Field

[001] The disclosure relates to the technical field of anchor assemblies useful for connecting structures to each other.

Background

[002] The art includes several examples of anchor assemblies useful for connecting structures to each other. The medical device art, for example, includes several designs for anchor assemblies that are used in procedures for correcting a variety of spinal conditions. Many of these designs include a threaded fastener, such as a bone screw, for insertion into a spinal component, such as a vertebrae, and a structural component that allows the threaded fastener to be connected to another device, such as a rod used to align several bone screws.

[003] In one example, described in U.S. Patent No. 7,066,937, a threaded fastener extends through an opening in a housing and into a passage to allow a longitudinal axis of the fastener to be positioned in any one of a plurality of angular positions relative to a longitudinal axis of the passage. In another example, described in U.S. Patent No. 6,485,491 , a saddle member includes a pair of upright portions that define a channel for receiving a rod and a hole to receive a threaded fastener. The saddle member and the threaded fastener can be coupled to allow the fastener to be positioned in any one of a plurality of angular positions.

[004] Despite these and other examples, a need exists for improved anchor assemblies.

Description of Figures

[005] FIG. 1 illustrates an embodiment of a bottom-loading anchor assembly. [006]

[007] FIG. 2 is an exploded perspective view of the anchor assembly illustrated in FIG. 1.

[008] FIG. 3 is a perspective view of the head member of the anchor assembly illustrated in FIG. 1 with an associated compression member and retaining member.

[009] FIG. 3A is a sectional view of FIG. 3, taken along line 3A-3A.

[0010] FIG. 4 is an exploded perspective view of the anchor assembly illustrated in FIG. 1.

[0011] FIG. 4A is a magnified partial sectional view of the anchor assembly illustrated in FIG. 1. The anchor is shown in a first position within the head member.

[0012] FIG. 4B is a magnified partial sectional view of the anchor assembly illustrated in FIG. 1. The anchor is shown in a second position within the head member.

[0013] FIG. 4G is a magnified partial sectional view of the anchor assembly illustrated in FIG. 1. The anchor is shown in a third position within the head member.

[0014] FIG. 5A is a perspective view of the head member of the anchor assembly illustrated in FIG. 1 with a plug.

[0015] FIG. 5B is a sectional view of the head member of the anchor assembly illustrated in FIG. 1 with an associated compression member and retaining member and a plug disposed within the head member.

[0016] FIG. 6 is an exploded view of another embodiment of a bottom- loading anchor assembly.

[0017] FIG. 7A is an exploded view of the head member and insert of the anchor assembly illustrated in FIG. 6. [0018] FIG. 7B is a perspective view of the head member and insert illustrated in FIG. 7A.

[0019] FIG. 8A is a perspective view of another head member with an associated compression member and retaining member.

[0020] FIG. 8B is a sectional view of FIG. 8A, taken along line 8B-8B.

[0021] FIG. 9A is a perspective view of another head member with an associated compression member and retaining member.

[0022] FIG. 9B is a sectional view of FIG. 9A, taken along line 9B-9B.

[0023] FIG. 10 is a sectional view of another head member with an associated compression member and retaining member.

Description of Embodiments

[0024] The following detailed description and the appended drawings describe and illustrate various example embodiments. The description and illustration of these examples are provided to enable one skilled in the art to make and use an anchor tower. They are not intended to limit the scope of the claims in any manner.

[0025] As used herein, the term "bottom-loading" refers to an ability of a proximal end of an anchor of an anchor assembly to be inserted into an opening defined by an end of a head member of the anchor assembly through which the anchor is disposed in the fully assembled anchor assembly. It does not preclude an ability of a proximal end of an anchor of an anchor assembly to be inserted through an opening defined by an end of a head member of the anchor assembly that is opposite an opening defined by an end of a head member of the anchor assembly through which the anchor is disposed in the fully assembled anchor assembly.

[0026] As used herein, the terms "top" and "bottom" refer to opposite portions of a body relative to each other. Neither term requires any specific positioning of the member to which the terms apply relative to any other item.

