WO2009007009A1

WO2009007009A1 - External fixator for angle correction on a bone, in particular on the head of the tibia

Info

Publication number: WO2009007009A1
Application number: PCT/EP2008/005157
Authority: WO
Inventors: Rainer Baumgart
Original assignee: Rainer Baumgart
Priority date: 2007-07-11
Filing date: 2008-06-25
Publication date: 2009-01-15
Also published as: DE202007009685U1

Abstract

The external fixator for angle correction on a bone has an elongate head element (10) which at each of its ends has a receiving opening (12, 13) and at one end has a laterally protruding bracket (11), provided with an end bore (30), and at its other end has a retaining flange (17) that protrudes from the same side as the bracket (11). The fixator further comprises an elongate shaft element (20) which at each of its ends has a receiving opening (22, 23) and at one end has an arm (24), inclined away from the shaft element (20) such that it encloses therewith an angle (α) of 110° to 160° and is provided with an end bore (31), and which has a further retaining flange (27) between its ends, on the side opposite from the arm (24). The fixator is also provided with a hinge screw (32) which can be inserted into the bores (30, 31) in the arm (24) and bracket (11), respectively, to form a hinge joint and which has a continuous central through-channel (34), with fastening elements (14) which are each held in clamping devices (16) of a receiving opening (12, 13; 22, 23) and can be fixed on the bone side, and with a distraction element (40) which at each of its ends is articulated (18, 28) on a retaining flange (17, 27).

Description

External fixator for angle correction on a bone, especially on the tibial plateau

The invention relates to a fixator external for angular correction of a bone, in particular on the tibial plateau.

Dislocation-related or accident-related malpositions in the area of the tibial plateau (tibial head) can lead to a one-sided overload and thus to premature osteoarthritis of the knee joint. An established treatment method is the correction of the leg axis with the aim to prevent damage to the overloaded cartilage or to relieve the already damaged cartilage. If the center of the malposition, as is very often the case, is located near the knee, the correction center must be selected knee-joint.

A common procedure is the surgical transection of the tibial plateau and stabilization with a plate after correction of the axis. While the very frequent corrections to valgus (X-leg) are less complicating, corrections for varus (O-leg) pose a significant risk of complications. The reason for this is the peroneus nerve, which, for developmental reasons, runs laterally around the head of the fibula (fibular head) before it dips into the ventral muscle group. In an acute correction in the direction of varus and stabilization with an osteosynthesis plate experiences the already tense nerve an additional acute extension, which can lead to temporary or permanent failures and thus to emotional disorders and / or loss of function (foot lifter).

Axis correction in both the varus and valgus directions can be achieved by closing the correction angle after a bone wedge has been removed (closed-wedge) and by opening the correction angle (open wedge). In a closed wedge correction, the leg is slightly shorter, but the advantage is the direct bone contact, which speeds healing. In an open wedge correction, the leg is slightly longer, at larger opening angles often spongiosa (bone softening substance) For example, be introduced from the iliac crest, so that a bony bridging results, which extends the intervention significantly. In both cases, the size of the correction angle must be accurately calculated in advance, as it will not be possible to perform a correction without reoperation. Another disadvantage of the plate osteosynthesis, regardless of whether the correction is in the direction of varus or valgus, is the need to remove the implant again, as not often in the case of previously damaged knee joints later prosthetic resurfacing is necessary, so that the implants are then in the way. A follow-up operation for metal removal after bone healing is therefore the rule.

The problems mentioned, especially the nerve complications, can be avoided when using external fixators, since the correction is slow and the nerves can also stretch slowly. If the correction speed takes place in a favorable range (about 1 mm / day), in the case of an open wedge correction, spontaneous bone formation can be expected in the opening correction angle and a bone attachment can be dispensed with. Another advantage is the precisely adjustable correction, controlled under load in an X-ray stand leg recording. When using an external fixator, the correction angle can be corrected as needed without reoperation. Also, after solidification of the bone removal of the fixator without reoperation by simple, almost completely painless unscrewing the bone screws is possible.

