Patent Application
20110270321
The present invention concerns engaging members and bone anchors, particularly useful for engaging a connecting element to one or more vertebrae. In a particular embodiment, the invention contemplates a bone anchor assembly with an engaging member having a cavity-base for engaging the connecting element to the bone anchor.
Several techniques and systems have been developed for correcting and stabilizing the spine and for facilitating fusion at various levels of the spine. In one type of system, a connecting element such as an elongated rod is disposed longitudinally along the length of the spine or several vertebrae of the spinal column. The rod may be bent to correspond to the normal or desired curvature of the spine in the particular region being instrumented. For example, the rod can be bent or angled to form a normal kyphotic curvature for the thoracic region of the spine, or a lordotic curvature for the lumbar region. In accordance with such a system, the rod is engaged to various vertebrae along the length of the spinal column by way of a number of bone anchors. A variety of bone anchors can be provided which are configured to engage specific portions of the vertebra. For instance, one such bone anchor is a hook that is configured to engage the lamina of the vertebra. Another type of bone anchor is a spinal screw which can be threaded into one or more aspects of the vertebral bone, such as the pedicle.
In one typical procedure utilizing a bendable, angled or linear rod, one or more of the rods is situated on one or both of the opposite sides of the spine or spinous processes. A plurality of bone screws are threadingly engaged to several vertebral bodies, such as to the pedicles of these vertebrae. One or more of the bone screws are maneuvered to manipulate the position or orientation of the vertebral body or bodies to which the bone screw is engaged. The rod(s) are connected or affixed to the plurality of bone screws to apply and maintain corrective and stabilizing forces to the spine.
The bone anchors in spinal procedures can have receivers with channels for the connecting element that, in some bone anchors, open upward, i.e. directly away from the bone to which the anchor is attached. Other bone anchors utilize channels that open along the medial or lateral side of the anchor to receive the connecting element. It is desirable in some procedures to utilize an engaging member to secure the connecting element to the bone anchor in the channel. However, the force applied to engage the engaging member to the bone anchor and the connecting element can introduce undesired stress into the construct. Additional improvements in the engagement of connecting elements to bone anchors are still needed.
The present invention generally relates to devices and methods that securely engage an elongated connecting element with a bone anchor. The bone anchor includes a bone engaging portion engageable to bony structure and a receiver that includes a passage or other structure for receiving the connecting element when the connecting element is positioned along the bony structure. An engaging member is engaged to the receiver and the connecting element to secure the connecting element with the bone anchor.
According to one aspect, the engaging member includes a base that is engaged to the bone anchor and a distal face at one end of the base. The distal face includes a cavity extending proximally into the base. The cavity receives a portion of the connecting element therein so that when the engaging member is securely engaged to the bone anchor with the distal face pressing against the connecting element, the engaging member deforms the connecting element into the cavity without penetrating the connecting element.
According to another aspect, a bone anchor assembly includes a bone engaging portion and a receiver extending proximally from the bone engaging member. The receiver defines a passage that receives an elongate connecting element therein. The connecting element is made from a polymeric material. The bone anchor assembly also includes an engaging member that is engaged to the receiver with a distal face of the engaging member facing the connecting element. The engaging member includes a cavity extending therein from the distal face, and the distal face defines a pressure surface extending around the cavity. Sufficient torque is applied to the engaging member so that the pressure surface of the distal face presses against the connecting element to deform the connecting element into the cavity.
According to another aspect, a spinal implant assembly includes a bone anchor member with a distal bone engaging portion engageable to a spinal column and a receiver at a proximal end of the bone engaging portion that defines a passage. An elongate connecting element is positionable along the spinal column through the passage of said receiver. The assembly also includes an engaging member engageable with the receiver. The engaging member extends along a rotation axis between a distal end and a proximal end. The distal end of the engaging member includes a pressure surface extending around the rotation axis. The pressure surface also extends around a cavity. The cavity extends proximally from the pressure surface into the engaging member to an end wall in the engaging member that is recessed from the pressure surface. The cavity receives a portion of the connecting element that deforms into the cavity when the pressure surface is compressingly engaged to the connecting element in the receiver.
