Patent Description:
During a surgical procedure, a patient is often positioned on an operating table or in a chair. Whether due to normal bodily functions (including voluntary and involuntary processes and/or reactions) or external stimuli such as surgical intervention, one or more anatomical features of the patient may move relative to the operating table or chair, relative to another external reference, and/or relative to another anatomical feature.

Surgical procedures may involve the use any number of surgical tools, including tools configured for cutting, grinding, roughing, cleaning, and otherwise interacting with soft and/or hard tissue, as well as tools configured for use with implant insertion. Such tools may be, for example, held and manipulated by a surgeon, held by a passive mechanical fixture or a robotic arm while being manipulated by a surgeon, held and manipulated by a robotic arm controlled by a surgeon, or held and manipulated by a robotic arm under autonomous control. <CIT> discloses a surgery table apparatus comprising a first support member, a second support member hingedly attached to each other to form a frame held by first and second connectors, and first and second piers which each comprise a base, a column and a positioning mechanism linked to the columns and the first and second connectors. Each positioning mechanism comprises a first arm and a second arm each having a proximal and a distal portion, wherein the first arm proximal portion is axially rotatable relative to the first column and the second arm proximal portion is axially rotatable relative to the distal portion of the first arm. Further, the surgery table apparatus comprises a rotational gear mechanism, motor drive and a motor for lateral tilt of the frame. <CIT> discloses a spinal stabilization implant for attachment to a portion of a spine.

The invention provide a fixation system according to claim <NUM>. Further embodiments of the invention are described in the dependent claims.

At least one of the first joint and the second joint may comprise a ball and socket. The central portion may be arranged substantially parallel to the axis. The central portion may be curved. The first end may comprise a bridge adaptor. The bridge adaptor may comprise a locking screw. The bridge member maintains a relative position of the first end to the second end independent of a rotational position of the bridge member relative to the first end and the second end. The bridge member may comprise a radiolucent material. The radiolucent material may be polyetheretherketone. The bridge member may comprise an end portion substantially perpendicular to the central portion.

In one or more examples, one or more steps of the described methods, processes, and techniques may be implemented in hardware, software, firmware, or any combination thereof.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors (e.g., Intel Core i3, i5, i7, or i9 processors; Intel Celeron processors; Intel Xeon processors; Intel Pentium processors; AMD Ryzen processors; AMD Athlon processors; AMD Phenom processors; Apple A10 or 10X Fusion processors; Apple A11, A12, A12X, A12Z, or A13 Bionic processors; or any other general purpose microprocessors), application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry.

Also, unless explicitly stated otherwise, terms such as "about" and "approximately" when used in connection with a stated value mean within ten percent of the stated value.

Embodiments of the present disclosure may be useful for any surgical procedure. During spine surgery, to take just one example, segmental motion of vertebrae may reduce guidance accuracy when using guided stereotactic systems such as robotics or navigation. Bone-mounted platforms or other anchors connected to the spinal anatomy and to the reference system may be used for restraining such relative motion. Bone-mounted platforms or other anchors may include spinous process clamps or pins, PSIS pins and bridge-type instruments. The reference system may include one or more navigation references and/or table mounted robotic systems.

During robotic and/or navigated spinal surgeries, desired tool trajectories may collide with a bone-mounted platform and thus prevent or eliminate the introduction of instruments or implants to the spine anatomy. Additionally, a bone-mounted platform may block a surgeon's line of sight to the anatomy, or the navigation system's line of sight to a navigation reference.

A rotatable fixation bridge as described herein is designed to maintain bridge end positions while allowing rotation of the middle portion of the bridge, so that collisions of the bridge with desired tool trajectories, and/or line of sight issues, may be reduced or avoided altogether. Rotation of the middle portion of the bridge maintains the position of the anatomical feature relative to the reference to which it is connected.

As described more fully below, a rotatable fixation bridge according to at least some embodiments of the present disclosure may be rigid, may include two concentric rotational hinges, may be made of a radiolucent material (e.g., polyetheretherketone, or PEEK) or thermoplastic resins with carbon-fiber reinforcement, may be designed for cleaning and sterilization so as to allow re-use, and may comprise one or more portions of one or more ball and socket joints to facilitate adjustability thereof.

