for the purposes of promoting an understanding of the principles of the invention , reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same . it will nevertheless be understood that no limitation of the scope of the invention is thereby intended , such alterations and further modifications in the illustrated devices , and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates . the present invention is useful for anterior internal fixation of the spine which is indicated for thoracolumbar burst fractures with significant canal compromise , vertebral body tumors , lesions due to infection , spondylolisthesis , degenerative discs , and post - laminectomy instability . this invention provides a top - loaded , low profile anterior fixation system which requires minimal instrumentation yet permits anterior load sharing and compression or distraction . the unique constructs of this invention permit fixation and compression or distraction with only two bolts , two rods and two rod connectors . a spinal fixation system 10 in accordance with a preferred embodiment of the present invention is depicted in fig1 . the system 10 includes a transverse connector 15 defining a thru - hole 16 and having a lower bone engagement surface 20 and an upper surface 23 . the transverse connector 15 engages a number of longitudinal members 11 by clamping surface 22 provided in a slot 21 defined in the connector 15 . preferably the longitudinal members 11 are spinal fixation rods . in one embodiment , the members 11 are smooth shot peened rods . referring to fig1 , and 3 , a number of fixation spikes 17 are fixedly attached to the lower surface 20 of the connector 15 . the lower surface 20 of the connector 15 in combination with an inner surface 19 of the fixation spikes 17 are configured to fit snugly around either side of a vertebra . in another application , the fixation spikes 17 may be slightly embedded into the vertebra . the end of each spike 17 is preferably beveled on its outer surface 24 so that each fixation spike 17 terminates in a wedge shape 18 which may aid in fixing and holding the connector 15 in place over a vertebra . bolts 30 are used to attach the system 10 to the vertebrae . it is understood that &# 34 ; bolt &# 34 ; refers to any of various bone fasteners , including a standard bone screw . the present invention is unique because it requires only one bolt per connector . previous devices have required two . fig4 shows one embodiment of a bolt 30 in detail . the bolt 30 has a vertebra engaging portion 31 at a first end 33 and a post 32 at a second end 35 . the vertebra engaging portion 31 of the bolt 30 may be configured , for example , with cancellous threads for fixation in the spongy bone of the vertebral body . the bolt also includes an integral flange 36 for supporting and clamping the connector 15 . in one embodiment , the second end 35 is configured to receive a driving tool . the configuration may include an internal or external hex as is well known in the art . the fixation system 10 can be top - loaded , i . e ., implanted over a bolt 30 after the bolt 30 is engaged to a vertebra . this is advantageous because it reduces the required size of the surgical opening and trauma to the patient . top - loading also provides a mechanical advantage during implantation of the system . after a bolt 30 is engaged to a vertebra by conventional means , the post 32 is insertable through the thru - hole 16 of the connector 15 . a fastener 40 is provided for each of the bolts 30 . the fastener 40 engages to the post 32 of the bolt 30 to secure the connector 15 to the bolt 30 and to clamp the longitudinal members 11 within the slot 21 of the connector 15 . thus , the longitudinal members 11 and the connector 15 are secured by a single bolt 30 . where the fastener 40 is a threaded nut , as in the preferred embodiment , the post 32 of the bolt 30 may included machine threads to engage with the nut . the nut or other fastener 40 is then top - tightened with a tool such as a socket wrench . the connector 15 may define recesses 41 surrounding each thru - hole 16 defined in the connector 15 . each recess can be configured to accept a fastener 40 in low profile so that the fastener 40 does not extend over the upper surface 23 of the connector 15 when it is engaged to a posts 32 . the recesses 41 can be concave to accept an arcuate underside of the fastener 40 . the spinal fixation system 10 may also be provided with a locking mechanism configured to prevent the bolts 30 from rotating relative to the connector 15 and the vertebra when the fastener or nut 40 is being tightened onto the bolt 30 . the locking mechanism also prevents the bolts from pulling out over time . in one embodiment of the invention , the locking mechanism includes an annular ring 45 defined on the lower surface 20 ( fig5 ) of the connector 15 and a mating face 50 affixed to each bolt 30 at a location between the post 32 and the vertebrae engaging portion 31 . the annular ring 45 on the lower surface 20 of the connector 15 is concentrically