Continuous passive motion device

A CPM device is disclosed having a single drive tube supporting the calf and thigh support members. Arms extend upwardly from the calf and thigh support members, each supporting an adjustable cradle in which the calf or thigh rests. The support arms are rotatable 180 degrees so that either leg may be supported over the single drive tube. A foot support is also cantilevered from the end of the calf support drive bar. The drive tube which supports the calf and thigh drive support bars is cantilevered from a unique support mechanism which attaches an end of the drive tube to the horizontal bed frame at the end of the hospital bed. A rack and pinion mechanism is combined with a unique gas spring in order to allow the drive tube to be easily rotated up above the hospital bed with the gas spring providing a power assist to the person lifting the drive tube off the bed in order that the drive tube may be easily rotated up off the bed without undue physical exertion.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings, FIG. 1 shows a CPM device with a patient's 
leg shown in phantom lines supported in the device. The device described 
herein comprises a calf support bar 2 and thigh support bar 4 connected at 
a hinged knee pivot section 6 which will be explained in detail with 
reference to FIG. 7. 
One end of the thigh support bar 4 is connected at a hip pivot 8 intended 
to be placed adjacent the patient's hip as illustrated in FIG. 1. The hip 
pivot mechanism is shown in detail in FIG. 5B. The end of the calf support 
bar 2 distal from hip pivot 8 is supported on a yoke 10 which is connected 
by a trolley 12 to drive means (which will be explained with reference to 
FIG. 4A) incorporated within the drive tube 14. 
The trolley 12 drives yoke 10 in reciprocating fashion along drive tube 14 
in the directions indicated by arrow 13. As the yoke moves back toward hip 
pivot 8, the patient's knee resting above pivot 6 is flexed at a sharp 
angle. The yoke 10 then moves toward the traction frame supported end 15 
drive tube, extending the patient's leg until the leg is fully extended as 
shown in FIG. 4A. The patient's knee is thus constantly exercised and 
rehabilitated. The design of the CPM device of the present invention must 
overcome a number of problems. The CPM device must be easy to use, as it 
is used by personnel unfamiliar with sophisticated mechanical devices. 
Considerable motive power must be applied through the yoke to the calf 
support bar to flex and extend the patient's knee. The patient's leg hangs 
to the side of the calf and thigh support arms 4, 2, applying significant 
torsional stress to these arms. The CPM must be movable off the hospital 
bed so that the patient can get on and off the bed, and the bed can be 
changed. 
The following will explain how these and other design issues were addressed 
in the design of the present invention, beginning with an explanation of 
how the patient's leg is supported on the CPM device. 
As can be seen more clearly in FIG. 2, the end of the calf support bar 2 
carries a foot support generally indicated at 16 which include a foot 
support plate 18 carried on an "L" tube frame 20. A soft boot 22 which is 
included in the patient kit which is supplied individually for each 
patient is wrapped around the foot support plate and the patient's foot as 
shown in FIG. 1. This foot support boot 22 may include a pocket on the 
rear surface thereof which slips over the top of the foot support plate 18 
to aid in maintaining the foot support boot 22 in position. Two straps are 
also provided, one of which 25 wraps around the top of the patient's foot 
to hold it in the foot support boot. 
The patient's calf and thigh are supported from the appropriate calf and 
thigh supports 24, 26 which comprise L-shaped bars connected at one end to 
the calf and thigh drive arms 2, 4. Each L-shaped support bar 24, 26 
supports a saddle 28, 30 which is a T-shaped metal frame 31 including a 
vertical element 32 as shown in greater detail in FIG 8A. The ends 37 of 
the saddle 28, 30 are designed to capture the openings 46 in the patient 
support element 40. This patient support element 40 which is shown more 
clearly in FIGS. 8B and 8C includes a soft central portion 40 of sheepskin 
or the like on which the patient's calf or thigh rests, and the attachment 
handles at each end 42. To mount the patient's leg from the saddle, it is 
only necessary to rest the leg on support 36, and using the handles 42, 
lift the leg into position and snap the ends of the patient handles 42 
over the ends 37 of the saddle 28, 30. In order to provide a clean patient 
support element for each patient, the central sheepskin portion 40 is 
detachable from the handles 42. The handles 42 include velcro strips 47 on 
the edge thereof, these strips mating with complementary material on the 
back of the sheepskin so that the handles can be used to lift the 
patient's leg up onto the saddle. 
