Bone screw threaded enlarger

A bone fastener system can comprise a fastener and a first sizing component. The fastener can comprise a shaft that provides an anchoring footprint. The first sizing component can be configured to be connected to the shaft and can include a first anchoring feature, or circumferential bone engaging feature, to increase a size of the anchoring footprint. The first anchoring feature can comprise a sleeve that radially expands a diameter of the threaded shaft. The first anchoring feature can comprise axially extending teeth. The system can further comprise a second sizing component including a second anchoring feature to increase the size of the anchoring footprint, the second anchoring feature being different from the first anchoring feature. The second anchoring feature can expand the diameter of the threaded shaft a greater amount than the first anchoring feature. The second anchoring feature can have a length greater than the first anchoring feature.

TECHNICAL FIELD

This document pertains generally, but not by way of limitation, to systems and methods for fixation of bones during orthopedic procedures. More particularly, this disclosure relates to, but not by way of limitation, vertebral bone anchors particularly suited for use in weakened or degenerative bone.

BACKGROUND

The spinal column of a patient includes a plurality of vertebrae linked to one another by facet joints and an intervertebral disc located between adjacent vertebrae. The facet joints and intervertebral disc allow one vertebra to move relative to an adjacent vertebra, providing the spinal column a range of motion. Diseased, degenerated, damaged, or otherwise impaired facet joints and/or intervertebral discs may cause the patient to experience pain or discomfort and/or loss of motion, thus prompting surgery to alleviate the pain and/or restore motion of the spinal column.

One possible method of treating these conditions is to immobilize a portion of the spine to allow treatment. Traditionally, immobilization has been accomplished by rigid stabilization. For example, in a conventional spinal fusion procedure, a surgeon restores the alignment of the spine or the disc space between vertebrae by installing a rigid fixation rod between pedicle screws secured to adjacent vertebrae. Bone graft is placed between the vertebrae, and the fixation rod cooperates with the screws to immobilize the two vertebrae relative to each other so that the bone graft may fuse with the vertebrae.

Dynamic stabilization has also been used in spinal treatment procedures. Dynamic stabilization does not result in complete immobilization, but instead permits a degree of mobility of the spine while also providing sufficient support and stabilization to effect treatment. Dynamic stabilization systems can include a flexible construct extending between pedicle screws installed in adjacent vertebrae of the spine.

Examples of stabilization systems are the Dynesys® System, the Sequoia® Thoracolumbar Pedicle Screw System and the Lineum® OCT Spine System available from Zimmer Biomet Spine, Inc. of Broomfield, Colo.

OVERVIEW

The present inventors have recognized, among other things, that a problem to be solved can include the need to provide bone anchors, such as threaded fasteners or screws, in bone that is degenerative or otherwise weakened. If bone anchors are inserted into weakened bone, there can be the potential for the fastener to move position or become dislodged, thereby rendering the anchoring effects provided by the fastener less effective or altogether ineffective.

The present subject matter can help provide a solution to various problems associated with the anchoring of fasteners in weakened or partially weakened bone by providing a sizing component that can be coupled to the fastener to enlarge the anchoring footprint of the fastener. The sizing component can be modular such that it can be attached to standard fasteners already typically maintained in inventory and/or can be combined with other sizing components to change the capabilities of the sizing component. Additionally, various sizing components can come in different shapes and configurations to accommodate bone that is weakened or degenerative in different capacities, thereby allowing a practitioner or surgeon the ability to choose from a variety of sizing components for use with particular bone defects of a particular patient. In various examples, the sizing component can be a sleeve into which a fastener is threaded to enlarge all or part of the shaft diameter of the fastener to provide radial anchoring in cancellous bone inside the bone, or a cap into which a fastener is threaded to provide axial anchoring into cortical bone at a surface of the bone.

In an example, the present subject matter can help provide a solution to this problem, such as by providing a bone anchor system comprising a fastener and a first sizing component. The fastener can comprise a shaft having a shaft diameter, an anchoring projection on the shaft, and a head at an end of the shaft. The bone screw system can have a variety of configurations, such as polyaxial, monoaxial, and uniaxial movement between the fastener and a housing. The first sizing component can be connected to the fastener. The first sizing component can comprise a first body portion having a first outer diameter larger than the shaft diameter, and a first bore extending through the first body portion, the first bore sized to receive the shaft diameter. The first sizing component can also include a first sizing located in the first bore to receive the anchoring projection on the shaft, a first outer surface at the first outer diameter, and a first circumferential bone engaging feature.

In another example, a bone anchor system can comprise a fastener, a first sizing component and a second sizing component. The fastener can comprise a threaded shaft configured to provide an anchoring footprint. The first sizing component can be configured to be connected to the threaded shaft. The first sizing component can include a first anchoring feature to increase a size of the anchoring footprint. The second sizing component can be configured to be connected to the threaded shaft. The second sizing component can include a second anchoring feature to increase the size of the anchoring footprint. The second anchoring feature can be different from the first anchoring feature.

