ARTIFICIAL JOINT WITH A HYDRAULIC DAMPING CYLINDER

Abstract: A device for damping of the turning movement of a joint, for example an artificial knee joint (10), is designed in such a way that the shaft (21) of one of the pivot points of the joint is provided with a gear-wheel (30) which in a hydraulic cylinder (1) influences a piston (27) connected to a rack-gearing (28). Channels (40, 41) with chokes and back valves (71, 91; 72, 92; 75, 93) connect the two sides of the piston of the hydraulic cylinder making possible adjustable damping in several steps for different parts of the turning movement. Moreover, a compact design of joint and damping cylinder is achieved. The application also refers to artificial joints including abovementioned devices for damping of the turning movement, especially artificial knee joints of the polycentric type with seven pivot points.

Description: Artificial Joint with a Hydraulic Damping Cylinder. The present invention relates to an artificial joint equipped with a hydraulic damping cylinder and a hydraulic damping cylinder designed to be a part of an artificial joint, especially of such an artificial knee joint, in which it is not possible to install conventional damping cylinders with a cylinder block into and out of which a piston rod is reciprocating. The present invention is especially adapted to be used with artificial knee joints of the type with seven pivot points which is further described in the Swedish patent application no. 91001183-4 and PCT/SE91/00240, but damping cylinders according to the present invention can also with advantage be utilized with artificial joints of other types such as for example with polycentric knee joints with four pivot points and even with joints having one single pivot point. The artificial joint type with seven pivot points which is described in the above mentioned patent publication makes a great progress per se in relation to the previous state of the art. Equipped with a hydraulic damping cylinder as described below and according to the claims the joint is also given a control of the swing phase which, together with the quality of stability of the joint, produces an artificial knee joint which lies very close to a natural leg functionally despite the lack of active components to replace muscle force. It is known in the art to arrange hydraulic damping cylinders with other artificial joints, see for instance EP 0097226. In its simplest design the damping cylinder comprises a piston and channels with chokes in the cylinder between the opposite sides of the piston. The present invention also relies on this principle. But at the present invention no piston rod moving into or out of the damping cylinder is used, because it will involve disadvantages and difficulties to build such conventional damping cylinders into for instance such knee joints with multiple pivot points as mentioned above. It has also been known for a long time, from the Swiss patent publication no. 248 586, to arrange hydraulic damping cylinders in such a way that the longitudinal movement of the piston is directly transferred to a turning movement by means of gear teeth on the piston in mesh with a gearwheel. This construction, mainly intended for door closers, has a built in spring with a spring force acting on the piston in one direction while the piston includes a spring loaded valve opening on movement against the spring force and a channel damping the return movement. Despite this construction has been known since 1947, before the present invention no similar construction has been used with an artificial joint, no less been adapted for it according to the present invention. An object of the present invention is to achieve an artificial joint with multiple pivot points integrated with a hydraulic damping cylinder in such a way that it not to any extent worth mentioning adds length to the joint or otherwise deteriorates the function of the joint. A second object is to achieve a damping cylinder, the damped movement of which consists of a turning of an axis instead of an axial movement, whereby tightening against leakage of hydraulic oil better can be achieved. A third object of the present invention is to bring about a damping cylinder in which the damping can take place in several stages with different magnitude. A further object of the invention is to place the damping cylinder in such a way in the joint that heat produced in it will be abducted in order not to reach too high a temperature. These and other objects are achieved with'an artificial joint and a damping cylinder given characteristics according to the claims following after the description. The invention will now be described more in detail with reference to the following drawings, in which Fig. 1 shows a joint with seven pivot points comprising 5 a pumphouse/upper bearing bridge (1) containing a damping cylinder according to the invention, Fig. 2 shows partly in section the pump house in Fig 1, Figs. 3-7 show different views, sections and details thereof, 10 Fig. 8 shows the shaft with gear-wheel of Fig. 2, Fig. 9 shows piston with rack in Fig. 2, and Fig. 10 shows how channels and valves are arranged in the pump house. 15. Fig. 1 shows an embodiment of such a joint 10, which is described more in detail in the above mentioned Swedish and PCT patent application. It presents seven pivot point axes 2- 8, one upper bearing bridge 1, a front link 9 with two pivot point axes, a back link 11 with three pivot point axes, a 20 cradle or balance 12 with three pivot point axes, which balance 12 joins the links 9 and 11 with a shank holder 13 at its upper pivot point axis 5 and a lower locking link 14 with two pivot point axes connecting the back link 11 with the shank holder 13 at its lower pivot point axis 8. As is more 25 in detail apparent from the above mentioned patent applications this construction with seven pivot points constitutes an especially advantageous artificial knee joint. Known cylinder-piston-arrangements for regulation and damping 30 of the swing movement of the lower-leg part can hardly be built into this joint unless the construction will be heavy and clumsy or it will be too long. The hydraulic