Patent Description:
External fixation systems are used in a variety of surgical procedures including limb lengthening, deformity correction, fracture reduction, and treatment of non-unions, mal-unions, and bone defects. A rigid framework comprising external fixators is placed externally around an affected limb and attached to bone segments using wires, pins, rods, etc. The external fixators of the rigid framework are interconnected by rods directly or in conjunction with uni-planar or multi-planar hinges, which allow a user to connect external fixators that are not parallel to each other at the time of application or to permit manipulation of anatomical joints within the region encompassed by the external fixation system.

For treatment of various pathologies, it is beneficial to allow for controlled movement about a hinge that is disposed between two external fixators. Introducing controlled movement can accelerate bone healing and improve mobility of joints. For example, it may be beneficial to secure one or more hinges between two external fixators to allow for limited pivotal movement of an anatomical joint. A hinge may allow for pivotal rotation of an anatomical joint such that movement may be reintroduced to a patient's joint. Such hinges, however, should provide for sufficient stability and reduce movement along axes other than those of the respective anatomical joint(s). Excessive movement along other axes may negatively impact the healing process and otherwise cause damage or pain to a patient. For example, translational movement (or "shearing") of a hinge during joint movement may harm the anatomical joint and impair healing.

Traditional mono-axial mechanical hinges have been used in orthopedic treatment but have significant limitations. They may not adequately conform to the anatomical axis of a joint, particularly if the joint axis changes dynamically. When a joint rotates or moves, the corresponding axis of rotation may shift in one or more directions. Furthermore, some anatomical joints are complex, such as the ankle and wrist, and are not constrained to a static axis of rotation. If an external fixation system has an axis of rotation that is out of alignment with the anatomical axis of rotation, pivoting of the joint could result in pain, discomfort, subluxation or dislocation of the joint, and/or damage to the joint or adjacent tissue.

A traditional coil spring may be used in hinges to allow for the axis of rotation to shift or adjust to the position of the anatomical axis of rotation of a particular joint during movement. However, many coil springs have inherent instability and fail to limit movement to one or more desired planes. When a coil spring bends in a particular direction, the internal layers that make up the spring are susceptible to shearing forces which can result in a shearing movement. Accordingly, traditional coil springs may fail to provide sufficient stability when used in external fixation systems.

Accordingly, there is a need for improved spring hinges that provide sufficient stability and limit pivotal movement of a joint to a finite number of planes or directions while also dynamically adapting to a shifting anatomical axis of rotation.

<CIT> discloses a joint fixator apparatus conforming to the natural axis of rotation of the joint in question, such as a patient's wrist or knee to avoid the possibility of bone fragment displacement and/or fracture reduction.

<CIT> discloses orthopedic hinge devices and systems suitable for use as part of external fixation systems.

<CIT> discloses a fixing device comprising at least two pin-holders and a connecting unit that is used to join said pin-holders.

<CIT> discloses an external bone fixator for use in the treatment of fractured bones such as the tibia.

The present disclosure relates in general to orthopedic hinges suitable for use with external fixators and as part of external fixation systems. In some embodiments, orthopedic hinges of the present disclosure may provide for pivotal movement about an axis of an anatomical joint while reducing or completely preventing unwanted pivotal movement about one or more other axes of the anatomical joint and unwanted translational or shearing movement of said anatomical joint.

The invention is set out in the appended set of claims <NUM>-<NUM>.

It is to be understood that both the foregoing general description and the following drawings and detailed description are exemplary and explanatory in nature and are intended to provide an understanding of the present disclosure without limiting the scope of the present disclosure. In that regard, additional aspects, features, and advantages of the present disclosure will be apparent to one skilled in the art from the following. One or more features of any embodiment or aspect may be combinable with one or more features of other embodiment or aspect.

The accompanying drawings illustrate implementations of the systems, devices, and methods disclosed herein and together with the description, serve to explain the principles of the present disclosure.

These Figures will be better understood by reference to the following Detailed Description.

For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the implementations illustrated in the drawings and specific language will be used to describe them. It will nevertheless be understood that no limitation of the scope of the disclosure is intended. Any alterations and further modifications to the described devices, instruments, methods, and any further application of the principles of the present disclosure are fully contemplated as would normally occur to one skilled in the art to which the disclosure relates. In addition, this disclosure describes some elements or features in detail with respect to one or more implementations or Figures, when those same elements or features appear in subsequent Figures, without such a high level of detail. It is fully contemplated that the features, components, and/or steps described with respect to one or more implementations or Figures may be combined with the features, components, and/or steps described with respect to other implementations or Figures of the present disclosure. For simplicity, in some instances the same or similar reference numbers are used throughout the drawings to refer to the same or like parts. Any embodiments, aspects or examples of the present description or disclosure that do not fall within the scope of the claims are provided for illustrative purpose only and not part of the present invention.

The present disclosure relates, in some embodiments, to orthopedic spring hinges suitable for use with external fixation devices. Orthopedic hinges of the present disclosure may be suitable for treatment of various anatomical joints including, but not limited to, the wrist, elbow, knee, or ankle.

<FIG> depicts an example external fixation system in accordance with the present disclosure. As depicted, an external fixation system <NUM> includes a plurality of external fixators including external fixation ring <NUM> and external fixator <NUM> which, in the illustrated embodiment, is a U-shaped external fixator. A plurality of rods <NUM> extend from fixtures secured to the external fixators and into bone, thereby securing the external fixation system <NUM> to the patient. One or more spring hinges <NUM> are secured between external fixators to permit, yet control, movement of one external fixator with respect to another. It should be appreciated that any number of rods, fixtures, spring hinges, and external fixators of any suitable shape(s) and type(s) may be used in the construction of an external fixation system.

Spring hinges of the present disclosure may comprise certain features that advantageously allow for pivotal movement about an anatomical joint while reducing or completely preventing unwanted translational or shearing movement across said anatomical joint. Further, embodiments of the present disclosure may limit the pivotal movement of an anatomical joint to a finite number of planes or directions, while also being able to dynamically adapt to the shifting anatomical axis of rotation during movement of a corresponding anatomical joint. For example, with regard to the illustrated example of <FIG>, the external fixation system <NUM> may limit the pivotal movement of the ankle joint to allow flexion and extension within the sagittal plane while preventing or limiting undesirable movement such as supination, pronation, and/or shear.

