Note: Descriptions are shown in the official language in which they were submitted.
CA 02216863 1997-09-26
CONTINUOUS PASSIVE MOTION DEVICE FOR
UPPER EXTREMITY FOREARM THERAPY
FIELD OF THE INVENTION
The present invention relates to continuous passive motion
devices for the rehabilitative and therapeutic mobilization of human synovial
joint and surrounding soft tissue, and more particularly, the invention
relates
to continuous passive motion devices for upper extremity forearm therapy.
BACKGROUND OF THE INVENTION
In recent years it has become evident that the rehabilitation and
treatment of injured joints and surrounding soft tissue can be expedited by
use
of continuous passive motion (CPM) applied to the involved joint. CPM entails
moving the joint via its related limbs through a passive controlled range of
motion without requiring any muscle coordination. Active motion is also
beneficial to the injured joint, however, muscle fatigue limits the length of
time
the patient can maintain motion therefore a device that provides continuous
passive motion to the joint is essential to maximize recovery. Numerous
studies
have proven the clinical efficacy of CPM to accelerate healing and maintain
range of motion.
Furthermore, the rehabilitation of joints and soft tissue through
CPM has become an important modality in the treatment of articular injuries.
The
need for a CPM device specific to the forearm is justified by the
complications
in the recovery process of distal radial fractures and fractures to the wrist.
The
wrist is one of the most frequently fractured bones in the human body. Present
protocols for wrist fracture treatment require the wrist to be immobilized
with the
result that the muscles that provide the forearm with the ability to pronate
and
supinate contract. This effectively limits the ability of the forearm to move
through its natural range of motion. The ability of the forearm to pronate and
supinate is essential in maintaining a normal functional lifestyle. Without
this
range of motion the patient's ability to undertake routine daily activities
such as
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turning a door knob, turning a key, eating with utensils may be severely
compromised.
United States Patent No. 5,503,619 issued to Bonutti discloses an
orthosis device for bending of wrists in extension and flexion. This patent
does
not provide for pronation or supination of the wrist joint. Similarly, United
States
Patent No. 5,067,479 issued to Saringer et al. is directed to a device for
continuous passive motion of the wrist joint in flexion and extension.
United States Patent No. 4,899,735 issued to Townsend et al. is
directed to a torsion bar splint for pronation and supination of the wrist and
forearm. This device is an active exercise device which includes a pair of
telescoping rods with the a bracket pivotally attached at one end of a first
rod for
limited pivotal movement about the longitudinal axis of the first rod, the
bracket
being adapted to be secured to the palm of the hand by a plaster cast. The
opposing end of the second rod engages a one-way clutch attached to a bracket
adapted to be affixed to the user's upper arm thereby locking the arm in
90°. The
two telescoping rods are locked together to prevent rotation with respect to
each
other by a locking screw and the user actively exercises the distal radioulnar
joint by rotating the wrist in the direction allowed by the one-way clutch
thereby
pronating or supinating the wrist. The one-way clutch retains the wrist in the
furthest extent of its range of motion and to release the joint to return to
its
relaxed position requires the user to loosen the locking screw to allow
rotation
of one rod with respect to the other rod. This type of device is awkward to
fit into,
is an active exercise device only, and requires constant readjustment by the
user.
Therefore, it would be very advantageous to provide a CPM device
for the forearm which provides for an adjustable range of motion during
therapeutic exercise.
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SUMMARY OF THE INVENTION
It is an object of the present invention to provide continuous
passive motion devices for the rehabilitation of the upper extremity forearm,
which provides a controlled passive and adjustable range of motion to the
forearm.
The present invention provides continuous passive motion (CPM)
devices for the synovial joints and surrounding soft tissue of the human body,
more specifically to the upper extremities.
The invention relates to continuous passive motion (CPM) devices
for the synovial joints and surrounding soft tissue of the human body, more
specifically to the upper extremities. The device forming the present
invention
comprises an upper arm support suitably fixed to a drive actuator and an
adjustable forearm support suitably fixed to the rotational center of the
drive
actuator. The rotational motion of pronation and supination is created by
aligning
the drive actuator's rotational center with the anatomical rotational center
of the
forearm. The rotational centers are concentric to minimize stresses on the
affected limb. The relative rotational motion between the upper support and
forearm support creates the passive anatomical motion of pronation and
supination. The forearm and upper arm supports have a means of fixing the arm
in their respective supports. In a preferred embodiment the proximal arm
support
fixes the elbow in substantially 90 degrees of flexion. The upper arm support
maintains the elbow in flexion in the preferred embodiment to ensure the
rotational motion generated is transmitted to the forearm and not dissipated
at
the shoulder. The distal forearm support member is comprised of two
components. A proximal end is fixed to the rotational center of the drive
actuator.
