Patent Description:
The disclosure relates to a telescopic strut for an external fixator, especially for use with an external ring fixator.

A plurality of compression-distraction apparatus has been designed and improved by Ilizarov and his group using two external rings to be placed around the limb to be fixed. There are usually at least two such rings, one proximal and one distal ring, which are connected with a plurality of struts or rods. Preferably, these struts are linked to the rings in a way that the attachment points can be pivoted and the length of the strut can be varied to enable adjustment of the external fixation rings.

It may be desirable for such telescopic struts to have the ability to gradually change length during the correction phase, and to also be able to rapidly change length during the assembly/implantation phase. This rapid length change may reduce the time necessary for each strut to be set to the initial length desired for connection to the fixator rings. However, it is important that the rapid length adjustment mode is not unintentionally activated during the correction phase in which strut lengths are to be gradually adjusted. Thus, it would be preferable for the struts to have mechanisms to change between a rapid length adjustment mode and a gradual length adjustment mode quickly and reliably. Document <CIT> discloses a ratcheting strut comprising: (a) a ratchet box including a through passage; (b) a first tube sized to extend at least partially through the passage, the first tube including teeth that engage corresponding teeth of the ratchet box; (c) a second tube mounted to the ratchet box in parallel with the first tube, the second tube operatively coupled to a second fixation adapter; and, (d) a threaded rod operatively coupled to a nut and a first fixation adapter, the threaded rod repositionably mounted to the first tube, where the nut is operatively coupled and repositionable with respect to the first tube.

According to an aspect of the disclosure, an adjustable length strut is for use in an external fixation system. The strut includes a generally hollow outer tube extending between a first end and a second end. The strut also includes an inner tube sized to fit within and translate relative to the outer tube. The inner tube extends in a length direction and has a circumferential direction. A plurality of texturized surfaces extends in the length direction of the inner tube, each of the plurality of texturized surfaces of the inner tube being spaced apart from each other in the circumferential direction of the inner tube. Each circumferentially adjacent pair of texturized surfaces of the inner tube is separated by a non-texturized surface. The strut also includes a first adjustment knob coupled to the second end of the outer tube. The first adjustment knob has an interior surface defining a channel, the interior surface extending in a length direction and having a circumferential direction. The inner tube passes through the channel. The interior surface has a plurality of texturized surfaces extending in the length direction of the interior surface. Each of the plurality of texturized surfaces of the interior surface is spaced apart from each other in the circumferential direction of the interior surface and each circumferentially adjacent pair of texturized surfaces of the interior surface is separated by a non-texturized surface. The first adjustment knob is rotatable relative to the outer tube and the inner tube between a locked condition and an unlocked condition. In the locked condition, the plurality of texturized surfaces of the inner tube engages the plurality of texturized surfaces of the interior surface of the first adjustment knob to prevent translation of the inner tube relative to the outer tube. In the unlocked condition, the plurality of texturized surfaces of the inner tube aligns with the plurality of non-texturized surfaces of the interior surface of the first adjustment knob to allow translation of the inner tube relative to the outer tube.

The strut may include a threaded rod, the inner tube may be generally hollow, and the threaded rod is sized to fit within the inner tube. The threaded rod may pass through the first end of the outer tube. The strut may include a first joint coupled to an end of the threaded rod, and a second joint coupled to an end of the inner tube, the first joint configured to couple to a first fixation ring of the external fixation system and the second joint configured to couple to a second fixation ring of the external fixation system. The strut may include a second adjustment knob coupled to the first end of the outer tube so that the second adjustment knob is translationally fixed to the outer tube. The threaded rod may pass through an aperture of the second adjustment knob. The second adjustment knob may include internal threading at the aperture configured to engage external threading of the threaded rod, so that rotation of the second adjustment knob relative to the threaded rod causes the threaded rod to translate into or out of the outer tube. The outer tube may include an outer tube slot, and the threaded rod may include a protrusion extending through the outer tube slot, the protrusion being rotatable relative to the threaded rod. An outer surface of the second end of the outer tube may include a circumferential recess. The first adjustment knob may include a first pin passing through the first adjustment knob, the first pin extending transverse the length direction of the interior surface of the first adjustment knob and being at least partially seated in the circumferential recess. The first pin may prevent translational movement of the first adjustment knob relative to the outer tube. The first adjustment knob may include a second pin passing through the first adjustment knob, the second pin extending parallel to the first pin, the channel of the first adjustment knob being positioned between the first pin and the second pin, the second pin being at least partially seated in the circumferential recess.

The strut may include a quick-release pin and spring both at least partially received within the first adjustment knob, the quick release pin including a shoulder extending toward the second end the outer tube. The second end of the outer tube may include a first detent circumferentially spaced from a second detent. When the shoulder of the quick-release pin is received within the first detent, the first adjustment knob may be in the locked condition, and when the shoulder of the quick-release pin is received within the second detent, the first adjustment knob may be in the unlocked condition. The spring may bias the shoulder into the first detent when the first adjustment knob is in the locked condition, and the spring may bias the shoulder into the second detent when the first adjustment knob is in the unlocked condition, the spring bias tending to prevent rotation of the first adjustment knob relative to the outer tube in the absence of applied forces. The second end of the outer tube may include an arcuate recess positioned generally diametrically opposed to the first detent and the second detent. The strut may include a rotation limiting pin at least partially received within the first adjustment knob, a terminal end of the rotation limiting pin extending into the arcuate recess. The arcuate recess may be bounded by a first limiting surface and a second limiting surface, and contact between the rotation limiting pin and the first and second limiting surfaces may define the extent to which the first adjustment knob is capable of rotation relative to the outer tube. When the terminal end of the rotation limiting pin is in contact with the first limiting surface, the shoulder of the quick-release pin may be received within the first detent and the first adjustment knob is in the locked condition, and when the terminal end of the rotation limiting pin is in contact with the second limiting surface, the shoulder of the quick-release pin may be received within the second detent and the first adjustment knob is in the unlocked condition. The plurality of texturized surfaces of the inner tube may include threads extending in the circumferential direction, and at least one of the threads of the inner tube may include a guide thread extending therefrom. The guide thread may be configured to guide the threads of the inner tube into engagement with corresponding threads of the plurality of texturized surfaces of the interior surface of the first adjustment knob as the first adjustment knob is rotated from the unlocked condition to the locked condition.

Referring to <FIG> there is shown a perspective view of a telescopic strut according to the prior art generally denoted as <NUM>. The telescopic strut comprises two free ends <NUM> and <NUM> being attachment points for connecting the rod with two external rings to be placed around the limb to be fixed. The attachment points <NUM> and <NUM> according to this embodiment comprise cylindrical knobs, but this entirely depends on the kind of fixation element for which the rod is used.

