Continuous passive motion devices and methods

A system for continuous passive motion of a limb or one or more fingers comprises a reciprocable carriage coupled to a drive belt which is driven by a motor through a disengageable clutch. A second drive belt also driven by the motor, and the first drive belt, carry elements whose positions can be sensed to control limits of motion. Individual finger actuators, adjustable in length and with internal springs, couple engagement means on the fingers to the carriage, which can be driven so as to provide predetermined dwell times at limits of flexion and extension.

BACKGROUND OF THE INVENTION 
This invention relates to devices for imparting continuous passive motion 
to a limb or digit, and more particularly to portable units for exercising 
joints of the hand, fingers and wrist. 
It has been standard medical procedure for many years to use exercise 
routines to restore mobility of limbs and joints after injury or 
immobilization, so as to overcome muscle degeneration and internal 
adhesions. It has more recently been recognized that "continuous passive 
motion" (CPM) exercises are desirable following traumatic incidents or 
operations. They can be initiated quickly, and by providing motion of a 
limb or digit, establish or maintain freedom of motion well before the 
musculature can function autonomously. Continuous passive motion devices 
have accordingly been developed in a number of forms, as evidenced by U.S. 
Pat. Nos. 4,487,199, 4,537,083 and 4,716,889. The devices depicted therein 
are not indicative of the state of the art, however, since units with 
additional features have been sold for some time by Kinetec of France, and 
by Toronto Medical Inc. of Yellow Springs, Ohio. Even such units, however, 
provide only a limited ability to supply motion effects and controls as 
dictated by a therapist for a given individual. The French system is a 
relatively cumbersome unit which must be operated from a power main. The 
Toronto Medical Inc. product is a portable battery operated device for 
exercising the fingers. A light weight battery operated CPM is very useful 
because of the frequency of occurrence of hand injuries, provided that a 
variety of manipulative CPM functions can be performed. It may be 
desirable, for example, to reciprocate the fingers from an intermediate 
partially flexed position to fully extended position, to reciprocate the 
fingers between partially flexed and fully clenched positions, or to use 
any other combination of finger or digit motions. It is evident that the 
same unit with minor adjustments or replacements should function for all 
desired finger positions. In addition, the unit should also be adaptable 
for imparting continuous passive motion to the thumb, and alternatively to 
the wrist. The unit should also permit a therapist to exercise only 
certain fingers and to introduce digit blocking or to exercise only 
particular fingers or joints. 
In addition, ease of attachment, setting and adjustment are of significant 
importance inasmuch as the patient must ordinarily operate the machine 
after selection of specific exercises by the therapist. Settings should be 
easily controllable by the patient or therapist, and the design should 
enable full motion of each finger, if desired, despite variations in hand 
size, finger length, and finger alignment. Not only the extent of travel 
but also the rate of travel should be controllable. 
As evidenced by the above referenced patents, it has been thought desirable 
to automatically reverse the reciprocating motion upon encountering a 
predetermined load. This type of control is very difficult to achieve, 
particularly because finger loadings are not uniform. Moreover with a 
properly adjusted device there is no need for such a function. In fact, it 
is often desirable to introduce stretching forces, in order to overcome 
adhesions and inhibiting forces, and to do so independently on each 
finger. Sometimes the fingers should be maintained in a given position for 
a dwell period at the end of a motion, providing a traction effect that 
enhances the healing process. Nonetheless, the action as far as each 
finger is concerned should be force limiting and a range of adjustment 
should cover the range of travel down to as little as one-quarter inch. 
Superimposed on all of these requirements, a portable CPM unit should not 
only be light in weight but efficient in operation so that it can operate 
for a long interval on battery power. Moreover, not only the range of 
travel but the speed of reciprocation should be adjustable. Various useful 
features, such as counting the number of cycles, automatic resetting and 
manual or automatic operation, should also be provided. 
SUMMARY OF THE INVENTION 
An improved battery powered CPM device for hand, thumb and wrist 
applications incorporates a double belt drive system in which the belts 
are drivable from a motor and engageable by an intercoupling clutch. A 
carriage engaged to a primary drive belt is the base for one or a number 
of telescoping finger actuators which are internally spring loaded and 
pivotable through limited angles. Flag elements coupled to the belts are 
separately settable to define opposite limit positions with the belt drive 
disengaged, by taking the fingers or wrist through the desired range of 
motion. Thereafter, simply engaging the clutch starts the run operation. 