<FIG> illustrate spring hinge <NUM> which comprises two coil springs <NUM> extending between an upper base member and a lower base member <NUM>. A bolt <NUM> may be attached to each base member <NUM> for securing the spring hinge <NUM> to an external fixation system as shown in <FIG>. A nut <NUM> may be used to secure the bolt <NUM> to the base member <NUM>. Although illustrated with two coil springs <NUM>, it should be appreciated that any number of coil springs <NUM> may be used in spring hinge <NUM> within the scope of this disclosure.

Each coil spring <NUM> may be formed of a plurality of spirals that are layered or stacked upon one another. When a coil spring is in an unexpanded state the layers of spirals may rest upon one another as shown in <FIG>. When in a flexed or bent state, one side of the layers of spirals may rest upon one another and the layers of spirals on the opposing side may be spaced apart as shown in <FIG>.

Utilizing two coil springs <NUM> helps limit bending of the spring hinge <NUM> to a forward/rearward direction within plane <NUM> in which both coil springs <NUM> bend as shown in <FIG> while resisting lateral bending within plane <NUM>. Specifically, lateral bending of spring hinge <NUM> is resisted at least in part because one coil spring must be expanded while the other remains unexpanded and in compression. Accordingly, a bending resistance of the spring hinge <NUM> in a first direction (e.g., within second plane <NUM>) is lower than a bending resistance of the spring hinge <NUM> in a second direction orthogonal to the first direction (e.g., within first plane <NUM>). In this regard, the spring hinge <NUM> may be oriented within an external fixation system such that pivotal movement of the spring hinge, and in turn the anatomy of the patient, is substantially limited to axis of rotation <NUM> which may translate up/down and/or forward/backward during pivoting of the spring. Because anatomical axes do not always align with a fixed axis, the up/down and/or forward/backward translation during pivoting may better accommodate the anatomical axes than fixed axis systems. By arranging spring hinge <NUM> as shown in the example of <FIG>, such that the coil springs <NUM> base members <NUM> are aligned within a frontal or coronal plane of the patient, pivotal movement of the ankle may be restricted to movement within the sagittal plane.

Coil springs <NUM> may be formed from any suitable materials including, but not limited to, stainless steel or tempered steel, and may be plated and/or coated with a plastic, polymer, and/or other resilient materials. Non-limiting examples of materials for use in forming coil springs and/or other external fixation system components discussed herein (such as spring hinge base members, external fixators, rods, bolts, nuts, etc.) include stainless steel, such as 304V, <NUM>, and 316LV stainless steel; mild steel; nickel-titanium alloy such as linear-elastic and/or super-elastic nitinol; other nickel alloys such as nickel-chromium-molybdenum alloys, nickel-copper alloys, nickel-cobalt-chromium-molybdenum alloys, nickel-molybdenum alloys, nickel-chromium alloys, nickel-molybdenum alloys, nickel-cobalt alloys, nickel-iron alloys, nickel-copper alloys, nickel-tungsten or tungsten alloys, and the like; cobalt-chromium alloys; cobalt-chromium-molybdenum alloys; platinum enriched stainless steel; titanium; aluminum, combinations thereof; and the like; reinforced (fabric) or non-reinforced plastics; or any other suitable materials with sufficient mechanical properties to limit and/or control movement of a joint during an orthopedic treatment.

Non-limiting examples of polymers for use in forming coil springs include polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), polyoxymethylene (POM), polyether block ester, polyurethane (for example, Polyurethane 85A), polypropylene (PP), polyvinylchloride (PVC), polyetherester, ether or ester based copolymers (for example, butylene/poly(alkylene ether) phthalate and/or other polyester elastomers), polyamide, elastomeric polyamides, block polyamide/ethers, polyether block amide (PEBA), ethylene vinyl acetate copolymers (EVA), silicones, polyethylene (PE), Marlex high-density polyethylene, Marlex low-density polyethylene, linear low density polyethylene, polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polytrimethylene terephthalate, polyethylene naphthalate (PEN), polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), poly paraphenylene terephthalamide, polysulfone, nylon, nylon-<NUM>, perfluoro(propyl vinyl ether) (PFA), ethylene vinyl alcohol, polyolefin, polystyrene, epoxy, polyvinylidene chloride (PVdC), poly(styrene-b-isobutylene-b-styrene), polycarbonates, ionomers, biocompatible polymers, other suitable materials, or mixtures, combinations, copolymers thereof, polymer/metal composites, and the like.

<FIG> is an exploded view of a spring hinge <NUM>. The coil springs <NUM> are spaced apart along a longitudinal axis <NUM> of each of the base members <NUM> such that the longitudinal axis <NUM> of each spring is generally transverse to the longitudinal axes <NUM> of the base members <NUM>. Connecting bolts <NUM> are secured to external fixators (not shown) at their outer ends and second to respective base members <NUM> at their inner ends with optional nuts <NUM> helping to prevent the bolts <NUM> from separating from the base members <NUM>. Coils springs <NUM> extend between the base members <NUM> and may be secured thereto as discussed below in relation to <FIG>, optionally including conical dowels <NUM>.

<FIG> illustrates a base member <NUM> of a spring hinge <NUM>. Base member <NUM> includes a bolt connection bore <NUM> centrally disposed to receive a bolt for connecting the spring hinge to an external fixator. As illustrated the bolt connection bore <NUM> is threaded to receive corresponding threads of a connection bolt such as bolt <NUM> of <FIG>. However, it should be appreciated that a connection bolt may be formed integrally with a base member <NUM> or may be affixed to the base member in any suitable manner. Disposed on either side of the bolt connection bore <NUM> are spring connection bores <NUM> configured to receive an end of a spring. In some examples, spring connection bores <NUM> are threaded with a thread size and pitch corresponding to the coil of a coil spring such that a coil spring may be directly threaded into a spring connection bore <NUM>, as may be seen in <FIG>. It should be appreciated that positioning spring connection bores <NUM> and bolt connection bores <NUM> in a common base member may help shorter the overall functional length (e.g., bending portion) of the spring hinge to allow the spring hinge to be installed in space-limited applications.

