WO2014182537A1

WO2014182537A1 - Apparatus and method for a directly molded prosthetic limb

Info

Publication number: WO2014182537A1
Application number: PCT/US2014/036363
Authority: WO
Inventors: Kevin Patrick KEENAHAN; German OM; Ian Graham; Rochelle DUMM; Brian JEON; Mark Hopkins
Original assignee: The Johns Hopkins University
Priority date: 2013-05-07
Filing date: 2014-05-01
Publication date: 2014-11-13

Abstract

The disclosure provides a prosthetic socket that may include an inner socket made of a re-moldable thermoplastic material and having a proximal end and a distal end, the proximal end of the inner socket being configured to receive a distal end of a residual limb of a subject; an outer shell having a proximal end and a distal end; and an interface, the interface being sandwiched between the inner socket and the outer shell and configured to adhere the inner socket to the outer shell.

Description

Apparatus and Method for a Directly Molded Prosthetic Limb

Cross-Reference to Related Application

This application is related to U.S. Provisional Patent Application Serial No.

61/820,663, filed May 7, 2013. The entire content of this patent application is hereby incorporated by reference herein.

Technical Field

The present invention relates generally to prosthetic limbs, and more particularly, to prosthetic limbs having a socket that may be directly molded to a subject's limb.

Background

A prosthesis, or prosthetic device, is an artificial device that functions to replace a missing body part lost through trauma, disease, or congenital defect. Prosthetic limbs are a common type of prosthetic device used for amputees who have lost part of an extremity such as a leg or an arm. Prosthetic limbs play an important role in facilitating the ability of an amputee to regain partial, or complete, function or mobility of a lost limb.

Prosthetic limbs are typically connected to a residual limb of an amputee by a socket, which represents the primary contact point between the residual limb of the amputee and the prosthetic limb. Consequently, the socket plays a very important role in the ability of the amputee to use the prosthetic limb. For example, in the case of a prosthetic leg, the socket functions, in part, to absorb and distribute the weight of the amputee across the surface area of the residual limb. If the socket of the prosthetic leg does not provide a good fit to the residual limb of the amputee, it may cause significant discomfort to the amputee.

Additionally, an improper fit between the socket and the residual limb may cause significant medical complications for the amputee such as, for example, swelling, edema, or even breakdown and drainage of the residual limb.

To improve the fit between the residual limb and the socket, the socket may be custom-built for the amputee using a direct mold technique. Conventionally, this may involve a complex multi-step process that involves the creation of multiple positive and negative molds that are used sequentially to form the socket structure. Disadvantageously, this custom-building process is expensive, time-consuming, and quite complex. Additionally, such custom-built molds do not have the ability to adapt to subsequent changes in the morphology of the residual limb of the amputee. For example, the residual limb may continue to atrophy over time, which requires subsequent reconstruction of the custom-built socket at great expense to the amputee. Unfortunately, this makes it cost prohibitive for many amputees in impoverished nations to obtain prosthetic devices. Accordingly, there is a need for an improved, low cost prosthetic limb socket.

Summary of the Invention

According to an aspect of the invention, a prosthetic device may include a socket that includes an inner socket made of a re-moldable thermoplastic material and having a proximal end and a distal end, the proximal end of the inner socket being configured to receive a distal end of a residual limb of a subject; an outer shell having a proximal end and a distal end; and an interface, the interface being sandwiched between the inner socket and the outer shell and configured to adhere the inner socket to the outer shell.

According to an embodiment, the inner socket is directly molded on the residual limb of the subject.

According to another embodiment, patellar tendon bearing (PTB) reliefs are applied to the residual limb before the inner socket is directly molded on the residual limb of the subject.

According to an embodiment, the thermoplastic material is polycaprolactone (PCL). According to an embodiment, the distal end of the outer shell includes a receiving end configured to attach a proximal end of a pylon to the outer shell.

