Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reissue Patent
1999-01-07
2001-12-18
Mancene, Gene (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S064000
Reissue Patent
active
RE037479
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device for fixing adjacent vertebrae to each other using a rod and unique hollow screws.
2. Description of the Related Art
Fixation (or fusion) of vertebral columns with bone material or rods and plates is a common, long practiced surgical method for treating a variety of conditions. Many of the existing procedures involve components that protrude outwardly that may contact and damage a body part, such as the aorta, the vena cava, the sympathetic nerves, the intestine and the ureter. Also, many constructions involve components that may loosen and cause undesirable problems. A Dunn device was on the market until pulled by the U.S. Food & Drug Administration because of problems with delayed rupture of the aorta secondary to the device being so bulky as to contact the aorta, erode its surface and lead to fatal hemorrhage in several cases.
U.S. Pat. No. 5,152,303 issued to Allen on Oct. 6, 1992 relates to an anterolateral spinal fixation system including a cannulated screw threaded into a vertebra and a rod attached to the screw. The process involves threading the cannulated screw into a pilot hole drilled into the vertebral body portion and fastening a rod at its lower and upper ends to the vertebral body by the cannulated screws. (Col. 3, lines 62-64; Col. 4, lines 5-8).
U.S. Pat. No. 4,059,115 issued to Jamashev et al. on Nov. 22, 1977 relates to a surgical instrument for operation of anterior fenestrated spondylodesis in vertebral osteochondrosis. The instrument includes a hollow cylindrical cutter with a cutting edge, and a handle. By rotation of the handle accompanied with slight pressure the cutter is worked into the bodies of the adjacent vertebras (abstract, Col. 6, lines 56-58).
U.S. Pat. No. 5,015,247 issued to Michelson on May 14, 1991 relates to a method of performing internal stabilization of a spine. The method involves seating a drill sleeve into the two vertebrae and drilling the vertebrae with the drill installed through the drill sleeve. Bagby U.S. Pat. No. 4,501,269 is mentioned. (Col. 6, lines 27-30, Col. 7, line 68, Col. 9, lines 22-25, 39).
Current devices have substantial deficiencies when osteoporotic bone is encountered. The soft, decalcified bone in such patients has poor pull-out strength for screws. Bone screws are known to have very little holding power in osteoporotic bone and loosen readily, severely limiting the holding power and fixation ability of current devices.
Some devices have designs that include hollow screws or screws with transversely drilled holes, presumably to improve holding power and allow bone to grow therethrough. These devices are all relatively small screws which are not capable of large surface area fixation.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.
SUMMARY OF THE INVENTION
The invention provides a method and device for fixing two or more vertebrae. The process is elegantly simple and solves many of the problems attendant with previous devices.
Each vertebra to be joined is prepared by forming a partial annular cut, as by a hole saw, preferably leaving the core plug of bone in place. A hollow screw is threaded into the annular ring recess thus formed. A channel is cut in the vertebral bone between each of the screws to accommodate a rod that is placed over each screw. A locking cap over each screw secures the rod to the screws and thereby fixes the spine as desired.
The method and device provide many advantages. The hollow screws are exceptionally strong, having greater holding surface area than conventional solid screws. The rod is held in the screw between two widely spaced slots. The rod is also held firmly by a third point by a dimple on the locking cap. The rod is secured to the screws by at least three points of fixation over a much greater distance than traditional systems. This provides a linkage which is significantly greater in terms of mechanical stability over the prior art.
Holes in the side walls of the hollow screws allow for bone ingrowth to further strengthen the connection. Since the bone plug is not removed, the screw's wall is very thin, bone can grow through the screw rapidly, thus securely fusing the screw to the vertebra and provides a better anchor to the vertebral bone. Additionally, as the bone grows through the holes in the screw, the bond becomes stronger with time. Prior art devices use screws that may slowly become less secure with age and the inevitable micromotion that occurs between the screw and the vertebral bone.
By varying the cross-section geometric structure and diameter of the rod, various degrees of stiffness may be imparted. Also, by varying the geometric cross-section structure of the rod, stiffness may be imparted selectively in the appropriate plane of motion. For instance, if increased flexion-extension stability is desired, the rod can be oriented in the flexion-extension plane and elongated such that it will provide greater stiffness in flexion-extension than in lateral bending. Such a feature will allow the surgeon to define the plane of stiffness necessary to match the pathology encountered.
The rods within the cut channels avoid the cantilever effect of prior art devices where the load is carried far from the center of the spine. Thus, the rod acts more like an intramedullary rod in the vertebrae. This is far preferable in that a rod nearer the center of the axis of rotation does not have the cantilever effect of prior art systems. This also presents no protrusions that may abut against vital body components.
The process is very simple, requiring only the drilling of a single hole saw cut in each vertebra, formation of channels therebetween and installation of the hollow screws, placement of the rod and securement with the locking caps.
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Mancene Gene
Robert Eduardo C.
Spineology Inc.
Vidas Arrett & Steinkraus
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