In yet another example, a method of fastening a bone anchor can comprise forming a bore having a shaft diameter into a boney structure for a fastener shaft that is threaded, trialing the bore to determine bone integrity, selecting a sizing component based on the trialing, the sizing component having an enlarger diameter larger than the shaft diameter and a circumferential bone engaging feature, assembling the selected sizing component to the fastener shaft, and inserting the fastener shaft into the bore to engage the sizing component with the boney structure.

DETAILED DESCRIPTION

Bone anchor10can be used to couple rod12or another elongate member to a boney structure. For example, shank23of fastener20can be inserted into and through upper housing40and lower housing50to connect to a pedicle of a vertebra. Retainer assembly13can be inserted into channel43to sit below rod12. Retainer ring14can be connected to upper housing40to lock wave washer15and seat16in housing30below threading42, thereby at least partially immobilizing fastener20within housing30. Rod12can fit into U-shaped channel43formed by opposing arms41, such as by being inserted into channel43from the top or proximal end of housing30. Closure member11, which can comprise a set screw or the like, can be threaded into threading42to push rod12down into channel43atop retainer assembly13, thereby at least partially immobilizing rod12within bone anchor10.

Bone anchor10can include particular degrees of adjustability that can help ensure that fastener20and elongate member12can be locked down at the particular locations and orientations desired by the practitioner or surgeon. For example, head21can be spherical in shape to allow rotation within housing30. In particular, bone anchor10can allow for angular deviation of bone screw20away from the axial orientation shown inFIG. 1. Such an angular deviation may be referred to as “angulation”, and desired angulations may exceed 35 degrees, 40 degrees, 45 degrees, or more, in some instances. Further description of such angulation is described in U.S. Pat. No. 9,289,244 to Hestad et al., which is hereby incorporated herein by this reference in its entirety.

Bone anchor10can be delivered or provided to or obtained by a practitioner in a semi-assembled state. In the exemplary design ofFIG. 1, housing30can be modular, thus formed of multiple components coupled together. For example, housing30can include two components that are longitudinally adjacent to each other, namely upper housing40and lower housing50. Thus, upper housing40and lower housing50can be pre-assembled. Also, fastener20can be pre-inserted into housing30. Housing30can have a bore that extends longitudinally through the upper housing40and lower housing50, generally coaxial with the longitudinal axis of bone anchor10. Upper housing can include bore46and lower housing50can include bore52which can each be aligned and centered along the central axial axis of fastener20when fastener20is assembled with housing30.

Fastener20can have threaded shank23that extends out from the bottom of lower housing50at bore52after passing through bore46. Head21can be sized such that head21can pass into bore46, but cannot pass through bore52.

Head21of fastener20can be generally spherical in shape, so that it may pivot with respect to housing30on lower housing50.

Prior to final assembly, shank23can be dropped downward or otherwise inserted into the top of housing30through upper housing40and lower housing50so that head21can rest on lower housing50. Alternatively, fastener20can be bottom-loaded into upper housing40, and then lower housing50can be positioned around shank23and coupled onto upper housing40, so that head21can be held in place within upper housing40atop lower housing50.

Head21of fastener20can be held in place by retainer assembly13, which can prevent fastener20from being pulled upward out of or otherwise displaced from housing30. Retainer assembly13can allow pivoting of screw head21with respect to housing30. Retainer assembly13can be typically in the form of one or more rings having a central aperture, which can allow the practitioner to insert a screwdriver through the apertures of the rings to engage a driver interface such as a keyed portion22on head21of fastener20. The exemplary retainer assembly13inFIG. 1can include seat16that can contact head21, biasing member or wave washer15, and retainer ring14farthest away from screw head21. Seat16can include a concave annular region that has a radius of curvature matched to that of screw head21, which facilitates pivoting of head21. The concave annular region can also increase the frictional contact with head21, which facilitates fastener20being held in place by seat16in the desired angular orientation.

Biasing member15can be inserted into channel43so as to be disposed on top of seat16. Retainer ring14can be coupled to housing30, such as via split-ring configuration, to secure biasing member15between seat16and retainer ring14. In an example, biasing member15and retainer ring14can fit around an annular portion of seat16. Next, rod12can be positioned on top of retainer ring14.

To lock the components of bone anchor10in place, the practitioner can screw closure member11into threads42at the upper portion of housing30until closure member11engages rod12. Closure member11can force rod12against the upper surface of seat16, pushing retainer ring14and biasing member15down around seat16, and in turn can force seat16against head21of the screw20. Prior to final tightening of closure member11, biasing member15can cause seat16to frictionally engage head21to resist movement of housing30with respect to fastener20, which can allow for repositioning of shank23. After complete tightening of closure member11, the frictional force between seat16of retainer assembly13and head21can be sufficient to lock fastener20in place with respect to housing30. In an example, U-shaped channel43can be deep enough so that closure member11does not force rod12against the bottom of U-shaped channel43, with rod12being immobilized between seat16and closure member11. In an example, retainer assembly13can be omitted, and closure member11can force rod12directly against head21of fastener20to secure fastener20in place. In an example, closure member11can push rod against portions of arms41forming the bottom of channel43to immobilize rod12, with or without retainer assembly14. In such an example with retainer assembly14, angulation of fastener20can be partially immobilized by biasing member15, and in such an example without retainer assembly14fastener20can be freely angulated (e.g. is not immobilized).

