U.S. patent number 3,800,334 [Application Number 05/208,364] was granted by the patent office on 1974-04-02 for arrangement in feet for leg prostheses.
This patent grant is currently assigned to Aktiebolaget K.A. Friberg. Invention is credited to Karl Axel Friberg.
United States Patent |
3,800,334 |
Friberg |
April 2, 1974 |
ARRANGEMENT IN FEET FOR LEG PROSTHESES
Abstract
An artificial leg for above-knee amputees comprising a thigh
section, a shank section and a knee joint connecting the thigh and
shank sections. The shank section is formed with an ankle to which
a foot section is pivotally mounted by means of a horizontal shaft
in said ankle. A mechanism is provided to bring about control over
the shank section motions during swing and stance phases, said
mechanism being housed in a shell-shaped calf section constituting
a part of the shank. The improved alignment provided by the
artificial leg in accordance with the invention is obtained by
positioning the horizontal ankle shaft ahead of the weight
supporting line passing through the thigh section, the knee joint
shaft, and the ankle and by articulating the lower end of the ankle
which is shaped as a plate, to a plate arranged on the foot section
by means of the horizontal shaft, in addition to which a resilient
means is provided behind said horizontal shaft between the foot and
ankle plates for forcing the plates apart.
Inventors: |
Friberg; Karl Axel (Oskarshamn,
SW) |
Assignee: |
Aktiebolaget K.A. Friberg
(Vaxjo, SW)
|
Family
ID: |
20256031 |
Appl.
No.: |
05/208,364 |
Filed: |
December 15, 1971 |
Foreign Application Priority Data
Current U.S.
Class: |
623/40; 623/49;
623/44; 623/50 |
Current CPC
Class: |
A61F
2/604 (20130101); A61F 2/68 (20130101); A61F
2/6607 (20130101); A61F 2/64 (20130101); A61F
2002/745 (20130101) |
Current International
Class: |
A61F
2/60 (20060101); A61f 001/08 () |
Field of
Search: |
;3/22-35,1.2,2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
87,730 |
|
Aug 1959 |
|
DK |
|
830,991 |
|
Feb 1952 |
|
DT |
|
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Frinks; Ronald L.
Attorney, Agent or Firm: Harness, Dickey & Pierce
Claims
What I claim is:
1. In an improved artificial leg, particularly intended for
above-knee amputees, comprising a thigh section, a shank section, a
knee joint shaft articulating said thigh section to said shank
section, an ankle section on said shank section, said ankle section
comprising an upper ankle plate forming the upper portion of said
ankle section, a horizontal shaft, a lower foot plate articulated
at the forward end of said ankle plate by means of said horizontal
shaft, and a spring being mounted between said foot plate and said
ankle plate behind said horizontal shaft for forcing them apart, an
artificial foot, means pivotally connecting said artificial foot to
said foot plate, and a mechanism for controlling the knee joint
functions, said horizontal shaft being located ahead of the
prosthesis weight supporting line passing through said thigh
section, said knee joint shaft and said ankle section, a vertical
bore in said upper ankle plate, a clamping element displaceable in
said bore, an elongate member clamped by said element and being
provided to actuate said knee-joint function controlling mechanism
as a result of the vertical displacement of the clamping element in
said bore, and a shoulder at the upper end of said bore for holding
said spring in a compressed state between said shoulder and said
clamping element.
2. An improved artificial leg as claimed in claim 1, further
including an inset of a resilient material arranged between said
ankle plate and said foot plate.
3. An improved artificial leg as claimed in claim 2, wherein said
resilient material is rubber.
4. An improved artificial leg as claimed in claim 1, wherein said
clamping means is provided with a flange and presents a head on its
lower part, said spring being arranged to press against said flange
to urge said head against said foot plate.
5. An artificial leg as claimed in claim 1, wherein a bolt is
arranged on said ankle plate, said bolt freely passing through said
foot plate behind said weight line, an inset of a resilient
material being arranged between said foot plate and a head of said
bolt projecting beneath said foot plate.
6. An artificial leg as claimed in claim 5, wherein the inset is
made from rubber.
7. An artificial leg as claimed in claim 4, wherein a bracket is
attached to the rear portion of said ankle plate, a lower portion
of said bracket adapted to engage the lower face of said foot
plate.
8. An artificial leg as claimed in claim 7, wherein an elastic
cover is provided on the upper face of said lower portion of said
bracket.
Description
BACKGROUND OF THE INVENTION
The use of single-axis knee joints in above-knee prostheses
predominates within the prosthesis technique. Despite its
deficiencies this single axis construction of the knee joint is
favored both on account of its simplicity and its reliability over
for instance so-called anatomic and polycentric knee joints. The
present invention relates to a leg prosthesis having a single-axis
knee joint.
