Extension-assisted hinged knee replacement implant

Abstract

An extension-assisted hinged knee replacement comprises a femoral component, a tibial component, and a torque actuator operably interfacing the two components. The torque actuator is configured to apply extension torque based on the flexion angle of the knee, with the torque peaking between 0° and 90° of flexion. The implant may include a passive biasing element, which can be compressed or tensioned to enhance torque application, particularly during critical phases of knee extension.

Description

Extension-Assisted Hinged Knee Replacement ImplantField of the Invention

[0001] The present specification relates to the field of orthopaedic implants, specifically to hinged knee replacement implants. More particularly, it concerns an extension-assisted hinged knee replacement implant designed to provide dynamic extension assistance to patients with extension lag, improving knee joint function and mobility.Background of the Invention

[0002] Knee replacement surgery is a common procedure aimed at relieving pain and restoring function in severely diseased knee joints. While conventional knee replacement implants have been successful in many cases, there remains a significant challenge for patients suffering from extension lag, a condition where the knee cannot be fully straightened due to muscle weakness or other biomechanical limitations. This condition can significantly impair mobility and quality of life, leading to an increased need for assistive devices or additional therapeutic interventions.

[0003] Traditional hinged knee replacement implants provide a fixed range of motion, primarily focusing on enabling flexion and extension of the knee. However, these implants do not address the specific needs of patients with extension lag. Consequently, patients with extension lag often experience suboptimal outcomes, with residual difficulties in achieving full knee extension, leading to compromised gait patterns and reduced overall function.Summary of the Disclosure

[0004] There is provided herein an extension-assisted hinged knee replacement implant includes a femoral component and a tibial component that interfaces with the femoral component. A torque actuator is operably interfaced between the femoral component and the tibial component, designed to apply extension torque dependent on the flexion angle between these components. This torque peaks at a flexion angle between 0° and 90° and preferably 20° and 60°, providing assistance in extending the knee joint during movement.

[0005] The torque actuator can also be configured to apply flexion torque beyond 90°, which helps in controlling the movement when the knee is deeply flexed. The femoral component may define a bearing surface, with the tibial component comprising a bearing block that interfaces with this surface, ensuring smooth articulation and reducing wear.

[0006] In some configurations, the torque actuator may include a passive biasing element that applies a linear biasing force around the implant’s centre of rotation. This biasing element can be compressed or tensioned between femoral and tibial connection points, allowing for tailored torque application based on patient needs. The biasing element may be of various types, including hydraulic pistons, conical disc springs, or compression springs, offering flexibility in design and performance. When tensioned, the biasing element might be a tension spring, which can be arranged in an overcentred configuration. This overcentred configuration allows the extension torque to peak precisely at or before a flexion angle of 90°, optimising the torque applied during the most demanding phases of knee extension.

[0007] Further, the implant can include a tibial yoke that rotatably engages a hub through an offset pivot connection, which defines the femoral connection point for the passive biasing element. This arrangement enhances the mechanical advantage of the implant, particularly during extension. The passive biasing element may be installed within a stem defined by the tibial component, with the tibial connection point being adjustable. This adjustability, facilitated by a threaded nut engaging the internal threading of the stem, allows for precise calibration of the extension torque during implantation.

[0008] For added versatility, the implant may be configured for the selective installation of the passive biasing element. The tibial yoke could be designed to be interiorly accessible or openable, enabling easy installation or adjustment of the biasing element during surgery.

[0009] Other aspects of the invention are also disclosed.Brief Description of the Drawings

[0010] Notwithstanding any other forms which may fall within the scope of the present invention, preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[0011] Figure 1 shows an extension-assisted hinged knee replacement implant according to a first embodiment.

[0012] Figure 2 shows the implant in accordance with a second embodiment.

[0013] Figures 3 to 6 show the implant in accordance with a third embodiment, illustrating various flexion angles and the interaction between the femoral and tibial components.

[0014] Figure 3 shows the implant at a flexion angle of 0°, representing the knee in a straightened position.

[0015] Figure 4 shows the implant at a flexion angle between 30° to 60°, illustrating the application of extension torque by the torque actuator.

[0016] Figure 5 shows the implant as the femoral connection point approaches the over-centred position, demonstrating decreasing extension torque.

[0017] Figure 6 shows the implant at a flexion angle of 90°, where the femoral connection point is in alignment with the over-centred position, resulting in zero extension torque.

[0018] Figure 7 illustrates an embodiment where the extension torque peaks at approximately 45°, with a specific torque profile throughout the knee's range of motion.

[0019] Figure 8 illustrates another configuration with an extension torque peak at approximately 30°, including a change in torque direction beyond 70°.

[0020] Figure 9 illustrates a further embodiment with an extension torque peak at approximately 20°, and the subsequent application of flexion torque beyond the overcentred position.Description of Embodiments

[0021] Figure 1 shows an extension-assisted hinged knee replacement implant 100 according to a first embodiment. Figure 2 shows the implant 100 in accordance witha second embodiment, and Figures 3 to 6 show the implant 100 in accordance with a third embodiment.

