LEG PROSTHESIS AND KNEE JOINT FOR A LEG PROSTHESIS

Abstract: A leg prosthesis provided with a knee joint, which is on the one hand attached to an upper leg part and which is on the other hand attached to a lower leg part. The lower leg part can pivot with respect to said upper leg part, from an extended position to a flexed position. The knee joint is constructed in such a manner that the lower leg part and the upper leg part are initially moved away from each other when flexing from a substantially extended position. The knee joint may comprise four parallel pivot axes, whereby two lower leg pivot axes occupy a fixed position with respect to the first lower leg part and two upper leg pivot axes occupy a fixed position with respect to the upper leg part. Connecting elements pivotally connect each lower leg pivot axis to an upper leg pivot axis.

Description: LEG PROSTHESIS AND KNEE JOINT FOR A LEG PROSTHESIS The invention relates to a leg prosthesis provided with a knee joint comprising more than one single pivot axis, which knee joint is on the one hand attached to an upper leg part and which is on the other hand attached to a lower leg part, so that said lower leg part can pivot with respect to said upper leg part from an extended position to a flexed position of the leg prosthesis. A leg prosthes s of this type may be used by a person whose leg has been amputated in such a manner that only part of the upper leg is left. In that case the leg prosthesis is attached to the upper leg in that the upper leg part of the leg prosthesis comprises a fitting envelope of the upper leg stump. A knee "joint of this type may comprise a single pivot axis, but also many other constructions for effecting the flexing of the joint are possible. The leg prosthesis may be used for walking, whereby a swinging movement is used, which can be made by the stump of the upper leg. After the leg prosthesis has been put on the ground in forward direction, a step may be made by swinging the extended leg prosthesis rearward. When subsequently the leg stump is swung forward again, the leg prosthesis will flex and be swung forward again in flexed condition, after which the leg prosthesis is placed on the ground again in extended condition so as to make the next step. The leg prosthesis is primarily kept in extended condition during walking because the stump of the upper leg exerts a force on the leg prosthesis during said movement. When the upper lea is not kept m the correct position, wnen it is swung backwards too slowly, for example, there is a danger that the leg prosthesis will flex prematurely, that is, before the wearer pushes off with the leg prosthesis. The object of the invention is to provide a leg prosthesis which has greater stability during walking, as a result of which the hip muscles tire less quickly and the risk of missteps during walking is reduced. In order to accomplish that objective the knee joint is constructed in such a manner that the lower leg part and the upper leg part are initially moved away from each other when moving from a substantially extended position to a flexed position, so that a temporary extension of the leg prosthesis occurs. The consequence of this is that as long as the person's weight is entirely or partially supported by the leg prosthesis, the flexing of the leg prosthesis requires a greater force than is the case when the weight load on the leg prosthesis is smaller. The force required to initiate the flexing of trie leg prosthesis will vary according to tne weight to be supported by the leg prosthesis. The consequence of this during walking is that it requires a greater effort flex tne leg during the part of the step which is to be made with the leg prosthesis in extended position than is the case when said part of the step is completed and the person's weight comes to rest on the other leg, so that the leg prosthesis can be swung forward again. The invention may be implerrented by means of a leg prosthesis, wherein the lower leg part can pivot with respect to the upper leg part in a substantially vertical plane and wherein the knee joint is provided with four pivot axes extending substantially perpendicularly to said plane, whereby two lower leg pivot axes occupy a fixed position with respect to the lower leg part and two upper leg pivot axes occupy a fixed position with respect to the upper leg part, and wherein connecting elements pivotally connect each lower leg pivot axis to an upper leg pivot axis, so that