WO2020188294A1

WO2020188294A1 - Passive actuator for articulated joint

Info

Publication number: WO2020188294A1
Application number: PCT/GB2020/050750
Authority: WO
Inventors: Malik SIDDIQUE
Original assignee: Malik Siddique Ltd.
Priority date: 2019-03-21
Filing date: 2020-03-20
Publication date: 2020-09-24
Also published as: GB201903899D0

Abstract

An implantable device is provided for an articulating, anatomical joint. The joint has a first anatomical member and a second anatomical member that are moveable relative to each other between a first position and a second position. The device comprises a first mount, fixedly attachable to the first anatomical member and a second mount, operably coupleable to the second anatomical member; a tension assembly. The tension assembly comprises a first engagement member that is fixingly coupleable to said first mount in at least a first locking position on said first mount, and a second engagement member that is fixingly coupleable to said second mount. Wherein, the tension assembly is adapted to resiliently bias said first mount and said second mount towards each other in situ.

Description

PASSIVE ACTUATOR FOR ARTICULATED JOINT

The present invention generally relates to implantable assemblies for articulated joints. More particularly, the present invention relates to a device for assisting and/or replacing impaired muscle function at an articulated joint

Introduction

Stroke is considered as one of the leading causes of disability throughout the world. Individuals suffering from stroke or other neurological disorders (e.g. cerebral palsy) may have reduced walking capacity, which can have a great impact on an individual’s daily life. Impaired walking skills, as well as, other motor skill disorders, may also be a consequence of any other disorder, such as, for example, spina bifida (birth defect), muscular dystrophy, Parkinson's disease, multiple sclerosis, spinal cord injury, Downs' Syndrome, idiopathic toe walking, or peripheral neuropathies. Further, relevant injuries to the nervous system and/or muscles can cause the loss of pure motor function. Limbs that may be affected by such injuries can include the hand (e.g. wrist), foot or toe(s), leading to respective wrist-, foot- or toe-drop conditions.

A condition known as“foot drop” (or“drop foot”) is a relatively common gait abnormality and refers to the inability or difficulty in moving the ankle and toes upward (dorsiflexion) while walking, for example, due to weakness, irritation or damage to the common fibular nerve including the sciatic nerve, or paralysis of the muscles of the anterior portion of the lower leg. Figure 1 shows an illustration of the peroneal nerve and its cutaneous distribution showing the areas affected by any damage to the peroneal nervous system. Foot drop may be temporary or permanent, depending on the extent of muscle weakness pr paralysis and it can occur in one or both feet. Foot drop may be caused by nerve damage alone or by muscle or spinal cord trauma, abnormal anatomy, toxins or disease. Toxins may include organophosphate compounds which have been used as pesticides and as chemical agents in warfare. The poison can lead to further damage to the body such as a neurodegenerative disorder called organophosphorus induced delayed polyneuropathy. This disorder causes loss of function of the motor and sensory neural pathways.

Figure 2 illustrates the phases in the normal gait cycle, including the initial heel contact, the stance phase, the heel strike, flat foot, toe-off and swing phase, i.e. initial swing - midswing - terminal swing, where the foot is off the ground.

Individuals with a foot drop condition (i.e. dorsal muscle weakness or incapacitation) are not able to lift the foot adequately in the midswing phase due to insufficient dorsiflexion, resulting, for example, in “toe dragging”, reduced walking speed, shortening of step length, a potential elevation in walking metabolism, as well as, a high risk of tripping. Figure 3 illustrates an example of a foot drop gait cycle, including the toe-off, foot-crash, mid-trip and eventual fall. Figure 4 illustrates differences between (a) a “normal” foot (i.e. capable of adequate dorsiflexion) and (b) a foot drop (i.e. no or reduced dorsiflexion).

Today, a number of treatments are available for ankle foot disabilities (e.g. foot drop), including, for example, surgical, therapeutic or orthotic interventions. Traditionally, foot drop treatment devices were limited to accommodative devices such as Ankle Foot Orthotic devices (AFO), that simply prevent the dragging of the toes. Examples of such simplistic devices are illustrated in Figure 5 (a) orthosis and (b) a simple foot support.

