fig1 - 10b illustrate an example of an intervertebral implant 10 , a selectively expandable cage ( sec ), having features of the invention . the implant 10 generally includes a housing 11 , a housing base 12 , an interlocking top end plate 13 , a bottom end plate 14 , an interior cavity 15 within the housing 11 and a pair of cylinders 16 . the top and bottom end plates are the bone engaging members of the implant , providing surfaces for engaging vertebrae above and below the implant when placed in the patient . upper lock supports 17 are attached to the underside of the top end plate 13 thus forming fixed lock members and have multi - stepped lower support surfaces 18 much like an inverted staircase . lower lock supports 20 , having multi - stepped upper support surfaces 21 surround cylinders 16 much like an upright staircase . the multi - stepped support surfaces form the locking surfaces of the lock supports . pistons 22 are secured to the under surface of top end plate 13 . seal members 23 are slidably disposed within the cylinders 16 and are mounted on pistons 22 . the upper surface 24 of bottom end plate 14 is provided with locking actuator channels 25 which partially receive spring locking actuators 26 . the base 12 of the housing 11 has arcuate slots 27 which are configured to slidably receive the depending elements 28 or locking actuator transfer element of the lower lock supports 20 and partially receive the spring locking actuators 26 . depending elements 28 engage the forward end 30 of spring locking actuators 26 . the spring locking actuators 26 are initially in a compressed configuration so that upon the extension of the top end plate 13 and the attached upper lock supports 17 , the lower lock supports 20 rotate about the cylinders 16 due to the force applied by the biased spring locking actuator 26 thus forming moveable lock members . this causes the lock support surfaces 21 of the lower lock supports 20 to engage support surfaces 18 of the upper lock supports so as to lock the top end plate 13 in an extended configuration . the support surfaces 18 of the upper lock supports 17 and the support surfaces 21 of the lower lock supports 20 are tiered with multiple steps so that the implant 10 can be locked at several different expanded heights . the underside stepped support surfaces 18 of the upper lock support 17 may be provided with increasing riser height ( alignment faces 46 ) in the upward direction to provide smaller incremental expansion near the end of the piston expansion . in addition or alternatively , the stepped support surfaces 21 of the lower lock support 20 may be provided with decreasing riser height in the upward direction for the same reason . a variety of riser heights of the upper lock support 17 or lower lock support 20 can be provided . the lowermost stepped support surface 18 of the upper lock support 17 and the uppermost stepped support surface 21 of the lower lock support 20 may be provided with various lengths and widths to ensure better support . as can be seen in fig2 there are two sets of upper lock supports 17 attached to the top end plate 13 and there are two sets of lower lock supports 20 in this embodiment , but a single set or more than two sets of upper and lower lock supports can also be used to lock the implant 10 in the expanded state . also shown , for example , in fig2 are cylinders 16 and pistons 22 , which provide one example of extension means in embodiments of the present invention . other examples of extension means are described herein below in connection with alternative embodiments of the invention . the implant 10 is configured to be implanted between opposing vertebral bodies in the spine to facilitate bony fusion between those vertebral bodies . the implant 10 is shown in its collapsed or contracted configuration in fig1 and in one example of its expanded configuration in fig2 . in the collapsed state , the implant 10 can be inserted easily into the intervertebral body space through a minimal incision and with minimal tissue removal . once in that space , the implant 10 can be expanded against the two opposing vertebral bodies to distract them and thereby restore height to the intervertebral space . this provides stable opposition of the implant 10 to both vertebral bodies and optimizes the bony fusion process . the fusion process can also be enhanced by filling the interior cavity 15 with autologous bone graft , a bone growth enabling matrix , and / or bone growth stimulating substances prior to and / or after insertion into the body . further details of individual parts of the implant are depicted in fig3 a and 4b . pistons 22 are attached to the underside of the top end plate 13 which are configured to support seal members 23 which run inside of cylinders 16 located in the housing 11 . when the cylinders 16 are pressurized as will be described in more detail below , the seals 23 running inside the cylinders 16 and pistons 22 slidably disposed within the seals are vertically displaced , translating the top end plate 13 vertically above the housing 11 . lower lock supports 20 are located around the outer wall of the cylinders 16 . when the top end plate 13 is vertically displaced , which in turn displaces the attached upper lock supports 17 , the lower lock supports are rotated by the biased locking actuators 26 to a locking position . arcuate locking actuator channels 25 in the top surface of bottom plate 14 and the arcuate slots 27 in the housing base 12 confines the locking actuators 26 to the housing 11 . additional details of the housing 11 are depicted in fig5 a and 5b . the housing 11 comprises an outer wall 31 and cylinders 16 which are secured to housing base 12 . the outer wall 31 supports a leading nose 32 on the distal end and a delivery boss 33 on the proximal end . the leading nose 32 has inwardly directed side tapered faces 34 and top tapered face 35 and bottom tapered face 36 . these tapered faces 34 , 35 and 36 enable non - traumatic insertion of the implant 10 past neural elements and between the vertebral bodies . the delivery boss 33 contains a delivery tool anchor 37 which allows secure attachment of the implant 10 to a delivery tool ( not shown ), which is illustrated in co - pending application ser . no . 11 / 535 , 432 , filed sep . 26 , 2006 , and ser . no . 11 / 692 , 800 , filed mar . 28 , 2007 for insertion into a vertebral space . the delivery boss 33 also contains pressure input ports 38 which are used to deliver a pressurized fluid to the interiors of cylinders 16 . the outer wall 31 of the housing 11 also provides side openings 40 which provide space for bony in - growth into central cavity 15 in the housing 11 and provide radiolucent openings for the radiographic imaging of the process of bony in - growth . the housing base 12 also contains pressure channels 41 which deliver pressurized fluid from the pressure input ports 38 to the interior of cylinders 16 . although the housing base 12 of implant 10 is depicted with independent pressure channel 41 for each cylinder 16 , other embodiments can contain one or more branching pressure channels for delivering pressurized fluid to two or more cylinders 16 . as previously mentioned , the housing base 12 also has locking actuator slots 27 which hold and guide the locking actuators 26 . the locking actuator slots 27 contain a wider portion , locking actuator opening 42 , to enable insertion of the locking actuator 26 into the channels defined by the locking actuator slots 27 in housing base 12 and the locking actuator channels 25 in the bottom end plate 14 . the housing base 12 also has optional alignment bosses 19 which align the bottom end plate 14 to the housing 11 via optional alignment holes 9 . fig6 a and 6b illustrate further details of the top end plate 13 and the lower lock support 20 . the two sets of pistons 22 and upper lock supports 17 are joined by connecting members or struts 44 . the pistons 22 have seal bosses 45 on which the seals 23 are mounted . the upper lock supports 17 have tiered lower support surfaces 18 and risers or alignment faces 46 . the tiered or stepped support surfaces 18 of the upper lock supports 17 engage the stepped or tiered support surfaces 21 of the lower lock supports 20 . the alignment faces 46 of the upper lock support are configured to engage the alignment faces 47 of the lower lock supports 20 . the uppermost support surface of the lower lock support 20 has a lock support stop 50 which engages with the lower most alignment faces 46 of the upper lock support to prevent the lower lock support 20 from over rotating as it engages the upper lock support 17 . the bottom of the lower lock support also has the locking actuator transfer element 28 which engages the forward end 30 of the spring locking actuator 26 to transfer the actuation force from the locking actuator 26 to the lower lock support 20 . fig7 through 10b show details of the selectively expanding locking sequence of implant 10 with the housing 11 removed . the collapsed configuration is shown in fig7 with the support surfaces 18 of the upper lock support 17 resting on the support surfaces 21 of the lower lock support 20 . the locking actuator 26 is a biasing element , such as a spring , that