Cervical plate with screw lock retention clip

A cervical plate having improved mounting screws that employ a retention clip for automatically engaging the head portion of the screw during insertion into countersunk apertures. The arrangement prevents the mounting screws from migrating out of the bone material during use.

FIELD OF THE INVENTION

This invention relates to the field of orthopedic surgery and, particularly, to the area of spinal implants for stabilizing the spatial relationship of vertebrae.

BACKGROUND OF THE INVENTION

The spine consists of vertebrae that are cauterized into sections known as the cervical, thoracic and lumbar section in a flexible arranged column. The vertebrae are separated by small cartilaginous cushions known as intervertebral discs. Intervertebral discs are oblate spherical structures that maintain the space between adjacent vertebrae. Each intervertebral disc consists of an outer annulus fibrosus, which surrounds the inner nucleus pulposus. The annulus fibrosus consists of several layers of strong annular fibrocartilage to contain the nucleus pulposus and distribute pressure evenly across the disc wherein a mucoprotein gel serves to absorb shocks.

Deterioration of an intervertebral disc results in limited mobility and can cause severe pain. For instance, normal aging causes the nucleus pulposus to lose fluid and contract in volume resulting in a reduction in the intervertebral space. Any reduction of space between adjacent vertebrae may put pressure on the nerves of the spinal column. Further, a reduction in volume of the nucleus pulposus reduces the disc's ability to absorb shock which can result in disc herniation. The bulge of a herniated disc may also put pressure on nearby nerve structures resulting in pain as well as diminished range of motion.

Surgical options are available including laminectomy and discectomy combined with vertebral fusion and/or dynamic stabilization. However, these surgical options are highly invasive and require prolonged hospitalization and recovery. More recently, artificial disc replacement prosthetics have been used to replace or augment all or part of the removed or resected intervertebral disc.

In order to reduce the pain associated with the movement of the intervertebral joint, surgical intervention is often indicated as a means to alleviate pressure upon the spinal cord while concomitantly stabilizing the associated vertebrae.

Spinal plates are well known in the orthopedic art for fixing bones or bone fragments in a pre-selected spatial orientation. The plates are usually attached to the bones or bone fragments by screws designed to make a secure and long lasting connection not affected by the loads caused by normal activities of the host.

SUMMARY OF THE INVENTION

Embodiments of the invention are directed, inter alia, to a cervical plate having improved mounting screws that employ retention clips which engage the plate and fit over the screw heads. The screw heads engage the retention clip during installation allowing ease of insertion wherein the mounting screws pushes aside a portion of the retention clip. If the mounting screw is not fully inserted, the retention clip will not engage the screw head providing a visual indicator of proper screw head positioning. The retention clip is constructed to automatically engage the head portion of the screws during insertion of the screw into countersunk apertures. The arrangement prevents the mounting screws from migrating out of the bone material during use.

In particular embodiments, a cervical plate having an improved mounting that employs a PEEK spring, or another material having a defined memory, is positioned in the mounting hole of a plate to maintain a mounting screw in position. The screw head engages the PEEK spring that is constructed and arranged to form a taper, wherein the screw head stretches the PEEK spring during installation and prevents the screw from reversing.

Therefore, it is an objective of this invention to provide a cervical plate having at least one screw receiver spaced along the length of the plate for accepting a screw. The retention clips are formed from a spring type material which engages the screw heads to allow the screws to be rotated inward or outward, until the screw head passes the retention clip and is locked into position.

Thus an objective of this invention is to provide a cervical plate having a locking mechanism that is operated simultaneously with the positioning of the screws in receivers along the plate.

A further objective of this invention is to provide a cervical plate having an automatic locking mechanism which engages each screw to prevent back out migration of the screws.

It is an objective of this invention to provide a cervical plate adapted to span the intervertebral space and having at least two screw receivers spaced along the length of the plate having screw receivers each have countersunk apertures for accepting the heads of mounting screws with a spring material to engage the screw head to prevent backing out of the screw.

A further objective of this invention is to provide a cervical plate having an automatic locking mechanism which engages each screw to prevent back out migration of the screws.