According to an embodiment, the receiving end may be configured to attach the proximal end of the pylon to the outer shell by a connector selected from the group consisting of a thread, a press-fit, a snap-fit, and a fastener.

According to an embodiment, the outer shell includes a plurality of proximal-distal oriented slits arranged around a circumference of the outer shell.

According to an aspect of the invention, a method of manufacturing a prosthetic socket includes: identifying anatomical locations for pressure relief on a residual limb of a subject; applying patellar tendon bearing (PTB) reliefs to the identified anatomical locations; fitting a sheet of thermoplastic material over the residual limb bearing the PTB reliefs to form an inner socket with a distal end corresponding to the distal end of the residual limb; inserting the inner socket into an outer shell; and adhering the inner socket to the outer shell via an interface.

According to an embodiment, the receiving end is configured to attach the proximal end of the pylon to the outer shell by a connector selected from the group consisting of a thread, a press-fit, a snap-fit, and a fastener.

Brief Description of the Drawings

Aspects of the present disclosure may be better understood with reference to the following drawings. Components of the drawing are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure.

Moreover, the drawings, like reference numerals designate corresponding parts throughout the several views.

FIGS. 1A to ID depict a prosthetic limb according to exemplary embodiments of invention. FIG. 1A depicts a front view and a side view of a socket and upper portion of a prosthetic limb according to an exemplary embodiment of the disclosure. FIG. IB depicts components of the prosthetic limb according to an exemplary embodiment of the invention. FIG. 1C depicts an exploded view of an upper adaptor ring according to an exemplary embodiment of the invention. FIG. ID depicts an exploded view of a lower upper adaptor ring according to an exemplary embodiment of the invention.

FIGS. 2A-2C depict a bottom perspective view, a top view, and a side view of a prosthetic limb socket according to an exemplary embodiment of the disclosure.

FIGS. 3A-3B depict a top view of a prosthetic limb socket after the direct molding process and a sock liner including Styrofoam-filled pockets, respectively, according to an exemplary embodiment of the invention.

FIGS. 4A-4D depict steps for forming a socket according to an exemplary embodiment of the invention.

FIGS. 5A-5D depict steps for fitting a socket according to an exemplary embodiment of the invention.

FIGS. 6A-6E depicts steps for using a balloon to apply retention pressure during an exemplary molding process of the invention.

Detailed Description of the Invention

The techniques herein provide for a prosthetic limb including a socket that may allow an amputee to be fit with a prosthetic device directly, without the use of expensive positive molding procedures. As described in detail below, the socket may include a low-temperature thermoplastic material that is molded directly from the residual limb of an amputee.

Advantageously, the below-described socket may be re-molded as the amputee's limb atrophies, without incurring significant additional cost to the amputee.

According to an exemplary embodiment of the disclosure, a prosthetic limb socket may include: an inner socket, an inner sock, a gel liner, an outer shell, a pylon, and a prosthetic foot. As shown in FIG. 1 A, the inner socket 110 may be positioned interior to, and coextensive with, outer shell 130. Additionally, inner socket 110 may be separated from outer shell 130 by interface 120, which may serve to adhere inner socket 110 to outer shell 130. Inner socket 110 has a proximal end into which the residual limb of an amputee is inserted. Outer shell 130 has a distal end that may receive pylon 140. Interface 120 may be sandwiched between inner socket 110 and outer shell 130, and may provide, for example, rigidity to the inner socket and shock absorption to the residual limb during use. It is contemplated within the scope of the invention that interface 120 may be comprised of a variety of materials or systems such as, for example, expanding foam (e.g., urethane foam), which may be used to fill the space between the inner socket and outer shell; a strap system, which would allow the inner socket 110 to be suspended in a strap system within the outer shell 130 (e.g., four straps may be passed through the outer socket and secured with screws to hold the system in place); a rubber gasket system, which would wrap rubber gaskets around inner socket 110 to act as spacers between inner socket and outer shell; a press-fit system in which a temperature source (e.g., a heat gun) may be used to shrink outer shell 130 to fit inner socket 110 (in such an application, one of skill in the art would appreciate that the outer shell thickness would have to be decreased to allow for shrinkage and to allow for more snug fit between outer shell and inner socket).

