Tension indicator

Abstract

The disclosure is directed to a tension indicator (1) suitable to be interconnected to at least one ligament (2, 3) in a patient's body, the tension indicator (1) comprising a deformation zone (4) configured to be deformed in relation to the tension in at least one ligament (2, 3) and a read-out element (5) for determining the tension in at least one ligament.

Description

[0001] Tension Indicator

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to a tension indicator suitable to be interconnected to at least one ligament in a patient’s body.

[0004] BACKGROUND OF THE DISCLOSURE

[0005] According to the prior art, spinal fusion by rigid metal rods attached to several vertebrae by screws for stabilizing them and if necessary insertion of intervertebral cages is a very common surgical procedure, among others in the treatment of degenerative disorders of the spine. However, spinal fusion is often associated with serious long-term complications such as adjacent segment degeneration, screw loosening, pseudo arthrosis, implant failure, and, in rare cases, neurovascular injury during implant insertion. Negative redistribution of loads with subsequently increased biomechanical stress are believed to act as accelerators of adjacent segment disease and proximal junctional kyphosis. Further, long fusions can lead to a relevant, irreversible loss of motion, which can cause postural changes. Although these challenges are well known, alternative techniques of spinal stabilizations have not yet yielded satisfactory results with broad clinical impact. Since about twenty years, a variety of semi-rigid fixation techniques has been proposed to overcome the above-mentioned challenges, but resulted in new complications at the implant-bone interface such as device breakage, dislocation or screw loosening. The above problems are successfully addressed in a particular way by a new method of soft spinal stabilization by posterior implementation and fixation of strap like implants in a manner, which does not negatively affect the biomechanics. A strap like implant is preferably in the form of a ligament. Good results can be achieved, when the implants, respectively the ligaments, are arranged in at least one closed loop or a series of parallel and / or intersecting loops entangling two spaced apart body components of the skeleton in a patient’s body and are then pretensioned in specific manner before being affixed. The component of the skeleton may e.g. be a vertebra or a rib. If the at least one loop entangles two or more of the same or different components, influence is taken on the resulting load path and load distribution. One difficulty, which occurs with this method is, that the implants which preferably are having a particular stress-strain characteristics, should be installed under an initial tension to bring the operating point of the resulting mechanical system to a defined value.

[0006] The present disclosure is directed to a tension indicator suitable to be interconnected to at least one ligament in a patient’s body. The at least one ligament may be an autograft ligament or allograft ligament or artificial ligament or a combination thereof. The tension indicator comprises a deformation zone configured to be deformed in relation to the tension in at least one ligament and a read-out element for determining the tension in at least one ligament, in particularly in a remote manner. Preferably, the tension indicator (as well as the ligament) are suitable to be fully implanted in a patient’s body. For reading out the read-out element, a read-out unit may be provided. The read-out unit may by arranged outside of the patient’s body. With such a tension indicator, it becomes possible to monitor the biomechanics in a non-invasive manner, e.g. by applying X-ray radiance. The tension indicator can further allow the application and fixation of said ligament in a controlled and gentle manner while the at least one ligament is under a specific tension. This is advantageous with respect to load distribution and thereby reduces the problems inherent to the prior art. It has been found that it is of particular importance, that the load level in the ligament is chosen in bio- mechanically appropriate manner.

[0007] The deformation zone of the tension indicator may be (primarily) elastically deformed. Advantageously, the deformation zone can be deformed in a continuous manner. Hence, the tension indicator may have multiple deformed positions, wherein each position can be associated with a respective tension in at least one interconnected ligament. Advantageously, the tension indicator in the deformed position can be matched to a calibration curve. The calibration curve thereby assigns each deformed position of the deformation zone a respective tension in at least one interconnected ligament. Usually, the ligament is pretensioned by a tensioning device during surgery while implanting the tension indicator and the at least one ligament. Initially (right after implantation) the ligament has thus an initial tension and the deformation zone of the tension indicator has a respective initial deformed position. Over time and during the healing process as well as during a possible dissolving of the ligament, the tension varies. Hence, the deformed positions vary over time. Thus, the tension in at least one ligament (or the respective deformed position) is an indicator for the healing process of the patient.

[0008] As mentioned above, the read-out element is preferably configured to be read out remotely, in particular from outside of the patient’s body. Thereby, the read- out element is configured to provide in a direct or indirect manner a read-out value associated with a deformed position of the deformation zone. The read-out value can be read-out by a read-out unit. The tension indicator and the read-out unit may be designated together as tension indicating unit. Depending on the application, the read-out unit may comprise a camera (such as e.g. a X-ray camera) to generate an optical image or a RFID reader, as explained in more detail below. Furthermore, the read-out unit may comprise a computational unit to automatically gauge the provided read-out value(s) from the optical image and process the read-out value(s) to provide a respective tension value of at least one ligament.

