The invention relates to a ligament-tensioning device for use in the implantation of joint or skeletal implants in accordance with the preamble of claim 1.
Ligament-tensioning devices having such a function are known. For example, WO 00/78225 A1 discloses a ligament-tensioning device which, in addition to having a prismatic, cylindrical or plate-shaped base body, which has a bearing surface for bearing against a first bone adjoining a non-spherical joint, has right and left tensioning levers having second bearing surfaces which are to be applied to the joint-side surface of a second bone adjoining the joint, the operation of associated handgrips and operating levers being co-ordinated. The opposing portions (bearing surfaces) are supported with respect to one another by four-bar lever mechanisms.
DE 103 48 585 A1 discloses a further ligament-tensioning device which comprises a first, distal bearing plate for bearing against a first skeletal part and a second, proximal bearing plate for bearing against a second skeletal part, the two bearing plates being displaceable relative to one another by a hydraulic drive means and, especially, being tiltable relative to one another by means of a central axis. In addition, they are joined to one another by means of a base body, the distal bearing plate in particular being joined rigidly thereto.
WO 2004/078047 A1 discloses a further ligament-tensioning device in accordance with the preamble, which comprises a distal bearing plate and two proximal bearing plates independently guided and displaceable relative thereto. Guidance is effected therein in each case by means of a double hinge connection and the drive is preferably likewise effected hydraulically.
According to current experiences, the known ligament-tensioning devices still have certain disadvantages in use. Those disadvantages relate especially to the desired exact alignment between the opposing bearing plates and to the expense associated with a hydraulic drive device. In addition, when the known ligament-tensioning devices are used, the joint in question has to be kept open, because substantial parts of the device protrude.
The invention is therefore based on the problem of providing an improved ligament-tensioning device having a wide variety of possible applications that is economical and reliably satisfies the requirements of practice.
That problem is solved by a ligament-tensioning device having the features of claim 1. The dependent claims relate to advantageous developments of the inventive concept.
The invention includes the basic concept of providing a ligament-tensioning device that is fully insertable into the joint in question, thus making it possible to close the joint capsule again after insertion. For that purpose, in particular the bearing plates are to be dimensioned to match the joint in question—for example a knee joint—and projecting parts (such as, for example, handgrips/levers or hydraulic lines which project in the prior art) are to the greatest possible extent to be avoided. In that respect the invention includes the concept of providing a purely internal drive means or internal displacement means for the relative displacement of the opposing bearing plates.
In a preferred configuration, the invention includes the concept of providing parallel guidance between the distal bearing plate and the proximal bearing plates that is precise in both the ventral-dorsal and the medial-lateral directions. The current view is that this can be realised especially advantageously by a suitable guide means in accordance with the scissors principle. Other two-plane parallel guide means also come into consideration, however, for example the use of two hinge joints that are not axially parallel to one another (especially enclosing an angle of 90° with respect to one another).
In a relatively independent characterisation, the invention also includes the concept of providing, as drive means for pushing the distal bearing plate and the proximal bearing plates apart from one another, a separate drive element in each case, that drive element being, moreover, a drive element that functions without auxiliary energy. In that characterisation, the invention includes finally the concept of assigning to each proximal bearing plate a spring element which, in a starting state in which the proximal bearing plate is spaced a minimum distance apart from the distal bearing plate, stores the drive energy and releases it for the purpose of increasing the spacing when the ligament-tensioner is brought into operation. Finally, in a preferred configuration, the invention also includes the concept of assigning to that spring element or to the opposing bearing plates a locking means for releasable fixing in the starting position.
In principle, however, a drive means having auxiliary energy, for example an electromotive, electromagnetic, hydraulic or pneumatic drive means, also comes into consideration. Such a drive means can drive both proximal bearing plates jointly, it being possible for the bearing plates to take up different end positions in force equilibrium with the surrounding capsule/ligament structure. The said drive means can, however, also be provided separately for each proximal bearing plate.