<FIG> shows the main components of the telescopic strut. There is an outer tube <NUM> in which the threaded rod <NUM> is partially located. The opposite thread <NUM> is located within the sleeve <NUM> and is better seen in <FIG> as well as <FIG> and will be described below. In the illustrated embodiment sleeve <NUM> comprises a bayonet groove <NUM> for a quick change between the desired quick length change mode and the fine adjustment mode. The sleeve <NUM> can be switched between two rotational positions for this, i.e. to lock and unlock the axial direction. Therefore the groove <NUM> has a U-form, the ends of the groove <NUM> defining the two positions with the help of a bolt <NUM> provided within the groove <NUM>. The ends of the groove <NUM> are oriented in axial direction of the telescopic strut. The ends show in the same direction, towards the spring <NUM> as can be seen in the exploded view of <FIG>, to allow displacement of the bolt <NUM> against the force of said spring <NUM>.

A security mechanism, to avoid unintentional switching, is realized by an additional nut <NUM>, blocking the bolt <NUM> in one of the free ends of groove <NUM>.

<FIG> shows a view in cross-section of the telescopic strut according to <FIG>. Sleeve <NUM> can be pushed against action of spring <NUM> provided on the outer tube <NUM> and which spring is biased with help of nut <NUM>. Then the sleeve <NUM> is turned around <NUM>° and is arrested within the other free end of the groove <NUM>. In this embodiment, it is preferred that this position is fixed through nut <NUM>.

The turning angle of <NUM> degrees is defined in view of the way the quick length adjustment mode is working. This can be seen in <FIG> being a representation of a cross section of the rod along line <NUM>-<NUM> in <FIG>. It can be seen from <FIG> that the sleeve <NUM> has a non-cylindrical inner bore. The bore can be e.g. elliptical. The shorter diameter of the bore is sufficient to accommodate the outer diameter of the foremost portion 25a of outer tube <NUM>, which is cylindrical. Foremost portion 25a comprises on both sides a plurality of preferably, four holes <NUM> to accommodate one ball <NUM> each. Of course, it is also possible to provide only two balls on each side or five or more. Three or four balls have been proven to be sufficient without lengthening the sleeve <NUM> too much.

The inner diameter of outer tube <NUM> is greater than the outer thread portion of the rod <NUM> which is cylindrical. Therefore, the rod <NUM> can be pushed into the outer tube <NUM>, when the bolt <NUM> is in a position which allows the sleeve <NUM> to be oriented as shown in <FIG>. Then the balls <NUM> can freely move against the inner wall of sleeve <NUM> and the rod <NUM> can be axially pushed. For that the sum of the outer diameter of the rod <NUM> and twice the diameter of the balls <NUM> is less or nearly equal to the inner diameter of the sleeve <NUM>.

It is avoided that the threaded rod <NUM> can be separated from the outer tube <NUM> through an abutment screw <NUM> which is screwed into a corresponding thread within the threaded rod <NUM> and which can abut on a corresponding shoulder within the tube <NUM> as shown in <FIG>.

By turning the sleeve <NUM> around the bolt <NUM>, i.e. by <NUM>°, the balls <NUM> will be moved because of the elliptic inner shape within the sleeve <NUM>. In this way the balls <NUM> are pushed through holes <NUM> towards the grooves of the thread <NUM> for interlocking, i.e. connecting the thread with the outer tube <NUM>, because the balls <NUM> stand within both parts and leave no room to allow a direct axial movement of the threaded rod <NUM>.

In this position the threaded rod <NUM> still can be moved axially through rotational movement of tube <NUM> being directly coupled via bolt <NUM> to sleeve <NUM> against the threaded rod <NUM> which can rotate in view of the balls <NUM> pressed in its threads. This allows the fine adjustment.

Thus the elements allow for a quick change between free axial adjustments of the telescopic strut, if the balls <NUM> do not engage the threaded rod <NUM>. If the balls do engage rod <NUM> then a fine adjustment through rotation of the outer tube <NUM> / rod <NUM> is allowed. The balls <NUM> are engaging the one or subsequent grooves of the threaded rod <NUM>, e.g. depending on the pitch of the rod. The pitch angle of the thread can be chosen e.g. between <NUM> and <NUM> degrees and especially between <NUM> and <NUM> degrees.

It is clear that this fine adjustment is only possible, if at least one free end <NUM> or <NUM> of the telescopic strut can be rotated while fixed within an external fixator ring.

The prior art quick-release or quick-change mechanism, described in <CIT>, which allows for easily adjusting between fine and gross length adjustments of a telescopic strut, is a suitable design for the intended use. However, one potential disadvantage of the prior art quick-release mechanism described above is that it may be relatively expensive to manufacture. Other attempts have been made to create alternative quick-release mechanisms. For example, <CIT> describes a quick-adjust mechanism that allows for rapid strut length adjustment or gradual strut length adjustment, but the gradual strut length adjustment relies on a compression member to press an outer sleeve against an inner sleeve. Relying on compression to maintain strut components engaged for gradual adjustment may be problematic, as such compression members are apt to fail, particularly when under load. If that compression member fails, the strut may unintentionally switch to a rapid adjustment configuration where the strut is free to change lengths, which could cause injury to a patient. Still further, <CIT> describes a strut with a quick-release mechanism that can transition between a rapid adjustment mode and a gradual adjustment mode by clamping threaded fingers of a collet onto an externally threaded component to provide engagement for gradual adjustment, and a rapid adjustment mode by allowing the collet to disengage the externally threaded component. However, this type of system may have drawbacks as well, and may also be likely to unintentionally transition from the gradual adjustment mode to the rapid adjustment mode when under a load that causes the threads of the collet member to disengage from the externally threaded member. The quick release mechanisms described below achieve a highly stable construct that is unlikely to unintentionally transition from the gradual adjustment mode to the rapid adjustment mode, while also being relatively inexpensive to manufacture compared to prior art systems.

<FIG> illustrates a perspective view of a telescopic strut <NUM> for use with an external fixation system, for example one including two fixation rings intended to be fixed to a bone on opposite sides of a bone deformity. As explained above, an external fixation system will typically include a plurality of the struts <NUM>, such as six struts, that couple the two rings together. Generally, strut <NUM> may include a joint <NUM> on one end of the strut <NUM>, and a joint <NUM> on an opposite end of the strut <NUM>. Joint <NUM> is illustrated as a universal joint with an opening to allow for a bolt to connect joint <NUM> to a first fixator ring through a hole of the first fixator ring, and joint <NUM> is similarly illustrated as a universal joint with an opening (not visible in <FIG>) to allow for a bolt to connect joint <NUM> to a second fixator ring through a hole of the second fixator ring. However, it should be understood that the joints <NUM>, <NUM> may take other forms, including constrained hinge joints, and the joints need not be the same type of joint as each other. Also, the mechanism for attaching the strut <NUM> to the fixator rings may be other than the bolt connection described above.