In practice, fastener20is threaded into bone that is structurally sound such that bone anchor10is substantially immobilized via engagement of threading on shank23extending radially from shank23into cancellous bone. However, sometimes bone at a location where it is desirable to provide anchoring by bone anchor10is inadequate for immobilizing a fastener. Such inadequate bone can arise from a variety of conditions, such as osteoporosis or other degenerative conditions that cause the bone structure to become compromised and weakened. Sometimes it is impractical to move bone anchor10to another location for a variety of reasons, such as there being no other available bone structure to provide anchoring or because a bore has already been drilled into the bone and it would unnecessarily further weaken the bone to drill another hole. The present disclosure addresses these issues in anchoring fasteners in boney structure by providing a sizing component that can be coupled to the fastener to increase the anchoring capacity or footprint of the fastener to reach a larger area and thereby reach healthy or otherwise structurally sound bone for anchoring.

FIG. 3is a perspective view of exemplary bone anchor60having sizing component62, which can comprise threaded sleeve64, enlarging threading66, first end68, second end70and central bore72. Bone anchor60can comprise fastener74and housing76. Fastener74can include shaft78, which can include anchor threading80.

Bone anchor60can function similarly to that of bone anchor10ofFIG. 1. For example, fastener74can include spherical head82that can rotate within housing76, which can include slot84for receiving a rod. Sizing component62can be sized to mate with shaft78of fastener74. For example, the outer diameter of shaft78can be sized to fit within the diameter of central bore72, and internal female threading (“sizing threading”) within central bore72can be sized to mate with male anchor threading80. Sizing component62, however, can be configured to operate with other bone anchor devices, such as bone anchor200ofFIGS. 7-9.

Sleeve64can extend along a central axis that is configured to be co-axial with the central axis of shaft78. Sleeve64can be tapered between first end68and second end70in order to provide a smooth transition between the outer diameter of shaft78and the outer diameter of sleeve64. First end68of sleeve64can have a diameter of the desired outer diameter of sizing component62. The diameter of first end68can be selected to increase the diameter of shaft78by any desirable amount to provide a larger anchoring footprint, as discussed below. Second end70can have a diameter that is just slightly larger than the outer diameter of shaft78sufficient to allow insertion of shaft78into sleeve64. Thus, the diameter of sleeve64can increase from second end70to first end68so that, as shaft78is threaded into bone, sizing component62can be eased or gradually inserted into the bore in the bone. However, the diameter of sleeve64need not increase in a steady manner such that the widest portion of sleeve64need not be located at first end68. Enlarging threading66on sleeve64can be sized to be the same as anchor threading80on shaft78. For example, threading66on sleeve64can have the same pitch as threading80on shaft78to facilitate smooth entry of fastener74into a bone bore, particularly one that is pre-tapped with threading. In other words, anchor threading80and enlarging threading66can have the same pitch, but with different diameters, to ensure fastener74and sizing component62advance into the bone at the same rate and prevent binding. As such, threading66can comprise a continuation of threading80that in aggregate extends from tip86, along shaft78, onto second end70, increasing in size along sleeve64and to first end68. In other examples, threading66can be dual lead and threading80can be single lead with double pitch and have larger valleys to provide deep anchoring in the bone structure, as is discussed in greater detail with reference toFIG. 13.

Sizing component62can comprises sleeve64that can enlarge the diameter of shaft78. Thus, as sleeve64is threaded onto shaft78, the outer diameter of sleeve64and threading66can radially increase the diameter of bone anchor60to allow shaft78to increase or enlarge the anchoring footprint of fastener74. In particular, shaft78can be configured to anchor bone anchor60into a bone bore having approximately the same diameter as shaft78. However, as discussed, the boney structure may be weakened or deficient such that threads80cannot take adequate hold in the boney structure, thereby leaving open the possibility of bone anchor60becoming dislodged or displaced. Sleeve64can enlarge shaft78such that bone anchor60can become engaged in bone outside of, or larger than, the diameter of shaft78. For example, sleeve64can be selected to have an outer diameter that is larger than a diseased or weakened bone area surrounding a bone bore into which shaft78is threaded. Thus, threading66of sleeve64can provide anchoring in healthy or structurally sound bone material.

