Note: Descriptions are shown in the official language in which they were submitted.
CA 02237880 1998-OS-13
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PROCESS AND APPARATUS FOR MAKING PROSTHESIS SOCKET
FIELD OF THE tNVENTtON
This invention relates to a method and apparatus for making a definitive
prosthesis socket for fitting residual limbs to prostheses and a resultant
prosthesis
socket.
I~ACKGROUND OF THE PRIOR ART
Definitive sockets for fitting prostheses to residua! limbs of amputees are
made by various processes in accordance with prior art techniques, including
molding thermosetting, thermoforming or other known resinous materials to
obtain
a final rigid socket shape that will receive a residual limb and structurally
react
toads between the prosthesis and the residua! limb without discomfort to the
user.
Such molded sockets without and with reinforcements are exemplified in U.S.
Patent Nos. 5,163,965, granted November 17, 1992 to Rasmusson and Fischl; and
5,263,990, granted November 23, 1993 to Handat, respectively.
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In accordance with a well known technique for molding definitive sockets
of resinous materials, a male or positive mold of the residual limb area is
made
from a plaster of Paris female or negative casting sleeve that has been formed
by
molding the sleeve directly against the residua! limb, sometimes with the aid
of a
known pressure casting system of the type exemplified by the ICECAST'" system
made by ~'?ssur h.f. of Reykjavik, lcetand. The positive mold is then.
adjusted or
"rectified" in accordance with well known techniques to provide relief for
sensitive
areas of the residual limb and to obtain a correctly sized socket that will
properly
fit the residual limb. The multiple step molding and rectification process is
well
known and has been extensively described in literature and texts known to
prosthetists. The process is time-consuming, expensive and heavily dependent
on
the individual skitis of the prosthetist.
Other procedures for molding interim or definitive sockets have been
described in the prior art, including a procedure whereby SCOTCHCAS'f'~ tape
7 5 made by 3M Company of Minneapolis, Minnesota, has been utilized to produce
an
interim prosthesis socket for below-knee amputees. The SCOTCHCAS'f~ tape was
wrapped directly over the residua! limb after a tube sock was applied to the
residual limb and manual compressive pressure was applied to the
SCOTCHCAST°
tape while it was curing to a hardened condition to provide relief for the
patellar
tendon area to form a PTB bar and to control the anterior-posterior diameter
for
weight bearing. (Wu et al., "SCOTCHCAS'f'~ P.V.C. Interim Prosthesis for Betow-
Knee Amputees", Bulletin of Prosthetics Research 1 O-36, Fall 1981, pp. 40-
45).
This process, however, has not been reported as being suitable for forming
definitive prosthesis sockets suitable for continuous long-term use.
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BRIEF SUMMARY OF THE INVENTION
The present invention is concerned with a molded residual limb definitive
prosthesis socket formed by using a single step pressure casting technique
that
enables the production of the socket with an internal form that is
substantially in
' 5 finished condition upon completion of the casting process. The socket is
molded
directly on a residual limb using a reinforced resinous material that in a
preferred
form of the invention is pre-formed as a pre-impregnated I"pre-preg") tubular
mat
or web of reinforcing strands or elements impregnated with a hardenable
uncured
or unhardened moldable preferably resinous material that is assembled with a
7 0 suitable prosthesis coupler that is ultimately unified with the molding
material
during molding and curing of the socket. Suitabte liner and covering fabric
layers
may be bonded to the inner and outer surfaces of the socket material during
molding and pressure relieving resilient material may be incorporated in the
socket
during molding as well.
7 5 The molding of the socket is carried out using a compressive pressure
casting technique modified so that tension is applied to the distal end of the
residual limb in the distal direction during hardening of the socket material.
In a
preferred embodiment of the invention, the tension is applied through a
resilient,
impermeable suction socket or steeve that has been placed on the residual limb
20 between the limb and the socket material. It has been discovered that the
application of such tension to the residual limb distally distends the soft
tissue of
the residual limb relative to the underlying skeletal bones) and reduces it in
size
diametrically. The application of such tension during pressure casting of the
socket
material produces a virtually final or definitive desired fit between the
residual limb
25 and the socket. Thus, this invention reflects the discovery that the
combination
of tension applied to the distal end area of the residual limb and compression
3
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casting of the socket material directly on the residual limb while under such
tension
enables a prosthetist to mold a definitive socket for prosthetic use in a
single step
using a moldable and hardenable socket material that possesses the necessary
load ,
bearing structural characteristics for a prosthesis socket.
A preferred moldable curable socket material in accordance with this
invention comprises a tubular mat of braided carbon fiber reinforcing strands
impregnated with a water curable poiyisocyanate type prepolymer. The exemplary
socket pre-form assembly includes a prosthesis coupler element integrated into
one
end of the socket assembly before molding and hardening.
pESCRIPTtON OF THE DRAWINGS
Figure 1 illustrates a side elevation section view of a pressurized casting
device constructed in accordance with the prior art;
Figure 2 shows a side elevation section view of a pressurized casting device
constructed in accordance with the invention with a residual limb, residual
limb
7 5 suction sleeve and socket pre-form in position for casting a residual limb
socket
intended to cooperate with a prosthesis;
Figure 3 is a side elevation section view showing a detail of the residual
limb
suction sleeve, prosthesis coupler and socket pre-form with pressure relief
inserts
in place;
Figure 4 shows a partial section elevation view of the tension connector
element of the pressurized casting device in accordance with this invention
incorporating a tension measuring arrangement;
Figure 5 is a partial section elevation view illustrating an alternate
arrangement of the residual limb socket sleeve and socket pre-form in position
for
casting;
4
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Figure 6 is a partial section view of a preferred embodiment of the
reinforcement used to form the socket pre-form;
Figure 7 is a detail section view showing the socket pre-form connected to
the prosthesis coupling member and the outer Payers covering the socket pre-
form;
Figure 8 is a section detail view showing the prosthesis socket and
prosthesis coupler after casting and curing of the socket pre-form in
accordance
with this invention;
Figure 9 is a side-elevation section view of an alternative embodiment of a
tension connector system usable with the pressurized casting device of the
invention;
Figure 10 is a section view taken along line 10-10 of Figure 9;
Figure 11 is a section view taken atong line 1 1-11 of Figure 9; and
Figure 12 is a section view taken along line 12-12 of Figure 9.