Still referring to <FIG>, strut <NUM> may additionally include a threaded rod <NUM>, an outer tube <NUM>, an inner tube <NUM>, a fine adjustment knob <NUM>, and a gross adjustment knob <NUM>. Although the term "knob" is used, these components may be generally referred to as actuators, and it should be understood that other designs may be suitable for use as an adjustment mechanism other than a "knob," and the term "knob" includes such alternative designs unless specifically noted otherwise. The strut <NUM> illustrated in <FIG> may be thought of as a "double" telescoping strut, as there are two pairs of components that are capable of telescoping relative to each other. However, the concepts described herein may be generally applicable to "single" telescoping struts, and the invention is not limited to double telescoping struts.

<FIG> are perspective views of inner tube <NUM>. In the illustrated embodiment, the inner tube <NUM> extends from a first end that includes a portion 104a of joint <NUM>, to a second end. It should be understood that joint portion 104a may take other forms than that illustrated, but in the illustrated example, joint portion 140a may be a yolk that includes two extensions with apertures configured to couple to a pin/bearing, which itself may be configured to couple to another yolk to complete the universal joint. The inner tube <NUM> may be generally hollow, and may be configured to receive threaded rod <NUM> therein, at least in certain conditions of the strut <NUM>.

<FIG> is a side view of inner tube <NUM>, and <FIG> is a cross-section of the inner tube <NUM> taken along section line 6D-6D of <FIG>. Referring to <FIG>, inner tube <NUM> may include a slot <NUM> that extends to and through one end of the inner tube <NUM> (the end opposite joint portion 140a), and to a second closed end a spaced distance from joint portion 104a. In other words, a length of inner tube <NUM> near joint portion 104a is fully circumferentially continuous and uninterrupted by slot <NUM>, with the slot <NUM> extending the remaining length of the inner tube <NUM> including at the terminal end of the inner tube <NUM> opposite the joint portion 104a. As best seen in <FIG>, the terminal end of the slot <NUM> nearer joint portion 104a may be generally rounded, and the terminal end of the slot <NUM> farthest away from the joint portion 104a may have a slightly narrowed width portion <NUM>. As is described in greater detail below, this narrowed width portion <NUM> may be sized to allow certain components sliding within slot <NUM> to pass beyond the narrowed width portion <NUM>, while restricting other components sliding within slot <NUM> from passing beyond the narrowed width portion <NUM>.

<FIG> is a top view of inner tube <NUM>, viewed so that the joint portion 104a is farthest away from the viewer. Referring to <FIG> and <FIG>, the tubular portion of inner tube <NUM> may have a generally rectangular or square shape, with four flat and/or unthreaded (or un-texturized) surfaces <NUM> (one of which defines slot <NUM>). At least one of the flat surfaces <NUM> may include indicia <NUM> that may be used to help indicate the length of the strut <NUM>. In the illustrated embodiment, indicia <NUM> take the form of hash marks with numbers printed or otherwise provided thereon - although it should be understood that other types of indicia <NUM> may be suitable. Each of the four flat surfaces <NUM> may couple or transition to each other by flat or rounded corners <NUM>. Each of the corners <NUM> may include texturized surfaces extending part of or the entire length of the inner tube <NUM>, excluding the j oint portion 104a. The texturized surfaces may be threads, serrations, ridges, or other similar features intended to engage with corresponding texturized surfaces 182a of the gross adjustment knob <NUM>, as described in greater detail below. It should be understood that, although the term "flat" is used in connection with surfaces <NUM> and corners <NUM>, these surfaces need not be perfectly flat and may include some level of contouring in the circumferential direction.

<FIG> is a perspective view of outer tube <NUM>. In the illustrated embodiment, the outer tube <NUM> extends from a first end (to the right in the view of <FIG>) configured to couple to inner tube <NUM> via gross adjustment knob <NUM>, to a second end (to the left in the view of <FIG>) configured to couple to the threaded rod <NUM> via fine adjustment knob <NUM>. The outer tube <NUM> may be generally hollow, and may be configured to receive portions of both the threaded rod <NUM> and the inner tube <NUM> therein, at least in certain conditions of the strut <NUM>.

<FIG> are side views of outer tube <NUM>, and <FIG> is a cross-section of outer tube <NUM> taken along section line 7D-7D of <FIG>. Referring generally to <FIG>, outer tube <NUM> may include a main body <NUM> that is generally cylindrical. As best seen in <FIG> and <FIG>, the main body <NUM> may define a slot <NUM> extending in the longitudinal direction of the main body <NUM>, the slot <NUM> being closed at each longitudinal end. The portion of main body <NUM> adjacent the slot <NUM> may be generally flat, with the remainder of main body <NUM> being generally cylindrical or circular. As described in greater detail below, the slot <NUM> may be sized and shaped to receive a portion of a length indicator <NUM> therethrough. The flat portion of main body <NUM> may provide a surface against which part of length indicator <NUM>- may slide and/or may help limit the length indicator <NUM> from protruding beyond the main body, which may help reduce the likelihood the length indicator <NUM> may get caught on some external structure like a patient's clothes, bed sheets, etc. The main body <NUM> may include indicia <NUM>, which may be in the form of hash marks and numbers printed or otherwise provided with the hash marks, to help indicate a length of the strut <NUM> in combination with the length indicator <NUM>. However, as with indicia <NUM>, indicia <NUM> may take other forms than hash marks with printed numbers.

One end of the main body <NUM> (to the left in the view of <FIG>) may include a collar <NUM>. The collar <NUM> may be integral with the main body <NUM>, or be formed separately and attached thereto. As best shown in <FIG>, the collar <NUM> may be generally cylindrical or circular, with a flat area that aligns with the flat portion of main body <NUM> adjacent slot <NUM>. A plurality of flexible extensions <NUM> may extend from the collar <NUM> in a direction away from the main body <NUM>. In the illustrated embodiment, four flexible extensions <NUM> are provided. The flexibility of the extension <NUM> may be achieved, for example, by forming them with relatively thin walls (e.g. compared to the walls of the main body <NUM>) and/or by providing slots between adjacent ones of the extensions <NUM>. In other embodiments, more or fewer than four flexible extensions <NUM> may be provided. Each extension <NUM> preferably ends in a protrusion or lip <NUM> extending radially outward from the center longitudinal axis of the outer tube <NUM>. As is explained in greater detail, the lips <NUM> may help secure the outer tube <NUM> to the fine adjustment knob <NUM>.