Sleeve64can be threaded onto shaft78up to the proximal end of threading80near spherical head82. As such, sleeve64can be configured to overcome deficient boney structure proximate a cortical bone surface surrounding the bone bore. Additionally, sleeve64can provide strengthening of shaft78near spherical head82in a location that can sometimes be subjected to stress during installation and use. The axial length of sleeve64allows sizing component62to engage healthy cancellous bone, displacing any weak or unhealthy cancellous bone. As discussed below, shaft78can be provided with a stop or locking feature (e.g. stop248ofFIG. 11) to prevent sleeve64from backing out of the bone bore and protruding beyond the cortical bone.

The diameter of sleeve64can vary in different embodiments of sizing component62. Likewise, the length of sizing component62between first end68and second end79can vary in different embodiments of sizing component62. Thus, a variety of sizing components62can be provided in inventory, such as in a system, set, kit or package, or as part of a surgical system, to allow a surgeon or practitioner to intra-operatively select one or more sizing components of desired length and diameter, or material to compensate for or overcome weakened or defective boney structure at a particular surgical site of a patient at a location where the procedure is performed.

FIG. 4is a perspective view of exemplary bone anchor60having sizing component90, which can comprise cap92having axial fixation teeth94and central bore96. Bone anchor60can be configured in the same manner as described with reference toFIG. 3and can function similarly as bone anchor10ofFIGS. 1 and 2. Bone anchor60can comprise fastener74and housing76, which includes slot84. Fastener74can include shaft78, which can include threading80, head82and tip86.

Sizing component90can be sized to mate with shaft78of fastener74. For example, the outer diameter of shaft78can be sized to fit within the diameter of central bore96, and internal threading within central bore96can be sized to mate with threading80. Sizing component90, however, can be configured to operate with other bone anchor devices, such as bone anchor200ofFIGS. 7-9.

Cap92can extend along a central axis that is configured to be co-axial with the central axis of shaft78. Cap92can have an octagonal or hexagonal outer perimeter surface shape in order to engage a driver device. As such, insertion and removal of sizing component90can be facilitated with an instrument such as an open end wrench. However, the shape of the outer perimeter of cap92can have other configurations, such as square or circular.

Cap92can have an outer perimeter size selected to increase the diameter or size of shaft78any desirable amount to provide a larger anchoring footprint, as discussed below. In particular, fixation teeth94can extend from rim98to engage cortical bone surrounding shaft78. Rim98can comprise a flange that can extend radially and/or axially from cap92to position fixation teeth94for engaging bone. Fixation teeth94can extend axially from rim98in a distal direction away from cap92. Fixation teeth94can have a circumferential orientation to facilitate insertion into the cortical bone as sizing component90is rotated. In an example, fixation teeth94can be oriented in a clockwise circumferential direction when viewed from the proximal end of shaft78near spherical head84(as depicted inFIG. 4) to facilitate insertion of fixation teeth94when cap92is rotated in a clockwise or right-hand thread direction. In other examples, fixation teeth94can have different shapes or can be replaced with textured or jagged surfaces along rim98for engaging bone.

As cap92is threaded onto shaft78, the outer size of cap92can radially increase the diameter of bone anchor60to allow shaft78to increase or enlarge the anchoring footprint of fastener74. In particular, shaft78can be configured to anchor bone anchor60into a bone bore having approximately the same diameter as shaft78. However, as discussed, the boney structure may be weakened or deficient such that threads80cannot take adequate hold in the boney structure, thereby leaving open the possibility of bone anchor60becoming dislodged or displaced. Cap92can enlarge shaft78such that bone anchor60can become engaged in bone outside of, or larger than, the diameter of shaft78. For example, cap92can be selected to have an outer size that is larger than a diseased or weakened bone area surrounding a bone bore into which shaft78is threaded. Thus, fixation teeth94of cap92can provide anchoring in healthy or structurally sound bone material that surrounds the bone bore.

Cap92can be threaded onto shaft78up to the proximal end of threading80near spherical head82. As such, cap92can be configured to overcome deficient boney structure proximate a cortical bone surface surrounding the bone bore. Shaft78continues to provide anchoring within the bone bore in cancellous bone. As discussed below, shaft78can be provided with a stop feature (e.g. stop248ofFIG. 11) to prevent cap92from backing out from engagement with the cortical bone.

The diameter of cap92can vary in different embodiments of sizing component90. Likewise, the shape, such as the length, of fixation teeth94can vary in different embodiments of sizing component90. Thus, a variety of sizing components90can be provided in inventory, such as in a system, set, kit or package, or as part of a surgical system, to allow a surgeon or practitioner to intra-operatively select one or more sizing components of desired length and diameter to compensate for or overcome weakened or defective boney structure at a particular surgical site of a patient at a location where the procedure is performed.

FIG. 5is a perspective view of exemplary bone anchor60having sizing component100, which can be configured similarly as sizing component90ofFIG. 4with the addition of extension sleeve102. Sizing component100can also include cap92, axial fixation teeth94, central bore96and rim98. Extension sleeve102can include threading104. Bone anchor60can be configured in the same manner as described with reference toFIG. 3and can function similarly as bone anchor10ofFIGS. 1 and 2. Bone anchor60can comprise fastener74and housing76, which includes slot84. Fastener74can include shaft78, which can include threading80, head82and tip86.

