while the present invention will be described more fully hereinafter with reference to the accompanying drawings in which particular embodiments and methods are shown , it is to be understood from the outset that persons of ordinary skill in the art may modify the invention herein described while achieving the functions and results of this invention . accordingly , the description that follows is to be understood as illustrative and exemplary of specific embodiments within the broad scope of the present invention and not as limiting the scope of the invention . in the following descriptions , like numbers refer to similar features or like elements throughout . ideally , an artificial corpectomy prosthetic provides the surgeon with an easy adjustment mechanism that allows the length of the prosthetic to be modified during surgery with a minimum of time and effort to fit the needs of the patient . the prosthetic must allow a significant range of adjustment because the size and number of vertebrae removed will vary from patient to patient . referring now to fig1 , one embodiment of a prosthetic is shown which includes an adjustable telescoping mechanism that allows the height 100 of the prosthetic to be expanded or contracted during surgery , and also prevents both accidental compression or expansion of the device once implanted in the patient . fig1 shows an embodiment with a short outer cage 30 . fig2 and 7 show a second embodiment with a longer outer cage 30 . referring now to fig4 , 4 a , and 4 b , the apparatus 10 comprises an inner member 20 ; an outer cage 30 ; a finger cage 40 ; and a lock ring 50 . in the embodiment shown , the inner member 20 includes a first endplate 21 that serves as the uppermost surface of the prosthesis and fits against the healthy vertebra adjacent to the uppermost removed bone . the first endplate 21 includes an upper surface 21 a and a lower surface 21 b . the upper surface 21 a of the first endplate 21 may include spikes 21 c , ridges , or some other protrusion or surface treatment in order to facilitate fusion between the prosthesis and the adjacent bone , thus providing better fixation of the prosthesis and increasing the life of the implant . in other embodiments , the first endplate 21 also can include an aperture 21 d , preferably located at or near the center of the first endplate 21 . in one embodiment , a cupped insert ( not shown ) is placed in the aperture 21 d . the purpose of the aperture 21 d , and the cupped insert , will be explained below . referring now to fig7 , the outer cage 30 includes a second endplate 31 that serves as the lowermost surface of the prosthesis and fits against the healthy vertebra adjacent to the lowermost removed bone . the second endplate 31 includes a lower surface 31 a and an upper surface 31 b . the lower surface 31 a of the second endplate 31 may include spikes 31 c , ridges , or some other protrusion or surface treatment in order to facilitate fusion between the prosthesis and the adjacent bone , thus providing better fixation of the prosthesis and increasing the life of the implant . the second endplate 31 also can include an aperture ( not shown ), preferably located at or near the center of the second endplate 31 . as can be seen in fig4 , the inner member 20 further comprises a hollow inner sleeve 22 that depends distally in the longitudinal direction from the lower surface 21 b of first endplate 21 . the inner sleeve 22 has an outer surface 22 a that includes a number of circumferential grooves 23 . preferably , the grooves are separated by thin ridges and are approximately one ( 1 ) millimeter wide , though many spacings and numbers are possible . the inner sleeve 22 further comprises a number of slots 24 that are spaced longitudinally along the outer surface 22 a of the inner sleeve 22 . referring again to fig7 , the outer cage 30 further comprises a hollow outer sleeve 32 depending distally in the longitudinal direction from the upper surface 31 b of second endplate endplate 31 . the outer sleeve has an outer surface 32 a and an inner surface 32 b . the perimeter of the inner surface 32 b of outer sleeve 32 is designed such that the inner sleeve 22 can fit within the outer sleeve 32 . when the inner sleeve 22 is in place within the outer sleeve 32 , it is free to slide axially relative to the outer sleeve 32 . the outer sleeve 32 also includes locking apertures 33 that allow access to grooves of inner sleeve 22 when inner sleeve 22 is in