The belts and carriage are reciprocated at a selected and variable rate 
between the defined limit positions under solid state electronic control 
which counts the cycles and reverses the motor, introducing dwell times as 
desired. The unit may be automatically reset whenever the range of travel 
is changed. 
The base unit is coupled to a unit holder which is mountable on the forearm 
and enables the carriage to be coupled to actuators for any or all of the 
four fingers or the thumb or via an attachment to the wrist. The fingers 
may be exercised through different ranges including from fully extended to 
flexed and from flexed to clenched, by reorientation of the elements. 
The telescoping finger actuators are mounted on the carriage so as to be 
pivotable through small diverging angles to conform to the shape of the 
hand and fingers of the individual patient. The finger actuators include 
base tubes receiving rod extensions which may be locked in selected axial 
positions. Terminal flexible spring wires on the actuators are engaged to 
finger attachments at their outer end, and are seated within the rod 
extensions between a pair of compression springs at their opposite end. 
Thus, whether moving the fingers toward the extended or clenched position, 
the actuators, which are readily adjusted to individual finger lengths, 
introduce a spring force against the fingers. 
The device is mounted on an arm cuff that fits on the forearm and provides 
a base that accommodates different arm sizes. The device may be mounted 
directly on the arm cuff, or on a separate unit holder, which may 
incorporate a pivotable base surface for providing a controlled degree of 
tilt relative to the wrist angle in the lateral and vertical planes. The 
anterior of the arm cuff includes a tang on which a thermoplastically 
deformable palm support or digit blocking device can be engaged after 
shaping to the particular needs of the patient's hand. 
Finger attachments for coupling to the finger actuators advantageously 
comprise arcuate elements partially encompassing a finger tip and 
including a protruding lever arm engageable to the flexible actuator 
wires. Forces exerted on the finger tips by the actuators act against the 
sides of the fingers in shear. Securement to the fingers can be within the 
attachment and elastic coupled to close the arcuate elements. The 
attachments may be placed on the fingers in inverted position so that 
motion can be introduced to provide a clenched fist. 
The same unit can be used to provide continuous passive motion of one or 
more digits, including the thumb. With an adaptor it may also be used to 
exercise the wrist. It can be increased in size and drive capability to 
move other limbs, such as the elbow and knee, with appropriate known types 
of attachments.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIGS. 1-3, devices in accordance with the invention 
comprise a housing 10 which contains or supports the principal drive 
elements and in addition a battery, motor and controller. The housing 10 
has a hinged cover 11 and is mounted on a support 12 which is affixed to 
the forearm, here positioning the housing 10 so that it is adjacent the 
palm of the hand, to enable the fingers to be flexed from a fully extended 
to partially flexed position in this example. A foam pad 13 (FIG. 1) is 
typically disposed on the wrist under the support 12. The cover 11 is 
mounted on the housing 10 by pivot hinges 14 along one edge and 
encompasses some of the exterior drive elements and controls, such as an 
on-off control switch 16, and a control lever 18. The lever 18 is 
shiftable manually between setup and run positions, and is moved 
automatically to the run position by the cover when the cover 11 is 
closed. 
The housing 10 supports a linearly movable carriage 20 which is coupled to 
a drive mechanism inside the body through a linear slot 22 that extends in 
the posterior/anterior direction. A number of finger actuator assemblies 
24 are individually mounted on pivot pins 25 on the posterior end of the 
carriage 20, extending outwardly toward the finger tips. The finger 
actuator assemblies 24 each include a base tube 26 having a tang 28 at its 
free end that is incurved to grip a slidable inserted hollow extension rod 
30 at a selected telescoping position. These positions are defined by a 
number of longitudinally spaced short peripheral slots 32 periodically 
spaced along the extension rod 30 and receiving the tips of the tangs 28. 
A first spring 34 is disposed in the extension rod 30 at the posterior 
end, as seen in FIG. 5, within end caps 35 which permit compressive forces 
to be exerted smoothly on the first spring 34. A strong but resilient wire 
element 36 having a terminating projection 37 at its end inside the 
extension rod 30 and an end loop 38 at its anterior end provides the means 
for coupling to an individual finger attachment. Between the terminating 
extension 37 and the anterior end, within the extension rod 30, is 
disposed a second spring 40 between end caps 41 having central apertures 
through which the wire 36 is inserted and moves. 