With reference first to <FIG>, a fixation system <NUM> according to at least one embodiment of the present disclosure comprises a rotatable fixation bridge <NUM>, a reference <NUM>, and an anchor <NUM>. The system <NUM> may be used to secure an anatomical feature of a patient to the reference <NUM>, so as to beneficially maintain or substantially maintain a relative position of the anatomical feature of the patient and the reference <NUM> during a surgical procedure.

The anchor <NUM>-which may be any known bone-mounted platform or anchor, including, for example, a clamp (e.g., a spinous process clamp), a screw (e.g., a Schanz screw), a pin (e.g., a spinous process pin, a PSIS pin), and/or a bridge-type instrument-may be secured to one or more vertebra of a spine or to any other anatomical element suitable for receiving the anchor <NUM>. The anchor <NUM> may securely grip one or more outside surfaces of the anatomical feature, and/or may extend into and/or through the anatomical feature. The anchor <NUM> may, in some embodiments, be threaded into the anatomical feature. The anchor <NUM> provides a rigid connection between the rotatable fixation bridge <NUM> and the anatomical feature.

The reference <NUM> may be, for example, a surgical robot or a component thereof. In some embodiments, the reference <NUM> is a base of a surgical robot, which may comprise one or more robotic arms extending from the base and usable in connection with a surgical procedure on the patient. In such embodiments, the surgical robot may operate autonomously, or based (whether in whole or in part) on user input from a surgeon or other user. Successful operation of the surgical robot may depend on the surgical robot maintaining a known, fixed (or at least substantially fixed) position relative to the patient, or to a target anatomical feature of the patient, or to a surgical site within the patient. The target anatomical feature may or may not be the anatomical feature to which the anchor <NUM> is attached.

In some embodiments, the reference <NUM> may be a structure supporting the patient, such as an operating table or chair, a platform, or any other structure. The reference <NUM> may alternatively be a ceiling, wall, floor, or any other portion of a building. In such embodiments, fixation of the patient (or of one or more anatomical features of the patient) may be useful or desired to facilitate proper functioning and/or use of a surgical navigation system, or to maintain a registration between or among two or more of a coordinate system of a surgical navigation system, a separate coordinate system of a patient, and/or another separate coordinate system of a surgical robot. Fixation of the patient (or of one or more anatomical features of the patient) may additionally or alternatively be useful or desired to reduce a risk that the patient will move, whether voluntarily or involuntarily, during a surgical procedure in which significant accuracy and/or precision is desired, regardless of whether the surgical procedure is being carried out by a surgeon, a surgical robot, or a combination thereof.

In some embodiments, the reference <NUM> may be an anatomical structure of the patient. For example, the pelvis, sacrum, or a lower vertebra of a patient may serve as a reference for a higher vertebra. Thus, in these embodiments, the rotatable fixation bridge <NUM> provides stability between different anatomical structures while increasing access to the anatomical features around the rotatable fixation bridge <NUM>.

The rotatable fixation bridge <NUM> comprises a bridge adaptor <NUM>, a locking screw <NUM>, a first extension <NUM>, a first end portion <NUM>, a central portion <NUM>, a second end portion <NUM>, and a second extension <NUM>. A rotatable fixation bridge <NUM> according to other embodiments of the present disclosure may comprise more or fewer components than those described herein with respect to <FIG>.

The bridge adaptor <NUM> may be shaped to complement a mount <NUM> of the reference <NUM>. More specifically, the bridge adaptor <NUM> may comprise a plate or member shaped to receive or be received by the mount <NUM>. The bridge adaptor <NUM> may be made of any metal, metal alloy, plastic, or other material, or any combination thereof, suitable for fixedly securing the rotatable fixation bridge <NUM> to the reference <NUM>. The bridge adaptor <NUM> may comprise one or more locking screws <NUM> for fixedly securing the bridge adaptor <NUM> to the mount <NUM> and thus to the reference <NUM>. Additionally or alternatively, the bridge adaptor <NUM> may be configured to attach to the mount <NUM> via a press fit, a snap fit, an interlocking fit, or any other attachment method and/or mechanism. The bridge adaptor <NUM> may form or define at least a portion of a socket in which a ball (such as the first ball <NUM> of <FIG>) of the rotatable fixation bridge <NUM> is received and secured.