A further and significant advantage of this approach to supporting the 
patient's leg from the CPM device, is that the use of the saddles to hold 
the patient kit allows us to push down on the leg from the top when the 
calf and thigh drive arms are descending. All previous devices have 
supported the leg from underneath. When the CPM device supports the leg 
from underneath, and the calf and thigh drive arms are moving away, 
eventually they may cease to pull the leg down, and a severely restricted 
case of knee motion will simply drop out from under the knee. In contrast, 
in this device, what happens is that the saddles push down on the leg from 
on top, and apply constant pressure to help break loose the cartilage and 
tissue that have formed around the knee and prevent its free movement. 
It is also possible, following the design of the present invention, to 
easily change the height at which the patient's leg is supported relative 
to the L-shaped tube 24 or 26. This is achieved by making the upright rod 
32 vertically adjustable relative to the attachment end of the L-shaped 
tube 24, 26. A plurality of slots 59 are cut in the side of the vertical 
element 32, and a spring-loaded pin 61 is inserted in one of the slots. 
The pin is carried at the end of a body 63, and a handle 65 is threaded on 
a rod 67 at the opposite end of the body from the pin 61. To change the 
height of the vertical support rod 32 relative to the L-shaped tube 24, 
26, the handle 67 is unscrewed, creating a space indicated by the arrows 
69. This space need only be greater than the length of the end portion of 
pin 61 which is inserted in the slot 59. By then using the handle to push 
the handle 65 to push on the body 63 against the force of the spring 73, 
the pin is effectively withdrawn from the slot 59, and the vertical 
support element 32 can be moved up or down to the desired height, 
whereupon the pin 61 is reinserted in the selected height 59 to hold the 
vertical element 32 in place. 
As is well known in the use of these CPM devices, the rehabilitation effect 
is provided by driving the calf support 2 and thigh support 4 back and 
forth relative to one another causing flexing of the knee at the joint 6. 
In the device, the motion is established by movement of the yoke 10 and 
the motor 14, which is shown in FIG. 4A, so that the knee of the patient 
is first fully flexed as shown at 6 in FIG. 1, and is then fully extended, 
as would occur when the calf and thigh drive arms 2, 4 reach the position 
shown in FIG. 4A. Movement of the yoke is achieved by providing a motor 14 
within the drive tube, connected through a drive screw arrangement 16 to a 
drive block 49 within the drive tube 14 attached to the trolley 12 of yoke 
10. The drive power is transmitted from the drive block 49 to the trolley 
12, which surrounds the top of the drive tube as is shown more clearly in 
FIG 5A. The drive block 49 is connected through pins or screws 51 directly 
to the bottom of the trolley. As the lead screw 16 turns, the drive block 
moves from its position, indicated by the letter A, where the calf and 
thigh bars 2, 4 would be fully flexed relative to one another, to the 
position B near the end of the path of travel where the yoke 10, calf bar 
2 and thigh bar 4 would occupy positions substantially as shown in FIG. 
4A. It is also apparent that as the trolley 12 moves back and forth over 
the surface of the drive tube 14, that considerable torsional effects are 
exerted on the yoke 10, because of the fact that the patient's leg is on 
one side or the other of the yoke, drive tube, and leg supports. 
Therefore, each end of the trolley 12 terminates in a bearings 53L and 53R 
shown in FIG. 5A which slides in the slots 55L and 55R on either side of 
the drive tube 14. Therefore, if the patient's leg is resting to the left 
of the drive tube illustrated in FIG. 5A, then the bearing will slide in 
the top of the right slot 55R, and on the bottom of the left slot 55L. In 
this way, proper alignment of the trolley with the drive tube is 
maintained throughout the path of motion of the trolley. 
Continuing with reference to the lower portion of FIG. 5A, which is a 
sectional view of the hip pivot section of the device, this FIGURE also 
illustrates the outer housing 56 of the hip pivot section, to which the 
end of the main tube 14 is affixed, and the inner section 57 which rotates 
inside the outer housing 56 around main axis 58. The thigh support bar 4 
terminates in the inner housing 57. The inner and outer housing are 
provided to allow for rotation of the calf bar inside the hip pivot region 
with extremely limited clearances between the inner and outer housings, so 
that the patient's hand or bed clothing or the sheets on the bed do not 
become caught or bound up in between the inner and outer housing as the 
thigh support arm rotates within the outer housing 56. A further feature 
of the hip pivot design is provided to account for the fact that when the 
thigh support drive arm 4 and calf support drive arm 2 are in their 
fully-extended positions as illustrated in FIG. 4A, it can be very 
difficult for the motor and lead screw arrangement to break the knee pivot 
free. 
