Prosthetic socket

A prosthetic socket is adapted to support a prosthesis and is also adapted to be worn on a stump of a partially amputated limb. This socket has a coupler for holding the prosthesis along a prosthetic axis. The socket also has a cup with an inside surface and an outside surface. This inside surface is adapted to fit on the stump. The coupler is centrally attached to the cup to face outwardly from the outside surface. The cup contains a separated plurality of contractible cavities distributed around the prosthetic axis between the inside surface and the outside surface to provide cushioning by allowing deflection of the cup along the prosthetic axis into the cavities to contract the cavities. The cup can be formed with a plurality of angularly spaced, elongate, blind holes extending away from a central location. These blind holes can be plugged to prevent intrusion of debris. In an alternative cup, a molded cap can be affixed over a molded boot, while leaving interspaces that form spaced, closed cavities.

FIELD OF THE INVENTION 
The present invention relates to a prosthetic socket, and in particular to 
a socket that provides cushioning between the prosthesis and the stump of 
an amputated limb. 
DESCRIPTION OF RELATED ART 
Amputees can wear a cup-shaped socket at the distal end of a stump. This 
socket can be molded around a threaded fitting having a dome-shaped 
flange. A prothesis with a concave, proximal end can have a stud that can 
be threaded into this fitting. A socket supporting the prosthesis should 
be able to sustain the various forces exerted at varying angles during 
walking or other activities. 
When a person loses part of a limb, usually there is very little extra skin 
or tissue at the stump to act as a cushion for a prosthetic device. 
Attempts to cushion the device by using pliable or flexible sockets have 
limitations. A socket should not deform to such an extent that the 
prosthesis feels wobbly. Maintaining an appropriate balance between 
comfort and stability can be difficult. A prosthetic socket should also be 
easily attached, allow the transference of forces during movement of the 
prosthetic device, and provide proper stability to prevent the socket from 
twisting or bending, while still feeling comfortable and offering 
sufficient cushioning. 
In U.S. Pat. No. 2,578,019 a socket is lined with side padding and bottom 
padding. These pads are foam or sponge rubber material provided with 
ventilation holes normal to the skin. These holes are open at both ends 
and will tend to accumulate debris. Also, the specification of this 
reference suggests that these holes are for ventilation, not cushioning. 
The main cushioning effect would be due to compression of the padding 
itself. Consequently, the pads will introduce instability to the 
prosthesis. 
U.S. Pat. No. 5,139,523 shows a socket that is fitted with an inflatable 
bladder that engages the distal end of a limb stump. This bladder 
communicates with a sidewall bladder. Both bladders can be inflated 
through an external valve fitting. Thus these bladders will tend to deform 
rapidly and destabilize the prosthesis. Also the bladders will tend to 
collapse rapidly on impact and this resulting bottoming will induce high 
impact forces into the stump. 
U.S. Pat. No. 2,634,424 shows inflatable compartments that surround the 
circumference of a leg stump. There is no subjacent support at the distal 
end of the stump. Instead, a fillet on the socket engages either the knee 
structure or the fleshy part of the buttocks to provide vertical support. 
U.S. Pat. No. 5,464,443 shows a socket with a pad for supporting the distal 
end of a stump. Liquid filled pouches encircle the circumference of the 
stump. Although the pouches appear to protrude partially under the pad, 
these do not appear to provide a cushioning effect for the pad. The pad 
instead appears to be rigidly supported by a post. 
U.S. Pat. No. 3,520,002 shows an artificial limb with a socket formed of a 
foam material. 
See also U.S. Pat. Nos. 4,923,474; 5,201,774; 5,480,455; and 5,507,834. 
Accordingly, there is a need for an improved prosthetic socket that can 
provide both support and comfort to the user. 