engages the depending element or locking actuator transfer element 28 to urge the alignment faces of the lock supports in a direction where they contact . thus , in one exemplary embodiment , the alignment faces 47 of the lower lock supports 20 are forced against the alignment faces 46 of the upper lock support 17 . the lock support stops 50 fit within the lower lock stop relief 52 ( shown best in fig6 a ) on the top end plate 13 . when the cylinders 16 are pressurized , the pistons 22 raise the top end plate 13 and attached upper lock supports 17 ( straight arrow ) moving the support surfaces 18 of the upper lock support 17 off of the support surfaces 21 and moving the lower alignment faces 46 past the upper alignment faces 47 . when the alignment faces 46 of the upper lock support 17 have cleared the alignment faces 47 of the lower lock support 20 , the locking actuators ( in this embodiment a compressed coiled spring ) engaging the locking actuator transfer element 28 force the lower lock supports 20 to rotate ( curved arrow in fig8 b and 9b ). the support surfaces 21 of the rotating lower lock supports 20 move to the next lower level of the support surfaces 18 of the raised upper lock supports 17 until the alignment faces 47 of the lower lock supports 20 engage the next level of the alignment faces 46 of the upper lock supports 17 . the lower lock support 20 and upper lock support 17 then lock the top end plate 13 at this expanded level . this process repeats itself at each locking level ( fig8 a , 8b , 9a , 9b and 10a ) until the top level ( or somewhere between ) is reached as shown in fig1 b . at this top level , the locking actuators 26 engage the locking actuator transfer elements 28 and the lower lock supports 20 are rotated so the lowermost alignment surface 46 of the upper lock support 17 engages lock support stop 50 of the uppermost support surface 21 of the lower lock support 20 . at this highest locked level only the lowest support surfaces 18 of the upper lock supports 17 and the highest support surfaces 21 are engaged providing all of the locking support . as can be seen from fig1 a and 10b the lowest support surfaces 18 of the upper lock supports 17 and the highest support surfaces 21 of the lower lock supports 20 can be wider than the other support faces to provide sufficient support material when only these two faces are engaged . fig1 a and 11b illustrate the operation of locking actuator 26 . in this embodiment the spring locking actuator 26 is compressed into an arc beneath the lower lock support 20 . one end of the spring locking actuator 26 is constrained by the housing 11 ( not shown ) and the other is engaged with the locking actuator transfer element 28 . when the lower alignment faces 46 of the upper lock support 17 are raised above the upper alignment faces 47 of the lower lock support 20 by the extension of piston 22 , the locking actuator 26 pushes against the locking actuator transfer element 28 and rotates the lower lock support 20 in a clockwise direction ( arrow ) as viewed from above . it should be noted that in the embodiment of the current implant as described thus far , the angular orientation of the tiered upper and lower support surfaces 18 and 21 can vary when there is more than one set of supports . as shown in fig3 the proximal lower support surfaces 21 are oriented clockwise as viewed from above and the distal lower support surfaces 21 are oriented counter - clockwise . this opposite orientation provides enhanced locking support for rotational forces applied to the implant . an alternative locking actuator 26 a is shown in fig1 c as a torsion spring . this locking actuator 26 a has constraining tab 53 secured to the lower lock support 20 and constraining tab 54 secured to the housing 11 . just as the compression spring shown in fig1 a and 11b applies a force to the lower lock support 20 to rotate it , the torsion spring in fig1 c does the same . an extension spring would work equally as well as a locking actuator 26 a . spring actuators can be made of an appropriate biocompatible material such as stainless steel , nitinol , titanium or a suitable polymer . locking actuators are not limited to springs . a wide variety of mechanisms can be used to actuate the lower lock supports 20 , including but not limited to , a linear drive , an externally actuated tensile member , a worm gear , an inflated member such as a balloon or bellows , a magnet , a rotational drive such as a micro motor , a super elastic shape memory element , and the like . fig1 a through 12c show variations of the lower lock support 20 described above . in fig1 a a tri - set lock support 20 a is shown whereby there are three sets of upper support surfaces 21 a , upper alignment surfaces 47 a and lock support stops 50 a rather than the two sets described above . this tri - set lower lock support 20 a has two advantages over the two sets design , 1 ) there are three support columns rather than two locking the implant 10 in an expanded state thereby creating a more stable lock and 2 ) the tri - set lower lock support 20 a has to move or rotate much less for each locking level . this last advantage is significant when the locking actuator is a spring such as spring locking actuator 26 as this places less strain on the spring to achieve the required locking force at each step . each lower lock support column will have a corresponding upper lock support column ( not shown ). the upper support surfaces 21 and lower support surfaces 18 are not limited to two or three sets of surfaces . any number of sets of support surfaces including a single set may be employed . fig1 b shows an inter - digitating lower lock support 20 b . each of the inter - digitating upper support surfaces 21 b on the inter - digitating lock support 20 b is paired with an inter - digitating stop 50 b which when paired with matching inter - digitating support surfaces and stops of an upper lock support ( not shown ) prevents the inter - digitating support surfaces 21 b from moving relative to the inter - digitating support surfaces of an upper lock support to unlock the implant without the inter - digitating lower support faces first lifting above the inter - digitating stop 50 b . this design provides an enhanced locking feature . upper alignment surfaces 47 b are again provided . generally the lower support surfaces 18 and the upper support surfaces 21 are horizontal to maximize vertical support in the locked implant . however , the locking support 20 c shown in fig1 c provides an enhanced locking feature by providing inclined support surfaces 21 c which have a slope relative to the horizontal which requires matching inclined lower support surfaces on the upper lock supports ( not shown ) to be lifted above the inclined upper support surfaces 21 c before the upper lock support can be rotated to unlock the implant . fig1 a and 12c show various lengths of locking actuator transfer elements or depending elements 28 . the locking actuator transfer element 28 can vary in length depending on how much engagement is desired between the locking actuator transfer element 28 and the locking actuator slots 27 . the locking actuator transfer element 28 includes one or more transfer element tabs 29 a and 29 c which vertically constrain the lower lock support 20 to the locking actuator slots 27 in the housing 11 . the wider locking actuator opening 42 described above ( see fig5 b ) enables insertion of the locking actuator transfer element 28 with transfer element tabs 29 a and 29 c into the locking actuator slots 27 in housing base 12 at the rotational position where the locking actuator transfer element 28 is aligned with the locking actuator opening 42 . in other rotational positions the transfer element tabs are constrained by lateral extensions on the sides of the narrower locking actuator slots 27 . in this manner the locking actuator transfer element 28 provides both the function of transferring force from the locking actuator 26 to the lower lock support 20 as well as constraining the lower lock support 20 to the housing 11 . this later function prevents the frictional forces between the lower alignment faces 46 and the upper alignment faces 47 created by the biased spring locking actuator 26 from lifting the lower lock support 20 along with the upper lock support 17 when the upper lock support 17 is lifted by the piston 22 . as an alternative to the locking actuator transfer element 28 , the embodiment shown in fig1 b depicts a locking actuator guide channel 80 . this locking actuator guide channel 80 engages a tensile member ( not shown ) which transfers actuation force from the locking actuator 26 to the lower lock support 20 . tensile members can be any of a number of known elements such as sutures made of polymers or natural materials , metal cable , plastic or metal rod and the like . fig1 a and 13b illustrate an alternative design of an implant 110 embodying features of the invention . the implant 110 has independent actuation of the distal piston 122 a and proximal piston 122 b . the two pistons 122 a and 122 b are interconnected by an articulating top end plate 113 which allows independent lift and locking of each side of the implant 110 . this independent lift