the present invention describes embodiments of an expandable implantable plate that is used for stabilization of a lamina in a laminoplasty procedure wherein the plate offers controlled opening of a space within a transected lamina with integrated fixation . in preferred embodiments the plate is comprised of a first plate component slidably coupled to a second plate component . in a typical laminoplasty procedure a lamina is first completely transected near the junction of the lateral mass and then a notch , often also referred to as a hinge , is created on the contralateral side the lateral mass . in a laminoplasty procedure utilizing an expandable plate of the present invention the distal end of either the first plate component or second plate component is fixedly attached to the lamina on one side of the transection and the distal end of the other component is fixedly attached to the lamina on the opposing side of the transection . the first plate component and the second plate component are then slidably adjusted to a desired overall plate length to expand the lamina at the transection thereby creating an open space or gap . finally , the two plate components are the locked relative to one another in the desired positions . in typical embodiments , the devices have one or more bone screw receiving holes at the distal ends of the first plate component and the second plate component , which permits fixed attachment to lamina facets with standard bone screws . such bone screw receiving holes can assume any suitable shape such as round or elongate slots . the locking of the position of a first plate component relative a second plate component can be achieved by a variety of means including , but not limited to , bolts , set screws , clamps , clips and the like . in certain preferred embodiments , wherein a first plate component is slidably coupled and disposed within a pocket of a second plate component , locking is achieved by incorporation of a ratchet mechanism . such a mechanism consists of tooth - like protrusions are set any acute angle of less than 90 degrees , preferably of less than 60 degrees and more preferably less than 45 degrees , along the surface of the first plate component and are skewed toward the opening of the second plate component pocket and the second plate component comprises a prawl for engaging the tooth - like protrusions of the first plate component , wherein the tooth - like protrusions and the prawl are dimensioned and configured to permit only unidirectional relative movement of the first and second plate components when the engaging flat ( opposite face of teeth and prawl ) surfaces of the are coplanar . the ratchet mechanism as herein described is intended to be exemplary and it is understood that variations of this and other ratchet mechanisms will be apparent to one skilled the art . in certain other preferred embodiments the distal end of at least of the first and second plate components has a lamina stabilizing flange which can be positioned to be in contact with an anterior , posterior , superior and inferior surfaces of a divided lamina functioning to grip a cut edge of the lamina and aiding in positioning and securing the plate to the lamina . suitable stabilizing flanges can be configured in a variety of forms including , but not limited to , a claw - like protrusion that engages an edge of a divided lamina , a cuff that substantially surrounds a portion of a divided lamina and a cup that completely encloses the first portion of the divided lamina . suitable stabilizing flanges are those described in the published us pat . appl . us 2004 / 0030388 to null et al ., which is being included herein in its entirety by way of reference . in certain laminoplasty procedures a bone or bone generating material of either a biologic or non - biologic nature is inserted into the gap . for use in such procedures embodiments of the expandable laminoplasty plates of the present invention are provided with a recess , a graft window or similar feature to assist in placement and / or retention of such bone generating material . a suitable configuration for such a bone graft retaining recesses or windows is disclosed in u . s . pat . no . 6 , 635 , 087 to angelucci et al ., which is being included herein in its entirety by way of reference . another suitable configuration for a bone graft or bone generating material retention is the configuration of the fixed - length as newbridge ™ laminoplasty fixation system available from orthofix spinal implants , mckinney , tex . usa . a list of appropriate bone or bone generating material for use in these embodiments includes , but is not limited to allografts such as fresh bone , freshly frozen bone , freeze - dried bone allograft ( fdba ), demineralized freeze - dried bone allograft ( dfdba ), demineralized bone matrix ( dbm ) containing bone morphogenetic protein ( bmp ), ceramics , calcium phosphates such as hydroxyapatite or tricalcium phosphate and the like . in situ expansion of the embodiments of an expandable laminoplasty plate of the present invention during a laminoplasty procedure can be achieved by a variety of means including , but