Reinforcement assembly for laminated structures

A reinforcement assembly to reinforce a selected site on a body, and methods of making and using such a universal reinforcement assembly. Several embodiments of reinforcement assemblies in accordance with the principles of the invention are well suited to support or reinforce laminated structures. In one embodiment, the reinforcement assembly has a reinforcement member configured to be attached to the selected site on the body and a universal attachment medium separately bonded to the reinforcement member. The reinforcement member may be a plate composed of a molding compound, a high density polymer, or another suitable high-strength material. The universal attachment medium, more specifically, may have a first section bonded to the reinforcement member and a second section extending from the reinforcement member to cover an area of the body substantially surrounding the selected site. The attachment medium may be composed of a self-conforming material that inherently conforms to the shape of the body to define an anchor stratum of the laminated structure having a shape corresponding to the area of the body substantially surrounding the selected site.

TECHNICAL FIELD 
The present invention generally relates to reinforcing laminated 
structures. More specifically, an embodiment of the present invention 
relates to a universal reinforcement assembly for reinforcing selected 
sites of prosthetic limbs. 
BACKGROUND OF THE INVENTION 
Prosthetic devices, such as prosthetic limbs, are typically lightweight 
components that replace damaged or missing body parts of a particular 
patient. Many prosthetic devices are subject to significant forces applied 
via complex, variable motions of the surrounding body parts. Selected 
sites on prosthetic devices are accordingly reinforced to withstand 
particularly large loads. However, reinforcing selected sites on leg 
sockets and other devices without increasing the weight and cost of the 
devices is difficult. 
FIG. 1A is an exploded isometric view of a conventional leg socket 10 that 
may be attached to a leg stump S of a particular patient P. The socket 10 
typically has a lightweight liner 12 composed of a thermoplastic or 
fiberglass sheet that is shaped to fit the contour of the leg stump S. The 
leg socket 10 may also have a connector assembly 20 having a base 22, a 
plurality of fingers or legs 24 projecting from the base 22, and an 
inverted pyramid 26 projecting from the base 22. The connector assembly 20 
is generally a rigid metal component attached to the distal end of the 
liner 12, and the inverted pyramid 26 is configured to engage a mating 
adapter on a pylon (not shown). Other connector assembly structures may, 
of course, be used, and an outer shell (not shown) is typically laminated 
over the liner 12 and the legs 24. 
FIG. 1B is a partial isometric view of the connector assembly 20 attached 
to the liner 12 of the leg socket 10. To attach the connector assembly 20 
to the liner 12, a prosthetist manually deforms the legs 24 of the 
connector assembly 20 to roughly fit the liner 12. The prosthetist, for 
example, generally bends the legs 24 downwardly from the base 22 and 
hammers selected points along each leg 24 to roughly fit each leg 24 to 
the particular area on the liner 12. After the legs 24 are deformed to 
roughly fit the particular geometry of the liner 12, the legs 24 are 
secured to the liner 12 with a plurality of fasteners 28. The prosthetist 
then laminates an outer sheet of fiberglass (not shown) to the legs 24 and 
the liner 12 with a resin binder to form the leg socket 10. 
Reinforcing the leg socket 10 with the connector assembly 20 generally 
increases the costs and reduces the performance of the prosthetic limb. 
For example, attaching the connector assembly 20 to the liner 12 is 
extremely time-consuming because the prosthetist manually deforms each of 
the metal legs 24 with a hammer to fit the geometry of the liner 12. 
Additionally, attaching the connector assembly 20 to the liner 12 is also 
imprecise because the legs 24 may not accurately conform to depressions 18 
(shown exaggerated) or other topographical features on the surface 16 of 
the liner 12. Many leg sockets 10 with metal connector assemblies 20 are 
thus subject to significant point loading at various locations between the 
legs 24 and the liner 12 or outer fiberglass layer (not shown). As a 
result, the thickness of the liner 12 and the subsequent outer fiberglass 
layer are increased to sustain the point loading caused by the connector 
assembly 20. It will be appreciated that the significant time requirements 
and additional materials increase the weight and cost of the leg socket 
10. 
FIG. 2A is a partial isometric view of another conventional leg socket 10a 
with an liner 12 and a connector assembly 20a connected to the liner 12. 
The connector assembly 20a has a plurality of cables 24a extending from 
the base 22. In operation, the prosthetist lays the cables 24a over the 
surface 16 of the liner 12 and laminates an outer sheet of fiberglass (not 
shown) over the liner 12 and the legs 24a. The connector assembly 20a does 
not require as much time to install as the connector assembly 20 shown in 
FIG. 1B because the prosthetist does not need to hammer each of the cables 
24a to fit the geometry of the liner 12. The connector assembly 20a, 
however, may produce significant point loading along the cables 24a 
because each cable 24a transmits forces to discrete, isolated areas of the 
liner 12 and the outer fiberglass layer. Moreover, most of the force 
applied to the connector assembly 20a acts against the resin and the outer 
fiberglass layer because the cables 24a are not fastened to the liner 12 
and the cables 24a act separately from the resin. Therefore, it is also 
necessary to make the socket 10a with substantially thick walls in the 
region of the connector 20a to withstand the forces generated in typical 
installations. 
