magnet to rotate a driver. The drive mechanism may further include an outer housing coupled to the inner housing by an engagement of the driver with the outer housing and a sliding bearing that engages the outer housing and the inner housing to prevent the inner housing from spinning freely within the outer housing. Rotation of the magnet assembly causes the gear reduction mechanism to rotate the driver to cause the inner rod to move along a longitudinal axis substantially without rotation relative to the outer housing. 
         [0007]    In accordance with yet other implementations, there is provided a growing rod that includes an outer housing and an inner housing disposed within the outer housing. The inner housing may include a magnet assembly including a magnet having a first pole and a second pole, and a gear reduction mechanism coupled to the magnet within the inner housing. A first rod is secured to the inner housing and a second rod is secured to the outer housing. The gear reduction mechanism reduces an output rotation of the magnet to rotate a driver that operates to move the inner housing along a longitudinal axis with respect to the outer housing. 
         [0008]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    The foregoing summary, as well as the following detailed description of several implementations of the device and methods of the present application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the growing rod or non-fusion scoliosis expandable spinal rod of the present application, there are shown in the drawings several implementations. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
           [0010]      FIG. 1A  illustrates a perspective view of a growing rod or non-fusion scoliosis expandable spinal rod in accordance with the present disclosure; 
           [0011]      FIG. 1B  illustrates a cross-sectional view of growing rod or non-fusion scoliosis expandable spinal rod of  FIG. 1A ; 
           [0012]      FIGS. 2A and 2B  illustrate exploded views of the growing rod or non-fusion scoliosis expandable spinal rod of  FIGS. 1A and 1B ; 
           [0013]      FIGS. 3A and 3B  illustrate an exploded view and cross-sectional view, respectively, of a magnet assembly; 
           [0014]      FIGS. 4A-4I  illustrate several views of magnetic activation of a magnet of the growing rod of  FIGS. 1A and 1B ; 
           [0015]      FIGS. 5A and 5B  illustrate a perspective view and exploded view, respectively, of a first stage planetary gearset; 
           [0016]      FIGS. 6A and 6B  illustrate a perspective view and exploded view, respectively, of a second stage planetary gearset; 
           [0017]      FIGS. 7A ,  7 B and  7 C illustrate additional details of the growing rod of  FIGS. 1A and 1B ; and 
           [0018]      FIGS. 8A ,  8 B and  8 C illustrate several views of lengthening of the growing rod of  FIGS. 1A and 1B . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower” and “upper” designate directions in the drawings to which reference is made. The words “inwardly” or “distally” and “outwardly” or “proximally” refer to directions toward and away from, respectively, the patient&#39;s body, or the geometric center of the several implementations of the non-fusion scoliosis expandable spinal rod and related parts thereof. The words, “anterior”, “posterior”, “superior,” “inferior”, “lateral” and related words and/or phrases designate preferred positions, directions and/or orientations in the human body to which reference is made and are not meant to be limiting. The terminology includes the above-listed words, derivatives thereof and words of similar import. 
         [0020]    Referring to  FIGS. 1-7 , a growing rod  100  in accordance with implementations of the present disclosure includes a first rod  102 , an outer housing  106 , an inner housing  108 , and a second rod  104 . A magnet assembly  300  and a gear reduction mechanism  124  are disposed within the inner housing  108 . As will be described below, rotation of the magnet assembly  300  drives the gear reduction mechanism  124 , which drives a threaded driver  214  within the outer housing. The rotation of the threaded driver  214  causes the inner housing to move along a longitudinal axis with respect to the outer housing, thus extending (or retracting the growing rod). 
         [0021]    With reference to  FIGS. 3A-3B , the magnet assembly  300  includes a magnet cover  302 , a magnet  110 , a cover lid  304  and a gear wheel  306 . The magnet  110  includes a pair of opposing flats  308  that receive the cover lid  304  during assembly. The magnet  110  may be made out of Neodym and may optionally include a protective epoxy layer. The protective layer may also be made from gold or silver and have a copper or nickel under layer. To assemble the magnet assembly  300 , the magnet  110  may be press fit within the magnet cover  302  and the cover lid  304  may be press fit to be received by the flats  308  to enclose the magnet cover  302 . Once the cover lid  304  is positioned, it may be welded to the magnet cover  302  to seal the magnet assembly  300 . The magnet assembly  300  may be sealed in such a manner in order to prevent any materials or liquid from contacting the magnet  110  and to provide for biocompatibility. As shown, the cover lid  304  forms a keyed slot  310  into which complementary-shaped shaft portion  312  of the gear wheel  306  is received to form the complete magnet assembly  300 . 