Optionally, any suitable fastener may be used to secure a coil spring <NUM> to a spring connection bore <NUM>. For example, a conical dowel <NUM> as shown in <FIG>, may be inserted into a spring connection bore <NUM> to further secure a coil spring <NUM> to a base member <NUM>. As shown in <FIG>, a conical dowel <NUM> includes an external thread <NUM> that corresponds to the coil dimensions of a coil spring <NUM>. In this regard, a conical dowel <NUM> may be threaded into the lumen formed in a coil spring <NUM>. For example, the illustrated embodiment of conical dowel <NUM> includes a tool-receiving recess <NUM> for rotating conical dowel <NUM> as it is threaded into an end of a coil spring <NUM> disposed in a spring connection bore <NUM> of a base member <NUM>. The conical shape of the conical dowel <NUM> causes the conical dowel to exert an increasing radially-directed compression force on the coil spring <NUM> as the conical dowel is threaded into the lumen of the spring, the spring being radially confined by the base member <NUM>. Base member <NUM> of <FIG> may represent both base members of the spring hinge <NUM> of <FIG>, but it should be appreciated that in some embodiments, an upper base member and a lower base member may have different properties or characteristics such as size, shape, features, etc..

Furthermore, it should be appreciated that any suitable means may be used to attach a coil spring <NUM> to a base member <NUM>. For example, a connection bore <NUM> may not form an aperture extending entirely through a base member <NUM> but may instead form a recess extending only partially through a base member. Alternatively, a coil spring may be welded or otherwise adhered to a base member without using a spring connection bore. For example, end caps may be threaded into the coil springs and may be attached to a base member with a bolt or other suitable hardware. For example, <CIT> entitled "ORTHOPEDIC SPRING HINGE SYSTEM AND METHODS THEREOF," describes end caps which may be used to install a spring in an external fixation system.

Rigidity of different springs in a spring hinge can be equal to each other or one (e.g., lateral) spring can be more rigid than the other (e.g., medial) spring. Differential rigidity of two springs can be achieved by using springs having different physical and mechanical properties which impact their bending characteristics. For example, spring length (longer or shorter), spring diameter (larger or smaller), or diameter of spring wire (thinner or thicker). Rigidity of a spring can be the same along the entire length of the spring or some parts of the spring can be less rigid providing a more static rotation axis, leading the anatomical joint to rotate around that axis. Differential rigidity of different parts of a spring can also be achieved by manipulation of spring diameter, coil wrap tightness, diameter of wire, or changing the spring profile (e.g., hourglass profile). The examples of coil springs <NUM> shown in <FIG> are constructed with varying physical and mechanical properties along their lengths which impact their bending characteristics. For example, the coil springs <NUM> of <FIG> have a first coil spacing in a first region <NUM> and a second coil spacing in a second region <NUM>. Further, a third region <NUM> has a third coil spacing which may be the same as or different that the coil spacing in the first region <NUM>. In the illustrated example, the coil spacing in the first region <NUM> and the third region <NUM> is closer or tighter than the coil spacing in the second region <NUM> disposed between the first region and the second region. In this regard, the tighter coil spacing in the end regions (i.e., first region <NUM> and third region <NUM>) may provide an increased number of coils for engaging with internal threads in the base member <NUM> to improve the connection. The wider spacing in the central region <NUM> may provide a reduced bending resistance of the coil spring <NUM> in that region. However, it should be appreciated that any number of distinct regions may be used in constructing a coil spring <NUM> and the respective coil spacings may be closer or further in any region with regard to any other region(s).

The coil springs <NUM> of <FIG> have a first coil diameter in a first region <NUM> and a second coil diameter in a second region <NUM>. Further, a third region <NUM> has a third coil diameter which may be the same as or different that the coil diameter in the first region <NUM>. In the illustrated example, the coil diameter in the first region <NUM> and the third region <NUM> is smaller than the coil diameter in the second region <NUM> disposed between the first region and the second region. In this regard, the smaller coil diameter in the end regions (i.e., first region <NUM> and third region <NUM>) may provide smaller coils for engaging with internal threads in the base member <NUM>. The wider coil diameter in the central region <NUM> may provide an increased bending resistance of the coil spring <NUM> in that region. However, it should be appreciated that any number of distinct regions may be used in constructing a coil spring <NUM> and the respective coil diameters may be smaller or larger in any region with regard to any other region(s).

It should be appreciated that the coil springs <NUM> of <FIG> may additionally or alternatively be constructed with other physical and mechanical properties which vary along the length of the coil. For example, in some embodiments, the coil diameter in a central region of a coil spring may be smaller than in regions nearer the ends of the coil spring. As another example, a wire thickness in one or more regions of a coil spring may be greater than a wire thickness in one or more other regions. For example, a coil spring <NUM> may be constructed using a wire having a greater thickness near its ends than near the center. In this regard, the bending resistance of the coil spring <NUM> may be reduced in a central region.

Furthermore, it should be appreciated that coil springs <NUM> may additionally or alternatively be constructed with physical and mechanical properties which vary around the circumference of the coil. For example, in some embodiments, a thickness of the coils may be smaller on one side, or two opposing sides, of the coil spring <NUM> than on the other side(s). Similarly, the cross-sectional shape of the wire forming the coils may be altered on one or more sides of the coil spring <NUM>. In this regard, bending resistance may be reduced in one or more desired directions while preventing shearing or bending in one or more other directions.

Additionally, while these features have been discussed in relation to coil springs as illustrated in <FIG>, other types of springs disclosed herein may also be constructed in a manner to impart varying physical (e.g., diameter, thickness, width, material, etc.) and mechanical (e.g., spring constant or "k-factor," bending resistance or "rigidity," etc.) properties in different regions of a spring.

As discussed above, the anatomical axis of a joint may change dynamically as the joint pivots. Some anatomical joints are not constrained to a static axis of rotation. That is, when a joint rotates or moves, the corresponding axis of rotation may shift in one or more directions. In this regard, varying the physical and mechanical properties of a spring along its length may facilitate construction of an external fixation system with an axis of rotation that moves dynamically in conjunction with the treated joint.

<FIG> illustrates a further example of a coil spring <NUM> in accordance with the present disclosure. Coil spring <NUM> of <FIG> has an integrated first connector <NUM> and/or an integrated second connector <NUM>. The coil spring <NUM> of <FIG>, including the integrated first and second connectors <NUM>,<NUM>, may be monolithically formed from a cylindrical tube. For example, mechanical or electro-chemical cutting may be used to form a coil spring <NUM> from a cylindrical blank. Although a coil spring according to the present disclosure may be constructed from a coiled cylindrically-shaped wire, the cross-sectional profile of a wire can be modified as shown in <FIG>, for example, to provide a desired bending elasticity in the plane of hinge movement (e.g., sagittal plane) while maintaining rigidity against undesired movements (e.g., translational shear movements in a horizontal plane).