Cap92can function similarly as described with reference toFIG. 4. Extension sleeve102and threading104can function similarly as threaded sleeve64and threading66of sizing component62ofFIG. 3. As such,FIG. 5depicts a combination of the embodiments ofFIGS. 3 and 4wherein first end68of threaded sleeve64extends from cap92.

Extension sleeve102can extend from cap92along a central axis that is configured to be co-axial with the central axis of shaft78. Extension sleeve102can be tapered between cap92and distal end106in order to provide a smooth transition between the outer diameter of shaft78and the outer diameter of sleeve extension102. The diameter of extension sleeve102can be selected to increase the diameter of shaft78any desirable amount to provide a larger anchoring footprint, as discussed herein. Distal end106can have a diameter that is just slightly larger than the outer diameter of shaft78sufficient to allow insertion of shaft78into extension sleeve102. Thus, the diameter of extension sleeve102can be tapered so that, as shaft78is threaded into bone, sizing component100can be eased or gradually inserted into the bore in the boney structure. Threading104on extension sleeve102can be sized to be the same as threading80on shaft78. For example, threading104on extension sleeve102can have the same pitch as threading80on shaft78to facilitate advancement into the boney structure at the same rate and prevent binding.

Sizing component100can comprises extension sleeve102that can be larger than the diameter of shaft78, and cap92that can be larger than the diameter of extension sleeve102. Thus, as sizing component100is threaded onto shaft78, the outer diameter of extension sleeve102and threading104can effectively radially increase the diameter of shaft78to increase or enlarge the anchoring footprint of fastener74, while cap92can further increase the size of the anchoring footprint. In particular, extension sleeve102can increase the anchoring footprint in the radial and axial directions to engage cancellous bone in a bone bore, while cap92and fixation teeth94can increase the anchoring footprint in the radial and axial directions to engage cortical bone. Thus, extension sleeve102can displace weak or unhealthy cancellous bone to engage healthy cancellous bone, while fixation teeth94can be extended radially beyond weak or unhealthy cortical bone to axially engage healthy cortical bone.

As discussed, the radial diameter of cap92and the axial length of teeth94can vary in different embodiments, and the radial diameter and axial length of extension sleeve102can vary in different embodiments such that different sizing components100can be used as components in different systems, sets, kits or packages. In the depicted example ofFIG. 5, extension sleeve102has a length sized to only engage cancellous bone near the cortical surface of a bone bore. However, as shown inFIG. 6, extension sleeve102can be sized to extend along substantially all of shaft78.

FIG. 6is a perspective view of exemplary bone anchor60having sizing component110, which can be configured similarly as sizing component100ofFIG. 4with the addition of extension sleeve102having a greater length. Sizing component110can also include cap92, axial fixation teeth94, central bore96and rim98. Extension sleeve102can include threading104. Bone anchor60can be configured in the same manner as described with reference toFIG. 3and can function similarly as bone anchor10ofFIGS. 1 and 2. Bone anchor60can comprise fastener74and housing76, which includes slot84. Fastener74can include shaft78, which can include threading80, head82and tip86.

As mentioned, sizing component110can be configured to operate in the same or a similar fashion as sizing component100ofFIG. 5except extension sleeve102is longer to engage a greater quantity of cancellous bone. Thus, distal end106can be positioned further down into a bone bore and the length of extension sleeve102can be used to displace a greater length of cancellous bone to allow threading104to engage a greater quantity of healthy cancellous bone. Sleeve102can extend across substantially all of shaft78except for the distal tapered end portion where tip86is located.

Bone anchor200can function similarly as bone anchor10ofFIG. 1and bone anchor60ofFIG. 3, except bone anchor200includes head216instead of spherical head82. As such, bone anchor200is not configured for use with housing76(FIG. 3). Instead, head216can be used with other components, such as plates, fusion systems, intra vertebral spacers and the like. Head216can be cylindrical for receding into another component. Head216can include socket22for receiving a drive tool, such as a screw driver or hex head wrench. In any event, fastener214can be used to secure bone anchor200to a boney structure.

Sizing component202can function similarly as sizing component60ofFIG. 3. For example, sizing component202can have first end208and second end210, with threaded sleeve204being tapered there-between to facilitate smooth insertion into bone. Threading206can be sized to match threading220of shaft218of fastener214. In other words, threading206and threading220can have the same pitch to ensure fastener214and sizing component202advance into the boney structure at the same rate and prevent binding. Sleeve204can extend along a central axis that is configured to be co-axial with the central axis of shaft218.

