Bottom-loaded bone anchor assembly with resistance-retaining ring and related method

Abstract

A bottom loaded bone anchor assembly and components thereof are disclosed that have a reduced profile and can be utilized with bone screws of various sizes. The bone anchor assembly (200) of the present disclosure includes a receiver member (206), a resistance retaining ring (204), and a shank (202). The retaining ring and shank can be proximally inserted into a bore in the receiver member. The resistance ring can have a base and a wall extending proximally therefrom. The resistance retaining ring can be disposed in a groove in the receiver member, with the base forming a seat for a shank head that can retain the shank in the receiver member. The wall of the resistance retaining ring can apply a resistance force to the shank head seated in the base to prevent unintended movement between the shank and the receiver member.

Description

Technical Field

[0001] This specification discloses a bottom-loading bone anchor assembly having a resistance retaining ring and related methods.

Background Art

[0002] Bone anchor assemblies can be used in orthopedic surgery to fix bone during healing, fusion, or other processes. For example, in spinal surgery, bone anchor assemblies can be used to fix a rod or other spinal fixation element to one or more vertebrae to rigidly or dynamically stabilize the spine. 12222da

[0003] Bone anchor assemblies typically can include a threaded shank configured to be fixed to bone and a head or receiving member attached to the shank and configured to receive a rod or other fixation element therein. The shank and receiving member can be assembled such that the head of the shank is retained within the receiving member and the threaded portion of the shank extends distally therefrom. In some configurations, the shank and receiving member can be provided as a multi-axis assembly, whereby the receiving member has free angular movement relative to the shank. This degree of freedom of movement can be useful when aligning the multiple components of the bone anchor assembly, but it can also pose challenges. For example, it can be difficult to maintain a desired angular orientation between the receiving member and the shank before locking the assembly. For this reason, during temporary positioning of the assembly embedded in bone, the receiving member can tend to "lift" or drop, requiring subsequent repositioning by the user to achieve the desired alignment or requiring a user or assistant to hold the receiving member in the desired position during introduction of the rod or other fixation element. This is cumbersome for the user and can add an unnecessary length to the surgical procedure.

[0004] Many bone anchor assemblies can be "top-loaded," in which a bone screw is inserted through a proximal opening in the receiving member, moved distally so that the screw head seats within the receiving member, and the threaded shank passes distally through the distal opening. However, such top-loaded assemblies have limited applications because the diameter of the bone screw shank is restricted by the diameter and size of the receiving member. Therefore, when a larger diameter shank is desired, bone anchor assemblies are often assembled in a "bottom-loaded" configuration, in which the shank head is loaded by passing it proximal through the opening at the distal end of the receiving member. Bottom-loaded bone anchor assemblies may have an enlarged size or shape of the receiving member to accommodate, for example, a larger shank and additional components necessary to hold the shank within the receiving member, thereby determining the placement of the vertebral fixation element relative to the bone. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] There is a need for improved bone anchor assemblies that address the shortcomings of conventional designs, such as bone anchor assemblies with reduced external dimensions and improved temporary positioning that can be assembled and used independently of the diameter of the bone engagement components. [Means for solving the problem]

[0006] This disclosure provides a bone anchor assembly and related methods having a reduced overall assembly size and usable across a wide variety of surgical procedures. The bone anchor assembly disclosed herein can enable bottom loading of various bone anchor components into a receiving member, thereby providing a common assembly procedure regardless of the maximum outer diameter of the bone engagement component, e.g., the bone shank. The bone anchor assembly disclosed herein may include a resistance retaining ring that can be advanced proximal to the receiving member during assembly and held within its distal portion. The resistance retaining ring can hold the head of the bone shank within the receiving member so as to allow desired multi-axial movement between the receiving member and the bone shank, but to provide resistance to unintended or accidental movement between them. More specifically, the resistance retaining ring may include a base configured to seat the head of the bone shank and a wall extending proximal to the base. The wall can contact the head of the shank and apply a radially inward resistance or frictional force to the shank head to resist unintended movement. In this way, the bone anchor assembly of the present disclosure can be positioned in a desired location relative to the shank by, for example, a surgeon or other user, and can be maintained in the desired position by the frictional force applied to the head of the shank by the wall of the retaining ring.

[0007] In one embodiment, a bone anchor assembly is disclosed, which includes a receiving member having a proximal end and a distal end, a central longitudinal axis extending between the proximal and distal ends, a longitudinal hole formed inside, and an opening provided at the distal end; a retaining ring; and a shank. The retaining ring is positioned in a groove formed within the receiving member and includes a base and a wall portion extending proximal to the base, the base of the retaining ring having a maximum outer diameter greater than the maximum outer diameter of the wall portion. The shank has a head portion seated within the base of the retaining ring and a bone engaging portion extending distally from the receiving member. The wall portion of the retaining ring is configured to resist the rotation of the head portion of the shank by applying a resistive force.

[0008] The apparatus and methods described herein may have many additional features and / or variations, all of which are included within the scope of this disclosure. For example, the retaining ring and shank may be configured to be inserted proximal through the distal end of the receiving member. A groove formed in the receiving member may be formed on the inner surface of the distal end of the receiving member. In some embodiments, the bone anchor assembly may further include a saddle positioned proximal to the retaining ring within the hole of the receiving member, the saddle configured to apply a distal force to the shank head seated within the retaining ring.

[0009] The walls of the retaining ring can be configured to contact the head of the shank at their maximum diameter. In some embodiments, the proximal end of the wall can extend proximal beyond the maximum diameter of the head of the shank when the shank is seated within the base of the retaining ring. In other embodiments, the proximal end of the wall can be configured to contact the head of the shank at their maximum diameter. The walls of the retaining ring may optionally include a first wall segment and a second wall segment circumferentially separated from the first wall segment. The retaining ring may include segments extending through the base and walls, configured to allow selective radial expansion and compression of the retaining ring.

[0010] The base of the retaining ring may have a maximum outer diameter greater than the diameter of the opening at the distal end of the receiving member. The distal portion of the base of the retaining ring may have an inner diameter smaller than the maximum diameter of the head of the shank. In some embodiments, the inner diameter of the distal portion of the base of the retaining ring may be smaller than the maximum outer thread diameter of the bone engagement portion of the shank.

[0011] In another embodiment, a method for assembling a bone anchor assembly is disclosed, comprising compressing a retaining ring positioned around a shank radially, the shank comprising a head and a bone engagement portion, and the retaining ring comprising a base and a wall portion extending proximal to the base. The wall portion of the base has a maximum outer diameter smaller than the maximum outer diameter of the base. The method further comprises passing the shank and the compressed retaining ring proximal through an opening at the distal end of a receiving member, and advancing the retaining ring proximal within the receiving member such that at least a portion of the base aligns with a first annular recess of a groove formed within the receiving member. The method also comprises expanding the retaining ring to hold at least a portion of the base within the first annular recess of the groove, and seating the head of the shank on the base of the retaining ring such that the maximum diameter of the head of the shank contacts the wall portion of the retaining ring and the bone engagement portion of the shank extends distally from the retaining ring.

[0012] As described above, various additional steps and / or modifications are possible and within the scope of this disclosure. For example, in some embodiments, the method may further include positioning a receiving member at a desired position relative to the shank and holding the receiving member at the desired position by a resistive force applied by the wall portion of the retaining ring against the head of the shank. Positioning the receiving member at the desired position may optionally include moving the receiving member in multiple axes relative to the shank. In some embodiments, the resistive force may be applied by the retaining ring at the interface between the base and the wall portion of the retaining ring. In other embodiments, the resistive force may be applied by the proximal end of the wall portion of the retaining ring. In certain embodiments, the method may further include embedding the shank in bone and applying a locking mechanism to lock the receiving member at a desired position relative to the shank.