and locking of both ends of the implant 110 enables the implant to conform to intervertebralend plates that have uneven lateral heights between them . further , this independent lift and locking allows the implant 110 to be used to create varying lateral heights between vertebralend plates which can be useful to compensate for a scoliosis in the spine . implant 110 has a housing 111 which has an alternative delivery tool anchor 160 located in it as well as alternative pressure input ports 137 . a variety of anchor designs or pressure ports can be used with any of the embodiments of the current device without departing from the scope of this invention . lock and unlock access ports 138 are also located on this housing 111 . these ports are used to guide lock and unlock mechanisms ( not shown ) which can be manipulated externally to the implant 110 to actuate the lower lock support 120 to not only move it under the upper lock support 117 to hold the piston 122 b and articulating end plate 113 in an expanded position , but also to move the lower lock support 120 away from the upper lock support 117 to allow the piston 122 b and articulating end plate 113 to collapse back into the housing 111 . this later action may be desirable to remove the implant 110 from or reposition the implant within the intervertebral space . a variety of lock / unlock mechanisms can be used with the current invention such as but not limited by , a tensile member including suture thread and metallic cable , a compressive member such as a metallic or polymer rod , pressurized fluid , a rotating drive , a super elastic shape memory element , and the like . fig1 a - 14c depict yet another alternative implant 210 that embodies features of the invention . implant 210 has an interfacing top plate 213 which connects to separate and freely rotating pistons 222 via the piston capture plate 270 on the interfacing top plate 213 and the piston heads 271 on the rotating pistons 222 ab . the rotating pistons 222 ab also interiorly contain upper lock supports 217 with support faces 218 and alignment faces 246 . seals 223 are mounted on the rotating pistons 222 ab and the seals 223 and rotating pistons 222 ab fit into internal cylinders 216 that are located on the housing 211 . the internal cylinders 216 have lower lock supports 220 with support surfaces 221 and alignment faces 247 as well as lower retaining features 273 . the housing 211 also contains one or more pressure input ports 238 . in use , the implant 210 is inserted into the intervertebral body space in a collapsed state and fluid pressure is delivered through the pressure input port ( s ) 238 to the internal cylinder ( s ) 216 to raise the seal ( s ) 223 and rotating piston ( s ) 222 ab out of the internal cylinder ( s ) thereby raising the interfacing top plate 213 and expanding the implant 210 . once the rotating pistons 222 ab have been raised such that the lower alignment faces 246 of the upper lock supports 217 have cleared the upper alignment surfaces 247 of lower lock supports 220 , an actuator ( not shown ) rotates the rotating pistons 222 ab such that the lower support surfaces 218 of the upper lock supports 217 are moved above the upper support surfaces 221 of the lower lock supports 220 , to thereby lock the implant 210 in the expanded configuration . the actuator can be one or more tensile members such as suture threads or cables that extend from the user into the implant 210 through the lock and unlock access ports 238 on the interfacing top plate 213 to the piston head 271 . applying tension to one or more tensile members when the piston is in an extended configuration will rotate the piston heads 271 such that the support surfaces 218 of upper lock supports 217 are moved above the support surfaces 221 of the lower lock supports 220 thereby locking the implant 210 . alternatively or in addition to applying tension to lock the implant 210 in an expanded configuration , applying tension to one or more tensile members will rotate the piston heads 271 such that the lower support surfaces 218 are moved away from the upper support surfaces 221 thereby unlocking the implant 210 and allowing the rotating pistons 222 ab to seat back into the internal cylinders 216 such that the implant 210 is once again in a collapsed configuration . fig1 illustrates an alternative implant design 310 embodying features of the invention which has a housing 311 , top end plate 313 and pistons 322 similar to the prior embodiments . this implant 310 has upper lock supports 317 and lower lock supports 320 within a central portion of the implant . the upper lock supports 317 are secured to the top end plate 313 and the lower lock supports 320 are secured to the base 314 with depending elements ( not shown ) as was described above and are moved as in the prior embodiments . fig1 illustrates an alternative implant design 410 embodying features of the invention which has a housing 411 , top end plate 413 and a centrally located piston 422 similar to the prior embodiments . this implant 410 has upper lock supports 417 and lower lock supports 420 distal and proximal to the centrally located cylinder 416 and piston 422 . the upper lock supports 417 are secured to the top end plate 413 and the lower lock supports 420 are secured to the base 412 and are moved as in the prior embodiments via depending elements ( not shown ) as was described above . fig1 shows another alternative implant 510 which has a pair of pistons 522 and which has a locking support system which includes ratchets 521 on the base 512 and pawls 517 pivotally mounted to and depending from the top end plate 513 . expansion of the pistons 522 causes the free ends 518 of pawls 517 to engage recesses 520 in the ratchets 521 so as to lock the top end plate 513 in an extended configuration . fig1 illustrates another alternative implant design 610 which is similar to that shown in fig1 . in this embodiment the free end of the pawl 617 has a plurality of teeth 618 to provide greater effective contact between the pawl 617 and the ratchet 621 for locking of the implant 610 . fig1 is a cross section embodiment , showing implant 710 embodying features of the invention . in this embodiment the pistons 722 are surrounded by upper lock support 717 which has at least one cantilever extension ending at the support surface 718 . the support surfaces 718 are captured by the recessed support surfaces 721 which are located on the inner wall of the housing 711 . once the pistons 722 are expanded in an upward direction , the support surfaces 718 of the upper lock support 717 engages the recessed support surfaces 721 locking the implant 710 in place . the upper lock support 717 can be rotated relative to the piston 722 and housing 711 to disengage the support surfaces 718 from the support surfaces 721 to unlock the implant 710 and lower the pistons 722 as needed . alternatively the implant 710 can be unlocked by rotating the upper lock support constraints 775 relative to the upper lock support 717 to press on the cantilever extensions and disengage the support surfaces 718 from the support surfaces 721 . fig2 a - 31 illustrate a variety of suitable means for locking extendable members such as pistons in extended configurations . fig2 a , 20b , 21a , 21b , and 22 - 31 show variations of lower lock supports and upper lock supports . in each of these variations there are support surfaces on the lower lock supports which engage support surfaces on the upper lock supports . in fig2 a and 20b support surfaces 818 comprise grooves set into the upper lock support 817 . the lower lock support 820 is a u - shaped tong which is configured to advance ( as indicated by the arrow in fig2 a ) towards the upper lock support 817 and to engage one of the grooves with its upper support surface 821 for locking an implant not shown in these drawings . lower lock support 820 is withdrawn ( as indicated by the arrow in fig2 b ) from the groove to disengage the lower lock support and unlock the implant . in the variation shown in fig2 a , the lower lock support 920 is a plate with an upper lock clearance opening 970 that is shaped to allow passage of the cylindrical flat - sided upper lock support 917 through the lower lock support 920 ( arrow ). as shown in fig2 b , once the lower lock support 920 is positioned at the desired location it can be rotated approximately 90 ° ( arrow ) to engage the support surfaces of the lower lock support 920 with the support surfaces 918 of the upper lock support 917 . the shape of the upper lock support 917 and mating upper lock clearance opening 970 on the lower lock support 920 are not restricted to the profile shown in fig2 a and 21b nor is the locking actuation restricted to 90 ° rotation of one of the elements but can vary to any number of shapes that allow passage in one configuration but constraint when one of the elements is moved to another configuration . in fig2 , the upper lock support 1017 is a cylinder with notches cut to create support surfaces 1018 . the lower lock support 1020 is a pivoting pin 1070 with a pawl 1071 for the lower support surface 1021 . in the configuration shown , the support surface is biased as indicated by the arrow 1072 to allow the upper lock