DETAILED DESCRIPTION OF PREFERRED
EMBODIMENTS OF THE INVENTION
In accordance with prior art techniques for making residual limb sockets
intended to receive a prosthesis for the limb, a female mold is typically
formed by
a casting technique whereby a water activatable moldable and hardenable or
curable wrapping (e.g., plaster of Paris bandage) is applied in soft pre-
hardened
condition over the distal residual limb area, the wrapping is permitted to set
up or
harden while it is pressurized by a pneumatically driven bladder or membrane
against the residual limb area, and after hardening (curing), the wrapping is
removed from the residual limb area so as to provide a female cavity
duplicating
the residual limb distal end contour.
5
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A positive cast of the residual limb distal end area is then made using the
female cavity as a female mold and finally after suitable adjustments or
rectifications of the mold are made, a definitive socket is molded by casting
or
forming a suitable hardenable socket structural material over the positive
cast.
Various finishing operations are then performed on the socket to make it ready
for
use and to receive the prosthesis.
fn a typical prosthesis socket assembly, the definitive socket will
incorporate
suitable hardware including adjustable prosthesis connector elements so as to
enable a rigid yet releasable connection to be made between the definitive
socket
i 0 and the prosthesis. One part of such hardware is referred to herein as the
prosthesis coupler for convenience and is intended to designate the end
fitting for
the socket that ultimately forms the distal toad reacting connection between
socket
and prosthesis. _
With reference to Figure 1, a prior art example of a pressurized casting
device 10 is shown that has been successfully used to support and pressurize
female mold casting sleeves applied to residual limb areas during hardening or
curing of the mold sleeves to ensure that the mold sleeves will conform
precisely
to the external configuration of the residual limb areas. The soft tissue of
the limb
is gently compressed under pneumatic pressure uniformly applied over
substantially
the entire external periphery of the residual limb area tpressure is avoided
at the
limb distal tip area) through such a casting system.
The casting device 10 includes a rigid outer housing that includes a
transparent tubular member 12, a proximal end cap 14 and a distal end cap 16.
The distal end cap 16 includes a pressurizing fluid admitting and venting
nipple 18
through which pressurizing medium (e.g., compressed air) may be admitted into
the pressurizing space 20 between the housing tube 12 and pressure membrane
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SUBSTITUTE SHEET (RULE 26)
CA 02237880 2004-10-04
or bladder 22 installed within the housing. The nipple 18 also permits
withdrawal
of air by suction from the pressurizing space 20 to expand the pressure
membrane
22 outwardly towards the tubular member 12, for purposes to be explained
below.
In this example, pressure membrane 22 comprises a compliant, elastomeric
silicone rubber tubular member clamped in fluid-tight relationship between the
clamping rings 24, 26 and the end caps 14, 16, respectively, so as to define
the
pressuring space 20 between the exterior of the membrane 22 and the interior
of
the tubular member 12 (and the interior of the end caps 14, 16, of course).
The end cap 14 is configured to provide an annular residual limb receiving
opening 28 at the proximal end of the tubular member 12, while end cap 16 is
shaped to provide an opening 30 having a reduced cross-sectional area as
compared with opening 28 at the distal end of the tubular member 12.
The tubular membrane 22 is installed in the tubular member 12 by stretching
the smaller silicone rubber tubular membrane radially outwardly at the
proximal end
of the tube and clamping it in place with ring 24, while the membrane is
clamped
in end cap 16 by an internal clamp ring 26 expanded within end cap 16 to about
the normal relaxed diameter of the membrane or slightly larger. The pressure
membrane 22 is maintained in longitudinal or axial tension along its length so
that
in its assembled condition it appears approximately as illustrated in Figure
1,
without wrinkled or collapsed portions.
An annual fitting ring 32 is removably clamped by a fastener 34 to the
proximal end of the end cap 14 to close the space between a residual limb
inserted
into the casting device and the proximal end of the end fitting 14 to prevent
blowing out of the membrane 22 through the proximal end of the tubular member
12 during a casting procedure when the membrane is pressurized. Various sizes
of fitting rings 32 are made available for use with the casting device to
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accommodate various sizes of residual Limbs over which the casting device is
to
be placed.
in operation, to create a casting sleeve using the exemplary casting device
shown in Figure 1, a residual limb area is first prepared by donning a
silicone
rubber sleeve of the type sold under the name, tCEROSS"', manufactured by
t3ssur
h.f. of Reykjavik, Iceland, over the residual limb area. This type of silicone
sleeve
gently stretches the soft tissue of the residual limb area in the distal
direction
beneath the sleeve when it is donned by rolling the sleeve over the limb
distal end
area and effectively stabilizes the soft tissue. However, the stretching
essentially
only occurs at the surface of the limb and is not to be considered the same or
equivalent to a tension applied from externally of the silicone sleeve to the
limb
distal end area. The silicone sleeve is also referred to as a suction socket
because
of how it interacts with the residual limb, which will be explained below.
A water settable moldable casting sleeve material, such as ptaster of Paris
impregnated tape or bandage, is soaked in water and then wrapped over the
suction socket while being formed by hand to smoothly conform to the limb
distal
end area shape. A fabric stocking may then be placed over the stilt soft
casting
sleeve material and then the pressure casting device 10 if fit over the
residual limb
area and casting material so that the residual limb enters the device 10
through the
proximal opening 28 tsometimes referred to herein as the residual limb
receiving
end of the casting device?. A suction is usually applied to the pressurizing
space
20 through nipple 18 before the residual limb is inserted in the casting
device 10
so as to draw the pressurizing membrane away from the central area of the
casting ,
device to provide space for the residual limb and the casting material within
the
central area.
8
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A spacer cup device (not shownl may be fitted within the pressure
membrane between the residual limb distal end and the distal end of the
pressure
casting device housing to limit or avoid pressurization of the distal tip end
of the
residual limb through the pressure membrane. A suitable spacer device may also
be used to ensure that a space is maintained between the distal end of the
Limb
with the casting material thereon and the cup device to permit expansion of
the
distal end of the soft tissue of the limb longitudinally towards the cup
device during
the pressurized casting procedure.