place within the outer sleeve 32 . as shown in fig3 , the finger cage 40 includes a ring 41 that fits over the outer sleeve 32 and rests on a ledge 31 f that is formed at the intersection of the outer sleeve 32 and the second endplate 31 . depending distally in a longitudinal direction from the ring 41 are one or more fingers 42 . preferably , there are a plurality of fingers 42 . each of the fingers 42 has a first end 42 a and a second end 42 b . the first end 42 a is the point of attachment with the ring 41 . the fingers 42 are preferably resilient , allowing the second end 42 b to bend inward under force toward the center of the ring 41 while maintaining the capability to return to their original position after the force is removed from the finger 42 . preferably , the fingers 42 are resiliently biased outwardly . each of the fingers 42 has a tab 43 at its second end 42 b . each tab 43 has an interior side 43 a and an exterior side 43 b . the interior side 43 a of each tab 43 has incrementally spaced male nubs 44 . each of the exterior sides 43 b of tabs 43 have locking grooves 45 . when the ring 41 of the finger cage 40 is in place on the ledge 31 f of the outer cage , the tabs 43 of the fingers 42 align with locking apertures 33 of the outer sleeve 32 . in resting position , with no force applied to the fingers 42 , the tabs 43 are located within the apertures 33 , but are not forced to engage the circumferential grooves 23 of the inner sleeve 22 . however , when inwardly - directed force is applied to the tabs 43 of fingers 42 , the tabs 43 push through the locking apertures 33 of the outer sleeve 32 and the male nubs 44 of tabs 43 meshingly engage with the grooves 23 of the inner sleeve 22 . when the male nubs 44 of finger cage 40 engage the grooves 23 of the inner sleeve 22 , the inner sleeve 22 is locked in place within the outer sleeve 32 , and the height 100 of the apparatus 10 is fixed . to effectuate the locking action , the apparatus 10 includes a locking ring 50 ( see fig5 and 6 ). the locking ring 50 fits over the second end 42 b of fingers 42 such that it fits within the locking grooves 45 located on the exterior side 43 b of tabs 43 . the locking ring 50 rotates about the grooves 45 about the longitudinal axis of the apparatus 10 . preferably , the locking ring 50 is rotatable between two positions — locked and unlocked . the locking ring 50 has an interior surface 51 and an exterior surface 52 . the interior surface 51 is in contact with the locking groove 45 of the tabs 43 . the interior surface 51 of locking ring 50 is cammed such that the thickness of the locking ring 50 varies over the course of its circumference in a manner allowing the locking ring to be rotated relative to the finger cage 40 between a first locked position and a second unlocked position . referring to fig6 , when the locking ring is in a first position within the locking groove 45 of the finger cage 40 , a thinner portion 51 a of the locking ring 50 is in contact with each of the locking grooves 45 of the exterior side 43 b of tabs 43 . in this position , the locking ring does not apply inwardly - directed force to the fingers 42 . therefore , the male nubs 44 of tabs 43 do not mesh with the grooves 23 of the inner sleeve 22 . conversely , when the locking ring is rotated to a second position , a thicker portion 51 b of the locking ring 50 is in contact with each of the locking grooves 45 of the exterior side 43 b of tabs 43 . in the second position , the locking ring 50 squeezes the resilient fingers 42 inward , bringing the male nubs 44 of tabs 43 into contact with the grooves 23 of the inner sleeve 22 . when the locking ring 50 is in the second , or locked , position , the inner sleeve 22 cannot slide axially relative to the outer sleeve 32 . therefore , the height 100 of the apparatus 10 is fixed . it is also possible to include a secondary locking mechanism , such as a locking screw ( not shown ), that prevents rotation of the inner sleeve 22 within the outer sleeve 32 after the desired height 100 of the apparatus 10 is determined and the locking ring 50 is rotated to the second , or locked , position . in one embodiment , the outer sleeve 32 may include one or more locking apertures 34 . once the locking ring 50 is rotated to the locked position , the inner sleeve 22 is rotated within the outer sleeve 32 such that the locking aperture 34 of the outer sleeve 30 is aligned with one of the slots 24 and can receive a screw in