It should be pointed out here that in the present description and the attached claims the terms “distal bearing plate” and “proximal bearing plate” are used with reference to preferred in-use positions of the ligament-tensioner, for example when used in the knee. For that application, it is also possible to speak synonymously of a tibia bearing plate and a femur bearing plate, respectively; the invention is also to be understood, however, as expressly including transpositions of the bearing plates in respect of their position further from or closer to the centre of the body (distal or proximal, respectively).
In a configuration that is preferred from the current standpoint, the spring element has a compression spring element which is arranged in a region of overlap between the proximal and distal bearing plates and is supported against both, the spring element having, especially, a steel or titanium helical spring having a suitable spring characteristic. It is distinguished by a spring constant matched to a predetermined tensioning force in order to provide, especially, a tensioning force that is substantially constant over its travel in the range between 50 and 90 N, especially 70 N.
In view of the special requirements of realising a relatively high and constant tensioning force and realising as small as possible an initial height of the spring element in the tensioned state, it is preferable to use special forms of the compression springs that are tailored thereto. A preferred form from the current standpoint is distinguished by the fact that the steel or titanium helical spring for increasing the travel is of conical or double-cone form and, especially, has a pitch indirectly proportional to the local winding diameter. The conical shape of the spring element is so chosen that the overall height in the tensioned state is substantially less than that of a comparable helical spring having a cylindrical basic shape.
In an alternative configuration, the spring element has a flexural spring element, more specifically, for example, a steel spiral or leaf spring.
The scissor-type guide means preferred as the parallel guide means preferably has two scissor joints arranged close to opposite ends of the proximal bearing plate, that is to say spaced as far apart from one another as possible. In various configurations of the invention it is possible for those scissor joints to be arranged in the ventral-dorsal direction (one behind the other) or in the medial-lateral direction (one next to the other). In an advantageous configuration of the scissor-type guide means, the ends of the scissor joints are inserted in grooves in the distal and proximal bearing plates and a limb or an end of each of the two limbs is rotatably fixed therein by means of bearing pins extending perpendicular to the run of the groove.
Additionally improved guidance and fixing to one another of the opposing bearing plates is obtained by providing at each end of the free limb or at the free end of each of the two limbs a slide peg for guiding the respective limb or end in a groove formed to match the slide peg. To increase the rigidity and to provide even better guidance, the scissor joints are preferably also joined to one another by means of at least one connecting rod mounted at the end of a limb of each scissor joint.
For adaptation to the specific anatomical conditions of different patients, the first and second proximal bearing plates each comprise an upper and a lower part, the lower part being provided with means for mounting the spring element and the scissor-type guide means and the upper part being fixed releasably on the lower part to increase the thickness of the bearing plate in question. The ligament-tensioning device can be used with a set of upper parts of different thicknesses to provide an especially precise solution to the mentioned adaptation problem.
The above-mentioned locking is advantageously released by the provision on the distal bearing plate or the first and second proximal bearing plates of releasable locking means for independent locking of the first and second proximal bearing plates to the distal bearing plate at a minimum spacing and with a maximum spring tension with respect thereto.
A preferred construction is obtained when the locking means each have a hook pivotally mounted on the respective bearing plate and engaging in the opposing bearing plate, on which hook there is provided a first tool-engagement portion for actuation. In view of the armoury of tools available in the field of application of the proposed ligament tensioner, the tool-engagement portion is preferably configured for engagement of a hex key tool, for example a 3.5 mm hex key.
In a first configuration of the locking means having a pivotable hook, an engagement portion for that hook is formed in the material of the first and second proximal bearing plates in spatial association with the hook articulated on the distal bearing plate.
