Polyaxial adjustment of facet joint prostheses

Abstract

Prostheses, systems, and methods are provided for replacement of natural facet joints between adjacent vertebrae using polyaxial attachment mechanisms for securing the prostheses to the vertebrae. A cephalad prosthesis attached to a superior adjacent vertebra replaces the inferior half of a natural facet joint. A caudal prosthesis attached to an inferior adjacent vertebra replaces the superior half of a natural facet joint. Both the cephalad and caudal prostheses are configured with artificial facet joint structures that include articulating surfaces that cooperate and form an artificial articular configuration. The polyaxial attachment mechanism permits adjustment of the position of the artificial facet joint structure along more than one axis at or after the time the cephalad or caudal prosthesis is attached to a vertebra.

1 . A facet joint prosthesis comprising an artificial facet joint element connected to a fixation element by a polyaxially adjustable connection.  
   
   
       2 . The facet joint prosthesis of  claim 1  wherein the polyaxially adjustable connection is adapted and configured to permit the artificial facet joint element to be rotated with respect to the fixation element around more than one axis.  
   
   
       3 . The facet joint prosthesis of  claim 2  wherein the polyaxially adjustable connection is further adapted and configured to permit the position of the artificial facet joint element to be continuously adjustable within an adjustability range with respect to the fixation element.  
   
   
       4 . The facet joint prosthesis of  claim 2  wherein the polyaxially adjustable connection comprises a limit stop.  
   
   
       5 . The facet joint prosthesis of  claim 1  wherein the artificial facet joint element is adapted to be movable medially with respect to the fixation element.  
   
   
       6 . The facet joint prosthesis of  claim 1  wherein the artificial facet joint lement is adapted to be movable laterally with respect to the fixation element.  
   
   
       7 . The facet joint prosthesis of  claim 1  wherein the artificial facet joint element is adapted to be movable superiorly with respect to the fixation element.  
   
   
       8 . The facet joint prosthesis of  claim 1  wherein the artificial facet joint element is adapted to be movable inferiorly with respect to the fixation element.  
   
   
       9 . The facet joint prosthesis of  claim 1  wherein the polyaxially adjustable connection is adapted and configured to permit the artificial facet joint element to be moved with respect to the fixation element after installation of the facet joint prosthesis in a patient.  
   
   
       10 . The facet joint prosthesis of  claim 1  further comprising a fastener adapted and configured to prevent movement between the artificial facet joint element and the fixation element.  
   
   
       11 . The facet joint prosthesis of  claim 1  wherein the artificial facet joint element comprises a cephalad facet joint bearing surface and a cephalad facet joint bearing surface support.  
   
   
       12 . The facet joint prosthesis of  claim 11  wherein the cephalad facet joint bearing surface and the cephalad facet joint bearing surface support are adapted and configured to be disposed laterally from a midline of a vertebra when the facet joint prosthesis is installed in a patient.  
   
   
       13 . The facet joint prosthesis of  claim 11  wherein the cephalad facet joint bearing surface and the cephalad facet joint bearing surface support are adapted and configured to be disposed approximately at a midline of a vertebra when the facet joint prosthesis is installed in a patient.  
   
   
       14 . The facet joint prosthesis of  claim 1  wherein the artificial facet joint element comprises a caudal facet joint bearing surface and a caudal facet joint bearing surface support.  
   
   
       15 . The facet joint prosthesis of  claim 14  wherein the caudal facet joint bearing surface and the caudal facet joint bearing surface support are adapted and configured to be disposed laterally from a midline of a vertebra when the facet joint prosthesis is installed in a patient.  
   
   
       16 . The facet joint prosthesis of  claim 1  further comprising a longitudinally adjustable connection between the artificial facet joint element and the fixation element.  
   
   
       17 . The facet joint prosthesis of  claim 16  wherein the artificial facet joint element comprises a facet joint bearing surface and a facet joint bearing surface support, the facet joint bearing surface support being adapted and configured to be longitudinally movable with respect to the fixation element.  
   
