Knee implant with braking and biasing mechanisms for controlled joint stability

Abstract

A knee implant provides enhanced joint stability and controlled movement. The implant comprises a femoral component, a tibial component, and a braking mechanism operative therebetween. The braking mechanism includes a barrel, a shaft, and clutch plates alternately keying the barrel and shaft in a non-rotatable manner. A plunger, displaced under compression force between the components, compresses the clutch plates to create frictional engagement, restricting or locking relative movement under weight-bearing conditions. This allows stability during standing and controlled mobility when compression is reduced. Optionally, a magnetic biasing mechanism applies variable torque between the components, adapting joint behaviour to different loading conditions. The combined braking and biasing mechanisms provide reliable support and improved control for patients requiring joint stability during functional activities.

Description

Knee Implant with Braking and Biasing Mechanisms for ControlledJoint StabilityField of the Invention

[0001] The field of the invention is orthopaedic implants and, more specifically, knee implants designed to provide controlled joint stability and support for patients with impaired knee joint function. The invention relates to knee implant systems that incorporate braking and optional biasing mechanisms to enhance stability and movement control under various load conditions.Background of the Invention

[0002] Arthrodesis of the knee joint, also known as knee fusion, is a surgical procedure that involves the fusion of the bones in the knee joint. It is usually performed to treat severe knee arthritis or joint instability when other conservative treatments have failed.

[0003] During the procedure, the cartilage surfaces of the knee joint are removed, and the bones of the thigh (femur) and shin (tibia) are fused together using screws, plates, or rods. The fusion eliminates the joint space and prevents any movement between the bones, resulting in a solid and stable knee.

[0004] Arthrodesis of the knee joint is typically considered a salvage procedure when all other attempts to preserve the joint or relieve pain have been unsuccessful. While it eliminates pain caused by joint movement, it also leads to loss of knee flexibility. Therefore, it is usually reserved for cases where the individual has significant functional limitations and is not suitable for knee replacement surgery.

[0005] Following arthrodesis of the knee joint (knee fusion), mobility problems are expected due to the elimination of joint movement. The fusion results in a solid connection between the femur and tibia bones, which restricts the normal bending and straightening motion of the knee.

[0006] Mobility issues associated with knee arthrodesis include loss of knee flexibility. Since the joint is fused, the ability to bend the knee and achieve a full range of motion is lost. The knee remains in a fixed position, usually at a slightly bent angle.

[0007] Furthermore, walking patterns are altered after knee fusion. The lack of knee movement affects the normal gait pattern, making it more difficult to walk with a smooth and natural stride. The individual may experience a limp or rely on compensatory movements from other joints, such as the hip.

[0008] Yet further, negotiating stairs becomes challenging after knee arthrodesis. The inability to bend the knee hampers the ability to flex and extend the leg adequately while climbing or descending stairs.

[0009] Also, activities that require significant knee movement, such as running, jumping, or squatting, are typically difficult or impossible to perform after knee fusion.

[0010] Furthermore, with the loss of knee joint function, adjacent joints such as the hip and ankle may experience increased stress. These compensatory movements can lead to accelerated wear and tear on these joints over time.

[0011] An alternative to arthrodesis of the knee joint (knee fusion) for individuals who have significant knee problems but wish to preserve some degree of joint mobility include total knee replacement (TKR) which involves removing the damaged portions of the knee joint and replacing them with artificial prosthetic components. This procedure allows for restoration of joint function, pain relief, and improved mobility. TKR is often recommended for individuals with severe arthritis or joint degeneration who desire increased knee flexibility.

[0012] An alternative to Arthrodesis or active knee joints is above knee amputation. Patients who undergo above knee amputation might achieve higher functional mobility scores compared to those who undergo arthrodesis. However, individuals with above knee amputation may encounter challenges with external sock prosthetic complications, such as skin sores, lesions, and pain. These issues can lead to a temporary reliance on wheelchairs until the skin and wounds have healed. Another drawback of external prosthetics is their high physiological cost index of mobility, demanding more energy for mobilisation. Additionally, the devices are costly, both in terms of the initial investment and the need for regular revisions / modifications as the patient's residual limb geometry changes over time.

[0013] Some types of advanced knee prosthesis incorporate components designed to enhance the functionality and performance of the artificial joint. Unlike traditional passive knee implants, which provide a fixed range of motion, active knee implants aim to replicate a more natural knee movement and improve overall joint function.

[0014] These implants may utilise active or passive actuators to provide controlled movement and adjust joint mechanics. These actuators can modify the joint's resistance, damping, or stiffness to accommodate different activities and improve stability.