The carriage 20 moves along the exposed surface of the housing 10, between 
a side rail 44 and a side wall of the cover 11, which restrict outward 
divergence of the finger actuators 24. The bases 45 of the actuators 24 
include holes fitting about the pivot pins 25, and are sized to limit the 
maximum angle of divergence between adjacent actuators 24. 
The end loops 38 on the wires 36 are each coupled to a finger attachment 
device 46 at a protruding lever arm 48, by passing through a transverse 
opening 49 on the lever arm 48. The finger attachment device 46, best seen 
in FIG. 9, comprises a curved base 50 which conforms to the pad of a 
finger tip and is bounded on each side by a hinge 51 joining to an 
adjacent side panel 52. Each side panel includes a protruding post 53, so 
that the device can be curved snugly about the finger by an elastic band 
58 coupling the posts 53. Such posts may be provided alternatively on the 
base 50 or the arm 48. A foam insert 60 having adhesive surfaces on both 
sides is disposed between the finger attachment device 46 and the finger 
to increase adhesion and resistance to shear forces. For some applications 
a foam insert will not be needed. The entire finger attachment device 46 
apart from the foam insert 60 and the elastic band 58 is conveniently 
molded as a single integral piece. 
The energy source and drive mechanism, as well as the internal sensing and 
control system, are disposed within the body, as may be seen by reference 
to FIGS. 3 and 4. A battery 62 is coupled via a controller 63 to a D.C. 
drive motor 64. The controller 63 also receives sensor signals via a P.C. 
board 65 and contains circuitry for controlling reciprocating motion at a 
selectable velocity between choosable limits, for enabling manual and 
automatic operation, and for providing an indication of the number of 
cycles of operation, as well as automatic reset. Such functions can be 
controlled individually by separate conventional circuits but the cost and 
flexibility of integrated circuit chips enable these features, together 
with many more if desired, to be provided at reasonable cost. 
The motor 64 is mounted in the housing 10, being principally supported in 
the motor mount 66 at its shaft 68 end, and the shaft being conventonally 
seated between bearing plates in the body. The shaft 68 extends in a 
direction perpendicular to the direction of reciprocation of the carriage 
20. A first drive belt 70 engages a first drive pulley 72 on the shaft 68, 
the first drive pulley being rotatable on the shaft 68, but having a 
clutch face with circumferentially spaced slots 73 on the side opposite 
the motor 64. It will be appreciated that the motor shaft need not be 
integral but may include one or more colinear sections or couplings. A 
clutch element 74 about the shaft 68 includes a set of protruding dogs 76 
configured to mate within the drive pulley slots 73, the clutch elements 
74 being axially movable toward the motor 64 by the control lever 18 as 
described hereafter. Thus when the clutch element 74 is engaged with the 
dogs 76 in the drive pulley slots 73, the clutch element, which is coupled 
to the shaft 68, rotates the first drive belt 70 with the shaft 68. 
A second drive belt 78, parallel to the drive belt 70 but spaced apart 
along the shaft 68 on the opposite side of the clutch element 74, is 
directly coupled to the motor shaft 68 by a second drive pulley 80, which 
is axially movable along the shaft on a splined section (not shown in 
detail). A leaf spring 82 mounted on the side of the device body 10 urges 
the second drive pulley 80 in the direction toward the motor 64, but 
engagement of the clutch device is controlled by the control lever 18. The 
upper end of the lever 18 is accessible through a slot from the top of the 
body 10, while the lower end is mounted on a pivot 84 in the wall of the 
body 10. A side of the control lever 18 engages the adjacent side of the 
first drive pulley 72 next to the slots 73, and in the "setup" position of 
the control lever 18 shifts the first drive pulley out of engagement with 
the dogs 76 on the clutch element 74. At the opposite limit of pivot 
position, the "run" position, the control lever 18 permits engagement of 
the dogs 76 into the drive pulley slots 73. A bracket 85 extending from a 
mid-region of the control lever 18 carries a wire arm 86 which, in the 
"run" position, engages a spring actuator 87 having a tab 88 which passes 
into the optical path of a position sensor 90 of the type having a small 
miniaturized light source on one side and a light sensor on the other. 
Signals from this sensor 90 are passed to the P.C. board 65 and controller 
63 for use in the system. 
