External fixation clamp

An insert for an external fixation has two jaws for clamping a rod-shaped element. The insert includes a locking element and is an angled piece having two free ends, with at least one engagement edge for engagement into the rod-shaped element being provided at its one free end. The insert has a recess or bore for engagement with a locking shaft of the clamp provided at the free end thereof that lies opposite to the free end having the rod engagement edge. The insert is angled so that it may extend through a passageway in one of the jaws and into a cavity formed in the jaw for receiving the rod. The insert rod engaging edges are tapered to bite into the rod to prevent its movement.

BACKGROUND OF THE INVENTION

The invention relates to an insert for a clamping element for clamping a rod-shaped element of an articulated connection, particularly for a clamping element of an articulated connection for stabilizing bone fractures. Furthermore, the invention relates to an articulated connection having two clamping elements and having a locking element. In particular, the invention relates to an insert for optimizing the fixation of round rods in an external fixation system.

An articulated connection is known from U.S. Pat. Nos. 5,741,252, 5,752,954, 6,080,153, 6,342,054, 6,616,664, and 6,702,814, respectively, which consists of two or four individual clamping jaw elements and a central shaft or screw. In the case of this articulated connection, it is possible to introduce one or two rod-shaped elements into the corresponding cavities from the side. In U.S. Pat. No. 5,752,954, a spring is disposed between the two center clamping jaw elements, and it is possible to clip the rod-shaped elements in, counter to its spring force, and thereby hold the articulated connection in place against the rod-shaped elements, before it is locked in position. In U.S. Pat. No. 6,616,664, narrow lever arms disposed on the side are provided, in order to hold rod-shaped elements that have been inserted from the side in place before the articulated connection is locked in position.

These known articulated connections are particularly used with frame-type systems for external treatment of bone fractures, also referred to as external fixators. By means of a suitable material pairing of the clamps of the articulated connection and of the rods, for example steels of different hardness or a combination of steel and aluminum, or also by means of suitable surface structures of the interior surface of the clamp and the mantle surface of the rod, the result can be achieved that the rod-shaped elements are sufficiently secured against rotation and axial displacement after the locking screws have been fixed in place.

It is desirable to construct such external fixators using non-metallic materials, for example plastic materials, particularly in order to achieve a weight reduction of such a system. If the modules or parts of such a clamp are made of plastic injection-molded materials, there may be the difficulty in finding suitable material pairings with which sufficient fixation can be achieved. This is a problem particularly because many plastics are characterized by negative creep behavior, which causes connections that have been tightened to gradually come loose, i.e. to lose their gripping power.

Another problem that arises with such configurations is the high pressure stress on the plastic parts when the screw connection has been tightened, and this stress can result in stress cracks due to irregular stress on the plastic structure. This is particularly dangerous because such defects only occur after a certain period of time, and are not clearly evident optically.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide an insert for a clamping element that allows insertion of rod-shaped elements from the side, and whereby the clamping element, used double, can be inserted directly as an articulated connection, whereby the aforementioned elements of the clamping element can consist of a non-metallic material, for example plastic, without any impairment of the safety of the resulting articulated connection in an external fixator.

Furthermore, it is an aspect of the present invention to provide a simple clamping element designed for use of such inserts.

Yet another aspect of the invention is an improved articulated connection.

It is one goal of the invention to offer a suitable system that allows an optimal and, to the greatest extent possible, a direct friction lock between the connecting clamp and the rod-shaped elements, which remains constant. At the same time, the locking does not result in overly great stress on the plastic parts and therefore helps to prevent structural damage. The permanent stability of frame configurations for external fixators, which are predominantly made of plastic, is guaranteed, in other words the reliability known from previous metal designs is assured. Furthermore, this design should be a design that can be easily produced and advantageously assembled, in order to obtain a relatively inexpensive product.

These and other aspects of the present invention are accomplished by a clamping element for engaging a rod of an external fixation system. The clamping element has a first jaw member having a bore therethrough and a rod receiving cavity spaced radially from the bore. The cavity may be part cylindrical shape extending along an axis. The clamp includes a second jaw member having a bore therethrough and a rod receiving cavity spaced from the bore. A locking shaft extends through the bores of the first and second jaw members in a direction generally perpendicular to the axes of the cavities in the jaw members. The locking shaft may be threaded at one or both ends to allow for the tightening of the clamping elements against the rod. The clamping element includes an insert having a first part with a bore or recess for receiving the locking shaft and a second part extending into the rod receiving cavity of at least one of the jaw members. The second part has a tapered or pointed edge for engaging an outer circumferential surface of the rod received within the cavities of the first and second jaw members. Once the jaws are tightened by the use of the locking shaft and any associated threaded locking element coupled thereto the tapered edge bites into the outer surface of the rod fixing it axially within the cavities. In addition, the insert takes part of the load clamping the rod between the jaw members.