First connector <NUM> may include a head having internal threads which facilitate attachment of the coil spring <NUM> to an external fixation system. For example, a bolt disposed within a base member (e.g., base member <NUM> of <FIG>) may be threaded into the head of the first connector <NUM>. In some embodiments, the coil spring <NUM> may include threads corresponding to such a bolt on the internal wall formed by the coils <NUM>. In this regard, the bolt may be threaded into the coiled portion of the coil spring <NUM>.

Second connector <NUM> may include external threads which may be threaded directly into corresponding threads of a base member. In some embodiments, a coil spring <NUM> may include two first connectors <NUM> or two second connectors <NUM> (one at each end). Further, in some embodiments, one or both of the first connector <NUM> and the second connector <NUM> may be separate and distinct components secured to the coils <NUM>.

The coil spring <NUM> of <FIG> includes wire which has a square or rectangular cross-section. The height and/or width of this cross-section may be altered to impart desired physical or mechanical properties into the spring hinge <NUM>.

While the illustrated examples of coil springs herein include cylindrical coil springs with wires having circular or rectangular cross-sections, it is contemplated that alternative coil spring shapes and wire cross-sections may be used. For example, <CIT>. entitled "ORTHOPEDIC SPRING HINGE SYSTEM AND METHODS THEREOF," includes a number of alternative spring shapes and wire cross-sections which may help resist shearing movement.

Further, it should be appreciated that the illustrated state of the coil springs <NUM> shown in <FIG> may be a resting (e.g., "relaxed," "unexpanded," or "neutral") state in some embodiments or may be an expanded state in which the base members <NUM> are pulled apart such that the coil springs <NUM> are in tension.

Differential rigidity of a spring hinge can also be achieved by relative shortening or lengthening of the bending portion of the spring using, for example, threaded components (e.g., bolts or short threaded rods) inserted inside the spring. <FIG> illustrates that an adjustment bolt <NUM> is selectively extended into or withdrawn from one or more springs of spring hinge <NUM>. The portion of a coil spring <NUM> in which an adjustment bolt <NUM> is positioned is prevented from bending due to the bending resistance of the adjustment bolt <NUM>, which is substantially greater than the bending resistance of a coil spring <NUM>. In this regard, spring hinge <NUM> is configured to have an adjustable bending length. Threading an adjustment bolt <NUM> further into a coil spring <NUM> reduces the length of a portion of the coil spring which is permitted to bend and, in turn, increases the bending resistance of the external fixation system. In contrast, threading an adjustment bolt <NUM> further outward from a coil spring <NUM> increases the length of the portion of the coil spring which is permitted to bend and, in turn, decreases the bending resistance of the external fixation system.

This adjustability may allow a user to selectively alter the rigidity of the external fixation system during different phases of treatment. For example, after initially installing an external fixation system around a patient's joint, it may be desirable for one or more adjustment bolts <NUM> to be fully inserted into a corresponding one or more coil springs <NUM> to maximize bending resistance and increase rigidity of the system. After a first period of treatment, it may be desirable to partially retract the adjustment bolts <NUM> to provide an intermediate degree of bending resistance. After a second period of treatment, it may be desirable to complete remove the adjustment bolts <NUM> to minimize the bending resistance to the inherent resistance provided by the coil springs <NUM>.

In some examples, an adjustment bolt <NUM> may be configured to be directly threaded into the coils of a coil spring <NUM>. In other examples, an adjustment bolt <NUM> may be configured to be threaded into a conical dowel which has a lumen extending through its length to accommodate the adjustment bolt such that the adjustment bolt <NUM> is indirectly secured within the coil spring <NUM>.

<FIG> illustrates an example of spring hinge <NUM> having primary springs <NUM> and secondary springs <NUM> extending between the base members <NUM>. In some embodiments, a secondary spring <NUM> may be disposed within a central cavity of a primary spring <NUM>. For example, the secondary spring <NUM> may have an outer width that is smaller than the inner width of the central cavity of the primary spring <NUM> and may have a length similar to or less than a length of the primary spring <NUM>. In other embodiments, the secondary spring <NUM> may have a length exceeding the length of the primary spring <NUM>. The secondary spring <NUM> may be positioned such that the secondary spring <NUM> and the primary spring <NUM> are concentric with one another. The secondary spring <NUM> and the primary spring <NUM> may share the same lengthwise axis.

One or both of a primary spring <NUM> and a secondary spring <NUM> may be substantially the same as any embodiment of a coil spring <NUM> described herein. Additionally or alternatively, one or both of a primary spring <NUM> and a secondary spring <NUM> may be substantially the same as any embodiment of other types of springs described herein. In some embodiments, a primary spring <NUM> may be a coil spring and a secondary spring <NUM> may be an elastic structure (e.g., plastic or polymer rod) insertable into the primary spring <NUM>. Such an elastic structure may complement or supplement the mechanical properties of the primary spring <NUM>, for example, to increase bending resistance of the spring hinge <NUM>. In some embodiments, a plurality of elastic structures may be provided and a user may adjust the rigidity of the external fixation system by removing a secondary spring <NUM> and replacing it with another secondary spring <NUM> having different physical and mechanical properties. Further in this regard, a plurality of different secondary springs <NUM> may be used simultaneously to vary the rigidity of a spring hinge <NUM> at one primary spring <NUM> as compared to another primary spring (e.g., left and right primary springs may be complemented with secondary springs having different properties) to favor certain bending planes of the external fixation system.

To stabilize an anatomical joint and substantially or completely reduce its motion (e.g., to keep the joint in a certain orientation as may be needed for walking), motion of a spring hinge can be blocked (or "locked"). <FIG> is an exploded view of a spring hinge with a locking structure in accordance with the present disclosure. The spring hinge <NUM> of <FIG> may be substantially the same as the spring hinge of <FIG>. In this regard, reference numerals have not been repeated to avoid obfuscating the illustration. The spring hinge <NUM> of <FIG> includes a locking structure configured to lock the spring hinge <NUM> in place and prevent bending. In the illustrated example of <FIG>, the locking structure <NUM> comprises a first locking plate and a second locking plate <NUM>. The first and second locking plates <NUM> may be positioned on either side of the coil springs and base members <NUM>. The first and second locking plates <NUM> may then be clamped together and secured to the spring hinge with any suitable locking mechanism. In the illustrated embodiment, the locking mechanism includes a locking bolt 190a extending through apertures in the locking plates <NUM> and a locking nut 190b.