[0015] The present invention seeks to provide a knee implant which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative.Summary of the Disclosure

[0016] The present disclosure relates to a knee implant designed to provide enhanced stability and controlled movement. The implant comprises a femoral component, a tibial component, and a braking mechanism operative between the femoral and tibial components. The braking mechanism includes a barrel, a shaft, and a series of clutch plates arranged along the shaft within the barrel, which alternately key the barrel and the shaft in a non-rotatable manner. A plunger within the braking mechanism is configured to be displaced relative to the barrel under compression force exerted between the femoral and tibial components, compressing the clutch plates against each other to create frictional engagement between the barrel and the shaft.

[0017] The braking mechanism utilises a structure that, under weight-bearing conditions, increases the frictional engagement to restrict or even lock movement between the femoral and tibial components. This design enables the knee implant to provide stability when required, such as during standing, while permitting movement when the compression force is reduced.

[0018] Additionally, the knee implant may optionally comprise a magnetic biasing mechanism configured to apply a biasing torque between the femoral and tibial components. This mechanism can provide enhanced control over the relativepositioning of the components, adapting the joint's behaviour to various loading conditions.

[0019] The braking mechanism, along with any optional features, facilitates controlled, stable joint mechanics, addressing issues related to knee joint stability in patients with mobility impairments.

[0020] According to one aspect, there is provided a knee implant comprising a femoral component, a tibial component, and a braking mechanism operative therebetween, the braking mechanism including a barrel, a shaft, and a series of clutch plates alternately keying the barrel and shaft, together with a plunger that, under compression force, compresses the clutch plates to frictionally engage the barrel to the shaft.

[0021] In some embodiments, the barrel may define internal grooves, with a barrelengaging set of clutch plates provided with external teeth for non-rotatable sliding engagement, while the shaft may define external grooves for engagement with corresponding internal teeth of a shaft-engaging set of clutch plates. This arrangement increases structural integrity and allows smooth assembly within the limited implant envelope.

[0022] The series of clutch plates can advantageously include alternating polymeric and metallic plates, with the polymeric plates engaging the barrel and the metallic plates engaging the shaft. Such alternation distributes load effectively, prolongs the operational life of the polymeric elements, and enhances overall frictional engagement between adjacent plates.

[0023] In further forms, the braking mechanism may include a barrel end cap attachable to the barrel, the end cap defining a bearing face against which the clutch plates are pressed. This facilitates a compact, sealed construction that prevents escape of debris and enhances implant longevity.

[0024] In an alternative configuration, the plunger may incorporate a wedge plate having corrugations, with an adjacent clutch plate bearing corresponding corrugations. Displacement of the wedge plate under compression force translatesdirectly into movement of the innermost clutch plate, thereby improving the responsiveness of the braking action.

[0025] Optionally, a magnetic biasing mechanism may be provided to apply a torque between the femoral and tibial components. The magnetic biasing mechanism can employ rotors with permanent magnet segments, where the induced torque varies depending on their rotational offset. This enables fine control of joint behaviour under different load conditions, providing stability at certain angular positions while reducing resistance at others.

[0026] Preferably, the magnetic rotors may comprise adjacent discs with axially operative magnets, or concentric rings with radially operative magnets, enabling flexible design options tailored to the required torque profile.

[0027] In still further embodiments, the braking mechanism may be housed within a dedicated structure, with a plunger housing recessed within a tibial bearing block. The plunger housing may define protrusions keying into the tibial block, thereby resisting twisting forces.

[0028] In a particularly advantageous arrangement, a spring mechanism may be compressed between the plunger and the housing to offset the applied compression force, providing a controlled restoring effect that complements the braking action. A chamber within the housing may slidably engage and seal against the plunger, thereby preventing debris escape and maintaining implant cleanliness.

[0029] Other aspects of the invention are also disclosed.Brief Description of the Drawings

[0030] 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:

[0031] Figure 1 is a disassembled view of the knee implant, illustrating the femoral component, tibial component, and the braking mechanism with its internal components, including the barrel, shaft, and clutch plates.

[0032] Figure 2 is a detailed view of the clutch plates within the braking mechanism, showing the arrangement of the barrel-engaging and shaft-engaging sets, as well as the internal and external grooves and teeth configurations.

[0033] Figure 3 is a perspective view which shows the braking mechanism assembled.

[0034] Figure 4 is an illustration of the tibial component with the metallic tibial tray, showing the locking formations for affixation to the undersurface of the polymeric tibial bearing block.

[0035] Figure 5 is a view of the plunger housing recessed within the channel of the tibial bearing block, including the connectors engaging sockets of the plunger housing and the arrangement of the plunger with the tibial tray.