The insert may be either angled or L-shaped The first part of the L-shaped including a bore for receiving the locking shaft with the second L-shaped portion extending through a passageway in at least one of the jaw members and into engagement with the cavity housing the rod. The tapered edge of the insert may be in the form of a plurality of points or may have a roughened surface for better biting into and engaging the rod and preventing its motion. The tapered engagement edge can extend both axially along the rod and perpendicular thereto to better prevent axial motion of the rod within the cavity. The insert may include an anti-rotation feature to prevent the insert from rotating out of alignment with the axis of the cavity. This can be accomplished by having a portion of the insert in the region of the bore engaging the locking shaft or a portion of the insert engaging a recess in the jaw member. Preferably, the passageway runs from the outside of the jaw member through the jaw member in a direction that is perpendicular to the axis of the cavity and through a surface that delimits the cavity so that the first part of the insert clamp can lie against the clamp outer surface with the second part extending generally at 90° thereto extending into the cavity which receives the rod. In a preferred embodiment of the outer side of the jaw with the insert has a recess extending along the face of the jaw member and recessed in the direction of the passageway to receive the first part of the jaw. The recess is sized to receive the first part of the insert as a press-fit so that the insert is retained on the outer side of the jaw member and is prevented from rotation with respect thereto. Also in the preferred embodiment the bore in the first part for receiving the locking shaft may be oblong so that the jaw member with the insert press-fit therein can be moved apart when a rod-shaped element is inserted in a direction perpendicular to the axis of the cavity. In a second embodiment the jaw member may have a beveled surface for engaging a beveled surface on the insert to provide support for the insert when engaging the rod.

In particular, an insert according to the invention allows a direct transfer of force from the screw or another locking element to the rod, in order to relieve stress on the plastic component.

In other embodiments, it is also possible to achieve the inserts as extrusion-coated parts. In this case, metallic parts are laid into the injection-molding mold and then coated with plastic by extrusion coating. This is a common technique, but it requires a complicated and accordingly expensive production process (robot-controlled placement of the metal parts or manual placement). A disadvantage of such a solution is that extrusion-coated parts are also subject to the creep phenomena mentioned.

DESCRIPTION

Referring toFIG. 1there is shown a cross-sectional side view of a preferred articulated connector100having two clamping elements10having inserts50according to a first exemplary embodiment of the invention.

Each clamping element10has two clamping jaws12and13that lie opposite one another and have a cavity11for accommodating a rod-shaped element101. Rod101may be formed of a polymeric or composite material such as carbon fiber reinforced PEEK. The clamping jaws12and13have a groove with a longer curvature portion14and having a short curvature portion14athat runs crosswise, in each instance, at their free ends15, which grooves together define the cavity11. At the free ends15, the outer edges16of the sides of the clamping jaws12and13that face one another are rounded, in order to facilitate the insertion of a rod-shaped element from the side. Opposite the cavity11and the free ends15, a hinge means17is provided, which can be seen inFIG. 2, and which connects the clamping jaws12and13with one another to form a single piece. A screw103that passes through clamping elements10and can be screwed into a nut106closes the articulated element100, and locks rods101that can be inserted into the latter in place. This screw/nut connection is a locking element that can also be implemented by way of levers and other elements.

Clamping elements10have a solid cross-section in their center region, forming two lateral cross-ribs21, which are particularly marked in the upper region of clamping jaw12. The region between cross-ribs21is recessed towards the front edge16, with the exception of a rectangular insert accommodation or recess18that can be seen in the top view ofFIG. 2. Insert accommodation18has a continuous bore centrally in the clamping element10, to accommodate screw103. Ribs21can also run completely on the outside of the clamping element, depending on the width of an insert50. Insert accommodation18can also consist of a second step, at a distance from ribs21.