Related features, aspects, embodiments, objects and advantages of the present invention will be apparent from the following description and the drawings.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates.
Devices and methods for securing a connecting element in an anchor assembly are provided for spinal and other bone stabilization surgical procedures. The anchor assembly includes a bone anchor and an engaging member engaged to the bone anchor. The engaging member includes a distal face that has a cavity and a pressure surface around the cavity. The pressure surface contacts and deforms the outer surface of the connecting element into the cavity to securely engage the connecting element to the bone anchor. The engaging member does not bite into or penetrate the connecting element, avoiding the creation of locations in the connecting element that could develop cracks or fractures when the connecting element is loaded, thus preserving the structural integrity of the connecting element. Since the deformation of the connecting element is maintained within the bone anchor assembly, the performance and integrity of the deformed connecting element in resisting spinal loads is not diminished. Furthermore, the amount of torque required to be applied to the engaging member to secure the connecting element with the desired axial grip in the bone anchor is reduced since the cavity of the engaging member captures a portion of the connecting element that is deformed into the cavity. Thus, axial movement of the connecting element relative to the bone anchor and engaging member is not only resisted by the frictional engagement between the pressure surface of the engaging member and the connecting element, but also by the resistance to axial shear forces developed by the portion of the connecting element that is received in the cavity.
Referring to
As shown in
Referring further to
Bone anchor assembly 10 may also include a seat member 70 that can be provided adjacent to head portion 118 of bone engaging portion 100 between connecting element 12 and head portion 118. Seat member 70 includes a body 72 having a concavely curved lower surface 74 for receiving head portion 118, and an opposite seating surface 78 against which connecting element 12 can be secured. Seat member 70 can also include a central aperture 76 through which a driving tool can be positioned to engage head portion 118 and secure anchor member 100 to the underlying bony structure. Seating surface 78 can be flat, as shown, or can include a concave curvature or other shape to at least partially receive connecting element 12 thereagainst.
One embodiment a bone anchor that is multi-axial in form has been described with respect to
Other embodiments contemplate other forms for the bone engaging portion of the anchor member. For example, the distal bone engaging portion can be in the form of a hook, staple, cable, tether, suture anchor, interbody fusion implant, artificial disc implant, bolt, or other structure engageable to bony tissue. The receiver defines a passage that receives a connecting element, such as a rod, tether, wire, cable, plate or other elongated linking member that can extend between one or more additional anchor assemblies secured to one or more additional vertebrae or other bony structure. The bone engaging portions can be configured as pedicle screws, bolts or other member sized and configured for engaging a pedicle of vertebra. The bone engaging portions can also be configured to engage other parts of a vertebra, or other bony structures in the patient. Furthermore, a set screw, washer, crown, cap or other device may be provided in addition to engaging member 40, 40′ for engagement within and/or about receiver to secure connecting element 12 thereto.
Receiver 20, 218 can be configured to receive connecting element 12 in passage 30, 220 with connecting element 12 top-loaded into receiver 20, 218 or loaded into receiver 20, 218 in an end-wise manner. Alternatively, the receiver can be configured so that the connecting element can be side-loaded or bottom loaded therein prior to engagement with engaging member 40, 40′. Furthermore, connecting element 12 can be engaged to two or more anchor assemblies 10, 210 along the spinal column, and provide stabilization for multiple spinal motion segments. Connecting element 12 can be a spinal rod connectable to one or more anchor assemblies to rigidly stabilize the spinal column. Connecting element 12 can also be flexible to allow motion of the spinal motion segment or segments to which it is attached. It is also contemplated that connecting element 12 can comprise multiple components. Various forms for the connecting element 12 are contemplated, including plates, wires, struts, cables, and other devices capable of engagement in a receiver of an anchor assembly with engaging members 40, 40′. Connecting element 12 can be a spinal rod comprised of any one or combination of metal, metal allow, plastic, polymer, tissue, fabric, or mesh material, for example.