[0027] As used herein, the term "channel" refers to a recess in a surface. The term does not require any particular cross-sectional shape of the recess with respect to a lengthwise axis of the channel or a portion of the channel. The term does not require any particular lengthwise configuration, either. Non-limiting examples of lengthwise configurations that can be used for the channels described herein include linear, curvilinear, segmented linear, and tortuous paths. The term does not require any particular length relative to another component of an anchor assembly, either. For example, a channel defined by a head member of an anchor assembly can have any suitable length relative to the head member. Non-limiting examples of channel lengths relative to a head member of an anchor assembly include circumferential, i.e. , a channel that extends along an entire circumference on a surface of a head member, such as along an entire circumference on an inner surface of a head member; and partial circumferential, i.e. , a channel that extends along only a portion of a circumference on a head member. In this context, the term "circumference" refers to a curved geometric shape on a surface, including, but not limited to, a circular shape.

[0028] As used herein, the term "ramp" refers to a surface that transitions from a first surface at a distance from a reference point to second surface at a different distance from a reference point. The term does not require the surface to be on a plane that lies at any particular angle with respect to the first and second surfaces between which it transitions. Accordingly, the surface can be on a plane that lies at any angle with respect to the first and second surfaces between which it transitions. Non-limiting examples of angles at which a plane containing a ramp described herein can lie with respect to one or both of the surfaces between which the ramp transitions include acute angles, obtuse angles, right angles, and substantially right angles. The term also does not require the surface to have any particular length, width or other dimension. [0029] Each of FIGS. 1 , 2, 3, 3 A, 4, 4A, 4B, 4G, 5A, and 5B illustrates an anchor assembly 10 or one or more components thereof. The anchor assembly 10 comprises a head member 12 and an anchor 14. A compression member 16 and a retaining member 18 are disposed within the head member 12 and a cap 20 is releasably connected to the head member 12. In the fully assembled anchor assembly 10, the anchor 14 is partially disposed within the head member 12.

[0030] The head member 12 has a proximal end 22, which can be referred to as the "top" of the head member 12, and a distal end 24, which can be referred to as the "bottom" of the head member 12. The head member 12 defines a proximal opening 26 at the proximal end 22 and a distal opening 28 at the distal end 24. A passageway 30 extends from the proximal opening 26 to the distal opening 28 along the length of the head member 12. The head member 12 includes a proximal portion 32 and a distal portion 34. The proximal portion 32 defines a proximal chamber 36 of the passageway 30 and the distal portion 34 defines a distal chamber 38 of the passageway 30. Each of the proximal portion 32 and the distal portion 34 has a width extending on an axis orthogonal to a lengthwise axis extending from the proximal end 22 to the distal end 24 of the head member 12. In the illustrated embodiment, the proximal portion 32 has a width that is greater than a width of the distal portion 34. A head member can be configured with an opposite arrangement, i.e. , with a distal portion having a width greater than a width of its proximal portion. Also, a head member can be configured with a proximal portion having a width that is the same as or substantially the same as a width of its distal portion.

[0031] The proximal portion 32 of the head member 12 defines a lateral opening 40. In the illustrated embodiment, the lateral opening 40 is continuous with the proximal opening 26 and is bounded by a u-shaped wall 42 of the head member. The lateral opening 40 can have any suitable size, shape and configuration, each of which can be based upon the size, shape and configuration of a member intended to be secured by the head member 40. The lateral opening 40 of the illustrated embodiment is suitable for use with a rod. Non-limiting examples of alternative shapes for the lateral opening 40 include v-shaped, rectangular shaped, square-shaped, curvilinear, linear, and segmented linear. A non- limiting example of an alternative configuration for the lateral opening 40 is an opening that is separate and distinct from the proximal opening 26.

