WO1999045864A1

WO1999045864A1 - Joint motion device

Info

Publication number: WO1999045864A1
Application number: PCT/GB1999/000710
Authority: WO
Inventors: Robert Brown; Ramon Tahmassebi; Mark Eastwood
Original assignee: University College London
Priority date: 1998-03-11
Filing date: 1999-03-10
Publication date: 1999-09-16
Also published as: AU2738199A; GB9805223D0

Abstract

A motion device for the human hand comprises an articulated structure for supporting the hand when lying over the dorsal aspect of the hand. Hinge means are provided which have axes of rotation that can be aligned, in use, with the effective axes of rotation of joints in the hand of the user. A motor and drive cable and elastic cords on the device can be operated to extend and flex the hand of the user in a controlled and adjustable manner. The device can be used for therapy of a patient, particularly following injury or surgery to the flexor tendons of the hand.

Description

- 1 -

JOINT MOTION DEVICE

This invention relates to devices for inducing motion in human or animal joints and for sensing motion in such joints. It particularly, but not exclusively, relates to a joint or joints in the human hand.

It has been found clinically that appropriate motion of a joint after injury or surgery can promote healing and prevent complications. To this end, manipulation of joints has been practised, but this requires the attention of a therapist and can in some cases be too harsh.

Alternatively active movement of the joint by the patient is a possibility, but this requires the co-operation of the patient to adhere to a particular regime. This may be difficult where pain or fear of pain inhibit the patient from moving the joint and is impossible if the patient is comatose. A passive motion device has been desired, passive in the sense that it does not require active muscle contraction by the patient.

A number of such devices have been proposed. Some of these are reviewed in Hand Clinics, volume 12, number 1, pages 109 to 127 (February 1996) . These particular devices relate to healing of hand injuries. One particular use is for the rehabilitation of flexor tendon repairs, where the flexor tendons, on the ventral surface of the hand have been damaged or severed and then reunited by means of a surgical suture. It has been found that the tendon tissue does not repair properly without a small load being applied to it and also that if the hand is immobilised the tendons can adhere to their sheaths by cellular infiltration which can have serious consequences such as impaired gliding, decreased range of movement, pain and in some cases permanent immobilisation of the joint or joints.

Some of the known devices consist of rods or cables attached to the tips or nails of one or more fingers and actuators attached to the wrist. Motion of the rods or cables by the actuator causes flexion of the fingers. However, with such devices, the path of the fingertips is essentially linear which does not correctly reproduce the natural motion of the joints. Some joints, e.g. the metacarpophalangeal joints, may be placed under adverse load and some joints, e.g. the distal interphalangeal joints, cannot be flexed through their full range of motion by this method. These devices cannot control the range of motion of specific joints. With some devices it is necessary for the patient to actively extend the joints which can place unnecessary tensile loads on some parts of the hand. Conversely, where the device extends the fingers, unless properly adjusted, the device may cause hyperextension.

Other proposed devices do produce more natural flexion arc motion of the hand, but are difficult to adjust, do not support the hand and do not allow the motion of specific joints to be controlled easily such as gradually increasing the range of motion or locking certain joints to only induce motion in other joints. Other proposals have included a hinged splint, but there are problems with the splint conforming to the hand both when flexed and extended.

Accordingly the present invention provides a motion device for a human or animal joint, said device comprising: at least two support members adapted to support externally portions of the body on proximal and distal sides of said joint; a hinge between each pair of adjacent support members to articulate said support members, wherein the or each said hinge has an axis of rotation alignable so as to be, in use, substantially coincident with the effective axis of rotation of said joint.

With the invention, more natural motion of the joint can be achieved. Preferably, the device further comprises an actuator mounted on a said support member and a drive cable for - 3 - rotating said at least two support members relative to each other about said hinge axis.

The actuator enables the support members to be moved to induce motion in the joint of a user without requiring active muscle contraction by the user.

Preferably, the device further comprises an upstanding portion on at least one of said splint members to space the drive cable apart from said hinge.

Such upstanding portions give the device mechanical advantage for the drive cable to operate the hinge.

Preferably, the device further comprises an elastic cord attached across a said hinge to bias said splint members to rotate in one sense relative to each other about said hinge axis. The elastic cord can be used to move a hinge in the opposite sense to that induced by the drive cable, again without active muscle contraction by the user, and to keep the drive cable taut to provide controlled motion.