The pressurizing space 20 is now pressurized via the nipple 7 8 by using
compressed air from a suitable regulated source to thereby force the pressure
membrane into compressive contact with the casting material and to uniformly
pressurize the casting material about the residual limb. The soft tissue of
the
residual limb reacts to the pressure as it was subjected to a hydrostatic
force
exerted uniformly over the entire surface of the residual limb, but not
against the
distal end of the limb due to the presence of the spacer cup.
In actuality, the pressure acting in the pressurized casting device tends to
urge the casting device and its associated elements longitudinally away from
the
distal end of the residual limb and to urge the residual limb back out of the
opening
28. However, the compression and tension forces ate stabilized within the
membrane 22 while the casting material is permitted to set up and harden in
place
within the pressurized casting device white pressure is applied to the casting
material and the contained residual limb. External tensioning is not applied
to the
residual limb area during this known procedure.
9
SUIBSTITUTE SHEET (RULE 26)
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After sufficient time has elapsed to permit curing of the casting sleeve
material, the pressurized space 20 is vented to release the casting sleeve
material
from pressurization and the casting device 1 O is removed from the residual
limb.
Again, a vacuum may be applied to the space 20 to draw the membrane 22 away
from the external surface of the cast sleeve to permit easy withdrawal of the
residual limb from the central area of the casting device.
The hardened casting sleeve material, now in the form of a female molding
sleeve, is removed from the residual limb area in accordance with known
techniques using a cutting toot to split the sleeve, if necessary. The sleeve
is then
subjected to further processing, and ultimately is used to make a male or
positive
mold of the residual limb area using the cast molding sleeve as a female mold.
The
positive mold is further processed or rectified to adjust the mold surface to
a final
size and configuration, and to take into account pressure points that are
known or
expected to exist between the residual limb and definitive socket. Typically,
pressure reliefs are needed in the final definitive socket to take into
account the
shape and configuration of the residual Limb distal area, the presence of bone
tissue near the surface of the limb, and other variables or factors that are
well
known to prosthettsts. The final or definitive prosthesis socket is thus
formed
using the male mold in accordance with known techniques.
The present invention contemplates apparatus and methodology for forming
a definitive prosthesis socket in essentially a single step casting operation
that
eliminates the need for making female casting sleeves and positive molds as
well
as much of the associated rectification and fitting work involved in the prior
art
procedure.
SUBSTITUTE SHEET (RULE 26)
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More specificatfy, with reference to Figure 2, the known pressure casting
device 10 is utilized in conjunction with a socket pre-form 36 made in
accordance
with this invention, the pre-form including an integrated prosthesis coupler
38 to
form a definitive prosthesis socket in a single casting step using both
compression
and tension simultaneously applied to the residual limb distal area during a
molding
procedure.
As shown in Figure 2 in the preferred embodiment of the invention, the
distal end of a residual limb 40 is covered first by a silicone suction sleeve
41 such
as the 1CEROSS'" described above. The silicone sleeve includes an integrated
end
fitting 42 into which a tension pin or rod (or tension transfer element) 44
may be
screwed or otherwise secured (see Figure 3) to provide a means for
transmitting
axial tension or compression force through the distal end wall of the silicone
steeve
41.
Tension pins such as pin 44 have been used with such silicone suction
sleeves for securing the sleeves in a prosthesis socket but have not been used
in
the manner set forth herein far tensioning a residual limb 40 during pressure
casting of a definitive prosthesis socket.
The socket pre-form 36 in accordance with a preferred form of this invention
comprises any suitable combination of hardenable moldable compounds and
reinforcement materials that wilt achieve the formation of a definitive socke*
having
physical characteristics necessary or desirable for such a definitive socket,
and a
prosthesis coupler or the equivalent. A preferred embodiment of a socket pre-
form
comprises a porous or web-like compliant tubular braided carbon fiber sleeve
46
(see figure 6) available from Atkins & Pierce, 2 Braid Way, Covington,
Kentucky
as product numbers WGM4, WGM5.00 and WGM6.00 (4", 5" and 6° biaxial
carbon fiber sleeves), pre-impregnated with a water curabte polyisocyanate
type
11
SUBSTITUTE SHEET (RULE 26)
CA 02237880 2004-10-04
type pre-polymer resin 47 available under I.D. No. 41-3701-0524-3 from
3M Company of Minneapolis, Minnesota. The resin is activated and rendered
moldable by the addition of water to the resin and after wetting the resin
cures to a hardened condition rapidly.
More specifically, the braided carbon fiber sleeve is impregnated with
the resin so that the ratio by weight of resin to the weight of fiber (not
counting the prosthesis coupler at the end of the sleeve) is about 50%. This
ratio could be varied to suit particular applications so that resin amounts as
little as about 35% by weight and as much as about 75% could theoretically
be used.
Resins and reinforcements potentially suitable for use in forming the
pre-form 36 are described in U.S. Patent Nos. 4,502,479 granted to
Garwood et al. on March 5, 1985; 4,667,661 granted to Scholz et al. on
May 26, 1987 and 5,228,164 granted to Graf et al. on July 20, 1993; all of
which are assigned to 3M Company; and U.S. Patent No. 4,411,262 granted
to Bonin et al on October 25, 1983, assigned to Bayer (Germany); and all of
which describe various formulations of water activatable polyisocyanate
resins and reinforcing materials potentially usable for making preforms that
may be used in the casting device and methodology described and claimed
herein.
Of course, resin-reinforcement combinations would be selected on
the basis of their storage (shelf life), molding and hardening characteristics
such that the final socket would be structurally rigid and capable of bearing
loads imposed on such sockets during actual use.
12
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The pre-form 36 normally is packaged in rolled-up condition in a hermetically
sealed pouch and is activated by soaking the pre-form in water to render the
pre-
form soft and compliant. The wet pre-form can be manually donned over the
residual limb and silicone sleeve by manipulation and also can be manually
smoothed and initially pressed against the limb area in preparation for
inserting the
limb, silicone sleeve, pre-form and their associated elements into the molding
device, all in accordance with the description presented hereinabove and
below.