Still another objective of this invention is to provide a cervical plate having a spring formed from a PEEK material that can be automatically stretched during installation and removed to permit post-operative removal of the screw is necessary.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures, set forth is a cervical plate10, the cervical plate10having improved mounting screws16that employ retention clips12that engage the plate and fit over the head portion14of the mounting screw16. The screw heads engage an edge18of the retention clip12during installation allowing ease of insertion wherein the mounting screw16pushes aside the edge18of the retention clip12. If the mounting screw16is not fully inserted, the retention clip12will not engage over the head portion14providing a visual indicator of proper mounting screw16positioning. The retention clip12is constructed to automatically engage the head portion14of the mounting screw16during insertion of the screw into countersunk apertures20. The arrangement prevents the mounting screws16from migrating out of the bone material during use. The retention clip12wraps around the plate, and includes a pass through aperture that can be viewed in the alternative embodiment set forth inFIGS. 1 and 6-9. In some embodiments, the cervical plate comprises visual or physical access ports70, optionally allowing the surgeon to view the correct positioning of the device and/or to allow for physical access of, for example, surgical or other instruments during the insertion of the cervical plate, if desired.

In some embodiments, the cervical plate10comprises improved mounting screws that employ retention clips that engage the plate and fit over the top of the screw, not shown. The screw heads engage an edge of the retention clip during installation allowing ease of insertion wherein the mounting screw pushes aside the edge of the retention clip. The retention clip is constructed to automatically engage the head portion of the screw during insertion into countersunk apertures. The arrangement prevents the mounting screws from migrating out of the bone material during use. Alternatively, the mounting screw16may include a groove17for engaging the first and second ends of the retention clips and preventing migration of the screws. The retention clip wraps around the plate and includes a pass through aperture.FIGS. 2-5show the lateral52retention clips. The retention clip comprises a central body55having an aperture54disposed therewith, a first arm56, a second arm57, wherein the first and second arms fold over creating opposing ends for wrapping around the plate53. The plate having grooves or recesses50wherein the grooves or recesses are anatomically shaped and dimensioned for receiving the retention clip, the grooves or recesses being disposed on the top surface60of the plate or the bottom surface61of the plate, or combinations thereof, and positioned laterally52.

In preferred embodiments, the arms of the retention clip can exhibit a degree of flexibility. The flexibility of the arms allow for the clips to insert the clips onto the cervical plate10. The degree of flexibility can be varied depending on the materials used to construct the retention clips, physical properties (for example modulus, elastic limit, etc, which might for example be introduced through different processing techniques), dimensions (cross-sectional size (for example diameter when the cross-sectional shape is circular, or width when it is square or rectangular), and cross-sectional shape (for example rounded, or polygonal etc), thickness of the materials, the angle of the fold in the arms of the retention clip, length of the arms and the like. In preferred embodiments, the retention clips comprise: shape memory alloys (e.g. nitinol), shape memory polymers, stainless steel and alloys thereof, titanium, titanium alloys, metallic alloys, polymeric materials, thermoplastics, thermoplastic composites, organic polymer thermoplastics (e.g., polyether ether ketone (PEEK)), plastics, plastic composites, ceramic or combinations thereof. In some embodiments, one or more components, e.g. first and second arms, planar center, of the retention clips can comprise any one or more materials.

If desired, the device components, for example, cervical plate, retention clips, biasing members, mounting screws, can be manufactured from one or more materials and, as such, would differ from one another.

Set forth inFIG. 10, is a cervical plate10having a mounting screw12that engages a spring biasing member15upon installation of the screw. The mounting screw head16engages the biasing member15to allow directional rotation of the mounting screw12into the mounting screw aperture or hole. During installation, the screw head16causes the biasing member to stretch into an open position and allow the screw head16to pass. The spring biasing member15is preferably made of polyether ether ketone (PEEK) which is an organic polymer thermoplastic. While PEEK is not traditionally a shape memory polymer, a variation of the PEEK material now allows shape memory behavior.

For installation, the plate10has a screw mount aperture20with a lip recess22formed beneath the surface24of the plate. The lip recess22is placed about the circumference of the screw mount20and is constructed and arranged to receive a portion of the spring biasing member15. The spring biasing member15having an outer surface28that has a recess engagement portion30and a support surface32. The support surface32providing a biasing position to allow entrance of a screw head16having a curved entrance surface34to pass a tapered inner surface36of the biasing member15.

Once the biasing member15has received the screw head16, the biasing member15prevents the screw from migrating out of the bone material during use of the device. The locking mechanism operates simultaneously with the placement of the screws into the screw mounting apertures. A lip40of the biasing member will engage the ceiling of the recess and force the biasing member15to close by engagement of tip42along the screw head surface44. The biasing members15can be removed by a screw driver or the like tool to permit post-operative removal of the implant if necessary.

Referring toFIG. 15, the angular movement of the screw12is illustrated by a positive10degree angle wherein the screw head surface44is angled to a position approaching point A on the biasing member15. Referring toFIG. 16, the angular movement of the screw12is further illustrated by a negative10degree angle wherein the screw head surface44is angled to a position approaching point B on the biasing member15.