Preferably, the device further comprises a respective elastic cord across each of a plurality of said hinges, wherein a different force is required to move at least two of said hinges thereby stretching said respective elastic cords .

The different forces required for motion of different hinges provide control of the sequence of extension and flexion of respective joints.

Preferably, the device further comprises stops on said splint members to limit the angular range of motion of the or a hinge. The provision of stops can prevent excessive angular motion of the hinges and also can allow adjustment of the range of motion.

According to another aspect of the invention there is provided a method of applying mechanical stress to joint tissue comprising the steps of: connecting a device according to any preceding claim - 4 - that is appendant to claim 3, to said tissue in vitro; and operating said actuator to induce stress in said tissue .

This method allows the effect of use of the device of the invention to be simulated conveniently.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 shows the skeletal structure of the human hand;

Figures 2(a) and (b) illustrate bones and joints of a human finger in extension and flexion respectively;

Figures 3 (a) and (b) illustrate an embodiment of the motion device of the present invention in partially extended and flexed positions respectively;

Figure 4 illustrates one segment of an embodiment of a device according to the present invention; and

Figure 5 illustrates schematically an experimental arrangement according to a method of the present invention. The following description of an embodiment of the present invention relates to a motion device for the joints of the human hand, but of course the invention is equally applicable to other joints and other animals. Figure 1 illustrates some of the joints in question, by way of example, and to introduce some nomenclature. Referring to figure 1, the joints of digit V are as follows in sequence starting from the fingertip: the distal interphalangeal joint (DIP) 10, the proximal interphalangeal joint (PIP) 12, the metacarpophalangeal joint (MCP) 14, and the carpometacarpal joint (CMC) 16. Although not labelled, digits II, III and IV have corresponding joints as does digit I (the thumb) except that the thumb has a single interphalangeal joint 18.

Figure 2 illustrates diagrammatically the positions of the phalanxes 20 (finger bones) when the hand is in extension (figure 2(a)) and in flexion (figure 2(b)). It - 5 - can be observed that the distance on the dorsal aspect from the MCP joint to the tip of its corresponding finger ray increases significantly when it is in the flexed position. This is due to the exposure of the articulating surfaces of the phalanxes during flexion. In particular this distance 24 in full flexion can be as much as 20 mm greater than distance 22 in extension for the middle finger. This presents the problem that a splint for supporting and moving the hand that is hinged over the dorsal aspect of the hand, if measured to accommodate the hand in full flexion it would be significantly longer than the hand when in extension.

Figures 3 (a) and 3 (b) are two views of a motion device embodying the present invention. The device comprises four segments 30, 32, 34 and 36 articulated by means of three joints 42, 44, 46 which in this embodiment correspond to the PIP joint 12, MCP joint 14 and CMC joint 16. Segment 30 could of course be divided into two pieces with an intermediate articulation corresponding to the DIP joint 10, but for simplicity this is not shown in the illustrated embodiment.

The joints 42, 44, 46 comprise portions of each segment that, in use, extend around the sides of the hand and overlap with the corresponding portion on an adjacent segment. A hinge pin such as a small bolt penetrates through .each overlapping portion to provide a pivot . For ease of motion, low friction nylon washers are provided between each pair of overlapping portions of the segments. Although only the near-side ones are visible in the Figures, overlapping joint portions and hinge pins are also provided on the far-side.

The location of the hinge pins on the side portions of the segments enables the motion device to be placed on a hand with the axis of rotation of each hinge substantially coincident with the effective axis of rotation of its respective hand joint. This alleviates the problem of accommodating the change in the length of the dorsal aspect of the hand with flexion and extension. The effective axis of rotation of a hand joint can be conveniently ascertained from the folds and creases in the skin at the joint. The tips of the creases mark the point where the strain on the tissue around the joint changes from tensile to compressive, and marks approximately the effective axis. A motion device could be custom built to suit a particular hand or the hinge pins could be provided in slots to allow adjustment of their distance from the dorsal surface of the hand.