[0032] While not illustrated in the Figures, the proximal portion 32 can define a second lateral opening if it is desirable to allow a member that will be secured by the head member 12 to extend away from the head member 12 in two directions. For example, if it is desirable to allow a rod to be secured by the head member in a manner in which the rod extends away from the head member in two directions, the head member 40 can define a second lateral opening. If included, a second lateral opening can be oriented on the head member in any desirable position relative to the first lateral opening 40. For example, a second lateral opening can be positioned opposite the first lateral opening 40 relative to a lengthwise axis extending from the proximal end 22 to the distal end 24 of the head member 12. Alternatively, the second lateral opening can be positioned at an angle to the first lateral opening 40 relative a lengthwise axis extending from the proximal end 22 to the distal end 24 of the head member 12. In these embodiments, any suitable angle can be used, included an orthogonal angle, a substantially orthogonal angle, an acute angle, and an obtuse angle.

[0033] Also, if included, a second lateral opening can have the same size, shape and configuration as those of the first lateral opening 40. Alternatively, a second lateral opening can have a different size, and/ or a different shape, and/ or a different configuration than those of the first lateral opening 40.

[0034] The proximal portion 32 of the head member 12 has an inner surface 44. The inner surface 44 can define structure that provides a desired functionality. For example, in the illustrated embodiment, the inner surface 44 defines a threaded surface 46 that mates with a threaded surface 78 of the cap 20 for securing the cap 20 to the head member 12. Other non-limiting examples of structure that can be defined by the inner surface 44 include one or more projections that facilitate retention of a member secured by the head member 12. Alternatively, the inner surface 44 can comprise a smooth or substantially smooth surface that is free of projections or other functional structure.

[0035] The proximal portion 32 can define additional openings, notches and/ or other additional structure as desired.

[0036] The distal portion 34 of the head member 12 has an inner surface that defines a channel 48. The channel 48 is in communication with the passageway 30 and, as described in detail below, is sized and configured to receive the compression member 16 and the retaining member 18 and to allow these components to function as described below. In the illustrated embodiment, the channel 48 is a circumferential channel that extends along a circular shape on the inner surface. As best illustrated in FIGS. 3A, 4A, 4B, and 4G, the channel 48 is bounded by first 50 and second 52 lateral walls and base wall 54. Base wall 54 defines a ramp 56, giving the channel 48 a proximal portion 58 having a first depth and a distal portion 60 having a second depth that is less than the first depth. The ramp 56 defines a transition between the proximal 58 and distal 60 portions.

[0037] In the illustrated embodiment, the ramp 56 comprises a circumferential ramp that extends along a circular shape on the inner surface of the distal portion 34 of the head member 12. Alternatively, a partial circumferential ramp can be used. In the illustrated embodiment, the ramp 56 lies on a plane that is disposed at an acute angle to the portion of the base wall 54 that is disposed in the distal portion 60 of the channel 48 and at an obtuse angle to the portion of the base wall 54 that is disposed in the proximal portion 58 of the channel 48. This configuration facilitates movement of the retaining member 18 away from and toward the distal portion 60 of the channel 48, as described below.

[0038] The anchor 14 is an elongate member having a head 62 and a shank 64. In the illustrated embodiment, the head 62 is a spherical body with a flattened proximal surface 66 that defines a recess 68. The head 62 has an apex 70 at the axial portion that defines the maximum outer diameter of the spherical body. The shank 64 defines a helical plane 72 that facilitates securement of the anchor 14 to a member, such as a bone or a member formed of another material, such as wood or plastic. In the illustrated embodiment, the helical plane 72 has a proximal portion 74 with a first pitch and a distal portion 76 with a second pitch. It is noted that the anchor 14 can include a shank having any suitable structure that allows the anchor 14 to perform as described herein. Inclusion of a helical plane is considered optional. Non-limiting examples of other suitable structures that can be defined by the shank of the anchor include a naillike structure and a barbed member. Similarly, the anchor 14 can include a head having any suitable structure that allows the anchor 14 to perform as described herein. Non-limiting examples of other suitable structures include a spherical body, a cube, and a block.