         [0022]    The magnet  110  can be in any shape (e.g. round, square, hexagonal, octagonal etc.) so long as it fits within the magnet cover  302 . As shown in  FIGS. 4A-4I , the magnet  110  can be formed having a hollowed center with diametric poles, can be massive with diametric poles, can have multiple diametrical poles, etc. As shown, by applying a magnetic field from an external magnet, the magnet  110  will be urged to rotate in a predetermined direction. 
         [0023]    As shown in  FIGS. 1 ,  2 ,  5  and  6 , the gear reduction mechanism  124  is provided within the inner housing  108 . The gear reduction mechanism  124  includes at least a two stage assembly of planetary gearsets. It is noted that other gear arrangements may be used, and planetary gearsets are shown as an exemplary implementation. A first stage  204 A/ 204 B is shown in  FIGS. 2B , SA and  5 B. The first stage  204 A/ 204 B includes a carrier  504  that receives, e.g., four (or other number) planet gears  502  that each rotate on a mount  500  that is press fit into the carrier  504 . A sun gear  506 , having a slotted shaft  510 , is received within a complementary slotted recess  508  formed in face the carrier. The first stage  204 A/ 204 B may be used as an input to the gear reduction mechanism  124 . 
         [0024]    In some implementations, such as shown in  FIG. 2B , more than one first stage  204 A/ 204 B may be included in the gear reduction mechanism  124  to achieve a desire reduction. In some implementations, the first stage is designed such that a plurality of first stages may be connected in series. In such an arrangement, as shown in  FIG. 7B , the planet gears of a subsequent first stage is driven by the sun gear of a preceding first stage. 
         [0025]    As shown in  FIGS. 2B ,  6 A and  6 B, a second stage  206  includes a carrier  604  that receives, e.g., four (or other number) planet  602  gears that each rotate on a mount  600  that is press fit into the carrier  604 . The number of gears in the second stage  206  is the same as the number provided in the first stage  204 A/ 204 B. The face of the carrier  604  in the second stage  206  includes a catch  612 . The catch  612  has a round base  606 , a midsection  608  having hexagonal cross-section and a circular upper section  610  separated from the midsection  608  by an annular recess  614 . The second stage  206  may be used as an output of the gear reduction mechanism  124 . 
         [0026]    Thus, the assembled gear reduction mechanism  124  may include, e.g., three stages. However, any number of sections may be provided in order to achieve a desired input reduction. For example, each stage may provide a 4× gear reduction. As such, the total reduction may be determined in accordance with the number of stages provided in the gear reduction mechanism  124 . The gear ratios may be changed according to the following relationship in Table 1: 
         [0000]                                    TABLE 1               Gear ratio   Modulus   Gear ratio total   Thread pitch   Turns for 1 mm       i   m   i 3     P   x       [—]   [—]   [—]   [mm]   [—]                   3.0   0.15   64.0   0.5   128.0                    
In accordance with the above, the gear reduction mechanism  124  may be configured such that 128 turns of gear reduction mechanism  124  extends or retracts the growing rod  100  by 1 mm. Other ratios may be used to control the rate at which the gear reduction mechanism  124  drives the growing rod  100 . Optionally or additionally, sizes of the gears within the stages may be different. For example, the stages closer to the input may be smaller, where the gears near the output are relatively larger.
 
         [0027]    To assemble the inner housing  108 , an inner bearing  201  is placed within the interior space of the inner housing  108 . The magnet assembly  300  is then pressed into the inner housing  108  such that a far end of the magnet assembly  300  is received within the inner bearing  201 . An outer bearing  202  is then placed in the inner housing  108  such that it is received by the cover lid  304  of the magnet assembly  300 . Next the first stage(s)  204 A/ 204 B are inserted such that an inner first stage receives the gear wheel  306  of the magnet assembly  300 . The gear wheel  306  of the magnet assembly  300  is a rotational input to drive the gear reduction mechanism  124 . As noted above, one or more first stages may be placed into the inner housing  108  as part of the gear reduction mechanism  124 , followed by a second stage  206  as an output. The assembly of the inner housing  108  is completed by placing a bearing shoulder  208  into the inner housing  108  that is, e.g., secured to the drive housing by pins  210 . As shown, four pins may be used to secure the bearing shoulder  208  to the inner housing  108 , but other numbers of pins may be used. The catch  612  of the second stage  206  protrudes through the bearing shoulder  208 . As a result, the magnet assembly  300  and gear reduction mechanism  124  are able to rotate freely within the inner housing  108 . 