[0013] In some embodiments, the method may further include advancing the saddle proximal through the distal opening of the receiving member and biasing the shank distally by the distal force applied to the head of the shank by the saddle. In some embodiments, the above method step of radially compressing a retaining ring positioned around the shank may further include radially compressing the retaining ring around the neck of the shank, which can help assemble the retaining ring into the receiving member. In some embodiments, with at least a portion of the base of the retaining ring held in the first annular recess of the groove, the distal surface of the retaining ring may be flush with the distal surface of the receiving member.

[0014] Any of the features or modifications described above can be applied in several different combinations to any particular aspect or embodiment of this disclosure. No specific combination is explicitly stated, simply to avoid redundancy in this abstract. [Brief explanation of the drawing]

[0015] The present invention will be more fully understood by examining the following detailed description in conjunction with the accompanying drawings. [Figure 1A] This is a perspective exploded view of the bottom-loaded bone anchor assembly. [Figure 1B] Figure 1A is a cross-sectional view of the bone anchor assembly. [Figure 2] This is an exploded perspective view of a bone anchor assembly with multi-element bone anchors. [Figure 3] This is a front cross-sectional view of one embodiment of a bone anchor assembly of the present disclosure. [Figure 4] Figure 3 is an exploded perspective view of the bone anchor assembly. [Figure 5] Figure 3 is a perspective view of one embodiment of the resistance-holding ring of a bone anchor assembly. [Figure 6] Figure 5 is a front view of the resistance retaining ring. [Figure 7] This is a front cross-sectional view of the drag-holding ring in Figure 5, along line AA in Figure 6. [Figure 8] It is a perspective view of an embodiment of a receiving member of the bone anchor assembly of FIG. 3. [Figure 9] It is a front cross-sectional view of the receiving member of FIG. 8 taken along line B-B of FIG. 8. [Figure 10] It is a front cross-sectional view of another embodiment of the bone anchor assembly of the present disclosure. [Figure 11] It is an exploded perspective view of the bone anchor assembly of FIG. 10. [Figure 12] It is a perspective view of an embodiment of a resistance holding ring of the bone anchor assembly of FIG. 10. [Figure 13] It is a perspective view of an embodiment of a receiving member of the bone anchor assembly of FIG. 10. [Figure 14] It is a view showing one step of an embodiment of a method of assembling the bone anchor assembly of FIG. 10. [Figure 15] It is a side view of the bone anchor assembly of FIG. 10 connected to a spinal fixation element. [Figure 16] It is a side view of two embodiments of the bone anchor assembly of the present disclosure and one conventional bone anchor assembly connected to a rod.

Mode for Carrying Out the Invention

[0016] Disclosed herein is a bottom-loaded bone anchor assembly that provides a reduced external profile for the bone anchor assembly and can be used with a variety of bone shanks regardless of thread diameter. Thus, this disclosure provides a general method and configuration of a bone anchor assembly suitable for use across a wide range of surgical procedures. More specifically, the bone anchor assembly of this disclosure includes a resistive retaining ring that (i) prevents separation between the bone engagement shank and the receiving member, and (ii) resists multiaxial movement between the shank and the receiving head, thereby applying a resistive force to the head of the shank, for example, allowing a surgeon to position the receiving member in a desired alignment relative to the screw. The resistive retaining ring (also referred to herein as the “retaining ring”) may include a base configured to seat or hold the shank head, and a wall extending proximal to the base that can apply a radially inward frictional resistive force to the shank head. The resistive force applied by the retaining ring can help maintain the relative position between the receiving member and the shank before the bone anchor is locked in place, thereby preventing unintended movement while still allowing free movement when intended by the user. The retaining ring and shank can be loaded from the bottom into the receiving member, i.e., inserted proximal through the distal opening of the receiving member, so that the bone anchor assembly of this disclosure can be adapted for use with small, medium, or large diameter bone shanks.

[0017] To provide a comprehensive understanding of the structure, function, manufacturing and use principles of the devices, systems, and methods disclosed herein, certain exemplary embodiments are described below. One or more examples of these embodiments are illustrated in the accompanying drawings. The devices, systems, and methods described herein and illustrated in the accompanying drawings are non-limiting embodiments. Features illustrated or described in relation to one embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of this disclosure.

[0018] In addition, to the extent that linear or circular dimensions are used in the description of the disclosed devices and methods, such dimensions are not intended to limit the types of shapes that may be used with such devices and methods. Equivalents to such linear and circular dimensions may be determined for different geometric shapes. Furthermore, similarly numbered components of embodiments may generally have similar characteristics. Moreover, the size and shape of a device, and its components, may depend at least on the anatomical form of the subject in which the device is used, the size and shape of the object in which the device is used together, and the method and procedure in which the device is used.

[0019] Figures 1A and 1B show a bone anchor 100 comprising an anchor portion or shank 102, a head or receiving member 104 for receiving a spinal fixation element connected to the shank 102, such as a spinal rod 106, and a fastener or closing mechanism 108 for capturing the spinal fixation element within the receiving member and fixing the spinal fixation element to the receiving member. The shank 102 includes a proximal head 110 and a distal shaft 112 configured to engage with bone. The receiving member 104 has a proximal end having a pair of spaced-apart arms 114A, 114B defining a recess or channel 116 between the arms, and a distal end having a distal end face defining an opening, through which at least a portion of the shank 102 extends. The closing mechanism 108 can be positioned between the arms 114A and 114B and engage with the arms 114A and 114B to capture the spinal fixation element (e.g., spinal rod 106) within the receiving member 104 and fix the spinal fixation element to the receiving member.

[0020] The proximal head 110 of the shank 102 is generally shaped like a truncated sphere with a planar proximal surface and a substantially spherical distal surface. The illustrated bone anchor 100 is a multi-axis bone screw designed for posterior implantation within the pedicle or lateral mass of a vertebra. The proximal head 110 of the shank 102 engages with the distal end of the receiving member 104 in a ball-and-socket-like mechanism, allowing the proximal head and distal shaft 112 to pivot relative to the receiving member. The mating surfaces within the distal end of the distal end of the proximal head 110 of the shank 102 and the receiving member 104 can have any shape to facilitate this mechanism, including, for example, spherical (as shown), toroidal, conical, frustoconical, and any combination of these shapes.

[0021] The distal shaft 112 of the shank 102 may be configured to engage with bone and, in the illustrated embodiment, includes a male thread for engaging with bone. The thread configuration of the distal shaft 112, including the number of threads, pitch, outer and inner diameters, and the shape of the threads, can be selected to facilitate connection with bone. Exemplary thread configurations are disclosed in U.S. Patent Application Publication No. 2011 / 0288599 filed May 18, 2011, and U.S. Patent Application Publication No. 2013 / 0053901 filed August 22, 2012, both of which are incorporated herein by reference. The distal shaft 112 may also include other structures for engaging with bone, such as a hook. For example, to facilitate delivery of the shank on a guidewire in minimally invasive procedures, the distal shaft 112 of the shank 102 may be cannulated by having a central passage or cannula that extends the length of the shank. For example, other components of the bone anchor 100, including the closure mechanism 108, the receiving member 104, and the compression cap or saddle 118 (discussed below), may be cannula-treated or have openings to allow delivery on a guidewire. To allow bone endografting or to allow distribution of bone cement or other material through the shank 102, the distal shaft 112 may also include one or more sidewall openings or windows communicating with a cannula. The sidewall openings may extend radially from the cannula through the sidewall of the distal shaft 112. Exemplary systems for delivering bone cement to the bone anchor 100, and alternative forms of bone anchors for facilitating cement delivery, are described in U.S. Patent Application Publication No. 2010 / 0114174, filed October 29, 2009, the disclosures of which are incorporated herein by reference. The distal shaft 112 of the shank 102 can also be coated with a bone growth-promoting material, such as hydroxyapatite, and the bone anchor 100 can be partially or completely coated with an anti-infective material, such as triclosan.