The knee joint of the natural leg seemingly operates like a hinge
connection but as a matter of fact it is much more complicated and
complex in function. The motions of the natural knee joint during
flexion and extension are determined as to their geometry by the
femoral and tibial configuration of the condyles and by the manner
in which these cooperate and are kept together by means of the
meniscus and ligaments. Upon bending motion of the natural knee
joint the tibia is moved backwards, resulting in a knee motion
which is a combination of rolling and sliding. The tibial condyles
then describe a curvature closely resembling the contour
configuration of the femoral condyles.
A step may be separated into two phases, a stance phase and a swing
phase. The stance phase is that part of the step when the foot has
contact with the floor (ground) and the swing phase that part
thereof when the foot is in the air without floor contact and is
either moving backwards as upon flexion of the knee joint or is
moving forwards as upon extension of the knee joint.
On account of its anatomy and geometry briefly described above the
natural knee joint brings about a shortening of the leg between the
two extreme positions thereof during the stance phase, i.e. the
heel contact at the beginning of the stance phase and the push-off
at the end of the stance phase and at the transition into the swing
phase.
It is obvious that a leg prosthesis of the single-axis type cannot
bring about a corresponding shortening of the leg during the
intermediate position of the leg during the stance phase. A leg
prosthesis having a single-axis knee joint has a fixed length,
which causes difficulties, well known to doctors and prosthetists,
in that the artificial foot does not clear the ground when it moves
past the sound foot during the forward swing of the artificial
foot. Amputees try to compensate therefor by elevating their hips
on the prosthesis side or by swinging the prosthesis outwards, so
called circumduction. Common measures taken by the prosthetist to
remove difficulties of this nature involve making the leg
prosthesis somewhat shorter than the sound leg or fixing the
prosthesis foot in a slightly upwardly directed position, i.e. at
an acute angle relative to the shank. The risk that the foot will
touch the ground when being swung forward is thereby
eliminated.
The measures enumerated above do not, however, involve desirable
solutions. In fact, they may even be harmful to the patient because
of the artificial leg being shorter than the natural leg. Above
all, they impede obtainment of a walking pattern resembling the
natural walk.
Certain prosthetic knee systems make use of a complicated pattern
of links to bring about a shortening of the prosthesis during the
swing phase, and in doing so they simulate the function of the
natural knee joint in this respect. Unfortunately, this desired
function is rendered possible only with the aid of a complicated
construction and at the expense of the so-called cosmesis, i.e. a
good design and an aesthetical appearance of the leg. Most
important, the cosmesis, possible in the use of knees of the above
type, becomes so poor and unsatisfactory that knee joints of this
construction have never been put to such an extensive use as is
warranted by the performance of the construction.
The purpose of the present invention is to eliminate the
fundamental drawbacks of using a single-axis knee joint as the
connecting and articulating means between the knee portion and
shank section of the prosthesis. The construction does, however,
demand that the methods of the so-called alignment of an above-knee
prosthesis are briefly described, together with the problem of
obtaining knee stability during the stance phase. By the
denomination "alignment" in this connection is understood the
relationship between the so-called weight supporting line through
the femoral socket of the prosthesis and the posterior-anterior
position of the knee center. This weight supporting line is often,
although not completely adequately, denominated the TKA-line, i.e.
the trochanter-knee-ankle line.
Anatomical deviations and the special functions of various knee
mechanisms call for variations from the above-mentioned basic
alignment. By shifting the socket with respect to the knee center,
the prosthetist is able to achieve that the body weight is
transmitted through the prosthesis along a line falling in the
desired position to the knee center, posterior to, on, or anterior
to it.
The stability of a thigh or hip prosthesis is, in the case of
conventional prostheses and provided no special mechanisms for the
stance phase control are used, a question of alignment. If the knee
joint shaft or pin is placed behind the weight supporting line
through the socket, which line is most easily imagined as one
passing between the trochanter and the ankle, hyperextension of the
knee joint is obtained upon loading of the prosthesis during
walking or in a standing position, whereby buckling or flexion of
the knee joint is prohibited. This is referred to as alignment
stability and the further behind the weight supporting line the
knee joint or shaft is placed the greater the stability obtained.
An increase of the stability, however, renders the initiation of
the flexion of the knee joint a more difficult and energy-consuming
task at the transition from the stance phase to the swing phase,
which in turn counteracts the possibility of obtaining a natural
gait and a pleasing and aesthetic walking pattern.