AFO’s, in particular, are utilized to limit the speed at which the foot plantar flexes during the loading response (foot slap) and therefore stops the foot from dropping during the swing phase of the gait cycle. As a result, the toe of the foot is prevented from “coming into contact” with the ground, therefore, decreasing the risk of stumbling. As illustrated in Figure 5(a), AFO’s may extend from a position distal of the metatarsal heads to a position just distal of the head of the fibula. Many other active and passive AFO designs exist, utilizing passive and active elements, such as springs, motors, controllers, feedback sensors, pneumatic, electric and magnetic actuators. In addition to AFO’s, active approaches, such as, Functional Electrical Stimulation (FES), have been shown to be beneficial. FES is a technique that uses electrical stimulation to contract muscles that are incapacitated by nerve damage, therefore, restoring at least some functionality of the incapacitated limb. Available FES systems can be transcutaneous or implantable and, in case of foot drop, are configured to apply stimulation to the common peroneal (CP) nerve in order to treat one specific problem (e.g. dorsiflexion).

FES systems are relatively complex electronic devices that include, inter alia, control systems, feedback sensors and energy sources. Further, FES systems do normally not allow for patients to acquire new motor patterns, because the actuation of the muscle only occurs when electric stimulation is applied. As a result, the patient is not re-trained to learn, for example, other muscle recruitment patterns.

Moreover, foot drop is just one of many possible walking deficits caused, for example, by a stroke, after which adults may not be able to effectively push with their plantar flexors on each step. However, electrical stimulation of these muscles has received little attention, despite the fact that about eighty percent of the acceleration force necessary to maintain walking comes from the plantar flexors.

For example, document US3,083,712 (James E. Keegan), describes a device for producing electrical muscle therapy utilizing electrodes to stimulate muscles via the common peroneal nerve. Stimulation is activated via a heel switch. Again, the required kit is relatively complex, including a controller, an energy source, electrodes, as well as, cables, therefore, making the device cumbersome, dependent on electric power and suitable nerve connections. Also, while addressing the problem of diminished muscle function resulting in foot drop, the document offers no information on how the device may be applied to other muscles that engage during walking.

Accordingly, it is an object of the present invention to provide an implantable actuator for articulated joints that is simplistic in design, yet, adaptable and effective in restoring functionality, while allowing the patient to adopt new movement patterns. Furthermore, it is an object of the present invention to provide a device that is versatile and easy to implement within the human body, robust, hardwearing and self-sufficient, while occupying a minimal footprint within the human body.

Summary of the Invention

Preferred embodiment(s) of the invention seek to overcome one or more of the disadvantages of the prior art.

According to a first embodiment of the invention, there is provided an implantable device for an articulating, anatomical joint, the joint having a first anatomical member and a second anatomical member moveable relative to each other between a first position and a second position, said device comprising:

a first mount, fixedly attachable to the first anatomical member;

a second mount, operably coupleable to the second anatomical member; a tension assembly, comprising a first engagement member fixingly coupleable to said first mount in at least a first locking position on said first mount, and a second engagement member fixingly coupleable to said second mount, and wherein said tension assembly is adapted to resiliently bias said first mount and said second mount towards each other, in situ.

Advantageously, said first mount may comprise a calibration mechanism adapted to selectively move said first engagement member between said first locking position and at least a second locking position on said first mount. Preferably, said calibration mechanism may be magnetically actuatable. Even more preferably, said calibration mechanism may be a screw-drive mechanism. Furthermore, said calibration mechanism may comprise a guide thread and said first engagement member may comprise a flange member configured to operatively cooperate with said guide thread.

Advantageously, when the implantable device is in situ, said first locking position may be at a first distance from said second mount, and said at least one second locking position may be at a second distance from said second mount, and wherein said second distance may be greater than said first distance.

Advantageously, said second mount may comprise at least one flexible linking structure fixedly attachable to at least one component of the second anatomical member. Preferably, said at least one flexible linking member may be permanently attached to said at least one component of the second anatomical member. Even more preferably, said flexible linking structure may be a synthetic textile implant adapted to form a permanent bond with the at least one component of the second anatomical structure.

