Bone Fixation Systems and Methods

Abstract

The bone shank may include a shank head and an extension extending from the shank head. The shank head may include an engagement surface facing away from the extension. The head assembly may be configured to secure the shank head to the rod. The head assembly may include an engagement surface shaped and positioned to engage the engagement surface of the shank head to limit pivotal movement of the shank relative to the engagement surface of the head assembly, but to allow some pivotal movement of the shank relative to the engagement surface of the head assembly. The engagement surface of the head assembly may be an engagement surface of a head clamp in an assembly head of the head assembly. The engagement surface of the head clamp may face distally toward the shank head when the clamp is positioned in the assembly head.

Description

[Technical Field] 【0001】 Field FIELD OF THE DISCLOSURE The present disclosure relates to bone fixation systems and methods. [Background technology] 【0002】 background Spinal fusion procedures utilizing pedicle screw and rod-type fixation assemblies can be used to treat spinal disorders such as degenerative disc disease, spondylolisthesis, spinal deformity, or other spinal disorders through minimally invasive or invasive spinal surgical techniques. For example, two or more bone anchor assemblies can be secured to the bony structure of a patient's vertebrae, with connecting rods secured between adjacent bone anchor assemblies to stabilize one or more facet joints of the patient. These connecting rods typically run longitudinally along the length of the patient's spine between adjacent bone anchor assemblies. However, connecting rods can be placed in various positions and / or configurations (including the use of multiple connecting rods and / or crossbars, if needed) in view of a patient's specific anatomy and / or specific spinal treatment. Summary of the Invention 【0003】 overview According to one example, a bone fixation system may include a shank configured to be fixed to a bone. The shank may include a shank head and an extension extending from the shank head. The shank head may include an engagement surface. The bone fixation system may also include a head assembly. The head assembly may include an assembly head and a head clamp. The assembly head may define a central bore extending therethrough in a proximal direction and a distal direction opposite the proximal direction. The assembly head may define a channel across the central bore. The assembly head may also include tabs extending proximally on either side of the channel and the central bore. The head clamp may be configured to be at least partially positioned within the central bore. The head clamp may be configured to receive the shank head and clamp onto the shank head such that the extension extends away from the head assembly to secure the shank head at least partially positioned within the assembly head. The head clamp may include an engagement surface shaped and arranged to engage the engagement surface of the shank head and limit pivotal movement of the shank relative to the head clamp to a movement pattern. At least a portion of the engagement surface of the head clamp may face distally toward the shank head. 【0004】 According to another example, the shank can be configured to be secured to bone. The shank can include a shank head and an extension extending from the shank head. The shank head can include an engagement surface facing away from the extension. The bone fixation system can also include a head assembly configured to secure the shank head to the rod. The head assembly can include an engagement surface shaped and positioned to engage the engagement surface of the shank head to limit pivotal movement of the shank relative to the engagement surface of the head assembly, but allow some pivotal movement of the shank relative to the engagement surface of the head assembly. The engagement surface of the head assembly can face the engagement surface of the shank head. 【0005】 According to yet another example, a bone fixation system may include a shank configured to be fixed to a bone. The shank may include a shank head and an extension extending from the shank head. The shank head may include an engagement surface facing away from the extension. The bone fixation system may also include a plurality of different head assemblies, each allowing a different pivotal movement pattern between the head assembly and the shank. A first head assembly of the head assemblies may include a first engagement surface shaped and positioned to engage the engagement surface of the shank head and limit pivotal movement of the shank to a first movement pattern relative to the first engagement surface of the first head assembly. The first engagement surface of the first head assembly may face the engagement surface of the shank head. 【0006】 According to yet another example, the method may include selecting a selected head clamp from a plurality of different available head clamps. The different available head clamps may be configured to produce different pivotal movement patterns between the head assembly (to which the head clamp is secured) and the shank (secured to the head assembly using the head clamp). The selected head clamp may be configured to produce the selected pivotal movement pattern. The method may also include securing the head assembly on a shank head of the shank in a motion-restricted configuration. The shank may be configured to be secured within bone. The head assembly may include a selected head clamp positioned at least partially within the assembly head in the motion-restricted configuration. The head assembly may be configured to secure the shank to the rod. Securing the head assembly may include receiving at least a portion of the shank head within the selected head clamp. The selected head clamp may also include an engagement surface shaped and positioned to engage an engagement surface of the shank head to restrict pivotal movement of the shank relative to the selected head clamp in the motion-restricted configuration to the selected pivotal movement pattern. The technique may further include pivoting the head assembly and the shank relative to one another through a selected pivotal movement pattern when the selected head clamp and the shank are in the motion-limited configuration, the pivoting may include pivoting at least a portion of the engagement surface of the shank head away from at least a portion of the engagement surface of the selected head clamp while bringing at least a portion of the engagement surface of the shank head and at least a portion of the engagement surface of the head clamp toward one another. 【0007】 This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Likewise, the present invention is not limited to the specific methods, tools, environments, disadvantages, or advantages discussed in the background, detailed description, or accompanying drawings. [Brief explanation of the drawings] 【0008】 BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 is a top perspective view of a bone fixation system (as used herein, the top is toward the proximal direction and the bottom is toward the distal direction, although terms such as top and bottom should not be considered absolute directions). 【0009】 [Figure 2] 2 is a top perspective view of a bone anchor assembly from the bone anchor system of FIG. 1 secured to a bone. 【0010】 [Figure 3] 3 is an exploded top perspective view of the bone anchor assembly of FIG. 2; 【0011】 [Figure 4] Figure 4 is a right side perspective view of the bone anchor assembly of Figure 2 in a locked configuration. The left side view is a mirror image of the right side view. 【0012】 [Figure 5] FIG. 5 is a cutaway cross-sectional view taken along line 5-5 of FIG. 【0013】 [Figure 6] 6 is a right side view of the bone anchor assembly of FIG. 2 in a split open configuration. The left side view is a mirror image of the right side view. 【0014】 [Figure 7] FIG. 7 is a cutaway cross-sectional view taken along line 7-7 of FIG. 【0015】 [Figure 8] 8 is a right side view of the bone anchor assembly of FIG. 2 in an open, loaded configuration. The left side view is a mirror image of the right side view. 【0016】 [Figure 9] FIG. 9 is a cutaway cross-sectional view taken along line 9-9 of FIG. 【0017】 [Figure 10] 10 is a right side view of the bone anchor assembly of FIG. 2 in a deployed closed configuration. The left side view is a mirror image of the right side view. 【0018】 [Figure 11] FIG. 11 is a cutaway cross-sectional view taken along line 11-11 of FIG. 【0019】 [Figure 12] 12 is a bottom perspective view of the assembly head of the bone anchor assembly of FIG. 2; 【0020】 [Figure 13] 13 is a top perspective view of a transverse uniaxial head clamp of the bone anchor assembly of FIG. 2; 【0021】 [Figure 14] 14 is a bottom perspective view of the head clamp of FIG. 13. FIG. 