The mentioned advantages of the treatment with an external fixator are faced with a multiplicity of well-known disadvantages. First and foremost, these are soft tissue irritations and severe pin infections. A key reason for this is that conventional fixators are designed for multiple applications, can not be positioned as needed and allow no need for relative movement of the components for angle corrections in the area of the tibial plateau. In addition, there is a considerable discomfort in conventional fixatives due to the voluminous structure, often wearing trousers is not possible.

So far, no external fixator system is known, which is optimized for angle corrections in the region of the tibial plateau and avoids or at least reduces the disadvantages mentioned. Therefore, the object underlying the invention is to provide an external fixator for angular correction on a bone, in particular on the tibial plateau, which has an ergonomic, space-saving fixator body and accurate, planned placement of the correction center, a continuous correction of the angular misalignment and a stable fixation the bone segments formed after transection allows.

This object is achieved by an external fixator for angular correction on a bone, in particular on the tibial plateau, which comprises an elongated head element, each having a receiving opening at its ends, at its one end a laterally projecting arm, which is provided with a bore end, and has at its other end a projecting on the same side as the cantilever retaining flange, an elongated shaft member having at its ends a respective receiving opening, at one end an arm which is inclined away from the shaft member so that he is at an angle of 110 ° to 160 °, preferably from 120 ° to 130 °, and the end has a bore, and between its ends on the side opposite the arm has a further retaining flange, one in the holes in the arm or arm to form a Hinged hinge insertable hinge screw having a continuous central guide channel,

Fasteners which are each held in clamping devices of a receiving opening and fixable on the bone side, and a distraction element, e.g. a threaded spindle, which is hinged at each end to a retaining flange.

The external fixator in the embodiment according to the invention allows an anatomical, space-saving and angularly stable arrangement and fixation of the fastening elements, a stable fixation of the two bone segments formed by cutting, an extremely File planned placement of the correction center and a continuous correction of the angular misalignment.

For a spatial optimization of the external fixator, the cantilever is arranged substantially perpendicular to the head element.

The head element and the shaft element may each have two auxiliary bores, each of which is advantageously arranged close to a receiving opening. By using guide wires, the head and shaft elements can be precisely aligned in advance and fixed in advance. They thus serve as alignment aids and simplify the surgical technique. The auxiliary bores may be both at an acute angle of e.g. 3 ° to 10 ° to each other, whereby the distance between the fixator elements is fixed to the bone, or be arranged parallel to each other, so that only the position is fixed in the frontal plane and the distance to the bone remains variable.

Conveniently, the bore of the boom is provided with an internal thread into which a male threaded portion is screwed to the hinge screw, the thread-free portion sits in the bore of the arm to form the hinge joint.

Preferred fastening elements are Schanz screws with a Doppelkonusverklem- tion whose design and setting is described for example in EP 0 517 939 Al. The Schanz screws preferably have a diameter of 5 to 7 mm.

Advantageously, the ratio of the lengths of head element to shaft element is 1: 1 to 1: 1.8.

As low has a ratio of the length of arm to head element of 1: 1.4 to 1: 2 proved.

Conveniently, all components of the fixator made of titanium, which is an optimum in terms of stiffness, lightness, strength and body compatibility. The longitudinal extent of the head element substantially corresponds to the transverse extent of the bone, for example of the tibial plateau. The shaft member is arranged substantially in the direction of the longitudinal extent of the bone.

Reference to drawings, an example embodiment of the invention will be explained in more detail. It shows:

Fig. 1 shows schematically in a front view an embodiment of the external fixator mounted on the head portion of a tibial bone and Fig. 2 in a view like Fig. 1 the fixator in an intermediate or end position of a

Angle correction.

The external fixator shown in FIGS. 1 and 2 has as base components a head element 10, an inner shaft element 20 and a distraction element 40.

On the head element 10, a substantially vertically projecting arm 11 with a bore 30 is provided at its one end.

The shaft member 20 has at its one end an arm 24, at the end of a bore 31 is formed. The arm 24 is inclined to the shaft member 20. In Fig. 1, the longitudinal axis of the shaft member 20 with A and the longitudinal axis of the arm 24 is designated B. In the embodiment shown, the angle α included between the axes A and B is about 125 °.