Outer shell 130 may have a solid construction as shown in FIG. 1A. As shown in

FIG. IB, the distal end of outer shell 130 may be connected to the proximal end of pylon 140 by an adapter ring 132 in an alternate embodiment. Upper adapter ring 132 may be a reducer bushing for PVC piping. Advantageously, this type of adapter may distribute the

compressive loads that are applied to the device and may also be easily acquired in resource poor areas such as developing countries. As shown in FIG. 1C, upper adapter ring 132 may be molded into the socket during alignment using additional thermoplastic. The "ball and socket" joint of upper adapter ring 132 allows alignment of the patient's socket and the pylon. A cup 152 as shown in the top portion of the image may be placed on the patient's distal residual limb for the drape molding of the thermoplastic. After the fitting process is complete, the ball 154 may be secured to the cup 152 with a bolt 156. Once proper alignment is completed, the bolt can be tightened to prevent the adapter from coming out of alignment. The body of the "ball" component is then press-fit into the proximal end of the pylon.

As shown in FIG. ID, the distal end of pylon 140 may be connected to the proximal end of foot 144 by a lower adapter ring 142, which may be, for example, a reducer bushing. In one embodiment, the interface between the pylon and the foot may be comprised of a reducer bushing, a spacer, a PVC cap, and a bolt. The base of the lower adapter ring 142 (e.g. reducer bushing) may be placed (but not attached) on top of the foot. Optionally, a spacer may be located inside lower adapter ring 142 with a PVC cap placed on top. The PVC cap may have a hole drilled in the center of the cap that is slightly bigger than the bolt diameter on top of the bushing (nestled inside). The cap, at an appropriate angle and lateral position, may be tightly bolted, locking the "ankle" in place. The pylon 140 may then be inserted into the cap. Advantageously, the "ball and socket" joint of lower adapter ring 142 may allow the foot to be positioned with three rotational degrees of freedom. As previously mentioned, proper alignment is crucial for comfortable and efficient ambulation. A bolt 162 may secure the ball 164 into the socket 166 such that no motion is possible after the alignment is set. The bolt 162 also secures the lower adapter ring 142 to the foot. Most SACH feet are secured through a single bolt through the heel of the foot. After foot alignment is set, the foot (now with the adapter attached) can be press-fit into the distal end of the pylon, as shown in FIG. IB.

In another exemplary embodiment, shown in FIGS. 2A-2C, outer shell 130 may have a fenestrated structure including a plurality of slits 210, a plurality of openings 230, a receiving end 240, and a pylon connector opening 250. In one embodiment, the plurality of slits 210 may be oriented in a proximal-distal direction and approximately equally distributed around the circumference of outer shell 130. Receiving end 240 may be located at the distal end of outer shell 130, and configured to receive a proximal end of pylon 140 by any of a number of joining techniques known to one of skill in the art such as, for example, a threaded connector, a snap-fit connector, a press-fit connector, a bolted connector, and the like. In an exemplary embodiment, receiving end 240 may include a pylon connector opening 250, which may be configured to align with a corresponding opening in the proximal end of pylon 140 and receive a fastener such as, for example, a bolt (not shown), that extends through the pylon connector opening 250 and the opening in the proximal end of pylon 140 so as to affix pylon 140 to outer shell 130 via receiving end 240.