FIG. 2B is a partial isometric view of yet another conventional leg socket 
10b with another connector assembly 20b attached to the liner 12. The 
connector assembly 20b has a base 22b with first and second slots 23 and 
25 extending perpendicular to one another across the top of the base 22b. 
A first strip 24b.sub.1 positioned in the first slot 23 projects from a 
first set of opposing sides of the base 22b, and a second strip 24b.sub.2 
positioned in the second slot 25 projects from a second set of opposing 
sides of the base 22b. The prosthetist attaches the connector assembly 20b 
to the liner 12 by positioning the strips 24b.sub.1 and 24b.sub.2 in the 
slots 23 and 25, and then laminating an outer sheet of fiberglass over the 
base 22b, the strips 24b.sub.1 and 24b.sub.2, and the liner 12. A separate 
pylon connector 30 with a pyramid 32 is then attached to the base 22b. The 
connector assembly 20b also reduces the installation time compared to the 
metal connector assembly 20 because the prosthetist can more easily deform 
the strips 24b, and 24b.sub.2 to conform to the geometry of the liner 12. 
However, as with the connector assembly 20a shown in FIG. 2A, the 
connector assembly 20b also produces point loading in the resin binder, 
the fiberglass outer sheet, and the liner 12. As a result, the leg socket 
10b also has thick walls in the region of the connector assembly 20b. 
SUMMARY OF THE INVENTION 
The present invention is a universal reinforcement assembly to reinforce a 
selected site on a body. Several embodiments of reinforcement assemblies 
are well suited to support or reinforce laminated structures. In one 
embodiment, the reinforcement assembly has a reinforcement member 
configured to be attached to the selected site on the body and a universal 
attachment medium separately bonded to the reinforcement member. The 
reinforcement member may be a plate composed of a molding compound, a high 
density polymer, or another suitable high-strength material. The universal 
attachment medium, more specifically, may have a first section bonded to 
the reinforcement member and a second section extending from the 
reinforcement member to cover an area of the body substantially 
surrounding the selected site. The attachment medium may be composed of a 
self-conforming material that inherently conforms to the shape of the body 
to define an anchor stratum of the laminated structure having a shape 
corresponding to the area of the body substantially surrounding the 
selected site. 
Several embodiments of universal reinforcement assemblies are particularly 
well suited for medical device applications. In one embodiment, for 
example, a universal reinforcement assembly for a prosthetic limb has a 
reinforcement member configured to be attached to a liner of the 
prosthetic limb at a selected site subject to force loading. A first 
section of a universal attachment medium is bonded to the reinforcement 
member and a second section extends from the reinforcement member to cover 
a force distribution area of the liner substantially surrounding the 
selected site. More specifically, the first section of the attachment 
medium may be fused to the reinforcement member to integrally bond the 
attachment medium to the reinforcement member at an integral joint. The 
second section of the attachment medium may be composed of a material that 
inherently conforms to a defined shape of the liner corresponding to a 
particular limb of a specific patient when the reinforcement member is 
positioned at the selected site. For example, the attachment medium may be 
a lax web that lays slack on the liner and follows the topography of the 
liner prior to laminating an outer layer over the attachment medium. 
Suitable types of webs are fiberglass sheets, woven or braided meshes of 
carbon graphite strands, or other highly flexible materials that conform 
to the shape of an object without significant manipulation. 
In one particular embodiment of a universal reinforcement assembly used on 
a leg socket, the reinforcement member may have first and second plates of 
a molding compound, and the attachment medium may be a tubular woven mesh 
of carbon graphite strands. The first and second plates of molding 
compound are positioned on opposite sides of an end portion of the tubular 
mesh that projects radially inwardly toward a center line of the tube. The 
first and second plates of molding compound are fused with the end section 
of the attachment medium using a curing process to form an integral joint 
connecting the attachment medium to the reinforcement member. The curing 
process also melds the first and second plates together to form a unitary 
block of rigid, high-strength molding compound. 
After the first section of the attachment medium is fused with the 
reinforcement member, the universal reinforcement assembly may be attached 
to the liner. More particularly, a prosthetist may place the reinforcement 
member at the selected site on the liner and laminate the attachment 
medium to the liner with an outer fiberglass sheet and a resin binder. 