[0022] The proximal end of the receiving member 104 includes a pair of spaced-apart arms 114A, 114B, which define a U-shaped recess 116 between them for receiving a spinal fixation element (e.g., a spinal rod 106). Each of the arms 114A, 114B may extend from the distal end to the free end of the receiving member 104. The outer surface of each of the arms 114A, 114B may include features such as recesses, indentations, notches, or projections to facilitate connection of the receiving member 104 to the device. For example, the outer surface of each arm 114A, 114B may include an arched groove at the free end of the arm. Such grooves are described in detail in U.S. Patent No. 7,179,261 issued February 20, 2007, the disclosure of which is incorporated herein by reference.

[0023] The distal end of the receiving member 104 includes a distal end face that is generally annular in shape, defining a circular opening through which at least a portion of the shank 102 extends. For example, the distal shaft 112 of the shank 102 can extend through the opening.

[0024] The shank 102 can be selectively fixed to the receiving member 104. Before fixing, the shank 102 is movable relative to the receiving member 104 within an angle-forming cone generally defined by the geometric shape of the distal end of the receiving member and the proximal head 110 of the shank 102. The bone anchor 100 may be a favored angle screw, for example, as disclosed in U.S. Patent No. 6,974,460 issued December 13, 2005, and U.S. Patent No. 6,736,820 issued May 18, 2004, the disclosures of which are incorporated herein by reference. Alternatively, the bone anchor 100 may be a conventional (non-biased) multi-axis screw, in which the shank 102 pivots by the same amount in all directions.

[0025] The spinal fixation element (e.g., spinal rod 106) can be in direct contact with the proximal head 110 of the shank 102, or it can be in contact with an intermediate element, such as a compression member or a saddle 118. The saddle 118 can be positioned within the receiving member 104 and interposed between the spinal rod 106 and the proximal head 110 of the shank 102, and can compress the distal outer surface of the proximal head into a fixed engagement with the distal inner surface of the receiving member 104. The saddle 118 may include a pair of spaced-apart arms 120A, 120B defining a U-shaped seating surface 122 for receiving the spinal rod 106, and a distal surface for engaging with the proximal head 110 of the shank 102.

[0026] The proximal end of the receiving member 104 may be configured to receive a locking mechanism 108 that can be positioned between the arms 114A and 114B of the receiving member and engage with the arms 114A and 114B. The locking mechanism 108 may be configured to capture a spinal fixation element, e.g., a spinal rod 106, within the receiving member 104, to fix the spinal rod to the receiving member, and to fix the shank 102 to the receiving member. The locking mechanism 108 may be a single set screw with a male thread for engaging with female threads provided on the arms 114A and 114B of the receiving member 104. However, in the illustrated embodiment, the locking mechanism 108 includes an outer set screw 124 that can act on the saddle 118 and an inner set screw 126 that can act on the rod 106. Alternatively, or in addition, various other closing mechanisms 108 can be used, such as a nut extending around the outer circumference of the receiving member 104, a cap or fastener sliding on the receiving member from the side, or a cap or fastener that locks onto the receiving member by a quarter turn.

[0027] The bone anchor 100 can be used in conjunction with a spinal fixation element such as a rigid spinal rod 106. In other embodiments, the spinal fixation element may be a dynamic stabilizing member that allows for controlled movement between the vertebrae to which the device is attached.

[0028] For use, the bone can generally be prepared to receive the bone anchor assembly 100 by drilling a hole in the bone that is appropriately sized to receive the shank 102. If not yet completed, the bone anchor 100 can be assembled such that the distal shaft 112 extends through an opening at the distal end of the receiving member 104 and the proximal head 110 of the shank 102 is received at the distal end of the receiving member 104. A driver tool can be attached to the shank 102 to drive the shank into the bone. The saddle 118 can be positioned within the receiving member 104 such that the arms 120A, 120B of the saddle align with the arms 114A, 114B of the receiving member 104 and the lower surface of the saddle 118 contacts the proximal head 110 of the shank 102. A spinal fixation element (e.g., a spinal rod 106) can be positioned in a recess 116 of the receiving member 104. The locking mechanism 108 can engage with the female threads provided on the arms 114A and 114B of the receiving member 104. Torsional force can be applied to the outer set screw 124, moving it within the recess 116 so as to press the saddle 118 against the proximal head 110 of the shank 102, thereby locking the angular position of the shank 102 relative to the receiving member 104. Torsional force can be applied to the inner set screw 126, pushing the spine rod 106 into engagement with the saddle 118, thereby fixing the spine rod 106 relative to the receiving member 104.

[0029] Further information regarding the bone anchor 100 can be found in U.S. Patent Application No. 2018 / 0325569, filed May 10, 2017, the disclosures of which are incorporated herein by reference.

[0030] Figure 2 shows a bone anchor assembly 100' similar to the bone anchor assembly 100 in Figures 1A and 1B, but the bone anchor assembly 100' includes a multi-element bone anchor 101', in which the shank 112' advances proximal into the receiving member 104' and engages with a spherical head or ball 110'. A clip 111' locks the head 110' to the shank 112'. The spherical head 110 engages with the distal end of the receiving member 104' in a ball-and-socket-like mechanism, to which the proximal head and distal shaft 112 connected thereto can pivot relative to the receiving member. The bone anchor assembly 100' may include a closing mechanism 108' and a compression member 118' as described above. The closing mechanism 108' may include an external set screw 124' and an internal set screw 126', and may be configured to capture a spinal fixation element, such as a spinal rod 106', within the receiving member 104' and to fix the spinal fixation element to the receiving member.

[0031] Further details of the bone anchor 100' can be found in U.S. Patent Application No. 9,775,660, filed March 14, 2013, which is incorporated herein by reference.

[0032] Figures 3 to 9 illustrate one embodiment of the bone anchor assembly 200 of this disclosure. The structure and configuration of the bone anchor assembly 200 and its various components result in a reduction in the size of the bone anchor assembly and enable a common assembly procedure regardless of the bone anchor thread size. For this purpose, several components of the bone anchor assembly 200 can be loaded from the bottom into a receiving member, which includes a resistance-holding ring that can hold the bone shank within the receiving member of the bone anchor and apply resistance thereto (described in detail below). As shown in Figures 3 and 4, the bone anchor assembly 200 may include a shank 202, a resistance-holding ring 204, and a receiving member 206. The bone anchor 200 may also include a compression cap or saddle 208 and a fastener or closing mechanism 210 (see Figure 8). Unless otherwise described herein or evident from this disclosure, the shank 202, receiving member 205, compression cap 208, and closing mechanism 210 may include any of the features of the corresponding components of the bone anchor 100 described above. For example, the shank 202 may have a head 202a and a distal shank or bone engagement portion 202b. The bone engagement portion 202b may include an external bone engagement thread. The receiving member 206 may include a pair of spaced arms 207a, 207b defining a recess 209 between them. The locking mechanism 210 is positionable between arms 214A and 214B and can engage with arms 207a, 207b, and within the receiving member 206, it captures a spinal fixation element (e.g., a spinal rod 206), fixes the spinal fixation element to the receiving member, and fixes the receiving member to the shank 202. The receiving member 106 may have a proximal end 206p, a distal end 206d, and a central longitudinal axis A1 extending between them. The receiving member 206 may include a longitudinal hole 211 capable of receiving at least a portion of the shank 202, retaining ring 204, compression cap 208, and closing mechanism 210. The shank 202 may include a central longitudinal axis A2. The shank 202 may be rotated and pivoted relative to the receiving member 206 about the central longitudinal axis A1 of the receiving member.