Inner socket 110 may be molded directly onto the residual limb of a patient (e.g., an amputee) and comprise a low temperature thermoplastic material capable of deforming upon heat treatment. For example, inner socket 110 may comprise a low-temperature

thermoplastic material such as, for example, polycaprolactone (PCL), which may be deformed by immersion in water heated to a temperature ranging from about 70°C to about 100°C. Preferably, the PCL may be deformed by immersion in water heated to a temperature of about 70°C. PCL is a biodegradable polyester with a low melting point of around 60°C and a glass transition temperature of about -60°C. PCL is a strong plastic, which makes it suitable for the large compressive loads that the socket will experience. It is also

contemplated within the scope of the disclosure that inner socket 110 may be comprised of any of a variety of other low-temperature thermoplastic materials suitable for use in a prosthetic device such as, for example, Solaris® or Aquaplast®. The inner socket 110 may be molded by heat-treating pellets of any suitable low-temperature thermoplastic material that deforms in water at a temperature ranging from about 65 °C to about 100°C and

working/forming the heat-treated pellets into a sheet, which may be applied directly to the patient' s residual limb. The applied material may then be cut to achieve the desired shape and comfortable fit. It is also contemplated within the scope of the invention that the inner socket 110 may be used as a stand-alone product in conjunction with any existing prostheses.

Outer shell 130 may be a load-bearing surface that also may provide an outer defense to the residual limb, which may be made of, for example, polypropylene. One of skill in the art will appreciate that outer shell 130 may be made of any of a variety of additional suitable materials. Outer shell 130 may be manufactured in a variety of sizes and shapes suitable for different applications (e.g., for use with a prosthetic leg or a prosthetic arm). In general, outer shell 130 may provide a rigid support structure to which inner socket 110 is adhered to via interface 120, and serves to absorb the full weight of the patient while walking.

Pylon 140 may made of any convenient, suitable material. For example, in the case of a prosthetic leg, pylon 140 may be made of a piece of PVC piping cut to the length appropriate for a particular amputee. Similarly, pylon 140 may also be made of materials such as, for example, wood, metal, or a variety of different types of plastics.

Advantageously, this flexibility in material choice facilitates production of prosthetic limbs in third world countries where the availability of certain materials may be limited, or cost prohibitive.

As shown in FIG. 3B, the disclosure also provides for an inner sock 310 comprised of at least two socks (e.g., two standard athletic socks) that are sewn together and configured to include a plurality of pockets 320. According to an exemplary embodiment, pockets 320 may include a shock absorbing material such as, for example, Styrofoam, which creates padded reliefs that serve to increase patient comfort. The amount of shock absorbing material placed in pockets 320 may be varied to achieve the desired level of cushioning. The number of pockets present in inner sock 310 may also be varied, depending upon the patient and the application. According to one embodiment, pockets 320 may be approximately equally distributed around the circumference of inner sock 310. One of skill in the art will appreciate that the number, size, and shape of pockets 320 may be varied to suit a particular application and to correspond to particular anatomical regions that may be suitable targets for pressure relief. Illustratively, pockets 320 may be positioned on inner sock 310 so as to correspond to pressure points that occur between inner socket 110 and a residual limb, which beneficially increases comfort of the person wearing the prosthetic device. Additionally, pockets 320 may reduce or eliminate the movement of the shock absorbing material (e.g., Styrofoam beads) that they contain. Inner sock 310 may generally be worn on the residual limb at all times during use of the prosthetic device in order to maximize comfort of the user.

According to an exemplary embodiment, the disclosure also provides for a fitting relief sock that may have thickened pads— referred to as patellar tendon bearing (PTB) reliefs— to relieve pressure on bony prominences and achieve a good PTB fit between the residual limb and the inner socket 110. The fitting relief sock may be applied to the residual limb before the molding of the inner socket 110. The fitting relief sock may also include colored regions to easily denote the anatomical locations of these PTB reliefs.