【0022】 [Figure 15] 15 is another top perspective view of the head clamp of FIG. 13. FIG. 【0023】 [Figure 16] Figure 16 is a front view of the head clamp of Figure 13. The rear view is a mirror image of the front view. 【0024】 [Figure 17] Figure 17 is a right side view of the head clamp of Figure 13. The left side view is a mirror image of the right side view. 【0025】 [Figure 18] FIG. 18 is a plan view of the head clamp of FIG. 【0026】 [Figure 19] 19 is a bottom view of the head clamp of FIG. 13. FIG. 【0027】 [Figure 20] 20 is a top perspective view of an in-line uniaxial head clamp that can be used in the bone anchor assembly in place of the transverse uniaxial head clamp of FIG. 13. FIG. 【0028】 [Figure 21] 21 is a bottom perspective view of the head clamp of FIG. 20. FIG. 【0029】 [Figure 22] 22 is a plan view of the head clamp of FIG. 20. FIG. 【0030】 [Figure 23] 23 is a bottom view of the head clamp of FIG. 20. FIG. 【0031】 [Figure 24] 24 is a top perspective view of a uniaxial head clamp that can be used in the bone anchor assembly in place of the transverse uniaxial head clamp of FIG. 13. FIG. 【0032】 [Figure 25] 25 is a bottom perspective view of the head clamp of FIG. 24. FIG. 【0033】 [Figure 26] 26 is a plan view of the head clamp of FIG. 24. FIG. 【0034】 [Figure 27] 27 is a bottom view of the head clamp of FIG. 24. FIG. 【0035】 [Figure 28] 28 is a top perspective view of a polyaxial head clamp that can be used in the bone anchor assembly in place of the transverse uniaxial head clamp of FIG. 13. FIG. 【0036】 [Figure 29] 29 is a bottom perspective view of the head clamp of FIG. 28. FIG. 【0037】 [Figure 30] 30 is a plan view of the head clamp of FIG. 【0038】 [Figure 31] 31 is a bottom view of the head clamp of FIG. 28. FIG. 【0039】 [Figure 32] FIG. 32 is a left side view of the bone anchor assembly of FIG. 2, with the shank pivoted relative to the head assembly rather than aligned with the head assembly as in the previous figures. 【0040】 [Figure 33] FIG. 33 is a cutaway cross-sectional view taken along line 33-33 of FIG. 【0041】 [Figure 34] FIG. 34 is a front view of another bone anchor assembly similar to the bone anchor assembly of FIG. 2 in a loaded closed configuration with the shank and head assembly aligned, but including the in-line uniaxial head clamp of FIGS. 20-23 instead of the transverse uniaxial head clamp of FIGS. 13-19. 【0042】 [Figure 35] FIG. 35 is a cutaway cross-sectional view taken along line 35-35 of FIG. 【0043】 [Figure 36] 36 is a front view of the bone anchor assembly of FIG. 34 in a deployed closed configuration with the shank and head assemblies pivoted relative to one another. 【0044】 [Figure 37] FIG. 37 is a cutaway cross-sectional view taken along line 37-37 of FIG. 【0045】 [Figure 38] FIG. 38 is similar to FIG. 34 but with an alternative in-line single axis head clamp. 【0046】 [Figure 39] FIG. 39 is a cutaway cross-sectional view taken along line 39-39 of FIG. 【0047】 [Figure 40] FIG. 40 is a flow chart illustrating the device assembly procedure. 【0048】 The description and drawings may refer to the same or similar features in different drawings by the same reference numbers. DETAILED DESCRIPTION OF THE INVENTION 【0049】 Detailed Description Example embodiments of the present disclosure can be understood by reference to the drawings. The components of the present disclosure, as generally described herein and illustrated in the drawings, can be arranged and configured in a wide variety of different configurations. Thus, the following more detailed description of example devices and methods, as represented in the drawings, is not intended to limit the scope of the present disclosure, as claimed in this application or any other application claiming priority to this application, but is merely representative of example embodiments of the present disclosure. 【0050】 Standard medical guidelines, planes of reference, and descriptive terminology are used herein. For example, anterior means toward the front of the body. Posterior means toward the back of the body. Superior means toward the head. Inferior means toward the feet. Medial means toward the midline of the body. Lateral means away from the midline of the body. Ipsilateral means on the same side of the body. Contralateral means on the opposite side of the body. The sagittal plane divides the body into right and left portions. The midsagittal plane divides the body into symmetrical right and left halves. The coronal plane divides the body into anterior and posterior portions. The transverse plane divides the body into superior and inferior portions. These descriptive terms may be applied to living or cadaveric specimens. As used herein, the terms "proximal," "proximally," "proximal," and similar terms generally refer to a direction along a component away from the tip of the shank (the end of the shank farthest from the shank head). As used herein, the terms "distal," "distal direction," "distally," and similar terms generally refer to a direction along a component toward the tip of the shank. For example, with respect to the head assembly component in the illustrated example, the distal direction generally extends from the set screw toward the shank head, parallel to the axis about which the set screw or other rotary fixation device rotates, e.g., to secure a rod to the head assembly; this distal direction is opposite the proximal direction. As another example, with respect to a threaded shank, the proximal direction extends from the tip of the shank toward the shank head along the shank's longitudinal axis (about which the shank can be rotated to screw into or unscrew from bone); the distal direction is opposite the proximal direction. Thus, the proximal direction for the shank may differ from the proximal direction of the assembly head when the shank is rotated relative to the assembly head. 【0051】 The terms "connected," "coupled to," and "in communication with" refer to any form of interaction between two or more things, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interaction. Two components can be functionally connected to one another even if they are not in direct contact with one another. The term "adjacent" refers to things that are in direct physical contact with one another, although they may not necessarily be bonded together. The term "fluid communication" means that two features are connected such that fluid in one feature can enter the other feature. 【0052】 I. Basic bone fixation system structure 1 , the bone fixation system 100 can secure different portions of the rod 110 to different bone regions (which can be regions of different bones or different regions of the same bone) to inhibit relative movement of these different bone regions. As an example, these different bone regions can be the pedicles of different vertebrae of the spinal column. For example, the bone fixation system 100 can include first and second bone anchor assemblies that can include different head assemblies to achieve different pivotal movement patterns of the shanks of the bone anchor assemblies relative to the assembly heads of the bone anchor assemblies. 【0053】 As one example, the translation pattern may be a uniaxial translation pattern, where the assembly is configured to inhibit substantial pivoting of the shank about an axis other than the shank's longitudinal axis, such as a bone screw that can be rotated about its longitudinal axis to drive into or out of bone, but is inhibited from substantially pivoting about other axes. As another example, the translation pattern may be a multiaxial translation pattern, where the assembly is configured to allow substantial pivoting of the shank about multiple axes other than the shank's longitudinal axis, but may allow rotation of the shank about its longitudinal axis and may limit the range of such motion, such as allowing plus or minus 30 degrees of pivotal movement about any axis perpendicular to the shank's longitudinal axis, but inhibiting pivotal movement beyond these limits. As another example, the movement pattern may be a uniaxial movement pattern, where the assembly is configured to allow rotation of the shank about its longitudinal axis and substantial pivoting of the shank about a single axis other than the shank's longitudinal axis, although it is possible to limit the range of such pivoting, such as allowing 30 degrees of pivoting about a single axis perpendicular to the shank's longitudinal axis, but preventing pivoting beyond these limits. For example, for a horizontal uniaxial pivoting movement pattern, this single axis may be parallel to the longitudinal axis of the rod, such that the assembly is configured to allow the shank to pivot substantially laterally in a plane perpendicular to the longitudinal axis of the rod. As another example, for an inline uniaxial pivoting movement pattern, this single axis may be perpendicular to the longitudinal axis of the rod, such that the assembly is configured to allow the shank to pivot substantially inline in a plane parallel to the longitudinal axis of the rod. Such a plane may or may not intersect the longitudinal axis of the rod. 