for ease of reference , a frame of reference identifying : upper and lower ; left and right ; and front and back ( including equivalents ) is taken relative to an installed condition with the patient standing upright , and the directions being the directions from the point of view of the patient ( rather than someone standing in front of the patient and facing the patient ). the exemplary implant 20 has a lower bone - engaging member 22 ( a bottom member or base ) and an upper bone - engaging 24 ( e . g ., a top member ). as is discussed further , the exemplary members may be articulated between a fully compressed / contracted / closed condition and a fully extended / expanded / opened condition . insertion / installation may be in a relatively compressed condition ( e . g ., including the fully compressed condition ) with subsequent expansion . the lower member has a bottom surface ( underside ) 26 for engaging an upper surface of the adjacent bone below ( e . g ., the sacrum ). the upper member has a top surface 28 for engaging an underside of the adjacent bone above ( e . g ., the l - 5 vertebra ). a linkage 30 guides the articulation between compressed and extended conditions . the exemplary linkage is a four - bar linkage wherein : the lower member forms a first bar ; the upper member forms a second bar ; one or more forward links 32 a , 32 b form a third bar ; and one or more rear links 34 a , 34 b form the fourth bar . the third and fourth bars each have fixed pivots with associated pivot axes 500 a , 500 b , 500 c , 500 d ( fig2 ) relative to the first and second bars . the exemplary lower and upper members each have lateral peripheral surfaces 40 and 42 . the peripheral surfaces are characterized by a central rear concavity 44 defining a partial channel for accommodating the spinal cord . the members 22 and 24 have a planform generally corresponding to the adjacent bone and / or replaced disk . a forward portion 46 is thus convex . the upper member , at its forward end , has an upwardly - extending flange or partial collar 50 having a concave inboard surface 52 for mating with the forward surface of the adjacent bone . the flange 50 has an aperture / hole 54 for receiving the shaft / shank 58 of a screw 56 to secure the upper member 24 to the bone above . the outboard surface 60 of the flange may have a counterbore for receiving the head 62 of the screw . the screw may have features for engaging a tool / driver ( e . g ., a hex socket feature ). in an exemplary use , the patient &# 39 ; s site is prepared ( e . g ., in a conventional manner ). this preparation may include prying apart adjacent bones ( e . g ., sacrum and l - 5 vertebra ), disk removal , and preparation ( e . g ., resurfacing ) of mating surfaces of the adjacent bones . the implant is installed in a relatively compressed condition ( e . g ., with the upper member racked forward relative to the lower member ). the flange of the upper member may then be secured to the vertebra via the screw ( e . g ., into a pre - drilled hole in the vertebra ). alternatively , the hole may be drilled and screw installed after implant extension ( described below ). the implant may then be further extended . an exemplary extension is performed via an extension tool 100 ( fig1 ) which has been preinstalled to the implant ( i . e ., installed to the implant prior to placing the implant between the sacrum and vertebra ). the exemplary tool operates by placing diagonal tension across the linkage . the exemplary tension is applied between the upper member 24 and lower member 22 . the exemplary tension is applied via a cable 102 ( fig5 ) having a terminal loop 104 engaging a hook 106 ( fig7 ) on the lower member near a rear end thereof . the counterforce is applied by a guide 108 through which the cable passes . the exemplary guide comprises a rigid tube 110 extending to an end portion formed as a ball 112 abutting the upper member . the ball is received in a socket 114 of the upper member ( e . g ., in a lower flange / collar 64 below the collar 50 ) to allow relative rotation . the cable passes through a hole 116 ( fig5 ) at the base of the socket . the ball may carry one or more rollers 118 to engage the cable during a lateral rotation of the tool relative to the implant . an actuator 140 ( fig1 ) may be formed at the proximal end 142 of the tool to draw the cable through the guide and , thereby extend the implant . the exemplary actuator is an inverted scissor action handgrip engaging a second end 144 of the cable . alternative actuators may include rotary grips , ratcheting handgrips , and the like . tightening of the cable draws the lower member forward , with the racking action of the four - bar linkage then driving it downward . during this movement , the interaction of the teeth on the underside of the lower member cause the adjacent bone to be drawn along with the lower member to restore anatomical alignment of the bones . when a sufficient degree of extension has been reached , one or more shims may be inserted between upper and lower members , allowing the cable tension to be released with the shim supporting the members in a relatively extended condition . further extension of the cable will release it from the hook allowing the tool to be disengaged . after the tool is disengaged , a lock 200 may be inserted to hold the implant extended . the exemplary lock further acts as an adjuster to permit a final adjustment of the degree of extension . the exemplary adjuster / lock comprises a screw mechanism the exemplary screw mechanism includes a screw 202 ( fig1 ) and an internally threaded sleeve or cylinder 204 receiving the screw . the end of the cylinder away from the screw head is provided with features for engaging the hook . in the exemplary embodiment , the end is formed as a clevis 206 ( fig9 ) carrying a pin 208 to capture the hook . upon installation of the adjuster ( e . g ., in the relative extension of fig1 ), the screw shaft / shank 210 may be screwed into the cylinder , with the underside 212 of the screw head 214 engaging the socket . further tightening can further extend ( fig1 and 12 ) the implant to a desired final extension . thereafter , the implant can be filled ( e . g ., with prepared ground bone initially harvested during site preparation ). the components of the implant and tool may first be manufactured ( e . g ., via machining from appropriate metal stock ) and then assembled . the exemplary implant materials are appropriate implantable materials such as titanium ( including its alloys ), cobalt ( including its alloys ), hastelloy , nitinol , and the like . more particular exemplary materials are medical grade titanium or titianium alloys . one or more embodiments of the present invention have been described . nevertheless , it will be understood that various modifications may be made without departing from the spirit and scope of the invention . for example , various features of existing or yet - developed implants may be incorporated . additionally , features of the implant may be customized to the particular implant location or in view of the particular ailment being addressed . accordingly , other embodiments are within the scope of the following claims .
a spinal implant has a first bone - engaging member , a second bone - engaging member , and a linkage coupling the first bone - engaging to the second bone - engaging member . the implant includes means for receiving a tensile force to extend the implant .