The first extension <NUM> extends between a ball or other object or mechanism fixedly secured to the reference <NUM> by the bridge adaptor <NUM>, and the first end portion <NUM>. Notably, the attachment between the first extension <NUM> and the first end portion <NUM> does not permit axial or translational movement of the first end portion <NUM> relative to the first extension <NUM>, but does permit relative rotational movement. In other words, when the bridge adaptor <NUM> is secured to the reference <NUM>, the first extension <NUM> is fixedly secured relative to the reference <NUM>, but the first end portion <NUM> may rotate around the first extension <NUM> (and thus around an axis <NUM> defined at least in part by the first extension <NUM>).

In some embodiments, the first end portion <NUM> may be lockable in a specific angular position relative to the first extension <NUM>, whether by way of one or more complementary protrusions and detents along an interface between the first extension <NUM> and the first end portion <NUM>, or using a pin and/or a set screw, or due to friction between the first extension <NUM> and the first end portion <NUM>, or otherwise.

The central portion <NUM> connects the first end portion <NUM> to the second end portion <NUM> to form a bridge member. The central portion <NUM> is offset from the axis of rotation <NUM> of the bridge member. The axis <NUM> may be defined, for example, by the coaxial axes of the first extension <NUM> and the second extension <NUM>. In some embodiments, rotational hinges other than those illustrated in <FIG> (comprising a cylindrical first extension <NUM> received by an aperture in a first end portion <NUM>, and a cylindrical second extension <NUM> received by an aperture in a second end portion <NUM>, respectively) may be utilized by the rotatable fixation bridge <NUM>. In such embodiments, the rotational hinges of the rotatable fixation bridge <NUM> may be concentric and/or coaxial, and may define the axis <NUM> of rotation of the rotatable fixation bridge <NUM>.

The central portion <NUM> may be substantially straight or linear, as shown in <FIG>. The central portion <NUM> may be substantially parallel to the axis <NUM> of rotation, as also shown in <FIG>. In some embodiments, the central portion <NUM> may not be substantially parallel to the axis <NUM> of rotation. For example, the central portion <NUM> may continuously curve from the first end portion <NUM> to the second end portion <NUM>. In such embodiments, the central portion <NUM> may have a constant radius of curvature, or a varying radius of curvature. The central portion <NUM> may comprise a curve that extends in substantially the same plane as the first end portion <NUM> and the second end portion <NUM>, or the curve may extend in a different plane. In other words, the central portion <NUM> may curve in a plane that is parallel to but does not include the axis of rotation <NUM>. In still other embodiments, the central portion <NUM> may comprise one or more curved portions, and/or one or more straight portions.

In some embodiments, whether a bridge member of the rotatable fixation bridge <NUM> comprising a straight central portion <NUM> or comprising a curved central portion <NUM> is selected for use in connection with a given surgical procedure may depend on the nature of the surgical procedure. For example, a curved central portion <NUM> may beneficially provide a large obstacle-free area in between the first end portion <NUM> and the second end portion <NUM> than a straight central portion <NUM>, and may therefore be more desirable when the rotatable fixation bridge <NUM> will extend, for example, directly over a surgical site.

In some embodiments, the central portion <NUM> may not be readily distinguishable (e.g., whether by a change of angle or curvature or otherwise) from the first end portion <NUM> and the second end portion <NUM>. In other embodiments, the central portion <NUM> may be perpendicular to at least a portion of the first end portion <NUM> and/or to at least a portion of the second end portion <NUM>.

The central portion <NUM> may be offset from the axis <NUM> by a maximum distance-as measured between the axis <NUM> and a surface of the central portion <NUM> that faces the axis <NUM>-of about half of one inch, or of about one inch, or of about two inches, or of about three inches. In some embodiments, the central portion <NUM> may be offset from the axis <NUM> by a maximum distance in a range between about one half-inch and about twelve inches, or in a range between about one inch and about eight inches, or in a range between about one inch and about five inches. Notwithstanding the foregoing, the present disclosure encompasses rotatable fixation bridges <NUM> having a central portion <NUM> offset from an axis <NUM> by any distance.