unit forming the damping cylinder according to the invention therefore has been built into the upper bearing bridge 1 which will thereby 35 also work as a pump house as is shown more closely in Fig. 2. Thus, the upper bearing bridge or pump house 1 is modelled in such a way that it has been provided with a cylindrical, drill hole 23 perpendicular to and partly intersecting the hole for pivot point axis 2. The open side of the drill hole 23 is closed by a lid 24. The drill hole 23, which constitutes a hydraulic cylinder, contains a piston device 20 comprising a piston 27 with a for hydraulic fluid tightening fit in the drill hole 23. The piston device 20 also includes a second part 28 extending from the piston 27 and forming part of the elongation of the piston with an axially arranged rack- gearing part 29. In the hole for the pivot point axis 2 a shaft 21 is arranged with a central gear-wheel part 30 meshing with rack-gearing part 29. Turning movement of shaft 21 is damped thereby that the movement of the piston 27 is influenced by a choke of the flow in a channel for hydraulic fluid connected with the drill hole 23 on both sides of the piston 27 through the orifices 25 and 26. Sealings are arranged to prevent the hydraulic fluid to escape at the shaft 21. A threaded throat 22 for attachment of a prothesis sleeve is arranged on the upper side of the pump housing 1. On the detailed figures concerning the pump housing 1 Fig. shows a view from the side, Fig. 4 view from above, Fig. 5 a central section C-C in Fig. 4, Fig. 6 shows a view from the front while Figs. 7A and 7B show section A-A and section B-B respectively. With reference to Figs. 3-5 is shown that the main part of the pump housing 1 seen from above consists of a rectangular part 31, from which the threaded throat 22 and two side parts 32 and 33 extends. The threaded throat 22 contains a bevelled surface 34 reaching from the threaded area to a central, countersinked surface 35. The two side parts 32 and 33 are drilled for the pivot point axis 3 and between them is space for the back link 11 for three pivot points. As appears from Figs. 6, 7A and 7B two longitudinal channels 40 and 41 are drilled from the front end of the pump housing 1 parallell to the cylindrical drill hole 23. The channels 40 and 41 are at 42, 43 and 44 and 45 respectively in connection with transversal channels 46, 47, 48 and 49 which in turn emerge into the central drill hole 23. Preferrably one more transversal channel 50 can be arranged and be in communication with the channel 40. See further the description in connection with Fig. 10. As can be seen in Fig. 8 the shaft 21 is composed of a screw 60 with a main part forming one end of the shaft provided with an internally threaded hole 61, the gear-wheel 30 threaded on to the screw 60 and a longish nut sleeve 63 threaded on the thread of the screw 62 forming the other end of the shaft 21. The screw 60, the gear-wheel 30 and the nut sleeve 63 are joined together making a strong, integrated part, for instance with a thread glue. It is also possible to make the part in such a manner that the gears do not reach out of the perimeter of the shaft, whereby the shaft and the central gear-wheel preferrably are made in one piece. As shown in section in Fig. 9 the piston 20 is preferrably made of one metal piece 66, and one sleeve part 67 surrounding the front and cylindrical part of the metal piece and that partly cylindrical part otherwise forming the rack- gearing 29. The sleeve part 67 ir preferrably made of a material with good sealing and wearing qualities, even if a metal chip or the like is present. Examples of such materials are polyacetate and polyurethane plastics. The piston part of the metal piece 66 is provided with a threaded hole 65 into which a screw 68 is threaded holding the sleeve part 67. The function of the channels 40 and 41 and the transversal channels and their connections with the hydraulic cylinder is shown in detail in Fig. 10. The transversal channels 46-50 are adapted for taking up adjustable screws 71-75 fitted with sealings in the form of o-rings 81-85 placed in grooves. The adjustment screws 71,72 and 75 are designed with ball seats and balls 91,92 and 93 working as chokes and back valves, while the adjustment screws 73 and 74 at the outlets are provided with filter 95 and magnet 94 respectively for ensuring a good function. The damping function of the device is such that when the piston 27 moves upwards in the figure, corresponding to a movement backwards of the shank, the movement is first damped depending on the adjustment of the adjustment screws 71 and 72 and thereafter, when the piston has moved past the outlet at the adjustment screw 72, the movement is damped stronger due to the choke at the adjustment screw 71 alone. In order to get a smooth change- over when the damping is increased the sleeve part 67 of the piston 20 can be shaped with a wedge-formed groove (not shown in the figures) tapering from the end of the piston at that part of the piston which is moving past the outlet at the adjustment screw 72. Movement in the other direction is damped only by the choke at the adjustment screw 75. In order to prevent damages if too heavy choke is adjusted with the adjustment screws 71,72 or 75 one or more security valves, for example in the form of spring loaded ball valves, may also be arranged in order to put an upper limit to the pressure difference between the both sides of the piston 20. Instead of the adjustment screws 71, 72 and 75, which together with ball seats and the balls 91, 92 and 93 both act as chokes and back valves, conventional back valves with spring loaded balls can be used, whereby no adjustable choke is achieved by the screws 71, 72 and 75 but the degree of damping is constant depending on the dimensions of the channels with possible permanent chokes, or adjustable in another way. One embodiment of the invention has now been described in detail. The invention can be carried out in many different ways, for example may damping cylinders according to the invention be used with a lot of different types of joints. The scope of the invention is only to be restricted by the wording of the claims.