【0054】 For example, the bone fixation system 100 of Figure 1 may include a first bone anchor assembly 130, which may include a shank 132 and a head assembly 134, which may limit pivotal movement of the shank 132 relative to the head assembly 134 to a first movement pattern, which may be a lateral uniaxial movement pattern, such as the shank 132 of Figure 1 being shown pivoted in a plane perpendicular to the longitudinal axis of the rod 110. The bone fixation system 100 of Figure 1 may also include a second bone anchor assembly 140, which may include a shank 142 and a head assembly 134, which may limit pivotal movement of the shank 142 relative to the head assembly 144 to a second movement pattern different from the first movement pattern. For example, the second movement pattern can be different from the first movement pattern (such as an in-line uniaxial movement pattern, a single-axis movement pattern, or a multi-axis movement pattern). Different head assemblies enabling different shank movement patterns can be selected by a surgeon during a surgical procedure, for example, depending on the needs arising from different patients and different surgical procedures. 【0055】 1-5, the first bone anchor assembly 130 of FIG. 1 will now be described in more detail. Other bone anchor assemblies may have the same features as the first bone anchor assembly 130, except that the clamps in those bone anchor assemblies may be configured to produce different pivotal movement patterns as described herein. 【0056】 As shown in FIG. 2, the shank 132 of the first bone anchor assembly 130 may be placed within or secured to the bone 150. The depiction of the bone 150 is not intended to represent the shape of any particular type of bone and is included for illustrative purposes. As noted above, the bone fixation system 100 may be used with different types of bone, such as vertebrae. Also, as shown in FIGS. 2-5, the shank 132 may be aligned with the head assembly 134 rather than pivoted at an angle relative to the head assembly 134 as illustrated with the first bone anchor assembly 130 in FIG. 1. 【0057】 The shank 132 can include a shank head 160, which can include a rounded clamping surface 162. The clamping surface 162 can form a partial sphere. The proximal end of the shank head 160 can form an engagement surface 164. The engagement surface 164 can be generally annular. The engagement surface 164 can face proximally. For example, the engagement surface 164 can be the inner edge of a surface that slopes distally as it extends outward from its inner edge. Alternatively, the engagement surface 164 can have some other shape, such as a flat surface extending in a plane perpendicular to the longitudinal axis of rotation of the shank 132. The shank head 160 can also define a tool-receiving aperture 166 extending distally into the shank head 160 from its proximal end. The engagement surface 164 extends around the periphery of the tool-receiving aperture 166. The shank 132 may also include an extension 170, which may extend distally away from the distal end of the shank head 160. For example, if the shank 132 is a bone screw, the extension 170 may be threaded. As shown, different portions of the extension may have different thread features. In this manner, the shank 132 may be configured to be screwed into or unscrewed from bone when rotated about its longitudinal axis. However, the shank extension may have different features depending on how the shank is configured to be secured to bone. 【0058】 Still referring to FIGS. 1-5 and further referring to FIGS. 6-12, the head assembly 144 may include an assembly head 180. The assembly head 180 may define a central bore 182 extending axially therethrough, which may be in a proximal and distal direction. The assembly head 180 may include a body 184 defining a distal cavity 186 that is a portion of the central bore 182. The body 184 may extend completely around the distal cavity 186 of the central bore 182. The inner surface of the body 184 may be tapered inward as it extends toward the distal end of the body 184. As a result, the inner diameter of the body 184 may decrease toward the distal end of the body 184. This tapered inner surface of the body 184 may be a clamp-engagement surface 188, as described further below. The inner surface of the body 184 may extend inward above the enlarged region of the cavity to form a shoulder. 【0059】 The assembly head 180 may also include a pair of tabs 192. The tabs 192 may be curved about a central axis of the assembly head 180 and may extend proximally from the body 184 on either side of a channel 193. The channel 193 may extend laterally within and intersect the central bore 182. The channel 193 may extend distally from the proximal end of the assembly head 180 and may be rounded at its distal base. The channel 193 may be sized to receive the rod 110 therein. The inner surfaces of the tabs 192 may face each other. These inner surfaces of the tabs 192 may define a distal aperture or groove 194 and a proximal aperture or groove 196, both of which extend circumferentially around the inner surface of the tabs 192. The inner surface of the tabs 192 may also define an internal thread 198 located proximally from the proximal groove 196. Additionally, the outer surface of the tabs 192 may define one or more apertures. For example, a hole 202 and an annular, circumferentially extending recess 204 may extend through the outer surface of each tab 192. A proximal shoulder 206 may be cut away to define the proximal edge of each recess 204, such that the shoulder extends distally outwardly from the center of the assembly head 180. 【0060】 The head assembly 144 may also include a set screw 220. The set screw 220 may include a distal portion having external threads 222 configured to threadably mate with the internal threads 198 of the assembly head 180. The set screw 220 may define a central tool-receiving aperture 224 that extends therethrough in a proximal-to-distal direction. The proximal portion of the set screw 220 may be a breakaway head 228. The breakaway head 228 may be configured to disengage from the distal portion of the set screw when a predetermined amount of torque is applied to the breakaway head 228 while tightening the set screw 220. 【0061】 12 , and with further reference to FIGS. 13-19 , the head assembly 144 may also include a head clamp 250. The clamp 250 may be a collar. The collar may include a main body 252. The main body 252 may be circular and may define a central axial bore 253 therein. The clamp 250 may include fingers 254 extending distally from the main body 252. The fingers 254 are separated by gaps 260 extending proximally into the clamp 250 between the fingers 254. The fingers 254 may be circumferentially spaced about the main body 252. As each finger 254 extends distally away from the main body 252, it may extend radially outward and then radially inward, such that each finger 254 may include a convex outer engagement surface 256 and a concave inner clamping surface 258. The concave inner clamping surfaces 258 of the fingers 254 and the inner portion of the main body 252 define a socket 262 configured to receive the shank head 160 with the fingers 254 wrapping around the shank head 160. The socket 262 may form a partial spherical shape. The convex outer engagement surfaces 256 of the fingers 254 may be configured to engage the clamp engagement surface 188 of the assembly head 180 at certain locations, as described below. 【0062】 The clamp 250 may also include flanges 270 extending proximally from the main body 252. The pair of flanges 270 may extend adjacent each of the tabs 192 of the assembly head 180 to define a channel 271 between the first pair of flanges 270 and the second pair of flanges 270. The channel 271 may be aligned with the channel 193 between the tabs 192 of the assembly head 180. Each flange 270 may also have a protrusion 272 extending radially outward from the proximal end. The protrusion 272 may extend into either a proximal groove 196 or a distal groove 194 of the assembly head 180, depending on whether the assembly head 180 and the clamp 250 are in an open or closed configuration relative to one another, as described below. 