Use of reinforcement materials and other elements constituting the final
definitive socket or the pre-form 36 that detract from moldability, shelf fife
or
strength are to be avoided for obvious reasons.
The presently preferred resin identified as 3M No. 4i-3701-0524-3 is
composed as follows:
13
SUBSTITUTE SHEET (RULE 26)
CA 02237880 2004-10-04
MATERIALS% BY WEIGHT
1,1'-methylenebis (isocyanatobenzene) 59.00
PPG 725 (glycol from Union Carbide) 25.03
PPG 425 (glycol from Union Carbide) 9.92
Pluronic F-108 (from BASF Wyandotte) 4.00
4-2-1-methyl-2-(4-morpholinyl) ethoy ethyl 1.34
morpholine (catalyst)
2,6-DI-tert-butyl-p-cresol .48
benzoyl chloride (stabilizer) .05
The resin is in liquid form when impregnated into the reinforcement and the
pre-
form is in relatively firm but pliable condition within the sealed storage
pouch
before activation by exposure to moisture.
The braided sleeve may be preassembled with a prosthesis coupler 38 by
folding the pre-formed sleeve over the outer surface of prosthesis coupler 38
and
securing the sleeve thereto in an appropriate manner, such as by using a
string 48
(see Figure 7) to hold the sleeve in a recess 30 provided in the coupler 38.
Of
course, any suitable attachment method could be used between fibers 46 and
coupler 38. In accordance with a preferred embodiment of the invention, the
braiding of the tubular form is carried out in a known "biaxial" pattern that
causes
the tubular form to be very compliant and to radially contract when the tube
is
stretched longitudinally. This enhances the compression molding of the socket
pre-form 36 during the molding and curing of the pre-form.
It is also contemplated that a socket pre-form material constituted of a
curable moldable and hardenable resin or the equivalent could be used for
making
a socket according to this invention without using a separate reinforcement or
reinforcement web, or the reinforcement could be in a different form than a
pre-
14
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preg web. !t is only required that the material be moldable and hardenabfe
during
compression molding to form a structurally sound socket for prosthesis
application.
To prepare the preferred exemplary socket pre-form 36 for molding, the pre-
form is immersed in water to activate the resin and render it moldable about
the
residual limb area by manual application, in a manner to be described below.
It is
to be understood that the socket pre-form 36 described above is exemplary only
and that other resins or curable (hardenable) compounds may be used in
combination with other reinforcement elements to form the socket pre-form 36.
Preferably, however, it is desirable to form the socket pre-form with its
associated
prosthesis coupler as a pre-formed, pre-preg assembly ready for use in the
pressurized casting device 10 with a minimum of manual handling of the pre-
form,
other than to apply an activator agent to the resin component of the pre-form
to
activate its hardening or curing and to don the pre-form over the residual
limb so
as to ptace the prosthetic coupler adjacent the distal tip end of the residual
limb.
Thereafter, the contact between the pressure membrane 22 and the pre-form 36
should be sufficient to mold the pre-form under compressive pressure in
intimate
contact with the residual limb 40 while the socket material hardens or cures
into
a final hardened condition. A suction sleeve 41 preferably is used between the
residual Limb tissue and the pre-form in the example shown.
Accordingly, as illustrated in the example shown in Figure 2, a socket pre-
form 36 with its associated prosthesis coupter 38 is placed over the distal
end of
a residual Limb 40 to which a silicone suction sleeve 41 and its associated
tension
pin 44 has been applied. The coupler 38 includes a central aperture 52 (see
Figure
7) that may or may not be threaded, depending on the molding arrangement to be
used, and may include other apertures 54 and other geometric or structural
features if desired for use as part of the prosthesis coupling arrangement.
The
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coupler 38 also may include any desired protuberances or teeth 56 or other
pronounced features such as shown to enhance the bonding and securing
characteristics between the coupler 38 and the pre-form 36 in the area of the
coupler 38 during molding and in the final cured socket. The coupler 38 and
resin
of the pre-form 36 ate intimately bonded together during the casting process.
An important feature of the present invention is the use of tension applied
to the silicone sleeve 41 distal end area via the end fitting 42 during
circumferentiai
compression of the socket pre-form 36 while the pre-form is curing and
hardening.
As noted above, the silicone sleeve 41 in accordance with this example is
often
referred to as a "suction socket" because it grips the residual limb in an
airtight,
non-slip manner. When used with a prosthesis socket, such a sleeve not only
provides a soft interface between the residual Limb and socket, but also
prevents
pumping action of the residual limb area at the distal end of the residual
limb, an
undesirable phenomenon that occurs with some other types of known prosthesis
sockets or sleeves. The silicone sleeve achieves this effect by maintaining
itself
in tight yet compliant contact with the residual limb area due to the gripping
force
exerted by the silicone against the residual limb, which prevents air from
entering
the sleeve interior between the sleeve and the residual limb.
To achieve application of a tension force on the distal end of suction sleeve
41 during compression molding or casting in the casting device 10, a tension
connector device generally indicated at 58 is used with the pressure casting
device
10. The tension connector 58 is intended to engage tension pin 44 and prevent
its motion back towards the proximal opening 28 of casting steeve 10 during
compressive pressurization of the socket pre-form 36. To facilitate engagement
between the pin 44 and the tension connector 58, a known one-way detent
gripper
60 is used whereby protrusions 62 on pin 44 may be pushed forwardly through
the
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gripper 60 without stoppage in a direction towards the connector 56 (i.e..
away
from the proximal opening 28), but reverse motion of pin 44 is braked and
locked
until it is desired to release the pin 44. The pin 44 is released by using a
suitable
gripper release knob, pin or other element 64 that may be appropriately
manipulated by the prosthetist.
The gripper 60 is well known in the art peg se and such elements are used
in practice to secure silicone suction sleeves, such as shown at 41, to
prosthesis
devices to aid in inserting a residual limb into a socket to be used with a
prosthesis
device. However, it is believed that such grippers have not heretofore been
used
in association with pressure molding or casting systems of the type described
herein.