[0033] Referring to Figure 3, the retaining ring 204 is positioned between the head 202a of the shank 202 and the distal portion 206d of the receiving member 206 so that it can (i) hold the shank head within the receiving member and (ii) apply a resistance force to the shank head. More specifically, the retaining ring 204 can be at least partially held within the groove 312 of the receiving member 206 (Figure 9), and the shank head 202a can be seated multiaxially within the retaining ring in a ball-and-socket configuration so that the shank 202 can pivot and rotate relative to the retaining ring and the receiving member. In the collinear orientation of Figure 3, i.e., when the longitudinal axis A2 of the shank 202 is aligned with the longitudinal axis A1 of the receiving member 206, the retaining ring 204 can apply a radially inward frictional force to the shank head 202a along its equator or maximum diameter D. The force applied by the retaining ring 204 can resist relative movement between the shank head 202a and the receiving member 206, thereby temporarily holding the shank 202 in the desired position relative to the receiving member, preventing the receiving member from falling or "floating." As will be described in detail below, the resistive force applied by the retaining ring 204 can arise from the interference fit between the wall portion 402 of the retaining ring (Figure 5) and the outer diameter of the shank head. Hereinafter, the various components of the bone anchor assembly 200 will be described in more detail with reference to Figures 5 to 9.

[0034] One embodiment of the retaining ring 204 is shown in detail in Figures 5-7. The retaining ring 204 can be substantially cylindrical, having a base 300 configured to seat the shank head 202a, and a wall portion 302 extending proximal from the base. The retaining ring 204 is configured to insert the shank 202 proximal into the hole 211 of the receiving member 206, and can be held in a groove 212 formed in the distal end 206d of the receiving member. The lumen 301 can extend through the retaining ring 204 having a distal opening 301d passing through the distal surface 300d of the base 300 (Figure 7). The distal opening 301d of the base has a diameter D smaller than the maximum diameter D of the head 202a of the shank 202. LIt can have a diameter D of the distal opening 301d of the base. L This can be made smaller than the maximum external thread diameter of the bone engagement portion 202b of the shank 202.

[0035] The proximal portion of the base 300 can be formed from an annular boss 304 having an outer diameter D1 that is larger than the outer diameter D2 of the distal portion 306 of the base. The wall portion 302 can extend proximal to the annular boss 304. The outer diameter D1 of the boss 304 can be larger than the outer diameter D3 of the wall portion 302 so that the outer diameter of the boss represents the maximum outer diameter of the retaining ring 204. The retaining ring 204 may include a radial division 308 that allows for selective radial expansion and compression of the retaining ring. The retaining ring 204 is shown with the radial division 308 extending through the base 300 and the wall portion 302, but the retaining ring may include additional or alternative features, such as slits or notches, to allow for radial expansion and compression. In this way, the diameter of the retaining ring 204 can be selectively adjusted, for example, by reducing the outer diameter of the retaining ring for proximal insertion into the receiving member 206, and then expanding the diameter to seat the retaining ring in the receiving member groove 412.

[0036] The inner surface 300i of the base 300 can form a seat for the shank head 202a. More specifically, the inner surface 300i of the base 300 can be sized and shaped to hold at least a portion of the shank head 202a therein, allowing for multiaxial movement of the shank head relative to the base. In some embodiments, the inner surface 300i can be adapted to the shape of the outer surface of the shank head 202a. For example, at least a portion of the inner surface 300i can have a spherical shape that can correspond to the outer spherical surface of the shank head 202a. The illustrated embodiment shows a shank head 202a having a spherical shape and an inner surface 300i of a retaining ring 204 having a complementary spherical surface, but other shapes of the shank head and / or inner surface are also within the scope of this disclosure. For example, in some embodiments, the inner surface 300i of the base 300 can be a chamfered surface (see 300i' in Figure 11) that can seat or receive a spherical shank head 202a. In other embodiments, the shank head 202a may have a different shape, and the shape of the inner surface 400i of the base may be formed such that the shank head 202a can be received or seated therein.

[0037] As described above, the wall portion 302 can impart a frictional or reactive force to the shank head 202a when the shank head is seated within the base portion 300. The reactive force can resist the multi-axial movement of the shank 202 relative to the retaining ring 204. The inner surface 302i of the wall portion 302 can have a geometric shape configured to apply a reactive force to the head 202a of the shank 202. For example, the inner surface 302i of the wall portion 302 can have a cylindrical shape, and the interface 310 between the spherical inner surface 300i of the base portion 300 and the cylindrical inner surface 302i of the wall portion 302 can have a stationary diameter smaller than the maximum diameter D of the shank head 202a. In this way, the wall portion 302 can apply a radially inward reactive force along a single line of contact with the shank head 202a at the interface 310. When the shank head is seated within the retaining ring base 300 and the interface 310 is aligned with the maximum diameter of the shank head, the wall portion 302 may have a height H such that the proximal end 302p of the wall portion extends proximal beyond the equator or maximum diameter D of the shank head 202a. The height H of the wall portion can be measured from the distal end 304d to the proximal end 302p of the wall portion on the proximal opposing surface 302p of the annular boss 304. The relative dimensions of the retaining ring 204 and other components of the bone anchor assembly 200 can be selected, at least in part, to achieve the desired resistance and contact between the retaining ring and the shank head 202a. In some non-limiting examples, the height H of the wall portion 402 may be about 0.5 mm. Therefore, once assembled, that is, when the retaining ring 204 is received in the groove 412 of the receiving member and the shank head 202a is seated therein, the wall portion 302 of the retaining ring can apply a radially inward frictional force to the head 202a of the shank 202 at the interface 310, resisting multi-axial movement between the head of the shank and the receiving member 206.

[0038] In some embodiments, the wall 302 may have two wall segments 312a, 312b that can be separated circumferentially by a recess or gap 314. The recess 314 between the wall segments 312a, 312b can assist in smooth retraction when the retaining ring 204 is advanced proximal to the receiving member 206. For example, in some embodiments, the recess 414 may have a substantially "U" shape, and the recess may extend from the proximal end 302p of the wall segments 312a, 312b to the distal end 302d of the wall segments. In a further non-limiting example, the gap 314 may have a substantially truncated "V" shape (Figure 11). The wall segments 312a, 312b may pivot or bend around a point opposite the slot 308 of the retaining ring 304. In some embodiments, a scalloped notch 311 (Figure 3) may be provided along the outer surface 302o of the wall portion 302 or wall segments 312a, 312b at its distal end 302d. The scalloped notch 311 can provide further flexibility to the wall portion 302 or wall segments 312a, 312b.

[0039] Figures 8 and 9 show the receiving member 206 in more detail. Figure 8 is a perspective view of the receiving member 206, and Figure 9 is a front cross-sectional view of the receiving member along axis AA in Figure 8. Referring to Figure 9, the distal end 206d of the receiving member 206 may include a groove 212 formed on its inner surface. The groove 212 may be configured to receive and at least partially seat the retaining ring 204. The groove 212 may have distal, intermediate, and proximal annular recesses or annular portions 212a, 212b, and 212c, each of which may be sized at least partially to correspond to the corresponding outer dimensions of the distal portion 306 of the base 300, the annular boss 304, and the wall portion 306 of the retaining ring 204, respectively. For example, the inner diameter D4 of the distal annular recess 212a may be equal to or slightly larger than the outer diameter D2 of the distal portion 306 of the base 300. Similarly, the inner diameter D5 of the intermediate annular recess 212b and the inner diameter D6 of the proximal annular recess 212c can be equal to or slightly larger than the outer diameters D1 and D3 of the wall portions 302 of the annular boss 304 and the retaining ring 204, respectively.