In a second configuration, a first bearing peg of a scissor joint of the first and second proximal bearing plates projects beyond the outer edge thereof and is so arranged relative to the hook pivotally mounted on the distal bearing plate that it forms a counter-bearing of the locking means. In that configuration—or alternatively independently thereof—in a practical structural solution a second bearing peg of a scissor joint of the first and second proximal bearing plates projects beyond the outer edge thereof and is so arranged relative to the hook pivotally mounted on the distal bearing plate that it forms the hinge pin thereof
Since, on account of the high forces necessary, a tool is also advantageously used for positioning the ligament tensioner at the site of use, a second tool-engagement portion, especially a cylindrical recess, is preferably provided on the side edges of the distal bearing plate and of the first and second proximal bearing plates for engagement of a positioning tool. The provision of a separate tool is especially advantageous with a view to realising a ligament tensioner that can be fully integrated into a joint.
A further advantageous configuration provides a construction for the releasable coupling-on of a sizer, which couples the proximal and distal skeletal parts in flexion so that axis transmission from the one skeletal part to the other, taking account of the ligament tension, is possible. In principle, the coupling-on also covers simply being in contact with suitably prepared bearing surfaces, but it preferably includes connecting means for fixing the sizer on the distal bearing plate. In a configuration that is advantageous from the current standpoint, the connecting means comprise two clip-like extensions on the distal bearing plate which, each engaging around a side edge of the proximal bearing plates, run to a base plate of the sizer.
Arrangements comprising the proposed ligament-tensioning device and a matching positioning tool and/or a sizer matched thereto are also to be regarded as being included in the scope of protection of the invention.
Advantages and functional features of the invention will otherwise be found in the dependent claims and in the following description of preferred exemplary embodiments with reference to the Figures:
The ligament-tensioning device 1 comprises a distal bearing plate 5, which is approximately kidney-shaped in plan view, and, arranged in parallel therewith and opposite thereto, two proximal bearing plates 7 and 9 each of which overlaps approximately half of the distal bearing plate, the proximal bearing plates each comprising a lower part 7a, 9a and an upper part 7b, 9b. For positioning the ligament-tensioning device 1 with the aid of the positioning tool 3 there are provided on the front side edges of the distal and proximal bearing plates respective cylindrical recesses 11 as engagement portions (
The proximal bearing plates 7 and 9 (or, more specifically, the lower parts 7a, 9a thereof) are joined to one another by means of a scissor-type guide means 13 and are tensioned against one another by a steel compression spring 15 as spring element. As can be seen most clearly in
The scissor-type guide means 13 comprises medial and lateral scissor joints 19, 21 which each comprise two limbs 19a, 19b and 21a, 21b pivotally connected by means of a hinge pin 23, 25, respectively. The limbs 19a, 21a are joined to one another at one end by means of an integrally formed bridge or connecting bar 27, while a slide peg or pin 29a, 31a is inserted in their other end for connection to the lower part 9a (omitted in
The opposite ends of the limbs 19b, 21b are in turn each provided with a separate slide pin 29b, 31b, respectively. Those slide pegs 29b, 31b engage (as can be seen most clearly in
As can be seen most clearly in
Whereas in
The above-described ligament-tensioning device 1 is constructed for use in a knee joint and is shown in that in-use state in various views in
The implementation of the invention is not confined to the exemplary embodiment described herein and the last-mentioned modification of the spring element, but is also possible in a multiplicity of modifications which lie within the scope of technical action. For example, in particular a configuration is possible having a scissor-type guide means which is turned through 90° with respect to the embodiment shown and in which some of the slide pegs or pins can be constructed simultaneously as bearing pins for the fixed positioning of a limb end in the associated bearing plate. In such a configuration it is also possible for such a bearing pin to be used simultaneously as hinge pin of the pivotable locking hooks. Furthermore, in the case of the proximal bearing plates it is also possible for the upper parts to be omitted, and numerous degrees of freedom exist in respect of the exact shape and relative dimensions of the bearing plates.
Number | Date | Country | Kind |
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10 2005 049 851.5 | Oct 2005 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2006/010052 | 10/18/2006 | WO | 00 | 10/22/2008 |