Posterior spinal arthroplasty-development of a new posteriorly inserted artificial disc and an artificial facet joint

Abstract

Lumbar disc and facet joint replacement prosthesis are provided. The lumbar disc prosthesis includes first member having a vertebral disc contact surface and a recessed portion on an opposing surface thereof and a second member having a vertebral disc contact surface and a protruding portion on an opposing surface thereof. The protruding portion of the second member engages the recessed portion of the first member in use. The first and second members are provided with at least a middle section and two end sections. The recessed and protruding portions are provided in the middle section of the respective members and each end section has a narrowing taper. The facet joint prosthesis includes a first member for attachment to a first posterior lumbar disc and a second member for attachment to a second posterior lumbar disc. At least a part of the first member is telescopically mounted in at least a part of the second member.

1 . A lumbar disc prosthesis, said lumbar disc prosthesis including a pair of disc members, a first member of said disc pair having a vertebral endplate contact surface and a recessed portion on an opposing surface thereof, a second member of said disc pair having a vertebral endplate contact surface and a protruding portion on an opposing surface thereof, the protruding portion of the second member engaging in the recessed portion of the first member in use, and wherein the prosthesis includes a further pair of disc members, said further pair of disc members also including first and second members.  
   
   
       2 . A prosthesis according to  claim 1  wherein the two pairs of disc member are mirror images of each other.  
   
   
       3 . A prosthesis according to  claim 1  wherein the pairs of disc members are inserted via a posterior route into a disc space in the patient.  
   
   
       4 . A prosthesis according to  claim 1  wherein each pair of disc members is independently inserted into the disc space in the patient and is located on either side of the dural sac.  
   
   
       5 . A prosthesis according to  claim 1  wherein the recessed portion of the first member is substantially curved and the curvature of a medial part of said recessed portion is asymmetrical to the curvature of a lateral part of said recessed portion.  
   
   
       6 . A prosthesis according to  claim 5  wherein the lateral part of said recessed portion corresponds to an arc of a circle which has a radius greater than that of an arc of a circle corresponding to the curvature of the medial half of the recessed portion.  
   
   
       7 . A prosthesis according to  claim 1  wherein an anterior part of the recessed portion is substantially symmetrical to a posterior part of the recessed portion.  
   
   
       8 . A prosthesis according to  claim 1  wherein the recessed and protrusion portions in each disc member pair are asymmetrical.  
   
   
       9 . A prosthesis according to  claim 1  wherein the protrusion portion in a disc member pair makes contact with only a part of the recessed portion of said disc member pair.  
   
   
       10 . A prosthesis according to  claim 1  wherein the protrusion portion is symmetrical in the medial-lateral plane and the anterior-posterior plane but the curvature in the medial to lateral plane may be different to that in the anterior to posterior plane.  
   
   
       11 . A prosthesis according to  claim 1  wherein one or both ends of each prosthesis pair have a narrowing taper towards said end or ends.  
   
   
       12 . A prosthesis according to  claim 1  wherein the vertebral endplate contact surfaces at one or both ends of said first and/or second member is provided at an acute angle to the horizontal such that the surfaces slopes towards the ends of the disc member(s).  
   
   
       13 . A prosthesis according to  claim 12  wherein the angled surface or surfaces are substantially planar in form.  
   
   
       14 . A prosthesis according to  claim 12  wherein with the vertebral endplate contact surfaces provided at an angle at both ends of said first and/or second member, the angle of the surface towards an anterior end is in an opposite direction to the angle of the surface towards a posterior end.  
   
   
       15 . A prosthesis according to  claim 14  wherein the anterior end angled surface is substantially smaller in dimensions that the posterior end angled surface.  
   
   
       16 . A prosthesis according to  claim 1  wherein the vertebral endplate contact surface of the first and/or second disc members are provided with attachment means thereon to allow attachment of the disc members to an adjacent vertebra in use.  
   
   
       17 . A prosthesis according to  claim 16  wherein the attachment means includes one or more apertures thereon for the location of screws or other attachment devices therewith.  
   
   
       18 . A prosthesis according to  claim 16  wherein the attachment means are provided adjacent a posterior end of the first and/or second disc members.  
   
   
       19 . A prosthesis according to  claim 16  wherein the attachment means includes one or more tapered members protruding outwardly of the vertebral endplate contact surface, the taper of said member narrowing from a posterior end towards an anterior end of the disc member.  
   
   
       20 . A prosthesis according to  claim 16  wherein the attachment means are provided towards a medial side of the first and/or second disc members.  
   
   
       21 . A prosthesis according to  claim 1  wherein the inner or opposing surfaces of the first and/or second members in a disc pair are divided into at least three sections; a middle section and at least two end sections, the recessed and protruding portions being provided in the middle section of the respective disc members.  
   
   
       22 . A prosthesis according to  claim 21  wherein the depth of the first disc member is less adjacent the middle section or recessed portion compared to the two end sections thereof.  
   
   
       23 . A prosthesis according to  claim 21  wherein the boundaries of the middle and end sections are arranged in the medial to lateral plane of each disc member.  
   
   
       24 . A prosthesis according to  claim 21  wherein the middle section is located substantially centrally of said first and/or second disc members.  
   
   
       25 . A prosthesis according to  claim 21  wherein the middle and end sections each comprise at least one third of a disc member surface.  
   
   
       26 . A prosthesis according to  claim 21  wherein one or both end sections of the opposing surfaces of the first and/or second disc members are provided at an acute angle to the horizontal.  
   
