Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-12-14
2002-07-02
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S070000, C606S071000, C606S064000
Reexamination Certificate
active
06413259
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a bone plate assembly including a bone plate, bone screws received in apertures in the bone plate, and a screw retaining member attached to the bone plate which covers at least a portion of the bone screws. When bone screws have been received by the bone plate and inserted into bone and/or tissue, the bone plate assembly can be used to fuse anatomical structures together, such as adjoining bones, or to heal a fracture in bone.
BACKGROUND OF THE INVENTION
The bones and connective tissue of an adult human spinal column consist of more than twenty discrete bones coupled sequentially to one another by a tri-joint complex. The complex consists of an anterior disc and two posterior facet joints. The anterior discs of adjacent bones are cushioned by cartilage spacers referred to as intervertebral discs. The bones of the spinal column are categorized as: cervical, thoracic, lumbar, or sacral. The cervical portion of the spine which comprises the top of the spine up to the base of the skull, includes the first seven vertebrae. The intermediate twelve bones are thoracic vertebrae, and connect to the lower spine comprising the five lumbar vertebrae. The base of the spine is a sacral bones (including the coccyx).
The spinal column of bones is a highly complex anatomical structure as evidenced by the sophisticated interaction between the bones which comprise it. Furthermore, the spinal column houses and protects critical elements of the nervous system. Despite its complexity, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.
Various types of problems can affect the structure and function of the spinal column. Such problems can be based on degenerative conditions of the intervertebral disc or the articulating joints, or trauma to the disc, bone, or ligaments supporting the spine. Other problems include 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 or 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 pathrodisis of the spine. This can be accomplished by removing the intervertebral disc and replacing it with bone and immobilizing the spine to allow the eventual fusion or growth of the bone across the disc space to connect the adjoining vertebral bodies together. The stabilization of the vertebrae 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 these techniques 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 should permit 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 healing can adversely affect the recovery. The device must be secure in its attachment to the spine to prevent migration of the implant or back out of the screws from the bone which could result in damage to the structures surrounding the spine, causing severe and potentially life threatening complications. The device must be safely and consistently implanted without damage to the patient.
The conventional method of installing 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 guided at the proper angle into the hole that has been created, as inadvertent misalignment can reduce pullout strength or result in damage to surrounding nerves or arteries.
Genetic or developmental irregularities, trauma, chronic stress, tumors and disease, however, can result in spinal pathologies which either limit this range of motion, or which threatens the critical elements of the nervous system housed within the spinal column. A variety of systems have been disclosed in the art which achieve this immobilization by use of a surgical implant. It is known that with cervical plates, the screw head may be provided with an arcuate shape, and the plate may be provided with a recess having a complimentary shape that receives the shape of the head. In this arrangement, the head and plate share load bearing responsibilities over an enlarged surface area. Further, since each of the head and recess have arcuate surfaces, the screw shaft is able to rotate in an arcuate path relative to its longitudinal axis. For instance, as shown in U.S. Pat. No. 5,534,027 at col. 4 lines 18-19 and
FIG. 5
, it is possible for “axis “A” of the screw 10 to be at an angle “AA” to axis “B” of the hole 31.
SUMMARY OF THE INVENTION
The present invention is directed to a bone plate assembly including a bone plate having apertures through which bone screws are received and a screw retaining member that covers at least a portion of the bone screws. The screw retaining member is provided with an aperture that receives a member such as a screw which fixes the screw retaining member to the bone plate. The bone plate assembly of the present invention can be fastened to at least two bones, or at least two portions of bones, in order to facilitate the healing process. The bone plate is provided with apertures through which bone screws are received and fitted into drill holes, in order to fasten the plate to bone.
In one embodiment, the screw holes in the bone plate are not provided with uniform dimensions. For example, in one embodiment, the size of a dimension D
1
of the apertures is greater than the size of a dimension D
2
of the apertures. In another embodiment, D
1
corresponds to the length dimension of the aperture and D
2
corresponds to the width dimension of the aperture. In yet another embodiment, length dimension D
1
of the aperture runs in the same direction as length dimension D
1
of the bone plate. The bone screws which are inserted into the apertures, which have a screw head, and a shaft, possess dimensions that permit the screw to move in the D
1
dimension.
In yet a further embodiment, the aperture of the screw retaining member is not provided with uniform dimensions. For example, in one embodiment, the size of a dimension D
1
of the apertures in the screw retaining members is greater than the size of a dimension D
2
of the apertures in the screw retaining members. In another embodiment, D
1
corresponds to the length dimension of the apertures and D
2
corresponds to the width dimension of the apertures. In yet another embodiment, length dimension D
1
of the apertures in the screw retaining members runs in the same direction as length dimension D
1
of the apertures
La Rosa Frank
Lyons Matthew
Blackstone Medical, Inc
Dreier & Baritz LLP
Philogene Pedro
LandOfFree
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