one of the holes therein . in another embodiment , the slots 24 of the inner sleeve 22 can align with one or more appurtenances in the inner surface 32 b so that the appurtenances ride in the slots 24 and prevent rotation . in another embodiment , shown in fig2 , the ring 41 of the finger cage 40 does not rest on a ledge 31 f formed at the intersection of the second endplate 31 and the outer sleeve 32 , but instead on a plateau 32 c that is located on the outer surface 32 a of outer sleeve 32 ( see fig7 ). below the plateau 32 c , the outer sleeve 32 extends distally in the longitudinal direction to second endplate 31 . the same finger cage 40 and inner member 20 are used in this embodiment . this embodiment is preferred when it is necessary for the apparatus 10 to replace a large amount of bone because the elongated outer sleeve 32 allows for a significantly taller prosthesis with which the components of the shorter apparatus 10 other than the outer sleeve 32 , such as the finger cage 40 and the inner member 20 , are still compatible . preferably , the first and second endplates 20 , 30 include bone openings 5 , allowing bone graft to be packed inside . this allows the bone graft to fuse to the prosthesis , then grow outward into the body after implantation and connect with the healthy bone adjacent to the prosthesis , improving fixation of the device within the body . the outer sleeve 40 and the inner sleeve 50 also preferably include openings 39 to allow more bone graft to be packed inside the hollow of the inner sleeve 50 such that it can grow out of the slots and fuse with adjacent bone . further , as mentioned above , the first endplate 21 includes an aperture 21 d , while the second endplate 31 can include an aperture . the aperture 21 d of the first endplate 21 and the aperture of the second endplate 31 , respectively , align with the hollow sections of the inner and outer sleeves 22 , 32 , respectively . this allows bone graft to be packed inside the hollow sections of the inner and outer sleeves 22 , 32 and grow out of the apertures 21 d , to fuse with the healthy bone adjacent the apparatus 10 . further , cupped inserts ( not shown ) can be placed within the aperture 21 d of the first endplate 21 and the aperture of the second endplate 31 , respectively . bone graft can be placed in the cupped inserts , ensuring that bone graft will be in contact with the adjacent healthy bone even if the device is expanded after the bone graft is packed into the hollow sections of the inner and outer sleeves 22 , 32 . the cupped inserts are preferably slotted , thus still allowing bone graft to be packed in the hollow sections of the inner and outer sleeves 22 , 32 and grow through the cupped inserts to fuse with the healthy bone . also , although it is not required , it is preferred that the prosthesis be made of titanium alloy , such as ti - 4al - 6va . the apparatus 10 is manufactured of materials that are suitable for implantation in the human body . many such materials are known presently . in the preferred embodiment , the apparatus 10 is made of titanium alloy , such as ti - 4al - 6va . while there has been described and illustrated particular embodiments of an adjustable corpectomy apparatus , it will be apparent to those skilled in the art that variations and modifications may be possible without deviating from the broad spirit and principle of the present invention , which shall be limited solely by the scope of the claims appended hereto which shall be limited solely by the scope of the claims appended hereto .
a spinal fixation apparatus comprising an upper and lower endplate . depending distally in a longitudinal direction from the upper endplate is an inner sleeve that fits inside an outer sleeve that depends distally in a longitudinal direction from the lower endplate . the inner sleeve includes grooves located on its outer surface . a finger cage including resilient fingers fits around the outer sleeve . the fingers have ends that include male grooves . the ends of the fingers fit into apertures located in the outer sleeve . the apparatus further includes a locking mechanism that pushes the tips of the fingers through the apertures of the outer sleeve such that they mesh with the grooves of the inner sleeve . when the locking mechanism is unlocked the tips of the fingers disengage from the grooves of the inner sleeve , and the inner sleeve slide axially within the outer cage , adjusting the height of the device .