A rotational joint assembly for a prosthetic leg has been devised, which enables an artificial foot to rotate slightly when a person is walking, running or turning. The prosthetic leg includes upper and lower tubular members with the rotational joint assembly interposed between them. The assembly includes a restrainer mechanism which consists of a pivotably mounted paddle element. This device applies limiting force to control the rotation of the foot and also restores torque to return the foot back to its initial position

Jones, W. C.

Owens, L. J.

English

NASA Technical Reports Server

United States Patent [I91 
Owens et al. 
[ I 1 1  4,038,705 
WI Aug. 2, 1977 
ROTATIONAL JOINT ASSEMBLY FOR THE 
PROSTHETIC LEG 
Inventors: 
Assignee: 
Appl. No.: 
Filed: 
Iot. c I . 2  .... 
U.S. a. .... 
Lester J. Owens, Titusville; William 
C. Jones, Merritt Island, both of Fla. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics nod Space 
Administration, Washington, D.C. 
710,032 
July 30, 1976 
............................................. 3/2: 3/21 
...................... A61F 1/08; A61F 1/04 
Field of Search .......................... 3/2, 7, 21, 30-35 
References Cited 
U.S. PATENT DOCUMENTS 
3,73 1,323 5/1973 Glancy ................................ 3/2 
3,842,443 10/1974 Weber .......................................... 312 
3,906,552 9/1975 Weber ..................................... 3/2X 
3,956,775 Vi976 Moore .......................................... 3/2 
Primary Examiner-Ronald L. Frinks 
Attorney, Agent, or Firm-James 0. Harrell; John R. 
Manning 
1571 ABSTRACT 
A rotational joint assembly for a prosthetic leg which 
enables an artificial foot to rotate slightly when a person 
is walking, running or turning. The prosthetic leg in- 
cludes upper and lower tubular members with the rota- 
tional joint assembly interposed therebetween. The 
rotational joint assembly includes a restrainer rnecha- 
nism which consists of a pivotably mounted paddle 
element engaging a resilient device for applying a limit- 
ing force to control the rotation of the foot and also 
restoring torque to return the foot back to its initial 
position. 
3 Claims, 4 Drawing Figures 
26 
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regulate the amount of force applied to and through the 
paddle element. 
Accordingly, it is an important object of the present 
invention to provide a rotational joint assembly for a 
prosthetic leg which may be interposed between an 
artificial knee or a natural knee and an artificial foot so 
as to enable the foot to be rotated slightly when walk- 
ing, running or turning. 
Another important object of the present invention is 
to provide a simple and efficient joint assembly for 
prosthetic legs which gives a controlled rotational 
movement to the foot for producing a more natural-like 
gait while walking and for minimizing the energy re- 
quired in walking. 
Still another important object of the present invention 
is to provide a joint assembly which controls the retard- 
ing and restoring forces of an artificial foot as such is 
rotated approximately plus or minus three degrees dur- 
ing walking. 
Still another important object of the present invention 
is to allow the installation of rotational joints in standard 
3Omm tubing commonly used in lower limb prostheses. 
These and other object and advantages of the inven- 
tion will become apparent upon reference to the follow- 
ing specification, attendant claims, and drawing. 
BRIEF DESCRIPTION OF THE DRAWING 
FIG. 1 is a perspective view illustrating a prosthetic 
leg with the rotational joint assembly constructed in 
accordance with the present invention, 
FIG. 2 is an enlarged, sectional view illustrating the 
rotational joint assembly constructed in accordance 
with the present invention, 
FIG. 3 is an enlarged sectional view illustrating a 
modified form of the rotational joint assembly con- 
structed in accordance with the present invention, and 
FIG. 4 is a sectional view taken along the line 4-4 of 
FIGS. 2 and 3. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Referring in more detail to FIG. 1 of the drawing, 
there is illustrated a rotational joint assembly 10 con- 
structed in accordance with the present invention as 
used with a conventional prosthetic leg 12. As illus- 
trated, the prosthetic leg 12 is cut into sections 14 and 16 
at a point located approximately, for example, eight 
inches from an artificial foot 18. Although the stump 
socket is indicated as being arranged for a below the 
knee amputation, it is to be understood that the pivot 
joint may be used with above the knee amputations as 
well. As illustrated, the sections 14 and 16 are tubular 
extensions extending from the rotational joint assembly 