The amount of offset of the central portion <NUM> relative to the axis <NUM> may be determined in whole or in part by a length of the first end portion <NUM> and of the second end portion <NUM> (e.g., when the central portion <NUM> is straight or linear, as shown in <FIG>), or by a radius of curvature of the central portion <NUM> (e.g., when the central portion <NUM> is curved), or by a combination of the foregoing. In some embodiments, the first end portion <NUM> and the second end portion <NUM> may be adjustable between or among a plurality of lengths in a direction substantially perpendicular to the axis <NUM>, so as to increase or decrease an offset of the central portion <NUM> relative to the axis <NUM>. In such embodiments, the first and second end portions <NUM> and <NUM> may be fixedly securable or lockable at each of the plurality of lengths, so that once set at a particular length, the length of the first and second end portions <NUM> and <NUM> does not inadvertently change. The first and second end portions <NUM> and <NUM> according to such embodiments may comprise one or more telescoping members, and/or one or more folding members, and/or one or more selectively attachable or detachable members.

The central portion <NUM> may have a length of between about one inch (<NUM> inch=<NUM>,<NUM>) and about thirty inches, or a distance of between about two inches and about twenty inches, or a distance of between about three inches and twelve inches. The central portion <NUM> may be about sixteen inches long, or about twelve inches long, or about eight inches long. In some embodiments, the central portion <NUM> may be adjustable between or among a plurality of lengths. In such embodiments, the central portion <NUM> may be fixedly securable or lockable at each of the plurality of lengths, so that once set at a particular length, the length of the central portion <NUM> does not inadvertently change. A central portion <NUM> according to such embodiments may comprise one or more telescoping members, and/or one or more folding members, and/or one or more selectively attachable or detachable members.

The central portion <NUM> may be or comprise a hand grip, so that a surgeon or other user may grip the central portion <NUM> and cause the central portion <NUM> to rotate about the axis <NUM> between a first rotational position and a second rotational position. As noted above, in some embodiments, the central portion <NUM> (together with the first end portion <NUM> and the second end portion <NUM>) may be lockable in a plurality of rotational or angular positions relative to the first extension <NUM> and the second extension <NUM> (and thus relative to the reference <NUM>, the anchor <NUM>, and the patient to which the anchor <NUM> is secured). In such embodiments, the central portion <NUM> (together with the first end portion <NUM> and the second end portion <NUM>) may be set at a first angular or rotational position and locked in place to prevent further unintentional movement thereof, and then unlocked, moved to a second angular or rotational position, and again locked in place to prevent further unintentional movement thereof.

In some embodiments of the present disclosure, the central portion <NUM> (together with the first end portion <NUM> and the second end portion <NUM>) may be held in a given angular or rotational position about the axis <NUM> with a frictional fit only (rather than with, for example, a mechanical locking mechanism).

<FIG> illustrates a fixation system <NUM> substantially similar to the fixation system <NUM>, except that the second end portion <NUM> of the rotatable fixation bridge <NUM> comprises a socket <NUM>. The socket <NUM> is fixedly secured to the second end portion <NUM>, and is configured to receive a ball that is rigidly secured to an anchor. In other words, whereas the rotatable fixation bridge <NUM> of the fixation system <NUM> comprises a second extension <NUM> supporting a ball (e.g., the second ball <NUM> of <FIG>) that is received by a socket in the anchor <NUM>, the rotatable fixation bridge <NUM> of the fixation system <NUM> comprises a socket <NUM> adapted to receive (and secure in a fixed position) a ball of an anchor such as the anchor <NUM>.