The distal end is slidably mounted to the proximal end, adjusting in length to
accommodate anthropometric variances in forearm length. The distal end portion
of the forearm support also includes a hand piece inclined to accommodate the
hand's natural grip angle in the wrist's neutral position. A pivot point
located at
the distal end of the forearm support is concentrically located with the
rotational
center of the drive actuator. The pivot serves to provide a mounting location
for
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the shoulder strap. The shoulder strap is provided so that the patient can
comfortably wear the device while ambulating. The pivot point also serves the
role of indicating the proper anatomical alignment of the user's forearm in
the
device, for proper patient application.
The actuator is electrically operated and is connected to a patient
controller. The patient controller allows the patient to turn the device off
and on
and incorporates a reverse-on-load electronic circuit. The circuit monitors
the
current through the motor and will reverse the motor's direction if the
current
exceeds a preset limit. If the patient is in pain and resists the direction
the
device is traveling the motor current will go up and the circuit will change
the
device's rotational direction of travel. The controller contains a
rechargeable
battery and a provision to recharge the battery. The actuator is provided with
two
mechanically set limit switches to control the amount of rotational motion
delivered to the forearm. The device can offer a complete range of motion or
be
limited to operate between a specific set range of motion as indicated by a
goniometer mounted on the drive actuator.
In one aspect of the invention there is provided a continuous
passive motion device for a forearm. The device comprises an actuator
including
a housing and defining a rotational axis. The device includes a proximal arm
support member attached to the housing and securing means for securing a
user's upper arm and elbow to the proximal arm support member. The device
includes a distal forearm support member attached to the actuator for
rotational
motion about the rotational axis and securing means for securing a user's
forearm to the distal forearm support member with the longitudinal anatomical
axis of the user's forearm substantially coincident with the rotational axis
with the
distal forearm support member spaced from the rotational axis so that, during
rotation of the distal forearm support member, the user's distal forearm
undergoes pronation or supination about the rotational axis.
In this aspect of the invention the proximal arm support member
may include an L-shaped stay member with a vertical member and a horizontal
member and may include a humeral cuff support affixed to the vertical member
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for securing the upper arm of the user above the elbow. An elbow cuff support
may be affixed to the horizontal member for securing the elbow of the user
with
the user's arm in substantially 90° flexion.
In this aspect the distal forearm support member may include a
forearm stay member pivotally attached to the actuator and rotatable about the
rotational axis by the actuator. A distal forearm cuff support may be
connected
to the forearm stay member adapted to firmly grip the ulna and styloid
processes.
In another aspect of the invention there is provided a continuous
passive motion device for a forearm comprising a proximal arm support member
including a proximal stay member and a distal stay member slidably attached at
a first end portion thereof to the proximal stay member and securing means for
securing a user's upper arm and elbow to the proximal stay member. The device
is provided with an actuator including a housing and defining a rotational
axis,
the housing being rigidly attached to an opposed end portion of the distal
stay
member. The device includes a distal forearm support member including a distal
forearm stay member attached to the actuator for rotational motion about the
rotational axis and distal forearm securing means for connecting a user's
forearm to the distal forearm stay member with the longitudinal anatomical
axis
of the user's forearm substantially coincident with the rotational axis so
that,
during rotation of the distal forearm stay member, the user's forearm
undergoes
pronation or supination about the rotational axis.
In this aspect of the invention the distal forearm stay member may
include a first stay member connected to the actuator at one end portion
thereof
and a torque isolating stay member hingedly connected to an opposed end
portion of the first stay member. The torque isolating stay member may be
pivotable from a closed position adjacent to the rotational axis to an open
position radially displaced from the rotational axis.
In this aspect of the invention the distal forearm securing means
may include a distal forearm cuff support connected to the torque isolating
stay
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member adapted to firmly grip the distal ulna and styloid processes in the
user's
forearm.
In another aspect of the invention there is provided a continuous
passive motion device for a forearm comprising an proximal arm support
member including an L-shaped stay member with a vertical section and a
horizontal section and securing means for securing a user's upper arm and
elbow to the L-shaped stay member. The device includes an actuator including
a housing and defining a rotational axis with the housing being rigidly
attached
to the vertical section. The device includes a distal forearm support member
including a proximal forearm stay member pivotally connected at one end
portion
thereof to the actuator and slidably connected at an opposed end portion
thereof
to an end portion of a distal forearm stay member. The proximal forearm stay
member and the distal forearm stay member are telescopingly movable for
length adjustment. The distal forearm support member includes a distal forearm
cuff support connected to the distal forearm stay member adapted to firmly
grip
the ulna and styloid processes with the longitudinal anatomical axis of the
user's
forearm substantially collinear with the rotational axis so that, during
rotation of
the distal forearm stay member, the user's forearm undergoes pronation or
supination about the rotational axis.