[0040] The distal annular recess 212a can be the most distal part of the groove 212 and can extend proximal from the distal surface 212 of the receiving member 206, thereby forming a distal opening 216 within the receiving member. The distal annular recess 212a can form a distal opening relative to the receiving member 206d such that the inner diameter D4 of the distal annular recess is equal to the distal opening of the receiving member. The intermediate annular recess 212b can be proximal to the distal annular recess 212a, and the inner diameter D5 of the intermediate annular recess is larger than the inner diameter D4 of the distal annular recess. The proximal annular recess 212c can be proximal to the intermediate annular recess 212b. The inner diameter D6 of the proximal annular recess 212c can be smaller than the inner diameter D5 of the intermediate annular recess 212b, and in some embodiments, it can be larger than the inner diameter D4 of the distal annular recess 212a. The longitudinal hole 211 can extend proximal to the proximal annular recess 212c with an inner diameter D7, and in some embodiments, the inner diameter D7 can be smaller than the inner diameter D6 of the proximal annular recess. In this way, the retaining ring 204 received in the groove 312 can be prevented from sliding proximal to the groove 212.

[0041] Another embodiment of the bone anchor 200 is described here with reference to Figures 3 and 4. Although this method is shown in relation to the bone anchor assembly 200 of Figures 3–9, this method can be used with any of the bone anchor assemblies or their modifications disclosed herein. The bone anchor assembly 200 can be assembled during manufacturing, before surgery, or before the shank 202 is implanted in the bone during surgery. When used, the compression cap 208 can be advanced proximal through the distal opening 216 of the receiving member into the hole 211. Before inserting the shank 202 into the receiving member 206, the retaining ring 204 can be snapped around a portion of the shank or otherwise positioned. In some embodiments, the retaining ring 204 can be snapped around the unthreaded portion of the shank 202 between the shank head 202a and the threads of the bone engagement portion 202b, i.e., the neck 202c of the shank, or otherwise positioned. For example, the neck 202c of the shank can be inserted into the retaining ring 204 by passing the retaining ring slot 308 laterally relative to the shank neck 202c, such that the shank neck is located within the lumen 301 of the retaining ring. The retaining ring can be compressed, for example, by applying a radial compressive force Fc (see Figure 14), thereby temporarily reducing the maximum diameter D1 of the retaining ring. The retaining ring 204 can be compressed such that the maximum diameter of the retaining ring, i.e., the outer diameter D1 of the annular boss 304, becomes smaller than the diameter D4 of the distal annular recess 214a in the groove 212 and the distal opening 216 of the receiving member 206.

[0042] With the retaining ring 204 in a compressed state and positioned around the shank 202, the shank and retaining ring can be advanced proximal through the distal opening 216 of the receiving member 206, i.e., loaded into the receiving member from the bottom. As the retaining ring 204 advances proximal, the annular boss 304 of the retaining ring can align with the intermediate annular recess 212b of the groove 212 formed in the receiving member 206. As described above, the inner diameter D5 of the intermediate annular portion 212b of the groove 212 can be substantially equal to or slightly larger than the outer diameter D1 of the annular boss. Thus, once the boss 304 of the retaining ring 204 aligns with the intermediate annular recess 212b of the groove 212, the retaining ring 204 can expand from its compressed state to its original or stationary state so that the retaining ring seats in the groove (Figure 3). More specifically, the distal portion 306 of the base 300, the annular boss 304, and the wall portion 302 of the retaining ring 204 can extend into and be held within the distal annular recess 212a, the intermediate annular recess 212b, and the proximal annular recess 212c of the groove 212, respectively. In some embodiments, with the retaining ring 204 seated in the groove 212, the distal opposing surface 300d of the retaining ring can be flush with the distal opposing surface 214 of the receiving member 206.

[0043] With the retaining ring 204 seated in the groove 212, that is, with a portion of the retaining ring held in the corresponding recess of the groove (as described above), the shank 202 can be moved distally within the longitudinal hole 211 of the receiving member 206 to seat the head 202a of the shank in the base 300 of the retaining ring. More specifically, the shank 202 can be moved distally such that the equator D of the shank head 202a contacts the inner surface 302i of the wall portion 302 of the retaining ring 204, and the distal opposing portion of the shank head contacts the inner surface 300i of the base 300. The neck 202c and bone engagement portion 202b of the shank 202 can extend distally from the retaining ring 204 and the receiving member 206. A portion of the shank head 202a can also extend distally beyond the retaining ring 204 and the receiving member 206. The retaining ring 204 is sized to prevent the shank head 202a from passing through the distal opening 301d, so that the head of the shank is held within the retaining ring 204 and therefore within the receiving member 206.

[0044] The bone anchor assembly 200 is embedded in bone (not shown) and can be driven to a desired depth along a desired trajectory using known techniques, for example, by using a screwdriver tool to screw the bone engagement portion 202b of the shank 202 into the bone. Once embedded, the receiving member 206 can be positioned in a desired orientation relative to the shank 202. For example, the receiving member 206 can be rotated multiaxially around the head 202a of the shank 202. Before attaching and / or tightening the closing mechanism 210 to the bone anchor 200, the receiving member 206 can be maintained in a desired orientation, for example, through a resistance force between the retaining ring 204 and the shank head 202a, more specifically, through a resistance force between the wall portion 302 of the retaining ring 204 and the shank head. A spinal fixation element, for example, a spinal rod (Figure 15), can be positioned in the recess 209 of the receiving member 206. When the spinal rod is in the desired position, the closing mechanism 210 can be tightened to bias the rod and compression cap 208 (if used) distally relative to the receiving member 206, thereby locking the bone anchor 200. Specifically, applying the closing mechanism 210 can be effective in locking the movement of the receiving member 206 relative to the shank 202. For example, the rod and compression cap 208 can apply a distal force to the shank 202 such that the shank contacts the inner surface 300i of the retaining ring base 300, causing the retaining ring 204 to expand radially until one of the outer diameters D1, D2, or D3 of the retaining ring base 300 contacts one of the inner diameters D4, D5, or D6 of the receiving member. During this radial expansion of the retaining ring base, the shank head 202a can be held within the wall portion 302 of the retaining ring 204, for example, by compression fitting. Applying the closing mechanism 210 can also be effective in locking the movement of the rod 206 relative to the receiving member 206.

[0045] In this way, the bone anchor assembly of the present disclosure enables assembly using a bottom-loading technique. This may be particularly advantageous for large-diameter shanks that are not sized to advance distally through the proximal end of the receiving member, for example, because sizing the receiving member to accommodate such a large-diameter shank would require an excessively large receiving member. Furthermore, a single component, namely a retaining ring, can maintain the connection between the receiving member and the bone shank, preventing unintended movement between the two components while allowing multi-axial adjustment of the bone shank to a desired position relative to the receiving member.

[0046] Figures 10 to 14 illustrate another embodiment of the bone anchor assembly 400 of the present disclosure. The bone anchor assembly 400 may include a shank 402, a resistance retaining ring 404, a receiving member 406, a compression cap 408, and a closing mechanism (not shown). Except as described below, the structure, operation, and use of this embodiment are the same as or identical to those of the bone anchor assembly 200, and components with similar numbering generally have similar characteristics. Therefore, for the sake of brevity, descriptions of the structure, operation, and use of such features are omitted herein. Similar to the embodiments described above, the resistance retaining ring 404 can apply a frictional or resistance force to the head 402a of the shank 402 to resist multiaxial movement between them. In the assembly configuration shown in Figure 10, that is, when the shank 402 extends coaxially with the central axis B1 of the receiving member 406, the retaining ring 404 can apply a frictional force along the equator or maximum diameter D' of the shank head 402a, similar to the bone anchor assembly described above. However, the retaining ring 402 can have an alternative structure compared to the retaining ring 204 described above, so that the proximal end 502p (Figure 12) of the wall portion 502 of the retaining ring 402 can apply a resistive force radially inward against the shank head 402a.