support 1017 to rise with an expandable member of an implant and to prevent the upper lock support from dropping . this allows the device to lock at each level when the subsequent support surface 1018 of the upper lock support 1017 engages the support surface 1021 of the lower lock support 1020 . in this variation having features of the present invention , the upper lock support 1017 can also be lowered by moving the pivoting pin 1070 of the lower lock support 1020 away from the upper lock support 1017 to disengage the support surface 1021 from the support surface 1018 . fig2 shows yet another embodiment having features of the invention where the lower lock support 1120 is a pin configured to engage ( arrow ) support surfaces 1118 located in the upper lock support 1117 . the lower lock support 1120 does not have to engage the full thickness of the upper lock support 1117 as shown in this figure , nor does the support surface 1118 have to extend through the entire thickness of the upper lock support 1117 but rather can engage any portion of the upper lock support 1117 that is sufficient to lock an implant in position . this embodiment also allows a variety of shapes of pins 1120 and matching support surfaces 1118 . in fig2 the lower lock support 1220 is a grip with two pivoting jaws 1270 , the ends of which have support surfaces 1221 . the upper lock support 1217 has a series of notches which have the support surfaces 1218 . a lock actuator such as a compressive spring ( not shown ) can apply force ( as shown by the arrows 1272 ) to the grip base extensions 1273 to lock the device . this variation having features of the invention allows the upper lock support 1217 to move upwards but prevents downward motion thereof . downward motion of the upper lock support 1217 can be allowed by reversing the force on grip base extensions 1273 . not all locking systems embodying features of the invention require the engagement of support surfaces of the upper lock supports directly on top of the support surfaces of the lower lock supports . a frictional support can be created to lock the device as shown in fig2 through 32 . in fig2 the upper lock support 1317 has one or more flat surfaces as the support surfaces 1318 . the lower lock support 1320 has one or more pivoting pawls that have a support surface 1321 that engage the support surface 1318 and supports a load ( arrow ). in fig2 the upper lock support 1417 has an exterior support face 1418 which is gripped by the support face 1421 on the inner diameter of the wrapped lower lock support 1420 . this lower lock support 1420 can be a torsion spring that in its free state grips the upper lock support 1417 and releases the upper lock support when a force ( arrows ) is applied to one or more of its ends 1470 as shown to increase the spring &# 39 ; s inner diameter . the reverse is possible where in its free state the lower lock support 1420 allows movement of the upper lock support 1417 inside the inner diameter . when a tensile force is applied to the ends 1470 to reduce the inner diameter , the lower lock support grips the support surface 1418 of the upper lock support 1417 to lock the implant . fig2 a and 27b show another variation which can be described as a canted washer type device . the lower lock support 1520 is a plate with an upper lock clearance opening 1570 which allows relative movement of the upper lock support 1517 as shown in fig2 a . when the lower lock support 1520 is canted as shown in fig2 b , the edge of the upper lock clearance opening 1570 comprises a lower support surface 1521 which engages the upper support surface 1518 which is the outer surface of the upper lock support 1517 locking it relative to the lower lock support 1520 . yet another variation of the gripping lock of the current invention is shown in fig2 . in this variation the lower lock support 1620 comprises one or more jaws which have support surfaces 1621 that are configured to be forced against the support surface 1618 of the upper lock support 1617 to produce friction to lock the device in place . fig2 illustrates a lower lock support 1720 which comprises a pivot and pawl as has been detailed above . the end of the pawl comprises a lower support surface 1721 which engages an upper support surface 1718 on the upper lock support 1717 . in this embodiment the upper lock support 1717 is rotated counter clockwise by an expanding element ( not shown ). this rotation in turn raises the piston 1722 which expands the implant . in this manner the upper lock support 1717 is integrated into the lifting mechanism to engage the lower lock support 1720 and lock the implant as it expands . fig3 illustrates yet another alternative implant 1810 , similar to that shown in fig1 except that the upper locking member 1817 and lower locking member 1818 have a linear shape rather than the arcuate shape of the prior embodiments . the implant 1810 generally has a housing 1811 , a top plate 1813 , a bottom plate 1814 , pistons 1822 and cylinders 1816 . the upper locking member 1817 has support surfaces 1818 and the lower locking member 1820 has support surfaces 1821 . the implant 1810 has a locking actuator ( not shown ). fig3 a - 31g illustrate another implant 1910 embodying features of the invention which have upper locking members 1917 with grooves 1970 having support surfaces 1918 and lower locking member 1920 with locking surfaces 1921 . the lower locking member 1920 is a wire - form which encircles the exterior of both upper locking members 1917 and is configured to seat within the grooves 1970 . expansion of the lower locking member 1920 ( arrows in fig3 b ) by the locking actuator ( not shown ) causes the lower locking member 1920 to be pulled out of the groove 1970 and allows the upper locking member 1917 to rise with the expansion of the implant . release of this expansion of the lower locking member 1920 ( arrows in fig3 a ) allows the lower locking member 1920 to seat back into the groove 1970 locking the implant 1910 . fig3 g illustrates a detail of an alternative implant 1910 a embodying features of the invention which have upper locking members 1917 a with grooves 1970 a having support surfaces 1918 a and lower locking member 1920 a with locking surfaces 1921 a . the lower locking member 1920 a is a wire - form which encircles the exterior of both upper locking members 1917 a and is configured to seat within the grooves 1970 a . the support surface 1918 a locks on the support surface 1921 a when there is a compressive or downward force ( hollow arrow ) on the upper locking member 1917 a locking the implant 1910 a . upward force or extension ( solid arrow ) of the upper locking member 1917 a causes the lower locking member 1920 a to ride on the disengaging surface 1919 a and out of the groove 1970 a allowing the upper locking member 1917 a to rise with the expansion of the implant 1910 a . in a further aspect of the present invention , a piston / cylinder and locking arrangement as described above may be used to deploy extendable bone anchors . for example , implant 10 a with conical bone engaging anchors 60 as shown in fig3 a and 32b may be constructed with pistons 22 and cylinders 16 as described above in connection with implant 10 and shown , for example , in fig2 and 4b . implant 10 a has a housing 11 as previously described and may include other previously described features such as interior cavity 15 for bone growth stimulating substances . however , in this embodiment , instead of upper interlocking end plate 13 , the two pistons 22 individually terminate with conical bone engaging anchors 60 . the bone engaging anchors , including sharp leading tip 62 , form surface for engaging the vertebral body . as shown in fig3 a , bone engaging anchors 60 are in a contracted configuration , within housing 11 , to facilitate insertion of implant 10 a . using hydraulic actuation as previously described , bone engaging anchors 60 are moved to an extended configuration as shown in fig3 b , wherein at least leading tip 62 extends beyond housing 11 to engage and anchor in the bone . in order to ensure that the bone engaging anchors remain firmly engaged in the bone , locking mechanisms including multi - stepped upper and lower lock supports 17 , 20 as previously described in connection with implant 10 and shown , e . g . in fig6 a - 12c , are provided to support each anchor 60 in the extended configuration . with this arrangement , the extended and locked anchor 60 helps to retain the implant in place . a variety of alternatives are possible for the bone engaging anchor according to the invention as illustrated in fig3 a - c . for example , implant 10 b in fig3 a includes bone engaging anchors formed as spike 60 a and blade 60 b . blade 60 b can be particularly effective in preventing motion along the insertion path after deployment . in this case , the length of the blade 60 b is aligned in the direction shown by arrow a . this is substantially orthogonal to the direction of implantation ( arrow b ) and would resist movement in that direction . implant 10 f , shown in fig3 b includes further possible variations . in this embodiment , the bone engaging anchors are formed as barbed spikes 60 c . barbs 61 along the shaft of the spikes