The locking plates <NUM> may each include recesses on an inner wall to receive the coil springs <NUM>. Ridges formed between the grooves on the first locking plate <NUM> may be drawn into contact with corresponding ridges on the second locking plate <NUM> when the locking structure is installed. The inner surfaces of the base members <NUM> (e.g., top surface of the lower base member and bottom surface of the upper base member) may rest against opposing end surfaces of the locking plates <NUM>. In this regard, the base members may be prevented from rotating with respect to one another when the locking structure is installed.

The spring hinge <NUM> of <FIG> may be substantially the same as the spring hinge of <FIG> and includes an alternative example of a locking structure configured to lock the spring hinge <NUM> in place and prevent bending. In the illustrated example of <FIG>, the first locking plate 188a may include a block <NUM> that extends between a flange <NUM> of each base member <NUM>. The flanges <NUM> of each base member <NUM> may rest on opposing end surfaces of the block <NUM>. In this regard, the flanges may be prevented from moving closer to one another which, in turn, prevents rotation of the base members <NUM> with respect to one another.

The second locking plate 188b may include a transverse groove <NUM> adjacent each end of the locking plate 188b configured to receive the flange <NUM> of a respective one of the base members <NUM>. The groove <NUM> may have a height that closely corresponds to the height of the flange <NUM> such that the flange is closely mated with the locking plate 188b on both the upper and lower sides of the flange. In this regard, the base members <NUM> may be prevented from rotating with respect to one another when the locking structure is installed. It should be appreciated that a locking structure may include two first locking plates 188a, two second locking plates 188b, or one of each as illustrated.

The spring hinge of <FIG> may be substantially the same as the spring hinge of <FIG> with an alternative example of a locking structure configured to lock the spring hinge in place and prevent bending. In the illustrated example of <FIG>, the locking structure comprises a lock plate receiver <NUM> on each base member <NUM>. The lock plate receivers <NUM> illustrated in <FIG> comprise a cuboidal protrusion extending from a front or rear surface of a respective base member <NUM> which includes a lock bore <NUM>. However, it should be appreciated that a lock plate receiver <NUM> may have any suitable configuration. In some embodiments, a lock plate receiver <NUM> may simply comprise a lock bore <NUM> extending into the planar front or rear surface of the base member <NUM>.

As shown in <FIG>, a lock plate <NUM> may be secured to the lock plate receiver <NUM> of each base member <NUM> with one or more lock bolts <NUM> disposed in the lock bores <NUM>. In some embodiments, a notch may be cut into the side of the lock plate such that the lock plate can be slid off the base members to a side when the lock bolts are loosened. The lock plate <NUM> may rigidize the spring hinge and prevent rotation of the base members <NUM> with respect to one another. In the illustrated embodiment, the lock plate <NUM> comprises a C-shaped plate that extends around three sides of each lock plate receiver <NUM>. However, any suitable shape (e.g., L-shaped plate) may be used without departing from the scope of this disclosure. For example, a flat plate may extend from the lock bore <NUM> of one base member to the other, as may be appropriate in an embodiment in which the locking plate receivers <NUM> are integrated into the planar front or rear surface of base member <NUM> of <FIG>.

<FIG> is an exploded view of a spring hinge with an alternative locking structure comprising tie rods <NUM>. The spring hinge <NUM> may be substantially the same as the spring hinge illustrated in <FIG>. Conical dowels <NUM> include an external thread <NUM> to engage the springs <NUM> or base members <NUM> as shown in <FIG>. Conical dowels <NUM> may also include an internal thread <NUM> on a central bore to engage corresponding threads of the tie rods <NUM>. For example, in the illustrated embodiment, the lower end of the tie rods <NUM> may be threaded to engage the lower dowels <NUM>. In another example, both ends of the tie rods may be threaded to engage respective conical dowels <NUM>. That is, in some embodiments, hinge motion can be blocked by placement of threaded components (e.g., standard threaded rod) inside one or both of the springs <NUM>. In that regard, the shape and diameter of the internal thread of the spring may match the external thread of a tie rod <NUM>.

A tie rod <NUM> may include a head with a larger external diameter to prevent the head from entering the central bore of a respective conical dowel <NUM>. A tool-engagement feature such as a hexagonal tightening countersink may be provided in one or more conical dowels <NUM>. Additionally or alternatively, external knurling may be provided on a surface of a tie rod <NUM> for a manual grip.

Although illustrated in <FIG> in the context of coil springs, it should be appreciated that the locking structures described herein may be similarly applicable to other spring types including, but not limited to, a flexible spring <NUM> as in <FIG>, a blade spring as in <FIG>, a slotted spring <NUM> as in <FIG>, a ribbon spring as in <FIG>, or the spring hinge designs of <FIG>.

<FIG> is a perspective view of a spring hinge <NUM> in accordance with the present disclosure having a flexible spring <NUM> in a flexed configuration. An elastic or super-elastic material such as a polymer or other elastomeric material may be utilized to construct such a flexible spring <NUM>. In the illustrated embodiment, the cross section of flexible spring <NUM> is generally rectangular providing elastic bending in one plane (e.g., sagittal plane) while preventing (minimizing) bending in the orthogonal plane (e.g., coronal plane). In the illustrated example, the flexible spring <NUM> is formed as a single blade of material. However, it should be appreciated that a plurality of flexible springs <NUM> each formed of separate blades may be provided in a spring hinge <NUM>.