10 to the stump socket and to the artificial foot. 
Referring to FIG. 2, the rotational joint assembly 10 
includes an upper tubular member 20 which may be the 
lower end of a standard 30mm aluminum tubing that is 
utilized in prosthetic devices. A similar lower member 
22 is connected to the artificial foot 18. The tubular 
members 20 and 22 can be the lower ends of tubular 
sections 14 and 16 or they can be inserted therein. 
A metal or plastic connector 24 is inserted in the 
lower end of the upper tubular member 20 and secured 
thereto by welding or screws (not shown). The connec- 
tor 24 provides a seat for receiving an elongated bolt 26. 
The bolt 26 is keyed to the connector 24 by a key 28 so 
as to insure that the bolt 26 does not rotate relative to 
the tubular member 20. A nut 30 is provided on an 
1 
ROTATIONAL JOINT ASSEMBLY FOR THE 
PROSTHETIC LEG 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the United States Government and may be manu- 
factured by or for the Government for governmental 
purposes without the payment of any royalites thereon 
or therefor. 
BACKGROUND OF THE INVENTION 
The present invention relates to a rotational joint 
assembly for a prosthetic leg and more particularly to a 
restrainer mechanism which applies a restraining force 
for limiting the rotation of an artificial foot during walk- 
ing and for applying a restoring torque thereto. 
In the normal function of the human leg during walk- 
ing, there is a rotation of the foot in relation to the hips. 
Lack of this rotational capability in a prosthetic leg 
results in an awkward gait requiring excessive efforts 
during walking and thereby producing an uneven wear 
of shoes. 
An example of a joint for allowing rotation of an 
artificial foot is disclosed in U.S. Pat. No. 3,842,443 
granted on Oct. 22, 1974. In this particular device, joint 
segments are attached to respective sections of a pros- 
thetic leg. A resilient sleeve is arranged about the joint 
segment for restoring same to a normal or predeter- 
mined relationship with respect to one another follow- 
ing the application of torsional forces to the joint. While 
this prior art device may operate satisfactorily for the 
purposes intended, there is no provision for limiting the 
degree of rotation of the foot during walking and for 
applying a restoring torque to the foot for returning it to 
its initial position. 
SUMMARY OF THE INVENTION 
The invention includes a rotational joint assembly for 
a prosthetic leg which aids in controlling the retarding 
and restoring forces which are applied to an artificial 
foot as it is rotated during walking, running or turning. 
The prosthetic leg includes an upper member adapted 
to be connected to the wearer’s body. This upper mem- 
ber may be connected to an artificial knee or through 
any suitable connector to a natural knee joint. The pros- 
thetic leg also includes a lower member which is con- 
nected to an artificial foot. The rotational joint assembly 
is interposed between the upper and lower members of 
the prosthetic leg and includes a restrainer mechanism 
for applying a controlled force to limit the degree of 
rotation of the foot during walking and for applying a 
restoring force to return the foot back to its initial posi- 
tion. The restraining mechanism includes a resilient 
device which is carried by one of the upper and lower 
members, and a contact means which is carried by the 
other member so that as the foot is rotated during walk- 
ing, the contact means bears against the resilient device 
deforming such. The degree of rotation of the foot is 
controlled by the deformation of the elastomer bearing. 
In one particular embodiment, the resilient device takes 
the form of a pair of spaced semicircular members hav- 
ing a space provided therebetween. The contact means 
includes a paddle element which is positioned between 
the semicircular members so that as such is rotated it 
will engage one or the other of the semicircular mem- 
bers. The surface of the semicircular member which 
engages the paddle element may be curved so as to 
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65 
490 
3 
upper threaded end of the bolt 26 for securing such to 
the connector 24. The bolt 26 extends into the lower 
tubular member 22 and the connection therebetween 
will be discussed more fully below. 
Interposed between the lower tubular member 22 and 
the upper tubular member 20 is a thrust bearing 31 
which sits on top of a bearing support 32 that is, in turn, 
supported on the upper end of the lower tubular mem- 
ber 22. Such is to enable the lower tubular member 22 to 
rotate slightly relative to the upper tubular member 20. 
The rotational joint assembly 10 further includes a 
restrainer mechanism for restraining or restricting the 