[0022] The implant 100 comprises a femoral component 101 and a tibial component 102. In the embodiment shown, the tibial component 102 comprises a metallic body defining an intramedullary stem 103 and a bearing plate 104 with fasteners 105 for engaging a polymeric bearing block 106. The femoral component 101 may define a bearing surface 107 that articulates against a conforming bearing surface of the bearing block 106.

[0023] The implant 100 includes a torque actuator 108 operably interfacing the femoral component 101 and the tibial component 102. The torque actuator 108 is configured to apply extension torque between the femoral component 101 and the tibial component 102 to straighten the knee. With reference to Figures 7 to 9, the torque actuator 108 is designed to apply extension torque based on the flexion angle between the femoral component 101 and the tibial component 102. Figure 3 shows a flexion angle of 0° when the knee is straight, such as when standing upright, and Figure 6 shows a flexion angle of 90° when the knee is bent at a right angle, such as when seated.

[0024] The torque actuator 108 is configured so that the extension torque peaks at a flexion angle between 0° and 90°, more preferably between 20° and 60°. As such, the implant 100 maximises the extension torque at a position when it is most required to straighten the knee for those needing assisted leg extension. However, when the leg is straight or bent at approximately 90°, the extension torque is minimised, thereby not hindering natural movement.

[0025] Figure 7 shows an embodiment wherein the extension torque peaks at approximately 45°, applies a torque of approximately 0.35 N-m when the leg is straight, and applies zero torque when the knee is at approximately 1 10°. Figure 8 shows another configuration wherein the extension torque peaks at approximately 30°, with the implant 100 applying a torque of approximately 0.5 N-m when the knee is straight and a change in torque direction from extension to flexion at approximately70° (i.e., the torque crosses the zero line at approximately 70°). At approximately 120°, the implant 100 applies a flexion torque of approximately -1 N-m.

[0026] Figure 9 shows a further embodiment wherein the extension torque is maximised at approximately 20°, with the implant 100 applying approximately 0.6 N-m of torque when near straight and applying a change in torque direction from extension to flexion at approximately 70°.

[0027] In a preferred embodiment, the implant 100 comprises a passive biasing element 109 that applies a linear biasing force around to a centre of rotation 1 10 of the implant 100 which translates into torque.

[0028] In one embodiment (not shown), the passive biasing element 109 is compressed between connection points 1 1 1 arranged to maximise compressive force and extension torque at the target flexion angle (i.e. between 0° and 90°, more preferably between 20° and 60°). In this embodiment, the passive biasing element 109 may be a hydraulic piston, conical disc spring, compression spring, or similar device.

[0029] According to the preferred embodiment shown in Figures 1 to 7, the passive biasing element 109 is tensioned between the connection points 1 1 1 and may comprise a tension spring 1 12. In this arrangement, the connection points 1 1 1 are configured to maximise tension force and thereby extension torque at the target flexion angle.

[0030] The passive biasing element 109 may be tensioned in an over-centred configuration, having a centre position 1 13B in advance of or at a flexion angle of approximately 90°.

[0031] Figure 1 shows an embodiment wherein the implant 100 comprises a tibial yoke 1 14 defining a tibial connection point 1 1 1 B, retaining an inferior end of the tension spring 1 12, and wherein the femoral component 101 defines the corresponding femoral connection point 1 1 1 A, retaining a superior end of the tension spring 1 12.

[0032] At 0°, the tension spring 1 12 is in position 1 13A. As the knee bends, the distance between the connection points 1 1 1 A and 1 1 1 B increases, thereby increasingthe extension torque as the tension spring 1 12 moves towards the over-centred position 1 13B. However, as the tension spring 1 12 moves closer towards the overcentred position 1 13B, the femoral connection point 1 1 1 A moves into alignment with the centre of rotation 1 10 from the perspective of the tibial connection point 1 1 1 B, thereby diminishing the extension torque, hence the extension torque peaks shown in Figures 7 to 9. Beyond the over-centred position 1 13B, the tension spring 1 12 is tensioned anteriorly, thereby applying increasing flexion torque, as is evident from Figures 8 and 9.

[0033] According to the third embodiment shown in Figures 3 to 6, the tibial yoke 1 14 may rotatably engage a hub 1 15 by a pivotable connection 1 16. As is evident from Figures 3 to 6, as the knee bends, this offset pivotal connection 1 16 causes the hub 1 15 to rotate within the yoke 1 14. The hub 1 15 further defines the femoral connection point 1 1 1 A, and the rotating action achieves mechanical advantage allowing for greater offset of the femoral connection point 1 1 1 A from the tibial connection point 1 1 1 B than could be achieved using the straight connection of the first embodiment shown in Figure 1 .