In the bore 30 of the arm 11 is rotatably seated a hinge screw 32 and forms with the bore 30 a hinge joint. The hinge screw 32 has an externally threaded portion which can be screwed into a formed in the bore 30 in the boom 11 internal thread end.

The hinge screw 32 has a head 33, for example with a polygon for receiving a screwdriver, and a central guide channel 34 for the passage of a guide wire, not shown. The axis of the central guide channel 34 is the pivot axis of the hinge joint, on the one hand, for example, on the in Fig. 1 dashed lines Trennli- never X, along which the tibial bone 51 is separated from tibial bone 52 for angular correction, and on the other hand, for example, is positioned on the outer bone contour.

The head element 10 has at its two ends a receiving opening 12 or 13 for receiving in each case a Schanz screw 14 with a clamping device 16, for example in the embodiment according to EP 0 517 939 A1. For receiving a screwdriver, e.g. four depressions 19 distributed over the circumference are provided in the clamping device 16. Close to each receiving opening 12 or 13, an auxiliary bore 15 is provided in the head element 10 in each case. The head member 10 has at its end opposite the boom 11 a retaining flange 17 which extends in the same direction as the boom 11. The retaining flange 17 has a joint 18th

The shank element 20 has at its arm-side end and at the opposite end in each case a receiving opening 22 or 23 for a Schanz screw 14 with a clamping device 16 (EP 0 517 939 A1). Close to each receiving opening 22 and 23, respectively, an auxiliary bore 25 is formed in the shaft member 20.

The shaft member 20 has between its two auxiliary holes 25 has a retaining flange 27 which is provided on the opposite side of the arm 24. The retaining flange 27 has a joint 28.

A distraction element 40, for example in the form of a screw spindle, is connected to the joint 18 of the retaining flange 17 of the head element 10 and to the joint 28 of the retaining flange 27 of the shaft element 20, with the aid of which the distance between the joints 18 and 28 can be changed.

As can be seen in Fig. 1, the two Schanz screws 14 positioned in the receiving openings 12 and 13, which fix the head element 10 on the tibial head, are arranged on a line parallel to the tibial articular surface. The entry point should be as far as possible medially or as far as possible laterally. Since in the sagittal plane, the articular surface drops to the caudal, the Schanz screws 16 must be introduced inclined caudally. Under these two conditions, the preferred inclination of the medial Schanz screw is 10 ° laterally and caudally, while the lateral Schanz screw is preferably 10 ° medially and caudally inclined. The Schanz screws 14 are preferably connected to a double-cone clamping device 16 according to EP 0 517 939 A1 with the head or shaft element. The essential features of this deadlock are an optimized fixation length of the Schanz screws, which prevents turning of the Schanz screw when tightening.

The shaft element 20 is likewise fastened in the receiving openings 22 and 23 on the tibial shaft with the aid of two Schanz screws 14 and a clamping device 16. According to FIG. 1, the axis A of the shaft element 20 extends at the beginning of the angle correction substantially perpendicular to a longitudinal axis C of the head element 10, since the tibia head shown has no malposition.

The auxiliary bores 15 of the head element 10 and the auxiliary bores 25 of the shaft element 20 generally have a diameter of 2 to 3 mm. Since the tibial head 51 can be of different sizes, in practice the head elements 10 are connected to e.g. three different length dimensions advantageous to allow as far as possible outside fixation of the head member 10 with respect to the tibial head 51. Correspondingly, the shaft element 20 correspondingly has different arm lengths.

In Fig. 2, the tibial head 51 is shown by extending the distraction spindle 40 about the hinge joint as a fulcrum starting from the dividing line X into the position indicated by the line X 'or pivoted by the angle β.

The operation for inserting the external fixator according to the invention proceeds as follows:

1. Patellar patellar alignment and horizontal alignment of tibial leading edge.

2. Vertical insertion of a guide wire with a diameter of 3 mm about 20 mm to 30 mm below the knee joint gap depending on the planning and marginally in the bone medial or lateral depending on the correction specification.

3. Selection of a suitable fixator so that the head element 10 projects beyond the bone, neither medially nor laterally, and is pushed onto the guide wire through the guide channel 34. 4. Aligning the head element 10 parallel to the knee joint and fixation with one or two guidewires through the auxiliary holes 15 therethrough.