Referring further to
First portion 42 can also include an inner tool recess 52 extending axially therein distally from bore 48 and about rotational center 43. Tool recess 52 can be engaged by a tool to allow further tightening or removal of base portion 42 when engaged to arms 22, 24 even if proximal portion 44 is removed or is not provided. Tool recess 52 can be smaller in cross-sectional size than bore 48 so that a tool sized to be received only in bore 48 cannot pass into distal tool recess 52. In the illustrated embodiment, tool recess 52 includes a hexagonal-type shape with rounded lobes to receive a driving tool, although any suitable driving recess is contemplated. Break-off region 46 is located slightly proximally of tool recess 52 so that base portion 42 remains intact when sufficient torque is applied to remove proximal portion 44. The threshold torque can be controlled or varied by controlling or varying the wall thickness at break-off region 46 during manufacture of engaging member 40. Profile 50 and recess 52 can include any suitable configuration for engagement with a driving tool to deliver driving forces to engaging member 40, including a hex shape, star shape, cross-shape, slotted shape, or other non-circular shape. Other embodiments contemplate one or more of the profile 48 and recess 52 could be omitted from engaging member 40. Still other embodiments contemplate a base portion that is internally threaded to engage the receiver, or includes non-threaded structures to engage the receiver.
First portion 42 includes a distal end that defines a pressure surface 60 positionable against connecting element 12 when connecting element 12 is located in passage 30 of receiver 20 or passage 220 of receiver 218. The distal end also defines cavity 41 extending proximally therein from pressure surface 60 to a material barrier 56 located between cavity 41 and tool recess 52. Pressure surface 60 presses against the outer surface of connecting element 12 as engaging member 40, 40′ is driven against connecting element 12. As shown in
As also shown in
Cavity 41 is centered on central rotation axis 43, and pressure surface 60 is planar and is concentric about cavity 41. In one embodiment, cavity 41 defines a width with a first dimension A orthogonally to central axis 43, and pressure surface 60 defines an overall width having a second dimension B orthogonally to central axis 43. Dimension A can range from more than zero to the major diameter of thread profile 54. In the illustrated embodiment, first dimension A is sized to provide pressure surface 60 with a connecting element contact width 2C along the distal face that corresponds to dimension B less dimension A. In one particular embodiment, the ratio of the contact width 2C of the pressure surface 60 along the distal face is about one third of width A of cavity 41 along the distal face so that the pressure exerted by pressure surface 60 is sufficient to deform the connecting element while the area and volume of the cavity 41 is sufficient to receive deformed material. Other embodiments contemplate other ratios for width 2C to width A, ranging from more than zero to one or more. In one particular embodiment, pressure surface 60 defines an area around central rotation axis 43 that is about three-fourths of the area of cavity 41. Other embodiments contemplate other ratios for the area of pressure surface 60, ranging from more than zero to one or more.
As shown in
Materials for the bone engaging portions, receivers, saddles, and engaging members disclosed herein can be chosen from any suitable biocompatible material, such as titanium, titanium alloys, cobalt-chromium, cobalt-chromium alloys, or other suitable metal or non-metal material. Connecting element 12 can be made from the same material as one or more of the components of the anchor assembly to which it is engaged, or from a different material. For example, connecting element 12 can be made from PEEK, plastic, titanium or titanium alloy, cobalt-chrome, composite material, or other material that is the same or different from the material of one or more components of the anchor assembly to which is engaged. In one embodiment, the engaging member 40, 40′ is made from metal material and the connecting element 12 is made from a polymeric material that is more readily deformed into cavity 41 by pressure applied with pressure surface 60.
Although various embodiments have been described as having particular features and/or combinations of components, other embodiments are possible having a combination of any features and/or components from any of embodiments as discussed above. As used in this specification, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a member” is intended to mean a single member or a combination of members, “a material” is intended to mean one or more materials, or a combination thereof. Furthermore, the terms “proximal” and “distal” refer to the direction closer to and away from, respectively, an operator (e.g., surgeon, physician, nurse, technician, etc.) who would insert the medical implant and/or instruments into the patient. For example, the portion of a medical instrument first inserted inside the patient's body would be the distal portion, while the opposite portion of the medical device (e.g., the portion of the medical device closest to the operator) would be the proximal portion.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that all changes and modifications that come within the spirit of the invention are desired to be protected.