rotation of the lower tubular member 22. Positioned 
within the tubular member 22 is another circular tubular 
member 34. Carried within the tubular member 34 is a 
resilient device consisting of a pair of spaced semicircu- 
lar elastomeric torque members 36 and 38 which are 
secured to the inner wall of the tubular member 34 by 
any suitable means such as adhesive. The inner surface 
of each of the semicircular elastomeric members 36 and 
38 is arcuate with the greatest thickness being at the 
center of the tubular member 34 such as best illustrated 
in FIG. 4. 
To restrain rotation of the lower tubular member 22, 
outwardly extending flanges 40 and 42 are welded to 
the shaft 26 to define a paddle element which is posi- 
tioned between the two elastomeric torque members 36 
and 38. These flanges 40 and 42 engage the elastomeric 
members 36 and 38 as the upper tube 20 is rotated rela- 
tive to the lower tube 22 thereby limiting the rotation 
therebetween to a predetermined number of degrees for 
the unit torque applied. The retarding force applied by 
the resilient device to the paddle element is controlled 
by the curvature of the inner walls of the elastomeric 
members 36 and 38. The resiliency of elastomeric mem- 
bers 36 and 38 depends on the material from which they 
are made, as well as their length. The elastomeric mem- 
bers 36 and 38 are deformed by the flanges 40 and 42 
engaging them and thereby causes a restricting of the 
rotational movement between upper and lower tubular 
members 20 and 22. then the rotational force is removed 
therefrom, a restoring torque is applied by the deformed 
elastomeric members 36 and 38, forcing the flanges 40 
and 42 of the paddle element to return the tubular mem- 
bers 20 and 22 back to their initial position and, conse- 
quently, the artificial foot to its initial position. The 
contour of the inner surface of the elastomeric members 
36 and 38 is such that as the angular rotation of the 
paddle element increases, the force required to rotate 
the paddle element further increases. It is to be under- 
stood that the restrainer mechanism may be constructed 
in such a manner that the resilient device has only one 
elastomeric member and the paddle element only one 
flange. 
A thrust bearing 44 is carried on the shaft 26 in 
contact with a bearing set 46 that in turn is pressed 
against the lower end of the circular housing 34. A 
spring 48 is interposed between the bearing 44 and a 
washer 50 so as to apply a preload compression between 
the upper member 20 and the lower member 22 for 
preventing looseness that could generate noise and to 
allow the joint to act like a column in compression with 
no bending moment on the paddle shaft when side loads 
are applied. A nut 52 is carried on a threaded lower end 
of the shaft 26 and it can be rotated for varying the 
compreqion. FIG. 3 illustrates a modified form of the 
invention wherein instead of using the trust bearing 31, 
a low friction plastic swivel joint 54 is interposed be- 
38,705 
4 
tween the upper tubular member 20 and the lower tubu- 
lar member 22. An elastomeric compression bearing 56 
is carried on the shaft 26 on the bottom side of the 
plastic swivel joint 54 and a washer 58 and nut 60 are 
5 provided for securing the assembly together. The shaft 
26 extends through the tubular member 34 and has a 
washer 62 provided on the lower end thereof and a snap 
ring 64 for securing the shaft in place against a hard 
rubber or metal disk shaped member 66 which is pressed 
10 against the lower end of the tubular member 34. There- 
fore, the nut 60 can be adjusted for varying the com- 
pression load between the upper member 20 and the 
lower member 22. In one particular embodiment, the 
low friction plastic swivel joint 54 is constructed of 
l5 Delrin with Teflon dispersed therein. The embodiment 
illustrated in FIG. 3 operates in the identical manner as 
the embodiment of FIG. 2 with the above mentioned 
exception. As previously mentioned, the restraining 
force applied by the elastomeric members 36 and 38 
2o may be varied by changing either the material from 
which the elastomer is manufactured or the length of 
the elastomeric material or by varying the curvature of 
the inner walls. 
In one particular embodiment, the elastomeric torque 
25 members 36 and 38 are constructed of silicone rubber. 
However, it is to be understood that they may be con- 
structed of any suitable material, such as, natural rub- 
ber. 
In operation, the rotational joint assembly can be 
30 installed in any suitable manner in a prosthetic leg nor- 
mally between a knee joint and a foot. The knee joint 
may be either an artificial knee or may be a natural knee 
with a stump thereon to which a socket engages. The 