The gripper 60, in the embodiment of the invention illustrated in Figure 2,
is carried by a tension connector support arrangement that includes a tubular
frame
66 and a gripper supporting plug 68 axially siidable into the distal end 69 of
the
frame 66. The plug 68 carries the gripper 60 and its associated mechanisms
including release knob 64, and the frame 66 includes openings providing manual
access to the gripper release knob 64. The frame 66, for example, may be
formed
of longitudinally extending struts that are circumferentially spaced to
provide a
cage-like enclosure for the gripper mechanism so that the release knob 64 may
be
manipulated through the openings in the cage-like enclosure. It will be
appreciated
that the plug 68 with the gripper 60 can be simply inserted into the end 69 of
frame 66 to cause one-way engagement between the pin 44 and the gripper 60
after the residual limb 40, silicone sleeve 41 and socket pre-form 36 have
been
placed as a unit into the tubular member 12, as shown in Figure 2. In this
position,
the socket pre-form 36 is in its casting position, and pin 44 extends axially
through
aperture 52 and coupler 38 associated with the socket pre-form 36.
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The frame 66 of tension connector 58 in accordance with this example of
the invention also includes a force transfer element or a longitudinal
movement
limiter or limiters 70 that are formed as one or more radiai protrusions on
the frame
that engage a radial face of the ring 26 or other appropriate structure of the
casting
device 10 to prevent axial or longitudinal motion of the frame relative to the
end
cap 16 during casting, at least in the direction towards the proximal end
opening
28 of the proximal end cap 14.
Thus, it will be evident that once the pin 44 is engaged with the gripper 60,
and residual limb 40, silicone sleeve 41 and socket pre-form 38 are located in
casting position, motion of pin 44 and the distal end of silicone sleeve 41
toward
the proximal end of molding device 10 is restrained by the coupling between
the
pin 44 and the gripper 60, and the longitudinal motion blocking engagement
between the protrusions 70 and the fixed ring 26.
The proximal end of frame 66 in accordance with the embodiment shown
in Figure 2 includes a threaded proximally extending axial extension 74 (see
Figure
2?. The coupler 38, in accordance with this embodiment, includes a threaded
central aperture 52 that is threadedly engaged with the axial extension 74 of
frame
66 of tension connector 58. In this manner, coupler 38 may be retained in
close
proximity to the proximal end area 76 of frame 66 of tension connector 58.
In accordance with this embodiment, a space or gap 77 may be maintained
between the distal end of silicone sleeve 41 and the inner or proximal side of
coupler 38 during the molding procedure. This space 77 is maintained by the
engagement between pin 44 and the gripper 60 during molding in the pressure
casting device 10.
When compressive pressure is applied to the socket pre-form 36 via the
pressure membrane 22 following pressurization of the pressurizing space 20 by
18
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compressed air, the compressive forces and the reaction loads tend to urge the
pressure casting device 10 in a distal direction relative to the residual limb
40 whsle
the limb itself remains stationary. By observing Figure 2, it will be noted
that any
movement of the casting device 10 in a distal direction is resisted by the
connection between the tension connector 58 and the pin 44. That is, forces
applied in a distal direction against the interior of the tubular member 12
and 'rts
associated end caps 14, 16 will be reacted against the tension connector 58 at
force transfer or movement iimiters 70 and such reaction will be transmitted
through the plug 68 to the gripper 60 and then to pin 44. The pin 44, in turn,
will
transmit distally exerted forces back into the silicone sleeve end fitting 42
so that
the silicone sleeve 41 effectively receives the full tension load reacted
through pin
44. The tension load applied to the silicone sleeve 41 is reacted into the
residua!
limb 40 as a distally exerted suction and stretching force that ef#ectivefy
stretches
the residual limb area in a distal direction while reducing its overall
diameter, to the
extent that the soft tissue in the residual limb area can accommodate such
distention and reduction in diameter.
Aetuai tension loads used in practicing the inventive process and using the
pressure casting device according to the invention will be determined
experimentally depending upon the shape, morphology and sensitivity of the
residual limb and the structure/materiais constituting the pre-form 36. In
practice,
using the preferred 3M wateractivatable polyisocyanate casting material
disclosed
above, a pressure of 220mm mercury within the pressurizing space 20 yielding a
tension force on the order of 17-30kgs has been found satisfactory to produce
a
definitive socket. However, other pressures and tension loads that do not
result
in a discomfort level for the amputee could be used. Also, the degree of
tension
used will depend upon the degree of tightness of fit between the residual limb
and
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the definitive socket that is desired. Also, in practice it has been found
useful to
pre-load the tension pin 44, 166 to a predetermined level on the order of 9-
12kgs
before compressing the pre-form. However, in any case, the tension produced by
,
compression of the pre-form should always exceed any pre-load set at the
tension
pin. "
During compression of the socket pre-form 36, it is hardening against the
tensioned and somewhat narrowed residual limb area of the residual limb 40. To
the extent that the compressive forces exerted against the residual limb area
cause
its axial elongation in the distal direction, it will be seen that this motion
is readily
taken up by the advancement of pin 44 further into gripper 60 so that the
distal
tip end of the residual limb is not effectively compressed so long as space 77
is
maintained. The threaded connection at the central aperture 52 of the coupler
38
and the threaded extension 74 of frame 66 causes the axial loads in the distal
direction that may be exerted by the casting device 10 to be reacted into the
1 b coupler 38 so that in effect the coupter 38 moves with the tension
connector 58
relative to the residual limb 40. Accordingly, since the coupler 38
effectively
moves with the tension connector 58 and end cap 16 of the casting device 10,
the
space 77 is maintained between the distal end of the residual limb and the
coupler
38 provided that the distal end of the residual limb does not expand
sufficiently to
take up all of the space 77.
The combination of compressive molding forces exerted on the socket pre-
form 36 while it is hardening and the tension applied in a distal direction to
the
residual limb area via the suction socket 41 results in forming a prosthesis
definitive socket having an internal geometry that requires little or no
further
rectification before use as a definitive load bearing socket.
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Since the braided reinfiorcement web of the pre-form 36 is constructed to
radially contract when the tubular web is elongated, tension force applied
through
the tension connector 58, tension pin 44, silicone sleeve 41 and coupler 38 to
the
socket pre-form 36 will tend to cause the pre-form 36 to initially contract
radiaily
to thereby enhance the compression force exerted by pressure membrane 22 while
the socket pre-form 36 is curing and hardening within pressure casting device
10.