resist forces that tend to move the tissue away from the implant along the axis of the anchor ( much as the screw threaded anchor described below would also resist this force ). also included in implant 10 f is a lateral bone engaging anchor 63 for anchoring in laterally oriented tissue . in the illustrated embodiment , lateral anchor 63 includes a plain spike 60 a . lateral anchor 63 is formed in the same manner and with the same components , i . e . piston , cylinder , locking mechanism , etc . as elsewhere described in this application , except that the components are oriented laterally as shown . to provide support for the bone anchor components in this lateral embodiment , housing 11 includes a central member 11 a that divides interior cavity 15 into two portions . in the configurations of implants 10 b and 10 f , the top of piston 22 can also become a bone engaging surface when the anchor member is fully received within the bone . fig3 c shows a further alternative implant 10 g , including anchors 65 extending obliquely from housing 11 , rather than orthogonally . this oblique arrangement is helpful in resisting side to side rotational forces ( for example when the patient / spine bends towards the side ) and expansion forces . once again , obliquely extending anchors 65 are essentially identical to other bone engaging anchors described herein except for the oblique orientation . here , holes 68 are provided in top end plate 66 for the spikes to pass through . in general , bone engaging anchors according to embodiments of the invention should have a relatively small termination ( e . g . tip 62 ) relative to the size of the piston diameter so that the force on the piston created by the hydraulic fluid is proportionally a much greater force at the small anchor termination to enhance its ability to extend into hard bony tissues . it will also be appreciated by persons skilled in the art that the various features of the bone engaging elements , e . g . spike , blade , barbs , etc ., described herein may be combined in any desired combination , in addition to the exemplary combinations shown in the figures of the present application . in another alternative embodiment , illustrated in fig3 a and 34b , implant 10 c includes screw - threaded members 64 as bone engaging anchors . implant 10 c also illustrates a further alternative wherein the bone engaging surfaces , such as the anchors , extend from opposite sides of the implant . in this exemplary embodiment , interlocking end plate 13 is replaced with an integrated top end plate 66 . holes 68 are provided for threaded member 64 to pass through . persons of ordinary skill in the art will appreciate that holes 68 will be located as needed ; in the illustrated embodiment one is in top end plate 66 and the other in bottom end plate 14 . threaded members 64 , as bone engaging anchors extend outwardly from pistons 22 . in order to rotate the threaded anchors into the bone when the pistons are extended , the inner wall of housing 11 is provided with a screw - threaded surface 70 that mates with corresponding threads 71 cooperating with pistons 22 . as previously described , seals 23 act between the pistons 22 and cylinders 16 to prevent leakage of hydraulic fluid . when fluid is pressurized within the cylinders as described for prior embodiments , the piston is extended , but also driven in a circular motion by the engagement between threaded surfaces 70 and 71 . the screw - threaded member 64 is thus driven into adjacent bone as it is extended to anchor the implant . once again , locking mechanisms as previously described and shown , for example , in fig6 a - 12c , may be employed to prevent the bone engaging anchors from becoming unengaged from the bone . in the cross - sectional views of fig3 a and 34b , upper and lower lock supports 17 , 20 are visible around the outside of the piston and cylinders . alternatively , depending on the depth and pitch of the threaded portions , use of a separate locking mechanism may not be required . as persons of ordinary skill will appreciate , the configuration of the threads alone may be sufficient to prevent the anchors from backing out . fig3 a and 35b illustrate a further aspect of the present invention wherein locking mechanisms as described are utilized to secure telescoping bone engaging surfaces in place . as used herein , telescoping refers to nested , extendable members including at least one intermediate member between a base and bone engaging member . referring first to fig3 a , implant 10 d has substantially planar bone engaging members 72 . bone engaging members 72 are thus similar to the bone engaging members of implant 10 , but instead individually actuated without interlocking end plate 13 . the piston / cylinder arrangement is also similar to that previously described except that here upper piston 74 is received in intermediate piston 80 . intermediate piston is in turn received in cylinder 16 as was previously described for piston 22 . upper piston 74 is sealed against intermediate cylinder 78 of intermediate piston by upper piston seals 76 ( see fig3 b ). the telescoping bone engaging members 72 are secured by locking mechanisms in a similar manner to the earlier described embodiments , with the addition of an upper lock support 82 for the upper piston . intermediate piston 80 is supported by upper lock support 17 and lower lock support 20 as previously described . upper lock support 82 includes upper and lower lock supports 84 , 86 . thus , upper piston 74 is secured to upper lock support 84 of the upper lock set . lower lock support 86 of the upper lock set is mounted on top of upper lock support 20 of the lower lock set . one difference from the earlier described embodiments is that separate spring actuators 26 are not required for the upper lock set as they may be rotated along with the lower lock set by actuators 26 . implant 10 e , as shown in fig3 b includes a further variation in which the planar portion of upper bone engaging surface 88 is effectively annular with a conical anchor 90 at the center . advantages of embodiments of the present invention including bone engaging anchors include the ability of the anchors to be extended lateral from the long axis of the implant ( i . e ., the insertion axis ) with a relatively high force using the relatively small connection to the implant of the hydraulic line . this is an advantage over other methods that require larger access or larger connections to the implant for lager tools or non - hydraulic extension forces to extend the anchors into the hard , bony tissue . although the previously described embodiments of the invention included cylinders 16 and pistons 22 expanded with a pressurized fluid as the mechanism used to lift the top end plate away from the bottom end plate , embodiments of the present invention are not limited to only such lift mechanisms . in fig3 a - c an alternative embodiment of the present invention comprising implant 10 f is shown wherein a pair of bellows 92 replaces the piston and cylinder pairs previously described . one end of bellows 92 is attached to housing 11 and the other end to top end plate 13 . a pressurized fluid added via pressure input ports 38 is directed through bellows orifice 94 into the inside of bellows causing the bellows to expand . the expanding bellows forces top end plate 13 away from housing 11 and lower lock supports 20 are rotated to lock the device in the expanded configuration as was previously described . bellows 92 can be made of any biocompatible material such as the 316 series of stainless steels , titanium or a titanium alloy , a cobalt chromium alloy , or an implantable polymeric material . the bellows can be of an accordion - like folding configuration as shown in fig3 a - c or any other regular or irregular configuration which can fit inside of the housing and lock supports in the collapsed configuration and expand sufficiently when pressurized to lift top end plate 13 the desired amount away from housing 11 . lower lock supports 20 and upper lock supports 17 provide a confining geometry for bellows 92 , which allows use of an irregular bellows configuration . with a bellows arrangement as shown in fig3 a and 36b , the amount of lift is not limited as is the case in a cylinder and piston to the amount that the collapsed cylinder and piston overlap . other exemplary embodiments do not rely on the use of a pressurized fluid for expansion . for example , fig3 a and 37b show an alternative rotating cam lift mechanism 93 . cam lift mechanism 93 includes cam 96 with a substantially curved cam surface 95 and a substantially flat top surface 97 , rotating shaft 98 , and shaft supports 99 . cam 96 is attached to rotating shaft 98 , and shaft 98 is supported by and rotates within shaft supports 99 . in an implant 10 g ( fig4 ) using this mechanism , the shaft supports 99 are anchored to the inside of housing 11 and rotation of shaft 98 ( depicted by curved arrows ) rotates the curved cam surface 95 against the bottom of top end plate 13 and moves top end plate 13 away from housing 11 as shown in fig3 a - 38b , 39a - 39b and 40 . the shape of cam 96 determines both the amount of lift that is possible and the relative amount