   
       18 . The facet joint prosthesis of  claim 17  further comprising a fastener adapted and configured to prevent relative movement between the facet joint bearing surface support and the fixation element.  
   
   
       19 . The facet joint prosthesis of  claim 17  wherein the facet joint bearing surface support is further adapted and configured to be rotatable about a support longitudinal axis.  
   
   
       20 . The facet joint prosthesis of  claim 1  wherein the polyaxially adjustable connection comprises a facet joint element connection surface and a fixation element connection surface, the facet joint element connection surface and fixation element connection surface being adapted and configured to be movable with respect to each other.  
   
   
       21 . The facet joint prosthesis of  claim 1  wherein the polyaxially adjustable connection comprises a base member attached to the artificial facet joint element and movable with respect to the fixation element.  
   
   
       22 . The facet joint prosthesis of  claim 21  wherein the base member is further adapted and configured to be movable with respect to the artificial facet joint element.  
   
   
       23 . A facet joint prosthesis comprising: 
 first and second artificial facet joint elements;    a fixation element; and    a polyaxially adjustable connection between at least one of the first or second facet joint elements and the fixation element.    
   
   
       24 . The facet joint prosthesis of  claim 23  wherein the first artificial facet joint element comprises an artificial cephalad facet joint element and the second artificial facet joint element comprises an artificial caudal facet joint element.  
   
   
       25 . The facet joint prosthesis of  claim 24  wherein the fixation element comprises a cephalad fixation element and the polyaxially adjustable connection comprises a cephalad polyaxially adjustable connection, the facet joint prosthesis further comprising a caudal fixation element and a caudal polyaxially adjustable connection between the artificial caudal facet joint bearing element and the caudal fixation element.  
   
   
       26 . The facet joint prosthesis of  claim 25  wherein the artificial cephalad facet joint element comprises a cephalad bearing surface and a cephalad bearing surface support.  
   
   
       27 . The facet joint prosthesis of  claim 25  wherein the artificial caudal facet joint element comprises a caudal bearing surface and a caudal bearing surface support.  
   
   
       28 . The facet joint prosthesis of  claim 23  wherein the first and second artificial facet joint elements comprise first and second artificial cephalad facet joint elements, respectively.  
   
   
       29 . The facet joint prosthesis of  claim 28  wherein the fixation element comprises a first cephalad fixation element and the polyaxially adjustable connection comprises a first cephalad polyaxially adjustable connection, the facet joint prosthesis further comprising a second cephalad fixation element and a second cephalad polyaxially adjustable connection between the second artificial cephalad facet joint element and the second cephalad fixation element.  
   
   
       30 . The facet joint prosthesis of  claim 28  wherein the first and second artificial cephalad facet joint elements comprise first and second cephalad bearing surfaces, respectively.  
   
   
       31 . The facet joint prosthesis of  claim 28  wherein the first and second artificial facet joint elements comprise first and second support arms, respectively, and at least one cephalad bearing surface supported by at least one of the first and second support arms.  
   
   
       32 . The facet joint prosthesis of  claim 31  wherein the cephalad bearing surface is disposed approximately at a midline of a vertebra when the prosthesis is installed in a patient.  
   
   
       33 . The facet joint prosthesis of  claim 32  wherein the cephalad bearing surface is adapted to rotate about the support arm or arms by which it is supported.  
   
   
       34 . The facet joint prosthesis of  claim 32  further comprising an artificial caudal facet joint element comprising a caudal bearing surface adapted and configured to mate with the cephalad bearing surface.  
   
   
       35 . The facet joint prosthesis of  claim 34  wherein the polyaxially adjustable connection is adapted and configured to permit at least one of the artificial facet joint elements to be rotated with respect to the fixation element around more than one axis.  
   