【0063】 Different clamps may have different engagement surfaces that may or may not engage with engagement surface 164 of shank head 160. In this example, clamp 250 is a lateral uniaxial clamp that restricts the pivotal movement of shank 142 to a lateral uniaxial movement pattern. To this end, clamp 250 may include a motion-restricting protrusion 274 that protrudes radially inward from main body 252 of clamp 250. Motion-restricting protrusion 274 may include a distally-facing shank-engaging surface 276. This shank-engaging surface 276 may reside on a distally-facing shoulder formed by motion-restricting protrusion 274. For example, shank-engaging surface 276 may be a distally-facing flat surface, such as an entire flat or non-flat surface, or a portion of a flat or non-flat surface, or may have some other shape, depending on the configuration of clamp 250 and shank 142 (see, e.g., Figures 38-39 below). As such, the engagement surfaces of the clamp 250 and the shank 142 may engage one another in point contact, line contact, or broader surface contact. The motion-restricting protrusion 274 may form a partial annulus extending inward from the portion of the main body 252 adjacent the pair of flanges 270. It may also abut one of the tabs 192 on the assembly head 180. The motion-restricting protrusion 274 may be shaped such that its shank-engaging surface 276 can engage the engagement surface 164 of the shank head 160 to restrict pivotal movement of the shank 142 relative to the clamp 250 and assembly head 180 to a lateral uniaxial movement pattern and prevent movement outside of such pattern. As described below, this movement pattern may not be produced by the clamp 250 in all positions. For example, this limited movement pattern may be produced in the closed-load position but not in the separated, open-load, or locked-load configurations. Such configurations are described below in the discussion of utilization of the bone fixation system. 【0064】 II. Different clamps for different pivoting patterns Different clamps can be used with other components of the bone fixing system 100 to create different movement patterns. These different movement patterns can be achieved simply by changing the clamp, without making any changes to other components of the bone fixing system 100. Examples of such different clamps are described below. As noted above, the lateral uniaxial clamp 250 shown in FIGS. 13-19 can limit movement to a lateral uniaxial movement. 【0065】 20-23, an in-line uniaxial clamp 310 can be identical in many respects to the lateral uniaxial clamp 250. For example, the in-line uniaxial clamp 310 can include a main body 252, fingers 254, a convex outer engagement surface 256, a concave inner clamping surface 258, a gap 260, and a socket 262. However, the motion-limiting protrusion 312 of the in-line uniaxial clamp with its engagement surface 314 can be located on the clamp side between two pairs of flanges 270 (and thus between two tabs 192 of the assembly head 180) rather than adjacent to one pair of flanges 270. This results in a movement pattern of the shank 142 relative to the in-line uniaxial clamp 310 and assembly head 180 that is an in-line uniaxial movement pattern rather than a lateral uniaxial movement pattern. Such a movement pattern may be produced by the engagement surface 314 of the in-line uniaxial clamp's motion-limiting protrusion 312 contacting the engagement surface 164 of the shank head 160 when pivotal movement attempts to exceed the movement allowed for the lateral uniaxial movement pattern. Similar to the lateral uniaxial movement pattern from clamp 250, the in-line uniaxial movement pattern from clamp 310 may only allow movement in one direction from the aligned configuration (opposite the position of the motion-limiting protrusion as shown in FIGS. 33 and 37, described below). However, pivotal movement in the opposite direction can be achieved by rotating the position of the uniaxial clamp 180 degrees about the primary axis of the clamp and assembly head 180 (by rotating the clamp relative to the assembly head or by rotating the clamp and assembly head together). 【0066】 24-27, as yet another example, the single-axis clamp 320 may be identical in many respects to the horizontal uniaxial clamp 250. For example, the single-axis clamp 320 may include a main body 252, fingers 254, a convex outer engagement surface 256, a concave inner clamping surface 258, a gap 260, and a socket 262. However, the single-axis clamp motion-limiting protrusion 322 having the engagement surface 324 may be a complete ring extending inward from the main body 252, rather than a partial ring as in the horizontal uniaxial clamp 250. This may result in a movement pattern of the shank 142 relative to the single-axis clamp 320 and assembly head 180 that is a uniaxial movement pattern rather than a horizontal uniaxial movement pattern. 【0067】 28-31, as yet another example, multi-axial clamp 330 may be identical in many respects to lateral uniaxial clamp 250. For example, multi-axial clamp 330 may include main body 252, fingers 254, convex outer engagement surface 256, concave inner clamping surface 258, gap 260, and socket 262. However, multi-axial clamp 330 may omit the motion-limiting protrusions and corresponding engagement surfaces. This may result in a movement pattern of shank 142 relative to in-line uniaxial clamp 310 and assembly head 180 that is a multi-axial movement pattern rather than a lateral uniaxial movement pattern. 【0068】 The motion-restricting protrusions may have shapes different from those shown in the figures. For example, such shapes may be other shapes that are entirely or partially circular. For example, the motion-restricting protrusions and corresponding engagement surfaces for single-axis movement may be shaped as arcs, crescents, or other shapes that engage with the shank head 160 to create a uniaxial movement pattern. Similarly, the motion-restricting protrusions and corresponding engagement surfaces for single-axis movement may be full disks or other shapes that engage with the shank head 160 to create a uniaxial movement pattern. Also, each motion-restricting protrusion and each corresponding engagement surface (as well as the engagement surfaces of the shank head) may be divided into multiple separate shapes with gaps between them. Such different shapes may cause pivotal movement that is not part of the generated allowed movement pattern to result in the engagement surface 164 of the shank head 160 contacting the shank engagement surface of the motion-restricting protrusion of the clamp, preventing such unauthorized pivotal movement. However, pivotal movement within the generated movement pattern can occur without that movement being prevented by contact between the engagement surface 164 of the shank head 160 and the shank engagement surface of the motion-limiting protrusion of the clamp. 【0069】 The components of the bone fixation system 100 described herein may be formed from materials that are sufficiently strong, rigid, and durable to be suitable for use in vivo. For example, the components may be formed from titanium alloys. However, other alternative materials, such as polymeric materials, composite materials, and / or other metals, may be used. Additionally, the dimensions of the components may be varied to produce desired properties, such as desired strength and flexibility characteristics. For example, the thickness of different regions of the component may be varied to provide a desired balance of strength and flexibility for different characteristics of the component. Manufacturing techniques for producing the components of the bone fixation system 100 may include standard methods for manufacturing and post-processing surgical implant components, such as molding, additive methods (such as 3D printing), and / or subtractive methods (such as milling, drilling, grinding, polishing, etc.). Additionally, each of the components of the assembly, including the shank 142, the assembly head 180, the clamps, including the clamp 250 and other clamps, and the set screw 220, may be monolithic parts. However, in alternative embodiments, one or more of these components may be comprised of multiple parts that are permanently or temporarily fixed. 【0070】 III. Use of bone fixation systems Use of the bone fixation system 100 will now be described. With reference to Figures 6-7, an example use of the bone fixation system will be described primarily with reference to the bone fixation system 100 including the transverse uniaxial clamp 250. However, as described herein, other clamps, such as the in-line uniaxial clamp 310, the monoaxial clamp 320, or the polyaxial clamp 330, may also be used in a similar manner with the bone fixation system 100, although such other clamps allow for different types of pivotal movement patterns as described above. 【0071】 6-7 show a separate-and-open configuration in which the components of the head assembly 144 are separated from the shank 142. In some applications, the shank may be secured to the bone 150 while separated from the shank 142. In other applications, the shank 142 may be secured to the bone 150 after being coupled to the components of the head assembly 144. As shown, the head assembly 144 may initially include an assembly head 180 and a clamp 250. 