   
       27 . A prosthesis according to  claim 26  wherein the angled surface of one or both end sections of said first and/or second disc members are substantially planar in form.  
   
   
       28 . A prosthesis according to  claim 16  wherein the end sections of the opposing surface of said first disc member are mildly concave in form.  
   
   
       29 . A prosthesis according to  claim 16  wherein when one of the disc members moves towards an end of the prosthesis in extension or flexion, a gap between the end sections of the disc members increases at an opposite end of the prosthesis.  
   
   
       30 . A prosthesis according to  claim 1  wherein the vertebral endplate contact surface and opposing surface of said second disc member form a narrowing taper towards one or both ends of said disc member.  
   
   
       31 . A prosthesis according to  claim 1  wherein the vertebral end plate contact surface and opposing surface of said first disc member form a narrowing taper towards one or both ends of said disc member.  
   
   
       32 . A prosthesis according to  claim 1  wherein the protrusion portion extends across substantially the whole of the second disc member in the medial to lateral plane.  
   
   
       33 . A prosthesis according to  claim 1  wherein the lateral side of the first and/or second disc members has one or more curved sections whereas the medial side of the first and/or second disc members is substantially straight or planar.  
   
   
       34 . A prosthesis according to  claim 1  wherein one or more apertures are provided at or adjacent the posterior end of the disc members.  
   
   
       35 . A prosthesis according to  claim 1  wherein said prosthesis is used in conjunction with a facet joint prosthesis.  
   
   
       36 . A facet joint prosthesis according to  claim 35  wherein a first member is provided for attachment to a first posterior lumbar disc in use and a second member is provided for attachment to a second posterior lumbar disc in use, and wherein at least a part of said first member is telescopically mounted in at least a part of said second member in use.  
   
   
       37 . A facet joint prosthesis according to  claim 36  wherein the first and/or second members are provided with or are associated with securing means for securing the members to a disc in use.  
   
   
       38 . A facet joint prosthesis according to  claim 37  wherein the securing means includes one or more pedicle screws.  
   
   
       39 . A facet joint prosthesis according to  claim 36  wherein the first member includes an elongate arm portion which is movably located in an elongate channel portion on said second member.  
   
   
       40 . A facet joint prosthesis according to  claim 39  wherein the arm portion and said channel portion are curved in form.  
   
   
       41 . A facet joint prosthesis according to  claim 39  wherein each of said arm portion and said channel portion communicate with a plate portion.  
   
   
       42 . A facet joint prosthesis according to  claim 36  wherein a slot is provided longitudinally of said channel portion.  
   
   
       43 . A facet joint prosthesis according to  claim 42  wherein said slot is of such a width to allow approximately 30% of the arm portion to be visible therethrough.  
   
   
       44 . A facet joint prosthesis according to  claim 36  wherein the arm portion is of slightly smaller dimensions than the interior dimensions of said channel portion, such that a small gap is provided therebetween to allow some movement between said arm portion and said channel portion.  
   
   
       45 . A facet joint prosthesis according to  claim 36  wherein with the arm portion located in the channel portion, the arm portion can undergo limited rotation, side ways movement and sliding movement to allow flexion and extension with respect to said channel portion.  
   
   
       46 . A facet joint prosthesis according to  claim 36  wherein the end of the arm portion engaging in said channel portion has curved end walls and curved side walls, the curvature of said side walls being less than the curvature of said end walls.  
   
   
       47 . A facet joint prosthesis according to  claim 36  wherein the open end of the channel portion in which the arm portion engages has curved end walls and curved side walls, the curvature of said side walls being less than the curvature of said end walls.  
   
   
       48 . A facet joint prosthesis according to  claim 35  wherein a pair of facet joint prosthesis are used for each disc.  
   
   
       49 . A facet joint prosthesis according to  claim 36  wherein a plurality of first members can be attached to a second member and vice versa to form stacking of said prosthesis.  
   
   
       50 . A prosthesis system, said system including a lumbar disc prosthesis and facet joint prosthesis as defined in  claim 1 .  
   
   
       51 . A first disc member for use with a lumbar disc prosthesis according to  claim 1 .  
   
   
       52 . A second disc member for use with a lumbar disc prosthesis according to  claim 1 .  
   
   
       53 . A facet joint prosthesis, said facet joint prosthesis including a first member for attachment to a first posterior lumbar disc in use and a second member for attachment to a second posterior lumbar disc in use, and wherein at least a part of said first member is telescopically mounted in at least a part of said second member in use.  
   
   
       54 . A prosthesis system, said system including a lumbar disc prosthesis and facet joint prosthesis as defined in  claim 53 .  
   
   
       55 . A method of attachment of a lumbar disc prosthesis in a patient, said lumbar disc prosthesis including a pair of disc members, a first member of said disc pair having a vertebral endplate contact surface and a recessed portion on an opposing surface thereof, a second member of said disc pair having a vertebral endplate contact surface and a protruding portion on an opposing surface thereof, the protruding portion of the second member engaging in the recessed portion of the first member in use, the prosthesis including a further pair of disc members, said further pair of disc members also including first and second members, said method including the steps inserting each pair of disc members via a posterior route.  
   
   
       56 . A method of attachment of a facet joint prosthesis in a patient, said facet joint prosthesis including a first member and a second member, at least a part of said first member is telescopically mounted in at least a part of said second member in use, said method including attaching a part of said first member to one of an upper or lower vertebrae in use posteriorly and attaching a part of said second member to the other of said upper or lower vertebrae in use posteriorly.