A ROTATION DAMPER IN A TOGGLE JOINT PROSTHESIS

Abstract: Rotation damper for toggle joints prosthesis (1), of the type, which is arranged for swing phase control of the prosthesis, and incorporates at least one chamber (13) having a damping medium, arranged to be displaced through a restriction (14a) at a swing motion of at least one pivot axle (6) in the prosthesis, whereby the damping medium is a visco-elastic compound, having an ability to exert a bigger resistance at rapid motion processes as compared to slower processes.

Description: 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. 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 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 is required a dampening device for reducing the stresses upon the joint system. For this purpose a rotation damper according to the invention can preferably be provided in 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 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 boron-siloxane-elastomer, marketed by the company Wacker Kemi AB, Stockholm, Sweden, under the trade name "Hϋpfender Kitt", as a therapeutic toy or a kneading lump, etcetera. 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 in 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 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 is 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 in both 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.

Claims: C L A I M S 1. Rotation damper for toggle joint prosthesis (1), of the type, which is arranged for swing phase control of the prosthesis, and incorporates at least one chamber (13) having a damping medium, arranged to be displaced through a restriction (14a) at a swing motion of at least one pivot axle (6) in the prosthesis, c h a r a c t e r i z e d t h e r e i n, that the damping medium is a visco-elastic compound. 2. Rotation damper as claimed in claim 1, c h a r a c t e r i z e d t h e r e i n, that the damper incorporates a pivot axle (6), arranged in a sealed off chamber (13) and provided with a projecting wing (12), arranged to follow the pivot movement of the pivot axle and thereby to displace the damping medium through a restriction in the form of a slot (14a) with limited flow area. 3. Rotation damper as claimed in claim 2, c h a r a c t e r i z e d t h e r e i n, that the size of the slot (14a) is adjustable. 4. Rotation damper as claimed in claim 3, c h a r a c t e r i z e d t h e r e i n, that the size of the slot (14a) is infinitely adjustable between a completely open slot and a completely closed slot. 5. Rotation damper ac claimed in claim 3 or 4, c h a r a c t e r i z e d t h e r e i n, that the size of the slot (14a) is adjustable by means of a member (15, 16), which is operable from outside the prosthesis. 6. Rotation damper as claimed in anyone of the preceeding claims, c h a r a c t e r i z e d t h e r e i n, that said chamber (13) is formed by a cylindrical bore ( 8 ) through a portion (2) of the toggle joint prosthesis, that said pivot axle (6) extends through the bore and supports sealing means (11) arranged to seal off the chamber (13) axially, and that the wing (12) of the pivot axle (6) is directed radially and extends axially between said sealing means (11). 7. Rotation damper as claimed in anyone of the preceeding claims, c h a r a c t e r i z e d t h e r e i n, that the restriction or slot (14a) is formed between the portion of the pivot axle (6) situated in the chamber ( 13 ) and a substantially cylindrical tap (15) projecting through a channel (7) opening in the wall of the chamber and in the front end surface provided with a diametrically extending ridge (16), arranged to engage the portion of the pivot axle situated in the chamber, and that the ridge (16) by rotation of the tap (15) in its channel (7) can be caused to vary the size of the slot (14a). 8. Rotation damper as claimed in claim 7, c h a r a c t e r i z e d t h e r e i n, that the tap (15) is secured in its axial position in the channel (7) by means of locking member ( 18) . 9. Rotation damper as claimed in claim 7 or 8 , c h a r a c t e r i z e d t h e r e i n, that the tap (15) with its end turned away from the ridge (16) is arranged to be accessible from the outside of the channel, and is provided with a key grip (19), arranged to indicate the position of the ridge (16) against a mark (20) on the outside of the housing and thereby the momentary flow through area of the slot (14a).

Inventors: GRAMNAES FINN, GRAMNAES, FINN
Applicants: GRAMNAES FINN, GRAMTEC INNOVATION AB, GRAMNAES, FINN
Application year: 1995
Main classification: A61F2
IPC codes: A61F2, F16F9