[0036] Figure 6 is a view of the magnetic biasing mechanism, showing the magnetic rotors with permanent magnet segments in a quadrant configuration.

[0037] Figure 7A is an example where the magnetic poles of the segments align, creating a magnetically repulsive state with zero torque, corresponding to a knee bend at 90°.

[0038] Figure 7B is a partially aligned position of the magnetic poles, maximising torque for a knee bend at 45°.

[0039] Figure 7C is an unaligned position of the magnetic poles, providing stable zero torque for a straight knee position.

[0040] Figure 8 is an embodiment of the magnetic biasing mechanism where the rotors are adjacent discs, with magnet segments operative axially between them.

[0041] Figure 9 is a view of the plunger with a wedge plate having corrugations, illustrating how the corrugations engage with the innermost clutch plate to translate displacement of the wedge plate under compression force.Description of Embodiments

[0042] Figure 1 shows a disassembled knee implant 100 comprising a femoral component 101 , a tibial component 102, and a braking mechanism 103 operative between the femoral component 101 and the tibial component 102. The braking mechanism 103 comprises a barrel 104, a shaft 105, and a series of clutch plates 106arranged along the shaft 105 and within the barrel 104. The clutch plates 106 non- rotatably key the barrel 104 and the shaft 105, respectively.

[0043] The braking mechanism 103 further comprises a plunger 107 that is displaced relative to the barrel 104 and the shaft 105 under compression force between the femoral component 101 and the tibial component 102, compressing the clutch plates 106 against each other to frictionally engage the barrel 104 with the shaft 105. In the embodiment shown, the femoral component 101 is fixed with respect to the shaft 105, and the tibial component 102 is fixed with respect to the barrel 104. When little or no weight is borne by the implant 100, the clutch plates 106 exhibit minimal frictional engagement, thereby allowing relatively free movement between the femoral component 101 and the tibial component 102. However, when weight is applied to the implant 100, such as when standing upright, the compression force causes the tibial component 102 to displace the plunger 107 relative to the barrel 104, compressing the clutch plates 106 to increase frictional engagement between the barrel 104 and the shaft 105, thereby resisting movement or even locking the femoral component 101 relative to the tibial component 102 until the weight is lifted.

[0044] The series of clutch plates 106 maximise frictional contact surface area, reducing wear, increasing operational longevity, and minimising debris shedding. Furthermore, use of multiple clutch plates 106 enhance the frictional engagement force achievable within the relatively small confines required for the implant 100.

[0045] With reference to Figure 2, the clutch plates 106 may comprise a barrelengaging set 106A and a shaft-engaging set 106B, which are alternately arranged or interleaved along the shaft 105. The barrel 104 may define internal grooves 108, and the barrel-engaging set 106A may define external teeth 109A that non-rotatably and slidably engage the internal grooves 108. Additionally, the shaft 105 may define external grooves, and the shaft-engaging set 106B may define internal teeth 109B that non-rotatably and slidably engage the external grooves of the shaft 105.

[0046] Preferably, the clutch plates 106 comprise an alternating arrangement of nonmetallic / polymeric and metallic clutch plates 106 to enhance frictional engagement between adjacent clutch plates 106 and to benefit from the resilientproperties of the metallic clutch plates 106. According to the arrangement shown in Figure 2, the barrel-engaging set 106A is polymeric, while the shaft-engaging set 106B is metallic. The polymeric barrel-engaging set 106A is relatively larger than the metallic shaft-engaging set 106B, reducing stress on the relatively weaker polymeric material. Additionally, the polymeric barrel-engaging set 106A has a greater number of teeth 109, which distributes torque force among them to improve the operational longevity of this relatively weaker material.

[0047] The braking mechanism 103 may comprise a barrel end cap 110 attachable to the barrel 104. As shown in Figure 1 , the end cap 110 and the barrel 104 may have twist-lock engagement formations and may be sealed with an O-ring or gasket to prevent escape of any shed debris. The end cap 110 may define a bearing face 111 against which the outermost clutch plate 106 is ultimately pressed.

[0048] With reference to Figure 9, the plunger 107 may define a wedge plate 112 with corrugations 113, where an innermost clutch plate 106 adjacent to the wedge plate 112 has corresponding corrugations 113B. These corrugations 113 translate the displacement of the wedge plate 112 relative to the barrel 104 under compression force into movement of the innermost clutch plate 106 along the shaft 105, thereby compressing the other clutch plates 106. The corrugations 113 may be nonsymmetric with respect to a displacement axis to control the rate of displacement under compression. Preferably, the wedge plate 112 is metallic and the innermost clutch plate 106 adjacent to it is polymeric.