<FIG> is a perspective view of a flexible spring <NUM> as may be used in a spring hinge in accordance with the present disclosure. A plurality of rigid hinge members <NUM> may arranged in series with corresponding features to facilitate bending in a desired direction. Each hinge member <NUM> may include a recess in the shape of a concave groove <NUM> extending along a longitudinal length of the hinge member <NUM> and may include a convex outer surface <NUM> corresponding to a shape of the groove <NUM> for engagement with an adjacent hinge member. The hinge members <NUM> are made of aluminum or other rigid material and encased in an elastomer <NUM> to provide anatomical joint rotation in conjunction with pivoting of the flexible spring <NUM> about rotation axis <NUM> (which may translate dynamically with the anatomical joint) while resisting torsion about longitudinal axis <NUM> due to the rigid hinge member <NUM> which constrain such rotation. If some amount of torsion about longitudinal axis <NUM> is desired, the hinge members <NUM> may be constructed of less rigid material than aluminum. Flexible spring <NUM> may have a height or length L, a width W, and thickness T. The flexible spring <NUM> is configured to prevent bending of the spring hinge within a plane in which the height and width of the flexible spring extend, and to permit bending of the spring hinge within a plane in which the height and thickness of the flexible spring extend.

<FIG> is a perspective view of an alternative embodiment of flexible spring <NUM> as may be used in a spring hinge in accordance with the present disclosure. In the embodiment of <FIG>, each rigid hinge member <NUM> may include a ridged convex protrusion <NUM> configured for mating engagement with a corresponding convex slot <NUM> formed between opposing arms of an adjacent hinge member <NUM>.

<FIG> is a perspective view of a blade spring <NUM> as may be used in a spring hinge in accordance with the present disclosure. The blade spring <NUM> includes a spring head <NUM> on each end configured to mate with a corresponding base member. One or both spring heads <NUM> may optionally include a tool-receiving recess <NUM> for use in spring hinges in which the blade spring <NUM> is rotatable, as discussed below in relation to <FIG>. Each spring head <NUM> may also include a circumferential groove <NUM> configured to receive an O-ring to mate the blade spring <NUM> with a base member at each end. A flexible blade <NUM> having a thickness T and a width W extends longitudinally between the first and second spring heads <NUM>. The blade spring <NUM> is configured to facilitate bending in the direction the thickness extends and to resist or prevent bending in the direction in which the width extends.

<FIG> is a perspective view of a spring hinge <NUM> including two blade springs 454a, 454b similar to those of <FIG>. In the illustrated example, two blade springs 454a, 454b (e.g., medial/lateral) are assembled into spring hinge <NUM> such that the first blade spring 454a is attached to the base members <NUM> in a fixed position while the second blade spring 454b is pivotably connected to the base members <NUM>. As shown, the second blade spring 454b is oriented to transversely with respect to the first blade spring 454a and the direction of bending of the spring hinge <NUM>, thereby blocking the movement of the spring hinge. The second blade spring 454b may be rotated <NUM>° via the tool-receiving recess <NUM> to align the flexible blade <NUM> of the blade spring 454b with the first blade spring 454a to permit bending of the spring hinge <NUM>. It will be appreciated that in some embodiments, both blade springs 454a, 454b may be rotatable and in other embodiments, both blade springs may be permanently attached to or integrally formed with the base members <NUM> such that no rotation along the longitudinal axes of the blade springs is permitted.

<FIG> is a perspective view of a slotted spring <NUM> as may be used in a spring hinge in accordance with the present disclosure. The slotted spring <NUM> may be formed from a flexible elastic rod forming the spring body <NUM> which extends between spring heads <NUM>. A plurality of slots <NUM> are formed into the spring body <NUM> in a transverse direction from opposing sides. A channel <NUM> extends across the internal end of each slot <NUM> may increase the flexibility of the slotted spring <NUM> in the desired direction. In alternative embodiments, all or a majority of the slots <NUM> may be formed into the slotted spring <NUM> from the same side. The channels <NUM> may also optionally be omitted from one or both sides.

Different bending resistances between an anatomical joint plane of motion and orthogonal planes of the spring body <NUM> can be achieved by altering the particular profile features of the spring body. For example, the width of all or some of the slots <NUM> may be increased or reduced. Similarly, the diameter of all or some of the channels <NUM> may also be increased or reduced. The slotted spring <NUM> may be formed in one-step, such as by casting or injection molding, or may be formed with the spring body <NUM> as a solid block with the slots <NUM> and channels <NUM> later being cut or drilled into the spring body <NUM>.

<FIG> is a perspective view of a ribbon spring <NUM> as may be used in a spring hinge in accordance with the present disclosure. The ribbon spring <NUM> may be formed from a flexible ribbon <NUM> which extends between spring heads <NUM>. A plurality of slots <NUM> are formed in the ribbon <NUM> in a transverse direction from opposing sides. The shape of the ribbon <NUM>, may provide flexibility in one plane while resisting rotation in orthogonal planes and resisting axial compression.

Different bending resistances between an anatomical joint plane of motion and orthogonal planes of the flexible rod can be achieved by altering the particular profile features of the ribbon <NUM>. For example, the width of all or some of the slots <NUM> may be increased or reduced. Similarly, the thickness of the ribbon <NUM> may be increased to increase bending resistance or reduced to reduce bending resistance. The ribbon spring <NUM> may be formed in one-step, such as by casting or injection molding, or may be formed from an elongated ribbon which is folded to form the slots.

Both the slotted spring <NUM> of <FIG> and the ribbon spring <NUM> of <FIG> may be substituted for one or both of the blade spring <NUM> of <FIG>. In this regard, the springs <NUM>, <NUM> each may include a circumferential groove at each for receipt of an O-ring and/or a tool-receiving recess to facilitate rotation. The springs <NUM>, <NUM> may also be integrally formed with base members <NUM>.

<FIG> is a perspective view of a spring hinge <NUM> in accordance with the present disclosure. Spring hinge <NUM> includes base members <NUM> each having a bolt connection bore <NUM> for receiving a bolt <NUM> or other mechanism for attaching the base members <NUM> to an external fixation system. Each base member <NUM> may also have a spring connection hole <NUM> to receive a respective end of the coil spring <NUM> (or any other suitable spring type such as those disclosed herein).

The spring hinge <NUM> may be constructed such that the longitudinal axis <NUM> of the spring <NUM> is offset from the longitudinal axis <NUM> of each of the bolt connection bores <NUM>. Use of a spring <NUM> with an eccentric bolt (or other mounting rod) orientation may help prevent impingement of joint contacting surfaces (e.g., at the ankle) due to hinge misalignment (e.g., too anterior or too posterior) relative to the joint axis of rotation. The spring hinge <NUM> may be rotated within an external fixation system about the longitudinal axis <NUM> to achieve desired alignment (e.g., anterior/posterior position in sagittal plane). In this regard, the eccentric arrangment provides caster-like behavior to allow the spring hinge <NUM> to self-align as a joint is flexed. Once aligned, the spring hinge <NUM> can be locked in place. Any residual misalignment may be compensated for by transverse spring deflection.