Advantageously, said flexible linking structure may be demountably coupleable to said second engagement member.

Advantageously, said tension assembly may comprise a first elastic member adapted to store and release mechanical energy. Preferably, said tension assembly may comprises at least one second elastic member operatively coupled to said first elastic member and adapted to store and release mechanical energy. Even more preferably, said first elastic member may be any one or any combination of a spring and an elastomer. Additionally, said at least one second elastic member may be any one or any combination of a spring and an elastomer.

Advantageously, said tension assembly may further comprise a telescopic housing configured to operatively receive and fluidly seal said first elastic member and/or said at least one second elastic member.

Advantageously, said tension assembly may be pivotably coupleable to said first mount. Brief Description of the Drawings

Preferred embodiments of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:

Figure 1 shows a simplified illustration of the peroneal nerve and cutaneous distribution within the lower leg;

Figure 2 shows a simplified illustration of a normal gait cycle;

Figure 3 shows a simplified illustration of a typical foot drop gait cycle;

Figure 4 shows (a) a side view of a portion of lower limb with normal dorsiflexion of the foot and (b) a side view of a portion of lower limb with foot-drop condition (i.e. no dorsiflexion of the foot);

Figure 5 (prior art) shows (a) an example of a known orthosis structure and (b) a simple brace system to prevent foot drop;

Figure 6 (prior art) shows a simplified illustration of an example system for functional electrical stimulation (FES) targeting the peroneal nerve to enable foot dorsiflexion;

Figure 7 shows a simplified schematic (front view) of the implantable device, in situ, after it was attached to the tibia and coupled to the suitable tendons (not shown) of the foot;

Figure 8 shows a simplified schematic, (a) side view and (b) front view, of an embodiment of the implantable device, in situ, with the telescopic housing removed;

Figure 9 shows an example embodiment of the implantable device (a) a perspective view of the implantable device in a retracted position, (b) a close-up perspective view of the implantable device, (c) a schematic side-view of the implantable device in a retracted position and (d) a schematic side-view of the implantable device in a telescopic extended position; Figure 10 (a) and (b) shows a perspective view of a first and a second example embodiment of the tension mechanism provided inside the telescopic (fluid sealed) housing of the implantable device;

Figure 11 (a), (b) and (c) shows perspective views of suitable first mounts (surface mounts and blade plates) for fixation of the implantable device;

Figure 12 shows a simplified illustration of the second mount, i.e. (a) foot tendon to implant fixation utilising (b) Neo-ligaments or Achilles cord plus;

Figure 13 shows an exploded view of a schematic illustration of another embodiment of the implantable device using a resilient member (e.g. polyurethane material) to provide the bias force (e.g. through tension force) between the tibia and the foot;

Figure 14 shows (a) a front view and (b) corresponding cross-sectional side view (along A-A) of the implantable device of Figure 13 in an unloaded state including couplings for tibia and foot, and

Figure 15 shows (a) a front view and (b) corresponding cross-sectional side view (along A-A) of another embodiment of the implantable device of the present invention in an unloaded state.

Detailed description of the preferred embodiment(s)

The exemplary embodiments of this invention will be described in relation to drop- foot treatment. However, it should be appreciated that the implantable device may be used with any suitable articulated joint and associated tendons and/or muscles.

Referring now to Figures 7 to 12, like reference numerals designate identical or corresponding elements throughout the figures. The drawings, which are provided by way of example and not limitation, illustrate embodiment(s) that are directed towards an apparatus and method for treating foot drop. However, the invention may also be utilised with other body joints. Further, the embodiment(s) described relate to an apparatus for providing a force between the articulating members of a joint, suitable to at least counter-act the gravitational force, but also the force applied during plantarflexion, acting on the joint members. For example, the device of the present invention may use one or more springs in any suitable combination, or any suitable resilient material in any shape size and form to provide the predetermined linear-elastic response. However, it is understood by the person skilled in the art that any other suitable mechanism may be used to provide such reactive tensioning force.

