Patent Publication Number: US-RE49138-E

Title: Ratcheted spinal devices

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to spinal implants and prostheses, and particularly to spinal implants having ratchet mechanisms, such as a spinal implant with joints that permit movement in different degrees of freedom, or a spinal implant with a force applicator to control a ratchet mechanism. 
     BACKGROUND OF THE INVENTION 
     Scoliosis is a spinal deformity affecting many people. Current surgical treatment involves affixing long fusion rods to the spine by pedicle screws. The rod system is intended to force the deformed spine into a more healthy position. Other spinal disorders which are often treated by fusion include hyperkyphosis and hyperlordosis. 
     As an alternative to fusion, PCT Patent Application PCT/US2011/035278 of the same inventor describes improved spinal devices that can be lengthened or shortened using a ratchet mechanism. The devices have a variable-length member that can be connected to standard pedicle screws as well as to other spinal rods, using appropriate connectors. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide further improved spinal devices. 
     In one embodiment, the spinal device is in the form of a spinal rod (the term rod, or rod assembly, refers to one or more elongate components that together function as a rod and which do not necessarily have a cylindrical shape but can also be bars and other shapes) that can be lengthened or shortened using a ratchet mechanism. The rod is a variable-length member that can be connected to standard pedicle screws as well as to other spinal rods, using appropriate connectors. The variable-length member can also be directly connected to, or be supported by, bony elements of the spine. 
     In one embodiment of the invention, the device can be set to three different configurations: 
     a. Ratchet mechanism active and the variable-length member (rod) can change in length (extend or contract) in one direction. 
     b. Ratchet mechanism not active and the variable-length member can move in opposite directions corresponding to the extending and contracting directions. 
     c. Locked position, wherein the length of the variable-length member is fixed. 
     In an embodiment of the invention, the selection of these configurations can be done by rotating an internal element of the assembly. For example, the rotation of the internal element can be done using a worm gear mechanism. The worm gear can be activated by a shaft, through a percutaneous procedure or by an implantable mechanism such as an electric motor, magnet arrangement or other means known to those skilled in the art. 
     In another embodiment of the present invention, the variable-length member can have two portions with different rigidity. For example, the variable-length member can have a flexible portion (e.g., when the ratchet is built such that the rod can be only shortened) like a flexible cable, a rope, a flexible mechanical joint and other means known to those skilled in the art. 
     In another embodiment of the invention, useful when the rod is supported directly by bone structure of the spine, the hook holding against the bone can have a second hook to fix it to the optimal position. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
         FIG. 1  is a simplified pictorial illustration of a ratcheted spinal device, constructed and operative in accordance with a non-limiting embodiment of the invention; 
         FIG. 2  is a simplified pictorial illustration of a ratchet mechanism of the ratcheted spinal device of  FIG. 1 ; 
         FIG. 3  is a simplified illustration of a force applicator that can adjust or advance the ratchet mechanism of the ratcheted spinal device of  FIG. 1 ; 
         FIG. 4  is a simplified pictorial illustration of a spinal device, including two rod assemblies that are connected between three vertebrae with three bone screws, constructed and operative in accordance with a non-limiting embodiment of the present invention, wherein there are connector assemblies that permit multiple degree-of-freedom movement; 
         FIG. 5  is a simplified top view illustration of one preferred embodiment of the connector assembly, in accordance with an embodiment of the present invention; 
         FIG. 6A  is a simplified cross-sectional illustration of the embodiment of  FIG. 5 ; and 
         FIG. 6B  is a simplified cross-sectional illustration of a modified version of the embodiment of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference is now made to  FIGS. 1-3 , which illustrates a ratcheted spinal device  10 , constructed and operative in accordance with another non-limiting embodiment of the invention. 
     The ratcheted spinal device  10  includes a variable-length member  12 . In the illustrated embodiment, the variable-length member  12  is a rod. The term “rod” encompasses any slender element of any size and cross-sectional shape, such as but not limited to, a rod, bar, wire and the like. 