The extensions <NUM>, in combination, may form a generally cylindrical surface that is interrupted by longitudinal slots between adjacent extensions <NUM>. This is best shown in <FIG>, which is an end view of the outer tube <NUM> with the extensions <NUM> being closest to the viewer in <FIG> is a cross-section of outer tube <NUM> taken along the section line 7F-7F of <FIG>. A base area may be positioned between the collar <NUM> and the beginning of each of the extensions <NUM>. That base may be generally cylindrical or circular, with circumferentially spaced flats <NUM>, best illustrated in <FIG>. Each flat <NUM> may be positioned on the base generally aligned with a slot between circumferentially adjacent extensions <NUM>. As is explained in greater detail below, these flats <NUM> provide for discrete rotational positions between the outer tube <NUM> and the fine adjustment knob <NUM> during gradual adjustment of the length of the strut <NUM>.

The other end of the main body <NUM> (to the right in the view of <FIG>) may include a number of features for use in engagement with gross adjustment knob <NUM>. <FIG> illustrates an end view of outer tube <NUM>, opposite the end shown in <FIG>. <FIG> is a perspective view of the end of outer tube <NUM> illustrated in <FIG>. Referring mainly to <FIG>, this end of main body <NUM> may include an aperture <NUM> extending through the wall of the main body <NUM>, the aperture <NUM> being longitudinally aligned with slot <NUM>. This aperture <NUM> may be configured to receive a pin <NUM> that also passes through slot <NUM> of inner tube <NUM>, helping to ensure that inner tube <NUM> and outer tube <NUM> remain rotationally fixed to one another. Pin <NUM> may have a width or diameter that is smaller than the width of slot <NUM>, but larger than the narrowed width portion <NUM> of slot <NUM>, such that the pin <NUM> also prevents the inner tube <NUM> from separating or pulling out of the outer tube <NUM>.

This end of the body may also include a circumferential groove or recess <NUM> that may receive a pin, bearing, o-ring, gasket, or other structure, which is also received within a portion of gross adjustment knob <NUM>, to allow for at least some rotation of gross adjustment knob <NUM> relative to outer tube <NUM>, while preventing relative axial or translational movement between the gross adjustment knob <NUM> and outer tube <NUM>. A first detent <NUM> and a second detent <NUM> may be provided in the terminal end of outer tube <NUM>, for example at about <NUM> degrees apart along the circumference of the outer tube <NUM>. As described in greater detail below, detents <NUM>, <NUM> may act to receive a portion (e.g. a shoulder 186c) of a quick-release pin <NUM> therein to lock the gross adjustment knob <NUM> in a locked or unlocked position. A recessed area <NUM> may be provided in the terminal end of outer tube <NUM>, and recessed area <NUM> may be generally diametrically opposed to the position of the detents <NUM>, <NUM>. As explained in greater detail below, a rotation limiting pin <NUM> of the gross adjustment knob <NUM> may be received within the recessed area <NUM>. The recessed area <NUM> may extend along about <NUM> degrees of the circumference of the outer tube <NUM>. As explained in greater detail below, this configuration may allow for the gross adjustment knob <NUM> to have a total available amount of rotation of about <NUM> degrees relative to the outer tube <NUM>.

Referring back to <FIG>, the threaded rod <NUM> may have a first end fixed to a portion of joint <NUM> (toward the top of the view of <FIG>). The majority of threaded rod <NUM> may be a solid generally cylindrical member with external threading that interacts with corresponding internal threading of fine adjustment knob <NUM>, described in greater detail below. The terminal end of threaded rod <NUM>, opposite the side of joint <NUM>, may exclude threading and have a collar member to which length indicator <NUM> is coupled. The length indicator <NUM> is preferably axially fixed with respect to threaded rod <NUM>, but rotationally free. The length indicator <NUM> may include a relatively narrow portion that is sized and shaped to protrude through both slot <NUM> in outer tube <NUM> and slot <NUM> in inner tube <NUM>. The end of length indicator <NUM> may be wider than the width of the slot <NUM>, and include extensions that are parallel to the hash marks of indicia <NUM>, to allow a user to readily identify what hash marks or other indicia <NUM> that the length indicator <NUM> is pointing. The relatively narrow portion of length indicator <NUM> may be narrower than the narrowed width portion <NUM> of slot <NUM> of inner tube <NUM>, so that the length indicator <NUM> may pass beyond the end of slot <NUM> in certain elongated conditions of strut <NUM>. Collar mechanisms to allow for axial fixation but rotational freedom of length indicator <NUM> are shown in more detail, for example, in <CIT>. As should be understood, as the threaded rod <NUM> rotates and telescopes into or out of the outer tube <NUM> (and/or into or out of the inner tube <NUM>), the length indicator <NUM> is capable of sliding along the slots <NUM>, <NUM> without rotation, even though the threaded rod <NUM> is rotating.

<FIG> illustrated various views of strut <NUM> in an assembled condition, focusing on the assembly of the gradual connection knob <NUM> to the threaded rod <NUM> and outer tube <NUM>. In particular, <FIG> shows a cross-section of the gradual correction knob <NUM> in an engaged or locked state, and <FIG> shows the same cross-section in a disengaged or unlocked state. Generally, gradual correction knob <NUM> may include a thumb knob <NUM> and a correction wheel <NUM>, although the terms "knob" and "wheel" do not necessarily require any specific structure related to a knob or a wheel.

The correction wheel <NUM> may include an aperture, for example along a central longitudinal axis, defined by an internally threaded structure of the correction wheel <NUM>. The internal threads may be complementary to and engage the external threads of the threaded rod <NUM> that extends therethrough, so that the correction wheel <NUM> is only able to translate relative to threaded rod <NUM> via relative rotation between the threaded rod <NUM> and the correction wheel <NUM>. The correction wheel <NUM> may be coupled to the thumb knob <NUM> by a plurality of pins <NUM> (e.g. two, three, four etc.). In the illustrated embodiment, the correction wheel <NUM> and thumb knob <NUM> each include channels therein that align with one another (e.g. four channels spaced circumferentially), the channels each configured to receive at least a portion of the pins <NUM> so that rotation of the thumb knob <NUM> causes rotation of the correction wheel <NUM>. In the illustrated embodiment, the thumb knob <NUM> may include bumps, ridges, or other textures to provide easier gripping of the thumb knob <NUM>.

The correction wheel <NUM> may include an internal recessed shoulder sized and shaped to receive the protrusions or lips <NUM> of the flexible extensions <NUM> of the outer tube <NUM>. One end of the thumb knob <NUM> may have an opening sized and shaped to receive the flexible extensions <NUM> of the outer tube <NUM> therethrough. With this configuration, when assembled, the flexible extensions pas through the center of the thumb knob <NUM> and into an interior area of the correction wheel <NUM>, with the protrusions or lips <NUM> of the flexible extensions <NUM> extending into the complementary recessed shoulder of the correction wheel <NUM>. This configuration helps ensure that, as the correction wheel <NUM> rotates relative to (and thus translates relative to) the threaded rod <NUM>, the outer tube <NUM> is pulled or pushed along with the gradual correction knob <NUM> as it translates along the threaded rod <NUM>. It should be understood that the external threads of the threaded rod <NUM> do not intermesh with any internal threading of the outer tube <NUM>, allowing for the outer tube <NUM> to translate along the threaded rod <NUM> without the outer tube <NUM> rotating.