Having described certain details of the device(s) and components thereof, various embodiments are provided. In one preferred embodiment, a device for immobilizing bones or bone fragments in a preselected spatial orientation comprises a plate, a retention clip, a mounting screw, a screw mount aperture, apertures or combinations thereof. In preferred embodiments, the plate is elongated and comprises a planar surface, a curved surface or combinations thereof.

In another preferred embodiment, the screw mount aperture comprises a lip recess disposed beneath the surface of the plate. In another preferred embodiment, the lip recess is placed about the circumference of the screw mount aperture and is constructed and arranged to receive a portion of a biasing member.

In yet another preferred embodiment, the biasing member comprises an outer surface having a recess engagement portion and a support surface, the support surface having a curved entrance surface and a tapered inner surface providing a biasing position for entrance of a screw head.

In preferred the mounting screw head engages the biasing member allowing for directional rotation of the mounting screw into the mounting screw hole. In another preferred embodiment, the screw head causes the biasing member to stretch into an open position, thereby allowing the mounting screw head to pass.

In another preferred embodiment, the retention clip comprises a central body having an aperture disposed therewith, a first arm, a second arm, wherein the first and second arms fold over creating opposing ends for wrapping around the plate. In preferred embodiments, the retention clips are removable.

In another preferred embodiment, the plate further comprises one or more apertures, ports, grooves or recesses, wherein the grooves or recesses are anatomically shaped and dimensioned for receiving a retention clip, the grooves or recesses being disposed on a top surface of the plate, a bottom surface of the plate, and positioned laterally or axially.

In yet another preferred embodiment, the mounting screws comprise a groove for engaging the first and second ends of the retention clips and preventing migration of the screws.

In yet another preferred embodiment, the retention clips are formed of one or more biocompatible materials comprising: shape memory alloys (e.g. nitinol), shape memory polymers, stainless steel and alloys thereof, titanium, titanium alloys, metallic alloys, polymeric materials, thermoplastics, thermoplastic composites, organic polymer thermoplastics (e.g., polyether ether ketone (PEEK)), plastics, plastic composites, ceramic or combinations thereof.

In yet another preferred embodiment, a device for immobilizing bones or bone fragments in a preselected spatial orientation comprising a plate having a screw mount aperture with a lip recess disposed beneath the plate's surface.

In some preferred embodiments, the lip recess is placed about the circumference of the screw mount and is constructed and arranged to receive a portion of a biasing member, wherein the biasing member comprises an outer surface having a recess engagement portion and a support surface, the support surface having a curved entrance surface and a tapered inner surface providing a biasing position for entrance of screw head.

In preferred embodiments, wherein, upon engaging a screw head, the biasing member prevents the screw from migrating out of bone material during use of the device.

In another preferred embodiment, a device for immobilizing bones or bone fragments in a preselected spatial orientation comprises a plate, a retention clip, a mounting screw, a screw mount aperture or combinations thereof. Preferably, the plate is elongated and comprises a planar surface, a curved surface or combinations thereof.

In preferred embodiments, the plate further comprises one or more apertures, ports, grooves or recesses. In preferred embodiments, the grooves or recesses are anatomically shaped and dimensioned for receiving the retention clip, the grooves or recesses being disposed on a top surface of the plate, a bottom surface of the plate, or combinations thereof, and positioned laterally or axially.

The retention clips are removable and comprise a central body having an aperture disposed therewith, a first arm, a second arm, wherein the first and second arms fold over creating opposing ends for wrapping around the plate.

The mounting screws comprise a groove for engaging the first and second ends of the retention clips and preventing migration of the screws. The retention clips are preferably formed of one or more biocompatible materials comprising shape memory alloys (e.g. nitinol), shape memory polymers, stainless steel and alloys thereof, titanium, titanium alloys, metallic alloys, polymeric materials, thermoplastics, thermoplastic composites, organic polymer thermoplastics (e.g., polyether ether ketone (PEEK)), plastics, plastic composites, ceramic or combinations thereof.

As used herein, the term “shape memory” is a property of select materials that have the ability to “remember” the shape given during original thermo-mechanical processing allowing the material to revert to that original shape when subjected to heat. For example, nickel titanium, or “Nitinol”, properties include the shape memory effect, superelasticity, and high damping capability.

As used herein, “shape-memory polymers” (SMPs) are polymeric smart materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape induced by an external stimulus (trigger), such as temperature change.