[0034] At 0°, as shown in Figure 3, the distance between the connection points 1 1 1 may be minimised, and the tension spring 1 12 may be untensioned, thereby applying little or no extension force. As the knee bends from 0° to approximately 30° to 60°, as shown in Figure 4, the distance between the connection points 1 1 1 increases, thereby increasing the extension torque applied by the torque actuator 108. However, as the femoral connection point 1 1 1 A approaches the over-centred position 1 13B, as shown in Figure 5, the femoral connection point 1 1 1 A moves towards alignment with the over-centred position 1 13B from the perspective of the tibial connection point 1 1 1 B, thereby exhibiting decreasing extension torque.

[0035] At 90°, as shown in Figure 6, the femoral connection point 1 1 1 A is in exact alignment with the over-centred position 1 13B, thereby applying no extension torque, as is evident from the extension torque crossing the zero line shown in Figures 7 to 9. Beyond this position (i.e., when the femoral connection point 1 1 1 A passes the overcentred position 1 13B posteriorly), flexion torque is increasingly applied.

[0036] Figure 2 shows an embodiment wherein a pivot arm 1 17 engaging the hub 1 15 reaches the tension spring 1 12 located within the stem 103. This configuration allows for a longer tension spring 1 12 and can be accommodated by the third embodiment shown in Figures 3 to 6.

[0037] Moreover, the tibial connection point 1 1 1 B may be adjustably offset from the femoral connection point 1 1 1 A by a threaded nut 1 18 engaging the internal threading of the stem 103. The threaded nut 1 18 may be adjusted during installation using a screwdriver or similar tool.

[0038] In some embodiments, the biasing element 109 can be selectively installed during surgery based on the patient's biomechanical requirements. Specifically, the implant 100 may be configured to function without the biasing element 109 for standard operation or with the biasing element 109 installed to provide extension assistance. In this regard, the interior of the yoke 1 14 may be accessible or the yoke 140 may be openable to selectively install the biasing element 109.

[0039] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that specific details are not required in order to practise the invention. Thus, the foregoing descriptions of specific embodiments of the invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed as obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.

Claims

Claims1. An extension-assisted hinged knee replacement implant, comprising: a femoral component; a tibial component; a torque actuator operably interfacing the femoral component and the tibial component, wherein the torque actuator is configured to apply extension torque between the femoral component and the tibial component dependent on a flexion angle between the femoral component and the tibial component; and wherein the extension torque peaks at a flexion angle of between 0° and 90°.

2. The implant according to claim 1 , wherein the extension torque peaks at a flexion angle of between 20° and 60°.

3. The implant according to claim 1 or claim 2, wherein the torque actuator is configured to apply flexion torque at a flexion angle beyond 90°.

4. The implant according to any one of the preceding claims, wherein the femoral component defines a bearing surface, and the tibial component comprises a bearing block interfacing with the bearing surface.

5. The implant according to any one of the preceding claims, wherein the torque actuator comprises a passive biasing element applying linear biasing force around a centre of rotation of the implant.

6. The implant according to claim 5, wherein the passive biasing element is compressed between femoral and tibial connection points.

7. The implant according to claim 6, wherein the passive biasing element is selected from the group consisting of a hydraulic piston, a conical disc spring, and a compression spring.

8. The implant according to claim 5, wherein the passive biasing element is tensioned between femoral and tibial connection points.

9. The implant according to claim 8, wherein the passive biasing element comprises a tension spring.

10. The implant according to claim 8 or claim 9, wherein the passive biasing element is tensioned in an overcentred configuration.1 1. The implant according to claim 10, wherein the overcentred configuration has an overcentre position at a flexion angle of approximately 90°.

12. The implant according to claim 10, wherein the overcentred configuration reaches the overcentre position before a flexion angle of 90°.

13. The implant according to claim 5, wherein a tibial yoke rotatably engages a hub by a pivot connection offset from a centre of rotation defined by the implant, and wherein the hub defines a femoral connection point for the passive biasing element.

14. The implant according to any one of the preceding claims, wherein the passive biasing element is installed in a stem defined by the tibial component.

15. The implant according to claim 14, wherein a tibial connection point within the stem is adjustable.

16. The implant according to claim 15, wherein a threaded nut engages internal threading of the stem.

17. The implant according to claim 16, wherein the threaded nut can be adjustably offset using a tool.

18. The implant according to any one of the preceding claims, wherein the implant is configured for selective installation of the passive biasing element.

19. The implant according to claim 18, wherein the implant defines a tibial yoke that is interiorly accessible or openable for selective installation of the passive biasing element.

20. A method of providing knee joint extension assistance using an extension- assisted hinged knee replacement implant according to claim 1 , comprising inserting the implant into a patient's knee joint wherein the torque actuator provides extension torque between the femoral component and the tibial component, with the extension torque peaking at a flexion angle between 0° and 90°, thereby assisting the extension of the knee joint during movement.

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