To aid in raising the thigh support drive arm 4 when it is in its fully 
horizontal position, which could be a difficult mechanical feat, the hip 
pivot 8 includes a leaf spring 50 which is mounted on thigh support 4. As 
the thigh support is lowered toward the drive tube 14, the spring 50 
rotates with the thigh support and its end is pressed against a roller 52 
fixed to the side of hip pivot housing 56. Thus, energy is stored in the 
leaf spring as it rotates down, and when the yoke 10 attempts to drive the 
calf and thigh drive arms back into the flexed position of FIG. 1, the 
leaf spring 50 will provide additional leverage to drive the thigh support 
back up away from the main drive tube 14. 
Referring next to FIG. 5A, the internal structure of several of the 
elements is illustrated in an end sectional view. The calf bar 2 appears 
at the top, and includes both inner and outer sections 60, 62 so that the 
length of the bar can be adjusted. 
The thigh bar 4 is shown attached to the inner housing 57, and also 
includes inner and outer sections 66, 68. The octagon-shaped portion 70 of 
the outer thigh bars is included to prevent twisting of one portion of the 
thigh bar relative to another. FIG. 5C, which also illustrates an 
alternative embodiment of the hip pivot region 8 designed to provide a 
shorter length for the main drive tube, also illustrates the differing 
outer and inner telescoping sections of the thigh support arm 4. The inner 
section is circular so that it slides easily within the octagon-shaped 
outer section 70. FIG. 5D illustrates how the inner housing 57 of this 
particular embodiment rotates in the outer housing 56 of the hip pivot 
region on axis 58. This also provides an end view of the inner tubular 
section 66 of the thigh support arm 4. 
The manner in which the inner tube section 66 slides inside the outer tube 
section 68, and their relative position is fixed is illustrated in FIGS. 
5E, 5F and 5G. The tubes 66, 68 are normally held in place relative to one 
another by the combination of a spring 69 and pressure bar 71, which 
presses down against the top of the inner section 66, coordinated with the 
pin 73 which engages in a series of holes 75 in the bottom surface of the 
inner tube 66. Thus, when it is desired to change the length of the thigh 
support by changing the relative position of the inner and outer 
telescoping sections 66, 68, the knob 79 is rotated lifting the engaging 
rod 71 up off the inner tube 66. The knob is then pressed down, 
disengaging the pin from the hole 75. The tubes are then slid to the new 
positions, and the locking device knob 79 is raised, causing the pin 73 to 
lock up into the newly selected hole 75. Thus, the two sections are now 
locked firmly in place, and rotation of the inner telescoping section 66 
relative to the outer telescoping octagonal section 68 is prevented by the 
position of the pin in the hole. 
The upper portion of FIG. 4A, together with FIGS. 7A and 7B, illustrates in 
further detail the knee joint 6. The joint 6 includes an inner and outer 
clevis 72, 74 so that the calf and thigh bars 4, 2 may pivot easily with 
respect to one another. The inner pivot is attached to the thigh bar 4, 
and rotates on bearings 79 relative to the outer clevis being attached to 
the calf bar. A potentiometer 76 is also provided having one fixed end 78 
located within the knee pivot. The other end is attached to the inner 
clevis as indicated at 80, so that the rotation of the knee can always be 
measured relative to a fixed reference. The body of the potentiometer is 
supported from the pin 80 on the inner clevis so that it has some free 
float within the knee joint 6. In this way, the potentiometer can be 
located directly within the knee joint to measure the relative movement of 
the inner and outer clevis, without tying down the body of the 
potentiometer directly to one side of the joint. Because of the twisting 
and bending which must necessarily occur in this knee joint, tying down 
the body of the potentiometer would necessarily result in significant 
damage to this potentiometer if the movement of both the stem and the body 
were severely restricted. The necessary cable to the potentiometer can be 
led in through the thigh support bar. 