In the illustrated embodiment, each overlapping portion is provided with a hole 50. When the motion device is in certain positions, such as fully extended, the holes are aligned so that a bolt can be fastened through them to lock one or more joints rigid to prevent motion. Several holes could be provided to enable each joint to be locked off at a range of different positions, or indeed the hinge pin 48 could comprise a nut and bolt that can be tightened to lock the joint at any desired angular position. Projections on the segments 30, 32, 34, 36 and their overlapping side portions limit extremes of angular motion of each joint, both in extension and in flexion. Within this range of extremes the full range of motion (ROM) of the joints can be achieved, for a typical hand the full

ROM's are 110° for the PIP joint, 90° for the MCP joint and 80° for the CMC joint. For therapeutic use of the device it is important that these full ROM's can be achieved.

Provision can also be made for a pin or pins to be inserted in one or more of the overlapping portions to limit the range of motion of the respective hinge and joint. By changing the position of the or each pin, the range of hinge motion could be progressively increased, for example as part of a therapeutic regime, building up to the full ROM.

For use as a splint, the segments 30, 32, 34 and 36 - 7 - are made of a rigid material, and for comfort of the user they are preferably lightweight. Suitable materials include polyform and sub-ortholene . Although the segments of the illustrated embodiment are fairly angular, the above-mentioned materials are mouldable for additional support and comfort. The segments could be formed by making a cast of the hand and then moulding the material over the cast at an elevated temperature. A range of standard size segments could be manufactured to construct devices capable of suiting all hand sizes. Alternatively the segments could be custom fabricated to suit a specific user or the segments could be provided with adjustment means such as sliding or screw joints to allow the length of the segment to be varied. By changing the length of one side of the segment relative to the other side it is possible to skew the angles of the axes of successive joints so that they are not necessarily parallel. Also the lengths of the segments could be adjusted to the average length between e.g. the MCP joints and the PIP joints for a whole hand splint or separate segments could be provided for one or more individual digits.

Figure 4 shows one segment 34 of the motion device in isolation. It includes a thumb support portion 52, and a palm support portion 54. Similar supports may be provided on the other segments for the ventral surface of the hand and fingers. Alternatively, or in addition, a glove, not shown, may be attached to the segments to provide support and control of an inserted hand.

A motion device for use in therapy, such as following flexor tendon surgery, will be provided with drive means for operating the joints. Any suitable drive means may be used, such as hydraulic, pneumatic, worm drive, rack and pinion, pulleys, springs and so forth.

The drive means in the embodiment illustrated in figures 3 (a) and 3 (b) comprises a motor 60 and drive cable 62 on the dorsal aspect of the hand and elastic cords on - 8 - the ventral aspect of the hand. The motor 60 is mounted on the segment 36 adjacent the forearm. Up-standing portions 64 are provided on each segment and the control cable 62 passes from a reel on the motor 60 through eyelets 66 in the upstanding portions 64 and is attached to the upstanding portion 64 on the farthest segment 30. The upstanding portions 60 space the control cable 62 away from the segments and provide mechanical advantage related to the distance of the eyelets 66 from the pivots 48. Preferably the eyelets are formed from a low friction material and the control cable 60 may be a relatively inextensible fibre such as a nylon fishing line.

Each articulation 42, 44, 46 is provided with an elastic cord passi-ng across the joint and attached to the segments on either side of each articulation. The elastic cords are provided on the underside of the segments and for clarity are omitted from the drawings. The elastic cords bias the segments to the flexed position and fit neatly between the digits of a user. Figure 3(b) shows the motion device in a partially flexed state. The elastic cords maintain the cable 62 taut. Operation of the motor 60 in an appropriate sense reels in the cable 62 and extends the motion device, and the hand of a user wearing the device, to a state similar to that shown in figure 3 (a) . The motor 60 is powerful enough to overcome the tension of the elastic -cords and in extending the device the cords are stretched. Subsequently operating the motor 60 in the opposite sense pays out the control cable 62 and the controlled contraction of the elastic cords reverts the motion device to the flexed state.

The controlled flexion and extension means that the device is gravity-independent so can be used on patients in any attitude. The fact that the control cable 62 is always taut ensures there are no undesirable effects such as rapid recoil from the elastic cords.