Flexion of the knee joint is most easily obtained and a pleasing
style of walking ensured if the knee joint or shaft is placed on or
adjacent the weight supporting line through the socket. This
unstable position, known as trigger alignment, does, however,
increase the risk of a sudden and unintentional flexion, for which
reason this alignment may only be used in the case of good and
functional femoral stumps which through a pressure backwards inside
the socket are capable of retaining the prosthesis in a stable
position and prevent buckling. This phenomenon usually is referred
to as voluntary knee control.
The trigger alignment arrangement may, in the case of weak and less
functional stumps and in the case of patients having other physical
or psychological deficiencies, only be used in connection with an
adequate mechanism for stance phase control, i.e. the position of
the gait cycle in which the foot is in contact with the ground.
The demand for knee stability is most important during the first
half of the stance phase, i.e. during the period from heel contact
to mid stance when the body is in upright position. To prevent
flexion of the knee joint during this period it is necessary to
rely on alignment stability of varying degree -- still providing
that no particular stance control mechanism is being used. The knee
shaft position behind the weight line varies from about 1
centimeter to about 5 centimeters or, in exceptional cases, even
more. During the latter half of the stance phase -- from a vertical
position to the rearwardly inclined position of the leg before
push-off and transition to the swing phase -- the same degree of
alignment -- or built-in stability is not as necessary as during
the first half of the stance phase. However, hitherto an
unchangeable degree of built-in stability during the entire stance
phase has been unavoidable.
In contrast the natural knee permits flexion without resistance
when the body weight is shifted onto the other leg, the artificial
knee, having a high degree of alignment stability, offers a strong
resistance against knee flexion, which is energy-consuming, creates
a time lag relative to the correct moment of flexion and retards
the transition of the prosthesis from the stance phase to the swing
phase, all of which has a considerable negative influence on both
walking comfort and the style of walking, in addition to which it
is highly energy-consuming and as a consequence thereof tires the
patient.
In single-axis knee joints adequate alignment stability during the
first half of the stance phase, when the body weight is applied
primarily on the posterior of the foot, would be ideal, whereas a
lower degree of alignment stability -- or ideally the
above-mentioned "trigger" alignment should prevail, when the body
weight is shifted onto the foot of the other leg. This ideal
condition may be denominated "self-adjusting alignment" and is
particularly favorable during those moments of stance phase when
the major portion of the artificial foot still has ground contact
but the bulk of the body weight has been shifted onto the other
leg.
This is achieved by means of the present invention in that the
horizontal shaft in the prosthesis ankle about which shaft the
artificial foot is journalled, is positioned ahead of the weight
line of the prosthesis, in that the lower portion of the ankle is
in the shape of an ankle plate at the forward end of which a foot
plate is articulated by means of said horizontal shaft, and in that
a spring means in inserted between the foot plate and the ankle
plate.
The spring means between the ankle plate and the foot plate is held
under a certain bias, whereby said plates, upon loading of the
posterior portion of the foot, assume a position wherein they are
practically parallel to each other but, in the absence of such a
load, they automatically assume positions in which they are
angularly displaced relative to each other. When the body weight is
shifted from the prosthesis onto the sound leg but the artificial
foot is still in contact with the ground over the entire sole
surface (complete ground contact), the relative angular position of
the plates causes the knee joint or shaft to be moved forward
relative to the weight line, i.e. a change or self-adjustment of
the prosthesis alignment occurs. When the artificial foot is lifted
clear of the ground, i.e. when ground contact ceases completely,
the spring means urges the plates further apart and the angle
between them increases even more. In addition, the plates no longer
exert an influence on the knee joint or shaft position, as any back
pressure from the ground has ceased. Owing to the arrangement of
the spring means, the anterior of the foot is thus lifted at this
stage. This toe "pick-up" results in elimination of the risk of the
foot touching the ground during the swing forward.
When the prosthesis carries the entire body weight, the knee joint
or shaft is thus in its extreme rear position providing maximum
safety against buckling, whereas when the body weight is being
shifted onto the other leg, the knee joint or shaft is moved
forwards and that prosthesis alignment which is most favorable for
flexion of the knee joint -- and as a consequence thereof for the
taking of one step -- is automatically established.