disposed around the thru - hole 16 and includes a number of radial splines 46 . referring to fig1 and 6 , the mating face 50 is concentrically disposed around and affixed to the bolt 30 and includes a number of opposing radial splines 51 for interdigitated engagement with the radial splines 46 on the lower surface 20 of the connector 15 . the annular ring 45 may alternately be a washer affixed to or a ring integrally formed on the lower surface 20 of the connector 15 . the clamping surface 22 provided by the slot 21 defined in the connector 15 may include a number of scallops ( fig6 ). the scallops are configured to receive the longitudinal members 11 in a manner that is well known in the art . for example , each scallop can be generally formed at a radius that is slightly smaller than the radius of the longitudinal member 11 which is to be situated within the scallop . the scallops provide means for fixing the spinal rods so that the longitudinal members 11 and connector 15 do not shift relative to each other . however , it is understood that the slot 21 defined in the connector 15 may be smooth and that other means may be provided to firmly fix the longitudinal members 11 . for example , in one embodiment , the slot 21 is smooth and the engagement of the longitudinal members 11 with the connector 15 is secured by a clamping action . the tightening of a fastener 40 on the post 32 causes a narrowing of the slot 21 of the connector 15 which in turn causes the connector 15 to securely clamp the longitudinal members 11 . another aspect of this invention provides means to vary the distance between vertebral bodies . according to the invention , a dynamic transverse connector 55 ( fig1 ) is slidable along the two longitudinal members 11 for compression and distraction of the vertebral bodies attached to the system 10 . one or more of other connectors 15 may be engaged to the longitudinal members at a fixed location . after compression or distraction is achieved , the dynamic connector 55 can be fixed by tightening the bolt 30 to which the connector 55 is fastened . the nuts 40 which attach to the bolts 30 can then be top tightened with a tool such as a socket wrench . the invention also provides methods for fixating the spine which include drilling a first hole in a first vertebral body and drilling a second hole in a second vertebral body . a bone bolt 30 is engaged to each of the first and second holes . the vertebrae are then supported with a fixation system 10 which includes two longitudinal members 11 , such as rods . a first connector 15 is attached to a first end of each of the longitudinal members 11 , and a dynamic rod connector 55 is slidably engaged to the longitudinal members 11 . one of the bone bolts 30 is engaged to the thru - hole 16 of the first connector 15 . the dynamic rod connector 55 is situated so that another bolt 30 engages a thru - hole 16 in the dynamic rod connector 55 . the dynamic rod connector 55 is then slid along the longitudinal members 11 to vary the distance between the first and second vertebrae . the post 32 of each bone bolt 30 is then engaged with a nut 40 to secure the fixation system 10 to the vertebrae . the dynamic rod connector 55 may be slid along the longitudinal members 11 in the direction towards the fixed connector 15 to compress the vertebrae before engaging the bone bolts 30 with the nuts 40 . the dynamic connector 55 may also be slid in a direction away from the fixed connector for distraction . the spinal fixation system 10 is preferably formed of medical grade stainless steel or similar high strength material . other materials are contemplated , provided the material is strong enough to endure the high loads transmitted through the components , and yet are biocompatible . specifically , the system could be manufactured in 6a14v titanium or 316lvm stainless steel . the system can be provided in several different sizes ranging from , but not limited to , 2 . 0 inches to 5 . 5 inches . while the invention has been illustrated and described in detail and the drawings and foregoing description , the same is to be considered as illustrative and not restrictive in character , it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected .
a transverse fixator assembly for spanning between a number of longitudinal members situated adjacent a patient &# 39 ; s vertebrae and methods for fixation of the spine which allow variation of the distance between two or more vertebrae . the assembly includes a number of connectors configured to span the distance between and engage the longitudinal members . the connectors define a thru - hole for engaging a bone bolt which is engaged to a vertebra plus a number of spikes projecting from the connector . a locking mechanism is configured to prevent the bolt from rotating relative to the connector when the nut is being tightened . one or more of the connectors may be a dynamic connector which is slidably engaged to the longitudinal members to vary the distance between the vertebrae for compression or distraction .