<FIG> illustrate embodiments of spring hinges in accordance with the present disclosure having at least one hinge connector linking the base members at respective ends of one or more springs. A hinge connector may prevent or reduce shear movement in the anterior-posterior and medial-lateral directions and also prevent or reduce rotation about certain axes while permitting rotation or pivoting about a desired axis. Although primarily illustrated with coil springs, it should be appreciated that the concepts of <FIG> are equally applicable to other spring types such as those disclosed herein.

<FIG> is a perspective view of a single spring hinge <NUM> with a double link in accordance with the present disclosure. A coil spring <NUM> extends along a longitudinal axis <NUM> between two base members <NUM>. Each base member <NUM> includes two arms <NUM> extending generally toward the other base member. First and second hinge connectors <NUM> extend between respective pairs of arms <NUM> and are secured thereto with a pin joint <NUM>. In this regard, the first base member is secured to the second base member with two hinge connectors <NUM>. Specifically, a first hinge connector <NUM> extends between a first arm <NUM> of the first base member <NUM> and a second arm of the second base member, and a second hinge connector extends from a third arm of the first base member to a fourth arm of the second base member. The first and second hinge connectors are both disposed internally with respect to the arms <NUM>. That is, a first end of the first hinge connector and a first end of the second hinge connector are both disposed in between the first arm and third arm of the first base member. A second end of the first hinge connector and a second end of the second hinge connector are both disposed in between the second arm and the fourth arm of the second base member.

The hinge connectors <NUM> and associated pin joints <NUM> prevent rotation of the spring hinge <NUM> (e.g., between the two base members) about the longitudinal axis <NUM> and first transverse axis <NUM> but facilitate rotation of the spring hinge <NUM> about the second transverse axis <NUM>. The hinge connectors <NUM> also prevent translation in planes parallel to the transverse axes. The first and second base members <NUM> are configured to be secured to an external fixation system such that a longitudinal axis of the hinge connector (parallel to axis <NUM> in the illustrated embodiment) is parallel to a plane in which an anatomical joint encompassed by the external fixation system rotates. The spring hinge <NUM> is configured such that the axis of rotation <NUM>, as the spring hinge bends in the plane in which the first transverse axis <NUM> and longitudinal axis <NUM> are disposed, translates dynamically in conjunction with translation of an anatomical axis of rotation of the treated joint.

<FIG> is a perspective view of a single spring hinge <NUM> with a double link in accordance with the present disclosure. A coil spring <NUM> extends along a longitudinal axis <NUM> between two base members <NUM>. Each base member <NUM> includes an arm <NUM> extending generally toward the other base member. That is, the arm <NUM> of the lower base member <NUM> extends generally upward and the arm <NUM> of the upper base member <NUM> extends generally downward. First and second hinge connectors <NUM> extend between respective pairs of arms <NUM> and are secured thereto with a pin joint <NUM>. In this regard, the first base member is secured to the second base member with two hinge connectors <NUM>. Specifically, a first hinge connector <NUM> extends between a first arm of the first base member and a second arm of the second base member, and a second hinge connector <NUM> also extends between the first arm of the first base member and the second arm of the second base member. The first and second hinge connectors are both disposed externally with respect to the arms <NUM>. That is, a first end of the first hinge connector and a first end of the second hinge connector are disposed on opposing sides of the first arm. A second end of the first hinge connector and a second end of the second hinge connector are disposed on opposing sides of the second arm.

<FIG> is a perspective view of a single spring hinge <NUM> with a single link in accordance with the present disclosure. A coil spring <NUM> extends along a longitudinal axis <NUM> between two base members <NUM>. Each base member <NUM> includes an arm <NUM> extending generally toward the other base member. That is, the arm <NUM> of the lower base member <NUM> extends generally upward and the arm <NUM> of the upper base member <NUM> extends generally downward. A hinge connector <NUM> extends between the arms <NUM> and is secured thereto with a pin joint <NUM>. In this regard, the first base member is secured to the second base member with the hinge connector <NUM>. Although shown with the hinge connector disposed internally with respect to the arms <NUM>, that is between the arms <NUM> and the coil spring <NUM>, the hinge connector <NUM> could alternatively be disposed externally with respect to the arms.

The hinge connector <NUM> and associated pin joints <NUM> prevent rotation of the spring hinge <NUM> (e.g., between the two base members) about the longitudinal axis <NUM> and first transverse axis <NUM> but facilitate rotation of the spring hinge <NUM> about the second transverse axis <NUM>. The hinge connector <NUM> also prevents translation in planes parallel to the transverse axes. The first and second base members <NUM> are configured to be secured to an external fixation system such that a longitudinal axis of the hinge connector (parallel to axis <NUM> in the illustrated embodiment) is parallel to a plane in which an anatomical joint encompassed by the external fixation system rotates. The spring hinge <NUM> is configured such that the axis of rotation <NUM>, as the spring hinge bends in the plane in which the first transverse axis <NUM> and longitudinal axis <NUM> are disposed, translates dynamically in conjunction with translation of an anatomical axis of rotation of the treated joint.

<FIG> is a perspective view of double spring hinge with a central link in accordance with the present disclosure. This embodiment of a spring hinge may be advantageous for use in external fixation systems about an ankle, knee, or other anatomical joint. Coil springs <NUM> each extend parallel to a longitudinal axis <NUM> between two base members <NUM>. Each base member <NUM> includes an arm <NUM> extending generally toward the other base member. That is, the arm <NUM> of the lower base member <NUM> extends generally upward and the arm <NUM> of the upper base member <NUM> extends generally downward. A hinge connector <NUM> extends between the arms <NUM> and is secured thereto with a pin joint <NUM>. In this regard, the first base member is secured to the second base member with the hinge connector <NUM>. The hinge connector is disposed internally between two branches 959a, 959b of each respective arm <NUM> and passes between the pair of coil springs <NUM>.