The control cable 62 and elastic cord could of course - 9 - be used in the opposite sense so that the motor 60 and cable 62 flex the joints and the elastic cord extends them. A further option is to have powered drive means for both flexion and extension i.e. without relying on a spring or elastic cord for return motion. It is presently preferred to use a motor 60 and drive cable 62 for extension and elastic cord for flexion, as illustrated. If necessary a gear box might be provided to step down the motor drive. Control circuitry, not shown, automates the activation of the motor 60. The length of time for which the motor 60 operates in a given direction can be controlled to adjust the range of motion that the device undergoes . A rest interval may also be provided for each reversal of the motor 60 direction. The speed of the motor 60 can be controlled to adjust the speed of motion of the device, which can of course be different for extension and flexion.

If separate drive means are provided for each articulation then their parameters of motion can be individually controlled. In the present embodiment, the elastic cords across the articulations are of different elastic moduli. Alternatively, the elastic cords could be pre-stressed, in the flexed state, to different respective tensions. In this way the sequence of motion of the joints can be controlled. By making the elastic cord between segments 30 and 32 be under the greatest tension of any of the elastic cords when the device is fully extended, operating the motor 60 will cause joint 42 to bend first in preference to the joint 44 or 46 as the control cable 62 paid out. When the tension decreases to that of one or other of the other elastic cords, a second joint will commence flexion and so on. Similarly, starting from a flexed state, operating the motor 60 will cause the joints to extend in the reverse sequence. In this way it is possible to control the sequence of motion of the joints to mimic that of the healthy hand or to provide a desired - 10 - therapy.

The control circuitry and drive means of the motion device enable a desired therapeutic regime to be established and adhered to. Examples of enhancements include the control circuitry commencing therapy with a warm-up period in which the range of motion is automatically and gradually increased. The versatility of the device also enables a course of therapy that may last several months to be provided. For example initially certain joints may be locked-off and then later released and the range of motion gradually built up.

Although in the illustrated embodiment the motion of the device is controlled and driven in both directions, it is possible for the motion to depend on active muscle contraction by the user in one or both directions. The motion could be against a controlled load so as to exercise the muscles for use for example in muscle toning or body building.

Alternatively, or in addition, the motion device may be provided with one or more sensors. Sensors could detect the angular position of each joint, the speed of motion of each joint and the applied stress. For example, a shaft encoder or potentiometer could sense the angular position of the motor 60 or any of the joints and a strain gauge could be placed on the cable 62. The values of the paramaters measured by the sensors could be used for adjusting the controller for the drive means of the device. A motion device with sensors could also be used in biometrics for measuring the range of motion of a user's joints or for example their grip strength. These paramaters could be useful for diagnosis of a patient or for input to a virtual reality system.

Another aspect of the present invention is illustrated in figure 5. The segments 32, 34, 36 of the motion device are clamped to a retort stand 70 so that operation of the motor 60 moves the end-most segment 30. - 11 -

An elastic cord 72 is attached to the tip of segment 30 and passes over a pulley 74 mounted on a second retort stand 76 and is then attached to an actuator rod 78. The rod 78 passes into a universal tube 79 also mounted on retort stand 76. The rod 78 can slide with respect to the universal tube 79 by means of a nylon washer. A tissue sample 80 is connected to the actuator rod 78 and to the base of the universal tube 79 by means of hooks. Operation of the motor 60 to extend the joint 42 between segments 30 and 32 applies a stress to the tissue sample 80 via the elastic cord 72 and actuator rod 78. Continued operation of the motor 60 increases the stress on the tissue sample 80, but the majority of the strain is accommodated by the elastic cord 72. Reversing the motor 60 decreases the stress on the tissue sample 80.

In this way the tissue sample 80 can undergo cyclic stressing similar to that of therapeutic use of the motion device on a patient. The tissue sample 80 may be a tendon that has been transected and united by means of a suture and this method can be used to asses the effects of mechanical stress on the healing of the tissue, and in particular the effects of the same mechanical stress as will be used in a patient's hand. The tissue sample 80 can be bathed in a suitable fluid and the whole apparatus can be placed in an incubator at 37°C.