In one example embodiment, the implantable device 100 of the present invention may comprise a telescopic housing 102 configured to fluidly seal a spring mechanism 104 that is operably mounted inside the housing 102. The housing 102 is provided with a first coupling 106, for example, provided at the proximal end (when in situ) of the housing 102, and a second coupling 108, provided at the distal end (when in situ) of the housing 102. A first base component 1 10 may be permanently fixed to the medial surface of the tibia using bone screws 1 1 1 (e.g. see Figure 1 1 ). The first base component 1 10 is configured to operably receive the first coupling 106 of the housing 102. The second coupling 108 may be connected to suitable tendons from the foot utilizing, for example, neo-ligament material 1 12 to couple the implantable device to the foot. The housing 102 may be made from bio-compatible material.

In the one example embodiment, the spring mechanism 104 comprises one or more springs 1 14 that is/are attached to respective first 106 and second couplings 108, so as to form a piston-like mechanism with the telescopic housing 102. In its relaxed (unloaded) state, distal and proximal end of the housing 102 are at a predetermined shortest distance from each other. The spring(s) 1 14 utilised with the spring mechanism 104 are suitable to counteract the weight of the affected foot, i.e. spring dimensions and spring material characteristics are chosen so as to provide a suitable tensioning force to the foot joint.

Additionally, a damper 1 16 may be coupled in series or in parallel with the one or more springs 1 14, so as to absorb at least some of the kinetic energy effected by the spring(s) 1 14 in response to the gravitational force or a force from plantarflexion acting on the foot during movement, therefore, allowing for a “smoother” movement of the foot during the gait cycle.

The device 100 may be implanted extra-articular within the subcutaneous tissue on the anterior aspect of the lower leg. During the surgical procedure, the device 100 may be inserted through incisions at the medial malleolus and medial condyle. As shown in Figure 1 1 , alternative versions of the first base component 1 10 may include a plurality of screw holes that are configured to receive the bone screws 1 1 1 or other suitable anchors to secure the first base component 1 10 to the patient’s bone.

The second coupling 108 of the device 100 is attached, for example, to the tendon(s) of the Tibialis Anterior, Extensor Hallux Valgus, Extensor Digitorum Longus via a second base component 1 15 and neo-ligament(s) 1 12, so that the implantable device 100 can passively respond like the impaired muscle, i.e. providing a suitable force for dorsiflexion of the foot during walking. The second base component 1 15 may simply be an interface between the second coupling 108 and the neo-ligament(s) 1 12.

In addition, the implantable device may comprise an adjustment or calibration mechanism (not shown) adapted to change a predetermined“loading” force of the spring mechanism 104 or any other suitable mechanism (e.g. utilising resilient material, or vacuum, or magnetic / electromagnetic force etc.) capable of providing dorsiflexion of the foot during walking.

When using a spring mechanism 104, as shown with this example embodiment, the calibration mechanism may be configured to linearly move the first coupling 106 with respect to the first base component 1 10, so as to increase/decrease the tensioning force provided by the spring mechanism 104 or a resilient member. The calibration mechanism may comprise a selectively actuatable screw-drive mechanism coupling the first coupling 106 to the first base component 1 10. The screw-drive mechanism may be configured to be indirectly actuatable, e.g. via a magnetic force. The spring mechanism 104 may be set to a predetermined tensioning force when installed, wherein the tensioning force may be adjusted at a later time by either operating the actuatable screw mechanism indirectly, or through surgical intervention (and direct operation of the mechanism). It is understood by the person skilled in the art that any other suitable adjustment or calibration mechanism may be used to increase/decrease the preloading force of the spring mechanism 104.

Further, it is understood by the person skilled in the art that any suitable tensioning mechanism may be used to provide the tensioning force for the foot joint (i.e. dorsiflexion of the foot) counter-acting / -balancing the gravitational force, as well as, the force applied during plantarflexion of the foot during walking.

Referring now to Figures 13, 14 and 15, two other example embodiments 200, 300 of the implantable device of the present invention using alternative materials / mechanisms to the coil spring mechanism 104 of the first embodiment are illustrated.