In the inner or lower clamping jaw13, cross-ribs21end in a ring flange22, which can have a flat, recessed, ring-shaped segment, for example, which can be followed by a recess that saves weight and material and is advantageous for injection-molding production, in the center of which a bore is provided. This continuous bore is oriented to align with the aforementioned continuous bore in the upper clamping jaw12. In the clamping element10, it runs perpendicular to the axis of the cavity11and parallel to the back of the hinge means17. However, it could also run at a slant. The ring flange22can be a carrier of engagement elements such as radial teeth, in order to prevent rotation of the clamping elements10relative to one another. A separate rotation element for insertion between the two clamping elements10can also be provided.

In the representation ofFIG. 1, preferred articulated element100is formed from two clamping elements10. The clamping elements10are provided, for example, for a rod having a diameter of 12 millimeters, for example. Then, the opening at the free ends has a diameter of 8 millimeters, for example, in the resting state. If the upper clamping element10is now supposed to be provided for a rod having a diameter of 4 to 6 millimeters, then the opening at the free ends15would have a diameter of 2 millimeters, for example, in the resting state.

In the preferred embodiment an insert50is inserted into insert accommodation or recess18; the former consists of an L-shaped profile that will be described in greater detail inFIG. 3and others. A continuous slit bore19is provided in upper clamping jaw12, in insert accommodation18, through which the tips of the L-shaped profile of insert50can project, into the region of the cavity11; slit bore19ends in groove14, preferably in the center of groove14. They can always project into the groove14by 1 millimeter, for example, because the profile surface of the insert50sits in the clamping jaw with a press fit.

FIG. 2shows a perspective view of the first embodiment according to the invention, with an inserted rod101. The same characteristics in the drawings are shown with the same reference symbols, in each instance. In lower clamping element10, the break-through of slit bore19and two teeth of lower insert50, which is held by the nut106, can be seen. Here, the connection between clamping elements10is pressed apart by way of a pressure spring23that has been inserted between them.

FIG. 3shows a perspective view of insert50according to the first embodiment,FIG. 4shows a bottom view of this insert50, andFIG. 5shows a side view of the insert50. In the top view, the insert50is essentially a rectangular plate having an oblong bore52. In cross-section, the insert50looks like an L-shaped small plate having a long side51and a shorter engagement side53. Here, the free end of the shorter engagement side53ends in two teeth54, which have a prism shape in cross-section. The insert50serves as an inserted part in the plastic part of clamping element10, which is placed into the coupling element10under screw head103or under nut106, respectively. Preferably, here insert50is a die-punched part. In this embodiment, metal part50is affixed to the outside of the articulated element100, making reference toFIGS. 1 and 2. Insert50is structured in such a manner that it can claw directly into a round rod-shaped element101, through the penetration or slit bore19in the clamping element10, with an angled front side53, and thereby results in a material deformation or notching in rod-shaped element101. As a result, an optimal friction lock between elements10(by way of insert50) and a rod101is achieved. The advantage is, in particular, that the friction lock comes about directly between screw103(or nut106) and rod-shaped element101, by way of insert part50, and plastic component10of coupling element100now serves only as a guide element. As a result, the stress on it is significantly relieved, and it can be optimally designed for this guide function. In this context, engagement edge55of teeth54is directed essentially axially in the direction of rod101, and prevents rotation in particularly excellent manner.

FIG. 6shows a perspective view of an insert60according to a second embodiment.FIG. 7shows a bottom view of the insert60according toFIG. 6, andFIG. 8shows a side view of the insert60according toFIG. 6. The insert60is essentially very similar to insert50, with the difference that here, four teeth64are provided, and that the engagement edge65of the teeth64, in each instance, stands crosswise to the longitudinal direction of rod101, into which it can engage. Therefore the engagement edge65of the teeth64stands essentially crosswise to the direction of rod101and prevents axial displacement of the clamping element10on rod101, in particularly excellent manner.

FIG. 9shows a perspective view of on insert70according to a third exemplary embodiment,FIG. 10shows a bottom view of the insert according toFIG. 9, andFIG. 11shows a side view of the insert according toFIG. 9. In this embodiment variant, the first and second exemplary embodiments are combined, in principle. The insert70has lengthwise teeth74having an engagement edge75that prevents rotation, and crosswise teeth76having an engagement edge that prevents axial displacements. Here, one central lengthwise tooth74and two crosswise teeth76disposed to the sides of the former are provided; two or more lengthwise teeth74and one crosswise tooth76on only one side, or, in advantageous manner, two or more crosswise teeth76, symmetrically, could be provided. It is essential in this exemplary embodiment that the teeth74and76, respectively, are oriented at a right angle to one another, in order to reliably prevent both lengthwise displacement of the rods101and their rotation.