[0047] Figure 12 shows the retaining ring 404 of the bone anchor assembly 400 in more detail. The retaining ring 404 can be substantially cylindrical, having a base 500 configured to seat the shank head 402a, and a wall 502 extending proximal from the base. The proximal portion of the base 500 can be formed from an annular boss 504 having an outer diameter D1' (see Figure 10) that is larger than the outer diameter D2' (see Figure 10) of the distal portion 506 of the base. The wall 502 can extend proximal from the annular boss 504 with an outer diameter D3' (see Figure 10) that is smaller than the outer diameter D1' of the boss. In such a structure, the retaining ring may include three “stepped” portions, i.e., portions with changing outer diameters: the distal base 506, the annular boss 504, and the wall 502. In the assembly configuration of the bone anchor assembly 400 (for example, Figure 10), the retaining ring 404 can be received at its distal end 406d in a groove 412 formed on the inner surface of the receiving member 406. As described above, the groove 412 may include three annular recesses, namely a distal annular recess 412a, an intermediate annular recess 412b, and a proximal annular recess 412c, which are configured to receive the distal portion 506 of the base 500, the annular boss 504, and the wall portion 502 of the retaining ring 404, respectively. Thus, the retaining ring 404 can be securely held in the groove 412 at the distal end 406d of the receiving member 406.

[0048] Returning to the retaining ring 404 and Figure 12, the retaining ring may have a radial division 508, or other slots, notches, etc., that can allow for selective radial expansion and compression of the retaining ring. In some embodiments, the division 508 may be sized to allow a portion of the shank 402, for example, the neck 402c of the shank, to pass through the division 508 and enter the retaining ring 404. The inner surface 500i of the base 500 may have a chamfered edge that can form a seat for the shank head 402a. The chamfered edge may extend from a point along the inner surface 500i of the distal portion 506 of the base 500 to a point along the inner surface at the proximal end 504p of the annular boss 504. The wall 502 may extend cylindrically from the freestanding proximal end 502p to the distal end 502d, terminating at the proximal end 504p of the annular boss. As shown in Figure 10, when the shank is seated coaxially within the retaining ring base 500, the proximal end 502p of the wall 502 can be configured to apply a drag force at the equator of the shank head 402a. For example, the proximal end 502p of the wall 502 can have an inner diameter smaller than the maximum diameter D' of the shank head. In some embodiments, the inner surface 502i of the wall 502 can have a chamfered edge at its proximal end 502p that can contact the shank head 402a and apply a frictional force thereto resist multiaxial movement between the shank head and the retaining ring. The wall 502 can extend to a height H' such that the proximal end 502p of the wall 502 can contact the shank head 402a at its maximum diameter D' when the wall 502p is seated collinearly or coaxially within the base 500 (for example, in the orientation shown in Figure 14).

[0049] As described above, in some embodiments, the wall portion 502 may include a first wall segment 512a and a second wall segment 512b circumferentially separated from the first wall segment by a gap or recess 514. In some embodiments, the recess 514 may have a substantially truncated "V" shape. A notch 511, groove, or other similar notch feature may extend along the outer surface of the wall portion 502 or wall segments 512a, 512b at the distal end 502d.

[0050] Figure 13 illustrates the receiving member 406 in more detail. Compared to the receiving member 206 described above, which has a pair of spaced-apart arms 207a, 207b at its proximal end 206p, the receiving member 406 can have a “closed” configuration. The closed configuration allows for a reduction in the size of the receiving member while providing sufficient strength to the receiving member 406 for use in high-load applications, for example, for implantation within the iliac spine. The proximal end 406p of the receiving member 406 can circumferentially surround a longitudinal hole 411 that extends distally from the proximal end of the receiving member into the receiving member body. Notches 413 can be formed on both sides of the receiving member body to form a rod receiving recess 409 through which a rod passes. Each of the notches 413 can have a closed outer circumference formed by the receiving member body. Such a structure is in contrast to, for example, the rod receiving recess 209 of the receiving member 206 shown in Figures 3 and 4, which is formed between spaced arms 207a and 207b and is open in the proximal direction. Returning to Figure 13, the notch 413 can be sized and shaped to laterally receive a spinal fixation element, such as a spinal rod, through it, so that the spinal fixation element can extend laterally through the receiving member 406 relative to the longitudinal hole 411. For example, in the illustrated embodiment of Figure 13, the notch 413 has a substantially elliptical shape to receive a spinal rod through it. The longitudinal hole 411 can receive a set screw or other fastening mechanism (not shown) for fixing the spinal fixation element in the rod receiving recess 409 relative to the receiving member 406. The groove 412 can be formed on the inner surface of the distal end 406d of the receiving member 406, which has an opening 416 passing through the distal surface 414 (Figure 10) of the receiving member, so that the shank 402 and the retaining ring 404 can advance proximal into the receiving member 406 and be held therein, as described above with respect to Figures 3 to 9.

[0051] The bone anchor assembly 400 can be assembled using the same or similar assembly procedure described above with respect to the bone anchor 200 in Figures 3-9. For example, referring to Figure 14, the compression cap 408 can be advanced proximal to the hole 411 through the distal opening 416 of the receiving member 406. Alternatively, the compression cap 408 can be loaded by advancing distally from the proximal end of the receiving member 406 through the hole 411. In some embodiments, the compression cap can be retained within the receiving member 406 by crimping. The retaining ring 404 can be snapped around the shank 402, for example, around the neck 406c of the shank, or otherwise positioned. The retaining ring 404 can be compressed, for example, by applying a radial compressive force Fc to the retaining ring, such that the outer diameter of the annular boss 504 can be reduced to less than the diameter of the distal opening 516 of the receiving member 506. The compressed shank head 402a and retaining ring 404 can be advanced proximally into the hole 411 through the distal opening 516 of the receiving member 506. The retaining ring 404 can advance proximally within the hole 411 until the annular boss 504 aligns with the intermediate annular recess 412b of the groove 412. With the annular boss 504 aligned with the intermediate annular recess 412b, the retaining ring 404 can expand radially into the groove 412 and be held therein. The shank 402 can be moved distally relative to the receiving member 406 so that the shank head 402a seats within the base 400 of the retaining ring 204 and contacts the wall 502 at the maximum diameter D' (Figure 10) of the shank head. A bone anchor can be embedded in bone (not shown), and the receiving member 406 can be manipulated to position it in a desired orientation relative to the shank 402. In some embodiments, the receiving member 406 can be moved in multiple axes relative to the shank 402. Referring to Figure 15, the spinal rod 420 can be inserted laterally into the receiving member 406 through the rod receiving recess 409. The locking mechanism 410 can be tightened to lock the spinal rod 420 against the receiving member 406. The locking mechanism 410 can also lock the receiving member 406 against the shank 402.

[0052] The bone anchor assemblies 200, 400 of this disclosure may have reduced overall size and shape, at least in part, due to the incorporation of the resistance retaining rings 204, 404 disclosed herein. Figure 16 shows two embodiments 500, 510 of the bone anchor assemblies of this disclosure and one known bone anchor assembly 600 connected to a vertebral rod 520. Three dimensions X, Y, and Z of the various bone anchor assemblies 500, 510, 600 are illustrated and described in detail below, where "X" represents the total height of each bone anchor assembly, measured from the most proximal opposing surface of the receiving member to the most distal opposing surface of the receiving member. "Y" represents the distance each receiving member extends distally below the vertebral rod, and "Z" represents the maximum width of each receiving member, measured parallel to the longitudinal axis of the vertebral rod when the vertebral rod is received within the bone anchor assembly.