In' one experiment, the tissue sample was repeatedly stressed with a peak load of about I N. In a 4 hour period, the load was applied 1200 times. During passive motion of flexor tendons in the hand, the forces transmitted are of the order of 1 N, so this experiment reproduced the conditions of therapeutic use of the motion device. During active flexion and extension, even without resistance, the load on flexor tendons is somewhat greater at approximately 2 to 4 N. This method therefore provides the ability to assess the results of the loading regime applied by the device, 99/45864

- 12 - clinically, on repair tissues and associated structures e.g. adhesions to gliding surfaces, nerves and blood vessels. These structures inherently cannot be easily biopsied to examine such repair effects in an actual patient.

Claims

- 13 -CLAIMS

1. A motion device for a human or animal joint, said device comprising: at least two support members adapted to support externally portions of the body on proximal and distal sides of said joint; a hinge between each pair of adjacent support members to articulate said support members, wherein the or each said hinge has an axis of rotation alignable so as to be, in use, substantially coincident with the effective axis of rotation of said joint.

2. A device according to claim 1, wherein said hinge comprises : hinge portions extending, in use, from each said support member adjacent each lateral side of said joint; and a hinge pin on each lateral side of said joint, wherein said hinge portions of adjacent support members overlap at least partially and said hinge pins connect said overlapping hinge portions and define the axis of rotation of said hinge.

3. A device according to claim 1 or 2 , further comprising an actuator mounted on a said support member and a drive cable for rotating said at least two support members relative to each other about said hinge axis.

4. A device according to claim 3, wherein said actuator comprises an electric motor.

5. A device according to claim 3 or 4 , wherein said actuator is adapted to pull said drive cable to move said joint to an extended state.

6. A device according to claim 3, 4 or 5 , further comprising an upstanding portion on at least one of said support members to space the drive cable apart from said - 14 - hinge .

7. A device according to claim 6, wherein said drive cable passes through an eyelet in said at least one upstanding portion.

8. A device according to claim 6 or 7, wherein said drive cable is fastened to one said upstanding portion.

9. A device according to any one of the preceding claims, further comprising an elastic cord attached across a said hinge to bias said support members to rotate in one sense relative to each other about said hinge axis.

10. A device according to claim 9, wherein, in use, said elastic cord biases said joint to a flexed state.

11. A device according to claim 9 or 10, further comprising a respective elastic cord across each of a plurality of said hinges, wherein a different force is required to move at least two of said hinges thereby stretching said respective elastic cords.

12. A device according to claim 11, wherein the elastic cords have different spring constants.

13. A device according to claim 11 or 12, wherein the elastic cords are pre-stressed under different respective tensions.

14. A device according to any one of the preceding claims, wherein at least one support member is extensible.

15. A device according to any one of the preceding claims, further comprising stops on said support members to limit the angular range of motion of the or a hinge. - 15 -

16. A device according to any one of the preceding claims, comprising at least three support members and at least two hinges, wherein at least one of said hinges is provided with locking means.

17. A device according to any one of the preceding claims, adapted to fit the human hand so that at least one of said hinges is alignable with a joint in the fingers of the human hand.

18. A device according to any one of the preceding claims, wherein one of said support members is adapted to engage a human forearm and the or a hinge is alignable with the wrist. ,

19. A device according to any one of the preceding claims, wherein said support members are adapted to lie over the dorsal surface of a human hand.

20. A device according to any one of the preceding claims, further comprising sensing means for sensing at least one parameter, such as angular position, angular velocity and stress, of said joint.

21. A method of applying mechanical stress to joint tissue comprising the steps of: connecting a device according to claim 3, or any preceding claim that is appendant to claim 3, to said tissue in vitro; and operating said actuator to induce stress in said tissue.

22. A method according to claim 21, wherein the device is connected to said tissue via a resilient member.

23. A method according to claim 21 or 22, wherein said tissue is tendinous. - 16 -

24. A device constructed and arranged to operate substantially as described herein with reference to the accompanying drawings .

25. A method of applying mechanical stress to joint tissue in vitro substantially as described herein with reference to the accompanying drawings.

26. A method of treatment of the human or animal body comprising the steps of: fitting a motion device, according to claim 3 or any one of claims 4 to 20 that is appendent to claim 3, to said body so that said axis of rotation of said hinge is substantially coincident with the effective axis of rotation of a joint of said body and so that said support members provide external support on proximal and distal sides of said joint; and operating said actuator to induce motion in said joint.