[0049] In the embodiment shown in Figure 1 , the shaft 105 extends through an aperture 114 defined by the wedge plate 112, and the clutch plates 106 are arranged on both sides of the wedge plate 112, allowing them to compress against respective bearing faces 111 of the end caps 110.

[0050] In a preferred embodiment, the implant 100 further comprises a magnetic biasing mechanism 115 configured to apply a biasing torque between the femoral component 101 and the tibial component 102. The magnetic biasing mechanism 115 may comprise a pair of magnetic rotors 116, which vary the magnetically induced torque based on their rotational offset relative to each other.

[0051] According to Figure 6, the rotors 116 may comprise permanent magnet segments 117. Figure 7A shows an example where the magnetic poles of the segments 117 align, creating an unstable, magnetically repulsive state with zero torque (such as when the knee is bent at 90°). Figure 7B shows a partially aligned position that maximises torque (such as when the knee is bent at 45°), and Figure 7C shows an unaligned, magnetically attractive position providing stable zero torque (such as when the knee is straight). The number of magnet segments 117 may be adjusted based on the desired biasing action. In the embodiment shown in Figure 6, each rotor 116 comprises a quadrant of permanent magnet segments 117, while the embodiment in Figure 7 shows eight magnet segments 117 per rotor.

[0052] The table below illustrates various potential configurations:

[0053] In embodiments, the implant 100 may utilise electromagnets instead of permanent magnets. According to the embodiment shown in Figure 8, the rotors may define adjacent discs 118 with the magnet segments 117 operative axially between them. Alternatively, Figure 7 shows rotors comprising concentric rings with the magnet segments 117 operative radially between them.

[0054] The magnetic biasing mechanism 1 15 may be contained within a housing defined between the barrel end cap 110 and an implant end cap 120. The implant end cap 120 may define a radial projection 121 with fastener apertures aligning with those of a femoral collar 122 to fix the femoral component 101 to the shaft 105. In this regard, the shaft 105 may define a distal geared end 123 that non-rotatably insertsinto a socket 124 with internal teeth within the implant end cap 120. The implant end cap 120 may define side buttresses 124 that non-rotatably key into a condylar component (not shown), which articulates against a bearing surface 125 of a polymeric tibial bearing block 126. With reference to Figure 4, the tibial component 102 may comprise a metallic tibial tray 127 defining locking formations 128 for affixation to an undersurface of the polymeric bearing block 126.

[0055] With reference to Figure 5, the implant 100 may further comprise a plunger housing 129, which may be slidably recessed within a channel 130 of the tibial bearing block 126 and fixed to a housing of the braking mechanism 103. The barrel end caps 110 may define connectors 131 that engage sockets 132 defined by the plunger housing 129. The plunger housing 129 slidably engages the plunger 107 to fix the plunger 107 to the tibial component 102. In this regard, the plunger 107 may define feet 137, which insert through apertures 138 in the plunger housing 129 and apertures 139 in the tibial tray 127.

[0056] The plunger housing 129 may define a series of side protrusions 133, and the channel 130 may have a corresponding cross-section to increase surface area and non-rotational keying between the plunger housing 129 and the tibial bearing block 126, resisting twisting forces.

[0057] A spring mechanism 134 may be compressed between the plunger 107 and the plunger housing 129 in opposition to any applied compression force. The plunger housing 129 may define a chamber 135, within which the plunger 107 slides and seals, preventing the escape of any shed debris from the braking mechanism housing. The plunger 107 may comprise a series of O-rings 136 to seal within the chamber 135.

[0058] In operation, the knee implant 100 is positioned within a patient such that the femoral component 101 is affixed to the distal femur and the tibial component 102 is affixed to the proximal tibia. During normal weight-bearing activity, compressive force is transmitted between the femoral component 101 and the tibial component 102, causing the tibial component 102 to displace the plunger 107 relative to the barrel 104. This displacement compresses the clutch plates 106 against each other alongthe shaft 105, thereby frictionally engaging the barrel 104 to the shaft 105. Under full weight-bearing, such as when the patient stands, the increased frictional engagement resists or locks relative movement between the femoral component 101 and the tibial component 102, enhancing joint stability.

[0059] When the patient reduces loading, for example during a swing phase of gait, the compressive force on the plunger 107 decreases, thereby relieving pressure on the clutch plates 106. Reduced frictional engagement between the barrel 104 and shaft 105 allows freer articulation of the femoral component 101 with respect to the tibial component 102, permitting smoother flexion and extension of the knee implant 100.