[0039] The compression member 16 is disposed within the proximal portion 58 of channel 48, proximal to the retaining member 18. In the illustrated embodiment, the compression member 16 comprises a coil spring. Any suitable compression member can be used, however. The compression member need only be able to allow the retaining member 18 to move in a first direction within the channel 48 and to effect movement of the retaining member 18 in a second, opposite or substantially opposite direction within the channel 48, as described below. Non-limiting examples of suitable compression members include helical springs, wave springs, and bushings. The compression member can be formed of any suitable material, including metal, plastic, and elastomeric materials. In the illustrated embodiment, the compression member 16 has a cross- sectional diameter that is less than a cross-sectional diameter of the retaining member 18.

[0040] The retaining member 18 is disposed within the distal portion 60 of the channel 48, distal to the compression member 16. In the illustrated embodiment, the retaining member 18 comprises a G-shaped member having a resting diameter that is greater than an inner diameter of the distal portion 34 of the head member 12 within the distal portion 60 of the channel 48. This provides the retaining member 18 with a radially compressed configuration and a radially expanded configuration. With this configuration, the retaining member 18 expands in a radially outward manner as the retaining member 18 moves from the distal portion 60 of the channel 48 to the proximal portion 58 of the channel 48. The retaining member 18 can have any suitable configuration, however. For example, retaining member 18 can alternatively have a semi-circular configuration or an annular configuration. The retaining member 18 need only be able to expand radially outward as it transitions from the distal portion 60 of the channel 48 to the proximal portion 58 of the channel 48. The compression member can be formed of any suitable material, including metal, plastic, and elastomeric materials. Also, the retaining member 18 can have any suitable cross-sectional shape, including circular, ovoid, and any other cross-sectional shape. In the illustrated embodiment, the retaining member 18 has a cross-sectional diameter that is greater than a cross-sectional diameter of the compression member 16.

[0041] In the illustrated embodiment, the compression member 16 and the retaining member 18 comprise distinct components. It is noted, however, that a single component that includes both a compression member and a retaining member can be used, however. For example, the illustrated compression member 16 and retaining member 18 could be secured to each other to provide a single component that includes both a compression member and a retaining member. Furthermore, it is noted that each of these components, can comprise a portion of another component. For example, in embodiments that include an insert positioned within the head assembly, such as the embodiments described below, a compression member can comprise a distal portion of the insert. A compression member could even be secured a head of an anchor in an embodiment.

[0042] The cap 20 is releasably connected to the head member 12. In the illustrated embodiment, the cap 20 defines a threaded surface 78 that mates with a threaded surface 46 of the inner surface 44 of the proximal portion 32 of the head member 12. It is noted, though, that the cap 20 can include any suitable structure that enables it to be releasably secured to the head member 12. Non-limiting examples of suitable structure includes projections, magnets and other structure suitable for securing a cap to a body. Inclusion of a cap is considered optional.

[0043] FIGS. 4A, 4B, and 4G illustrate movement of the compression member 16 and the retaining member 18 as the head 62 of the anchor 14 is moved into the distal opening 28 of the head member 12. FIG. 4A illustrates proximally-directed movement, represented by arrow 80, of the head 62 of the anchor 14 into the distal portion 34 of the head member 12 and the distal chamber 38 of the passageway 30. In the position illustrated in FIG. 4A, the apex 70 of the head 62 of the anchor 14 is distal to the distal portion 60 of the channel 48. As a result, compression member 16 is maintaining retaining member 18 in the distal portion 60 of the channel 48.

[0044] FIG. 4B illustrates radially-outward movement of the retaining member 18, represented by arrow 82, that occurs as the apex 70 of the head 62 of the anchor 14 enters the distal portion 60 of the channel 48. As proximally-directed movement of the head 62 of the anchor 14 continues, the apex 70 engages the retaining member 18 and moves it toward the proximal portion 58 of the channel 48, along the ramp 56. As the retaining member 18 moves in this manner, it expands radially outwardly.