   
       36 . The facet joint prosthesis of  claim 35  wherein the polyaxially adjustable connection is further adapted and configured to permit the position of at least one of the artificial facet joint elements to be continuously adjustable within an adjustability range with respect to the fixation element.  
   
   
       37 . The facet joint prosthesis of  claim 35  wherein the polyaxially adjustable connection comprises a limit stop.  
   
   
       38 . The facet joint prosthesis of  claim 23  wherein the polyaxially adjustable connection is adapted and configured to permit at least one of the artificial facet joint elements to be moved with respect to the fixation element after installation of the facet joint prosthesis in a patient.  
   
   
       39 . The facet joint prosthesis of  claim 23  further comprising a fastener adapted and configured to prevent relative movement between at least one of the artificial facet joint elements and the fixation element.  
   
   
       40 . The facet joint prosthesis of  claim 23  further comprising a longitudinally adjustable connection between at least one of the artificial facet joint elements and the fixation element.  
   
   
       41 . The facet joint prosthesis of  claim 40  wherein at least one of the artificial facet joint elements comprises a facet joint bearing surface and a facet joint bearing surface support, the facet joint bearing surface support being adapted and configured to be longitudinally movable with respect to the fixation element.  
   
   
       42 . The facet joint prosthesis of  claim 41  further comprising a fastener adapted and configured to prevent relative movement between the facet joint bearing surface support and the fixation element.  
   
   
       43 . The facet joint prosthesis of  claim 41  wherein the facet joint bearing surface support is further adapted and configured to be rotatable about a support longitudinal axis.  
   
   
       44 . The facet joint prosthesis of  claim 23  wherein the polyaxially adjustable connection comprises a facet joint element connection surface and a fixation element connection surface, the facet joint element connection surface and fixation element connection surface being adapted and configured to be movable with respect to each other.  
   
   
       45 . The facet joint prosthesis of  claim 23  wherein the polyaxially adjustable connection comprises a base member attached to at least one of the artificial facet joint elements and movable with respect to the fixation element.  
   
   
       46 . The facet joint prosthesis of  claim 45  wherein the base member is further adapted and configured to be movable with respect to at least one of the artificial facet joint elements.  
   
   
       47 . A facet joint prosthesis comprising: 
 first and second fixation elements;    an artificial facet joint bearing surface adapted and configured to be disposed approximately at a midline of a vertebra when the facet joint prosthesis is installed in a patient; and    first and second polyaxially adjustable connections between the facet joint bearing surface and the first and second fixation elements, respectively.    
   
   
       48 . The facet joint prosthesis of  claim 47  wherein the first and second polyaxially adjustable connections are each adapted and configured to permit the first and second fixation elements to be rotated with respect to the artificial facet joint bearing surface around more than one axis.  
   
   
       49 . The facet joint prosthesis of  claim 47  further comprising first and second fasteners adapted and configured to prevent relative movement between the artificial facet joint bearing surface and the first and second fixation elements, respectively.  
   
   
       50 . The facet joint prosthesis of  claim 47  further comprising first and second longitudinally adjustable connections between the artificial facet joint bearing surface and the first and second fixation elements, respectively.  
   
   
       51 . The facet joint prosthesis of  claim 50  further comprising a first support arm disposed between the first fixation element and the artificial facet joint bearing surface and a second support arm disposed between the second fixation element and the artificial facet joint bearing surface, the first and second support arms each being adapted and configured to support the artificial facet joint bearing surface and to be longitudinally movable with respect to the first and second fixation elements, respectively.  
   
   
       52 . The facet joint prosthesis of  claim 51  further comprising first and second fasteners each adapted and configured to prevent relative movement between the facet joint bearing surface support and the fixation element.  
   
   
       53 . The facet joint prosthesis of  claim 51  wherein the first support arm is further adapted and configured to be rotatable about a first support arm longitudinal axis and the second support arm is further adapted and configured to be rotatable about a second support arm longitudinal axis.  
   