BRIEF DESCRIPTION OF THE DRAWINGS
The following is a description, by way of example only, of
continuous passive motion devices constructed in accordance with the present
invention, reference being had to the accompanying drawings, in which:
Fig. 1 is a perspective view of a continuous passive motion {CPM)
device for exercising constructed in accordance with the present invention;
Fig. 2a is a orthographical top view of the device of Fig. 1;
Fig. 2b is a side view of the device of Fig. 1;
Fig. 2c is an end view along arrow 2c of Fig. 2a;
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Fig. 3a is a orthographical top view of the device of Fig. 1
illustrating the relative position of the humerus, radius, ulnar, carpal,
metacarpal
and digit skeletal structures of a patient's arm secured into the device;
Fig. 3b is a side view of the device in Fig. 3a;
Fig. 4 is an illustration of the CPM device of Fig. 1 showing patient
application in the ambulatory mode;
Fig. 5 is a perspective illustration view of an alternate embodiment
of a continuous passive motion (CPM) device for exercising, constructed in
accordance with the present invention;
Fig. 6 is an illustration of an alternate embodiment of the forearm
CPM device of Fig. 5 showing patient application in the ambulatory mode;
Fig. 7 is an elevation view of the device of Fig. 5 deployed and
ready to be fitted to a user; and
Fig. 8 is a view similar to Fig. 7 showing a user adjusting the
device to adjust the fit to the user's arm.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figs. 1, 2a and 2b, a continuous passive motion
(CPM) device for therapeutic exercising the forearm is shown generally at 10.
An actuator 20 contains a motor in housing 21. A rectangular mounting block 18
is rigidly fixed to housing 21 of actuator 20. Two range of motion limit
switches
26 are slidably mounted on either side of circular front of drive actuator 20
(only
one shown} for adjusting the rotational movement, both clockwise and counter-
clockwise, of drive disc 30 mounted to drive actuator 20 to rotate about a
rotational axis, to be described in detail hereinafter, and a goniometer 28 is
rigidly mounted to drive actuator 20 and indicates the angle through which
drive
disc 30 rotates. The CPM device 10 includes an L-shaped proximal upper arm
support stay 12 rigidly fixed to rectangular mounting block 18 so that upper
arm
stay 12 remains stationary when actuator 20 is actuated. A humeral cuff
support
14 fabricated of flexible material is rigidly fixed to the vertical section 13
of the
upper arm stay 12 for securing the upper arm above the elbow of a patient into
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the device. A proximal forearm cuff support 16 fabricated of a flexible
material
is rigidly mounted to the horizontal section 15 of upper arm stay 12. Flexible
strap 22 on cuff support 16 and strap 24 on cuff support 14 fix respectively
the
user's upper forearm just below the elbow joint and upper arm above the elbow
in the device.
CPM device 10 includes a longitudinal forearm support comprising
a proximal support stay 32 which is rigidly fixed to drive disc 30 at one end
thereof and two spaced connecting glides 36 fabricated out of a low friction
material which are located at the other end portion of stay 32. An L-shaped
distal support stay 34 is slidably mounted at one end portion thereof to
proximal
stay 32 by the two spaced glides. Glides 36 permit stays 32 and 34 to
telescope
relative to each other to provide an adjustment in length to accommodate
anthropometric variances in forearm length between individuals.
A distal forearm cuff support 38 including a rigid bracket 43 with
softgoods 39 attached thereto is rigidly fixed to stay 34 through two
standoffs 42
(only one shown). A strap 40, made of a flexible material is attached to cuff
38
for securing the arm of the patient into forearm cuff support 38. A hand-piece
44
inclined to accommodate the hand's natural grip angle in the neutral position
of
the wrist is rigidly mounted to stay 34 to be gripped by the user's hand with
a
restraining hand strap 64 (see Figs. 1 and 4) being provided.
With reference to Fig. 4, an attachment ring 48 is pivotally
mounted to a vertically extending end 35 of longitudinal support 34 by a pivot
46
fabricated of a low friction material. Attachment ring 48 rotates about an
axis 50
concentric with the rotational axis 50 of drive actuator 20. Pivot 46 and ring
48
provide a mounting location for a shoulder strap 62 so the patient can
comfortably wear the device while ambulating. Secondary to a pivotally mounted
fixation point the pivot point also indicates the proper anatomical alignment
of
the forearm in the unit, for proper patient application.