     As similarly described in PCT Patent Application PCT/US2011/035278, spinal device  10  includes a ratchet mechanism  14  ( FIG. 2 ), which has an operative configuration that allows a change in length of variable-length member  12  in one direction and prevents a change in length of the variable-length member  12  in an opposite direction. Ratchet mechanism  14  has ratchet teeth  16  ( FIG. 3 ; also called ratchet rack  16 ) formed along an axial portion of variable-length member  12 , and a pawl  18  ( FIGS. 2-3 ) arranged to catch on one of the teeth  16 . Pawl  18  extends from a controller element  20  ( FIG. 2 ) mounted about a pivot  22  ( FIG. 2 ) and provided with an eccentric cam  24  ( FIGS. 2-3 ). Rotation of eccentric cam  24  moves pawl  18  to one of three positions: a) in ratchet engagement with teeth  16  so that variable-length member  12  can incrementally move in one direction, b) in locked engagement with teeth  16  so that variable-length member  12  cannot move at all, and c) moved out of engagement with teeth  16  so that variable-length member  12  can move in both directions freely. 
     As seen in  FIG. 1 , one end  23  of variable-length member  12  is arranged to linearly move through an aperture  28  formed in a housing  30 . Variable-length member  12  includes two polyaxial-joint attachment members  32 . Both polyaxial-joint attachment members  32  are used to attach device  10  to available bone structure of the spine. 
     In contradistinction to PCT Patent Application PCT/US2011/035278, in the present invention, spinal device  10  includes a force applicator  40  to control ratchet mechanism  14 . Force applicator  40  includes, without limitation, a cam  42  which has a tooth  44  ( FIG. 3 ). The head  46  of cam  42  is shown in  FIG. 2  (e.g., hexagonal head); head  46  is not shown for simplicity in  FIG. 3 . By turning head  46  with a suitable tool, such as a wrench (not shown), in the clockwise direction of  FIG. 3 , the tooth  44  of cam  42  forcefully moves ratchet rack  16  (upwards in the sense of  FIG. 3 ), so that the tooth in which pawl  18  is engaged moves out of engagement with pawl  18  and the next lower tooth of ratchet rack  16  moves into engagement with pawl  18 . Accordingly, force applicator  40  adjusts or advances the ratchet mechanism  14 . 
     Reference is now made to  FIG. 4 , which illustrates a spinal device  50 , in accordance with an embodiment of the present invention. 
     In the illustrated embodiment, spinal device  50  includes two rod assemblies  52  that are connected between three vertebrae  49  with three bone screws  54 . The rod assemblies  52  may be constructed, without limitation, as ratcheted spinal devices  10  or other spinal devices. Connector assemblies  56  form jointed connections between rod assemblies  52 . Connector assemblies  56  permit multiple degree-of-freedom movement of rod assemblies  52  (e.g., variable-length members  12 ), as will be explained below. 
     It is noted that any number of vertebrae can be selected, since the design of the system is modular. It is also noted that the middle jointed connection of the two rod assemblies  52  does not have to be connected to any vertebra, meaning one or more vertebrae can be skipped, depending on the application. In the drawing figure, bone screws  54  are inserted in the pedicles, but other insertion locations can be used. 
     Reference is now made to  FIGS. 5 and 6A , which illustrate one preferred embodiment of the connector assembly  56 , in accordance with an embodiment of the present invention. 
     Connector assembly  56  includes a bolt  58  (e.g., a central threaded bolt) having a head  60 , and which passes through a hole formed in a first hinge member  62  and a second hinge member  64 , which may lie on top of, or be adjacent to, first hinge member  62 . Each hinge member is formed with a receiver  66  ( FIG. 6A ) for receiving therein a pivot pin  68  ( FIG. 5 ). One of the pivot pins  68  is pivotally received in an end  70  of one of the rod assemblies  52 , and the other pivot pin  68  is pivotally received in an end  72  of another of the rod assemblies  52  ( FIG. 5 ). Thus adjacent rod assemblies  52  can pivot with respect to one another by means of connector assembly  56 . A locking element  74  (such as a nut) secures pins  68  in place ( FIG. 6A ). Another locking element  76  (such as a nut) is threaded on the end of threaded bolt  58  to complete the assembly ( FIG. 6A ). 
       FIG. 6B  illustrates a variation of the embodiment of  FIG. 6A . Like elements are designated by like numerals. The main differences are the shape of locking element  74  and the receiver  66  of the first hinge member  62  has a closed aperture instead of the open aperture of  FIG. 6A . Other variations are also possible within the scope of the invention. 
     Connector assemblies  56  permit multiple degree-of-freedom movement of rod assemblies  52 . Rotation is permissible about the longitudinal axis of central threaded bolt  58 , and independently about the longitudinal axis of each pin  68 , which are perpendicular to the longitudinal axis of central threaded bolt  58 .