Use of mechanical ball and socket joints to secure the rotatable fixation bridge <NUM> to a reference <NUM> and/or to an anchor <NUM> beneficially enables the rotatable fixation bridge <NUM> to be oriented as needed, independent of the location of the anchor <NUM> (and thus of the anatomical feature of the patient to which the anchor <NUM> is fixedly connected) relative to the location of the reference <NUM>. In other words, provided that the mount <NUM> generally faces the anchor <NUM> (or that a ball or socket of the anchor <NUM> generally faces the mount <NUM>), the rotatable fixation bridge may be positioned to extend from the mount <NUM> and toward the anchor <NUM> (or from the anchor <NUM> and toward the mount <NUM>) at any one of a plurality of angles. In contrast, if the rotatable fixation bridge <NUM> were only fixedly securable to the mount <NUM> and/or to the anchor <NUM> at one angle, or at one of a few predetermined angles, then the reference <NUM> and the anchor <NUM> could only be secured to each other in a corresponding one or a corresponding few relative positions. This, in turn, might result in an increased workload for the surgeon and/or other user(s) of the fixation systems <NUM> and/or <NUM>, who may need to spend extra time positioning the reference <NUM> relative to the anchor <NUM> so that a rotatable fixation bridge <NUM> may be secured therebetween.

Notwithstanding the foregoing, the present disclosure encompasses fixation systems in which the rotatable fixation bridge <NUM> is fixedly secured to the reference <NUM> and/or to the anchor <NUM> using a mechanical ball and socket joint, a hinge joint, a saddle joint, or any other joint or attachment mechanism that is or can be fixed or secured in at least one specific position. In some embodiments, at least a portion of any such joint (e.g., a ball, or a socket) may be part of the rotatable fixation bridge <NUM>.

<FIG> illustrates an exploded view of a rotatable fixation bridge <NUM> according to at least some embodiments of the present disclosure. The rotatable fixation bridge <NUM> of <FIG> includes the bridge adaptor <NUM>; the locking screw <NUM>; the first extension <NUM>; a bridge member <NUM> comprising the first end portion <NUM>, the central portion <NUM>, and the second end portion <NUM>; and the second extension <NUM>, all as described above. Also shown in <FIG> are a first ball <NUM>, an aperture <NUM>, a rotation mount <NUM> of the first extension <NUM>, caps <NUM> and <NUM>, screws <NUM> and <NUM>, a rotation mount <NUM> of the second extension <NUM>, a second ball <NUM>, a pin <NUM>, a set screw <NUM>, and an aperture <NUM>.

Each of the first ball <NUM> and the second ball <NUM> is adapted to be received by a corresponding socket. The first ball <NUM> is configured to be received by a socket of a reference <NUM>, which may be at least partially defined by a mount <NUM> on or in the reference <NUM>. The socket may also be at least partially defined by the bridge adaptor <NUM>, such that when the bridge adaptor <NUM> is secured to the mount <NUM>, a complete socket is defined, with the first ball <NUM> secured therein. A pin <NUM>, driven by a set screw <NUM>, is configured to extend through the bridge adapter <NUM> and into the socket that receives the first ball <NUM>, so as to engage the first ball <NUM> and lock the first ball <NUM> in a fixed position relative to the reference <NUM>. In some embodiments, a plurality of pins <NUM>, set screws <NUM>, and/or other devices may be used to lock the first ball <NUM> in a specific orientation within the socket. Also in some embodiments, the bridge adaptor <NUM> is configured to lock the first ball <NUM> in a specific orientation within the socket, once the bridge adaptor <NUM> is secured to a mount <NUM> (or otherwise secured to the reference <NUM>).

The bridge adaptor <NUM> comprises an aperture <NUM> that is sized to allow the first extension <NUM> to pass therethrough, but to prevent passage of the first ball <NUM> therethrough. The aperture <NUM> thus defines an opening of the socket that receives the first ball <NUM>, and enables the first ball <NUM> to be secured within the socket while still being connected (e.g., via the first extension <NUM>) to the first end portion <NUM>.

The first extension <NUM> is rotatably secured to the first end portion <NUM> via the rotation mount <NUM>. The rotation mount <NUM> is a cylindrical portion of the first extension <NUM> sized to fit within a corresponding aperture <NUM> of the first end portion <NUM>. The rotation mount <NUM> has a diameter less than a maximum width or diameter of the first extension <NUM>. With the rotation mount <NUM> extending through the aperture <NUM>, the cap <NUM> may be secured to the rotation mount <NUM> with the screw <NUM>. Once so assembled, the wider portion of the first extension <NUM> and the cap <NUM> abut the axial sides (e.g., the sides perpendicular to the axis <NUM>) of the first end portion <NUM> and prevent translational motion of the first end portion <NUM> (relative to the first extension <NUM>) in a dimension parallel to the axis <NUM>, while the rotation mount <NUM> prevents translational motion of the first end portion <NUM> (relative to the first extension <NUM>) in any other dimension. However, the first end portion <NUM> may still rotate around the rotation mount <NUM>.