Because the attachment medium is self-conforming, it inherently conforms 
to the force distribution area on the liner as the reinforcement member is 
placed at the selected site. Therefore, an embodiment of the attachment 
medium is ready to be laminated to the liner without significant 
mechanical manipulation and it distributes the forces applied to the 
reinforcement member over a large surface area to reduce point loading in 
the laminated structure.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is an apparatus and method for reinforcing a portion 
of a laminated structure or other type of body. Many specific details of 
certain embodiments of the invention are set forth in the following 
description and in FIGS. 3-5B to provide a thorough understanding of such 
embodiments of the invention. One skilled in the art, however, will 
understand that the invention may have additional embodiments and may be 
practiced without several of the details described in the following 
description. 
FIG. 3 is an exploded isometric view of a portion of a leg socket 100 with 
an embodiment of a reinforcement assembly 120 for reinforcing a distal end 
of the leg socket 100. The leg socket 100 and the reinforcement assembly 
120 illustrate only one application and one embodiment of reinforcement 
assemblies in accordance with the invention. In this particular 
embodiment, the reinforcement assembly 120 covers a portion of a shell or 
liner 110 that has an outer surface 112 and a cavity 114. The liner 110 is 
shaped so that the leg stump (not shown) of a particular patient 
comfortably fits in the cavity 114. The liner 110, therefore, is typically 
custom made from a mold corresponding to the leg stump of the particular 
patient. 
The reinforcement assembly 120 shown in FIG. 3 has a reinforcement member 
122 configured to be positioned at a selected site on the liner 110 where 
additional strength is required. The reinforcement member 122 may be a 
rigid, high-strength plate or bar composed of a sheet molding compound 
(SMC), a bulk molding compound (BMC), high-density acetyl polymers (e.g, 
Dehrin.RTM. manufactured by E. I. Dupont de Nemours of Wilmington, Del.), 
or other suitable strength materials. The size and shape of the 
reinforcement member 122 is a function of the shape of the body and the 
forces exerted on the reinforcement member 122. In the embodiment of the 
leg socket 100 shown in FIG. 3, the reinforcement member 122 is generally 
a circle or square block with a thickness between 0.25 and 0.75 inches to 
provide an adequate base for supporting a pylon connector 150. A number of 
threaded sleeves 128 are preferably inserted into holes of the 
reinforcement member 122 to receive fasteners 157 that attach the pylon 
connector 150 to the reinforcement member 122. It will be appreciated, 
however, that the reinforcement member 122 is not limited to a thickness 
of 0.25-0.75 inches, and that many other sizes and shapes of reinforcement 
members may be used. 
The reinforcement assembly 120 shown in FIG. 3 also has an attachment 
medium 124 with a first section 125 bonded to the reinforcement member 122 
and a second section 126 extending from the reinforcement member 122. The 
first section 125 of the attachment medium 124 may be fused to the 
reinforcement member 122 to form an integral joint connecting the 
attachment medium 124 to the reinforcement member 122. In another 
embodiment, the first section 125 may be bonded to the reinforcement 
member 122 with an adhesive to form a cemented joint. The particular bond 
between the first section 125 of the attachment medium 124 and the 
reinforcement member 122 depends upon the particular application of the 
reinforcement assembly 120. When the reinforcement assembly 120 is used in 
a leg prosthesis, the first section 125 of the attachment medium 124 is 
fused with the reinforcement member 122 by cocuring the attachment medium 
124 and the reinforcement member 122 under high temperature and pressure 
conditions. 
The second section 126 of the attachment medium 124 extends from the 
reinforcement member 122 to preferably cover a force distribution area of 
the liner 110. The particular force distribution area is a function of the 
type of body to which the reinforcement assembly 120 is to be attached and 
the forces applied to the reinforcement member 122. In the embodiment of 
the leg socket 100 shown in FIG. 3, the force distribution area surrounds 
the selected site at the distal end of the liner 10. As such, the second 
portion 126 of the attachment medium 124 preferably is a contiguous web 
that extends from the full perimeter of the reinforcement member 122 to an 
intermediate line around the liner 110. It will be appreciated, however, 
that the attachment medium 124 does not need to cover all of the surface 
area surrounding the selected site, and that the second section 126 may 
have other configurations. 
The attachment medium 124, or at least the second section 126 of the 
attachment medium 124, preferably inherently conforms to the topography of 
the surface 112 of the liner 110. More specifically, the attachment medium 
124 may be a lax web, braid or mesh that: (1) bonds well with the 
reinforcement member 122; (2) self-conforms to the body to which the 
reinforcement assembly 120 is attached; (3) bonds well with the body; and 
(4) has good stress/strain characteristics to withstand and distribute the 
forces exerted on the reinforcement member 122. In one particular 
embodiment, the attachment medium 124 is a woven mesh of carbon graphite 
strands 127 that lays against the surface 112 of the liner 110. However, 
other suitable materials from which the attachment medium 124 may be 
composed include fiberglass or any other web that generally conforms to a 
topography of the body by simply smoothing the web over the surface. 