The distal end of the thumb knob <NUM> may include flat areas positioned in a complementary way to the flats <NUM> adjacent the collar <NUM> of the outer tube <NUM>. For example, if the outer tube <NUM> includes four flats <NUM> arranged in a square pattern, the distal end of the thumb knob <NUM> may include a corresponding four flats in a square pattern. However, it should be understood that different numbers of corresponding flats may instead be provided. With this configuration, when the gradual correction knob <NUM> is in the locked or engaged condition shown in <FIG>, the flats <NUM> of the outer tube <NUM> engage the corresponding flats of the thumb knob <NUM>, restricting the ability of the thumb knob <NUM> (and thus the correction wheel <NUM>) from rotating relative to the outer tube <NUM>. This locked or engaged position may be the default position. This default position may be maintained by a biasing element, for example spring <NUM>, which may have a first end pressing against the thumb wheel <NUM> and a second end pressing against the correction wheel <NUM>. In order to transition the gradual correction knob <NUM> to the disengaged or unlocked condition, a user may pull the thumb wheel <NUM> proximally toward the correction wheel <NUM> to compress the spring <NUM>. With the spring <NUM> compressed, as shown in <FIG>, the flats of the distal end of the thumb wheel <NUM> clear the corresponding flats <NUM> on the outer tube <NUM>, freeing the thumb wheel <NUM> (and thus the correction wheel <NUM>) for rotation relative to the outer tube <NUM> and relative to the threaded rod <NUM>. As the thumb wheel <NUM> is rotated, the pins <NUM> transfer force to the correction wheel <NUM> to cause the correction wheel <NUM> to rotate, resulting in translation of the gradual correction knob <NUM> (and thus the outer tube <NUM>) up or down the threaded rod <NUM>. As rotation continues, the flats <NUM> of the outer tube <NUM> will again soon align with corresponding flats of the distal end of the thumb wheel <NUM>, with the force of spring <NUM> pressing the thumb wheel <NUM> back into engagement with the flats, automatically returning the gradual correction knob <NUM> to the locked or engaged condition shown in <FIG>. This allows for discrete, gradual, and incremental adjustment of the length of strut <NUM> via discrete "clicks," with each "click" representing a quarter turn of the gradual correction knob <NUM>. However, it should be understood that if more flats, e.g. eight flats in an octagon pattern, are provided, each "click" would represent a smaller increment of a full turn, and vice versa.

Although not shown in <FIG>, an additional gear mechanism <NUM> may be provided below the thumb wheel <NUM>, as shown in <FIG>. This gear <NUM> may be adapted to engage a complementary gear of a motorized adjustment module (not shown) that may be snapped onto the strut. When the motorized adjustment module is snapped onto the strut, a collar may be positioned between the proximal end of the gear <NUM> and the distal end of the thumb knob <NUM>, causing the spring <NUM> to remain compressed while the motorized adjustment module is coupled to the strut <NUM>. This allows for infinitesimally small length adjustment by rotating gear <NUM> via the complementary gear of the motorized adjustment module as long as the motorized adjustment module is coupled to the strut.

<FIG> are various views of gross adjustment knob <NUM> that may, along with other components, function as a "quick-release" or "quick-change" mechanism to allow for rapid adjustment of the length of strut <NUM>, typically during coupling of the struts <NUM> to the rings of the external fixation frame. The use of this quick-release mechanism is described in greater detail below following the description of the structure of the components that form, at least in part, this quick-release mechanism.

The gross adjustment knob <NUM> may include bumps, ridges, or other textures to provide easier gripping of the gross adjustment knob <NUM>. The gross adjustment knob <NUM> may define an aperture extending therethrough, the aperture defining a channel that is generally cylindrical, with certain exceptions noted below. The gross adjustment knob <NUM> may define a plurality of threaded areas 182a extending along part of the length of the channel. In the illustrated embodiment, there are four threaded areas 182a, each threaded area 182a being circumferentially spaced from an adjacent threaded area 182a by a non-threaded area 182b. Although four threaded areas 182a and four non-threaded areas 182b are illustrated, it should be understood that more or fewer threaded areas 182a and non-threaded areas 182b may be provided, primarily depending on the number of threaded corners <NUM> provided on the inner tube <NUM>. In other words, the number of threaded corners <NUM>, threaded areas 182a, and non-threaded areas 182b are preferably equal, whether four of each are provided as in in the illustrated embodiment, or if more or fewer are provided. Further, as with threaded corners <NUM>, although the term threaded area <NUM> is used, the area may include texturizations other than threads, such as serrations, ridges, etc., as long as the texturization is configured for robust engagement with the corresponding texturizations on threaded corners <NUM>. The engagement of inner tube <NUM> with gross adjustment knob <NUM> is described in more detail below after the structural description of gross adjustment knob <NUM>. As best seen in <FIG> and <FIG>, the texturization of threaded areas 182a extends radially inward toward a center of the channel of the gross adjustment knob <NUM>, so that a circle traced along the threaded areas 182a has a smaller diameter than a circle traced along the non-threaded areas 182b. As is described in great detail below, this allows for selective engagement between the threaded areas <NUM> and the threaded corners <NUM> of inner tube <NUM>.

As best seen in <FIG>, the gross adjustment knob <NUM> may include a quick-release pin channel <NUM> extending partially therethrough, in a direction generally parallel the central longitudinal axis. One end of the quick-release pin channel <NUM> may be closed, and the opposite end may be open. As described in greater detail below, the quick-release pin channel <NUM> may be sized and shaped to receive a spring (or other biasing member) <NUM> therein, and to also receive a quick-release pin <NUM> at least partially therein. The quick-release pin <NUM> is illustrated in <FIG>. Briefly, quick-release pin <NUM> may include a generally cylindrical protrusion 186a sized to pass into the center of a spring <NUM> (illustrated in <FIG>) so that a face of spring is in contact with a larger generally cylindrical body 186b of the quick-release pin <NUM>. As described in further detail below, the quick-release pin <NUM> may also include a shoulder 186c, and a textured or grip portion 186d which the user may handle.