The second example embodiment 200 shown in Figures 13 and 14(a), (b) comprises a telescopic housing 202 configured to fluidly seal a resilient member 204 (e.g. a polyurethane material) that is operably mounted inside the housing 202. The total length of the resilient member 204 and telescopic housing 202 may be customised to the anatomical requirements of the patient. The housing 202 is provided with a first coupling 206, for example, a screw thread provided at the proximal end (when in situ) of the housing 202, and a second coupling 208, such as a screw thread provided at the distal end (when in situ) of the housing 202. A first base component 210 may be permanently fixed to a surface of the tibia using bone screws (see for example bone screws 1 1 1 in Figure 1 1 ). The first base component 210 is configured to be coupled with the first coupling 206 of the housing 202, e.g. by screwing the two components together using a screw 213.

The second coupling 208 and attached second base component 215 may be connected to suitable tendons from the foot utilizing, for example, neo-ligament material (e.g. neo-ligaments 1 12 shown in Figure 12) to couple the implantable device 200 to the foot. The housing 202 may be made from any suitable material, such as, but not limited to‘stainless steel-316’ or any other bio-compatible material (e.g. ceramic, polymer, carbon etc. or any suitable composites thereof).

Further, the second 200 and third 300 example embodiments include a resilient biasing mechanism 204, 304 comprising at least one resilient member 205, such as, for example, a polyurethane rod that is attached to respective first 206 and second couplings 208 within the piston-like housing mechanism of the telescopic housing 202. In this particular example, the elastic properties of the polyurethane rod 205 may be utilised from compression or expansion of the resilient member 205. For example, the resilient biasing mechanism 204 may comprise a suitable mechanism to utilise compression of the resilient member 205 in order to provide a biasing force between the first and second base components 210, 215 when pulled apart, e.g. by plantarflexion of the foot. Alternatively, expansion of the resilient member 205 may be utilised to provide the biasing force between the first and second base components 210, 215 when pulled apart, e.g. by plantarflexion of the foot.

Figure 14 shows the implantable device 200 in its relaxed (unloaded) state, distal and proximal end of the housing 202 are at a predetermined shortest distance from each other. The resilient member 205 (e.g. polyurethane rod) utilised for the resilient biasing mechanism 204 is suitable to counteract the weight of the affected foot, i.e. rod dimensions and material characteristics are chosen, so as to provide a suitable elastic response to movement of the foot during the gait cycle.

A third example embodiment 300 of the implantable device of the present invention is illustrated in Figure 15. The implantable device 300 comprises a single housing 302 on its proximal end adapted to receive a resilient member 305, e.g. a polyurethane rod, a first base component 310 coupled to a first coupling 306 of the housing 302 and a second base component 315 coupled directly to a distal end of the resilient member 305 (e.g. polyurethane rod). The first base component 310 may comprise two tabs 317 bent at 90 degrees with respect to the main contact surface, so as to provide a“key point” into the bone. The connection to the distal end of the resilient member 305 (e.g. polyurethane rod) may include a ball joint 317 to enable rotation between the first and second base components 310, 315. The second base component 315 may be connected to suitable tendons from the foot utilizing, for example, neo-ligament material (e.g. neo-ligaments 112 shown in Figure 12) to couple the implantable device 300 to the foot.

First and second example embodiments 200, 300 of the implantable device of the present invention may use one or more urethane / polyurethane rods for the resilient biasing mechanism 204, 304, though any other suitable polymer may be used. The operating temperature of the resilient material is between -17.8 Degrees Celsius and +93.3 Degrees Celsius. Suitable resilient material may be chosen based on its hardness, e.g. using ASTM D2240 Standard Test Method for Rubber Property, Durometer Hardness. This particular test method covers twelve types of rubber hardness measurement devices known as durometers: Types A, B, C, D, DO, E, O, OO, OOO.

Accordingly, the implantable device 100, 200, 300 of the present invention provides an improvement of the dropped position of the impaired foot by assisting or even replacing the“lost” muscle(s) and tendon(s). As described above, the “muscle power” is provided by the stored kinetic energy from gravity and the forces generated by the muscles involved in the plantarflexion of the foot (i.e. gastrocnemius, soleus and plantaris). It has been shown that the implantable device 100, 200, 300 of the present invention significantly improves the gait by providing assistance and/or therapy (resistance training) to the impaired person.