FIG. 12shows a cross-sectional side view of a second articulated connection110having two clamping elements20having inserts80according to a fourth embodiment of the invention, andFIG. 13shows a perspective view of this fourth embodiment according to the invention, with an inserted rod101. The clamping elements20correspond to a second embodiment of clamping elements as compared with clamping elements10, since they have been appropriately modified to accommodate the inserts80, which will be described in connection withFIG. 14 to 17.FIG. 14shows a perspective view of insert80according to the fourth embodiment,FIG. 15shows a bottom view of it,FIG. 16shows a side view, and finally,FIG. 17shows a top view of insert80according toFIG. 14.

The lower clamping jaw13has a flat contact surface on its underside, on which the inner side86of the insert80rests (in contrast to the riffled or serrated flange22shown inFIGS. 1 and 2).

Furthermore, the clamping element20has a slit bore29that corresponds to slit bore19, and opens into groove14of clamping jaw13, analogously. The insert80is structured in U shape, and, similar to insert50, has a plate surface81that is configured here to be round, and is flattened on the side of the engagement side83. In the embodiment shown, two teeth84having engagement edges85which may be tapered to a pointed edge, are provided. It is clear that other configurations corresponding to the above second and third exemplary embodiments can also be implemented.

On the side lying opposite the engagement side83, a locking bar88is provided, which runs essentially parallel to the engagement side83. The locking bar88runs in a slit of clamping elements20that runs parallel to the bore that accommodates the screw, and has a locking projection89that can press into the material of clamping element20in the depth of the slit.

In this embodiment variant, two inserts80come to rest on one another directly, between the two parts of the clamping elements20, which are made of plastic, for example, and additionally take on the function of a rotation lock87of clamping elements20. In this case, the plastic parts do not have any teeth on the underside. Preferably, the insert is produced as a die-punched part. The radial teeth of rotation lock87engage into one another when the screw103is tightened, and, in order to improve the rotation lock, the insert additionally has a locking bar88that engages into clamping jaw13of plastic part20.

In addition, this insert80can be configured with hooks89and engagement side83, as a clip or snap, and this simplifies assembly, since the parts can thereby be clicked onto the clamping element20. In this variant, as well, the teeth that engage in the rods101can be configured in the most various forms, of which the exemplary embodiments shown only form an advantageous selection. For example, round conical points can also be provided, instead of teeth54,64,74,76,84, or in addition to them. These are engagement elements, in each instance. Any such means that can be referred to as a means for generating high friction forces can be viewed as being an engagement element. This can simply have a rough surface, one or very many carpet-like little points can be present, or the engagement element can assume other embodiment forms mentioned in the specification and in the claims.

FIG. 18shows a perspective view of an insert90according to a fifth embodiment, andFIG. 19shows a side view of this insert90according toFIG. 18. The only difference between the fourth and the fifth embodiment is that the insert90does not have a locking bar88. Therefore the teeth84that claw into rods101when the articulated element is fixed in place are the only elements that simultaneously prevent rotation of the plastic clamps10and20. Therefore the rotation lock87is secured only on one side, and particularly utilizes the positive lock in the slit bore29only asymmetrically.

It is clear that insert50according to the first embodiment can also be equipped with a locking bar88, if a corresponding recess is provided in clamping jaw12.

It is directly evident that two inserts80and90, respectively, provided for the inner clamping jaws13, have a round bore82, while the inserts50,60, and70, respectively, provided for the outer clamping jaws12, have rectangular bores or oblong bores. This is due to the fact that in order to insert the rods101, the clamping jaws12and13must be pressed apart. In doing so, clamping jaws12move about a pivot point of hinge part17and thereby relative to screw103or nut106, thereby making it necessary for a corresponding clear space to be present for the path of the screw103or nut106. Instead of the closed bore, a U-shaped slit can also be provided, which at least partially surrounds a clamping element103,106.

FIG. 20shows a perspective view of an inset190according to a sixth embodiment.FIG. 21shows a side view of the insert190according toFIG. 20, andFIG. 22shows a bottom view.