the positions of the pivot axes in said plane form an irregular quandrangle having sides of a fixed length, whereby the pivot axes are positioned such, that the upper leg pivot axes are located closer to the lower leg part than the lower leg pivot axes in the extended position of the leg prosthesis. The term pivot axis used in this context is understood to mean the geometrical axis, which axis actually forms the central axis of one or more physical pivots about which the respective parts pivot. As a result of this form of construction according to the invention the upper leg part hangs in the lower leg part, as it were, when the leg prosthesis is in its extended position, whereby a tensile force is exerted on the aforesaid connecting elements between the pivot axes in question. When the leg prosthesis is flexed, the irregular quadrangle is deformed into a more elongated shape, as a result of which the two lower leg pivot axes will be positioned closer to the two upper leg pivot axes, seen in vertical direction, causing the lower leg part and the upper leg part to move slightly apart at the start of the flexing movement. According to another aspect of the invention tne mutual distance between the upper leg pivot axes is greater than the mutual distance between the lower leg pivot axes, or the mutual distance between the lower two pivot axes is greater than the mutual distance between the upper two pivot axes, seen m the aforesaid vertical plane and in the extended position of the leg. The consequence of this is that when the leg prosthesis is flexed, the lower leg part will remain slightly behind relative to the upper leg part, seen in the direction of walking. The invention relates to a leg prosthesis as well as to a knee joint to be used in a leg prosthesis. According to one aspect of the invention the knee joint may comprise a first base part and a second base part, whereby the connecting elements connect said base parts in such a manner that said base parts can pivot with respect to each other, whereby said first base part extends to within said second base part, so that said first base part is at least partially surrounded oy said second base part. It is thereby preferred to attach the lower leg part to said first base part and to attach the upper leg part to said second base part. This will be explained in more detail yet by means of an embodiment. According to another aspect of the invention three connecting elements are provided, whereby the two front pivot axes are interconnected by one connecting element ana whereby the two other pivot axes are interconnected by two spaced-apart connecting elements, seen in the direction of walking with the leg in its extended position. The first base part can thereby move between the two latter connecting elements, at least during the flexing of the leg prosthesis, whilst the presence of three connecting elements ensures a sufficiently stable connection. According to another aspect of the invention one base part may be provided with a stop, against which the other base part or a connecting elements butts m the extended position of the leg prosthesis. Said stop may be adjustable, so that the extended position of the leg prosthesis can be adjusted according to the wearer's personal preference, whereby a stable position is ensured with every setting. The leg prosthesis may be provided with spring means, which push the prosthesis to the extended position of the knee joint. Said spring may be a coil spring or a gas spring, which is on the one hand attached to the lower leg or to the upper leg and which is on the other hand connected to a suitable part of the knee joint. Such a spring may make it easier for the leg prosthesis to return to its extended position before being placed on the ground during walking. Further aspects of the invention, which may be used both separately and in combination with each other, are disclosed in the description of the Figures and are defined in the claims. Hereafter an embodiment of a knee joint and the movement of a leg prosthesis will be described by way of illustration with reference to the drawing. Figure 1 is a front view of the knee joint; Figure 2 is a rear view of the knee joint; Figure 3 is a sectional view along line III-III in Figure 2; Figure 4 is a plan view of the knee joint; Figure 5 is a bottom view of the knee joint; Figure 6 shows the movement of a leg prosthesis; and Figures 7 - 11 are perspective views of the knee joint according to Figures 1 - 