of lift to the amount of rotation of the cam . the cam is not limited by 90 degrees of rotation depicted in the figures . any shape of a cam that is rotated by any amount from as little as 10 degrees to as much as 355 degrees is possible without departing from the scope of the present invention . shaft rotation can be accomplished by several means as will be discussed in more detail below . use of cam lift mechanism 93 as the lifting mechanism along with lower and upper locking supports 20 and 17 for implant 10 g allows the lift mechanism to support only the initial lifting loads and not have to support the repetitive long - term supporting loads on implant 10 g which are borne by the locking supports . cam 96 does not require a substantially flat top surface 97 as shown in the exemplary embodiment to support top end plate 13 , but such a surface provides a rotational endpoint for the surgeon rotating shaft 98 . another alternative embodiment is implant 10 h shown in fig4 , 43a and 43b . implant 10 h uses a rotating screw lift mechanism 193 as shown in fig4 . this mechanism includes shaft 98 , shaft supports 99 , worm gears 170 attached to shaft 98 and a shaft input end 178 at one end of shaft 98 . the mechanism also includes lift screws 172 , which have lower lift threads 174 and transfer gear 176 and supporting boss 186 . applying a torque via shaft input end 178 turns shaft 98 , which turns the attached worm gears 170 . worm gears 170 turn transfer gear 176 on lift screw 172 . lift screw 172 is contained within housing 11 by way of its supporting boss 186 , which is seated in housing bearing 188 . rotation of lift screw 172 transfers force from lower lift threads 174 to upper lift threads 182 on upper lift nut 180 . upper lift nut 180 is attached to top end plate 13 so that rotation of shaft input end 178 lifts upper end plate 13 away from housing 11 . the relative pitch of worm gears 170 and matching transfer gears 176 and the lower lift threads 174 and matching upper lift threads 182 can be varied to achieve the desired amount of lift relative to the amount of rotation and torque . the torque can be applied by any means well known by those skilled in the art including but not limited to electric motor , pneumatic or hydraulic turbine , or manual rotation of an actuator . shaft input end 178 is shown as a hexagonal post , but any alternative input end can be used without departing from the scope of the present invention , such as , but not limited to , a square or star - shaped post , a square , star or hexagonal - shaped socket , or a keyed shaft . as shown in fig4 , an alternative embodiment of the implant 10 i includes a linking element 202 that connects the lower lock supports 20 a and 20 b . the linking element 202 coordinates the action of the lower lock supports 20 a and 20 b . when the locking actuator 26 actuates the leading lower lock support 20 a , the linking element 202 in turn actuates the following lower lock support 20 b . in this embodiment the implant 10 i may require only a single locking actuator 26 , however plural locking actuators as described above ( see , for example , fig3 ) may be employed for greater actuation force as needed . in addition to actuating the following lower lock support 20 b , the linking element 202 prevents the leading lower lock support 20 a from actuating until the alignment faces 46 of both the leading upper lock supports 17 a and the following upper lock supports 17 b each clear the alignment faces 47 of both the leading lower lock support 20 a and the following lock support 20 b . in this manner the linking element 202 ensures the coordinated actuation of the lower lock supports 20 a and 20 b to ensure that the implant 10 i will always lock at the same height on both sides . this can be advantageous for certain implants placed in the spine where an even expansion of the implant is desired . linking plural lower lock supports , such as supports 20 a and 20 b , with a linking element 202 for even expansion in the manner described may be advantageous over an implant with a similarly sized single lock support 20 , and single cylinder 16 and piston 22 due to the increase in the number of support elements , the broader support base , and the increase in expansion force due to the increased number of cylinder and piston pairs . increasing the size of a single lock support would still have disadvantages of a larger width that would limit the ability for implantation in minimally invasive surgery . embodiments of the invention are not limited to just the pair of lower locking supports 20 a and 20 b as shown in , for example , fig3 . rather , any number of sets of cylinders 16 , pistons 22 , upper lock supports 17 , and lower lock supports 20 , with a locking actuator 26 and the appropriate number of linking elements 202 are possible . for the embodiment illustrated in fig4 , linking element 202 is configured to fit inside attachment grooves 204 on the lower lock support 20 a , b . alternatively , linking element 202 may be configured to rest on the outside diameter of the lower lock support 20 a , b . the linking element 202 can also be configured to run underneath the lower lock supports 20 a , b as shown in fig4 a - d . for implant 10 i in fig4 both of the lower lock supports 20 a and 20 b rotate in the same direction when actuated . elements of an alternative implant shown in fig4 a - b include lower lock supports 20 that actuate with rotation in opposite directions . the linking element 202 is guided between the lower lock supports 20 through a link channel 210 in housing 11 ( fig4 b ). the linking element 202 is constrained in the link channel 210 by a channel cover 208 . the linking element 202 is connected to the lower lock supports 20 by means of link pins 206 . the linking element can be made from any of a variety of implantable materials including : a titanium wire , a titanium cable , a stainless steel wire or cable , a nitinol wire , a braided or mono - filament suture from any manner of suture material such as silk , polyester , polypropolyene , eptfe , or uhwpe . an implantable material that has a tensile strength sufficient to transfer the actuation force from the leading lower lock support 20 a to the following lower lock support 20 b as well as flexibility sufficient to follow the link channel 210 and / or rotate around the lock supports 20 may be used . linking element 202 can be attached to the lower lock supports 20 in a number of ways known to those practiced in the art , the selection of which depends on factors such as the linking element material and the lower lock support material . suitable techniques include laser welding , resistance welding , adhesive bonding , crimping , attaching with clamps , pins , or screws , or being threaded through an opening and securing with a knot . turning now to fig4 a , b and c an implant 10 j with an additional feature , an unlocking tether 212 is shown . unlocking tether 212 is attached to the following lower lock support 20 b in attachment groove 204 . unlocking tether 212 is attached in the opposite direction as the linking element 202 and can be attached in any of the ways described above for attaching the link element 202 . the proximal end 214 of the unlocking tether 212 exits the housing 11 of the implant 10 j through the unlock port 216 . the proximal end 214 can be actuated by an external force or mechanism ( not shown ). actuation of the proximal end 214 of the unlocking tether 212 to translate it away from the implant 10 j causes rotation of the following lower lock support 20 b , which will tension and translate the linking element 202 which will rotate the leading lower lock support 20 a . in this manner the unlocking tether 212 can be used to unlock the implant 10 j so that it can collapse to a lower or to its original height . in fig4 b the implant 10 j is collapsed and the unlocking tether 212 is extended a maximum distance out of the unlock port 216 . fig4 c shows the same implant 10 j with the top plate 13 fully expanded above the housing 11 and locked . the unlocking tether 212 has shortened as it was drawn into the implant 10 j as the lower lock supports 20 rotated into locking position . tensioning or pulling on the unlocking tether 212 will unlock the lower lock supports 20 and allow the top plate 13 to collapse back into the housing 11 . the ability to unlock and collapse the implant 10 j can be highly advantageous to a physician placing the device if there is a need to reposition or replace the device after it has been expanded in - vivo . turning now to fig4 , another embodiment of an implant 10 k is shown with lower lock supports 20 that are located inside the cylinders 16 of the housing 11 . in this embodiment the linking element 202 is a solid bar that can transfer compressive as well as tensile loads . the locking actuator 26 rotates the leading lower lock support 20 a , which pushes on the linking element 202 . the linking element 202 in turn pushes and rotates the following lower lock support 20 b . the lower lock supports 20 a and 20 b engage the upper lock supports 17 that are located inside the pistons 22 ( shown in fig1 c ). the rotation of the following lower lock support 20 b pulls the