As was discussed at some length in the background of the invention, it is 
important to be able to raise the entire device off the hospital bed so 
that the sheets can be changed or the patient, who may be relatively 
immobile, can be moved easily onto and off of the bed without the CPM 
device being in the way. To achieve this goal, the end of the drive tube 
14 incorporates a vertical lift assembly 15, shown generally in FIG. 4A 
and in detail in FIG. 4B. This vertical lift assembly incorporates a 
standard clamp 90 for clamping the entire CPM device to the traction frame 
at the end of the hospital bed. Once the CPM device is clamped to the end 
of the hospital bed using the clamp 90, then the entire CPM device can 
easily be rotated up off the bed in the direction of arrow 92 (FIG. 3) 
using the power assist shown in FIGS. 4A and 4B. 
Because of the presence of the motor and the like, the CPM device can be 
heavy to lift out of the way. Means are provided in the vertical lift 
assembly to aid in the rotation of the CPM device. Specifically, the axis 
100 about which the CPM device will rotate includes a spur gear 102 having 
a plurality of gear teeth which mesh with a rack gear 104 provided inside 
the tube 106 of the vertical lift assembly and specifically attached to 
the side of the piston 105 of gas spring 108. As the doctor or nurse lifts 
the CPM device out of the way, the gear teeth 102 engage gear rack 104, 
driving the piston 105 of a gas spring assembly 108 down toward the base 
of the support tube 106. The upper end of the gas spring is fixedly 
mounted to the top of the tube at 110. When the gas spring 108 is driven 
far enough, the force exerted by the spring aids in the movement of the 
rack and the gear, and in fact provides most of the force in the direction 
of the arrow 112, rotating the CPM device upwardly. When the CPM device is 
at its full height, as shown in FIG. 3, the gas spring will aid in keeping 
it at that height, although a lock FIG. 6 is provided adjacent the axis 
100. When the CPM device is to be lowered onto the hospital bed, the drive 
tube 16 is grasped and pulled down toward the bed. The gas spring force is 
overcome, and the rack 104 with the attached piston 105 of the gas spring 
will move back up toward the top 110 of the support tube 106. As it does, 
for at least a portion of the rotation of the CPM device about the axis, 
the gas spring will provide some resistance, preventing an unnecessarily 
quick lowering of the CPM device onto the bed. 
As a further safety measure and to avoid inadvertent movement of the CPM 
device relative to the hospital bed, a lock is provided mounted above the 
wheel which supports the spur gear 102. This lock which may be mounted on 
the face of the support post 106, which is shown in FIG. 6, comprises a 
pall 122 which cooperates with recesses 124 spaced around the periphery of 
the gear wheel 102. When the device is in the horizontal position 
illustrated in FIG. 4A, then the recess 124 holds the pall 122 to prevent 
inadvertent upward movement. When it is desired to lift the CPM device off 
the bed, the knob 126 is rotated clockwise, turning the pin 128 in slot 
130 to provide an effective camming action, which converts the rotary 
motion of the knob to a lifting motion of the pall against the biasing 
force of spring 132 which normally holds the pall in the recess. With this 
lifting motion completed, the CPM device indicated by the drive tube 14 
can be lifted off the bed and rotated upward. When the drive tube 14 is 
vertical relative to the bed, the pall is allowed to slip back into the 
next adjacent recess 124, locking the drive tube and CPM device safely 
above the hospital bed. 
A further advantage of the present invention is illustrated in FIGS. 1 and 
2. Because a single drive tube extends from the bed support post 106 to 
the hip alignment point 8, it is very easy to arrange this CPM device for 
use with either the left or right leg of a patient. Specifically, to 
change this device from use with the right leg of a patient as illustrated 
herein to the left leg of a patient, the two leg support arms 24, 26 are 
simply rotated 180.degree. about their connection points 122, 124 to drive 
arms 2, 4. The foot support is also rotated 180.degree.. A new patient kit 
being used for each patient, new calf and thigh supports as illustrated in 
FIGS. 2B and 2C, and a foot support as appears in FIG. 1 are provided to 
hold the patient's foot in place. 
Modifications to the preferred embodiment of the present invention may 
occur to a person of skill in the art who studies the present invention 
disclosure. Therefore, the scope of the present invention is to be limited 
only by the following claims.