[0009] Depending on the application, the read-out element may comprise at least two measuring points having in an undeformed position (tension less state) a certain distance A, respectively a characteristic relation to each other. Depending on the tension in the interconnected ligament, the distance A, respectively relation varies in a predetermined manner. Depending on the design of the tension indicator, the distance A may be larger or smaller in relation to the tension in the interconnected ligament.

[0010] The at least two measuring points can be with respect to the deformation zone opposite of each other. Furthermore, the at least two measuring points can be with respect to the deformation zone opposite of each other in a first direction. The first direction may be arranged in the direction of at least one ligament. Preferably, the at least two measuring points each have a structural marker. The structural marker may e.g. comprise a geometry with a different density or radiation absorption capacity, e.g. in the form of a local thin spot of the structure of the tension indicator, than the adjacent areas of the tension indicator surrounding the structural marker. Hence, the structural marker(s) are easily and preferably automatically identifiable by the computational unit in an image to gauge the relevant distance A from the at least two measuring points (read-out value) of the embedded tension indicator in relation to the tension present in the at least one ligament. Knowing the initial distance A, a respective tension value present in at least one ligament interconnected to the tension indicator can be identified e.g. by the computational unit using a calibration curve.

[0011] Alternatively or in combination, the read-out element may comprise a reference geometry detectable by optical imaging methods, more particularly through X-ray radiation. The reference geometry may e.g. be an inner or outer contour of the tension indicator. Alternatively or in combination, a structural marker may be used (as explained above). The structural marker may e.g. be a line, being deformable together with the deformation zone. The read-out value of the read-out element may then be e.g. a curvature of the reference geometry (respectively the structural marker) in the deformed position of the deformation zone. Another example of the read-out value is e.g. an opening angle of the reference geometry.

[0012] For a good deformation quality, the tension indicator may comprise a super elastic material. However, it may be sufficient if at least the deformation zone comprises the super elastic material. A super elastic material is hereby understood as a type of material that can undergo large deformations while still being able to return to its original shape once the deformation is removed. This property is also known as "pseudo elasticity" or "shape memory" because the material can "remember" its original shape and return to it when stress is released. The superelastic materials can be a metal alloys, such as e.g. a nickel-titanium alloy.

[0013] Depending on the application, the tension indicator may comprise additionally or alternatively a biocompatible material. The biocompatible material can be a titanium (or alloy thereof), stainless steel, a ceramic or a polymer (e.g. polyethylene, in particular an ultra-high-molecular-weight polyethylene). Hence, in terms of a good biocompatibility and elastic deformation behavior, the tension indicator can comprise a nickel-titanium alloy.

[0014] Depending on the intended application, the tension indicator may have different shapes. The tension indicator and / or the deformation zone can e.g. be at least partially ring-shaped. A ring-shape can e.g. be at least partially round, elliptical and / or polygonal. The ring shape can also be interrupted by a gap, such that a c- shape is formed. Depending on the application, it may be advantageous, if the ring-shape is essentially round or elliptic in the undeformed initial position. In the deformed position, the ring-shape may be (more) elliptic. Thereby the local thickness of the tension indicator can vary along a circumferential direction of the tension indicator. If the read-out element is a reference geometry (e.g. in form of an inner or outer contour of the ring-shape the mathematical parameters of the ellipse may be calculated from one or more points of the reference geometry and used by the computational unit to determine the respective tension in at least one ligament. E.g., a calibration curve can be used, which associates each elliptical shape with a specific tension. Alternatively or in addition, the deformation zone may extend at least partially in the first direction in a zigzag form or in a waveform. In that case, at least the deformation zone may be made from a wire. In a deformed position, the tension indicator may thus expand in the first direction. The expansion is due to a smoothing out of the zigzag form or the waveform of the deformation zone in the first direction (under tension). In the deformed position, an opening angle between two adjacent legs of the zigzag shape may e.g. be larger than in the initial position. The opening angle may thus be a respective read-out value. Thereby the local thickness of the tension indicator can vary along a longitudinal direction of the tension indicator.