   
       54 . The facet joint prosthesis of  claim 51  wherein the first and second support arms comprise two separate pieces.  
   
   
       55 . The facet joint prosthesis of  claim 51  wherein the first and second support arms comprise one integral piece.  
   
   
       56 . The facet joint prosthesis of  claim 47  wherein the artificial facet joint bearing surface is adapted and configured to be a cephalad facet joint bearing surface.  
   
   
       57 . The facet joint prosthesis of  claim 47  further comprising third and fourth polyaxially adjustable connections between the facet joint bearing surface and the first and second fixation elements, respectively.  
   
   
       58 . A facet joint prosthesis comprising: 
 an artificial facet joint bearing surface supported by first and second support arms adapted and configured to dispose the artificial facet joint bearing surface approximately at a midline of a vertebra when the facet joint prosthesis is installed in a patient; and    first and second fixation elements adapted and configured to attach the first and second support arms, respectively, to a vertebra.    
   
   
       59 . The facet joint prosthesis of  claim 58  wherein the first and second support arms and the artificial facet joint bearing surface comprise one integral piece.  
   
   
       60 . The facet joint prosthesis of  claim 58  further comprising first and second polyaxially adjustable connections between the first and second arms and the first and second fixation elements, respectively.  
   
   
       61 . The facet joint prosthesis of  claim 60  further comprising third and fourth polyaxially adjustable connections between the facet joint bearing surface and the first and second fixation elements, respectively.  
   
   
       62 . A method of installing an artificial facet joint prosthesis, the prosthesis comprising a facet joint element and a fixation element, the method comprising: 
 attaching the prosthesis to a vertebra with the fixation element; and    adjusting positions of the facet joint element and the fixation element to a relative orientation.    
   
   
       63 . The method of  claim 62  wherein the adjusting step comprises moving the facet joint element medially with respect to the fixation element.  
   
   
       64 . The method of  claim 62  wherein the adjusting step comprises moving the facet joint element laterally with respect to the fixation element.  
   
   
       65 . The method of  claim 62  wherein the adjusting step comprises moving the facet joint element superiorly with respect to the fixation element.  
   
   
       66 . The method of  claim 62  wherein the adjusting step comprises moving the facet joint element inferiorly with respect to the fixation element.  
   
   
       67 . The method of  claim 62  wherein the attaching step is performed prior to the adjusting step.  
   
   
       68 . The method of  claim 62  wherein the attaching step is performed after the adjusting step.  
   
   
       69 . The method of  claim 62  wherein the adjusting step comprises rotating the facet joint element with respect to the fixation element around more than one axis.  
   
   
       70 . The method of  claim 69  further comprising preventing further rotation of the facet joint element after the rotating step.  
   
   
       71 . The method of  claim 62  wherein the facet joint element comprises a facet joint bearing surface, the adjusting step comprising positioning the facet joint bearing surface laterally from a vertebra midline.  
   
   
       72 . The method of  claim 62  wherein the facet joint element comprises a facet joint bearing surface, the adjusting step comprising positioning the facet joint bearing surface approximately at a vertebra midline.  
   
   
       73 . The method of  claim 62  wherein the facet joint element comprises a facet joint bearing surface, the adjusting step comprising positioning the facet joint bearing surface to face caudad.  
   
   
       74 . The method of  claim 62  wherein the facet joint element comprises a facet joint bearing surface, the adjusting step comprising positioning the facet joint bearing surface to face cephalad.  
   
   
       75 . The method of  claim 62  wherein the adjusting step comprises moving the facet joint element longitudinally with respect to the fixation element.  
   
   
       76 . The method of  claim 75  further comprising preventing further longitudinal movement of the facet joint element after the moving step.  
   
   
       77 . The method of  claim 75  wherein the adjusting step further comprises rotating the facet joint element about a facet joint element longitudinal axis.