Sleeve204of sizing component202can enlarge the diameter of shaft218to radially increase the diameter of bone anchor200to allow shaft218to increase or enlarge the anchoring footprint of fastener214. In particular, shaft218can be configured to anchor bone anchor200into a bone bore having approximately the same diameter as shaft218. However, as discussed, the boney structure may be weakened or deficient such that threads220cannot take adequate hold in the boney structure, thereby leaving open the possibility of bone anchor200becoming dislodged or displaced. Sleeve204can enlarge shaft218such that bone anchor200can become engaged in bone outside of, or larger than, the diameter of shaft218. For example, sleeve204can be selected to have an outer diameter that is larger than a diseased or weakened bone area surrounding a bone bore into which shaft218is threaded. Thus, threading206of sleeve204can provide anchoring in healthy or structurally sound bone material.

Sleeve204can be threaded onto shaft218up to the proximal end of threading220near head216. As such, sleeve204can be configured to overcome deficient boney structure proximate a cortical bone surface surrounding the bone bore, and can be used to strengthen shaft218. The axial length of sleeve204allows sizing component202to engage healthy cancellous bone, displacing any weak or unhealthy cancellous bone.

As with other examples and embodiments described herein, the sizes, e.g. length and diameter, of sleeve204can vary in different embodiments of sizing component202to permit a variety of sizing components202to be provided in inventory, such as in a system, set, kit or package, or as part of a surgical system, to allow a surgeon or practitioner to intra-operatively select one or more sizing components of desired length and diameter to compensate for or overcome weakened or defective boney structure at a particular surgical site of a patient at a location where the procedure is performed. However, first end208can include countersink or socket224, which can allow for multiple sizing components202to be used in conjunction with each other to increase the axial anchoring footprint of sizing component202, as shown inFIGS. 9 and 10. In other examples, socket224can be omitted from sizing component202to, for example, provide additional contact with the threaded fastener.

FIG. 9is a side view of first sizing component202A, such as sizing component200shown inFIGS. 7 and 8, axially abutted with second sizing component202B of similar construction.FIG. 10is a cross-sectional view of first and second sizing components202A and202B ofFIG. 9.FIGS. 9 and 10are discussed concurrently.

As mentioned, second ends210A and210B can be tapered to provide smooth transitions with shaft218of fastener214. Sockets224A and224B can be shaped in the mirror images of the tapers of second ends210A and210B to allow the tapering to be fully recessed into sockets224A and224B. For example, socket224B can receive all or nearly all of the tapering of second end210A such that there is no change in the diameter of the joined sizing components202A and202B between sleeves204A and204B at junction226. Sockets224A and224B can include threading228A and228B, respectively to receive threading of a mating sizing component. For example, socket224B of sizing component202B can include threading228B to receive threading206A of sizing component202A. Thus, multiple sizing components202can be axially stacked together to increase the effective length of the sizing component. This can reduce the number and variety of different sizing components needed in inventory to form different systems, sets, kits and packages as described herein.

FIG. 11is a cross-sectional view of a portion of fastener214ofFIG. 8having stop248and an exemplary sizing component250having cap252with axial fixation teeth254and sleeve256. Sizing component250can also include central bore258and rim260. Sizing component250is similar to sizing component100ofFIG. 5, except being particularly sized for use with fastener214. As such, central bore258can be sized to receive the diameter of shaft218of fastener214, and central bore258can include female sizing threading262to receive male anchor threading220of shaft218. However, as discussed, any of the sizing components described herein can have different dimensions in different embodiments for use with a variety of different fasteners and bone anchors.

Cap252can be shaped to have surfaces to engage a drive tool, such as a wrench or the like. Rim260can extend from cap252to position teeth254radially outward of sleeve256. Rim260can extend radially outward from cap252and axially away from cap252. Teeth254can extend axially from rim260to provide axial anchoring in bone surrounding fastener shaft218. Sleeve256can extend axially from cap252within teeth254. Sleeve256increases the diameter of shaft218such that threading266of sleeve256can increase the anchoring footprint of fastener214beyond what is provided by threading220. Sleeve256and threading266can be shaped to smoothly mate with shaft218and threading220. For example, sleeve256can be tapered to allow for a smooth entry of shaft218and sizing component250into a bone bore. Also, threading266can have the same pitch as threading220to allow for entry of shaft218and sizing component250into a bone bore without binding.

The various embodiments and examples of sizing components described herein can be made of a variety of different materials in different embodiments. In an example, the sizing components can be made of porous metal or biocompatible metal or alloys. In particular examples, the sizing components can be made from titanium or Trabecular Metal™, which is commercially available from Zimmer Inc. In other examples, the sizing components can be made of a polymer, such as polyether ether ketone (PEEK). In yet other examples, the sizing components can be made of autograft or allograft bone.

FIG. 12is a flow chart diagramming method300of implanting a sizing component of the present application. Method300can include the steps of forming a bone bore in a boney structure302, tapping the bone bore304, trialing the bone bore306, selecting a sizing component for use in the bone bore308, assembling the sizing component with a fastener310, inserting the fastener into the bone bore312, engaging one or more portions of the sizing component with the boney structure314and increasing the anchoring footprint of the fastener with the sizing component316.