[0015] Depending on the application, the tension indicator can comprise at least one section to interconnect the tension indicator to at least one ligament. Depending on the application, the at least one section may comprise a clamping element to clamp the at least one ligament. If the tension indicator is at least partially ringshaped, the at least one section may be inside of the ring-shape or outside of the ring-shape or part of the ring-shape. The at least one section may thereby be curved in a manner, to prevent slipping of an attached ligament. The at least one section may e.g. curved outwards and / or inwards to prevent slipping of the attached ligament along the ring shaped tension indicator. Alternatively, the at least one section may comprises a thread eye to attach the ligament. At least one thread eye might also serve as a structural marker, respectively the first and / or second thread eye might also serve as a structural marker. Depending on the application, the tension indicator can comprise a (first) section to interconnect the tension indicator via a (first) ligament to a (first) body component. In addition, the tension indicator may comprise a second section to interconnect the tension indicator via a second ligament to a second body component. However, it is also possible, that the second section is also interconnectable via the first ligament to the second body component. Hereby, the first section can comprise a first thread eye to attach the first ligament. Equivalently, the second section may comprise a second thread eye to attach the first or the second ligament. Alternatively, the second section may also be designated to interconnect the tension indicator directly to the second body component, e.g. by an interconnection element such as a screw or an anchor. Preferably, the deformation zone is at least partially arranged between the first section and the second section in the first direction.

[0016] Depending on the application, the tension indicator can comprise at least three sections (e.g. three or four sections) to interconnect the tension indicator to at least one ligament. Three or four sections may be advantageous for applications of the tension indicator for the knee region of a patient’s body. However, at least three sections may also be used for spinal applications. If multiple sections are present, the tension indicator is preferably designed symmetrical with respect to a central axis. The respective sections may have the same distance (in an undeformed position) to the central axis of the tension indicator. Furthermore, if the tension indicator is ring-shaped, the respective sections are preferably evenly distributed along the circumference of the ring-shape. Between the respective adjacent sections, a deformation zone may be present. Hence, multiple deformation zones are possible. Depending on the application, the read-out element may comprise a scaling element. The scaling element is preferably not deformable. The scaling element serves to provide an additional (second) read-out value that may be used to correct the (first) read-out value due to distortions caused by the orientation of the tension indicator with respect to the read-out unit. The scaling element may comprises two additional measuring points, having a fixed distance from each other in (all) deformed positions. Additionally or alternatively, the scaling element may comprises an additional reference geometry, having e.g. a defined angle in (all) deformed positions.

[0017] Depending on the application, the read-out element may also be a RFID (Radio Frequency Identification) chip. Hereby, the RFID chip can be medical-grade RFID chip designed to be biocompatible. The RFID chip can be passive (meaning it does not have its own power source) or active (meaning it has its own battery). The RFID chip may be interconnected to a strain gauge. The strain gauge is advantageously placed in the area of the deformation zone. Thus, the RFID chip can provide a strain value (as a read-out value) to be read out remotely, in particular from outside of the patient’s body. Furthermore, the RFID chip may provide multiple strain values. E.g., the RFID chip can provide a strain history with multiple strain values over time. For reading out the RFID chip, the read-out unit comprises a RFID reader, in particular placed outside of the patient’s body.

[0018] It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS The herein described disclosure will be more fully understood from the detailed description given herein below and the accompanying drawings, which should not be considered limiting to the disclosure described in the appended claims. The drawings are showing:

[0020] Fig. 1 a first variation of a tension indicator according to the disclosure in an initial undeformed state;

[0021] Fig. 2 the first variation of a tension indicator according to Figure 1 in a deformed state;

[0022] Fig. 3 a second variation of a tension indicator according to the disclosure in a deformed state; Fig. 4 a third variation of a tension indicator according to the disclosure;

[0023] Fig. 5 a fourth variation of a tension indicator according to the disclosure;

[0024] Fig. 6 a fifth variation of a tension indicator according to the disclosure. DESCRIPTION OF THE EMBODIMENTS

[0025] Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all features are shown. Indeed, embodiments disclosed herein may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.

[0026] Figure 1 shows a first variation of a tension indicator 1 according to the disclosure in an initial undeformed state and Figure 2 in a respective deformed state. The first variation refers to a ring-shaped tension indicator 1 . The tension indicator 1 comprises a first section 6 to interconnect the tension indicator 1 via a first ligament 2 to a (schematically shown) first body component 8 and a second section 7, which may serve to interconnect the tension indicator 1 via a second ligament 3 to a (schematically shown) second body component 9. In the shown variation the ligaments 2, 3 are threaded through the ring-shaped tension indicator 1 in the area of the first and second section 6, 7. However, it is also possible that the first section 6 comprises a first thread eye to attach the first ligament 2 and / or the second section 7 comprises a second thread eye to attach the second ligament 3. Also possible is that the first section 6 and the second section 7 are curved outwards with respect to the shown ring-shape to prevent slipping of the attached ligaments 2, 3.

