Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1998-10-23
2001-05-22
Recla, Henry J. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S064000, C606S070000
Reexamination Certificate
active
06235034
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a bone plate for assisting with the surgical arthrodesis (fusion) of two or more bones together, and a bone screw guide mechanism to assist in the proper drilling, tapping and placement of the bone screws to secure the plate.
BACKGROUND OF THE INVENTION
The spinal column of vertebrates provides support to bear weight and protection to the delicate spinal cord and spinal nerves. The spinal column comprises a series of vertebrae stacked on top of each other. There are typically seven cervical (neck), twelve thoracic (chest), and five lumbar (low back) segments. Each vertebra has a cylindrical shaped vertebral body in the anterior portion of the spine with an arch of bone to the posterior which covers the neural structures. Between each vertebral body is an intervertebral disk, a cartilaginous cushion to help absorb impact and dampen compressive forces on the spine. To the posterior the laminar arch covers the neural structures of the spinal cord and nerves for protection. At the junction of the arch and anterior vertebral body are articulations to allow movement of the spine.
Various types of problems can affect the structure and function of the spinal column. These can be based on degenerative conditions of the intervertebral disk or the articulating joints, traumatic disruption of the disk, bone or ligaments supporting the spine, tumor or infection. In addition congenital or acquired deformities can cause abnormal angulation or slippage of the spine. Slippage (spondylolisthesis) anterior of one vertebral body on another can cause compression of the spinal cord or nerves. Patients who suffer from one of more of these conditions often experience extreme and debilitating pain, and can sustain permanent neurologic damage if the conditions are not treated appropriately.
One technique of treating these disorders is known as surgical arthrodisis of the spine. This can be accomplished by removing the intervertebral disk and replacing it with bone and immobilizing the spine to allow the eventual fusion or growth of the bone across the disk space to connect the adjoining vertebral bodies together. The stabilization of the vertebra to allow fusion is often assisted by a surgically implanted device to hold the vertebral bodies in proper alignment and allow the bone to heal, much like placing a cast on a fractured bone. Such techniques have been effectively used to treat the above described conditions and in most cases are effective at reducing the patient's pain and preventing neurologic loss of function. However, there are disadvantages to the present stabilization devices and to the available tools to implant them.
The spinal fixation device needs to allow partial sharing of the weight of the vertebral bodies across the bone graft site. Bone will not heal if it is stress shielded from all weight bearing. The fixation device needs to allow for this weight sharing along with the micromotion that happens during weight sharing until the fusion is complete, often for a period of three to six months or longer, without breakage. The device must be strong enough to resist collapsing forces or abnormal angulation during the healing of the bone. Loss of alignment during the healing phase can cause a poor outcome for the patient. The device must be secure in its attachment to the spine to prevent migration of the implant or backout of the screws from the bone which could result in damage to the structures surrounding the spine, resulting in severe and potentially life threatening complications. The device must be safely and consistently implanted without damage to the patient.
Several types of anterior spinal fixation devises are in use currently. One technique involves placement of screws all the way through the vertebral body, called bicortical purchase. The screws are placed through a titanium plate but are not attached to the plate. This device is difficult to place, and overpenetration of the screws can result in damage to the spinal cord. The screws can back out of the plate into the surrounding tissues as they do not fix to the plate. Several newer generation devices have used a unicortical purchase of the bone, and in some fashion locking the screw to the plate to provide stability and secure the screw from backout. Problems have resulted from over ridged fixation and stress shielding, resulting in nonunion of the bony fusion, chronic micromotion during healing resulting in stress fracture of the fixation device at either the screw or the plate, insecure locking of the screw to the plate resulting in screw backout, or inadequate fixation strength and resultant collapse of the graft and angulation of the spine.
The conventional method for placing the bone screws entails drilling a hole, tapping the hole and threading the bone screw into the bone. To drill the hole a guide is held next to or attached to the plate. A drill is inserted into the guide and the hole drilled into the bone. The guide is removed and a tap is threaded through the hole attempting to follow the same angle as the drill hole. Caution must be used to prevent the sharp edges of the tap from damaging surrounding tissues or in creating too large a tap hole by toggling the handle of the tap. This will reduce the security of the screw bite into the bone and increases the likelihood of screw pullout. After tapping, the screw must be freehand guided at the proper angle into the hole created, inadvertent misalignment can reduce pullout strength or result in damage to surrounding nerves or arteries. Thus a need exists for a method of placing the screws that avoids these problems and risks to the patient.
SUMMARY OF THE INVENTION
The present invention is directed to a bone plate for stabilizing adjacent vertebrae or holding two portions of a bone together, e.g., a broken bone, while it heals. The bone plate comprises a base plate having at least two screw holes, at least two bone screws, and a bone screw locking means. The preferred bone screw locking means is a retaining plate. The bone plate is placed over at least two different bones or bone portions, and the bone screws are placed into each bone or bone portion through the bone screw holes in the base plate. The retaining plate is placed over the heads of the bone screws and fixedly attached to the base plate to prevent the bone screws from backing out of the bone. The bone screws have heads shaped to allow the bone screws to toggle within the screw holes in the base plate, preferably radiused heads. By controlling the amount of toggle, one can control the amount of weight borne by the bone plate.
The present bone plates are particularly useful for spinal fixation. For such a use, the base plate can be part of a larger device or structure. An example of such a device is a disk replacement spacer for stabilizing a portion of the spine. Such a device is described, for example, in U.S. patent application Ser. No. 08/764,089, the disclosure of which is incorporated herein by reference.
The present bone plates also can be used anywhere in the body where anti-backout is important, i.e., where it is important to be sure that bone screws will not back out. It also is particularly useful anywhere in the body where partial weight bearing of bone graft is important. Such uses include, for example, small figment bone sets from arm fractures, wrist fractures, ankle fractures, and hand fractures. The bone plate could also be used to secure hips in place, for femur fractures or the like.
The present invention is also directed to a bone screw guide mechanism for placing bone screws in the bones. The bone screw guide mechanism comprises a tubular member with open ends and a base fixedly attached at a predetermined angle to the tubular member at its bottom end. The base is mountable on the base plate of a bone plate so that the tubular member is generally coaxial with a bone screw hole in the base plate. Alternatively, the base can be mounted directly on the bone. Preferably, a handle is attached to the base or tubular member to p
Christie Parker & Hale LLP
Recla Henry J.
Woo Julian W.
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