Forming a bone bore at step302can comprise producing a bore or hole within a boney structure for receiving a bone anchor. A drill or an awl can be used to produce a channel through cortical bone and into cancellous bone. The bone bore can have a diameter that substantially matches the diameter of a fastener, such as a threaded fastener. As such, the diameter of the bone bore can be sized to accommodate threading of a fastener shaft.

Tapping the bone bore at step304can comprise using a thread tap to produce threading in the bone bore to match the threading of a desired threaded fastener of a bone anchor to be used in the bone bore. Any conventional thread tap can be used. In other examples, the bone bore may not be pre-threaded. As such, self-tapping bone fasteners can be used.

Trialing the bone bore at step306can comprise assessing the quality of bone at and around the bone bore via a variety of means. For example, the bone bore can be visually inspected by the surgeon or practitioner to assess the extent of damaged or unhealthy bone in and around the bone bore. Additionally, various instruments can be inserted into the bone bore to determine the extent of unhealthy or damaged bone. For example, a probe can be inserted into the bone bore to allow the surgeon or practitioner to feel the depth of any bone damage. Additionally, a bone anchor may be inserted into the bone bore to evaluate the effectiveness of a fastener used with the bone anchor. For example, a threaded fastener can be inserted or screwed into the bone bore and the surgeon or practitioner can tactilely feel if the fastener provides adequate anchoring support.

Selecting a sizing component at step308can comprise using information determined during trialing of the bone bore at step306to select one or more of the various sizing components described herein. For example, the radius of any damaged or unhealthy bone surrounding the bone bore can be used to select a sizing component of adequate diameter, and the depth of any damaged or unhealthy bone into the bone bore can be used to select a sizing component of adequate length.

Assembling the sizing component with the fastener at step310can comprise connecting the selected sizing component to the selected bone anchor. For example, a fastener of the selected bone anchor can be inserted or threaded into a sleeve or cap of a selected sizing component. In other examples, the sizing component can be connected to the fastener by other mechanisms. In yet other examples, the sizing component can be inserted into the bone first and the fastener can be passed through the sizing component second.

Inserting the fastener into the bone bore at step312can comprise threading the shaft of the fastener of the bone anchor into the bone bore. The shaft can be partially inserted into the bone bore before any sizing component engages boney structure of the bone bore. Alternatively, the sizing component can be initially threaded into the bone bore such that the fastener does not actually contact the bone bore.

The fastener can be advanced such that the sizing component engages the bone structure at step314. The sizing component can engage the boney structure in a variety of different ways. In an example, the sizing component can be used to displace cancellous bone within the bone bore at step314A, which can be accomplished by engaging enlarging threading of the sizing component, such as that disposed on a sleeve surrounding the shaft of the threaded fastener, with cancellous bone in the bone bore at step315A. In an example, the sizing component can be used to engage cortical bone surrounding the bone bore at step314B, which can be accomplished by engaging axially extending teeth of the sizing component, such as teeth that extend from a rim surrounding a cap surrounding the shaft of the threaded fastener, to engage cortical bone surrounding the bone bore at step315B. Additionally, sizing components can be configured to engage both cortical and cancellous bone such that steps315A and315B can be achieved concurrently (or in quick succession as the fastener with the sizing component is advanced into the bone). As a result of step314, the anchoring footprint of the bone anchor can be increased with the sizing component(s) at step316. As such, the bone anchor can be more securely held in place in the bone bore with a reduced risk of becoming displaced.

FIG. 13is a side view of exemplary bone anchor400including fastener402having first external thread pitch P1and sizing component404having second external thread pitch P2. Sizing component404can comprise threaded sleeve406having threading408extending between first end410and second end412of threaded sleeve406. Fastener402can comprise head414and shaft416. Shaft416can include threading418that extends between a tip (not shown) and head414.

Bone anchor400can operate similarly to bone anchor200ofFIG. 7with the exception that threading418can be at a different pitch than threading220. In particular, threading408can be dual lead and threading418can be single lead with double pitch. Threading418can be configured to have large, deep valleys and can be widely-spaced between threading to provide for deep anchoring in cancellous bone structure. Threading408can be configured to have small, shallow valleys and can be closely-spaced to provide abundant anchoring in cortical bone. In one example, pitch P1can be approximately 3.0 mm and pitch P2can be approximately 1.5 mm.

VARIOUS NOTES & EXAMPLES

Example 1 can include or use subject matter such as a bone fastener system that can comprise: a fastener and a first sizing component. The fastener can comprise: a shaft having a shaft diameter; an anchoring projection on the shaft; and a head at an end of the shaft. The first sizing component can be connected to the fastener. The first sizing component can comprise: a first body portion having a first outer diameter larger than the shaft diameter; a first bore extending through the first body portion, the first bore sized to receive the shaft diameter; a first sizing located in the first bore to receive the anchoring projection on the shaft; a first outer surface at the first outer diameter; and a first circumferential bone engaging feature extending from the first outer surface.