[0053] A known bone anchor assembly 600 can be a bottom-loading assembly for use with a large bone screw. The first bone anchor assembly 500 of this disclosure can be sized and configured for use with small and medium bone screws (e.g., bone screws having a maximum outer thread diameter of about 4 mm to about 8 mm). The second bone anchor assembly 502 of this disclosure can be sized and configured for use with a large bone screw (e.g., bone screws having a maximum outer thread diameter of about 7.5 mm or more). In particular, a bone anchor assembly 510 of this disclosure configured for use with a large bone screw can have the same overall height X'' as a bone anchor assembly 500 configured for use with a small or medium bone screw and can extend distally by the same distance Y'' below the vertebral rod 520. In non-limiting examples, in some embodiments, the overall heights X', X'' of bone anchor assemblies 500, 510 can be less than about 16 mm, less than about 15.5 mm, or about 15 mm. In some embodiments, the distance Y', Y'' between the distal end of the receiving member of the bone anchor assembly 500, 510 and the distal surface of the vertebral rod 510 can be less than about 6.5 mm, less than about 6 mm, or about 5.5 mm to about 6 mm. In contrast, a known bone anchor assembly 600 can have a height X''' of about 16.2 mm or more and can extend below the vertebral rod by a distance Y''' of about 6.9 mm or more. The bone anchor assemblies 500, 510 of this disclosure can also have a reduced width Z', Z'' compared to the width Z''' of a known bone anchor 600. As a non-limiting example, the overall width Z', Z' of the bone anchor assemblies 500, 510 can be less than about 12 mm in some embodiments and less than about 11 mm in some embodiments. A known bone anchor 600 can have a Z''' greater than about 12 mm. The reduced dimensions of the bone anchor assemblies 500, 510 of this disclosure allow for the fixation of bone fixation elements, such as the vertebral rod 520, closer to the bone into which the bone anchor assemblies are embedded. Furthermore, the smaller size can improve ease of placement and handling by minimizing the portion of the surgical site occupied by, for example, spinal devices.

[0054] The assemblies and components disclosed herein may be composed of any of the various known materials. Exemplary materials include metals such as stainless steel, titanium, cobalt-chromium, or alloys and combinations thereof; polymers such as PEEK; ceramics; carbon fiber; and other materials suitable for use in surgical applications. The various components disclosed herein may have varying degrees of rigidity or flexibility appropriate for their use. The size of the assemblies and / or components may also vary considerably depending on the intended use and the biomimetic structure of the surgical site. Furthermore, certain components may be formed from different materials than other components. One or more components or parts of an instrument may be formed from radiopaque materials to facilitate visualization under fluoroscopy and other imaging techniques, or from radiopaque materials such as carbon fiber and / or high-strength polymers to avoid interference with the visualization of other structures.

[0055] The devices and methods disclosed herein can be used in minimally invasive surgery and / or incisional surgery. Although the devices and methods disclosed herein are generally described in the context of surgery in human patients, it will be understood that the methods and devices disclosed herein can be used in any human or animal subject in any variety of surgical or non-surgical procedures.

[0056] While specific embodiments are described above, modifications may be made within the spirit and scope of the concepts described. For example, a receiving member having a "closed" configuration, as described with respect to the bone anchor assembly 400 in Figures 10-14, can be used with the elements of the bone anchor assembly 200 in Figures 3-9. A receiving member having an "open" configuration, as described with respect to the bone anchor assembly 200 in Figures 3-9, can be used with the elements of the bone anchor assembly 400 in Figures 10-14. Similarly, various embodiments of the resistance holding rings 204, 404 described herein can be used with the components of various embodiments of the bone anchor assemblies 200, 400 described herein and are included within the scope of this disclosure. Further features and advantages based on the embodiments described above are possible and are within the scope of this disclosure. Therefore, this disclosure is not limited to what is specifically shown and described. All publications and references cited herein are incorporated in their entirety by reference, except for any definitions, waivers of subject matter, or denials, and unless the incorporated references conflict with the express disclosures herein, in which case the language in these disclosures shall prevail.

[0057] Examples of the embodiments described above may include the following: 1. A bone anchor assembly, A receiving member having a proximal end and a distal end, wherein a central longitudinal axis extends between the proximal and distal ends, and the distal end of the receiving member has a longitudinal hole with an opening, A retaining ring positioned in a groove formed in a receiving member, having a base and a wall portion extending proximal to the base, wherein the base has a maximum outer diameter greater than the maximum outer diameter of the wall portion, The device comprises a shank having a head portion seated within the base of the retaining ring and a bone engagement portion extending distally from the receiving member, A bone anchor assembly in which the wall portion of the retaining ring is configured to resist the rotation of the shank head by applying a drag force.

[0058] 2. The assembly according to claim 1, wherein the retaining ring and shank are configured to be inserted proximal through the distal end of the receiving member.

[0059] 3. The assembly according to claim 1 or 2, wherein the groove is formed on the inner surface of the distal end of the receiving member.

[0060] 4. The assembly according to any one of claims 1 to 3, wherein the maximum outer diameter of the base of the retaining ring is greater than the diameter of the opening at the distal end of the receiving member.

[0061] 5. The assembly according to any one of claims 1 to 4, wherein the inner diameter of the distal portion of the base of the retaining ring is smaller than the maximum diameter of the head of the shank.

[0062] 6. The assembly according to any one of claims 1 to 5, wherein the inner diameter of the distal portion of the base of the retaining ring is smaller than the maximum outer thread diameter of the bone engagement portion of the shank.

[0063] 7. The assembly according to any one of claims 1 to 6, wherein the wall portion of the retaining ring is configured to contact the head of the shank at its maximum diameter.

[0064] 8. The assembly according to claim 7, wherein when the shank is seated within the base of the retaining ring, the proximal end of the wall of the retaining ring extends proximal beyond the maximum diameter of the head of the shank.

[0065] 9. The assembly according to any one of claims 1 to 8, wherein the wall portion of the retaining ring includes a first wall segment and a second wall segment circumferentially separated from the first wall segment.

[0066] 10. The assembly according to any one of claims 1 to 9, wherein the retaining ring includes a segment extending through the base and wall, configured to allow selective radial expansion and compression of the retaining ring.

[0067] 11. The assembly according to any one of claims 1 to 10, further comprising a saddle positioned within the hole proximal to the retaining ring and configured to apply a distal force to the shank head.

[0068] 12. A method for assembling a bone anchor assembly, The method involves radially compressing a retaining ring positioned around the shank, wherein the shank includes a head and a bone engagement portion, and the retaining ring includes a base and a wall portion extending proximal to the base, the wall portion having a maximum outer diameter smaller than the maximum outer diameter of the base. The compressed shank and retaining ring are passed proximal through the opening at the distal end of the receiving member, The retaining ring is advanced proximal within the receiving member such that at least a portion of its base aligns with the first annular recess of a groove formed within the receiving member. The retaining ring is expanded to hold at least a portion of its base within the first annular recess of the groove, A method comprising seating the head of a shank within the base of a retaining ring such that the maximum diameter of the head of the shank contacts the wall of the retaining ring and the bone engagement portion of the shank extends distally from the retaining ring.

[0069] 13. Positioning the receiving member at the desired position relative to the shank, The method according to claim 12, comprising holding a receiving member in a desired position by a resistive force applied to the head of the shank by the wall portion of the retaining ring.

[0070] 14. The method according to claim 13, wherein positioning the receiving member at a desired position includes moving the receiving member in multiple axes relative to the shank.