As shown in FIGS 4 and 5, the above-described prosthetic limb socket may be directly molded to a residual limb of a patient. FIG. 4A depicts a first step in an exemplary molding process in which a suitable amount (e.g., 0.25 pound, 0.5 pound, 0.75 pound, 1 pound, 1.5 pounds, 2.0 pounds, etc.) of PCL pellets may be placed into a water bath at a temperature ranging from about 65°C to about 80°C. Preferably, the PCL pellets may be placed into a water bath at a temperature ranging from about 65°C to about 70°C. Once heated, the PCL pellets become translucent when they are ready to be molded. Once removed from the water bath, the heated PCL pellets may have a working time ranging from between about 5 and about 10 minutes (depending on thickness) before the material solidifies. As shown in FIG. 4B, the heated PCL pellets may be rolled into a sheet with an approximately uniform thickness of about 5 mm. It is contemplated within the scope of the invention that the thickness of the sheet may be varied from between about 2.5 mm to about 20 mm, depending upon the application. The residual limb may be prepared for the direct molding process by using gauze pads to create PTB reliefs on the residual limb. For example, gauze pads may be taped over anatomically determined regions to build up layers that correspond to regions of the residual limb that should not be loaded. As shown in FIG. 4C, a normal cotton sock may then pulled over the limb on which the PTB reliefs have been loaded in the correct regions to prevent the PTB reliefs from being displaced during the fitting process. As shown in FIG. 4D the prepared PCL sheet may then be draped over the limb and worked to maintain uniform thickness.

As the molding process continues, the person fitting the mold (e.g., the fitter) may press firmly onto the soft tissue regions of the residual limb that may comfortably be loaded. For example, as shown in FIG. 5A, the fitter may press down just below the kneecap onto the patellar tendon. As shown in FIG. 5B, the portions of the PCL sheet corresponding to the bottom (distal end) and the back (posterior side) of the residual limb are crimped together (e.g., PCL binds to itself easily) to maintain a snug fit and collect excess material. The excess material may be trimmed with scissors while the material is still work-able, and the excess may be recycled for future moldings (see e.g., FIG. 5C). As shown in FIG. 4D, the socket may be removed from the patient and the top (proximal regions) trimmed to prevent edges from contacting the patient's knee. The back may be trimmed slightly to allow for unimpeded knee motion. Once the excess material is trimmed, the socket may be assembled.

In one embodiment, a balloon 610 may be used to apply pressure during the molding process as shown in FIG 6. For example, balloon 610 may be used to secure inner sock 310 onto the amputee's limb. Balloon 610 may also be used to secure the thermoplastic (e.g. PCL) during the molding process. As shown in FIG. 6A, a first end 615 of an inflated balloon 610 may be pushed against the distal end of an amputee' limb 620 so that the first end 615 of balloon 610 engulfs the distal end of an amputee' limb 620 as shown in FIG. 6B. The distal end of an amputee' limb 620 may continue to be inserted into the inflated balloon 610 to the desired degree, at which point balloon 610 may be deflated as shown in FIG. 6C. Optionally, as shown in FIG. 6D, after the balloon has been pushed over the residual limb, the distal end may be cut. This releases air from the balloon and allows it to completely constrict over the patient's residual limb. This uniformly compresses the limb, reducing volume and allowing for a more snug fit of the eventual socket. When this method is optionally performed again over the drape molded thermoplastic, it may serve the same purpose: to tighten the fit between the thermoplastic and the residual limb. Advantageously, this reduces wobble in the socket and increases comfort. As shown in FIG. 6E, after the end of the balloon is cut and all the air has evacuated the balloon, the user may pull the balloon completely over the residual limb to provide additional compression.

