Impact reducing prosthetic pylon

An impact reducing prosthetic pylon has a distal component which can be attached to a prosthetic foot and includes a housing within which the proximal component can slidably fit. A resilient bumper-like member formed of a foam is positioned within the housing and is compressed by the proximal component when the prosthesis is under a load. Relative rotation of the proximal and distal components is prevented, but a limited, resiliently damped rotation may be permitted.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to a prosthetic pylon. More particularly, 
it is directed to an impact reducing prosthetic pylon. 
2. Description of the Related Art 
A prosthetic pylon is the generally solid or tubular member connecting a 
prosthetic part such as a foot to an amputee's residual body part, 
typically through an intermediary part such as a socket for an amputee's 
residual limb. The pylon may be made of a variety of metals or composite 
materials, but most often is a thin-walled aluminum tube. 
Such a rigid pylon has a drawback, however, in that it transmits the impact 
loads of running and jumping directly to the amputee's residual limb. Even 
walking can cause some dynamic type of loads to be transmitted to the 
residual limb, possibly resulting in shear of the amputee's skin, sores, 
skin blisters and wear and tear on the remaining anatomical structures. 
The conventional rigid metal pylon also transmits torsional stresses to 
the residual limb, for example, those resulting from the twisting of the 
foot during walking. This can also lead to shear on the skin of the 
residual limb, causing skin breakdowns and wear and tear on the remaining 
joints. 
U.S. Pat. No. 5,458,656 discloses a prosthetic leg including a impact 
reducing pylon. The shock absorbing pylon of U.S. Pat. No. 5,458,656 has a 
pair of telescoping tubes connected by a composite leaf spring which is 
mounted longitudinally along the pylon and deflects outward as the tubes 
compress. However, whatever shock absorption this conventional pylon 
provides, it requires complex fabrication and, due to its bulkiness, is 
not totally compatible with standard prosthetic components. For example, 
it is extremely difficult to apply a finishing cosmetic foam cover over 
the pylon which appears natural. The pylon is also very expensive, putting 
it out of reach of many amputees who would benefit greatly from a shock 
absorbing device, and is relatively long compared to the average 
prosthesis, prohibiting its use on amputees with long residual limbs. 
Finally, it requires continuous maintenance, e.g., lubrication of 
components, and the need to hand fit the parts, preventing interchange of 
components in case of component breakage. 
U.S. Pat. No. 4,883,493 also uses long telescoping tubes with a mechanical 
metal coil spring connecting the two tubes. It has an internal pneumatic 
cylinder for providing additional damping action. This device is also 
relatively long and heavy, and so has not been commercially successful. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an impact reducing 
prosthetic pylon which is compact in size, economical and simple to 
manufacture, and compatible with standard prosthetic components. 
It is a further object of the invention to provide an impact reducing 
prosthetic pylon which reduces impacts by compression of a body of 
resilient material. 
According to one aspect of the invention, the above and other objects are 
carried out by an impact reducing prosthetic pylon comprising a distal 
component attachable to a prosthetic body part, a proximal component 
attachable to a residual body part, and a joint between the distal and 
proximal components. The joint comprises a housing formed on at least one 
of the distal and proximal components, the other of the distal and 
proximal components being movably fitted in the housing such that it fits 
in the housing by a variable degree. A compressively resilient member is 
located in the housing and elastically limits the degree of fitting of the 
other of the components in the housing. 
Preferably, the compressively resilient member comprises a foam body and 
the housing is formed at an end of the distal component. 
Preferably, means are provided for limiting rotation of the distal 
component about the proximal component and for absorbing torsional 
stresses generated in the distal component and reducing transfer of the 
torsional stresses to the proximal component. Means may also be provided 
for preventing separation of the distal and proximal components. 