【0072】 In the split-open configuration, the clamp 250 can be positioned within the assembly head 180 in the open position. The protrusion 272 of the flange 270 of the clamp 250 can extend into the proximal groove 196 of the assembly head 180 to temporarily hold the clamp 250 in place relative to the assembly head 180. The clamp 250 can be placed in such position by distally inserting the clamp 250 into the central bore 182 of the assembly head 180. In this manner, the clamp 250 can pass between the tabs 192, at least partially through the body 184, and at least partially into the distal cavity 186 of the assembly head 180. Similarly, the fingers 254 of the clamp 250 can be bent inwardly toward each other to allow them to pass through the assembly head 180 and into the open position. 【0073】 With the clamp 250 and assembly head 180 in an open position relative to one another, the head assembly 134 can be positioned over the shank head 160 while at least partially receiving the shank head 160 within the socket 262 of the clamp 250. The open position of the clamp 250 relative to the assembly head 180 allows the fingers 254 to be positioned within the distal cavity 186 of the assembly head 180, which provides space for the fingers to splay outward from one another. As the shank head 160 begins to enter the socket 262, and as the shank head 160 moves proximally relative to the clamp 250, the shank head 160 pushes the fingers 254 of the clamp 250 to flex outward from one another, spreading the distal ends of the socket 262 of the clamp 250 and allowing the shank head 160 to enter the socket 262. This allows for the open-fit configuration shown in FIGS. 8-9 . In this manner, the head assembly 144 can be configured to be mounted over the shank head 160 without the entire extension passing through the assembly head. 【0074】 8-9, clamp 250 may not restrict the pivotal movement of shank 132 to the defined movement pattern for clamp 250. This is because shank head 160 may not be securely held within socket 262 because fingers 254 of clamp 250 flex outward to allow movement of shank head 160 out of the socket. However, as described below, clamp 250 can restrict pivotal movement of shank 142 in the closed position of the closed, loaded configuration of FIG. 【0075】 With the first bone anchor assembly 130 in the open loaded configuration of Figures 8-9, an instrument can be used to pull the assembly head 180 proximally and push the clamp 250 distally. For example, such an instrument can engage opposing holes 202 and / or opposing recesses 204 in the assembly head 180 to push the assembly head 180, and the instrument can engage the top of the flanges 270 and / or the proximally facing surface of the clamp 250 between the flanges 270 to push the clamp 250. For example, the instrument can operate similarly to a rod reduction tool. By pulling assembly head 180 proximally and pushing clamp 250 distally, assembly head 180 can be moved proximally relative to clamp 250 such that clamp 250 and shank head 160 slide distally within assembly head 180 until protrusion 272 of flange 270 of clamp 250 pops out of proximal groove 196 in the assembly head and into distal groove 194 of the assembly head. This movement places the bone anchor assembly in the loaded closed configuration shown in FIGS. 10-11. 【0076】 In the installed closed configuration, the head assembly 134 can retain the shank head 160 within the socket 262 of the clamp 250. Specifically, in that configuration, the convex outer engagement surface 256 of each finger 254 can engage the clamp engagement surface 188 of the assembly head 180 to prevent outward bending movement of the fingers 254. Furthermore, the concave inner clamping surface 258 of each finger 254 of the clamp 250 can extend around and engage the clamping surface 162 of the shank head 160 to prevent movement of the shank head 160 out of the socket 262. Thus, in the installed closed configuration, the clamp 250 can retain the shank head 160 within the assembly head 180. 【0077】 Additionally, in the loaded closed configuration, the clamp 250 can limit the pivotal movement of the shank 132 relative to the clamp 250 and relative to the assembly head 180 to a movement pattern defined by the clamp 250 . 【0078】 Thus, in the illustrated example, a lateral unidirectional movement pattern can be permitted. This can include pivoting the shank 132 and head assembly 144 relative to one another in a plane perpendicular to the direction of the channel 193. For example, this can include pivoting the shank 132 and head assembly 144 relative to one another from the aligned position shown in FIGS. 10-11 to the oblique position (which can be at a 30-degree angle) shown in FIGS. 32-33. As seen in at least FIGS. 11 and 33, the shank engagement surface 276 of the clamp 250 can define an engagement plane (a plane coplanar with the engagement surface 276 in the examples of FIGS. 11 and 33). A first portion (the portion on the left in FIG. 33) of the engagement surface 164 of the shank head 160 can pass through this plane to permit the pivoting shown in FIG. 33. However, a second portion of engagement surface 164 of shank head 160 (the portion on the right in FIG. 33 ) may be prevented from passing through that plane by engagement between engagement surface 164 of shank head 160 and shank engagement surface 276 of clamp 250. For multi-axial clamps (e.g., multi-axial clamp 330), such an engagement plane may not be defined due to the lack of a similar shank engagement surface on the clamp. Also, for uni-axial clamps (such as uni-axial clamp 320), the entire engagement surface 164 of shank head 160 may be prevented from passing through the engagement plane. As with the example of FIGS. 32-33 , in some instances, the engagement plane may be perpendicular to the axial direction of assembly head 180. However, in other instances, the engagement plane may face in other directions. Also, in some instances, the engagement surface may not be a flat surface but still prevent pivoting in one or more directions while allowing pivoting in one or more other directions. The engagement between the engagement surface 164 of the shank head 160 and the shank engagement surface 276 of the clamp 250 can be a direct abutment engagement. Alternatively, one or more structural features may be positioned between the engagement surface 164 of the shank head 160 and the shank engagement surface 276 of the clamp 250, such that the engagement would be an indirect engagement through the one or more structural features. 【0079】 Similarly, the in-line uniaxial clamp 310 of FIGS. 20-23 in the installed closed configuration can allow for an in-line unidirectional movement pattern. This can include pivoting the shank 132 and head assembly 144 relative to one another in a plane parallel to the direction of the channel 193. For example, this can include pivoting the shank 132 and head assembly 144 relative to one another from the aligned position shown in FIGS. 34-35 to the oblique position shown in FIGS. 36-37. The oblique position can be a 30-degree pivot angle. As shown in these figures, in some embodiments, the shank head 160 can define an inclined surface 350 that is neither perpendicular nor parallel to the axis of rotation of the shank 132 and at least partially defines the engagement surface 164, such that the engagement surface 164 can be an inner edge of the inclined surface 350. The slope of the ramp 350 may help prevent the shank head 160 from interfering with the rod 110 when the rod is positioned within the channel 193 between the tab 192 and the flange 270. In addition to or instead of such a ramp 350, the shank head may include an engagement surface perpendicular to the axis of rotation of the shank 142 to provide sufficient distance between the shank head 160 and the rod 110 as the shank head 160 rotates, and / or the clamp 250 and assembly head 180 may be configured to increase the proximal-distal height between the shank head 160 in the socket 262 of the clamp 250 and the rod 110 in the channel 193. This may be done by increasing the height of the body of the clamp 250 and the assembly head 180. Such an increase in distance may increase the pivot angle of the head assembly 144 relative to the shank 132 without the shank head 160 interfering with the rod 110. 