It has been observed that the requirement for a space 77 may not exist in
all cases and the embodiment of the invention in accordance with Figure 5 may
be
utilized if such a space 77 is not required.
The embodiment of the invention illustrated in Figure 5, wherein like
reference numerals are utilized for elements corresponding to the elements
already
described, inctudes a silicone suction sleeve 41, sleeve end fitting 42, and
tension
pin 44 having protuberances 62 thereon for engagement with a gripper (not
illustrated) carried by a frame 66 of tension connector 58. !n this
embodiment, an
axial extension 78 of proximal end wail 76 of tension connector 58 is not
threaded,
but is generally cylindrical so as to engage a corresponding cylindrical
aperture 80
in coupler 38 through which the extension 78 extends. The extension 78 thus
serves to center the coupler in the casting device. The pin 44, as in the
previous
embodiment, extends through both the axial extension 78 and the aperture 80 in
ZO the coupler 38. It will be observed that, as illustrated in Figure 5, when
the socket
pre-form 36, silicone sleeve 41 and residual limb 40 are located in the
casting
position, the distal end of the silicone sleeve 41 virtually clamps the
coupler 38
between the distat end of the residual limb 40 and the proximal end wail 76 of
frame 66 of tension coupler 58.
In accordance with the embodiment of Figure 5, casting or molding of the
socket pre-form is carried out in the same manner as described previously in
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connection with Figure 2, whereby fluid pressure is applied by pressure
membrane
22 to the exterior of the socket pre-form 36 to thereby cause both radial
compression and a tension to be applied to the residual limb 40, the silicone
sleeve
41 and the pre-form 36 during the casting process while the pre-form 36 is
hardening. The beneficial results described previously obtained by applying
such
compression and tension to the residual limb within the socket pre-form during
curing may be obtained with the embodiment in accordance with Figure 5 as
well.
!t is contemplated that, for some applications, it may be desirable to
measure or monitor the tension applied or reacted by pin 44 to the distal end
of
silicone sleeve 41. (n accordance with the embodiment of Figure 4, a gripper
60
is carried by a gripper and load cell assembly 82 that may be axially inserted
within
the distal opening of tension coupler 58 to engage the pin 44 before the
socket
pre-form 36 and residua( limb 4_0 are pressurized in the casting device. The
assembly 82 includes a suitable force sensing device or toad cell 84 that may
be
electrically actuated via leads 86 so as to measure and/or monitor the tension
applied to the gripper 60 during compression molding of the casting sleeve 36.
Of
course, the load cell 84 may take any suitable form that enables measurement
of
the force, whether tension or compression, reacted by pin 44 against a
relatively
fixed element associated with the casting device. Also, the load cell 84 may
be
mechanically or electromechanically operated in accordance with known state of
the art techniques and arranged to receive electrical signals to and transmit
load
signal from toad cell 84 via appropriate leads (not shown). A suitable
indicator
adapted to receive load signals and indicate load forces (not shown) may be
provided to enable an observer to detect the amount of tension exerted by pin
44
against the distal end of the silicone sleeve 41. An exemplary load cell
element
that may be used is the model 802 Planar Beam Sensor made by Revere
22
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Transducers incorporated of Cerritos, California, which is an electrical
strain gage
and beam system, and which may be used in a stacked arrangement as shown to
reduce errors.
It is typically desirable to provide pressure relieving soft areas or
formations
within a definitive socket, such pressure relief formations normally being
incorporated in the socket constructed in accordance with prior art techniques
during the final definitive socket molding operation. The present invention
provides
a technique whereby such pressure relief formations may be incorporated into
the
socket pre-form 36 prior to pressure casting of the socket. As illustrated in
Figure
3, soft silicone rubber or foam pressure relief formations 90 or similar
materials or
elements providing equivalent functions may be provided within the socket pre-
form 36 by first applying a thin smooth fabric inner liner layer 92 (for
example, a
finely woven or knit nylon) to the outer surface of the silicone sleeve 41
followed
by application of the pressure relief formations 90 to the outer surface of
the liner
layer 92. The skilled prosthetist will understand how and where the pressure
relief
formations must be provided in accordance with known techniques whereby, when
the socket pre-form 36 is hardened, the formations 90 wilt be bonded into
ptace
against the inner surface of the socket 36 by the resin and wilt be in proper
position to provide pressure relief for sensitive areas of the residual limb
40 during
use.
After the pressure relief formations 90 are applied to the liner layer 92, the
socket pre-form 36 and coupler 38 may be applied over the liner 92 to prepare
the
assembly for compression casting. The assembly is then placed within the
pressure casting device 10 and the casting procedure as outlined above is
carried
out in a manner to exert tension against the distal end of the silicone sleeve
41
while the socket pre-form 36 is curing or hardening under compression.
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A smooth fabric outer covering layer 94, for example, a finely woven or knit
nylon, (see Figure 7), will normally be applied to the exterior of the socket
pre-form
36 before compression and molding to provide a finished appearance on the
cured
socket.
A section of a finished definitive socket substantially ready for use after
removal from the casting device 10 is illustrated in Figure 8. The material in
socket
pre-form 36 has hardened and, if resinous, reached a partially or fully cured
state
that provides a rigid definitive socket having an interior cavity that wilt
precisely
accommodate and tit the exterior contours of the residuat limb with which it
will
be used. Further curing steps can be carried out if necessary at this stage,
provided that such does not adversely affect the fit of the socket.
A prosthesis connector or joint structure will be attached to the coupler 38
and the final outer contour of the socket finished so as to provide such
typical
support and relief areas as are normally provided on such definitive sockets,
particularly at the proximal end thereof.
With reference to Figures 9-i 2, an alternate embodiment of a preferred
tension connector is illustrated. This arrangement permits accommodation of
shorter residual limb lengths within the casting device and facilitates
engagement
and disengagement of a tension pin by a gripper mechanism.