SUMMARY OF THE INVENTION 
In accordance with the illustrative embodiments demonstrating features and 
advantages of the present invention, there is provided a prosthetic socket 
adapted to support a prosthesis and adapted to be worn on a stump of a 
partially amputated limb. The socket has a coupler for holding the 
prosthesis along a prosthetic axis. The socket also has a cup with an 
inside surface and an outside surface. The inside surface is adapted to 
fit on the stump. The coupler is centrally attached to the cup to face 
outwardly from the outside surface. The cup contains a separated plurality 
of contractible cavities distributed around the prosthetic axis between 
the inside surface and the outside surface to provide cushioning by 
allowing deflection of the cup along the prosthetic axis into the cavities 
to contract the cavities. 
According to another aspect of the invention, there is provided a method 
for making a prosthetic socket that is adapted to support a prosthesis. 
The method includes the step of forming a cup having a plurality of 
angularly spaced, elongate, blind holes extending away from a central 
location. Another step is plugging the blind holes to prevent intrusion of 
debris. 
According to still another aspect of the invention, there is provided a 
method for making another prosthetic socket also adapted to support a 
prosthesis. The method includes the step of molding a cap and molding a 
boot. Another step is affixing the cap over the boot while leaving 
interspaces that form spaced, closed cavities. 
By employing apparatus and methods of the foregoing type, an improved 
prosthetic socket can be achieved, which provides stable support for the 
prosthesis and comfort to the user. In the preferred embodiment, the 
prosthetic socket fits over the distal end of a leg stump. The socket has 
a cup with an inside surface that engages the stump. A receiving coupler 
is preferably molded into the socket for attachment to the prosthesis. The 
cup of the socket is made of a deflectable material, which provides the 
required support, stability, reliability and maintainability. 
The preferred socket has a plurality of cavities distributed inside the 
cup. In one preferred embodiment, non-intersecting, elongate holes diverge 
laterally from a location near the axis of the prosthesis. In that 
embodiment the cavities are balanced around the prosthetic axis and shaped 
to avoid destabilization of the prosthesis. The cup of the socket can 
provide cushioning when the material of the cup deflects into the 
cavities, causing them to contract in a direction parallel to the 
prosthetic axis. This arrangement of cavities is also designed to disperse 
the load forces over a large surface to provide better support and 
comfort. 
In an alternate preferred embodiment, the prosthetic socket contains a 
plurality of compact cavities each having an essentially cylindrical 
shape. These cavities can be formed by attaching an elastomeric cap over a 
cup-shaped boot, while leaving an interspace that forms the cavities.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1, 1A, 2 and 3, a prosthetic socket 10 is shown made of 
resilient material that is molded into a cup 11; specifically, a 
truncated, hollow ovoid. The outside surface 15 of the cup 11 is also 
ovoidal in shape to distribute forces and provide a mating surface to the 
curved base of prosthesis P (shown in phantom in FIG. 2). 
Molded into the top of cup 11, below outside surface 15 is a metallic 
coupling 12 that has a dome shaped, perforated flange 12A with a beaded 
edge 12B. Flange 12A has a circular border and is curved to conform to the 
outside surface 15 of the prosthetic socket 10. The center boss 19 of the 
coupling 12 is a hexagonal prism with internal threads used to engage the 
threads of the prosthetic device P, which may be an artificial leg. 
The sidewall 17 of the cup 11 is essentially cylindrical in shape and is 
approximately 1/2 inch (12.7 mm) thick, but tapers down to a thickness of 
0.79 inch (2 mm). The sidewall thickness may be varied for individual 
comfort and strength. This preferred sidewall will have an appropriate 
balance between flexibility, comfort, and the strength required to support 
the prosthesis P. 
The cylindrical sidewall 17 is approximately 13.54 inches (34.4 cm) long, 
with an overall length, including the cup 11 (but excluding boss 19), of 
15.45 inches (39.2 cm). The specific length, however, may be varied to 
accommodate limbs of various lengths or to provide a different level of 
support, comfort, etc. 