In an exemplary application, a patient may be seated with a healthy leg on the floor. A sock may be placed over the patient's residual limb, and flexible inserts (e.g., PTB reliefs) about ¼" - ½" thick may be made by layering strips of gauze. Inserts may be made large enough to fill an area of shapes on a template form, and then cut down to fit the individual patient to ensure that sensitive areas are protected. The flexible inserts may then be applied to the sock on the patient's residual limb. The entire residual limb may be wrapped with plastic wrap, covering the sock. Another sock may be pulled over plastic wrap. The uniform thickness thermoplastic sheet (e.g., a PCL sheet) may be heated in 160°F water and draped over the patient's residual limb. A seam may be formed along the bottom and back of the leg. The fitter may then apply pressure to the malleable plastic to create an intimate fit with the residual limb. Excess thermoplastic may then be removed with trauma scissors. After the thermoplastic has cooled, the socket may be removed. The thermoplastic inner socket may be placed into the polypropylene outer socket, and the space will be filled with an expanding foam to create interface 120. A pylon 140 of desired length may then be constructed by trimming an extra- long segment of PVC pipe to a suitable length. The PVC pipe may then be connected (e.g., press fitted into the outer socket) to create an interface between the two parts. Screws or bolts may then be inserted into the pylon-outer socket interface to increase its structural stability. To complete the prosthetic, a foot 144 (e.g., a Jaipur foot) may then be screwed onto the bottom of the pylon.

It is contemplated within the scope of the invention that the above-described prosthetic limb may be provided in the form of a kit. In one illustrative embodiment, a kit may be in the form of a "technician kit" comprising a large pot for PCL preparation, a heating element for PCL preparation, spare PCL for repair, and a process Manual. In another illustrative embodiment, a kit may be in the form of an "amputee kit" comprising a PVC pylon, a foot (e.g., acquired from a third-party supplier), PCL, adapter ring 132, a foot adapter ring 142, a balloon, and a prosthetic sock.

Claims

CLAIMS What is claimed is:

1. A prosthetic socket, comprising:

an inner socket made of a re-moldable thermoplastic material and having a proximal end and a distal end, wherein the proximal end of the inner socket is configured to receive a distal end of a residual limb of a subject;

an outer shell having a proximal end and a distal end; and

an interface, wherein the interface is sandwiched between the inner socket and the outer shell and configured to adhere the inner socket to the outer shell.

2. The prosthetic socket of claim 1, wherein the inner socket is directly molded on the residual limb of the subject.

3. The prosthetic socket of claim 3, wherein patellar tendon bearing (PTB) reliefs are applied to the residual limb before the inner socket is directly molded on the residual limb of the subject.

4. The prosthetic socket of claim 1, wherein the thermoplastic material is polycaprolactone (PCL).

5. The prosthetic socket of claim 1, wherein the distal end of the outer shell comprises a receiving end configured to attach a proximal end of a pylon to the outer shell.

6. The prosthetic socket of claim 5, wherein the receiving end is configured to attach the proximal end of the pylon to the outer shell by a connector selected from the group consisting of a thread, a press-fit, a snap-fit, and a fastener.

7. The prosthetic socket of claim 1, wherein the outer shell comprises a plurality of proximal-distal oriented slits arranged around a circumference of the outer shell.

8. A method of manufacturing a prosthetic socket, comprising:

identifying anatomical locations for pressure relief on a residual limb of a subject; applying patellar tendon bearing (PTB) reliefs to the identified anatomical locations; fitting a sheet of thermoplastic material over the residual limb bearing the PTB reliefs to form an inner socket with a distal end corresponding to the distal end of the residual limb; inserting the inner socket into an outer shell; and

adhering the inner socket to the outer shell via an interface.

9. The method of claim 8, wherein the thermoplastic material is polycaprolactone (PCL).

10. The method of claim 8, wherein the distal end of the outer shell comprises a receiving end configured to attach a proximal end of a pylon to the outer shell.

11. The method of claim 10, wherein the receiving end is configured to attach the proximal end of the pylon to the outer shell by a connector selected from the group consisting of a thread, a press-fit, a snap-fit, and a fastener.

12. A prosthetic socket manufactured by the method of claim 8.

13. A kit for producing a prosthetic limb, comprising:

a mixing container for preparing a polycaprolactone (PCL) preparation;

a heating element for heating the PCL preparation;

additional PCL; and

instructions for producing a prosthetic limb.