【0080】 38-39, alternatively, an in-line uniaxial clamp 360 may include a motion-limiting protrusion 362 defining an inclined clamp-engagement surface 364 that mates with the inclined surface 350 of the shank head 160. This allows for greater surface engagement between the clamp-engagement surface 354 of the clamp 360 and the engagement surface 164 of the shank head 160 (i.e., the engagement surface 164 may be a larger portion of the inclined surface 350 instead of the inner edge of the inclined surface 350). Thus, the inclined surface 350 may have a frustoconical side profile, and the clamp-engagement surface 364 may be a portion of the matching frustoconical side profile. Also, alternatively, the clamp-engagement surface 354 may have an even larger mating surface than that shown in FIG. 39. In this case, the clamp-engagement surface may extend further outward along the inclined surface 350 of the shank head 160, perhaps extending to the outer edge of the inclined surface 350. As a result, an even larger area of ​​the inclined surface 350 may form the engagement surface 164. Aside from the difference in the motion-limiting protrusion 362 of clamp 360, the structure and operation of the features of the example shown in Figures 38-39 can be identical to those of the example shown in Figures 34-37. The shank-engaging surface of one or more of the other uniaxial clamps and / or single-axis clamps described herein may also be sloped to match the sloped clamp-engaging surface 364 of the shank head in a similar manner (e.g., the sloped surface of the other uniaxial clamps may be a similar portion of a frusto-conical side profile, or the sloped surface of the single-axis clamp may be a full frusto-conical side profile (or a portion thereof that can possibly still prevent pivoting of the shank relative to the clamp)). 【0081】 The lateral uniaxial clamp 250 or the in-line uniaxial clamp 310 can rotate the clamp 180 degrees about the proximal-distal axis to reverse the direction of rotation allowed for the movement pattern restricted by the clamp to pivot between the shank 132 and the head assembly 144. For example, if the lateral uniaxial clamp 250 allows 30 degrees of pivotal movement in a first direction from an oblique position, rotating the clamp 180 degrees can create a permitted movement pattern with 30 degrees of pivotal movement in a second direction opposite the first direction. Similarly, if the in-line uniaxial clamp 310 allows 30 degrees of pivotal movement in a first direction from an oblique position, rotating the clamp 180 degrees can create a permitted movement pattern with 30 degrees of pivotal movement in a second direction opposite the first direction. 【0082】 28-31 in the installed closed configuration may allow for multi-axis movement patterns, which may include pivoting the shank 132 and head assembly 144 relative to one another about multiple axes and in multiple planes, including planes parallel to the direction of the channel 193, planes perpendicular to the direction of the channel 193, and other planes at different angles relative to the direction of the channel 193. 【0083】 24-27 in the closed mounted configuration may allow for a single axis movement pattern, which may include preventing the shank 132 and head assembly 144 from pivoting relative to one another. 【0084】 In addition to the pivotal movement described above, the lateral uniaxial clamp 250, the in-line uniaxial clamp 310, the single-axis clamp 320, or the multi-axial clamp 330 allow the shank 132 to rotate about its longitudinal axis relative to the head assembly 144 in the closed mounted configuration, for example, to screw into or unscrew from the bone 150. 【0085】 Aside from limiting the pivotal movement of the shank 132 relative to the head assembly 144 with a motion limiting protrusion on the clamp, pivotal movement may also be limited by other engagements, such as the engagement of an extension 170 on the shank 142 with the distal end of the clamp and / or assembly head 180 (see FIG. 33). This may include having a feature engaging the shank 142 that prevents the shank head 160 from pivoting so much that it interferes with the rod 110 when the rod is seated in a channel 193 between a tab 192 on the assembly head 180 and a flange 270 on the clamp. 【0086】 With the shank 132 secured to the bone 150 and the first bone anchor assembly 130 in the loaded closed configuration with the head assembly 134 pivoted to a desired angle relative to the shank 132 (which may be aligned so that the angle is zero), the rod 110 can be positioned within the channel 193 between the tabs 192 of the assembly head 180 and the channel 271 between the pair of flanges 270 of the clamp 250. The rod 110 can be moved distally relative to the head assembly 134 until the rod 110 rests at the base of the channel 271 between the pair of flanges 270 of the clamp 250 (resting at its base on either side of a bore extending axially through the main body 252 of the clamp 250 in a proximal-distal direction). This may include performing a rod reduction using a rod reduction instrument. 【0087】 With the rod 110 positioned within the channel 193, the set screw 220 can thread into the internal threads 198 of the tab 192 of the assembly head 180, as shown in the locked position and configuration in FIG. 5 . For example, the set screw 220 can be tightened using an instrument that engages a central tool-receiving aperture in the disengagement head 228. The set screw 220 can be tightened until the disengagement head 228 disengages from the set screw 220. As the set screw 220 is tightened, it can push the rod 110 distally relative to the assembly head 180, forcing the rod 110 against the clamp 250 at the base of the channel 271 in the clamp 250 at both ends of the channel 271, thereby forcing the clamp 250 distally relative to the assembly head 180. This pushing of the clamp 250 distally relative to the assembly head 180 can force the convex outer engagement surfaces of the fingers 254 of the clamp 250 against the clamp engagement surface 188 of the assembly head 180. This compression between the clamp 250 and the assembly head 180 can urge the fingers 254 inward toward one another, thereby forcing the concave inner clamping surfaces 258 of the fingers 254 of the clamp 250 against the clamping surface 162 of the shank head 160. Increasing the clamping force on the shank head 160 in this manner can lock the shank head 160 in place relative to the head assembly 144. This may include preventing pivotal movement of the shank 142 relative to the head assembly 144. Surface texture on the clamping surface 162 of the shank head 160 and / or the concave inner clamping surface 258 of the clamp 250 can enhance this prevention of movement. For example, such texture can include surface grooves, ridges, or other small protrusions and / or apertures. 【0088】 Thus, referring to FIG. 40 , the techniques described herein may include one or more apparatus assembly techniques in which a head clamp may be selected (4010) from a plurality of different available head clamps. The clamp selection may include simply selecting the clamp itself or selecting an assembly including the selected clamp from a plurality of different head assemblies. The different available head clamps may be configured to produce different pivotal movement patterns between the head assembly to which the head clamp is secured and the shank secured to the head assembly using the head clamp. The selected head clamp may be configured to produce the selected pivotal movement pattern. The plurality of different head assemblies may include different clamps with the same assembly head design but different designs. 【0089】 The technique may include securing 4020 a head assembly on a shank head of the shank in the motion-restricted configuration. The shank may be configured to be secured within bone. The head assembly may include a selected head clamp at least partially positioned within the assembly head in the motion-restricted configuration. The head assembly may be configured to secure the shank to the rod. Securing 4020 the head assembly may include receiving at least a portion of the shank head within the selected head clamp. The selected head clamp may include an engagement surface shaped and positioned to engage an engagement surface of the shank head to limit pivotal movement of the shank relative to the head clamp in the motion-restricted configuration to a selected pivotal movement pattern. 【0090】 The securing 4020 may include mounting the head assembly on the shank head in an open position in which the shank head can be moved in and out of a selected head clamp 4020, and moving the head assembly to a closed position in which the head assembly prevents the shank head from moving out of a selected head clamp 4040. The motion-limiting configuration may include the head assembly in the closed position. 【0091】 The technique may further include pivoting 4050 the head assembly and shank relative to one another through a selected pivotal movement pattern when the selected head clamp and shank are in the motion-limited configuration, the pivoting 4050 may include pivoting at least a portion of the engagement surface of the shank head away from at least a portion of the engagement surface of the selected head clamp while bringing at least a portion of the engagement surface of the shank head and at least a portion of the engagement surface of the head clamp toward one another. 