unlocking tether 212 into the housing 11 through the unlocking port 38 . the unlocking tether 212 can be tensioned away from the housing 11 to reverse the process and unlock the implant 10 k . the use of tension and compression elements as described above are not the only means for coordinating the controlled locking and unlocking of the device . in fig4 an alternative embodiment of the implant 10 l is shown wherein thread gears 226 a and 226 b are used to both lock and unlock the lower lock supports 20 thus forming a combined linking and unlocking element . threaded gears 226 a and 226 b are mounted on a shaft 224 that is contained in the base of the housing . the proximal end of shaft 224 has a keyed head 228 that can protrude from or rest in the locking port 222 . an external tool ( not shown ) can interface with the keyed head 228 to rotate it in either direction . rotating the keyed head 228 will in turn rotate the shaft 224 and the threaded gears 226 a and 226 b . the threaded gears 226 a and 226 b transfer the force to the lower lock supports 20 through the geared bottom face 220 . in the embodiment shown in fig4 the threaded gear 226 a is oriented opposite of the threaded gear 226 b . this allows rotation of the shaft 224 to rotate the lower lock supports 20 in opposite directions relative to each other . it is obvious to those schooled in the art that the threaded gears 226 a and 226 b can be oriented in the same direction if it is desired to rotate the lower lock supports 20 in the same direction . in either case the shaft 224 can be rotated in one direction to rotate the lower lock supports 20 in the locking direction , and the shaft 224 can be rotated in the opposite direction to rotate the lower lock supports 20 in the unlocking direction . an unlocking tether as described herein can be engaged and tensioned by any number of means including but not limited to gripping the unlocking tether between articulating grips , a collet or split ring clamp , crimping the unlocking tether to a tensioning wire or rod and cutting the unlocking tether to disengage after use , mounting a magnet on the proximal end 214 ( fig4 a ) of the unlocking tether and engaging the magnet with a mating magnet attached to a tensioning wire of rod , adding a female or male thread to the proximal end 214 or the unlocking tether and engaging it with a mating thread on the end of a tensioning rod or wire , or providing a continuous unlocking tether all the way to the point external to the body for tensioning and then cutting the unlocking tether near the implant after use to disengage . it is obvious to those schooled in the art that the unlocking tether can alternatively be pushed or compressed rather than tensioned as long as it is configured to rotate the lower lock supports 20 a and b in the unlock direction and deliver sufficient load without buckling when pushed . fig4 illustrates an alternative embodiment of an implant 10 m with a pushable unlocking tether 212 a . in this embodiment , unlocking tether 212 a engages the proximal lower lock support 20 b to rotate it in the unlock direction when the unlocking tether 212 a is advanced towards the proximal lower lock support 20 b . the link 202 transfers that rotation from the following lower lock support 20 b to the leading lower lock support 20 a . the link 202 contains engagement pins 230 , which extend into receiving slots 232 on the lower lock supports 20 a and 20 b in order to transfer the lateral movement of the link 202 into rotation of the lower lock supports 20 a and 20 b . in much the same way , the unlocking tether 212 can contain an engaging pin ( not shown ) to extend into a receiving slot ( not shown ) on the following lower lock support 20 b to transfer the lateral compressive force applied to the unlocking tether 212 a into rotation of the lower lock supports 20 b . this is just one method for attaching or engaging the unlocking tether 212 to the lower lock support 20 the numerous methods previously described herein for attaching or engaging the link 202 to the lower lock supports 20 can be used for attaching or engaging the tether 212 as well . one advantage to pushing the unlocking tether 212 a to unlock the implant 10 m is that the method for engaging the unlocking tether is simplified . unlocking tether 212 a , which is pushed to unlock the implant 10 m can be contained within the implant 10 m and a push rod ( not shown ) can be easily directed into the implant 10 m through the unlock port 216 to actuate the unlocking tether 212 a and unlock the implant 10 m such that it can collapse . this eliminates the need to attach to the unlocking tether 212 a which is required when the unlocking tether 212 a is tensioned to unlock the implant 10 m . fig5 a - d illustrate an alternate embodiment of the implant 10 n embodying features of the invention . similar to the implant 110 as shown in fig1 a and 13b , the top end plate 113 of the implant 10 n articulates relative to the distal piston 122 a and proximal piston 122 b . the ends of the articulating top plate 113 have spherical projections 2001 a and 20001 b which are contained within mating pockets 2002 a and 2002 b in the two pistons 122 a and 122 b . split rings 2006 a and 2006 b are placed over the spherical projections 2001 a and 20001 b and into the pistons 122 a and 122 b to vertically constrain the articulating top plate 113 to the pistons . this geometry provides articulation of the top plate 113 along not only the long axis ( the axis extending along the line 50 c in fig5 c ), as with the implant 110 shown in fig1 a - b , but also provides articulation in a side - to - side direction , which is an advantage for providing congruence of the implant to the intervertebral space . thus , the articulating top plate 113 is polyaxially movably coupled to the pistons 122 a and 122 b , allowing the plate 113 to articulate about at least two axes . also shown in fig5 d are vertical constraints 2003 a and 2003 b which are attached to the distal piston 122 a and proximal piston 122 b . these two constraints 2003 a and 2003 b fit inside channels 2004 a and 2004 b in the housing 111 . the top portion of the channels 2004 a and 2004 b have a narrowed portion 2005 a and 2005 b that prevent the vertical constraints 2003 a and 2003 b from advancing out of the housing 111 . in this manner these vertical constraints 2003 a and 2003 b limit the maximum vertical movement of the pistons 122 a and 122 b relative to the housing 111 . fig5 a - b illustrate another alternative embodiment . fig5 a - b illustrate an implant 10 p that can have features similar to features in the embodiments illustrated in fig1 a , 14a - c , and 49 . the implant 10 p has the articulating top plate 113 similar to that shown in fig1 a which pivots relative to the distal piston 122 a and proximal piston 122 b about a distal pivot pin 2101 a and a proximal pivot pin 2101 b . the implant 10 p has a distal piston 122 a and a proximal piston 122 b . as with the pistons 222 a and 222 b shown in fig1 a - c , the pistons 122 a and 122 b can have internal upper lock supports 217 . unlike implant 210 , in the illustrated embodiment , the pistons 122 a and 122 b do not rotate relative to the housing 111 as is the case in the implant 210 . instead , lower lock supports 20 a and 20 b similar to those shown in fig4 rotate relative to the housing 111 and the two pistons 122 a and 122 b to lock the height of the expanded implant . in this manner , benefits of several of the previously described embodiments are combined to provide and implant 10 p that can lock at different distal and proximal heights . fig5 a - f illustrate an alternative embodiment of the present invention , exemplified by implant 10 r . in this embodiment , implant 10 r can include a distal piston top plate 2222 that can be completely separate from a proximal piston top plate 2223 . as shown in fig5 b - d , the two piston top plates 2222 and 2223 can each expand to different heights relative to the housing 111 . thus , the independently adjustable top plates and their respective pistons provide a simple construct that can achieve variable expansion similar to the articulating top plate 113 in implants 10 n and 10 p . in some embodiments , the extendable members , such as pistons 122 a and 122 b , may be actuated by a common actuator such as a single syringe or other pressurized fluid source but constrained as described herein to rise to independent / different heights . such constraint may be provided by specific constraint means as described , by a common top plate such as shown in fig5 d or a combination thereof . as shown in fig5 f , the implant 10 r can include a proximal lower lock support 20 b that can have stepped support surfaces that have shorter increments than the stepped support surfaces on a distal lower lock support 20 a . the mating stepped support surfaces on the proximal upper lock support ( not shown ) in the proximal piston 122 b can also have shorter increments than the stepped support surfaces on the upper lock support in the distal piston 122 a . this variation in stepped support surface can be designed to produce a specifically desired expanded height difference between the expanded distal piston top plate 