The inside surface 20 of socket 10 is tapered inwardly to form a domed 
shape that mates to the stump (not shown) at the distal end of the leg. 
This section provides support and distributes the force from the 
prosthesis P along most of the inside surface of the prosthetic socket 10. 
In some embodiments surface 20 may be lined with a curable silicone that 
is molded by the stump itself to provide a custom-fitted surface. 
The domed base of cup 11 containing coupler 12 is thickened and is 
approximately 1 inch (2.5 cm) thick, but may have different thickness 
depending on the desired stiffness, strength, cushioning, etc. This dome 
shaped region contains cavities 14, which provide cushioning. In this 
embodiment cavities 14 are elongate cavities, but may be filed with a 
compressible material in other embodiments having a different hardness. 
Cup 11 is shown molded with eight cavities 14 arranged in a balanced 
fashion around the circumference of the socket. The cavities 14 are 
elongate tunnels designed to provide cushioning without destabilizing the 
supportive structural properties of the socket 10. To prevent a buildup of 
moisture, debris and other contamination, the open ends of the cavities 14 
are sealed with plugs 16 made of the same material and shaped to fit into 
the cavities. The plugs 16 are fitted flush with the outside of the socket 
and are bonded in place by glue, heat sealing or the like. 
The cavities 14 are blind holes having an elliptical cross-section and 
extending outwardly to side of cup 11. Cavities 14 extend from a location 
near the prosthetic axis PA at an acute angle, directed slightly away from 
coupler 12. 
As shown in FIG. 3, cavities 14 are spaced equiangularly along the outside 
circumference of cup 11 with a separation of 45 degrees from each other. 
Their size is determined by the amount of strength, cushioning and 
stiffness needed, in dependence on the size of the prosthesis P and the 
cup 11. Cavities C and G are the deepest with cavities A and E the next 
deepest. Cavities B, D, F and H are of equal depth and are the shallowest. 
The cavities are straight elliptical tunnels that penetrate at an angle of 
approximately 20 degrees from prosthetic axis PA, although other angles of 
inclination are possible depending upon the geometry of cup 11. 
The thickness of the material in the vicinity of cavities 14 and coupler 12 
must be sufficient to avoid tearing and prevent the coupler from being 
torn out of the prosthetic socket. The thickness will therefore also 
depend upon the size and weight of the individual using the device. The 
cup 11 of the prosthetic device is designed to provide the cushioning to 
the stump end of the leg and provide the strength required to support the 
prosthetic device. 
The material used to form the main body of cup 11 is preferably a silicone 
elastomer. This material can be clear, non-toxic, easily sterilized, as 
well as being easily molded. In alternate embodiments, different materials 
can be used to provide either stiffer or softer support. For example, one 
may use soft vinyl, natural latex, rubber, millable gum material or other 
silicone polymers. Alternate materials may also be required if an allergic 
reaction to the elastomer occurs. Decreasing the hardness of the elastomer 
increases the cushioning effect, but decreases its stability and strength. 
The material of the cup 11 must be sufficiently strong to avoid breaking or 
tearing. A silicone elastomer may have a tensile strength of about 630 
psi. The total projected area of the cup 11 may be approximately 12 square 
inches (77 square centimeters), but the effective "load area" is in the 
vicinity of 7 square inches (45 square centimeters), encompassing 
approximately a 3 inch (7.6 cm) diameter. The cavities reduce the 
effective load area across the elastomer by about 50%. This yields a net 
tensile strength of about 3,800 pounds (1727 kg), although other tensile 
strengths may be designed into other embodiments. 
The elastomer should be essentially non-compressible. Still, each time a 
force is applied some deformation will occur and the elastomer will bend 
or deflect before returning to its original shape. The hardness 
(durometer) of the elastomer will be selected to strike a balance between 
stability and comfort. The design will also be affected by the strength of 
the material used, its resiliency, as well as the affect on resiliency and 
strength caused by the location and size of the cavities. 