【0092】 The method may further include locking the shank relative to the head assembly in a locked configuration that prevents the shank and head assembly from pivoting relative to one another. This locking may include positioning a rod within the head assembly and securing the rod within the head assembly with a set screw. The set screw may apply a locking force to lock the shank in a pivoted position relative to the head assembly. As described herein, the set screw may then become part of the head assembly. Additionally, the shank, assembly head, clamp, and set screw may all be part of a bone anchor assembly. One or more bone anchor assemblies may be secured to one or more rods to form a bone fixation system. If there are multiple bone anchor assemblies, all or part of the assembly method described above may be repeated for each bone anchor assembly in the bone fixation system. 【0093】 This assembly procedure can also be part of a surgical procedure that can include securing the shank to the bone either before or after attachment to the shank head. The pivoting 4050 can be performed while the shank is secured to the bone. 【0094】 IV. Aspects of bone fixation systems According to one aspect, a bone fixation system may include a shank configured to be fixed to a bone. The shank may include a shank head and an extension extending from the shank head. The shank head may include an engagement surface. The bone fixation system may also include a head assembly. The head assembly may include an assembly head and a head clamp. The assembly head may define a central bore extending therethrough in a proximal direction and a distal direction opposite the proximal direction. The assembly head may define a channel traversing the central bore. The assembly head may also include tabs extending proximally on either side of the channel and the central bore. The head clamp may be configured to be at least partially positioned within the central bore. The head clamp may be configured to receive the shank head and clamp onto the shank head such that the extension extends away from the head assembly to secure the shank head at least partially positioned within the assembly head. The head clamp may include an engagement surface shaped and arranged to engage the engagement surface of the shank head and limit pivotal movement of the shank relative to the head clamp to a movement pattern. At least a portion of the engagement surface of the head clamp may face distally toward the shank head. 【0095】 The engagement surface of the shank head may face away from the extension, and the head clamp may be configured to be secured to the assembly head while the head clamp is at least partially located within the central bore. The engagement surface of the head clamp may be shaped and positioned to engage the engagement surface of the shank head to limit pivotal movement of the shank relative to the assembly head. 【0096】 The head assembly can be configured to allow pivotal movement of the shank relative to the head clamp in a movement pattern. By way of example, the movement pattern can be a uniaxial movement pattern. 【0097】 The head assembly may be configured so that all of the extensions are mounted onto the shank head without being threaded into the assembly head. 【0098】 The head clamp can be a collar having a central hole therethrough. The engagement surface of the head clamp can form a shape that is at least a portion of a circle, such as at least a portion of a ring. The engagement surface can be on a shoulder that faces distally when the head clamp is at least partially positioned within the assembly head. 【0099】 The assembly head can be configured to move proximally relative to the head clamp to a closed position to secure the shank head relative to the head clamp and assembly head while still allowing a movement pattern of the shank relative to the head clamp and assembly head. The channel can be configured to receive a rod. The head assembly can be configured to secure the rod to the shank. Securement of the rod to the shank can apply pressure to lock the shank relative to the head clamp and assembly head. 【0100】 The head clamp may be a first head clamp, the engagement surface of the first head clamp may be a first engagement surface, and the movement pattern may be a first movement pattern. The bone fixation system may further include a second head clamp configured to be positioned at least partially within the central bore in place of the first head clamp. The second head clamp may be configured to receive the shank head and clamp onto the shank head, with the extension extending away from the head assembly to secure the shank head at least partially within the assembly head. The second head clamp may be shaped differently from the first head clamp to limit movement of the shank to a second movement pattern different from the first movement pattern. As an example, the first movement pattern may be a uniaxial movement pattern. The second movement pattern may be a uniaxial movement pattern, a multiaxial movement pattern, or a single-axis movement pattern different from the first movement pattern. 【0101】 In yet another aspect, the shank can be configured to be secured to bone. The shank can include a shank head and an extension extending from the shank head. The shank head can include an engagement surface facing away from the extension. The bone fixation system can also include a head assembly configured to secure the shank head to the rod. The head assembly can include an engagement surface shaped and positioned to engage the engagement surface of the shank head to limit pivotal movement of the shank relative to the engagement surface of the head assembly, but allow some pivotal movement of the shank relative to the engagement surface of the head assembly. The engagement surface of the head assembly can face the engagement surface of the shank head. 【0102】 The engagement surface of the shank head may be at an end of the shank head opposite the extension. The engagement surface of the head assembly may form a shape that is at least a portion of a circle, such as at least a portion of a ring. 【0103】 In yet another aspect, a bone fixation system can include a shank configured to be fixed to a bone. The shank can include a shank head and an extension extending from the shank head. The shank head can include an engagement surface facing away from the extension. The bone fixation system can also include a plurality of different head assemblies, each allowing a different pivotal movement pattern between the head assembly and the shank. A first one of the head assemblies can include a first engagement surface shaped and positioned to engage the engagement surface of the shank head and limit pivotal movement of the shank to a first movement pattern relative to the first engagement surface of the first head assembly. 【0104】 As an example, the first movement pattern can be a uniaxial movement pattern. 【0105】 A second head assembly of the head assembly may include a second engagement surface shaped and positioned to engage the engagement surface of the shank head and restrict pivotal movement of the shank relative to the second engagement surface of the second head assembly to a second movement pattern, which is either a single-axis movement pattern or a multi-axis movement pattern. 【0106】 The first head assembly may include an assembly head defining a central bore therethrough and a channel traversing the central bore. The assembly head may include a tab extending proximally opposite the channel. The head assembly may also include a head clamp configured to be positioned at least partially within the central bore. The head clamp may be configured to receive the shank head and clamp onto the shank head such that the extension extends away from the head assembly to secure the shank head at least partially within the assembly head. The head clamp may include a first engagement surface. 【0107】 The subject matter defined in the appended claims is not necessarily limited to the advantages described herein. Particular embodiments of the present invention may provide all, some, or none of the advantages described herein. While operations for various techniques are described herein in a particular sequential order for purposes of illustration, it should be understood that this method of description encompasses rearranging the order of operations unless a specific order is required. For example, operations described sequentially may, in some cases, be rearranged or performed simultaneously. Also, features may be omitted, and different features may be combined in any manner not negated by the features themselves or the language describing them in the description. 【0108】 While particular examples have been described above, it will be understood by those skilled in the art that various changes can be made in form and detail without departing from the spirit and scope of the invention.