2222 and the expanded proximal piston top plate 2223 . in addition , the expanded height difference can vary with the amount of expansion . this variation can be valuable , for example , for creating lordotic congruence between the implant 10 r and the vertebral bodies as the amount of lordosis required for proper congruence and spinal foraminal opening can increase along with the increase in distance between the vertebral bodies . the implant 10 r can also have vertical constraints 2005 a and 2005 b which can be attached to the housing 111 . in the illustrated embodiment , the vertical constraints 2005 a and 2005 b can prevent wide portions 2003 a and 2003 b of the distal piston 122 a and proximal piston 122 b from advancing out of the housing 111 . in this manner , these vertical constraints 2005 a and 2005 b can limit the maximum vertical movement of the pistons 2222 and 2223 relative to the housing 111 . fig5 illustrates yet another alternative embodiment . as shown in fig5 , an implant 10 s can have a distal piston 122 a that can have both a horizontal vertebral engagement surface 2240 and an angled vertebral engagement surface 2242 , such that the distal piston 122 a can have a variation in vertebral engagement surface angles . these variations in vertebral engagement surface angles can be beneficial for providing even better congruence between the implant 10 s and the vertebral bodies when a lordotic or variable height expansion is desired . the implant 10 s can also have a proximal piston 122 b with a higher horizontal vertebral engagement surface 2244 and a lower horizontal vertebral engagement surface 2246 , which can also improve congruence between the implant 10 s and the vertebral bodies when a lordotic or variable height expansion is desired . as will be recognized by a person of ordinary skill in the art , any combination of these varied vertebral engagement surfaces can be employed on either the distal piston 122 a , the proximal piston 122 b , the articulating top plate 113 or the posterior surface of the housing 111 to provide optimal vertebral body congruency . the features of the current invention have been described in terms of an implant comprised of a pair of cylinder / piston / lock / and related features , however it is obvious to those schooled in the art that the described features can be included in an implant with only a single set or more than two sets of these features . a lateral cage implant , as illustrated for exemplary embodiments of the present invention herein , is particularly advantaged by the use of anchors as described herein because the lateral approach to the spine is a long and narrow approach , which limits the ability of the surgeon to use other instrumentation to extend anchors from the cage ( as can be done more readily , for example , with an anterior approach where the access is not as narrow ). however , as will be appreciated by persons of ordinary skill in the art , while particular , additional advantages may be presented in connection with the lateral approach and cages designed therefore , anchors according to embodiments of the present invention are advantageous for any approach as they can produce the required extension forces regardless of patient anatomy or other restrictions on the use of alternative extension means by the surgeon . elements of the description herein focused on the manner in which the locking elements are configured to lock the implant in extended configurations . although this locking action resists the forces placed on the implant that would tend to force it back into a collapsed configuration , that is not the only force the locking elements address . once inserted between vertebral bodies the implant is subject to lateral forces and torsion moments as well as compressive forces . the locking features along with the other elements of the invention are designed to resist all of these forces to provide an implant that provides stable fixation and distraction . a partial or complete discectomy is usually performed prior to the insertion of the spinal implant having features of the invention between vertebral bodies . the implant is introduced in its unexpanded state to enable it to be inserted posteriorly with minimal trauma to the patient and risk of injury to nerve roots . once in place the implant can be expanded to provide both medial and lateral spinal correction . the implant has an unexpanded height of about 5 to about 15 mm , typically about 7 mm and is expandable to at least 130 % to about 180 % of the unexpanded height . typically the implant is about 9 to about 15 mm wide , typically about 12 mm wide and about 25 to about 55 mm long , typically about 35 mm long to facilitate minimally invasive insertion and thereby minimize trauma to the patient and risk of injury to nerve roots . additional details of the implant such as the attachment of hydraulic lines and lines for transmission of a slurry or liquid bone graft material , device and hydraulic fluid delivery accessories and the like can be found in co - pending application ser . no . 11 / 535 , 432 filed on sep . 26 , 2006 and ser . no . 11 , 692 , 800 , filed on mar . 28 , 2007 , which are incorporated herein by reference . it will be appreciated that the implant , including its various components should be formed of biocompatible , substantially incompressible material such as peek or titanium , and preferably type 6 - 4 titanium alloy or other suitable materials which will allow for long - term deployment within a patient . while the invention has been described in connection with what are presently considered to be the most practical and certain preferred embodiments , it is to be understood that the invention is not limited to the disclosed embodiments and alternatives as set forth above , but on the contrary is intended to cover various modifications and equivalent arrangements included within the scope of the following claims . for example , while implants described herein are expanded by hydraulic fluid , other expansion means may be employed . for example , the screw mechanism described herein may be employed to expand scissor jacks within the implant to engagement adjacent vertebral surfaces . further , the implant can be provided with load or pressure sensors that register differential pressure and pressure intensity exerted on the engaging surfaces of the sec by the patient &# 39 ; s vertebrae end plates to generate corrective signals , for example by computer control , that are used , e . g . by the surgeon or by a computer - controlled mechanism to realign the patient &# 39 ; s spine . the invention may further include a system that makes these adjustments , responsive to sensor signals , in real time and on a continual basis , such that the shapes of the implant changes to realign the patient &# 39 ; s spine or mechanism . preferably , such system is contemplated for use in setting the positions of the pistons during installation of the implant . while particular forms of the invention have been illustrated and described herein , it will be apparent that various modifications and improvements can be made to the invention . additional details of the spinal implant devices may be found in the patents and applications referenced herein . to the extent not otherwise disclosed herein , materials and structure may be of conventional design . moreover , individual features of embodiments of the invention may be shown in some drawings and not in others , but those skilled in the art will recognize that individual features of one embodiment of the invention can be combined with any or all the features of another embodiment . accordingly , it is not intended that the invention be limited to the specific embodiments illustrated . it is therefore intended that this invention be defined by the scope of the appended claims as broadly as the prior art will permit . terms such as “ element ”, “ member ”, “ component ”, “ device ”, “ means ”, “ portion ”, “ section ”, “ steps ” and words of similar import when used herein shall not be construed as invoking the provisions of 35 u . s . c § 112 ( 6 ) unless the following claims expressly use the terms “ means for ” or “ step for ” followed by a particular function without reference to a specific structure or a specific action . all patents and all patent applications referred to above are hereby incorporated by reference in their entirety .
a spinal implant which is configured to be deployed between adjacent vertebral bodies . the implant has at least one extendable support element with a retracted configuration to facilitate deployment of the implant and an extended configuration so as to expand the implant and effectively distract the disc space , stabilize the motion segments and eliminate pathologic spine motion . the implant has a minimal dimension in its unexpanded state that is smaller than the dimensions of the neuroforamen through which it typically passes to be deployed within the intervertebral space . the implant is provided with a locking system having a plurality of linked locking elements that work in unison to lock the implant in an extended configuration . bone engaging anchors also may be provided to ensure secure positioning .