Insert190is configured to be rectangular with rounded corners, and, similar to insert50, has a plate surface51that makes a transition into the engagement side93on one side, at a slant. This can be achieved by means of punching, for example. The angle between the surface51and the engagement side93can be 45 degrees, for example, but other values, advantageously between 30 and 60 degrees, are also possible. An oblong hole92is disposed in the surface51; its longitudinal direction is oriented perpendicular to the punch line of the engagement side93. The smaller diameter of the oblong hole92essentially corresponds to the diameter of the screw103provided for the clamping element30according toFIG. 23. Oblong hole92has a region that extends into the slant of the engagement side93. This is advantageous because in this way, in the case of the clamping element30, groove14for rod101can be brought closely up to screw103, which runs crosswise. The region of the engagement side93, which is thereby shortened, is advantageous since two rods101are thereby rigidly coupled with one another, tightly, by way of screw103, and little load acts on the clamping elements30that compose the articulated element120.

In the exemplary embodiment shown, two lateral teeth94are provided with engagement edges95. This can also be described as an engagement edge95that is set back in the center region. It is clear that other engagement configurations, in accordance with the above first through fifth exemplary embodiments, can also be implemented.

On the side lying opposite the engagement side93, no locking bar is provided here, which would run perpendicular to the surface51. Such a locking element, similar to the locking bar88, is, of course, possible, in order to support the locking effect.

In this embodiment variant, the two inserts190come to rest directly between the two clamping jaws12and13of each clamping element30. For this purpose, the clamping jaw12has a bevel38that can rest against the engagement side93. In this context, the screw103passes through the opening92, which is configured as an oblong hole, in order to allow a movement of insert190crosswise to the orientation of rod101.

FIG. 23shows a perspective view of an articulated connection120having two clamping elements30having inserts190according to the sixth exemplary embodiment of the invention, with an inserted rod101, andFIG. 24shows a cut side view of this articulated connection120according toFIG. 23. The clamping elements30correspond to a third embodiment as compared with the clamping elements10, since they are appropriately modified to accommodate the inserts190.

In the lower part ofFIG. 24, it can be seen that the insert190rests on the clamping jaw12due to gravity. In this context, the engagement side93can rest against the bevel38of the clamping jaw12, but it does not have to do so, because the oblong hole92permits a movement of the insert190relative to the screw103. The engagement edge95projects into the cavity11. In this context, engagement edge95is oriented approximately centered in height between the clamping jaws12and13. When the rod101is inserted by pressing it over the edges of the clamping jaws12and13, as shown in the upper part ofFIG. 24, the rod101comes to rest in the groove14. In doing so, it displaces the engagement side93towards the edge of the groove14and, in particular, against the bevel38. Then engagement edge95engages in the rod101.

In the case of this variant, as well, the teeth that engage in the rods can be configured in the most various shapes, of which the exemplary embodiments shown form only an advantageous selection. For example, round conical points can also be provided, instead of the teeth54,64,74,76,84, in each instance, or in addition to them. They are engagement elements, in each instance.

In the case of all the exemplary embodiments shown, the insert forms an angled support that directly engages on a rod, with a friction lock. Therefore the clamping elements10,20, or30are now used only as a guide and spacer part; they are therefore subject to less stress. This permits an even greater material selection for the clamping elements10,20,30. In this context, the insert50,60,70,80,90or190engages in the locking element, here103,106, on the other side.

The inserts50,60, and70are shown fitted into a recess18. This recess18can be configured, in particular, in such a manner that inserts50,60, and70have no play in it, but rather fit into a press fit. They can then not fall out, and form a single-piece unit for the user. The same can also be achieved for the insert80, by means of a corresponding deformation of the lower clamping jaw13. As a result, a similar effect as that of the locking bar can also be achieved with reference to the rotation lock, particularly if the insert90is configured to be angular rather than round, whereby the characteristics that prevent rotation, for example radial grooves, are provided on the side lying opposite the flat side86.

Finally, the inserts can also be provided as injection-coated parts in a clamping element.

The exemplary embodiments shown in the drawings, and the characteristics of various exemplary embodiments mentioned in the present description, respectively, should not necessarily be understood as embodiments independent of one another. Instead, it is possible that each characteristic described in one of the exemplary embodiments can be combined with one or more of any other characteristics of other exemplary embodiments, so that other exemplary embodiments result, which are not literally described or shown in the drawings, but lie within the scope of protection claimed in the present claims.