5. The Figures are merely schematic representations of the embodiment, with like parts being numbered alike in the various Figures. The knee joint according to the invention is provided with a first fastening means 1 for attaching the knee joint to a lower leg part, and with a second fastening means 2 for attaching the knee joint to an upper leg part of the leg prosthesis. Said fastening means 1, 2 may be constructed in various ways, in the present embodiment said fastening means are shaped such that they can be clamped in a correspondingly shaped part of the respective leg part or be secured thereto in a different manner. Of course also screwed connections or bolted connections or the like are possible. In the embodiment said first fastening means 1 is connected to a first base part 3, which extends to within the second base part 4, which second base part partially surrounds said first base part 3, as it were. The front side 5 of second base part 4 thereby extends beyond the upper end of first base part 3, up to the front upper leg pivot axis 6, at the location of which the front connecting element 7 is pivot-mounted to base part 4. The other end of said front connecting element 7 is pivot- mounted to the first base part 3 at the location of the front lower leg pivot axis 8. Two rear connecting elements 9 are provided at the rear side of the knee joint, which elements are on the one hand pivotally journalled in first base part 3, at the location of rear lower leg pivot axis 10, and which are on the other hand pivot-mounted to second base part 4 at the location of rear upper leg pivot axis 11. In particular from Figure 3 it is apparent that when base part 4 is kept stationary, base part 3 can pivot to the right, whereby pivot axes 6 and 11 remain stationary, whilst pivot axes 8 and 10 follow the pivoting movement of base part 3. In the extended position of the knee joint as illustrated in the Figures first base part 3 is prevented from pivoting to the left (Figure 3) in that the front connecting element 7 butts against stop 12, which stop 12 is secured to base part 4. As a result of this connecting element 6 can only pivot to the right with respect to pivot axis 6, seen in Figure 3. Said stop may be provided on other parts of the knee joint for the same purpose, for example, the one base part may strike a stop on the other base part. If desired a stop 12 may be provided with an adjus t ing screw or another means by which the extended position of the leg prosthesis can be slightly adjusted to a personal preference. Figure 6 schematically shows the flexing movement of a leg prosthesis. This Figure schematically shows six positions side by side, wherein the upper leg part and the lower leg part are represented by triangles 15, 16 having fixed sides, so that said triangles cannot oe deformed, whilst the knee j oint is represented by an ^rregular quadrangle having fixed sides and pivot axes 6, -, 10, II on the corner points. A leg prosthesis in extended position is thus schematically illustrated on the left in Figure 6. Upper leg part 15 and lower leg part 16 are practically in line thereby. The two leg parts 15, 16 overlap in the knee joint 17, because lower leg pivot axes 8, 10 are positioned higher than upper leg pivot axes 6, 11. Furthermore the mutual distance between the two lower leg pivot axes 8, 10 is smaller than the mutual distance between the two upper leg pivot axes 6, 11. Arrow 18 in Figure 6 indicates in what direction the upper leg part will pivot in order to flex the leg prosthesis. It is apparent from the successive situations shown in Figure 6, seen from the left to the right, that the length of the leg prosthesis initially increases during flexing, whilst upon further flexing of the leg prosthesis the length of the leg prosthesis becomes smaller than the original length in extended position. In this latter position the leg prosthesis can thus be readily swung forward during walking. By varying the position of pivot axes 6, 8, 10, 11 the extent to which the described elongation of the leg prosthesis takes place at the beginning of the flexing movement can be varied as desired. Figures 7 - 11 are perspective views of the knee joint according to Figures 1 - 5, wherein the various parts are indicated by the same numerals. The illustrated embodiment of the invention should be considered as an example only, variants and other constructions and other embodiments of the invention are possible within the scope of the invention.