According to a further feature of the invention, the above and other 
objects are accomplished by an impact reducing prosthetic pylon comprising 
a distal component having one end attachable to a prosthetic body part and 
having a housing at another end, the housing comprising a substantially 
annular wall centered substantially parallel to a line connected at the 
ends of the distal component. The annular wall defines a mouth comprising 
the other end of the distal component. A proximal component attachable to 
a residual body part is slidably fitted in the housing, and a 
compressively resilient member is disposed in the housing for resiliently 
limiting a degree of entry of the proximal component into the mouth of the 
housing, thereby reducing the transfer of impacts between the distal and 
proximal components. 
The compressively resilient member may comprise a bumper-like body having a 
bore extending therethrough and the proximal part may comprise an adapter 
body having an upper adapter including means for attachment to a residual 
body part, a substantially annular sleeve closely fittable within the 
substantially annular wall of the housing such that the upper adapter 
extends from the mouth of the housing by a variable degree, and a 
projecting part which projects through the bore in the compressively 
resilient member and into the housing in a direction parallel to the axis 
of the substantially annular sleeve. 
Means may be provided for limiting rotation of the distal component about 
the proximal component, the means for limiting rotation comprising a 
non-circular opening in a bottom wall of the housing and the projecting 
part slidably fitting in the non-circular opening, the projecting part 
having a non-circular shape mating with that of the non-circular opening. 
Means may also be provided for preventing the adapter body from being 
removed from the housing and for absorbing torsional stresses generated in 
the distal component and reducing transfer of the torsional stresses to 
the proximal component. The means for absorbing torsional stresses may 
include a guide bushing mounted in the bottom wall of the housing and 
defining the non-circular opening therein, whereby the guide bushing 
rotates with the projecting part when the projecting part is fitted in the 
non-circular opening, and a resilient member positioned in the 
non-circular space between the guide bushing and the bottom wall of the 
housing for resiliently limiting the rotation of the guide bushing. 
A low friction liner may be positioned between the substantially annular 
sleeve and the substantially annular wall, and the guide bushing may be 
formed of a low friction material. 
The resilient material of the compressively resilient member comprises an 
elastomeric foam having high compressive strength and it is compressed 
such that the upper adapter is fully inserted in the mouth of the housing 
when the pylon is under load. Holes may be provided in the housing or 
proximal component for permitting air pressure equalization in the housing 
during movement of the proximal component therein. 
A washer may be positioned between the compressively resilient member and 
the bottom wall of the housing for retaining the guide bushing in the 
bottom wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Nonlimiting embodiments of the present invention will now be described with 
reference to the accompanying figures, in which the same reference 
numerals will be used to designate the same or corresponding parts 
throughout the several views. 
Referring to the first embodiment of FIGS. 1-7, an impact reducing 
prosthetic pylon according to the present invention comprises four major 
components: a distal component 10, a proximal component 40, a compressibly 
resilient member 70 and a guide bushing 80. 
Referring especially to FIGS. 4A-4C, the distal component comprises a tube 
12 of a conventional material such as aluminum. One end 14 of the tube may 
be connected to a prosthetic part such as a prosthetic foot (not shown). 
The length of the tube may vary and is tailored to a given amputee. 
The other end of the distal component forms a housing 16 which is 
incorporated into the joint between the distal component 10 and the 
proximal component 40. The housing 16 takes the form of a substantially 
annular, in this case circular, wall 18 centered on the longitudinal axis 
of the tube 12. The wall 18 is unitary with the tube and has an open mouth 
20 and a bottom wall 22. The bottom wall has a passage structure 
appropriate for accepting the guide bushing 80, which will be described 
further below. The passage structure includes a circular bore portion 24 
in the bottom wall and a non-circular bore portion 26 having flats 28, 
both being centered on the longitudinal axis of the distal component. 
Guide bushing 80 is formed of a low friction material such as acetyl or 
nylon and is primarily comprised of a cylindrical part 82 having a square 
section internal bore 84. A circumferentially extending shoulder 85 is 
formed integrally with the cylindrical part 82 and has a pair of flats 86 
at circumferentially opposed positions. The cylindrical part and shoulder 
are sized such that the cylindrical part may be press fit or slip fit 
within the passage portion 24 of the distal component, and the 
circumferential shoulder 85 fits tightly within the passage portion 26 
with the flats 86 aligning with the flats 28. The guide bushing 80 is 
therefore non-rotatably held within the distal component, with the square 
section bore 84 thereof being centered on, and parallel to, the 
longitudinal axis of the distal component 10. 