Referring again to <FIG>, the gross adjustment knob <NUM> may include two pin channels <NUM> extending in a direction transverse or orthogonal to the central channel, with each pin channel <NUM> being generally parallel to each other and positioned on opposite sides of the central channel. These pin channels <NUM>, best shown in <FIG>, may be located in the portion of the gross adjustment knob <NUM> with the ridges, and may each be sized and shaped to receive a translation limiting pin <NUM> (illustrated in <FIG>, <FIG>, <FIG>), so that the translation limiting pins <NUM> are positioned at least partly within groove or recess <NUM> of the outer tube <NUM> to allow for at least some rotation of the gross adjustment knob <NUM> with respect to the outer tube <NUM>, while limiting any axial translation of the gross adjustment knob <NUM> with respect to the outer tube <NUM>. Gross adjustment knob <NUM> may also include an additional pin channel <NUM> extending partially therethrough, generally parallel to quick-release pin channel <NUM> but on an opposite side of the central passageway. As described in greater detail below (illustrated in <FIG>), the additional pin channel <NUM> may be sized and shaped to receive a rotation limiting pin <NUM> so that a portion of the rotation limiting pin <NUM> protrudes beyond the additional pin channel <NUM> and into the recessed area <NUM> of the outer tube <NUM>.

<FIG> illustrate various views of strut <NUM> to better illustrate the components involved with gross adjustment knob <NUM>. For example, <FIG> is a side view of strut <NUM>, and <FIG> is a cross-section taken along the section line 11B-11B of <FIG>. <FIG> provide additional views focused on the section of the strut <NUM> in which gross adjustment knob <NUM> is located. As shown in these figures, when the strut <NUM> is fully assembled, pin <NUM> passes through aperture <NUM> of outer tube <NUM> and through the slot <NUM> of inner tube <NUM>, helping to ensure that the outer tube <NUM> and inner tube <NUM> remain rotationally fixed to one another during relative translation. Further, as noted above, the pin <NUM> is sized so that it cannot pass through the terminal end of the slot <NUM> of inner tube <NUM> at the narrowed width portion <NUM>, helping to ensure that the inner tube <NUM> cannot disconnect from the outer tube <NUM> during relative translation. Pin <NUM> may be positioned radially inward of the quick-release pin <NUM>, so that the movement of quick-release pin <NUM> is not inhibited by pin <NUM>.

As best shown in <FIG>, <FIG>, and <FIG>, the two translation limiting pins <NUM> extend through the corresponding pin channels <NUM> of gross adjustment knob <NUM> an partially within portions of the recess or groove <NUM> of the outer tube <NUM> so that the gross adjustment knob <NUM> is translationally fixed to, and partly overlies, the terminal end of outer tube <NUM>. As described above, these translation limiting pins <NUM> themselves do not inhibit rotation of the gross adjustment knob <NUM> relative to the outer tube <NUM>.

As best shown in <FIG>, <FIG>, and <FIG>, rotation limiting pin <NUM> is received within the additional pin channel <NUM> of gross adjustment knob <NUM>. A portion of the rotation limiting pin <NUM> protrudes up beyond the end of the additional pin channel <NUM>, and into the recessed area <NUM>. As the gross adjustment knob <NUM> rotates relative to the outer tube <NUM>, the rotation limiting pin <NUM> will eventually contact one or the other end of the recessed area <NUM>, limiting further rotation. In the illustrated strut <NUM>, the rotation limiting pin <NUM> has a maximum travel of about <NUM> degrees (or one eighth of a full rotation), although as noted above, in other embodiments the rotation limit could be greater or smaller.

As best shown in <FIG>, <FIG>, and <FIG>, spring <NUM> (or another biasing member) and quick-release pin <NUM> are both received within the quick-release pin channel <NUM> of the gross adjustment knob <NUM>. In particular, a first end of the spring <NUM> may abut the closed end of the quick-release pin channel, with protrusion 186a extending into the center of the spring <NUM> so that the second end of the spring <NUM> abuts the larger cylindrical body 186b. The shoulder 186c of the quick-release pin <NUM> is positioned to abut the terminal end of the outer tube <NUM>. However, the quick-release pin <NUM> is positioned so that the shoulder 186c can only be positioned adjacent first detent <NUM>, second detent <NUM>, or positions between the two detents. This is a result, at least in part, of the fact that, when the rotation limiting pin <NUM> is in contact with one end of the recessed area <NUM>, the shoulder 186c is aligned with the first detent <NUM>, and when the rotation limiting pin <NUM> is in contact with the opposite end of the recessed area <NUM>, the shoulder 186c is aligned with the second detent <NUM>. When the shoulder 186c is aligned with the first detent <NUM>, the spring <NUM> presses the shoulder 186c into the first detent <NUM>, limiting any further rotation. In order to rotate the gross adjustment knob <NUM>, the spring <NUM> must be depressed (e.g. by pressing the grip portion 186d of quick-release pin <NUM>) so that the shoulder 186c moves beyond the first detent <NUM>. While the spring <NUM> is depressed, the gross adjustment knob <NUM> may be rotated, and rotation may continue until the shoulder 186c aligns with the second detent <NUM>, at which point the spring <NUM> pushes the shoulder 186c into the second detent <NUM> to limit further rotation, again until the spring <NUM> is later depressed.

With the configuration described above, the gross adjustment knob <NUM> is translationally fixed to the outer tube <NUM>, and is capable of <NUM> degrees of rotation relative to the outer tube <NUM>, with the gross adjustment knob <NUM> locking against further rotation when at the maximum amount of rotation in either direction. The gross adjustment knob <NUM> may be unlocked by depressing the quick-release pin <NUM>, and then manually rotating the gross adjustment knob <NUM> while the spring <NUM> is depressed. In other words, this configuration allows for two discrete stable rotational positions of the gross adjustment knob <NUM> relative to the outer tube <NUM>, with each of these positions automatically locking to prevent any further unintentional rotation.

As best shown in <FIG>, the inner tube <NUM> extends through the interior of the gross adjustment knob <NUM> and into the interior of the outer tube <NUM>, with the inner tube <NUM> and outer tube <NUM> being coupled by the pin <NUM>. The inner tube <NUM> is positioned relative to the gross adjustment knob <NUM> so that, when the gross adjustment knob <NUM> is at maximum rotation relative to the outer tube <NUM> in one direction, the threaded corners <NUM> of the inner tube <NUM> engage corresponding threaded areas 182a of the gross adjustment knob <NUM>. However, when the gross adjustment knob <NUM> is at the maximum rotation to the outer tube <NUM> in the opposite direction, the threaded corners <NUM> of the inner tube <NUM> align with the non-threaded areas 182b of the gross adjustment knob <NUM>. In other words, as shown in <FIG>, in one discrete rotational position, the threaded areas 182a of the gross adjustment knob <NUM> engage with or mesh with the threaded corners <NUM> of the inner tube <NUM>, so that the inner tube <NUM> is not capable of axial movement relative to the gross adjustment knob <NUM>. In order to allow for a rapid length adjustment of the strut <NUM>, the quick-release pin <NUM> may then be depressed, and the gross adjustment knob <NUM> may be rotated (for example <NUM> degrees, which may be the maximum rotation allowed by rotation limiting pin <NUM>), until the threaded corners <NUM> of the inner tube <NUM> align with the non-threaded areas 182b of the gross adjustment knob <NUM>, as shown in <FIG>. In this unlocked condition shown in <FIG>, the threaded corners <NUM> of the inner tube <NUM> do not engage or mesh with any corresponding threads of the gross adjustment knob <NUM>, and the threaded areas 182a of the gross adjustment knob do not engage or mesh with any corresponding threads of the inner tube <NUM>. In other words, in the unlocked condition shown in <FIG>, the inner tube <NUM> is generally free to translate into or out of the gross adjustment knob <NUM>.