In addition, the efficiency of muscle groups opposing the implantable device 100, 200, 300 may be improved from the resistance provided by the device 100, 200, 300. Furthermore, the stretching effect caused by the device 100, 200, 300 with every step allows the opposing muscles to improve control by redeveloping the “lost” gait cycle events. Sensations provided by the heel and the sole of the foot are used by any unaffected muscles to re-establish a normal walking and running pattern. In addition, due to its passive simplicity (i.e. no electrical impulse or active power generation), the implantable device 100, 200, 300 can be used in conditions where there is no nerve supply available to affected muscles, and the implantable device 100, 200, 300 is therefore not dependent on the person’s own nerve or muscle tendon unit. As a result of the simplistic and non-electric nature of the device 100, 200, 300 (i.e. using no external energy and working in synergy with the body’s physiology), it may be used for more than one joint at the same time. Also, the implantable device 100, 200, 300 is easy to maintain. In the event of failure, damaged parts of the modular mechanism are simply replaced. For example, the telescopic housing 102, 202 of the implantable device 100, 200 (incl. first coupling 106, 206 and second coupling 108, 208) may simply be detached from the first base component 110, 210 and“unhooked” from the neo-ligament 1 12 that is coupled with the foot tendons and replaced by a new unit, or, the resilient biasing mechanism 104, 204, 304 (e.g. spring mechanism 104, or polyurethane rod 204, 304) may be removed and repaired or replaced.

It will be appreciated by persons skilled in the art that the above embodiment(s) have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims. For example, it is understood that any suitable biasing mechanism can be used without departing from the basic inventive concept.

Claims

1 . An implantable device for an articulating, anatomical joint, the joint having a first anatomical member and a second anatomical member moveable relative to each other between a first position and a second position, said device comprising:

a first mount, fixedly attachable to the first anatomical member;

a second mount, operably coupleable to the second anatomical member;

a tension assembly, comprising a first engagement member fixingly coupleable to said first mount in at least a first locking position on said first mount, and a second engagement member fixingly coupleable to said second mount, and wherein said tension assembly is adapted to resiliently bias said first mount and said second mount towards each other in situ.

2. An implantable device according to claim 1 , wherein said first mount comprises a calibration mechanism adapted to selectively move said first engagement member between said first locking position and at least a second locking position on said first mount.

3. An implantable device according to claim 2, wherein said calibration mechanism is magnetically actuatable.

4. An implantable device according to any one of claims 2 and 3, wherein said calibration mechanism is a screw-drive mechanism.

5. An implantable device according to claim 4, wherein said calibration mechanism comprises a guide thread and said first engagement member comprises a flange member configured to operatively cooperate with said guide thread.

6. An implantable device according to any one of claims 2 to 5, wherein, in situ, said first locking position is at a first distance from said second mount and said at least one second locking position is at a second distance from said second mount, and wherein said second distance is greater than said first distance.

7. An implantable device according to any one of the preceding claims, wherein said second mount comprises at least one flexible linking structure fixedly attachable to at least one component of the second anatomical member.

8. An implantable device according to any one of claim 7, wherein said flexible linking structure is a synthetic textile implant adapted to form a permanent bond with the at least one component of the second anatomical structure.

9. An implantable device according to any one of claims 7 and 8, wherein said flexible linking structure is demountably coupleable to said second engagement member.

10. An implantable device according to any one of the preceding claims, wherein said tension assembly comprises a first elastic member adapted to store and release mechanical energy.

1 1 . An implantable device according to claim 10, wherein said tension assembly comprises at least one second elastic member operatively coupled to said first elastic member and adapted to store and release mechanical energy.

12. An implantable device according to claim 1 1 , wherein said first elastic member is any one of a spring and an elastomer.

13. An implantable device according to any one of claims 1 1 and 12, wherein said at least one second elastic member is any one of a spring and an elastomer.

14. An implantable device according to any one of claims 10 to 13, wherein said tension assembly further comprises a telescopic housing configured to operatively receive and fluidly seal said first elastic member and/or said at least one second elastic member.

15. An implantable device according to any one of the preceding claims, wherein said tension assembly is pivotably coupleable to said first mount and/or said second mount.