DESCRIPTION OF THE DRAWINGS
Further characteristics of the invention and the advantages
obtained thereby will become apparent upon reading of the following
detailed description of a preferred non-limiting embodiment of the
invention. In the drawings:
FIG. 1 is a vertical longitudinal section through a leg prosthesis
in accordance with the invention,
FIG. 2 is a similar longitudinal section at an angle of 90.degree.
relative to the view in FIG. 1,
FIGS. 3 and 4 illustrate on an enlarged scale a vertical
longitudinal section through the joint connecting the ankle and the
foot in various angular positions thereof,
FIGS. 5, 6, and 7 illustrate schematically the alignment of
prostheses adapted for various lengths of the legs,
FIG. 8 illustrates on an enlarged scale various angle positions of
the joint between ankle and foot,
FIG. 9 illustrates on the same scale as in FIGS. 3 and 4 a vertical
section through the prosthesis ankle plate,
FIG. 10 shows the plate of FIG. 9 from beneath,
FIG. 11 is a vertical section through the prosthesis foot
plate,
FIG. 12 illustrates the plate of FIG. 11 from underneath, and
FIG. 13 is a similar vertical section as in FIG. 3 but in
accordance with another embodiment.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The upper (thigh) section or socket-and-knee part 1 is, as
illustrated in FIG. 1, by means of a knee joint or shaft 2
connected to a lower (shank) section 3 at the lower end of which is
attached an ankle 4 which is articulated to an artificial foot 5.
From the knee part of the thigh socket 1 there extends forwardly an
arm 6 which by means of a pivot 7 is journalled to the upper end of
a hydraulic knee control mechanism 8 enabling a swinging motion of
the shank section 3 relatively the thigh socket 1 over an angular
section of approximately 130.degree.. In accordance with the
embodiment illustrated on the drawings the hydraulic mechanism 8
comprises two cylinders 9, 10 which are located in co-axial
positions relative to each other in the longitudinal direction and
which contain liquid, one piston (not shown) being arranged for
displacement in each cylinder. The pistons are securely attached on
a common piston rod 11. Reference number 12 designates the
attachment loop of the lower cylinder 10. The piston rod projects
through a bushing in a valve housing 13 positioned intermediate the
two cylinders 9, 10. The valve housing encloses a valve 14 serving
to close off a channel intercommunicating the interior of cylinder
9 with that of cylinder 10, thus providing blocking of the knee
joint in a particular position. A traction spring 15 is provided to
turn the valve to closing position.
The knee control mechanism 8 is articulated at its lower end to a
fork-like member 17 by means of a bolt 16, said fork-like member 17
being detachably secured to a base portion 19 by means of a bayonet
catch 18 at the lower end of the shank section 3. Preferably, the
base portion 19 is made integral with the lower portion of the
shank section 3, which lower portion is designed as a shell-shaped
calf portion. In the fork-like member 17 about a pin 20 (or bolt)
is pivotally mounted the one end of a lever 21, the opposite end 22
of which is connected to the lower portion 24 of the valve arm 14
by means of a thread-like wire 23. The upper end 25 of a coupling
wire 26 which freely passes through a vertical channel 27 made in
the fork-like member 17 is secured to the lever 21. The lower end
of the wire 26 is by means of a chuck 28 attached to an operating
device 29, which device is actuated by the verticalmovements of the
artificial foot and is vertically displaceable in the ankle 4.
The ankle 4 comprises an ankle plate 31 articulated to the
artificial foot 5 by means of a horizontal shaft 30, and a tubular
upright 33 with a flange 32 thereon is attached to said ankle plate
31. The upper end 34 of the upright 33 is adapted to be received in
a clamping sleeve 35 extending downwardly from the shank section
base portion 19. The clamping sleeve 35 is provided with a
vertically extending slit 36 and the clamping sleeve sections on
either side of said slit 36 may be tightened about the upper
upright end 34 by means of a clamping screw 37.
The shaft 30 passes through two lugs 38 on the lower face of the
ankle plate 31 and also through a lug 39 at at the forward end of a
foot plate 40 incorporated in the artificial foot 5. A universal
joint 41 connects the foot plate with the artificial foot 5. The
sole thereof is designated 42. In the artificial foot 5 is inserted
a cushion or pad 43 or the like of a compressible material, such as
plastics or rubber, shaped so as to allow the artificial foot to
perform angular movement about the joint 41 in various planes
relative to the plate 40.
Into the rear end of the ankle plate 31 is screwed from behind a
nipple 44 having a downwardly projecting pin 45 freely passing
through a bore 46 in the foot plate 40. Between a flange 47 on the
nipple 44 and the foot plate 40 is inserted an insert or washer 48
of rubber or some other suitable resilient material. Also on the
lower face of the foot plate 40 between said face and a head 49 on
the lower end of the pin 45 is mounted an insert on washer 50 of
rubber or similar resilient material. These two washers 48 and 50
serve to dampen noise. The head 49 of the pin 45 and a washer 49'
arranged inside said head limit the relative angular movements of
plates 31 and 40. Said plates are urged apart when the washer 50 is
being compressed under the influence of a helical spring 51 held
between a flange 52 on the chuck 28 and the top 53 of the bore 54
in which the chuck 28 is vertically displaceable. The movement of
the chuck 28 in a downwards direction is limited by a bayonet catch
55 retaining the chuck in the ankle 4. The lower end of the chuck
28 presents a head 56, preferably made from steel or a
wear-resisting material of plastics by means of which the chuck 28
is held pressed against the foot plate 40 by means of the spring
51.