Referring again to Fig. 1, CPM forearm device 10 includes a
patient controller 56 electrically connected to actuator 20 by a cord set 52.
A
switch 54 on controller 56 is a three position switch with one of the
positions
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being ON. Controller 56 is connected to power supply 60 via cable 58 and
contains rechargeable batteries so that CPM device 10 may be operated with or
without being connected to a wall outlet. Controller 56 may include a belt
clip
(not shown) to be hooked to the user in the ambulatory mode. Controller 56 is
provided with a reverse-on-load electronic circuit. The circuit monitors the
current
through the motor in the actuator and wilt reverse the rotational direction of
the
motor if the current exceeds a preset limit. If the patient is in pain and
resists the
direction in which the arm supports 32 and 34 are rotating, the motor current
will
increase and the circuit will reverse the rotational direction of travel of
the
supports.
More specifically, controller 56 contains control circuitry which
includes a three position switch 54, position one corresponding to ONlOFF,
position two corresponding to 50% of full load, and position three
corresponding
to 100% of full load. Controller 56 contains the reverse-on-load technology to
monitor the motor current which is disclosed in l~.S. Pat. No. 4,716,889. The
actuator pivoting shaft (not shown) operates within preset values and if a
preset
value is exceeded, the motor changes direction to move the motor shaft and
drive disc 30 in the opposite direction. If a patient resists the motion of
the
actuator motor shaft, the motor current increases .and once the threshold
current
is exceeded, the unit reverses direction. Actuator 20 has provisions to
control the
degree of rotational motion delivered to the forearm. Since the rotational
motion
is controlled by the two mechanically set limit switches 26, the CPM device 10
can offer a complete range of motion or be limited to operate between a
specific
set range of motion as indicated by the goniometer 28 mounted on the drive
actuator 20.
In operation, the patient secures his or her arm into cuff supports
14, 16 and 38. When the drive disc 30 is rotated by the actuator motor the
forearm support stays 32 and 34 are rotated therewith. The upper arm support
stay 12 fixes the elbow in substantially 90° of flexion to ensure the
rotational
motion generated by actuator 20 is transmitted to the user's forearm through
stays 32 and 34 and not dissipated at the shoulder of the patient. The
rotational
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motion of pronation and supination is created by aligning the rotational
center
axis 50 of actuator 20 with the anatomical rotational center of the forearm.
With
specific reference to Figures 3a and 3b, axis of rotation 50 of actuator 20
corresponds to the anatomical center of the forearm 70 when the forearm is
secured in CPM device 10. The rotational centers are concentric (or put
another
way the longitudinal axis 50 is substantially coincident with the anatomical
axis
of the user's forearm) to minimize stresses on the affected limb. The relative
rotational motion between the upper arm support stay 12 and forearm support
(comprising stays 32 and 34) creates the passive anatomical motion of
pronation
and supination of the forearm.
It will be understood that the upper arm support fixes the elbow in
flexion, and preferably in 90° of flexion so that most or all of the
rotational motion
generated by actuator 20 is transmitted to the forearm and not dissipated at
the
shoulder of the patient. In addition, 90° of flexion is preferred for
patient
convenience in, for example, an ambulatory mode. However, it will be
understood that the principle of the present invention could be applied with
the
elbow in the neutral position albeit rotational motion generated by the device
for
pronation and supination would be transmitted in part to the shoulder.
Referring to Fig. 5, another embodiment of a continuous passive
motion (CPM) device according to the present invention for exercising the
forearm is shown generally at 310. The forearm CPM includes an L-shaped
humeral or upper arm support stay 312 telescopically mounted to a radial
support stay 334 by two glide brackets 336 fabricated from a low friction
material
to allow the humeral stay 312 and radial stay 334 to telescope relative to
each
other to provide a length adjustment for the forearm length of the user. The
distal
end portion of stay 334 is rigidly attached to a rectangular mounting block
318.
A drive actuator 320 is rigidly attached to mounting block 318.
A humeral cuff support 314 is fabricated of flexible material and is
slidably mounted to the upper vertical portion 313 of humeral stay 312. An
elbow
cuff support 316 is fabricated of a flexible material and is rigidly mounted
to a
horizontal component 315 of humeral stay 312 through two standoffs 342.
CA 02216863 1997-09-26
Flexible straps 322 and 324 fix the patient's proximal forearm and upper arm
in
cuff supports 316 and 314, respectively. Two range of motion limits 326 (only
one shown) are slidably mounted to the circular front of drive actuator 320. A
goniometer 328 is rigidly mounted to drive actuator 320 and illustrates the
angle
drive disk 330 rotates through during operation. Drive disk 330 is pivotally
mounted to drive actuator 320.