3s tubular members 20 and 22 may be the normal exten- 
sions from the stump socket and the artificial foot. 
It has been found that in walking there is a normal 
rotation of the foot of approximately plus or minus 3 
degrees. However, in artificial limbs, it has been diffi- 
40 cult to reproduce this rotational movement and, as a 
result, the shoe on the artificial foot tends to be scuffed 
or dragged along the surface increasing the forces nec- 
essary to walk. Accordingly, as the user walks with the 
rotational joint installed, the foot will rotate approxi- 
45 mately 3 degrees causing the flanges 40 and 42 of the 
paddle element to deform the elastomeric members 36 
and 38. As the elastomeric members 36 and 38 are being 
deformed, they impart a retarding force to the rotation 
of the paddle element thereby limiting the rotation of a 
50 foot to approximately 3 degrees while walking. How- 
ever, the more active the wearer of the prosthetic leg 
becomes, the greater the need for larger rotational an- 
gles and greater force transmission. As the rotation 
increases, the force required to rotate the foot further 
55 also increases due to the curvature of the elastomeric 
members. After the foot has been rotated when the leg 
is swung forward, then the elastomeric member imparts 
a restoring torque to the paddle element to return the 
foot to its initial position. 
Both of the flanges 40 and 42 of the paddle element 
will bear against the surfaces of the elastomeric mem- 
bers 36 and 38 when the paddle element is in its neutral 
position. 
However, when the patient is turning to the right or 
65 the left, such will in turn cause each flange on the pad- 
dle element to bear against only one of the surfaces of 
the elastomeric members depending upon which way 
the patient is turning. 
60 
4,038,705 
5 6 
While a preferred embodiment of the invention has 
been described using specific terms, such description is 
for illustrative purposes only, and it is to be understood 
that changes and variations may be made without de- 
parting from the spirit or scope of the following claims. 
members secured to an inner wall of said tubular 
housing; and 
extending flange carried by said 
shaft positioned between said spaced diametrically 
opposed semicircular elastomeric members 90 that 
said flange engages said semicircular elastomeric 
members when said artificial foot is rotated. 
c. said 
5 
What is claimed is: 
1- A rotational Joint assembly for a Prosthetic leg 
which applies retarding and restoring forces to an artifi- 
3. A rotational joint assembly for a prosthetic leg 
which aids in controlling the retarding and restoring 
cia1 foot as it rotated during the walking, running and 10 forces applied to an artificial foot as it is rotated during 
turning of a wearer of said prosthetic leg, said joint the walking, running and turning of a wearer of said 
assembly comprising: prosthetic leg, said rotational joint assembly compris- 
A. an upper member adapted to be connected to the 
wearer’s body; 
c. a lower tubular member adapted to be connected to artificial foot; C. bearing means connecting said upper and lower 
members and permitting relative rotation therebe- d. &ring interposed between said upper and 
tween; 20 lower tubular members; 
D. a resilient means carried by one of said members; e. a resilient means secured to an inner wall of said 
E. a shaft carried by said other member; and lower tubular member; 
F. an outwardly extending flange carried by said shaft f. a shaft carried by and extending downwardly from 
said upper tubular member into said lower tubular 
G. whereby as said foot is rotated during walking, 2s member; 
for engaging said resilient means as said upper tubu- restricting the degree of rotation of said foot and for lar member is rotated relative to said lower tubular 
member; restoring said foot to its normal position. 
flange engaging and deforming said resilient means 
and said deformed resilient means forcing said 
flange and said foot back to their initial position. 
a. an upper tubular member; 
B. a lower member adapted to be connected to said l5 b. means for attaching said upper member to the wearer’s body; 
said artificial foot; 
for engaging said resilient means; 
wid flange bears against said resilient means for g* outwardly extending flange carried by said shaft 
2. The rotational joint assembly 85 set forth in C 1 8 h  1 30 h. whereby rotation of said foot is by further comprising: 
A. a tubular housing carried by one of said members; 
B. said resilient means including a pair of spaced 
dimetrically opposed semicircular elastomeric * + + * +  
3s 
40 
45 
so 
5s 
65 


Rotational joint assembly for the prosthetic leg

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