Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-05-14
2001-07-31
O'Connor, Cary (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S063000
Reexamination Certificate
active
06267764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to osteosynthesis systems for the spinal column.
2. Description of Related Art
Document FR-2 659 546 discloses an osteosynthesis system for the spinal column or backbone which has anchor members for fixing to a series of vertebrae of the spine, and at least one rigid link element designed to interconnect the anchor members. Once the system has been fixed to a series of vertebrae and once it has been assembled, it constitutes a rigid device preventing the vertebrae from moving relative to one another. This rigidity enables the device to support all or part of the stresses instead of the series of vertebrae concerned. Nevertheless, the first vertebra adjacent to the series is quite free to move relative to the series of vertebrae made rigid. A sharp discontinuity in the distribution of stresses along the spine can then arise between the last vertebra of the series and the first free vertebra. Consequently, the disk between these two vertebrae is overtaxed, and indeed an abnormal increase in stresses is observed at the disk. Very often this accelerates degeneration of the disk. This can be referred to as the “new-hinge” syndrome.
Document WO 94/21185 presents an osteosynthesis device for the spinal column in which two pedicular screws are interconnected by a link member having a flexible central portion that is U-shaped and offset laterally. Thus, when the two vertebrae are subjected to stresses tending to displace the two anchor members in relative rotation about an deformation axis, the link member is itself subjected to a bending moment and it bends elastically about the deformation axis. It therefore supports these stresses in part. The system recreates in part the biomechanical organization of the functional unit made up of the two fixed vertebrae together with the intervertebral disk. Nevertheless, that device has the drawback that the possibility of relative rotation between the two pedicular screws is essentially a function of the elasticity of the intermediate portion. In other words, the suitability of the intermediate portion for deforming relies on said elasticity. Unfortunately, when said elasticity is high so as to restrict relative displacement, then the vertebrae can be subjected to high levels of stress which can be harmful to them. Conversely, when the elasticity is low, support provided to the vertebrae is mediocre.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to provide an osteosynthesis system enabling the deformation ability of the intermediate portion for deformation to be controlled without constraining the choice of elasticity.
To achieve this object, the invention provides an osteosynthesis system for the spinal column, the system comprising at least two anchor members adapted to be fixed to two vertebrae of the spinal column, and a link member adapted to interconnect the two anchor members and exerting stresses against movement of the two anchor members in translation towards each other, the link member being elastically deformable in bending about at least one deformation axis, the link member having at least two fixing portions adapted to be fixed to the two anchor members, and at least one intermediate portion such that the two fixing portions are connected to each other solely by the intermediate portion, the intermediate portion being offset from an alignment axis defined by the two fixing portions. For the or each intermediate portion, the link member further has two abutments facing each other and disposed so as to come into abutment against each other when the link member is deformed about the deformation axis, or at least one of the deformation axes, in a given direction of rotation and through an angle equal to a predetermined limit value.
Thus, the amplitude of the deformation of the link member in this direction of rotation is limited. The abutments thus serve to control the ability of the link member to deform without that having any influence on the elasticity selected for the intermediate portion.
When the system has three anchor members with two of the anchor members rigidly connected to each other and with two of the anchor members interconnected by the deformable link member and located at one end of the series, a rigidity or transition gradient is established between the rigid portion of the spine and its free portion. Consequently, a better distribution of stresses is obtained along the spine. This avoids the appearance of a sudden discontinuity in stress distribution between the last vertebra of the rigid series and the first free vertebra, and on the contrary, it is easier to obtain a harmonious distribution of stresses along the spine. In addition, when the system relates to two vertebrae only, a flexible arthrodesis is provided between those two vertebrae.
Advantageously, the deformation axis or at least one of the deformation axes extends perpendicularly to a longitudinal direction of each anchor member and to a longitudinal direction of the link member.
Advantageously, the deformation axis or at least one of the deformation axes extends substantially parallel to a longitudinal direction of each anchor member.
Advantageously, the deformation axis or at least one of the deformation axes extends parallel to a longitudinal direction of the link member.
Thus, each of these axes corresponds to an axis of relative displacement in rotation of the two anchor members relative to each other, because of the movement of the vertebrae. Depending on circumstances, the intervertebral disk is relieved at least in part of the stresses corresponding to said respective displacements.
Advantageously, the alignment axis lies between the intermediate portion and the two abutments.
Advantageously, the intermediate portion has an outer face of spherical shape.
Advantageously, each of the two abutments has an outer face of spherical shape.
Thus, in these two cases, since the system is designed to be located inside the body, the number of sharp edges is limited and the sharp edges are placed so as to reduce the risk of harm due to the presence of the system in the body of the patient.
Advantageously, the spherical face of the intermediate portion and the spherical faces of the two abutments have a common center of curvature.
Advantageously, for the or each pair of fixing portions, the link member has a junction part contiguous with the two fixing portions, the junction part associated with the or at least one of the pairs of fixing portions being a single piece.
Advantageously, for the or each pair of fixing portions, the link member has a junction part contiguous with the two fixing portions, the junction part associated with the, or at least one of the, pairs of fixing portions having first and second mutually distinct link elements and fixing means for fixing the first and second link elements together.
Thus, the link member is made easier to fabricate when the junction part is in two parts or the link member has a large number of two-part junction parts relative to the total number of junction parts.
Advantageously, the fixing means are adapted to enable the distance between the two associated anchor members to be adjusted in the longitudinal direction of the link member.
Thus, the length of the link member is adjustable. While the system is being installed, it is thus possible to set the distance between the two anchor members to the position desired for the two vertebrae associated with said anchor members.
Advantageously, the second link element comprises a rod and the first link element has a housing suitable for receiving the rod, the first link element including locking means for locking the rod inside the housing in a plurality of positions along the longitudinal direction of the link member.
Advantageously, the system is adapted so that the alignment axis lies between the intermediate portion and the vertebrae.
Thus, when the two vertebrae are subjected to stresses tending to move the two anchor members towards each other in translation along
Blakely & Sokoloff, Taylor & Zafman
O'Connor Cary
Stryker France S.A.
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