A plurality of holes 30 are formed in the annular wall 18 of the housing 
16, for a reason which will be explained below. The holes 30 may instead 
be vertical passages located in the upper adapter part of the proximal 
component 40. 
The proximal component 40 is formed as an adapter body and may be made of 
metal, plastic or composite. It includes an upper adapter 42 which is 
conventional in construction and may include, e.g., set screws 43 for 
attachment to an amputee's stump socket or prosthetic knee. A projecting 
part 44 projects downward from the central part of the upper adapter, 
while a substantially annular sleeve 46 depends from the adapter body such 
that the projecting part 44 lies substantially on the central axis of the 
annular sleeve 46. The annular sleeve is sized so as to closely fit within 
the annular wall 18, while the projecting portion 44 has a square outer 
section which slidably fits within the square section of the guide bushing 
bore 84, as best seen in FIG. 3. 
The adapter body may be fitted into the housing 16, projecting part 44 
first. The projecting part 44 then slidably fits into the bore 84 of the 
guide bushing, while the annular sleeve 46 slides within, and is guided 
by, the interior of the annular wall 18 of the housing 16. The proximal 
component 40 is therefore able to slide axially within the housing, but 
not to rotate with respect thereto, while being guided by the bore 84 of 
the guide bushing and the annular wall 18 of the housing. 
A cylindrical low friction sleeve 88 may be positioned within the housing 
between the annular wall 18 and the annular sleeve 46 for reducing 
friction during the sliding movement of the distal component. 
A larger diameter base portion 48 of the projecting part 44 and the annular 
sleeve 46 together define an annular recess 50 (FIG. 5) whose inner 
diameter corresponds substantially to the outer diameter of the 
cylindrical part 82 of the guide bushing. 
The compressibly resilient member 70 may take the form of a cylindrical 
elastomeric foam body having an axial bore 72 extending therethrough. The 
inner and outer diameters of the foam body are such that it can be 
positioned within the housing 16 with the axis of the resilient member 
extending substantially colinear to the longitudinal axis of the distal 
component. In this case, the lower portion of the wall of the bore 72 fits 
tightly around the upper portion of the cylindrical part 82 of the guide 
bushing. The annular recess 50 of the proximal component 40 fits over the 
upper portion of the resilient member 70. As can be seen in FIG. 2, the 
projecting part 44 then extends through the bore 72 of the resilient 
member 70 and the bore 84 of the guide bushing 80, whose top portion is 
fitted within the bore 72 of the resilient member 70. 
The resilient member 70 is formed of a foam having high compressive 
strength, high resistance to permanent deformation and the ability to 
compress by up to 50% of its original height without significantly 
bulging. An example of a material which may be used for the resilient 
member 70 is microcellular polyurethane foam. The compressive strength of 
the material of the resilient member 70 is important for supporting the 
weight of the amputee during active sports, while the high resistance to 
permanent deformation is important for preventing gaps which can cause 
play. The ability of the material to deflect by up to 50% of its free 
length without significant bulging is important for maximizing deflection 
while minimizing the physical size of the device. 
The size and composition of the resilient member 70 is selected such that 
the upper adapter extends from the mouth of the housing when the 
prosthesis is not under load, i.e., when the weight of the amputee is not 
placed thereon. The set screws 43 are then accessible for adjusting the 
mounting of the prosthesis on the amputee. Conversely, the size and 
composition of the resilient member 70 is preferably selected such that 
when the weight of the amputee is placed on the prosthesis, the adapter 
body fully enters the housing 16 so as to minimize the length of the 
device. 