Similarly, the second ball <NUM> is configured to be received by a socket of an anchor <NUM>. One or more set screws or other devices (not shown) may be used to lock the second ball <NUM> in a specific orientation within the socket of the anchor <NUM>.

The second extension <NUM> is rotatably secured to the second end portion <NUM> via the rotation mount <NUM>. The rotation mount <NUM> is a cylindrical portion of the first extension <NUM> sized to fit within a corresponding aperture (not visible in <FIG>) of the second end portion <NUM>. The rotation mount <NUM> has a diameter less than a maximum width or diameter of the second extension <NUM>. With the rotation mount <NUM> extending through the aperture of the second end portion <NUM>, the cap <NUM> may be secured to the rotation mount <NUM> with the screw <NUM>. Once so assembled, the wider portion of the second extension <NUM> and the cap <NUM> abut the axial sides (e.g., the sides perpendicular to the axis <NUM>) of the second end portion <NUM> and prevent translational motion of the second end portion <NUM> (relative to the second extension <NUM>) in a dimension parallel to the axis <NUM>, while the rotation mount <NUM> prevents translational motion of the second end portion <NUM> (relative to the second extension <NUM>) in any other dimension. However, the second end portion <NUM> may still rotate around the rotation mount <NUM>.

When assembled, the first ball <NUM> (together with the first extension <NUM>, the bridge adaptor <NUM>, the locking screw <NUM>, the pin <NUM>, and/or the set screw <NUM>, in some embodiments) defines a first end or a reference interface of the rotatable fixation bridge <NUM>, and the second ball <NUM> (together with the second extension <NUM> and any other components of the rotatable fixation bridge <NUM> useful for securing the second ball <NUM> to a socket of the anchor <NUM>), in some embodiments) defines a second end or an anchor interface of the rotatable fixation bridge <NUM>. In embodiments of the present disclosure in which one or both of the first ball <NUM> and the second ball <NUM> are replaced with a socket, then the socket proximate the first end portion <NUM> (together with any other components useful for securing a ball of the reference <NUM> in the socket) would define the first end or reference interface, and the socket proximate the second end portion <NUM> would define the second end or the anchor interface. Regardless of the joint or attachment mechanism used to secure the rotatable fixation bridge <NUM> to the reference <NUM> and/or to the anchor <NUM>, the portion of the rotatable fixation bridge <NUM> that allows the rotatable fixation bridge <NUM> to be secured to the reference <NUM> comprises the first end or the reference interface, and the portion of the rotatable fixation bridge <NUM> that allows the rotatable fixation bridge <NUM> to be secured to the anchor <NUM> comprises the second end or the anchor interface.

Each of the various components of the rotatable fixation bridge <NUM> may be made of a metal, a metal alloy, a plastic, a composite, any other suitable material that enables the component to achieve the purpose thereof as described herein, and/or any combination of the foregoing. In some embodiments, one or more components of the rotatable fixation bridge <NUM> may be made of a radiolucent material, such as polyetheretherketone (PEEK), polyetherimide, or thermoplastic resins with carbon-fiber reinforcement. In other embodiments, none of the components of the rotatable fixation bridge <NUM> are radiolucent. The material(s) from which the various components of the rotatable fixation bridge <NUM> are made may be selected to enable the rotatable fixation bridge and/or one or more portions thereof to be cleanable, sterilizable (whether by heat, chemical treatment, or otherwise), and/or reusable. Additionally and/or alternatively, the material(s) from which the various components of the rotatable fixation bridge <NUM> are made may be selected to ensure that the rotatable fixation bridge is strong enough to withstand forces of any expected magnitude during the course of a surgical procedure.