When the prosthesis supports the entire body weight, the knee shaft
2 occupies its extreme posterior position providing maximum safety
against buckling. This position is illustrated schematically in
FIG. 5. The knee shaft 2 is then positioned behind the broken line
representing the weight line 57 between the hip joint 58 and the
ankle 4. In this position the washer 48 (FIG. 3) is in a compressed
state. The longitudinal line 60 of the shank section 3 forming a
right angle 61 with a line 62 passing through the shaft 30 and
extending in parallel with the foot plate 40 when the prosthesis is
loaded, then extends obliquely rearwardly and upwards such that the
knee shaft 2 will occupy a position behind the weight-supporting
line 57 and good stability is obtained. When the body weight is
shifted to the sound leg with the sole 42 still in contact with the
ground 59 the spring 51, being heavily compressed during loading,
may expand, whereby the chuck 28 together with the head 56 press
against the upper surface of the foot plate 40. Because the foot
plate 40 cannot be urged downwards to any considerable extent (as
the foot sole 42 still rests against the ground 59) the ankle plate
31 is urged to assume an angularly displaced position relative to
the foot plate 40 and the upright 33 that is attached to the ankle
plate 31, and the entire shank section will be swung forward as a
result of the thrust to the position illustrated in FIG. 5 by line
63, while the washer 50 (FIG. 4) is being slightly compressed,
whereby the knee shaft 2 will be positioned ahead of, or
alternatively on, or in any case closer to the weight-supporting
line 57. Upon this swinging upwardly and forwardly of the ankle 4
there is a relative displacement between the chuck 28 and the
ankle, resulting not only in a swinging motion of the ankle 4 to
bring the toe portion of the foot 5 into a position wherein it is
at a more acute angle relative to the shank but also having the
result that the valve in the valve housing 13 between the cylinders
9 and 10 is opened through the intermediary of the coupling wire 26
and the wire 23, and the valve 14 whereby the mechanism 8
controlling the knee joint functions is released and the swing
phase of the leg may be initiated.
In FIGS. 6 and 7 is indicated the alignment of leg prostheses of
different lengths in the position assumed by the leg immediately
before the beginning of the swing phase.
The self-adjusting alignment described above in a leg prosthesis in
accordance with the present invention during the stance phase
together with the change of foot angle and toe pick-up during the
swing phase make it possible to impart extremely desirable
functions to a single-axis knee joint prosthesis as well as a
highly satisfactory performance.
FIG. 13 illustrates a similar longitudinal section through the
artificial foot as FIG. 3 but the connection between the ankle
plate 31 and the foot plate 40 is slightly different. In accordance
with FIG. 13 the nipple 44 and the bolt 45 have been replaced by a
bracket 65, preferably made from sheet metal, which is attached by
means of one or several bolts 66 to the ankle plate 31 at the rear
part thereof in such a position as to engage with required play 67
with the lower face of the foot plate 40 by means of its lower
portion 68. The upper surface of this lower portion 68 of the
bracket 65 is provided with an elastic covering 69, preferably
consisting of rubber.
This constructional arrangement considerably facilitates the
disassembling of the artificial foot as well as the mounting
thereof, while at the same time ensuring movability between the
ankle plate and the foot plate and also the movability of the foot
relative to the foot plate.
The embodiments as illustrated and described are to be regarded as
examples only and the device enabling the self-adjusting alignment
described above may be constructively altered in many ways within
the scope of the appended claims. The resilient means 51 need not
necessarily act on a chuck 28 to securely clamp a coupling wire or
coupling rod for operating the valve of a hydraulic mechanism
controlling the knee joint functions. Furthermore, the invention is
not either limited to a particular construction of such a
mechanism. The device in accordance with the invention may be used
in connection with other types of artificial feet, for instance the
so called SACH foot. In this case the universal joint 41 is
replaced by an attachment plate secured to the lower face of foot
plate 40. Alternatively, the foot plate 40 may simply be altered
for attachment directly on the foot. The mechanism for controlling
the knee joint functions need not necessarily consist of a more or
less complicated hydraulic device, but the invention is also
applicable to a simple friction-operated device to achieve the
swing and stance phase control.
* * * * *