[0045] FIG. 4G illustrates distally-directed movement of the retaining member 18, represented by arrow 84, that occurs as the apex 70 of the head 62 of the anchor 14 passes the retaining member 18 proximally and enters the proximal portion 58 of the channel 48. In the illustrated embodiment, the compression member 16 maintains a distally-directed compressive force on the retaining member 18. Accordingly, once the apex 70 reaches a sufficient position on a lengthwise axis of the head member 12, the distal portion 60 of the channel 48 provides sufficient space to accommodate the retaining member 18 and the compressive force provided by the compression member 16 moves the retaining member distally along the ramp 56 and, ultimately back into the distal portion 60 of the channel 48. Once this occurs, as illustrated in FIG. 4G, the head member 12 forces the retaining member 18 to adopt its non- expanded configuration, which prevents the head 62 of the anchor 14 from exiting the head member 12, effectively securing the head 62 of the anchor 14 in the head member 12.

[0046] FIGS. 5A and 5B illustrate an optional plug 86 that is releasably secured to the distal portion 34 of the head member 12 prior securing an anchor 14 to the head member 12. The plug 86 defines a body 88 that can be passed through the distal opening 28 and that extends proximally beyond the channel 48. A flange 90 remains external to the head member 12. When secured to the head member 12 in this manner, the plug 86 provides a barrier that blocks access to the compression member 16 and the retaining member 18.

[0047] Each of FIGS. 6, 7A and 7B illustrates another anchor assembly 1 10 or one or more components thereof. The illustrated anchor assembly 1 10 is similar to the anchor assembly 10 illustrated in FIGS. 1 and 2 and described above, except as described below. Thus, the anchor assembly 1 10 comprises a head member 1 12 and an anchor 1 14. A compression member 1 16 and a retaining member 1 18 are disposed within the head member 1 12 and a cap 120 is releasably connected to the head member 1 12. In the fully assembled anchor assembly 1 10, the anchor 1 14 is partially disposed within the head member 1 12.

[0048] In this embodiment, the compression member 1 16 comprises a ring member formed of a compressible material. The compression member 1 16 is sufficiently compressible to enable the compression member 1 16 to function as described above in connection with the anchor 10 illustrated in FIGS. 1 and 2. As such, the compression member 1 16 can be formed of any suitable material that provides a suitable level of compressibility. Non-limiting examples of suitable materials include elastomeric materials and rubber materials. [0049] In this embodiment, the anchor assembly 1 10 includes an insert 200 that is disposed within the passageway 130 of the head member 1 12. The insert 200 has a circumferential wall 202 that defines first 204 and second 206 stanchions and a notch 208 that extends between the stanchions 204, 206. In the illustrated embodiment, the notch 208 has a semi-circular shape that extends along the circumferential wall 202, but any shape can be used. A shape that compliments an outer surface of a member adapted to be secured by the head member 1 12, such as a rod, can be used. Accordingly, non-limiting examples of suitable shapes for the notch include semi-circular, arcuate, u-shaped, v-shaped, and rectangular-shaped, square-shaped. Also, a shape that is the same as or similar to the shape of the lateral opening 140 of the head member 1 12 is suitable.

[0050] As best illustrated in FIG. 7A, the insert 200 can define third 210 and fourth 212 stanchions and a second notch 214 that extends between the third 210 and fourth 212 stanchions. If included, a second notch can be oriented on the insert 200 in any desirable position relative to the first notch 208. For example, as illustrated in FIG. 7A, a second notch 214 can be positioned opposite the first notch 208 relative to a lengthwise axis of the insert 200. Alternatively, the second notch 214 can be positioned at an angle to the first notch 208 relative a lengthwise axis of the insert 200. In these embodiments, any suitable angle can be used, included an orthogonal angle, a substantially orthogonal angle, an acute angle, and an obtuse angle.