As seen in FIG. 2, a screw 52 is threaded into a bore 54 extending from the 
bottom of the projecting part 44. The head of the screw presses a washer 
56 onto the end of the projecting part. An elastomeric gasket 56 A may be 
positioned between the washer 56 and the bottom wall of the housing for 
absorbing impacts of the washer on the bottom wall. The diameter of the 
washer 56 is sufficiently large that it engages the lower surface of the 
bottom wall 22 of the housing around the passage portion 24 when the 
prosthesis is not under load, and thereby prevents the proximal component 
40 from being further removed from the housing 16. 
As the amputee walks using the prosthesis, the load of the amputee's weight 
is successively applied to, and released from, the distal component 10 via 
the proximal component 40. As this occurs, the proximal component 40 
reciprocally slides within the housing 16 and while being guided by the 
engagement between the projecting portion 44 and the bore 84 of the low 
friction guide bushing 80, and by the sliding of the annular sleeve 46 
within the annular wall 18, through the intermediary of the low friction 
sleeve 88. The resulting large surface area of contact reduces stresses 
resulting from bending forces and thereby reduces the likelihood of the 
proximal component binding during such movement. Additionally, the 
compression of the resilient member 70 during the application of load to 
the prosthesis resiliently absorbs the transmission of impacts to the 
residual limb of the amputee. The holes 30 permit pressure equalization in 
the housing as the proximal component slides therein. 
During use, the rotation of the proximal component 40 relative to the 
distal component 10 is prevented by the mating square shapes of the 
elements 44 and 84. Since the guide bushing 80 is fixed within the distal 
component 10, it cannot rotate relative to the distal component and so 
prevents rotation of the proximal component. In the alternative embodiment 
shown in FIGS. 8 and 9, however, a limited, resiliently damped, rotation 
between the guide bushing 80 and the distal component 10 is permitted in 
order to absorb torsional stresses and prevent their transmission to the 
resilient limb of the amputee. As seen in FIGS. 8 and 9, the guide bushing 
80 fits within the passage portion 24 with a slip fit, so that it can 
rotate about its axis. Additionally, the circumferential shoulder 85 is 
not press fitted within the passage portion 26, but is spaced therefrom so 
as to form an annular gap within which is positioned an elastomer spring 
90. The guide bushing can therefore rotate by an angle limited due to the 
compression of the resilient elastomer spring 90 between the shoulder 85 
and the wall of the passage portion 26. 
The embodiment of the FIGS. 8 and 9 also has a metal washer 92 which may be 
positioned between the bottom of the resilient member 70 and the bottom 
wall 22 of the housing 16 in order to hold the guide bushing 80 in place 
during rotation. An elastomeric gasket (not shown) may be positioned 
between the washer 92 and the bottom wall 22 of the housing in order to 
minimize the impact of the metal washer 92 on the bottom wall 22 during 
the stroke of the proximal portion within the housing. This gasket may be 
made of a rubber based copolymer manufactured by DeRoyal Industries of 
Powell, Tenn. 
The present invention therefore provides an impact reducing prosthetic 
pylon which produces reduced impact loading on the residual limb of the 
amputee. The ability of the resilient member 70 to deflect and absorb the 
impact forces reduces the trauma applied to the residual limb, including 
shear, tears and bruises. 
It is a simple matter to remove the resilient member 70 by simply removing 
the screw 52 and lifting the adapter body out of the housing 16. Different 
resilient members of different stiffnesses are therefore easily 
interchangeable to allow the prosthetic pylon to be tailored to each 
patient. 
The overall dimensions of the device are compact both in length and 
diameter. The short length is important to permit use by amputees having 
amputations near the ankle. The small diameter is important for cosmetic 
purposes since it is then easy to form a flexible foam cover about the 
prosthesis and thereby create a life-like shape. 
Finally, the device is compatible with existing conventional prosthetic 
components and can be assembled with conventional tools. Low friction 
materials reduce wear and maintenance, and all of the components are 
easily replaced if needed. Both active and geriatric amputees can 
therefore use the device with greater comfort and reduced impact 
transmission. 
Obviously, numerous 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 herein.