not limited to , manual separation of the slidably coupled first and second plate components and use of various surgical tools or instruments . in certain preferred embodiments separation of the slidably coupled first and second plate components is conveniently achieved by the use of forceps designed such that the gripping ends separate as the grasping ends are brought together . an embodiment of the invention attached to a lamina in the final position after a laminoplasty procedure is illustrated in fig1 wherein a lamina 20 has been transected near the junction of the lateral mass 21 and a hinge 22 has been created on the contralateral side . the bone fixation device 10 comprises a second plate component 11 the proximal end of which is essentially a flat plate slidably coupled within a pocket formed within the proximal end of the first plate component 12 , wherein the distal end of the second plate component 11 is fixedly attached to a facet of the lamina by a bone screw 15 while the distal end of the first plate component 12 is fixedly attached to a facet of the lamina by a bone screw 16 and the second plate component 11 is fixedly attached to a facet of the lamina by a bone screw 16 . since the second plate component 11 and first plate component 12 are slidably coupled , the length of the plate is conveniently adjusted to a desired length thereby expanding the gap 23 in the lamina 20 to a desired dimension . an optional locking means for fixing the relative positions of the second plate component 11 and first plate component 12 is depicted in fig1 as setscrew 17 . also in the embodiment illustrated in fig1 a bone allograft 24 has been inserted within the gap 23 . another embodiment of the invention is illustrated in fig2 wherein an expandable lamina fixation device 30 is depicted in a relatively closed or contracted position along with device - expanding forceps 40 . the expandable fixation device 30 comprises and second plate component 31 slidably coupled and disposed within a pocket within a first plate component 32 . in this embodiment the second plate component 31 comprises part of a ratchet mechanism in the form of tooth - like protrusions 35 set an acute angle such to be skewed toward the opening in the first plate component 32 and the first plate component 32 comprises a prawl 36 for engaging tooth - like protrusions 35 , wherein the tooth - like ratchet components 35 and the prawl 36 are dimensioned and configured to allow only unidirectional relative movement of the first plate component 31 and the second plate component 32 when the engaging flat ( opposite face of teeth and prawl ) surfaces of the elements are coplanar . an additional feature of this embodiment is the claw - like protrusion 33 positioned near the distal end of first plate component 31 and which functions to grip a cut edge of a lamina and aids in positioning and securing the device 30 to a lamina . in fig3 is illustrated the same expandable lamina fixation device depicted in fig2 , wherein the lamina fixation device 30 is in an expanded or open position along with plate - expanding forceps 40 . this illustration clearly depicts the ratchet teeth 35 disposed along a surface of first plate component 31 as well as the prawl 36 disposed within the opening second plate component 32 . fig3 also clearly depicts bone screw receiving holes 37 and 38 at the distal ends of components 32 and 31 respectively wherein the holes are sized to accept standard bone screws 39 . in use , the lengthening of the device 30 the positioning of the first plate component 31 and second plate component 32 relative to one another along the longitudinal axis effects distraction of a lamina ( i . e . expanding the space in a lamina ) to create a gap and further stabilizes the distracted lamina . another embodiment of the present invention is illustrated by fig4 depicting an expandable bone plate 50 in an expanded or open position . the plate 50 comprises a first or inner plate component 51 slidably disposed within a second or outer plate component 52 . the first plate component 51 further comprises a lamina stabilizing flange 53 in the form of a claw - like protrusion positioned near the distal end of inner component 51 and which functions to grip a cut edge of a lamina and aids in positioning and securing the bone plate 50 to the lamina . the expandable bone plate 50 also comprises screw - receiving holes 54 and 55 at the distal ends of components 52 and 51 respectively wherein the holes are sized to accept bone screws 56 . the expandable bone plate 50 also comprises a set screw 57 that functions as a locking mechanism to secure the position of inner component 51 and outer component 52 relative to one another . fig5 a , 5 b and 5 c depict an expandable bone plate assembly 60 provided with a ratchet mechanism that allows the plate to be expanded ( lengthened ) along the longitudinal axis while preventing the plate from returning too a shortened position . fig a is an orthogonal top view of a disengaged inner component 61 and outer component 62 ; fig5 b is an orthogonal side view of disengaged inner component 61 and outer component 62 ; and fig5 c is an isometric