[0051] Also in this embodiment, as best illustrated in FIG. 7B, the inner surface 144 of the proximal portion 132 of the head member 1 12 defines projections 216, 218 that provide mechanical stops to proximal movement of the insert 200 within the passageway 130 of the head member 1 12. Any suitable number of projections can be included, including two, as illustrated, one, three, four or more. While not visible in the Figures, the illustrated embodiment includes four projections, which is equal to the number of stanchions defined by the insert. [0052] Each of FIGS. 8A and 8B illustrates a head member 312 useable as a component of an anchor assembly, and an associated retaining member 318. The illustrated head member 312 is similar to the head member 12 illustrated in FIGS. 1 and 2 and described above. Thus, the head member 312 has a proximal end 322 and a distal end 324, a proximal opening 326 at the proximal end 322 and a distal opening 328 at the distal end 324. A passageway 330 extends from the proximal opening 326 to the distal opening 328 along the length of the head member 312. The head member 312 includes a proximal portion 332 and a distal portion 334. The proximal portion 332 defines a proximal chamber 336 of the passageway 330 and the distal portion 334 defines a distal chamber 338 of the passageway 330. The distal portion 334 of the head member 312 has an inner surface that defines a channel 348 in communication with the passageway 330. In this embodiment, channel 348 is bounded by first lateral wall 350, circumferential surface 351 , and base wall 354. Base wall 354 defines a ramp 356, giving the channel 348 a proximal portion 358 having a first depth and a distal portion 360 having a second depth that is less than the first depth. The ramp 356 defines a transition between the proximal 358 and distal 360 portions.

[0053] In this embodiment, a sleeve 400 eliminates the need for a compression member within the head member 312. The retaining member 318 is disposed within a slot 402 defined by sleeve 400. Sleeve 400 also defines a flange 404. A compression member 406 is disposed on the sleeve 400 between the flange 404 and the distal end 324 of the head member 312. Positioned in this manner, the compression member 406 allows the sleeve 400 to be moved proximally with respect to the head member 312. As the sleeve 400 is moved in this manner, the retaining member 318 moves from the distal portion 360 of the channel 348 to the proximal portion 358 of the channel 348, expanded radially outwardly in the process. Thus, when the sleeve 400 is moved proximally by a sufficient amount with respect to the head member 312, the retaining member 318 adopts its expanded configuration within the channel 348, which permits an anchor to be inserted into the head member 312 as described above. Then, distally-directed movement of the sleeve 400, produced by compression member 406 following release of a pushing force on the sleeve 400, returns the retaining member to the distal portion 360 of the channel 348, effectively securing the anchor to the head member 312.

[0054] Each of FIGS. 9A and 9B illustrates a head member 512 useable as a component of an anchor assembly. The illustrated head member 512 is similar to the head member 12 illustrated in FIGS. 1 and 2 and described above. Thus, the head member 512 has a proximal end 522 and a distal end 524, a proximal opening 526 at the proximal end 522 and a distal opening 528 at the distal end 524. A passageway 530 extends from the proximal opening 526 to the distal opening 528 along the length of the head member 512. The head member 512 includes a proximal portion 532 and a distal portion 534. The proximal portion 532 defines a proximal chamber 536 of the passageway 530 and the distal portion 534 defines a distal chamber 538 of the passageway 530. The distal portion 534 of the head member 512 has an inner surface 546 that defines a channel 548 in communication with the passageway 530. In this embodiment, channel 548 is bounded by first lateral wall 550, circumferential surface 551 , and base wall 554. Base wall 554 defines a ramp 556, giving the channel 548 a proximal portion 558 having a first depth and a distal portion 560 having a second depth that is less than the first depth. The ramp 556 defines a transition between the proximal 558 and distal 560 portions.

[0055] Similar to the embodiment illustrated in FIGS. 8A and 8B, a sleeve 600 eliminates the need for a compression member within the head member 512. In this embodiment, however, a plurality of ball bearings 519 is used in place of the expandable retaining member of the embodiments described above. The ball bearings 519 are disposed within a groove 620 defined by sleeve 600. Sleeve 600 also defines a flange 604. A compression member 606 is disposed on the sleeve 600 between the flange 604 and the distal end 624 of the head member 612. The compression member 606 allows the sleeve 600 to be moved proximally with respect to the head member 512. As the sleeve 600 is moved in this manner, the ball bearings 519 move from the distal portion 560 of the channel 548 to the proximal portion 558 of the channel 548. Thus, when the sleeve 600 is moved proximally by a sufficient amount with respect to the head member 512, the ball bearings 519 can be moved outwardly with respect to a longitudinal axis of the head member 512, which permits an anchor to be inserted into the head member 512 as described above. Then, distally-directed movement of the sleeve 600, produced by compression member 606 following release of a pushing force on the sleeve 600, returns the ball bearings 519 to the distal portion 560 of the channel 548, effectively securing the anchor to the head member 512.

