Note: Descriptions are shown in the official language in which they were submitted.
WO 96/10969 ~ PCT/SE95/01106
1
A ROTATION DAMPER IN A TOGGLE JOINT PROSTHESIS
The present invention refers to a rotation damper for so
called swing phase control at toggle joint prosthesises.
This swing phase control provides a dampening of the forward
swing motion of a limited swing angle, which occurs when the
lower part of the toggle joint prosthesis after a finished
step is moved forward rapidly for initiation of the next
step. Without such a rotation dampening of the joint the
prosthesis bearer will get a bumpy walk, which is not only
unnatural, but which also causes increased stresses on the
prosthesis and body parts cooperating therewith.
For such rotation dampening of toggle joint prosthesises in
more simple cases earlier have been used dampening rubber
blocks and at more sophisticated embodiments, more or less
complex hydraulic systems, with valves and pistons of
rather small dimensions, and manufactured with high
precision. This means that such earlier rotation dampers
have been expensive components, which have furthermore often
meant intricate sealing problems, in order to prevent the
hydraulic fluid from leaking out.
The purpose of the present invention is to provide such a
rotation damper for a toggle joint prosthesis, which
eliminates the above mentioned problems and provides a leak
proof, reliable mechanism, which furthermore is inexpensive
to produce and can be manufactured in different embodiments.
This has been achieved in that the rotation damper has been
given the features defined in the accompanying claims.
Hereinafter the invention will be further described with
reference to an embodiment schematically shown in the
accompanying drawings.
WO 96/10969 ~ ~ ~ ~ ~ PCT/SE95/01106
2
Fig. 1 shows in a side view a non-limiting embodiment of a
toggle joint prosthesis, which can be equipped with a
rotation damper according to the invention,
Fig. 2 is a corresponding view of the toggle joint
prosthesis according to Fig. 1 with the joint in a
rearwardly extended position,
Fig. 3 shows the toggle joint prosthesis according to Fig.
1 in a view straight from the front,
Fig. 4 shows schematically a cross section through a portion
of the toggle joint prosthesis according to Fig. 1, with the
rotation damper forming part thereof in a completely open
position,
Fig. 5 is a view corresponding to Fig. 4 but with the
rotation damper according to the invention in a completely
closed position,
Fig. 6 shows another section through an upper attachment
forming part of the toggle joint prosthesis with a rotation
damper provided therein, and
Fig. 7 shows in side view a pivot axle forming part of the
rotation damper according to Fig. 6.
Fig. 1 shows in a side view a toggle joint prosthesis 1,
which, without being a limitation for the invention, can be
an appropriate mechanism for application of the rotation
damper according to the invention. The prosthesis
incorporates an upper attachment 2 and a lower attachment 3.
The attachments 2 and 3 are mutually articulated by means of
a system of links 4, 5, pivotably journalled to each other,
and which permit that the upper and lower attachments 2, 3
can be angled to each other so relative to each other, that
the prosthesis gives a very natural walking pattern. Such a
prosthesis is known e.g. from SE-A-9001183-4, and it '
therefore will not be described in detail in this
specification. '
The forward pair of links 4 is articulately attached to the
upper attachment 2 via a pivot 6, whereas an rearward link
4a, in the same manner is articulated to the upper
WO 96110969 ~ PCTlSE95101106
3
attachment in a pivot 6a. As can be seen from Fig. 2,
wherein the prosthesis is shown with the lower part in a
rearwardly bent position, i.a. the link 4 at the swing
motion has moved about the pivot 6. At this movement, and
also at the consecutive forward swing motion to stretched
knee joint, it a.s required a dampening device for reducing
the stresses upon the joint system. Forthis purpose a
rotation damper according to the invention can preferably be
provided a.n this joint 6. The manoeuvring of the rotation
damper is effected through an opening 7 at the forward part
of the upper attachment.
Fig s 4 and 5 show schematically in cross section the upper
attachment 2 with its links 4 and 4a, resp., which are
equipped with pivot axles 6 and 6a, resp. In the embodiment
shown thereby only the forward joint 6 is designed as a
rotation damper according to the invention. The pivot axle
6 is via splines non-rotationally connected to the links 4,
which are arranged one on each side of the housing formed by
the upper attachment 2, which has a through-opening 8,
through which the pivot axle 6 extends, supported in ball
bearings 9. Inside the position of the ball bearings 9 the
pivot axle 6 is equipped with radial flanges 10, which
support sealing means 11, which seal off the space inside
thereof to a chamber 13. Between the two flanges 10 the
pivot axle 6 is equipped with a wing 12, which extends over
the entire length of the chamber and is arranged on a
portion 14 of the pivot axle 6, having smaller diameter than
the rest of the pivot axle.