Claims

[Claim 1] a shank configured to be secured to bone, the shank having a shank head with an engagement surface and an extension extending from the shank head; A head assembly, an assembly head defining a central bore extending therethrough in a proximal direction and in a distal direction opposite the proximal direction, the assembly head defining a channel across the central bore and having tabs extending in the proximal direction on either side of the channel and the central bore; a head clamp configured to be positioned at least partially within the central bore, the head clamp configured to receive the shank head and clamp onto the shank head so that the extension extends away from the head assembly to secure the shank head at least partially within the head assembly, the head clamp having an engagement surface shaped and positioned to engage the engagement surface of the shank head to restrict pivotal movement of the shank relative to the head clamp to a movement pattern, at least a portion of the engagement surface of the head clamp facing in the distal direction toward the shank head; a head assembly including A bone fixation system comprising: [Claim 2] The bone fixation system of claim 1 , wherein the engagement surface of the shank head faces away from the extension. [Claim 3] 2. The bone fixation system of claim 1, wherein the head clamp is configured to be secured to the assembly head while the head clamp is at least partially positioned within the central bore, and the engagement surface of the head clamp is shaped and positioned to engage the engagement surface of the shank head to limit pivotal movement of the shank relative to the assembly head. [Claim 4] The bone fixing system of claim 1 , wherein the head assembly is configured to allow pivotal movement of the shank relative to the head clamp in the movement pattern. [Claim 5] The bone fixing system of claim 1 , wherein the movement pattern is a uniaxial movement pattern. [Claim 6] The bone fixation system of claim 1 , wherein the head assembly is configured to be mounted onto the shank head without all of the extensions being threaded into the assembly head. [Claim 7] The bone fixing system of claim 1 , wherein the head clamp is a collar having a central hole therethrough. [Claim 8] The bone fixing system of claim 7 , wherein the engagement surface of the head clamp forms a shape that is at least a portion of a circle. [Claim 9] The bone fixation system of claim 7 , wherein the engagement surface is on the distally facing shoulder when the head clamp is at least partially located within the assembly head. [Claim 10] 2. The bone fixing system of claim 1, wherein the assembly head is configured to move proximally relative to the head clamp to a closed position to secure the shank head relative to the head clamp and the assembly head while still allowing the movement pattern of the shank relative to the head clamp and the assembly head. [Claim 11] 2. The bone fixing system of claim 1, wherein the channel is configured to receive a rod, and the head assembly is configured to secure the rod to the shank, and wherein securing the rod to the shank applies pressure to lock the shank against the head clamp and the assembly head. [Claim 12] the head clamp is a first head clamp, the engagement surface of the first head clamp is a first engagement surface, the movement pattern is a first movement pattern, and the bone fixation system comprises: a second head clamp configured to be positioned at least partially within the central bore in place of the first head clamp, the second head clamp configured to receive the shank head and clamp onto the shank head so that the extension extends away from the head assembly and secures the shank head at least partially within the head assembly, the second head clamp being shaped differently from the first head clamp to restrict movement of the shank to a second movement pattern different from the first movement pattern; Further provided with The bone fixing system of claim 1 . [Claim 13] 13. The bone fixing system of claim 12, wherein the first movement pattern is a uniaxial movement pattern, and the second movement pattern is one of a uniaxial movement pattern, a multiaxial movement pattern, or a single-axis movement pattern different from the first movement pattern. [Claim 14] a shank configured to be secured to bone, the shank having a shank head and an extension extending from the shank head, the shank head having an engagement surface facing away from the extension; a head assembly configured to secure the shank head to a rod, the head assembly having an engagement surface shaped and positioned to engage the engagement surface of the shank head to limit pivotal movement of the shank relative to the engagement surface of the head assembly, but to allow some pivotal movement of the shank relative to the engagement surface of the head assembly, the engagement surface of the head assembly facing the engagement surface of the shank head; A bone fixation system comprising: [Claim 15] The bone fixation system of claim 14 , wherein the engagement surface of the shank head is at an end of the shank head opposite the extension. [Claim 16] The bone fixing system of claim 14 , wherein the engagement surface of the head assembly forms a shape that is at least a portion of a circle. [Claim 17] selecting a selected head clamp from a plurality of different available head clamps, the different available head clamps configured to produce different pivotal movement patterns between a head assembly to which the head clamp is secured and a shank secured to the head assembly using the head clamp, the selected head clamp configured to produce a selected pivotal movement pattern; and securing a head assembly in a motion-restricted configuration on a shank head of a shank, the shank configured to be secured within bone, the head assembly including the selected head clamp positioned at least partially within the assembly head in the motion-restricted configuration, the head assembly configured to secure the shank to a rod, securing the head assembly including receiving at least a portion of the shank head within the selected head clamp, the selected head clamp including an engagement surface shaped and positioned to engage the engagement surface of the shank head to restrict pivotal movement of the shank relative to the selected head clamp in the motion-restricted configuration to the selected pivotal movement pattern; pivoting the head assembly and the shank relative to one another within the selected pivotal movement pattern when the selected head clamp and the shank are in the motion-restricted configuration, the pivoting including pivoting at least a portion of the engagement surface of the shank head away from at least a portion of the engagement surface of the selected head clamp while causing at least a portion of the engagement surface of the shank head and at least a portion of the engagement surface of the head clamp to face one another. method. [Claim 18] 18. The method of claim 17, further comprising locking the shank relative to the head assembly in a locked configuration that prevents the shank and the head assembly from pivoting relative to one another. [Claim 19] 18. The method of claim 17, wherein the fixing includes mounting the head assembly on the shank head in an open position in which the shank head can be moved in and out of the selected head clamp, and moving the head assembly to a closed position in which the head assembly prevents the shank head from moving out of the selected head clamp, and the motion-limiting configuration includes the head assembly in the closed position. [Claim 20] 18. The method of claim 17, further comprising anchoring the shank to a bone, and the pivoting occurs while the shank is anchored to the bone.

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