At the end of their linear paths opposite from the motor 64, the first and 
second drive belts 70, 78, are turned about driven pulleys 92, 93 mounted 
on a common shaft 94 coupled to the body 10. A bracket 98 coupled to the 
first drive belt by a U-shaped element 99 is coupled to the carriage 20 
through the linear slot 22 (not seen in FIG. 3), to control carriage 
motion and position. A flag 100 on the bracket 98 extends in the anterior 
direction, along a path adjacent to the first drive belt 70, and at a 
predetermined limit position near the driven pulleys 72, 73, passes into 
the optical path of a second position sensor 102. A fixture 104 mounted on 
the second drive belt 78 carries a flag 105 directed in the posterior 
direction which intercepts the optical path of a third position sensor 108 
at a limit position. 
On top of the body 10, referring to FIGS. 1 and 2, the control switch 16 
has automatic, manual and off positions accessible to the user. A digital 
display 112 visible to the user provides the count generated by the 
controller 63. Rotatable control buttons 114, 115, designated P and S can 
be used to adjust the dwell time before reversal of direction and the rate 
of travel of the carriage 20, respectively. In manual operation a pair of 
depressible buttons 116, 117 labeled "Extend" and "Flex" respectively, can 
operate the motor in the given directions. 
As best seen in FIG. 6, the support 12 may comprise an arm cuff 120 having 
an anterior tang 122 and a shaped configuration for fitting smoothly about 
the base of the wrist, with the tang 122 extending onto the palm. At the 
posterior end of the arm cuff 120 are provided slots 124, which establish 
flexible side wings 126 so that the arm cuff may be fitted onto forearms 
of substantially varying sizes. Straps 128 with conventional means for 
joinder, such as snaps or "Velcro" are placed about the arm cuff 120 and 
the forearm. The housing 10 may be inserted directly with a snap 
attachment into the arm cuff 120, or optionally may be mounted, as seen in 
FIGS. 6 and 10, on a hinged base support or unit holder 130 having an 
upper surface 131 which can be raised to different angular positions for 
best fitting to the particular hand or function. Alternatively also, a 
digit blocker 132 having a shaped slot 134 may be fitted onto the tang 122 
on the arm cuff 120, so as to restrict movement of individual joints in 
any fashion that a therapist may desire. The anterior portion of the digit 
blocker comprises a shaped body 136 of thermoformable plastic. Plastic 
materials are available which are rigid at ambient temperature but which 
become plastic at moderate temperatures (e.g. hot water below boiling) and 
which may therefore be shaped, cut and fit by a therapist to fit the palm 
and particular needs of an individual patient, and then allowed to cool to 
rigidity. 
The operation of the system of FIGS. 1-6 proceeds by first attaching the 
finger attachments 46 to the fingers as desired. For use in continuous 
passive motion between the fully extended and partially clenched 
positions, the finger attachments 46 are seated with the lever arms 48 
protruding from the finger tip pads, and the wires 36 are then engaged to 
the lever arms by inserting the end loops 38, which permit bidirectional 
motion. The base tubes 26 can conveniently be kept on the pivot pins 25, 
and the extension rods 30 can be temporarily extracted for this 
attachment. The fingers are then fully extended, and the extension rods 30 
are extended or contracted to given positions, within the base tubes 26, 
by rotating the rods 30 through a small angle so that the slots 32 are not 
in alignment with the tangs 28 on the base tube 26. Thus each finger can 
be precisely adjusted in length, and the tension at the fully extended 
position can also be controlled, by the length of the extension. The 
springs 34, 40 inside the extension rod 30 have approximately equal 
compliance and thus will compress slightly under light force, as 
determined by a therapist or user. With the support 12 strapped onto the 
wrist, and the housing 10 of the device attached, the hinged cover 11 can 
be opened to permit these adjustments to be made. The control lever 18 is 
shifted to the "setup" position, which frees the first drive belt 70 from 
the motor shaft 68, allowing the carriage 20 to be moved, along with the 
fingers, posteriorly to a selected flex position. Prior to this time, 
however, the controller 63 automatically drives the motor 64 to bring the 
second drive belt 78 toward the rearward position, until the flag 105 on 
the fixture 104 for the second drive belt 78 intercepts the third position 
sensor 108. This therefore provides a reference for the flexed position of 
the drive system. When the carriage 20 is moved, along with the fingers, 
to the desired flex position, only the first drive belt 70 moves with it, 
starting from the fully extended position in which the flag 100 on the 
bracket is at the second position sensor 102. 