[0027] In the shown variation, the tension indicator 1 features a read-out element 5, which comprises at least two measuring points each having a structural marker. The structural marker is detectable by optical imaging methods, in particular through X-ray radiation. The distance A of the at least two measuring points from each other in the at least one deformed position is thereby a read-out value of the read-out element 5. In Figure 2 the tension indicator 1 in shown in a deformed position in a patient’s body 14. It can be seen that the round shape of the tension indicator 1 in the initial undeformed position (Figure 1) has in the deformed position (Figure 2) an elliptical ring-shape. Thus, the distance A of the structural markers from each other in the undeformed position is reduced compared to the deformed position. Outside of the patient’s body 14, the read-out unit 10 is shown schematically. The tension indicator 1 and the read-out unit 10 may be designated together as tension indicating unit 1 1. The read-out unit 10 comprise a camera 13 to generate an optical image (such as e.g. a X-ray camera). Furthermore, the read-out unit 10 comprises a computational unit 12 to automatically gauge the (indirectly) provided read-out value in form of the distance A from the structural marker from the optical image and process the read-out value in a respective tension value of at least one ligament 2, 3, e.g. with the help of a calibration curve. Alternatively, the read-out element 5 may also be a reference geometry in form of an inner or outer contour of the ring-shaped tension indicator 1 . From one or more points on the contour, e.g. the mathematical parameters of the ellipse may be calculated by the computational unit 12, which again may be associated with a respective tension in at least one ligament 2, 3 through at least one calibration curve.

[0028] Figure 3 shows a second variation of a tension indicator 1 according to the disclosure in a deformed state. The second variation differs from the first variation in that the read-out unit 10 and the read-out element 5 are different. In the second variation, the read-out element 5 is a RFID chip interconnected to a strain gauge 15 of the tension indicator 1. The strain gauge 15 is placed in the deformation zone 4. Thus, the RFID chip 5 (directly) provides a strain value (as a read-out value) to the read-out unit 10 remotely. Consequently, the read-out unit 10 (which in the shown example is placed outside of the patient’s body 14) comprises a RFID reader 16 as well as a computational unit 12. With the computational unit 12 and a calibration curve the tension in the at least one ligament 2, 3 can be determined from the transmitted strain value.

[0029] Figure 4 and Figure 5 display further variations of a tension indicator according to the disclosure. Figure 4 thereby refers to the deformation zone 4 of the tension indicator 1 extending in a first direction in a waveform and Figure 5 refers to the deformation zone 4 extending in a first direction in a zigzag form. Both variations are depicted in the undeformed initial position of the deformation zone 4. In a deformed position, the respective zigzag and waveform is smoothed out in the first direction. Both tension indicators 1 have a first section 6 to interconnect to first ligament 2 and a second section 7 to interconnect a second ligament 3. Through the ligaments 2, 3 the tension indicator 1 is interconnected to a first and a second body component 8, 9 of the patient’s body 14. As a read-out element 5 different approaches can be chosen for both variation. For interconnecting the ligaments 2, 3, the first and the second section 6, 7 each comprise a thread eye. These thread eyes may e.g. serve as structural markers of the read-out element 5. Consequently, the distance A between the thread eyes may serve as a readout value. Alternatively, a curvature of the wave of the wave-formed deformation zone 4 (Figure 4) or an opening angle between two adjacent legs of the zigzag shaped deformation zone 4 (Figure 5) may serve as a read-out value. In the deformed position, the opening angle between two adjacent legs of the zigzag shape may e.g. be larger or the curvature of the waves smaller than in the initial position. Alternatively, different structural markers can be placed on other parts the tension indicator 1 or (equivalently to the second variation) a strain gauge and an RFID chip can be used.