Claims: CLAIMS 1. A device for damping of the turning movement of a joint, for example an artificial knee joint with at least one first pivot point, using a hydraulic damping cylinder, characterized in that the shaft hole (2) of the first pivot point extends transverse a hydraulic cylinder (20), that a shaft (21) is arranged in the shaft hole of the first pivot point, a link (9) is locked to the shaft (21) which is connected to a gear-wheel (30) which at least partly extends into the hydraulic cylinder (23), that the gear-wheel (30) is meshing with a rack-gearing (29) connected with the piston (27) of the hydraulic cylinder, and that movement of the piston (27) is influenced by the resistance against the flow of hydraulic fluid in channels (40, 41) for the hydraulic fluid leading from one side of the hydraulic cylinder to the other, and that back valves (91,92,93) are arranged in the channels in such a way that hydraulic fluid is lead in different channels for each direction of movement. 2. A device according to claim 1, characterized in that the movement of the piston (27) is influenced by the resistance from at least one adjustable choke (71, 91;72 , 92 ; 75,93) in at least one of the channels (40,41). 3. A device according to claim 2, characterized in that at least one of the channels (40) for hydraulic fluid also has a second outlet into the hydraulic cylinder that can be provided with an adjustable choke (72,92) making possible selective damping for different segments of the turning movement. 4. A device for damping of the turning movement of a joint, for example an artificial knee joint, using a hydraulic damping cylinder, characterized in that the hydraulic damping cylinder (1) is provided with at least one channel (40,41) for hydraulic fluid connecting one side of the hydraulic cylinder with the other, that adjustable chokes and back valves (71, 91;72, 92;75, 93) are arranged to ' regulate the flow of hydraulic fluid in such a way that the degree of damping can be adjusted and that at least one extra outlet is arranged between channel and cylinder so that it is closed by the piston of the damping cylinder making possible different damping for different parts of the piston movement. 5. A device according to claim 4, characterized in that the piston (20) of the damping cylinder is shaped with a wedge-shaped groove extending from the front end of the piston and backwards, situated opposite the extra outlet and giving a smoother closing of the extra outlet when the piston (20) moves by. 6. A device for damping of the turning movement of an artificial joint, characterized in that one of the legs of the joint is firmly connected with a hydraulic cylinder, that a second of the legs of the joint in connected to the first leg with a shaft connected to a gear-wheel which at least partly extends through the hydraulic cylinder, that the gear-wheel is meshing with a rack-gearing connected to the piston of the hydraulic cylinder, and that the movement of the piston is influenced by the resistance in at least two channels, alternatingly leading hydraulic fluid from one side of the hydraulic cylinder to the other depending on the direction of movement of the piston. 7. A device according to claim 6, characterized in that movement of the piston is influenced by the resistance from at least one adjustable choke in at least one of the channels. 8. A device according to claim 6 or 7, characterized in that at least one of the channels for hydraulic fluid has one further outlet in the hydraulic cylinder which can be provided with an adjustable choke making possible selective damping of the turning movement for different segments of the turning movement. 9. An artificial joint, particularly knee joint, characterized in that it includes a device for damping of the turning movement of the joint according to any of claims 1 to 8. 10. An artificial joint according to claim 9, characterized in that it is constituted by a joint of the polycentric type with seven pivot points .

Inventors: GRAMNAES FINN, GRAMNAES, FINN
Applicants: GRAMNAES FINN, GRAMNAES, FINN
Application year: 1993
Main classification: A61F2
IPC codes: A61F2, F16F9