5. Aligning the shaft member 20 parallel to the tibial shaft 52 and fixing with one or two guidewires through the auxiliary holes 25 therethrough.

6. Screwing of drill sleeves into the clamping device of the head and shaft element according to EP 0 517 939 A1.

7. Screwing self-tapping Schanz screws 14 directly without pre-drilling into the tibial plateau 51. The Schanz screws 14 project beyond the dorsal cortex in the lateral beam path by no more than 2 mm.

8. Make parallel holes through the drill sleeves in the diaphyseal shaft area and screw in self-tapping Schanz screws 14th

9. Removing the hinge screw 33 and pulling the shaft member 20 of the two parallel Schanz screws 14 in the shaft 52 to ventral.

10. Tissue conserving osteotomy (dashed line X in Figure 1) to the placed guidewire (at the pivot point of the hinge joint) and control for completeness under imager and wound closure. Removal of the guide wire.

11. Placing the shaft member 20 and re-screwing the hinge screw 32nd

12. Shortening the Schanz screws 14 and fixing with the Verklemmungsvorrichtungen 16th

13. Attach Distraction Spindle 40.

14. Performing a continuous postoperative angle correction with the distraction spindle 40, wherein the end correction is shown in ventral view in FIG. 2 and the external fixator is inserted on a right tibial plateau 51 for valgization of the axis of the tibial shaft 52 with the medial opening angle β.

Claims

An external fixator for angular correction on a bone with an elongate head element (10) having at its ends a respective receiving opening (12, 13), at one end a laterally projecting arm (11), the end with a bore (30) is provided, and at its other end on the same side as the cantilever (11) projecting retaining flange (17), with an elongate shaft member (20) at its ends in each case a receiving opening (22, 23), at its one End having an arm (24) inclined away from the shaft member (20) so as to enclose therewith an angle (α) of 110 ° to 160 ° and having a bore (31) at its end, and between its ends the arm (24) opposite side has a further retaining flange (27), with a in the bores (30, 31) in the arm (24) or boom (11) for forming a hinge joint usable hinge screw (32) having a continuous central guide channel (34) has, with fastening elements (14), each in Verklemmungsvorrichtungen (16) of a receiving opening (12, 13; 22, 23) are held and can be fixed on the bone side, as well as with a distraction element (40) which is articulated at each end to a retaining flange (17, 27) (18, 28).

2. fixator external according to claim 1, characterized in that the arm (11) is arranged substantially perpendicular to the head element (10).

3. external fixator according to claim 1 or 2, characterized in that the head element (10) and the shaft element (20) each have two auxiliary bores (15, 25), each of which close to a receiving opening (12, 13; 22, 23 ) is arranged.

4. fixator external according to one of the preceding claims, characterized in that the auxiliary bores are arranged parallel to each other or at an acute angle of 3 ° to 10 ° to each other.

5. fixator external according to one of the preceding claims, characterized in that the bore (31) in the arm (11) is provided with an internal thread into which a male threaded portion on the hinge screw (32) is screwed, the thread-free portion in the bore ( 30) in the arm (24) to form the hinge joint sits.

6. fixator external according to one of the preceding claims, characterized in that the arm (24) and shaft member (20) enclosed angle (α) is 120 ° to 130 °.

7. fixator external according to one of the preceding claims, characterized in that the fastening elements Schanz screws (14) with Verklemmungsvorrichtun- conditions (16).

8. fixator external according to claim 7, characterized in that the Verklemmungs- device (16) has a Doppelkonusverklemmung for the fasteners.

9. fixator external according to one of the preceding claims, characterized in that the ratio of the lengths of the head element (10) to shaft member (20) is 1: 1 to 1: 1.8.

10. External fixator according to one of the preceding claims, characterized in that the ratio of the length of the arm (24) to head element (10) is 1: 1.4 to 1: 2.

11. Fixator external according to one of the preceding claims, characterized in that its components consist of titanium.

12. fixator external according to one of the preceding claims, characterized in that the distraction element (40) is a threaded spindle.