[0071] 15. The method according to claim 13 or 14, wherein the resistance force is applied by the retaining ring at the interface between the base and the wall of the retaining ring.

[0072] 16. The method according to claim 13 or 14, wherein the resistance is applied by the proximal end of the wall portion of the retaining ring.

[0073] 17. Implanting the shank into the bone, The method according to any one of claims 13 to 16, further comprising tightening a closing mechanism to lock a receiving member in a desired position relative to the shank.

[0074] 18. To advance the saddle proximal through the distal opening of the receiving member, The method according to any one of claims 12 to 17, further comprising biasing the shank distally by a distal force applied to the head of the shank by the saddle.

[0075] 19. The method according to any one of claims 12 to 18, further comprising compressing a retaining ring around the neck of the shank.

[0076] 20. The method according to any one of claims 12 to 19, wherein at least a portion of the base of the retaining ring is held in the first annular recess of the groove, and the distal surface of the retaining ring is flush with the distal surface of the receiving member.

[0077] [Implementation Method] (1) A bone anchor assembly, A receiving member having a proximal end and a distal end, wherein a central longitudinal axis extends between the proximal end and the distal end, and the distal end of the receiving member has a longitudinal hole with an opening, A retaining ring disposed in a groove formed in the receiving member, having a base and a wall portion extending proximal to the base, wherein the base has a maximum outer diameter greater than the maximum outer diameter of the wall portion, The shank comprises a head portion seated within the base of the retaining ring and a bone engagement portion extending distally from the receiving member, A bone anchor assembly wherein the wall portion of the retaining ring is configured to apply a resistive force to the head portion of the shank, thereby resisting its rotation. (2) The assembly according to Embodiment 1, wherein the retaining ring and the shank are configured to be inserted in the proximal direction through the distal end of the receiving member. (3) The assembly according to Embodiment 1, wherein the groove is formed on the inner surface of the distal end of the receiving member. (4) The assembly according to Embodiment 1, wherein the maximum outer diameter of the base of the retaining ring is greater than the diameter of the opening at the distal end of the receiving member. (5) The assembly according to Embodiment 1, wherein the inner diameter of the distal portion of the base of the retaining ring is smaller than the maximum diameter of the head of the shank.

[0078] (6) The assembly according to Embodiment 1, wherein the inner diameter of the distal portion of the base of the retaining ring is smaller than the maximum outer thread diameter of the bone engagement portion of the shank. (7) The assembly according to Embodiment 1, wherein the wall portion of the retaining ring is configured to contact the head of the shank at its maximum diameter. (8) The assembly according to Embodiment 7, wherein when the shank is seated within the base of the retaining ring, the proximal end of the wall of the retaining ring extends proximal to the maximum diameter of the head of the shank. (9) The assembly according to Embodiment 1, wherein the wall portion of the retaining ring includes a first wall segment and a second wall segment separated circumferentially from the first wall segment. (10) The assembly according to Embodiment 1, wherein the retaining ring includes a segment extending through the base and the wall, configured to allow selective radial expansion and compression of the retaining ring.

[0079] (11) The assembly according to Embodiment 1, further comprising a saddle positioned in the hole proximal to the retaining ring and configured to apply a distal force to the shank head. (12) A method for assembling a bone anchor assembly, The method involves radially compressing a retaining ring positioned around a shank, wherein the shank includes a head and a bone engagement portion, and the retaining ring includes a base and a wall portion extending proximal to the base, the wall portion having a maximum outer diameter smaller than the maximum outer diameter of the base. The shank and the retaining ring in the compressed state are to be passed proximal through the opening at the distal end of the receiving member, The retaining ring is advanced proximal within the receiving member such that at least a portion of the base aligns with the first annular recess of the groove formed within the receiving member. The retaining ring is expanded to hold at least a portion of the base within the first annular recess of the groove, A method comprising seating the head of the shank within the base of the retaining ring such that the maximum diameter of the head of the shank contacts the wall of the retaining ring and the bone engagement portion of the shank extends distally from the retaining ring. (13) Positioning the receiving member to a desired position relative to the shank, The method according to embodiment 12, further comprising holding the receiving member in the desired position by a resistive force applied to the head of the shank by the wall portion of the retaining ring. (14) The method according to embodiment 13, wherein positioning the receiving member at the desired position includes moving the receiving member in multiple axes relative to the shank. (15) The method according to embodiment 13, wherein the resistance force is applied by the retaining ring at the interface between the base and the wall of the retaining ring.

[0080] (16) The method according to embodiment 13, wherein the resistance is applied by the proximal end of the wall portion of the retaining ring. (17) embedding the shank into the bone, The method according to embodiment 13, further comprising tightening a closing mechanism to lock the receiving member in the desired position relative to the shank. (18) Moving the saddle forward in the proximal direction through the distal opening of the receiving member, The method according to Embodiment 12, further comprising biasing the shank distally by a distal force applied to the head of the shank by the saddle. (19) The method according to embodiment 12, further comprising compressing the retaining ring around the neck of the shank. (20) The method according to Embodiment 12, wherein at least a portion of the base of the retaining ring is held in the first annular recess of the groove, and the distal surface of the retaining ring is flush with the distal surface of the receiving member.

Claims

1. A bone anchor assembly, A receiving member having a proximal end and a distal end, wherein a central longitudinal axis extends between the proximal end and the distal end, and the distal end of the receiving member has a longitudinal hole with an opening, A retaining ring disposed in a groove formed in the receiving member, having a base and a wall portion extending proximal to the base, wherein the base has a maximum outer diameter greater than the maximum outer diameter of the wall portion, The shank comprises a head portion seated within the base of the retaining ring and a bone engagement portion extending distally from the receiving member, The wall portion of the retaining ring is configured to apply a drag force to the head portion of the shank and resist its rotation. The retaining ring includes a segment extending through the base and the wall, configured to allow selective radial expansion and compression of the retaining ring. The divided portion of the retaining ring has a size that allows a part of the shank to pass through laterally. The portion of the shank moves through the divided portion of the retaining ring in the lateral direction and into the lumen of the retaining ring, so that the retaining ring is positioned around the portion of the shank. A bone anchor assembly in which the retaining ring is positioned around a portion of the shank, and while the retaining ring is compressed in the radial direction, the retaining ring and the portion of the shank move proximal to be inserted into the longitudinal hole of the receiving member through the opening at the distal end of the receiving member, and then the retaining ring expands radially so that the portion of the retaining ring having the maximum outer diameter at its base seats in the groove of the receiving member.

2. The assembly according to claim 1, wherein the groove is formed on the inner surface of the distal end of the receiving member.

3. The assembly according to claim 1, wherein the maximum outer diameter of the base of the retaining ring is greater than the diameter of the opening at the distal end of the receiving member.

4. The assembly according to claim 1, wherein the inner diameter of the distal portion of the base of the retaining ring is smaller than the maximum diameter of the head portion of the shank.

5. The assembly according to claim 1, wherein the inner diameter of the distal portion of the base of the retaining ring is smaller than the maximum outer thread diameter of the bone engagement portion of the shank.

6. The assembly according to claim 1, wherein the wall portion of the retaining ring is configured to contact the head portion of the shank at its maximum diameter.

7. The assembly according to claim 6, wherein when the shank is seated within the base of the retaining ring, the proximal end of the wall of the retaining ring extends proximal to the maximum diameter of the head of the shank.

8. The assembly according to claim 1, wherein the wall portion of the retaining ring includes a first wall segment and a second wall segment separated circumferentially from the first wall segment.

9. The assembly according to claim 1, further comprising a saddle positioned in the hole proximal to the retaining ring and configured to apply a distal force to the head portion of the shank.

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