Referring to FIGS. 1 and 4, previously mentioned coupler 12 is shown having 
a circular outline. The rim 12B of the coupler is beaded to increase 
strength and rigidity without excessively increasing its weight or size. 
The flange portion 12A is domed between boss 19 and rim 12A to better 
conform to the outside surface of the prosthetic socket 10. The coupler 12 
has a diameter of approximately 25/16 inch (5.9 cm), but can be varied 
depending upon the size of the prosthetic socket 10. 
The flange portion 12A of the coupler contains eight, equiangularly spaced 
holes 26, approximately 1/8 inch (3.2 mm) in diameter, but can be of 
different diameters depending upon the application. The holes allow the 
material of the cup 11 to infiltrate and integrate with the coupler 12 to 
prevent the coupler 12 from rotating or being otherwise dislodged from its 
location. Boss 19 of coupler 12 is approximately 1/2 inch (1.3 cm) tall, 
but can be varied if required to fit the prosthesis. The coupler 12 has 
the shape of a hexagonal prism with an internally threaded center bore 30. 
The internal threads are designed to accept attachment of the prosthesis. 
Referring to FIG. 7, a mold is shown for making the socket shown in FIGS. 1 
through 3. The mold is made of an upper portion 33 with a concave molding 
surface and a lower portion 35 with a convex molding surface. Rods 34 
having an elliptical cross section are inserted transversely through the 
mold section 34 to the desired depth to obtain the correct cavity 
configuration. The minor transverse axes of the rods 34 are directed 
axially. The coupler 12 is secured to the top of the mold section 33 
before the mold sections 33 and 35 are closed. Elastomer is then injected 
through holes 36 of the mold and allowed to harden or cure. The rods 34 
are then removed and the sections 33 and 35 separated to allow removal of 
the prosthetic socket. 
In the alternate preferred embodiment shown in FIGS. 5 and 6, the 
prosthetic socket has three distinct components. Upper portion 38 is a 
domed, molded cap having on its concave underside seven blind holes 40 
that ultimately form internal cylindrical cavities in the finished unit. 
The convex outside surface 41 of cap 38 is shaped to distribute the forces 
and to provide a mating surface to the prosthesis. 
The cavities 40 are approximately 3/4 inch (19 cm) in diameter and 
approximately 1/4 inch (6.35 cm) high, but can have different dimensions 
to provide different strength, stability and cushioning effects. Cavities 
40 are arranged with one concentric hole surrounded by six equiangularly 
spaced holes as shown in FIG. 5. The holes are spaced far enough apart to 
avoid tearing or cracking that would reduce the life of the socket. 
Cap 38 also contains the coupler 12 previously shown in FIG. 4. Coupler 12 
is embedded by being molded into cap 38. 
The third or bottom portion 42 is a cup-shaped boot. Boot 42 may be made of 
the same material as cap 38, although in other embodiments boot 38 may be 
made of a different material with a different durometer. The sidewall 43 
of the boot 42 is essentially cylindrical in shape and has a flexibility 
and strength required to support the prosthesis. Boot 42 has a domed base 
shaped to mate with cap 38. The two pieces 38 and 42 are bonded together 
to form a sealed unit by gluing, heat sealing or the like. The joint may 
be colored by a pigment for cosmetic reasons. When so joined the underside 
of cap 38 is sealed to close the openings of its cavities 40. 
The cavities thus formed in this and other embodiments can have a volume 
providing a desired level of strength and cushioning, as well as a 
reduction in overall weight. Besides the configurations just described, 
alternate cavities can be arranged in a set of concentric arcs, segmented 
to form independent cavities. The arcs may be isolated from each other to 
keep a balanced presence of solid material around the prosthetic axis PA 
to enhance stability. In some embodiments the cup can have more than two 
layers and every interface between the layers can have cavities. In 
addition, the cavities can be fully or partially filled with different 
materials (solid, liquid compressible, etc.) to vary the quality of the 
cushioning and stability. The arrangement of the cavities and their size 
must be balanced with the material properties to provide the durability 
required of the prosthetic socket. 