[0060] Where the magnetic biasing mechanism 115 is employed, the rotors 116 with permanent magnet segments 117 generate a variable torque dependent on their angular offset. At specific ranges of motion, such as around 45° of knee flexion, the magnetic biasing mechanism 115 provides stabilising torque, whereas at other positions, such as full extension or 90° flexion, the torque is reduced or neutral. This behaviour allows the implant 100 to adapt its resistance profile to the functional requirements of walking, stair negotiation, or standing.

[0061] The combined action of the braking mechanism 103 and the magnetic biasing mechanism 115 thus enables the implant 100 to maintain stability during weightbearing while preserving controlled motion during non-weight-bearing phases, providing the patient with enhanced joint function relative to conventional fixed or purely passive implant systems.

[0062] 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 theprinciples 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. A knee implant comprising: a femoral component; a tibial component; and a braking mechanism operative between the femoral component and the tibial component, wherein the braking mechanism comprises: a barrel; a shaft; a series of clutch plates arranged along the shaft and within the barrel, the clutch plates alternately non-rotatably keying the barrel and the shaft, respectively; a plunger that is displaced with respect to the barrel under compression force between the femoral component and the tibial component to compress the clutch plates against each other along the shaft to frictionally engage the barrel to the shaft.

2. The knee implant of claim 1 , wherein the barrel defines internal grooves and a barrel-engaging set of the clutch plates defines external teeth that non-rotatably and slidably engage the internal grooves.

3. The knee implant of claim 1 , wherein the shaft defines external grooves and a shaft-engaging set of the clutch plates defines internal teeth that non-rotatably and slidably engage the external grooves.

4. The knee implant of claim 1 , wherein the barrel-engaging set is polymeric, and the shaft-engaging set is metallic.

5. The knee implant of claim 1 , wherein the braking mechanism further comprises a barrel end cap attachable to the barrel, and wherein the end cap defines a bearing face against which the clutch plates are compressed.

6. The knee implant of claim 1 , wherein the plunger comprises a wedge plate having corrugations, and wherein an innermost clutch plate adjacent to the wedge plate has corresponding corrugations, the corrugations being configured to translate displacement of the wedge plate under the compression force into movement of the innermost clutch plate along the shaft.

7. The knee implant of claim 6, wherein the shaft extends through an aperture of the wedge plate, and wherein the clutch plates are arranged on the shaft on both sides of the wedge plate.

8. The knee implant of claim 1 , further comprising a magnetic biasing mechanism configured to apply biasing torque between the femoral component and the tibial component.

9. The knee implant of claim 8, wherein the magnetic biasing mechanism comprises magnetic rotors that vary magnetically induced torque between them depending on their rotational offset with respect to each other.

10. The knee implant of claim 9, wherein one of the magnetic rotors is connected to the shaft.

11. The knee implant of claim 9, wherein the magnetic rotors comprise adjacent disks having respective axially operative magnets.

12. The knee implant of claim 9, wherein the magnetic rotors comprise concentric rings having respective radially operative magnets.

13. The knee implant of claim 9, wherein the magnetic biasing mechanism comprises a magnetic biasing mechanism housing defined by a barrel end cap attachable to thebarrel and an implant end cap, the barrel end cap and the implant end cap housing the magnetic rotors therebetween.

14. The knee implant of claim 1 , wherein the braking mechanism has a braking mechanism housing, and wherein the implant further comprises a plunger housing fixed to the braking mechanism housing and slidably engaging the tibial component, the plunger housing slidably engaging the plunger therethrough to fix the plunger to the tibial component.

15. The knee implant of claim 14, wherein the plunger housing is recessed within a tibial bearing block.

16. The knee implant of claim 14, wherein the plunger housing defines a radial arrangement of protrusions keying the tibial bearing block.

17. The knee implant of claim 14, further comprising a spring mechanism compressed between the plunger housing and the plunger to offset compressive force applied between the femoral and tibial components.

18. The knee implant of claim 14, wherein the plunger housing defines a chamber slidably engaging the plunger, and wherein the plunger seals against the chamber to seal the braking mechanism housing.

19. A method of operating a knee implant as claimed in claim 1 , comprising applying weight-bearing force between the femoral component and the tibial component to displace the plunger relative to the barrel, thereby compressing the clutch plates against each other along the shaft to increase frictional engagement and restrict relative movement of the femoral component with respect to the tibial component.

20. A method of providing controlled joint stability in a knee implant as claimed in claim 8, comprising rotating magnetic rotors of the magnetic biasing mechanism relative to each other such that the induced magnetic torque varies according to the angular offset of the magnetic rotors, thereby adjusting the biasing torque applied between the femoral component and the tibial component to stabilise the joint under different loading conditions.

Images