FIG. 4 is a cross-sectional view of a complete leg socket 100 in which the 
reinforcement assembly 120 is part of a laminated structure. In this 
embodiment, the liner 110, the reinforcement assembly 120, and an outer 
fiberglass sheet 142 are laminated together with a resin binder 144 to 
form a laminated structure. The resin binder 144 is preferably spread over 
the liner 110, the attachment medium 124 and the outer fiberglass sheet 
142 to securely bond these items together into a high-strength, low-weight 
structure. As best seen in FIG. 4, the first section 125 of the attachment 
medium 124 is fused to the reinforcement member 122 at an integral joint 
130, and the second section 126 of the attachment medium 124 conforms to 
the topography of the outer surface 112 of the liner 110. The second 
section 126 of the attachment medium 124 accordingly defines an anchor 
stratum in the laminated structure having a size and shape corresponding 
to the force distribution area on the liner 110. Additionally the 
fasteners 157 may be threadably engaged with the sleeves 128 in the 
reinforcement member 122 and a back-plate 115 in the cavity 114 to attach 
the pylon connector 150 and further secure the reinforcement member 122 to 
the assembly. 
The embodiment of the reinforcement assembly 120 illustrated in FIGS. 3 and 
4 provides several advantages compared to conventional connector 
assemblies attached to conventional leg sockets. For example, compared to 
the conventional connector assemblies described above in FIGS. 1A-2B, the 
reinforcement assembly 120 significantly reduces the time required to 
construct the leg socket 100 because the attachment medium 124 inherently 
conforms to the shape of the liner 110. As a result, the prosthetist is 
not required to machine or hammer the attachment medium 124 to fit the 
particular geometry of the liner 110. A prosthetist may accordingly 
manufacture more leg sockets in a given period of time to significantly 
increase the production of prosthetic devices. 
Another advantage of the embodiment of the reinforcement assembly 120 is 
that it distributes and absorbs forces to reduce point loading in the 
laminated structure. Unlike conventional connector assemblies, an 
embodiment of the attachment medium 124 conforms to the contour of the 
liner 110 and covers a substantial surface area of the liner 110 adjacent 
to the selected site to which the reinforcement member 122 is positioned. 
The forces exerted on the reinforcement member 122 are accordingly 
distributed over a large, conformal medium that reduces force 
concentrations at particular points in the laminated structure. 
Additionally, the fibers in the second section 126 of the attachment 
medium 124 and the resin 144 proximate to the fibers absorb some of the 
forces to reduce the magnitude of force transferred to the liner 110 and 
the fiberglass layer 142. The thickness of the laminated structure in the 
leg socket 100, therefore, is substantially less than that of conventional 
leg sockets. Thus, the leg socket 100 is generally lighter and more 
comfortable than conventional leg sockets. 
FIG. 5A is a schematic cross-sectional view that illustrates one stage in a 
method for making an embodiment of the reinforcement assembly 120. In this 
embodiment, first and second plates 122a and 122b of a molding compound 
are positioned on opposite sides of the first section 125 of the 
attachment medium 124. The first and second plates 122a and 122b are 
preferably partially cured or "B-stage" SMC or BMC that is not fully 
hardened prior to curing. A pair of male and female tools 161 and 163 
configured to shape the first and second plates 122a and 122b in the 
desired shape of the reinforcement member 122 are then pressed together in 
a heated environment to meld the first and second plates 122a and 122b 
into a unitary reinforcement member 122 of cured molding compound. The 
high-pressure and temperature curing process also fuses the first and 
second plates 122a and 122b with the first section 125 of the attachment 
medium 124 to form an integral joint 130 around the perimeter of the 
reinforcement assembly 122 (FIG. 5B). In a specific application of the 
process in which the first and second plates are composed of SMC and the 
attachment medium 124 is a carbon and graphite mesh, the male and female 
tools 161 and 163 are pressed together at 1000 psi under a temperature of 
250.degree. F. for five minutes. 
From the foregoing it will be appreciated that, although specific 
embodiments of the invention have been described herein for purposes of 
illustration, various modifications may be made without deviating from the 
spirit and scope of the invention. For example, the reinforcement assembly 
may have a plurality of separate reinforcement members bonded to a single 
attachment medium. Additionally, the reinforcement assemblies may have 
reinforcement members composed of a single plate of molding compound that 
is fused to the attachment medium under suitable pressure, temperature and 
time conditions. Accordingly, the invention is not limited except as by 
the appended claims.