[0030] Figure 6 displays a further variation of a tension indicator 1 according to the disclosure. The tension indicator 1 comprises four sections 6, 7, 17, 18 to interconnect the tension indicator to at least one ligament. Another number of sections is also possible. Each section 6, 7, 17, 18 is thereby a protrusion extending outwards from the ring shaped tension indicator 1 . The respective sections 6, 7, 17, 18 may have a thread eye (not shown) to interconnect the ligament(s). Alternatively, the same ligament can be interconnected to all sections or multiple ligaments can be interconnected. Figure 6 depicts the case, where each section is interconnected to a different ligament 2, 3, 19, 20. As can be seen, the tension indicator 1 is designed symmetrical with respect to a central axis around which the ring-shaped tension indicator 1 extends in a circumferential direction. Furthermore, the sections 6, 7, 17, 18 are evenly distributed along the circumference of the ring-shape in the undeformed position. Between the respective adjacent sections 6, 7, 17, 18 a deformation zone 4 is present. The thickness of the tension indicator 1 may vary along the circumferential direction of the tension indicator 1 . E.g. can the thickness be reduced in the area of the respective deformation zones 4. In the shown variation, the tension indicator 1 features a read-out element 5, which comprises four measuring points with a structural marker. The structural markers are detectable by optical imaging methods, in particular through X-ray radiation. The distance of at least two measuring points from each other in the at least one deformed position may thereby represent a read-out value of the readout element 5. Having multiple deformation zones 4 and respective read-out values may give insight in an uneven tension in the different ligament 2, 3, 19, 20.

[0031] Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the scope of the disclosure.

[0032] LIST OF DESIGNATIONS

[0033] 1 Tension Indicator 11 Tension indicating unit

[0034] 2 First ligament 12 Computational unit

[0035] 3 Second ligament 13 Camera

[0036] 4 Deformation zone 14 Patient’s body

[0037] 5 Read out element 15 Strain gauge

[0038] (measuring point) 16 RFID reader

[0039] 6 First section 17 Third section

[0040] 7 Second section 18 Fourth section

[0041] 8 First body component 19 Third ligament

[0042] 9 Second body component 20 Fourth ligament

[0043] 10 Read-out unit 21 Body (patient)

Claims

PATENT CLAIMS1 . A tension indicator (1 ) suitable to be interconnected to at least one ligament (2, 3) in a patient’s body (21 ), the tension indicator (1 ) comprising: a. a deformation zone (4) configured to be at least partially deformed in relation to the tension in at least one ligament (2, 3); and b. a read-out element (5) for determining the tension in the at least one ligament (2, 3).

2. The tension indicator (1 ) according to claim 1 , wherein the read-out element (5) is configured to be read out remotely.

3. The tension indicator (1 ) according to any of the preceding claims, wherein the read-out element (5) is configured to provide directly or indirectly one or multiple read-out values associated with at least one deformed position of the deformation zone (4).

4. The tension indicator (1 ) according to claim 3, wherein the read-out element (5) comprises at least two measuring points (5) detectable by optical imaging methods, in particular through X-ray radiation, and the read-out value is a distance of the at least two measuring points from each other in the at least one deformed position.

5. The tension indicator (1 ) according to claim 4, wherein the at least two measuring points are with respect to the deformation zone (4) opposite of each other.

6. The tension indicator (1 ) according to claim 4 or 5, wherein the at least two measuring points each have a structural marker is a geometry with a different density or radiation absorption capacity.

7. The tension indicator (1 ) according to claim 1 to 3, wherein the read-out element (5) comprises a reference geometry detectable by optical imaging methods, in particular through X-ray radiation.

8. The tension indicator (1 ) according to claim 3 and 7, wherein the read-out value of the read-out element (5) is a curvature or an opening angle of the reference geometry in the deformed position of the deformation zone (4).

9. The tension indicator (1 ) according to one of the preceding claims, wherein the tension indicator (1) comprises a biocompatible material.

10. The tension indicator (1 ) according to one of the preceding claims, wherein the tension indicator (1) is at least partially ring-shaped.11 . The tension indicator (1 ) according to one of the preceding claims, wherein the deformation zone (4) extends in a first direction in a zig-zag manner or in a waveform.

12. The tension indicator (1 ) according to one of the preceding claims, wherein the tension indicator (1 ) comprises a first section (6) to interconnect the tension indicator (1 ) to a first ligament (2) to a first body component (8) and / or a second section (7) to interconnect the tension indicator (1 ) a. via a second ligament (3) to a second body component (9); b. via the first ligament (2) to the second body component (9); or c. directly to the second body component (9).

13. The tension indicator (1 ) according claim 12, wherein the first section (6) comprise a first thread eye to attach the first ligament (2) and / or the second section (7) comprises a second thread eye to attach the first or the second ligament (2, 3).

14. The tension indicator (1 ) according to claim 10 and 12, wherein the first section (6) and / or the second section (7) are curved outwards with respect to the ring-shape to prevent slipping of the attached ligament (2, 3).

15. The tension indicator (1 ) according to any of the preceding claims, wherein the read-out element (5) is a RFID chip.

16. A tension indicating unit (1 1 ) comprising a tension indicator (1 ) according to one of the preceding claims and a read-out unit (10) to read-out the read- out-element (5) of the tension indicator (1 ).

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