As shown in Figures 9-12, a tension connector 100 comprises an elongate
cylindrical member (or housing) 102 having a generally smooth inner bore 103,
a
proximal end 104 and a distal end 106. As shown in Figures 10 and 1 1, the
outer
circumference of the tubular member 102 as shown in Figures 10 and i 1 has a
smooth cylindrical periphery except for locking grooves or detents 109 that
have
been molded, or cut otherwise formed into the periphery of the tubutar member
102 in longitudinatty and circumferentially spaced relationship. The bottom of
each
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SUBSTITUTE SHEET (RULE 26)
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decent groove 109 is flat, as shown in Figure 1 1. The outer circumference~of
the
tubular member 102 between the circumferentially spaced sets of detent grooves
109 as shown at 108 is smooth and uninterrupted longitudinally.
The distal end cap 1 10 of the casting device (that is otherwise constructed
' 5 in accordance with Figure 2) is provided with a longitudinally extending
cylindrical
section 1 12 having internal threads 1 14 arranged to receive a tension
connector
locking device 1 16 which, as illustrated, includes external threads
cooperating with
the internal threads 1 14 of the tubular extension 112. Pressure membrane 118
is
held assembled to the end cap 110 when the tension connector Locking device
116
is securely threaded into the end cap as shown. Other arrangements can be
utilized for securing the tension connector locking device 1 16 within the end
cap
110 in accordance with any suitable technique that would be evident to a
person
skilled in the art. Tension connector tocking device 1 16 includes locking
teeth
120 projecting radially inwardly as shown in Figures 9 and 11 for selective
engagement with the decent grooves 109 in tubular member 102. The tension
connector locking device 116 essentially comprises a thin annular flexible
tube
having discontinuous side wail portions resiliently biasing and supporting the
teeth
120 whereby the teeth 120 can be sprung or deflected radialty outwardly from a
normal locking position against the bias of the material forming the tension
connector locking device. For example, the tension connector locking device
could
be made of a molded synthetic resin such as nylon which would provide inherent
resiliency for accommodating outward springing movement of teeth 120 in a
manner to be described below.
From viewing Figures 9 and 11, it will be evident that rotation of tubular
member 102 about its longitudinal axis will cause teeth 120 that are in
locking
engagement with grooves 109 to be deftected radialty outwardly when the smooth
SUBSTITUTE SHEET (RULE 26)
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outer surface portions 108 of the member 102 are moved under the teeth to
cause
the teeth to be cammed outwardly from the grooves 109. When the teeth engage
the smooth outer surface 108, the tubular member 102 is free to move
longitudinaity within the tension connector locking device without engagement
or
locking of the teeth 120 with any grooves 109 so long as member 102 is not
rotated. Slight rotation of the tubular member 102 to align the grooves 109
with
teeth 120, however, will permit teeth 120 to snap radially inwardly into the
closest
available grooves 109 on the exterior of tubular member 102 to thereby lock
the
tubular member 102 against further longitudinal movement relative to the
tension
connector locking device 1 18 and the end cap 1 10 of the pressure casting
device.
Since the grooves 109 are closely spaced together, fine incremental adjustment
of
the position of tubular member 102 relative to the end cap 1 10 is enabled
simply
upon manipulation of the tubular member 102 in a rotational and longitudinal
sense. The flat bottom configuration of the grooves tends to prevent
inadvertent
rotation of the tubular member 102 when locked.
The length of the tubular member 102 is selected such that it can be moved
within the casting device end cap 1 10 in a longitudinal sense towards and
away
from a residual limb within the casting device and an end fitting associated
with
a silicone sleeve within the casting device, as will be explained more fully
below.
In this embodiment, the length of the tubular housing 102 is selected such
that it
may be moved within the end cap 110 to engage a tension pin associated with a
shortest residual limb expected to be fitted with a molded socket while
leaving
sufficient length outside the end cap 1 10 to permit manipulation of the
tubular
member.
The tension connector 100 also includes a proximal end fitting 122 fitted to
the proximal end 104 of tubular member 102, the end fitting including a
concave,
26
SUBSTITUTE SHEET RULE 2fi)
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conical end surface 123 and a central cavity 123'. A longitudinally extending
central bore extends through the end fitting 122, as shown in Figure 9. End
fitting
. 122 is secured by threads 126 to cylindrical force rod 124 that extends
longitudinally within tubular member 102 from the proximat end area of the
tubular
member 102 towards the distal end thereof. The force rod 124 is connected at
its
distal end by fastener 130 to a load cell 128 by fastener 130. The load cell
128
may be the same type of mechanism is described previously in connection with
load cell 84 illustrated in Figure 4 or any other suitable load cell that will
function
in an equivalent manner.
A gripper mechanism 132 is provided in the central cavity of end fitting 122
and is retained therein by a suitable biasing means (not illustrated) normally
maintaining the gripper 132 displaced to one side of the longitudinal axis of
the end
fitting 122. The gripper 132 includes internal teeth or detests arranged to
engage
external teeth or detests provided on a tension pin 166 such that the gripper
permits longitudinal movement of the tension pin 166 towards the distal end of
the
tubular member 102 but prevents return movement of the pin until the gripper
is
released. This arrangement of gripper and tension pin corresponds with the
arrangement described previously in connection with the embodiment of the
invention illustrated in Figure 2.
A gripper release device 134 comprises a tubular member having a conical
nose end 136 arranged to engage a conical surface 138 of gripper 132. Conical
nose end 136 of release 134 can be moved axially towards and away from the
gripper 132 such that, when the nose end 136 is advanced towards the gripper
132, it acts as a cam surface and the conical surface 138 of gripper 132 acts
as
a follower surface so that the gripper 132 is displaced transversely or
radiaily with
respect to the longitudinal axis of the end fitting 122 when the release 134
is
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SUBSTITUTE SHEET (RULE 26)
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advanced towards the gripper 132. Essentially, the conical nose end 136 of
release 134 causes centering of the gripper 132, thereby releasing its teeth
from
the teeth of the tension pin 166.
The gripper release 134 is supported in sliding relationship within the inner
bore of the cylindrical force rod 124, as illustrated in Figure 9. The gripper
release
134, however, is secured by means of pin 140 extending through a iong'rtudinal
slot 142 in force rod 124 to a gripper release actuator rod 144 that extends
longitudinally within the inner bore of tubular member 102 (see Figure 10).