This sequence is very simply established for the therapist or user, and if 
the stroke adjustment are not as desired, the sequence maybe quickly 
repeated to achieve final settings. By setting the posterior reference 
point using the second drive belt 78, and the anterior reference point 
using the first drive belt 70, in accordance with actual positions of the 
fingers, there is no possibility of mistake. The system may then be 
shifted from the "setup" mode to the "run" mode simply by shifting the 
control lever 18 and closing the cover 11. It is advantageous to position 
the control lever 18 as shown, so that this shift in control lever 
position automatically occurs when the cover 11 is closed. 
The unit thus operates continuously, at the selected advance and return 
velocities, in reciprocating fashion, with the limiting positions of the 
carriage 20 being sensed by the second and third optical sensors 102, 108, 
respectively. The cycles of movement are counted and displayed, and if the 
system is reset, the count, in this example, is started over again. 
The physical movement of the finger tips is precisely controlled, because 
the divergence of the finger actuators 24 corresponds to actual finger 
alignment, and because the arrangement of the finger attachments 46 aids 
in proper vectorial distribution of forces. The forces which draw the 
fingers inwardly and extend them reciprocally act on the lever arms 48, 
but are absorbed in shear at the side panels 52, rather than the fleshy 
part at the pad of the finger. 
As seen in FIG. 7, if it is desired to move the fingers between partially 
flexed and fully clenched position, the finger attachments 46 are reversed 
or inverted, with the protruding lever arms extending outwardly from the 
fingernails. Now, as seen in FIG. 7, the fingers can be drawn from a 
partially flexed position down into contact with the palm of the hand. The 
same carriage 20 and base tube 26 arrangement are employed, but the 
extension rod 30' is terminated by a bracket 130 supporting a transverse 
bar 132 which fits through the holes in the finger attachments 46. This 
enables movement to form a complete fist. 
In either mode of operation, the finger actuator structure plays an 
important part in the distribution of forces. The wire elements 36 
compress the first springs 34 when extending, and compress the second 
springs 40 when flexing the fingers. When the fingers are fully flexed, 
the actuators can be adjusted to provide a given tension force on them, by 
placement of the tension rods 30 relative to the base tubes 26. This 
provides an important therapeutic advantage, because it is often useful to 
hold the fingers under tension at a limit position for a period of time 
prior to continuing with the reciprocating motion. This dwell time can be 
adjusted using the controller 36 and the selector buttons 114, 115. 
The same unit, with the single finger actuator, can be used for controlling 
the motion of the thumb through different ranges as shown in dotted lines 
in FIG. 1. The attachment 46 to the end of the thumb can be placed as 
desired, and the wire element 36 extending from the finger actuator 24 is 
typically substantially bent, but still functions to provide the control 
thumb motion that is desired. 
In another example in accordance with the invention, as seen in FIG. 8, the 
entire wrist can be exercised in continuous passive motion. A wrist 
adaptor 140 fitting about the back or palm of the hand includes an 
upwardly extending lever 142 to which the wire loop 38 is attached at one 
of a number of spaced apart holes 144. The body of the adaptor 140 
includes slots 146 for receiving attachment straps 148 by which the unit 
can be affixed to the extensor surface of the patient's forearm. The 
nature and arc of the continuous passive motion can be selected by using 
different ones of the holes 144. 
The ability to control the motion of any one or more digits including the 
thumb, is very useful for patients and therapists, but is only one of many 
structural, operative and therapeutic advantages. The ability to introduce 
a controlled dwell interval, in both flexion and extension if desired, 
with tension being maintained during the dwell interval because of the 
internal springs, adds a new therapeutic capability. Because the actuators 
are individually adjustable to finger length and can accommodate finger 
position and direction to an acceptable degree, there is no danger of 
excessive strain. For this reason and because of the compression springs, 
resistance by one or more digits against movement is reacted against by 
compliance and there is no need for direction reversal. 
The device can be mounted on either forearm so as to function with either 
hand. If a cast is in place the unit holder can be strapped directly onto 
it, without an intervening arm cuff. 
While various forms and modifications have been described above, it will be 
appreciated that the invention is not limited thereto but encompasses all 
forms and variations within the scope of the appended claims.