<FIG> is a perspective view of double spring hinge <NUM> with a central link in accordance with the present disclosure, which is similar to the spring hinge <NUM> and uses flexible blades (similar to those of <FIG>) instead of coil springs. Flexible blades <NUM> each extend parallel to a longitudinal axis <NUM> between two base members <NUM>. Each base member <NUM> includes an arm <NUM> extending generally toward the other base member. That is, the arm <NUM> of the lower base member <NUM> extends generally upward and the arm <NUM> of the upper base member <NUM> extends generally downward. A hinge connector <NUM> extends between the arms <NUM> and is secured thereto with a pin joint <NUM>. In this regard, the first base member is secured to the second base member with the hinge connector <NUM>. The hinge connector is disposed internally between two branches 1059a, 1059b of each respective arm <NUM> and passes between the pair of flexible blades <NUM>.

<FIG> illustrate perspective views of a double spring hinge <NUM> with a central link in an unexpanded and a flexed configuration, respectively, in accordance with the present disclosure. Coil springs <NUM> each extend parallel to a longitudinal axis <NUM> between two base members <NUM>. Each base member <NUM> includes two arms <NUM> extending generally toward the other base member. That is, the arms <NUM> of the lower base member <NUM> extend generally upward and the arms <NUM> of the upper base member <NUM> extend generally downward. A hinge connector <NUM> extends from first and third arms of the first base member to second and fourth arms of the second base member and is secured with pin joints <NUM>. In this regard, the first base member is secured to the second base member with the hinge connector <NUM>. The hinge connector is disposed internally between the respective arms <NUM> of each base member and passes between the pair of coil springs <NUM>.

The hinge connector <NUM> and associated pin joints <NUM> prevent rotation of the spring hinge <NUM> (e.g., between the two base members) about the longitudinal axis <NUM> and first transverse axis <NUM> but facilitate rotation of the spring hinge <NUM> about the second transverse axis <NUM>. The hinge connector <NUM> also prevents translation in planes parallel to the transverse axes. The first and second base members <NUM> are configured to be secured to an external fixation system such that a longitudinal axis of the hinge connector (extending between the pin joints) is parallel to a plane in which an anatomical joint encompassed by the external fixation system rotates. The spring hinge <NUM> is configured such that the axis of rotation <NUM>, as the spring hinge bends in the plane in which the first transverse axis <NUM> and longitudinal axis <NUM> are disposed, translates dynamically in conjunction with translation of an anatomical axis of rotation of the treated joint.

<FIG> is an exploded view of the spring hinge of <FIG>.

<FIG> is a side view of an external fixation system including the spring hinge of <FIG> in an ankle fixation application. An external fixation system <NUM> includes at least two external fixators, including external fixation ring <NUM> and external fixator <NUM>. A plurality of pins <NUM> extend from the external fixators into respective bones around the ankle. A first spring hinge <NUM> is disposed between the external fixators to facilitate rotation of the ankle joint within the plane <NUM> while preventing other undesirable movement of the ankle. A second spring hinge <NUM> (not shown) may be disposed on an opposing side of the external fixation system <NUM>.

As the foot of the patient is rotated downward or upward about the ankle, the anatomical axis of the ankle will translate. The spring hinges <NUM> may similarly permit the first and second external fixators <NUM>, <NUM> to rotate with a translating axis of rotation.

<FIG> is a side view of an external fixation system including the spring hinge of <FIG> in an elbow fixation application. An external fixation system <NUM> includes at least two external fixators, including external fixator <NUM> and external fixator <NUM>. A plurality of pins <NUM> extend from the external fixators into respective bones (e.g., ulna, radius, and humerus) around the elbow. Spring hinges <NUM> are disposed between the external fixators to facilitate rotation of the elbow joint within the plane <NUM> while preventing other undesirable movement of the elbow.

<FIG> is a side view of an external fixation system including the spring hinge of <FIG> in a knee fixation application. An external fixation system <NUM> includes at least two external fixators, including external fixator <NUM> and external fixator <NUM>. A plurality of pins <NUM> extend from the external fixators into respective bones (e.g., femur, fibula, and tibia) around the knee. Spring hinges <NUM> are disposed between the external fixators to facilitate rotation of the knee joint within the plane <NUM> while preventing other undesirable movement of the knee.

As will be understood by those skilled in the art who have the benefit of the instant disclosure, other equivalent or alternative devices, methods, and systems for orthopedic hinges can be envisioned without departing from the description contained herein. Accordingly, the manner of carrying out the disclosure as shown and described is to be construed as illustrative only.

Persons skilled in the art may make various changes in the shape, size, number, and/or arrangement of parts without departing from the scope of the instant disclosure. For example, the position and number of spring hinges may be varied. In some embodiments, the size of a device and/or system may be scaled up (e.g., to be used for adult subjects) or down (e.g., to be used for juvenile subjects) to suit the needs and/or desires of a practitioner. Where the verb "may" appears, it is intended to convey an optional and/or permissive condition, but its use is not intended to suggest any lack of operability unless otherwise indicated. Where open terms such as "having" or "comprising" are used, one of ordinary skill in the art having the benefit of the instant disclosure will appreciate that the disclosed features or steps optionally may be combined with additional features or steps. Such option may not be exercised and, indeed, in some embodiments, disclosed devices, systems, and/or methods may exclude any other features or steps beyond those disclosed herein.

In embodiments of any of the compositions and methods provided herein, "comprising" may be replaced with "consisting essentially of" or "consisting of". As used herein, the phrase "consisting essentially of" requires the specified integer(s) or steps as well as those that do not materially affect the character or function of the claimed invention. As used herein, the term "consisting" is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), property(ies), method/process steps or limitation(s)) only.

Claim 1:
An orthopedic spring hinge (<NUM>) connectable between external fixators, comprising:
a first base member;
a second base member; and
a flexible spring (<NUM>) extending from the first base member to the second base member along a longitudinal axis, the flexible spring (<NUM>) having a length in a direction of the longitudinal axis and a width less than the length,
characterized in that,
the flexible spring (<NUM>) has a thickness less than the width, the flexible spring (<NUM>) comprising a plurality of rigid hinge members (<NUM>, <NUM>) each extending parallel to the width of the flexible spring, the plurality of rigid hinge members (<NUM>, <NUM>) being embedded in an elastomer (<NUM>);
wherein the flexible spring (<NUM>) is configured to prevent bending of the spring hinge (<NUM>) within a first plane in which the length and width of the flexible spring (<NUM>) extend, and to permit bending of the spring hinge (<NUM>) within a second plane in which the length and thickness of the flexible spring (<NUM>) extend.