Example 2 can include, or can optionally be combined with the subject matter of Example 1, to optionally include an anchoring projection that can comprise threading and the first sizing comprises mating threading.

Example 3 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 or 2 to optionally include a first circumferential bone engaging feature that can comprise first enlarging threading on the first outer surface.

Example 4 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 3 to optionally include a pitch of the first enlarging threading that can match a pitch of the threading on the shaft.

Example 5 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 4 to optionally include a second sizing component that can comprise a second body portion having a second outer diameter larger than the shaft diameter, a second bore extending through the second body portion, and mating threading located in the second bore to receive the threading on the shaft.

Example 6 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 5 to optionally include a second outer diameter that can be approximately equal to the first outer diameter.

Example 7 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 6 to optionally include a first sizing component that can include a tapered distal tip, and a second sizing component that can include a countersunk proximal end, wherein the tapered distal tip fits into the countersunk proximal end.

Example 8 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 7 to optionally include a shaft that can further comprise a tapered end portion opposite the head, the shaft can extend over a first length from the head to the tapered end portion, and a first body portion that can have a second length approximately equal to the first length.

Example 9 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 8 to optionally include a first circumferential bone engaging feature that can comprise axially extending teeth.

Example 10 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 9 to optionally include a first body portion that can further include a radially extending flange connected to the first outer surface and from which the axially extending teeth extend.

Example 11 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 10 to optionally include axially extending teeth that can be circumferentially oriented.

Example 12 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 11 to optionally include tool-engaging surfaces located on the first body portion on an opposite side of the radially extending flange as the axially extending teeth.

Example 13 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 12 to optionally include first enlarging threading on the first outer surface.

Example 14 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 through 13 to optionally include a stop located along the shaft to abut the first body portion.

Example 15 can include or use subject matter such as a bone anchor system that can comprise: a fastener, a first sizing component and a second sizing component. The fastener can comprise a threaded shaft configured to provide an anchoring footprint. The first sizing component can be configured to be connected to the threaded shaft, the first sizing component can include a first anchoring feature to increase a size of the anchoring footprint. The second sizing component can be configured to be connected to the shaft, the second sizing component can include a second anchoring feature to increase the size of the anchoring footprint, the second anchoring feature being different from the first anchoring feature.

Example 16 can include, or can optionally be combined with the subject matter of Example 15, to optionally include a first anchoring feature that can comprise a sleeve that radially expands a diameter of the threaded shaft.

Example 17 can include, or can optionally be combined with the subject matter of one or any combination of Examples 15 or 16 to optionally include a second anchoring feature that can expand the diameter of the threaded shaft a greater amount than the first anchoring feature.

Example 18 can include, or can optionally be combined with the subject matter of one or any combination of Examples 15 through 17 to optionally include a second anchoring feature that can have a second length greater than a first length of the first anchoring feature.

Example 19 can include, or can optionally be combined with the subject matter of one or any combination of Examples 15 through 18 to optionally include a second anchoring feature that can comprise axially extending teeth.

Example 20 can include or use subject matter such as a method of fastening a bone anchor, the method can comprise: forming a bore having a shaft diameter into a boney structure for a fastener shaft; trialing the bore to determine bone integrity; selecting a sizing component based on the trialing, the sizing component having a diameter larger than the shaft diameter and a circumferential bone engaging feature; assembling the selected sizing component to the fastener shaft; and inserting the fastener shaft into the bore to engage the sizing component with the boney structure.

Example 21 can include, or can optionally be combined with the subject matter of Example 20, to optionally include a circumferential bone engaging feature comprising external threading, and threading the fastener shaft into the bore to engage the external threading of the sizing component with cancellous bone in the bore in the boney structure.

Example 22 can include, or can optionally be combined with the subject matter of Examples 20 or 21, to optionally include a circumferential bone engaging feature that comprises axially extending teeth, and threading the fastener shaft into the bore to engage the axially extending teeth of the sizing component with cortical bone of the boney structure surrounding the bore.

Example 23 can include, or can optionally be combined with the subject matter of one or any combination of Examples 20 through 22 to optionally include tapping the bore to form threading that mates with the fastener shaft.

Example 24 can include, or can optionally be combined with the subject matter of one or any combination of Examples 20 through 23 to optionally include assembling the sizing component with the fastener shaft until the sizing component engages a stop feature.

Example 25 can include, or can optionally be combined with the subject matter of one or any combination of Examples 20 through 24 to optionally include engaging two or more sizing components together along the fastener shaft.

Example 26 can include, or can optionally be combined with the subject matter of one or any combination of Examples 20 through 25 to optionally include trialing the bore comprises probing the bore to determine an extent of weakened bone adjacent the bore; and selecting the sizing component comprises determining a size of the sizing component to compensate for the extent of the weakened bone.