view of inner component 61 and outer component 62 when engaged . in this embodiment the inner component 61 comprises a series of linear ratchet components 65 in the form of tooth - like protrusions set an acute angle such that they are skewed toward a pocket - like opening the outer element 61 and the outer element 61 comprises a prawl 66 for engaging ratchet components 65 , wherein the ratchet components 65 and the prawl 66 are dimensioned and configured to allow only unidirectional relative movement of the inner element 61 and the outer element 62 when the engaging flat ( opposite face of teeth and prawl ) surfaces of the elements are coplanar . effectively when the engaging surfaces of the elements are coplanar which limits the plate to expansion of the length . however , in certain embodiments the ratchet mechanism is dimensioned and configured such that a ratcheted plate can be restored to a contracted or closed position by adjusting the orientation of the elements to one another . another feature of the embodiment depicted in fig5 is the lamina stabilizing flange 69 which can be positioned to be in contact with an anterior , posterior , superior and inferior surfaces of a divided lamina . round screw - receiving holes 67 and 68 are also depicted . in fig6 a is illustrated an orthogonal top view of an embodiment of an expandable bone plate 70 and in fig6 b a is illustrated cut sectional end view of the same expandable bone plate 70 , wherein an first or inner component 71 is slidably disposed in pocket within second or outer component 72 . the cut sectional view fig6 b clearly shows the inner component 71 disposed within a fully closed pocket or envelope in outer component 72 . round screw - receiving holes 73 are also depicted in fig6 a in fig7 a is illustrated an orthogonal top view of an embodiment of an expandable bone plate 80 and in fig . & amp ; b a is illustrated cut sectional end view of the same expandable bone plate 80 wherein an inner component 81 is slidably disposed within an outer component 82 and wherein the plate comprises a set - screw locking mechanism 83 . the cut sectional view 7 b clearly shows the inner component 81 disposed and maintained within a partially closed pocket or envelope in outer component 82 and wherein the inner component is locked in place with the outer component by the pressure exerted against the inner component 81 by the setscrew 83 . furthermore in this embodiment the partial opening 85 in the pocket outer component 82 provides a recess that is a suitable bone graft - engaging portion of the expandable bone plate 80 . round screw - receiving holes 84 are also depicted in fig7 a . in fig8 a is illustrated an orthogonal bottom view of an embodiment of an expandable bone plate 90 , in fig8 b an orthogonal top view of the expandable bone plate 90 and in fig8 b is illustrated cut sectional end view of the same expandable bone plate 90 wherein an inner component 92 is slidably disposed within an outer component 91 and wherein the plate comprises a set - screw locking mechanism 95 . in this embodiment the inner component 92 has a rectangular recess 94 configured to provide a bone graft - engaging portion of the expandable bone plate 90 and wherein a partial opening 93 in the pocket of the outer component 91 forms an additional rectangular recess to act as bone graft - engaging feature . it should be understood that certain features of the expandable bone plate fixation system configurations depicted in the accompanying figures are for illustrative purposes and that many variations are possible and in certain embodiments necessary . for example , there is no limitation with respect the angles formed between the ends of the plate and the major plate body which can be anywhere in the range of 0 ° to 90 ° and is chosen to conform to the geometry as dictated by the surgical procedure . materials useful for fabrication of embodiments of the implants of the present invention include any bio - compatible material having sufficient strength to maintain the open position of the divided lamina . examples of suitable materials include , but are not limited to , titanium , titanium alloys , ceramics , composites , plastic composites , peek ( polyetheretherketone ) or paek ( polyaryletherketone ) as well as bioresorbable materials such as polylactides , polyglycolides and copolymers and blends thereof . the laminoplasty plates can also be constructed of a material that is radiolucent and / or bone growth inducing . in certain specific embodiments , a particularly suitable material is the titanium alloy designated as cp ti grade 2 alloy . other embodiments of the devices and methods of the present invention will become apparent to those skilled in the art based on the description and drawings of the embodiments presented herein and the present invention is in no way limited to these embodiments .
the present invention relates to a medical implant for bone surgery , and more specifically to a vertebral fixation system with an expandable configuration . such implants are particularly useful for securing and expanding transected spinal vertebrae following laminoplasty procedures .