In a typical use of a plurality of struts <NUM> with an external fixation system that includes two fixator rings, the external fixation system has a desired initial position on the patient that may be determined before or during the surgery. In order to achieve the desired initial position, each strut <NUM> may have a desired initial length. When assembling the struts <NUM> to the fixator rings, each strut <NUM> may be set to the unlocked condition shown in <FIG> to allow for rapid length adjustment of the strut <NUM>. Each strut may be rapidly adjusted to the initial desired length, which may be confirmed, at least in part, by comparing the position of the gross adjustment knob <NUM> to the indicia <NUM> on the inner tube <NUM>, as best shown in <FIG>. When the initial desired length is achieved, the gross adjustment knob <NUM> may be rotated (after depressing the quick-release pin <NUM>) until the gross adjustment knob <NUM> transitions to the locked condition, as shown in <FIG>. Preferably, although it is not required, the threaded rod <NUM> is at (or near) a maximum or minimum position relative to the outer tube <NUM> at this initial phase, which may allow for maximum length adjustment during the correction phase. After each strut <NUM> is set to its desired initial length, switched to the locked position, and attached to the fixator rings, the correction phase may begin in which the length of each strut <NUM> is gradually adjusted to correct the bone deformity. As described above, the fine adjustment knob <NUM> may be actuated in order to drive the threaded rod <NUM> into or out of the outer tube <NUM> to decrease or increase the length of the strut <NUM>, respectively. It should be understood that the fine adjustment should typically only be performed when the gross adjustment knob <NUM> is in the locked condition, in order to ensure the struts <NUM> only change length the precise desired amount. During correction of the bone deformity, it would be undesirable for the struts <NUM> to unintentionally switch to the unlocked or "quick-adjust" mode, as the external fixation system may partially or entirely lose stability while connected to the patient's bone. The meshing or engagement between the threaded corners <NUM> of the inner tube <NUM> and the threaded areas 182a of the gross adjustment knob <NUM> provide for a very robust connection between the gross adjustment knob <NUM> and the inner tube <NUM>, ensuring that the gross adjustment knob <NUM> will remain in the locked condition unless and until the gross adjustment knob <NUM> is intentionally actuated to transition to the unlocked condition.

Compared to prior art systems, the quick-release mechanism described herein may provide various benefits. First, as noted above, some prior art systems rely on compression to maintain the strut in the locked or engaged condition for gradual or fine adjustment, but such compression mechanisms are prone to failure. On the other hand, the thread-to-thread (or serration-to-serration, etc.) type of engagement in strut <NUM> to maintain the strut <NUM> in the locked or engaged condition for fine or gradual length adjustment is significantly more robust and less prone to failure compared to prior art mechanisms. For example, although <CIT> discloses a collet with flexible fingers with threads that engage threads of another member to maintain a device in a locked condition, the device in the '<NUM> Patent still relies on compression via a clamp to maintain the locked engagement. The mechanisms described above do not similarly rely on compression. Further, the configurations described herein may be relatively simple and inexpensive to produce compared to other robust locking mechanisms of the prior art, such as that shown in <FIG>.

The features described above in connection with the quick-release mechanism may be used, with or without modification, in other struts besides double-telescoping struts with universal joints. For example, <FIG> illustrates a strut <NUM>' that is identical in most respects to strut <NUM>, with the exception of joints <NUM>, <NUM>. In a bone transport frame, similar to that shown in <CIT>, the struts may lack jointed connections to the proximal and distal rings, and may each be generally parallel to each other during use. Strut <NUM>' may be suitable for use in a bone transport frame, with the joints being removed. Instead, for example, the distal end of strut <NUM>' may include a connector portion <NUM>' with female threads to accept a bolt that passes through a distal-most ring of the bone transport frame. The fine and gross adjustments of strut <NUM>' function identically to those described above in connection with strut <NUM>.

<FIG> are various views of another embodiment of gross adjustment knob <NUM>' that is similar to gross adjustment knob <NUM> in most respects. Thus, for brevity, only the feature of gross adjustment knob <NUM>' that are different from gross adjustment knob <NUM> are described below. It should be understood that other features and uses of gross adjustment knob <NUM>' may be similar or identical to the corresponding features of gross adjustment knob <NUM> described above.

The gross adjustment knob <NUM>' may include bumps, ridges, or other textures to provide easier gripping of the gross adjustment knob <NUM>', and may define an aperture extending therethrough, the aperture defining a channel that is generally cylindrical. The gross adjustment knob <NUM>' may define a plurality of threaded areas 182a' extending along part of the length of the channel. In the illustrated embodiment, there are four threaded areas 182a', each threaded area 182a' being circumferentially spaced from an adjacent threaded area 182a' by a non-threaded area 182b'. Although four threaded areas 182a' and four non-threaded areas 182b' are illustrated, it should be understood that more or fewer threaded areas 182a' and non-threaded areas 182b' may be provided, primarily depending on the number of threaded corners <NUM> provided on the inner tube <NUM>. As with gross adjustment knob <NUM>, gross adjustment knob <NUM>' may include a quick-release pin channel (not visible in <FIG>) sized and shaped to receive a spring (or other biasing member) therein, and to also receive a quick-release pin <NUM> at least partially therein. Also, as with gross adjustment knob <NUM>, gross adjustment knob <NUM>' may include two pin channels <NUM>' (one of which is visible in <FIG>) sized and shaped to receive translation limiting pin <NUM>, and an additional pin channel (not visible in <FIG>) sized and shaped to receive rotation limiting pin <NUM>.

As described above in connection with <FIG>, in order to transition gross adjustment knob <NUM> to the locked condition, the gross adjustment knob <NUM> may be rotated until threads <NUM> of the threaded corners <NUM> of the inner tube <NUM> align with and engage the threaded areas 182a of the gross adjustment knob <NUM>, as shown in <FIG>. However, when transitioning from the unlocked condition of <FIG> to the locked condition of <FIG>, there is a possibility that the edges of one or more of the threads of threaded areas 182a may contact the edges of one or more of the threads <NUM> of threaded corners <NUM>, instead of the threads of threaded areas 182a aligning between adjacent threads <NUM> of threaded corners <NUM>. In other words, due to tolerances in manufacturing of the threads of threaded areas 182a and threaded corners <NUM>, the threads may not always perfectly mesh with one another when transitioning to the locked condition of <FIG>, resulting in "sticking" of the locking mechanism. Such "sticking" may make it difficult or impossible to fully transition the gross adjustment knob <NUM> to the locked condition. This problem may be solved, or at least mitigated, by introducing one or more scallops, leading edges, or guide threads 187b' onto one or more threads 187a' of threaded areas 182a'. It should be understood that the terms scallops, leading edges, and guide threads are intended to be used interchangeably.