Referring to FIG. 8, a mold is shown for making cap 38 of the prosthetic 
socket shown in FIGS. 5 and 6. The mold sections 44 and 46 produce the 
cavities used for cushioning. The lower section 46 of the mold has 
embossments for forming these cavities. The coupler 12 is attached to the 
roof of the upper section 44 of the mold. The mold is closed before 
elastomer is injected through holes 48. After the elastomer hardens, the 
mold is separated and the molded cap removed. The boot 42 is molded in a 
similar manner. 
To facilitate an understanding of the principles associated with the 
foregoing, the use of the embodiment of FIGS. 1 through 4 will be 
described for a leg prosthesis. It will be appreciated that the operation 
of other embodiments will be similar. 
A spray lubricant may be applied to the surface of socket 10 shown in FIG. 
2. This allows the socket to be easily rolled and placed onto the stump of 
the amputee. The sidewall 17 of the socket is rolled up to expose as much 
as possible of the inside surface 20 of cup 11. The surface 20 is then 
placed securely against the stump and the socket sidewall 17 is rolled 
back over the limb. The alignment of the coupler 12 is important, as the 
prosthesis P must transfer forces to coupler 12 without inducing lateral 
strain. The prosthetic device P is then screwed into coupler 12. 
When walking, each step produces a variety of forces on the prosthetic 
socket 10 that form a cycle of compression and relaxation. As a step is 
taken the force from the heel of the foot is applied along the axial 
length of the prosthesis P, which is then transferred to the prosthetic 
socket. This force may be applied at an angle to prosthetic axis PA. As 
the pressure on the foot is transferred from the heel to the ball of the 
foot, the net force applied to the socket 10 may shift angularly. This 
produces a changing force that tends to deflect or deform the socket. 
During the use of the prosthetic socket, forces are applied to the device 
in a cyclic fashion each time a step is taken. The forces will be applied 
to the top surface of cup 11 primarily through coupler 12. Since the 
forces are not applied equally along the surface they tend to deform cup 
11. The device must be designed to withstand these forces and still 
provide cushioning to reduce the pressure on the stump. 
In response to these forces, the cavities 14 will contract and therefore 
absorb some of the applied forces. The elastomer material is relatively 
noncompressible but the cavities 14 produce some cushioning without 
destabilizing the prosthesis P. The walking forces tend to spread from the 
center of the prosthetic axis PA and tend to deflect the solid material of 
cup 11. In effect, the cavities 14 contract in a direction parallel to 
prosthetic axis PA as the material of cup 11 deflects. This deflection 
favors resilience along the prosthetic axis PA but without a significant 
tendency for the prosthesis P to wobble (angularly deflect relative to the 
leg). The cavities 14 are placed in a balanced pattern around the socket 
to allow deflection of the material of cup 11 into the cavities 14 without 
a specific bias. 
Although the total projected area of the cup 11 is approximately 12 square 
inches (77 square centimeters), the "load area" is in the vicinity of 7 
square inches (45 square centimeters), encompassing approximately a 3 inch 
(7.6 cm) diameter. Consequently, compression deflection into the cavities 
14 can approach 0.25 inch on each cycle for cushioning the limb on each 
step 
Since the cavities 14 are sealed and separated from each other, they act as 
individual pistons to provide cushioning and balanced stability to the 
socket. This also disperses the walking forces transferred by the socket 
to the stump, while producing a cushioning effect on the stump. Also, the 
cavities 14 are sized to stay uncollapsed during normal walking. The 
opposing inside surfaces of the cavities 14 are sufficiently separated to 
avoid touching or bottoming during normal use. Such bottoming would 
produce a hard feeling or shock to the stump. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims, the invention may be 
practiced otherwise than as specifically described.