A rotatable fixation bridge as described herein, such as the rotatable fixation bridge <NUM>, beneficially maintains a relative position of the first end thereof (which may be attached to, for example, a surgical robot or other reference) and the second end thereof (which may be attached to, for example, an anchor that is in turn attached to an anatomical feature of a patient), independent of a rotational position of the bridge member relative to the first and second ends. As a result, if the bridge member of the rotatable fixation bridge presents an obstacle to achieving a desired tool trajectory or obtaining a desired image or observing along a desired line of sight during a surgical procedure in which the rotatable fixation bridge is being used, the bridge member may simply be rotated to a different angular position, thus removing the obstacle and permitting the desired tool trajectory to be achieved, or the desired image to be obtained, or the desired line of sight to be observed.

With reference now to <FIG>, a method <NUM> of securing an anatomical feature to an external reference comprises fixedly securing an anchor interface of a rotatable fixation bridge to an anchor (step <NUM>). The fixedly securing may comprise fixedly securing a ball of the anchor interface into a socket of the anchor. The fixedly securing may additionally or alternatively comprise securing the anchor interface to the anchor with one or more bolts, screws, or other mechanical fasteners. The anchor may be the same as or similar to the anchor <NUM> and/or any clamp, screw, or pin described herein, and/or may be any other device that may be fixedly secured to an anatomical feature.

The method <NUM> further comprises fixedly securing a reference interface of the rotatable fixation bridge to an external reference (step <NUM>). The external reference may the same as or similar to the reference <NUM>, and/or any other reference described herein. The fixedly securing may comprise fixedly securing a ball, such as the first ball <NUM>, into a socket. The fixedly securing may comprise securing bridge adaptor, such as the bridge adaptor <NUM>, to the external reference (or to a mount thereof, such as the mount <NUM>). The fixedly securing may comprise threading a locking screw such as the locking screw <NUM> through the bridge adaptor and into the external reference, and/or driving a pin such as the pin <NUM> into the first ball <NUM> using a set screw such as the set screw <NUM>, so as to secure a ball such as the first ball <NUM> into a specific position within the socket.

The method <NUM> further comprises rotating a bridge member of the rotatable fixation bridge to a first angular position relative to the anchor interface and the reference interface (step <NUM>). The bridge member comprises a central portion offset from an axis of rotation of the bridge member. The rotation does not change a position of the anchor interface relative to the reference interface. However, because the bridge member comprises a central portion offset from an axis of rotation of the bridge member, the rotation results in at least the central portion assuming a first position that is unique as compared to the position of at least the central portion when the bridge member is rotated to any other angular position relative to the anchor interface and the reference interface.

The method <NUM> further comprises rotating the bridge member to a second angular position different than the first angular position (step <NUM>). Here again, the rotation does not change the position of the anchor interface relative to the reference interface, and therefore maintains the position of the anchor (and of the anatomical feature to which the anchor is connected, be it a vertebra or other spinal feature or any other anatomical feature) relative to the reference. Additionally, because the bridge member comprises a central portion offset from the axis of rotation of the bridge member, the rotation results in at least the central portion assuming a second unique position different than the first unique position. As a result, if the bridge member or a portion thereof, when in the first angular position, presents an obstacle to achieving a desired tool trajectory, or to obtaining a desired image, or to any other aspect of a given surgical procedure, the bridge member can be rotated to the second angular position, thus removing the obstacle and enabling the desired tool trajectory to be achieved, the desired image to be obtained, or any other step of the surgical procedure that was inhibited due to the location of the bridge member to be performed.

Claim 1:
A fixation system (<NUM>) comprising:
a bone-mountable anchor (<NUM>) configured to be mounted to an anatomical feature of a patient; and
a rotatable fixation bridge (<NUM>) comprising:
a first end fixedly connectable to a reference (<NUM>) via a first joint (<NUM>, <NUM>), and defining at least a portion of the first joint (<NUM>, <NUM>);
a second end fixedly connectable to the anchor (<NUM>) via a second joint (<NUM>; <NUM>), and defining at least a portion of the second joint (<NUM>; <NUM>); and
a bridge member (<NUM>) extending between and rotatably secured to the first end and the second end via first (<NUM>, <NUM>) and second (<NUM>) concentric rotational hinges, respectively, defining an axis of rotation (<NUM>), relative to which the bridge member (<NUM>) is rotatable, the bridge member (<NUM>) comprising a central portion (<NUM>) offset from the axis (<NUM>).