Referring to <FIG>, gross correction knob <NUM>' is illustrated with four threaded areas 182a' (although only two are fully visible in <FIG>), each threaded areas 182a' including a plurality of individual threads 187a', with the bottom-most (in the orientation of the view of <FIG>) thread 187a' including an additional guide thread 187b' extending therefrom. <FIG> is an enlarged view of one of the threaded areas 182a', better illustrating the guide thread 187b' extending from one of the threads 187a'. As shown in <FIG>, the guide thread 187b' may extend from an end of a thread 187a' and may extend farther in a circumferential direction toward the adjacent non-threaded area 182b' compared to the threads 187a' that do not include a guide thread 187b'. In some embodiments, the guide thread 187b' may be a portion of a lead-in thread at the beginning of the threaded area 182a', which for example may be formed with a chamfer at the end of the threaded area 182a'.

<FIG> is an end view of gross correction knob <NUM>' that illustrates each threaded area 182a' may include a single guide thread 187b' extending from a corresponding thread 187a' in each threaded area 182a'. <FIG> illustrates the same view but also illustrates the inner tube <NUM> with threaded corners <NUM> aligned with the non-threaded areas 182b' in the unlocked condition. As shown in <FIG>, when in the unlocked condition, each guide thread 187b' terminates in a position immediately before engagement with (in other words very slightly spaced from) a corresponding thread <NUM> of a threaded corner <NUM> of inner tube <NUM>. The threads 187a' that do not include a guide thread 187b' are each spaced farther away from the corresponding threads <NUM> of the threaded corner <NUM> compared to the guide thread 187b'. In the unlocked condition shown in <FIG>, the inner tube <NUM> is still capable of sliding axially relative to the gross correction knob <NUM>' for quick adjustment. However, as soon as a user begins to rotate or turn the gradual correction knob <NUM>', the guide thread 187b' begins to engage a trough <NUM> between a pair of threads <NUM> of the threaded corner <NUM>. As the guide thread 187b' meshes with the threads <NUM> of the threaded corner <NUM> and the rotation of gradual correction knob <NUM>' continues, the remaining threads 187a' are forced into alignment with the corresponding threads <NUM> of threaded corner <NUM> to reduce or eliminate the likelihood of the ends of the threads colliding and causing the "sticking" described above.

<FIG> is a close up view of a portion of a threaded corner <NUM> of inner tube <NUM>, illustrating both threads <NUM> and troughs <NUM> between adjacent peaks of the threads <NUM>. As should be understood, the space D1 between adjacent threads <NUM> at the peaks of the threads <NUM> is relatively large, compared to the space D2 between adjacent threads <NUM> at the trough <NUM> of the threads <NUM>. When the gradual correction knob <NUM>' is in the unlocked condition, shown in <FIG>, each guide thread 187b' may be positioned just adjacent threaded corner <NUM>, nearer the larger space D1 than the smaller space D2. This relative positioning may allow for a greater "landing area" for the guide thread 187b' to fall within to avoid the "sticking" described above. In the absence of such guide threads 187b', as the gradual correction knob <NUM>' is rotated to the locked condition, the threads 187a' may tend to engage with threads <NUM> nearer the smaller space D2 than the larger space D1, potentially increasing the likelihood of threads colliding and resulting in "sticking" of the locking mechanism.

Although the main difference described above between gradual correction knob <NUM> and gradual correction knob <NUM>' is the inclusion of four guide threads 187b', it should be understood that more or fewer guide threads may be provided, in any combination of locations. For example, guide threads 187b' may be provided on less than all of the groups of threaded areas 182a' or all of the groups of threaded areas 182a'. Further, in each threaded area 182a' that includes a guide thread 187b', a single guide thread 187b' may be provided in any particular location (e.g. at the bottom thread, top thread, or any thread in between). Still further, in each threaded area 182a' that include a guide thread 187b', more than one guide threads 187b' may be provided. For example, every thread of one or more threaded areas 182a' may include a guide thread 187b', or only particular threads (e.g. every other thread, every third thread, every fourth thread, etc.) may include a guide thread 187b'. And if multiple guide threads 187b' are provided within a particular threaded area 182a', they need not be regularly spaced relative to each other.

Claim 1:
An adjustable length strut (<NUM>, <NUM>', <NUM>") for use in an external fixation system, the strut (<NUM>, <NUM>', <NUM>") comprising:
a generally hollow outer tube (<NUM>) extending between a first end and a second end;
an inner tube (<NUM>) sized to fit within and translate relative to the outer tube (<NUM>), the inner tube (<NUM>) extending in a length direction and having a circumferential direction, a plurality of texturized surfaces (<NUM>) extending in the length direction of the inner tube (<NUM>), each of the plurality of texturized surfaces (<NUM>) of the inner tube (<NUM>) being spaced apart from each other in the circumferential direction of the inner tube (<NUM>) and each circumferentially adjacent pair of texturized surfaces (<NUM>) of the inner tube (<NUM>) being separated by a non-texturized surface (<NUM>); and
a first adjustment knob (<NUM>) coupled to the second end of the outer tube (<NUM>), the first adjustment knob (<NUM>) having an interior surface defining a channel, the interior surface extending in a length direction and having a circumferential direction, the inner tube (<NUM>) passing through the channel, the interior surface having a plurality of texturized surfaces (182a) extending in the length direction of the interior surface, each of the plurality of texturized surfaces (182a) of the interior surface being spaced apart from each other in the circumferential direction of the interior surface and each circumferentially adjacent pair of texturized surfaces (182a) of the interior surface being separated by a non-texturized surface (182b), the first adjustment knob (<NUM>) being rotatable relative to the outer tube (<NUM>) and the inner tube (<NUM>) between a locked condition and an unlocked condition;
wherein (i) in the locked condition, the plurality of texturized surfaces (<NUM>) of the inner tube (<NUM>) engage the plurality of texturized surfaces (182a) of the interior surface of the first adjustment knob (<NUM>) to prevent translation of the inner tube (<NUM>) relative to the outer tube (<NUM>), and (ii) in the unlocked condition, the plurality of texturized surfaces (<NUM>) of the inner tube (<NUM>) align with the plurality of non-texturized surfaces (182b) of the interior surface of the first adjustment knob (<NUM>) to allow translation of the inner tube (<NUM>) relative to the outer tube (<NUM>).