In the housing formed by the attachment 2, as mentioned
above, there is also provided an opening 7, which extends as
a cylindrical channel from the front part of the attachment
and opens in the chamber 13. In the channel 7 there is
inserted an adjustment device cooperating with the pivot
axle wing 12 and being in the form of cylindrical tap 15,
which at its end projecting into the channel is provided
WO 96/10969 ~ ~ ~ ~ ~ ~ PCT/SE95/01106
4
with diametrically extending ridge 16. The cylindrical
surface of the tap is sealed off against the wall of the
channel, e.g. by means of a circumferential sealing ring 17,
positioned in a groove. The tap 15 is secured in its axial
position in the channel 7 by means of a stop ring 18
inserted in a groove in the channel wall. The tap 15 however
is rotatably arranged in the channel and to this purpose in
its outwardly positioned end, it has a grip 19 for a tool,
in the embodiment shown a diametrical groove for a
screwdriver. Hereby the tap can be rotated thus in the
channel 7, that its ridge 16 can be turned stepless from the
position shown in Fig. 4 with its longitudinal direction
perpendicularly against the axial extension of the chamber
13 and to the position shown in Fig. 5, wherein the
longitudinal direction of the ridge coincides with the axial
extension of the chamber. In this manner it is possible
infinitely to set a flow section area between completely
open according to Fig. 4 and completely closed according to
Fig. 5.
In the outer side of the housing and adjoining the opening
of the channel 7 there is preferably provided a marking 20,
which can act as an index for establishing the current
rotational angle of the tap, and thereby the position for
the ridge 16 and the size of the slot 14a, by comparison
with the groove 19 provided diametrically in the tap.
In the manner now described has been created a simple
rotational damper, which shall operate with a dampening
medium, which at swinging motion of the links 4, by means of
the wing 12 rigidly connected to the pivot axle 6, is caused
to move through the slot 14a formed between the portion 14
of the pivot axle and the ridge 16 on the tap 15.
By using a visco-elastic compound as a damping medium
instead of the usual hydraulic oil, a number of advantages
are achieved. An appropriate visco-elastic compound is a
WO 96110969 ~ ~ ~ ~ ~ ~ ~ PCTlSE95101106
boron-siloxane-elastomer, marketed by the company blacker
Kemi AB, Stockholm, Sweden, under the trade name "Hiipfender
Kitt", as a therapeutic toy or a kneading lump, etcetera.
5 An advantage with such a visco-elastic compound is that it
does not require a big sealing accuracy, i.e. the
cooperating sealing surfaces need not have particularly
accurate tolerances, which means lower manufacturing costs
and furthermore a lower risk for leakages. The compounds
used even function thus, that compound tending to penetrate
out through the sealing slot under rapid swing motions,
again will pull itself into the sealed off space, after the
motion has ceased. Another advantage with this type of
visco-elastic compounds, which is very important a.n this
contest, is that when heavily kneaded, i.e. at a rapid swing
motion of the links 4 and therefore of the wing 12 on the
pivot axle 6, will exert a substantially bigger flow
resistance as compared to a slow motion.
From this it is also evident that a reduced flow through
area caused by the tap 15 and its diametrical ridge 16,
which increases the flow velocity, means a more forceful
kneading of the compound and thereby a bigger resistance to
the rotational motion.
However, the invention is not limited to this visco-elastic
compound, but other corresponding compounds with similar
properties can also be used.
In Fig. 6 is shown in cross section the upper attachment 2
with the members forming part thereof and belonging to the
rotation damper according to the invention, i.e. the pivot
axle 6 with its wing 12 and the cylindrical tap 15 and its
forward diametrical ridge 16 intended for adjusting the flow
area. The only difference as compared to the design
according to Fig s 4 and 5 is that the tap 15 in its outward
surface has a tool grip 19a in the form of a hexagonal
WO 96/10969 ~ ~ ~ '~ ~ ~ PCT/SE95/01106
6
recess. In the shown position of the tap 15 the flow area is
completely closed, as the ridge 16 extends axially along the
extension of the wing 12 and therefore has sealed off the ,
through-flow slot completely.
In Fig. 7 the pivot axle 6 is shown by itself in side view.
The invention a.s not limited to the embodiment shown and
described in connection thereto, but modifications may occur
within the scope of the accompanying claims.
Thus it is not necessary that the visco-elastic rotation
damper according to the invention has a wing attached to the
pivot axle, and which at the pivot motion of the joint tends
to displace the visco-elastic compound through a flow slot,
the size of which is adjustable in a manner such as
described, but the swing motion may be transferred in other
manners into a displacement of a visco-elastic compound
through a restrictable opening, e.g. by means of a piston
arrangement.
The tap 15 may furthermore, e.g. instead of or as a
complement to the ridge have inserted therein an adjustable,
restricted non-return valve, for setting the resistance
individually inboth directions.
The embodiment shown in the accompanying drawings and
described in connection thereto however is considered as a
well operating and from cost aspects advantageous solution.