         [0028]    With reference to  FIGS. 1B and 2A , to engage the inner housing  108  with the outer housing  106 , a bearing  212  is slide fit around the outer circumference of the inner housing  108  at a far end. An inner surface of bearing  212  mates with a ribbed outer surface of the inner housing  108  to prevent rotation of the bearing  212  around the circumference of the inner housing  108 . A threaded driver  214  having a hexagonally-shaped center hole is received and mounted to the catch  612  and secured thereto by a snap-fit locking clip  216 . An insert  218  is placed within the outer housing  106  to act as a stop. 
         [0029]    To assemble the growing rod  100 , the outer housing  106  is placed over the inner housing  108  and rotated to threadedly retract the inner housing  108  into the outer housing  106  by cooperation of an inner threaded surface of the outer housing  108  and the threaded driver  214 . The inner housing  108  is retracted into the outer housing  106  until reaching the insert  218 . As the inner housing  108  is retracted, flats  213  provided in the bearing  212  snap fit to an inner surface of the outer housing  106  to complete the assembly. Four flats may be provided with the bearing  212 . The flats serve to secure the far end of the outer housing  106  to the inner housing  108  and to counteract the moment produced by the inner housing  108  as it rotates. Thus, the flats  213  prevent the inner housing  108  from spinning freely within the outer housing  106 . 
         [0030]    Referring now to  FIGS. 1B and 2A , the first rod  102  is secured to the inner housing  108  by the threaded pins  222 A/ 222 B that engage a circumferential recess  116 . A rounded end  118  of the first rod  102  has at least one flat surface that is received by a complementary flat surface within the inner housing  108  to prevent rotation of the first rod  102  with respect to the inner housing  108 . In some implementations, the threaded pins  222 A/ 222 B are inserted into threaded holes  220  of the inner housing  108  from the inside of the inner housing  108 . Each threaded pin  222 A or  222 B includes a locking surface that engages a ledge of a respective threaded hole  220  to prevent the threaded pin from falling out of the inner housing  108 . The threaded pins  222 A/ 222 B may be screwed from the outside using an appropriate tool to secure the first rod  102  within the inner housing  108 . 
         [0031]    The second rod  104  is secured to the outer housing  106  by the threaded pins  226 A/ 226 B that engage a circumferential recess  120 . A rounded end  122  of the second rod  104  has at least one flat surface that is received by a complementary flat surface within the outer housing  106  to prevent rotation of the second rod  104  with respect to the outer housing  106 . Similar to the inner housing, the threaded pins  226 A/ 226 B used in the outer housing  106  may be inserted into the threaded  224  holes from the inside. Each threaded pin  226 A or  226 B may include a locking surface that engages a ledge of a respective threaded hole to prevent the threaded pin from falling out of the outer housing  106 . The treaded pins  226 A/ 226 B may be screwed from the outside using an appropriate tool to secure the second rod  104  within the outer housing  106 . 
         [0032]    Thus, in view of the assembly noted above the completed, assembled growing rod  100  may be exemplified by that illustrated in  FIGS. 1A and 1B . The growing rod and its components may be constructed of titanium or titanium alloys but are not so limited and may be constructed of cobalt chromium material, polymeric materials or nearly any bio-compatible material. Such materials should be relatively strong and stiff, able to take on the general size of the growing rod and its components and able to withstand normal operating conditions of the growing rod. The bearings and the insert may be constructed of a Polyether ether ketone (PEEK) material that is biocompatible and has a relatively low coefficient friction. The bearings are not limited to constructions utilizing PEEK materials and may be constructed of nearly any material that permits the associated parts to rotate (e.g., ball bearings). The outer housing  106  and the inner housing  108  may be made from any material that does not exhibit magnetic properties, in order to allow the magnetic field of the external magnet to pass there through to affect the magnet  110  within the growing rod. 
         [0033]    In some implementations, the outer surface of the growing rod  100  may be polished to substantially remove any rough surfaces to reduce the likelihood that the body will attach to the growing rod. A coating may be placed on the growing rod for a similar purpose. In yet other implementations, the magnet assembly  300  may be replaced by an electric motor that rotationally drives the gear reduction mechanism  124 . 
         [0034]    To actuate the growing rod  100  to expand within, e.g., a patient undergoing treatment, an external magnet may be used as a source of a magnetic field to cause rotation of the magnet  110 . As show in  FIG. 8 , the growing rod initially have a contracted length. Upon excitation by the external magnetic field, the magnet assembly  300  drives the gear reduction mechanism  124  to rotate the threaded driver  214 . As the threaded driver  214  rotates, the inner housing is driven outwardly by cooperation of the threaded driver  214  and the inner threaded surface of the outer housing  106  to laterally drive the inner housing  108  with respect to the outer housing  106 . 
         [0035]    It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this disclosure is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present disclosure as defined by the present description.