[0056] While a plurality of ball bearings 519 is described and illustrated, it is understood that any suitable number of ball bearings can be used, including one ball bearing, two ball bearings, three ball bearings, or more. Indeed, the number of ball bearings included need only be at least one ball bearing.

[0057] FIG. 10 illustrates a head member 712 useable as a component of an anchor assembly. The illustrated head member 712 has a proximal end 722 and a distal end 724, a proximal opening 726 at the proximal end 722 and a distal opening 728 at the distal end 724. A passageway 730 extends from the proximal opening 726 to the distal opening 728 along the length of the head member 712. The head member 712 includes a proximal portion 732 and a distal portion 734. The proximal portion 732 defines a proximal chamber 736 of the passageway 730 and the distal portion 734 defines a distal chamber 738 of the passageway 730. The distal portion 734 of the head member 712 defines a channel 748 in communication with the passageway 730.

[0058] In this embodiment, a compression member 716 and a retaining member 718 are disposed within the channel 748 of the head member 712. Compression member 716 comprises a wave spring. A wave spring comprises one or more loops of flat wire with one or more waves in the loop. In embodiments using a wave spring as the compression member, any suitable type of wave spring can be used, including single-turn, multi- turn and nested wave springs. A single turn wave spring comprises a single such loop while a multi-turn wave spring comprises two or more such loops stacked with their waves extending in opposing directions. In the illustrated embodiment, compression member 716 comprises a multi- turn wave spring comprising three loops. A nested wave spring comprises two or more such loops stacked with their waves extending in the same directions. Use of a wave spring as the compression member in an embodiment may provide a lower work height than that of a coil spring or other compression member, while providing the same force.

[0059] In this embodiment, channel 748 is bounded by first lateral wall 750, second lateral wall 752, and base wall 754. Base wall 754 defines a sloped surface extending between the first lateral wall 750 and the second lateral wall 752. In the illustrated embodiment, the base wall 754 is a frustoconical surface, making channel 748 a circumferential channel without a ramp. It is noted that a channel having a partial-circumferential or other channel configuration in which a base wall comprises a sloped surface extending between a first lateral wall and a second lateral wall, or any two surfaces, could also be used. In use, the retaining member 718 moves expands radially outwardly as it is moved proximally within the channel, and contracts radially inwardly as it is moved distally within the channel.

[0060] The anchor assemblies are useful for connecting structures to each other. An anchor assembly according to an embodiment can be used to connect a structure to which the anchor of the anchor assembly is attached with another structure that can be secured by the head member of the anchor assembly. For example, the anchor can be secured to a first member, such as a member having a relatively broad surface into which or through the anchor can be disposed; a second member, such as an elongate member, can be secured by the head member to form a connection between the first and second members. Thus, the anchor assemblies can be used in a variety of situations and contexts. In one example use, an anchor assembly is used to secure a bone, such as a vertebra, to a rod, such as is done in surgical and minimally invasive spinal treatment procedures. In these procedures, a single rod can be secured to multiple anchor assemblies, effectively connecting the items connected to the anchors, such as two or more vertebrae. Connecting multiple anchor assemblies in this manner allows a user to manipulate the relative positioning of the vertebrae.

[0061] A head member, along with a compression member and retaining member, is useful for connecting to and providing additional structure for an anchor, such as a screw, nail, or barbed member.

[0062] All components of the anchor assemblies can be made from any suitable material. Non-limiting examples of suitable materials include metals, such as stainless steel, titanium, cobalt-chromium, and other metals, and plastics commonly used in medical devices. Non-limiting examples of materials considered specifically suitable for use in the compression member and retaining member include Nitinol and other superelastic materials, polyurethane materials, silicone materials, and polyether ether ketone (PEEK) materials.

[0063] Those with ordinary skill in the art will appreciate that various modifications and alternatives for the described and illustrated embodiments can be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are intended to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.