Claims: CLAIMS 1. A leg prosthesis provided with a knee joint comprising more than one single pivot axis (6; 8; 10; 11) , which knee joint is on the one hand attached to an upper leg part and which is on the other hand attached to a lower leg part, so that said lower leg part can pivot with respect to said upper leg part, from an extended position to a flexed position of the leg prosthesis, wherein the knee joint is constructed in such a manner that the lower leg part and the upper leg part are initially moved away from each other when moving from a substantially extended position to a flexed position. 2. A leg prosthesis according to claim 1, wherein said lower leg part can pivot with respect to said upper leg part in a substantially vertical plane and wherein said knee joint is provided with four pivot axes (6,8,10,11) extending substantially perpendicularly to said plane, whereby two lower leg pivot axes (8,10) occupy a fixed position with respect to the lower leg part and two upper leg pivot axes (6,11) occupy a fixed position with respect to the upper leg part, and wherein connecting elements (7.9) pivotally connect each lower leg pivot axis (8.10) to an upper leg pivot axis (6,11), so that the positions of the pivot axes (6,8,10,11) in said plane form an irregular quandrangle having sides of a fixed length, whereby said pivot axes (6,8,10,11) are positioned such, that the upper leg pivot axes (6,11) are located closer to the lower leg part than the lower leg pivot axes (8,10) in the extended position of the leg prosthesis. 3. A leg prosthesis according to any one of the preceding claims, characterized in that the mutual distance between the the lower two pivot axes (6,11) is greater than the mutual distance between the upper two pivot axes (8,10), seen in the aforesaid vertical plane and in the extended position of the leg. 4. A leg prosthesis according to any one of the preceding claims, characterized in that said knee joint comprises a first base part (3) and a second base part ( A ) , whereby the connecting elements (7,9) connect said base parts (3,4) in such a manner that said base parts (3,4) can pivot with respect to each other, whereby said first base part (3) extends to within said second base part (4), so that said first base part (3) is at least partially surrounded by said second base part (4) . 5. A leg prosthesis according to claim 4, characterized in that said lower leg part is attached to said first base part (3) and that said upper leg part is connected to said second base part (4) . 6. A leg prosthesis according to any one of the preceding claims, characterized in that three connecting elements (7,9) are provided, whereby the two front pivot axes (6,8) are interconnected by one connecting element (7) and whereby the two other pivot axes (10,11) are interconnected by two spaced- apart connecting elements (9), seen in the direction of walking with the leg in its extended position. 7. A leg prosthesis according to claim 4, characterized in that one base part (3;4) is provided with a stop (12), against which the other base part (4;3) or a connecting element (7,9) butts in the extended position of the leg prosthesis, whereby said stop (12) may be adjustable. 8. A leg prosthesis according to any one of the preceding claims, characterized in that spring means are provided, which push the prosthesis to its extended position. 9. A knee joint for a leg prosthesis as defined in any one of the preceding claims, provided with first fastening means (1) for attaching the knee joint to a lower leg part, and with second fastening means (2) for attaching the knee joint to an upper leg part. 10. A knee joint according to claim 9, comprising a first base part (3) and a second base part (4), on which said first fastening means (1) and said second fastening means (2) respectively are provided, whereby connecting elements (7,9) connect said base parts (3,4) in such a manner that said base parts (3,4) can pivot with respect to each other, whereby said first base part (3) extends to within said second base part (4), so that said first base part (3) is at least partially surrounded by said second base part (4), and furthermore comprising four parallel pivot axes (6,8,10,11) , whereby two lower leg pivot axes (8,10) occupy a fixed position with respect to said first base part (3) and two upper leg pivot axes (6,11) occupy a fixed position with respect to said second base part (4), and wherein connecting elements (7,9) pivotally connect each lower leg pivot axis (8; 10) to an upper leg pivot axis (6;11), so that the positions of the pivot axes (6,8,10,11) in a plane perpendicularly to their direction form an irregular quandrangle having sides of a fixed length, whereby said pivot axes (6,8,10,11) are positioned such, that said upper leg pivot axes (6,11) are located closer to said first fastening means (1) than said lower leg pivot axes (8,10) in the extended position of the knee joint.

Inventors: GROOTENBOER HENDRICUS JOHANNES, HENDRIKS PAUL JOSEPHUS HENDRIK, GROOTENBOER, HENDRICUS, JOHANNES, HENDRIKS, PAUL, JOSEPHUS, HENDRIKUS
Applicants: GROOTENBOER HENDRICUS JOHANNES, HENDRIKS PAUL JOSEPHUS HENDRIK, UNIV TWENTE, GROOTENBOER, HENDRICUS, JOHANNES, HENDRIKS, PAUL, JOSEPHUS, HENDRIKUS, UNIVERSITEIT TWENTE
Application year: 1996
Main classification: A61F2
IPC codes: A61F2