The
rod 144 includes an elongate slat 146 extending through the proximal end of
the
rod 144, white the remainder of the exterior surface of the rod 144 is
cylindrical
in contour as shown in Figure 12. An enlarged head 148 is provided on the rod
744 to provide a close fit within the bore 103 of tubular member 102 and to
act
as a bearing surface between the head 148 and the bore 103.
A compression spring 150 on force rod 124 is retained by retainer discs
152, 154 and located at the proximal end of the actuator rod 144 for
maintaining
the rod 144 located such that the enlarged head 148 of the rod is located at
the
distal end 106 of tubular member 102. The compression spring 150 tends to
spread the discs 152 and 154 apart, but the disc 154 is locked against
longitudinal
movement by an enlarged stop 156 provided on cylindrical force rod 124. Thus,
spring 150 urges disc 152 and the proximal end of rod 144 towards the distal
end
of tubular member 102. The rod 144, on the other hand, is displaceable against
the force of the compression spring 150 by moving the enlarged head 148
inwardly along the length of tubular member 102 so as to drive pin 140 and
gripper '
release i 34 longitudinally towards the gripper 132 to thereby selectively
effect
release of the gripper 132 in the manner described above. Upon return of the
enlarged head 148 by, the spring i 50, rod 144 is urged towards the distal end
of
28
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tubular member 102 and withdraws the gripper release from the gripper 132 to
enable the gripper to return to its normat position eccentric of the
Longitudinal axis
of end fitting 122. It will be noted that the spring 150 tends to hold the
discs l 52.
154 apart longitudinally within tubular member 1 OZ to thereby drive the rod
144
back towards its normal position at the distal end 106 of tubular member l 02.
Thus, release of gripper 132 can be accomplished remotely by manually pressing
the enlarged head 148 effectively as a push-button.
The load cell 128 is rigidly connected to the distal end of force rod 124 by
a suitable fastener 130, as previously described. The load cell 7 28 is also
connected to a toad transmitting member 160 through an adjustable fastener or
the
like 158. The load transmitting member 160 is located within an enlarged
portion
of the inner bore 103 of tubular member 102 and engages a suitable metallic
ring
l 62 or the equivalent retained in shoulder 164 of tubular member 102 at the
end
of the enlarged section of the bore 103 (Figures 9 and 12f. Thus, toad
transmitting
member 160 is prevented from axial movement within the bore 103 beyond the
ring 162 in the direction of the proximal end of tubular member 102.
It will thus be seen that tension Toad generated during the casting process
as previously described and transmitted through end cap l l 0 to the tension
connector Pock l 3 6 and its teeth 120 is in turn transmitted through tubular
member
102 to cause load transmitting member 160 to move with the tubular member 102
and end cap 1 10 in a distal direction during casting.
The load transmitted through load transmitting member l 60 is transmitting
to the load cell l 28 through the adjustable fastener 158 and this load is
reacted
by the force rod 124 in tension. This tension force transmitted through force
rod
124 in turn is transmitted to the gripper 132 through the end fitting l 22
which
engages the tension pin 166, as previously described. Thus, axial Loading
between
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the end cap 1 10 and the residual limb within the casting device is
transmitted
through the load cell 128 which, as previously described, is electrically
actuated
so as to produce an electrical output signal indicative of the toad. An
appropriate
lead or teads 161 connected to an electrical connector 163 located in the
enlarged
end 148 of gripper release rod 144 enables energization of the load cell 128
and
the availability of output signals indicative of the load sensed by the toad
cell atthe
connector 163.
Further in accordance with this embodiment of the invention, tension pin
166 is provided with a threaded head end 168 that extends through prosthesis
coupler 170 via a central bore 172. The threads of the head end 168 of pin 166
are received by the threaded socket 174 provided in the end fitting l 73 of
silicon
sleeve 176 that is in direct engagement with a residual limb to be fitted with
a
prosthetic socket in accordance _with the invention. The head 168 of pin 166
effectively clamps the prosthesis coupler 170 to the silicone sleeve 176 and
its end
fitting 173 so that tension loads applied through pin 166 will be transmitted
to the
silicone sleeve 176 as well as the terminal end of the pre-form 36 during
hardening
of the pre-form while it is under compression through the pressure membrane 1
18.
It will be noted that the concave conical end surface 123 of end fitting 122
enables the pin 166 to be located in the center of the end fitting to enable
the pin
to extend through gripper 132 when tension connector 100 is moved in the
direction of the proximal end of the casting device.
In operation, the embodiment of the invention in accordance with Figures '
9-12 operates in essentially the same manner as the embodiment described in
Figures 2-5. After the silicone sleeve 41 or 176 has been donned over the
residual
limb 40, the pre-form 36 with its associated prosthesis coupler 38 or 170 is
rolled
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up over the silicone sleeve and pressed into close engagement with the stesve
and
its contained residual limb. The tension pin 44 or 166 is threaded into the
end
fitting 42 or 173 so that it extends in a distal direction within pressure
membrane
22 or 118.
The assembled tension connector 58 or 100 is then advanced longitudinally
through the end cap 16 or 1 10 such that the tension pin extends through the
gripper associated with the tension connector of alt embodiments. In
accordance
with the embodiment of Figures 9-12, a slight pre-tension may be applied to
the
tension pin 166 by pulling on the tension connector after the pin 166 has been
engaged by the gripper 132. The tension connector 100 is then rotated
sufficiently to lock the cytindrica( member 102 into engagement with the teeth
120
to thereby secure the tension connector 100 against tongitudinal movement
relative
to end cap 1 10.
In ail embodiments, application of a pressurized fluid into the pressurizing
space 20 (Figure 4) causes external pressurization of the pre-form 36 in the
manner described previously and a resultant reaction load to be applied in a
distal
direction to the tension pin 132. Hardening of the pre-form 136 then proceeds
to
completion, following which the tension pin is released from its gripper and
the
residual limb with the molded and hardened socket are removed from the
proximal
end of the casting device. The molded socket is removed from the residual limb
and final cutting, shaping (trumpeting) and finishing operations are performed
thereon in accordance with known techniques.
It is to be understood that preferred or best mode embodiments of the
invention have been described for illustrative purposes only and that the
scope of
the invention is to be limited only by the scope of the claims that follow.
31
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