A distal forearm support member comprises a forearm drive stay
340 rigidly fixed to drive disk 330 so that when actuator 320 rotates drive
disk
330, stay 340 is rotated. A torque isolating stay 342 is pivotally mounted at
344
about the end portion of forearm drive stay 340 so it pivots about axis 346.
The
distal forearm support member includes an L-shaped stay 350 pivotally mounted
to a glide bracket 352 and glide bracket 352 in turn is slidably mounted to
torque
isolating stay 342 to allow the position of stay 350 to be adjusted according
to
the taper of the user's forearm. The distal forearm support member includes
two
L-shaped distal forearm support cuffs 348 and 349 with cuff 348 being rigidly
secured to L-shaped stay 350 with two nuts (not shown). Support cuffs 348 and
349 are fabricated of a hard formable plastic and connected to together by
straps 354 which allow the distal forearm of the user to be fixed into cuff
supports 348 and 349 with the ulna and styloid processes in contact each with
a different inner surface of the two cuffs. The contacting surfaces of cuffs
348
and 349 provide an effective means of applying motion to the forearm. A rigid
palmar handle 356 is rigidly mounted to the forearm drive stay 340.
Longitudinal
axis 353 is the anatomical center of the limb when it is engaged in device
310.
The rotational drive axis of actuator 320 is concentric with the anatomical
axis
of the user's forearm.
CPM forearm device 310 includes a patient controller 360. CPM
device 310 is electrically connected to the patient controller 360 by cord set
362.
A switch 364 on patient controller 360 turns the CPM device 310 off and on.
Patient controller 360 is connected to power supply 372 via cable 370. Patient
controller 360 contains rechargeable batteries and can supply power to
actuator
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320 with or without being connected to a wall outlet to provide mobility for a
patient using the device in an ambulatory fashion, see Fig. 6.
Referring to Fig. 7, in operation the user fully extends humeral stay
312 in the direction of the arrow and lifts the torque isolating stay 342. The
user's arm is then placed into the device with the user gripping hand piece
356
and the elbow in substantially 90° flexion. The humeral stay 312 is
then slid
forward until the proximal forearm cuff support 316 and humeral cuff support
314
engage the arm whereupon the proximal forearm cuff 316 is secured about the
arm. The torque isolating stay 342 is lowered onto the user's forearm. The
user
inserts his or her distal forearm into distal forearm cuff supports 348 and
349
with the styloid processes of the ulna and radius bearing against the rigid
cuff
inserts and straps 354 are tightened. The humeral cuff 314 is then slid
upwards
as high as is comfortable for the user and strap 324 is engaged.
When the user's arm and hand are properly positioned in the CPM
device (best seen in Fig. 8) the rotational axis 353 of actuator 320 is
concentric
with the anatomical rotational axis of the user's forearm. Anthropometric
variances in forearm geometry between different users are accommodated by
the telescoping stays 312 and 334, the distal forearm supports 348 and 349
being slidable and pivotable along stay 342 and the upper arm cuff support 314
being slidable on stay 312, see Fig. 8.
The preferred means of securing the hand is via the rigid palmar
support 356 and a flexible strap 358 (Figure 5) across the dorsal portion of
the
user's hand. The flexible strap 358 is suitably fixed to the dorsal portion to
ensure the uniform pressure across the metacarpals of the hand.
The present CPM device offers a complete range of motion or may
be limited to operate in a specific range of motion set by limit switches 326
as
indicated by the goniometer 328. Rotational motion generated at actuator drive
disk 330 is transmitted along to the forearm via the forearm drive stay 340 to
the
torque isolating stay 342 to the forearm support 348 which is suitably fixed
to the
patient's forearm. The torque isolating stay 342 is pivotally attached to the
forearm drive stay 340 and pivots radially from the anatomic axis 353, thereby
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transmitting torque only to the forearm and minimizing detrimental eccentric
loading of the limb. In addition, the forearm support 348 being slidably and
pivotally attached to the torque isolating stay 342 advantageously minimizes
the
axial and radial loading of the forearm. Therefore, the design of the present
CPM device advantageously avoids eccentric, axial and radial loading of the
limb in the CPM device while providing the desired motion of pronation and
supination concentric with the anatomical rotational axis of the forearm.
The foregoing description of the preferred embodiments of the
invention has been presented to illustrate the principles of the invention and
not
to limit the invention to the particular embodiment illustrated. It is
intended that
the scope of the invention be defined by all of the embodiments encompassed
within the following claims and their equivalents.
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