SHIFT DEVICE FOR A PROSTHETIC LIMB

Abstract: A shift device for a prosthetic limb comprises: first and second plates (10, 12) having adjoining flat faces in sliding contact. Spaced parallel ribs (14) on an outer face of each plate (10, 12) define a slideway (16). Guides in the slideways (16) of the first and second plates (10, 12) enable the plates (10, 12) to move generally at right angles to one another. The guides include first and second guide bars (26) slideably received in each slideway (16). One or more longitudinal slots (20) in each slideway (16) permit limited relative translational movement of the plates (10, 12). Clamping screws (30) pass through each slot (20) of each of the first and second plates (10, 12) into the guide bar (26) in the slideway (16) of the other plate (12, 10). The clamping screws (30) are releasable to allow relative movement of the plates (10, 12) and on re-tightening immobilise the plates (10, 12).

Description: This invention relates to a shift device for a prosthetic limb, which is particularly though not exclusively intended for use as part of a prosthetic leg. Such a device produces a shift of its movable components on one plane without movement of the components in a direction orthogonal to that plane. A shift device that works by a combination of rotational and translational movements is described in Patent Specification No. GB-A-2162069 (Vessa). This device comprises (inter alia) two cooperable members having adjoining flat faces in sliding contact whereby a sliding relative movement between these two members can take place (in only one direction) and is assisted by a screw which is slideably received in an oversized slot. A shift device that works by a multiplicity of ribbed plates defining an orthogonal pair of linear bearings is described in Patent Specification No. GBA-1028421 (Rubery Owen). This invention provides a shift device whose principal components are a pair of plates each of the same fundamental form as the other and that can be released for relative movement and refixed simply by undoing and re-tightening clamping screws. Accordingly the invention provides a shift device for a prosthetic limb comprising: first and second plates in face to face sliding contact; means on each plate defining a slideway; means guiding the slideways of the first and second plates for movement generally at right angles to one another; said means including first and second guide bars slideably received in each slideway; means in each slideway defining one or more longitudinal slots whose length permits limited relative translational movement of the plates; and clamping screw means passed through each slot of each of the first and second plates into the guide bar in the slideway of the other plate, said clamping screw means being releasable to allow relative movement of the plates and on re-tightening immobilising the plates. The above device has the further advantage of occupying only a short distance along the limb. Advantageously there are two open slots in each slideway extending from its ends partway therealong and each guide bar receives a pair of clamping screws passed through the slots. Each plate may be flanged to either side of the slideway and elongate closed slots through which the clamping screws pass are formed in each flange and advantageously the clamping screws are a clearance fit in the elongate closed slots to permit limited relative rotational movement of the plates. Each plate may be formed with through-holes for attachment of adjacent limb parts. A compact article may be made if each plate is formed with four through holes disposed in a pattern that is offset relative to a pattern of slots in the plate so that the plates are movable between one extremity of their relative travel when the fixing holes are aligned and other positions within the range of relative travel where the fixing holes are offset. The holes in the first plate may be plain and have larger diameter counterbores from the blind face of the plate for receiving a head of an eventual clamping screw, the second plate having at least one relatively large diameter through-hole movable into register with the counterbores to permit clamping screw insertion and to give key or screwdriver access to the head. For fine adjustment of the relative translational position of the first and second plates the shift device may be used in association with releaseable jacking means attached to one of the plates at an end of a slideway and including a jacking screw registering with the guide bar therein for effecting controlled translational movement of the other plate. The jacking means are normally used in pairs attached to opposed ends of the slideway and may be removed when the prosthetist is satisfied with the alignment of the limb. The invention also provides a prosthetic limb in which a shift device as aforesaid is fitted between a knee joint and upper parts of the leg such as a stump socket. An alignment device may then be attached between the knee joint and lower parts of the leg, said alignment device permitting adjustment of the angle between the knee and lower parts of the leg in an anterior-posterior and in a medial-lateral plane. Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figures 1 and 2 are perspective views of a shift device according to the invention shown exploded and assembled respectively; Figure 3 is a plan of a clearance plate forming part of the shift device of Figures 1 and 2 and Figure 4 is a transverse section of a first form of the plate on the line A-A of Figure 3; Figure 5 is a plan of a tapped plate forming part of the shift device of Figures 1 and 2 and Figure 6 is a transverse section of the plate on the line B-B of Figure 5; Figure 7 is a side view of the knee region of a leg prosthesis showing a socket cup, shift device, prosthetic knee and alignment device; and Figure 8 is a view of a pair of plates of a second form. In the drawings, a shift device for a prosthetic limb comprises first and second plates 10, 12 each generally octagonal in plan and having adjoining planar faces in sliding contact with one another. Each plate 10, 12 has on its visible face a central slideway 16 defined between a pair of spaced parallel ribs 14 that extend across the plate. Each rib 14 has a flat central region 14a and tapered end regions 14b. Beyond the ribs 14 the plates 10, 12 are formed with side flanges 18. Slots 20 extend from the ends of the slideway 16 partway towards its middle and are directed along the centre line of the slideway. The flanges 18 are formed with oval slots 22 midway therealong and directed parallel to the ribs 14. End bores 24 are formed in the ribs 14. In the assembled device the plates 10, 12 are superposed with their slideways 16 directed generally at right angles to one another and with the slots 16 of one plate in register with the slots 22 of the other plate. A guide bar 26 with threaded holes 28 adjacent its ends is a sliding fit in each slideway 16. Clamping screw 30 fit from the visible face of one plate 10, 12 through slots 22 of that plate and through slots 20 of the other plate 12, 10 into the guide bar 26 of the other plate 12, 10 where they are inserted into the holes 28. A thrust plate 32 and spring washer 34 fit on the stem of each screw 30. Each plate is capable of a limited translational movement relative to the other in an X or Y direction on release of the screws 30 which slide along the slots 20, 22, the plates 10, 12 being movable in either direction at 90° independently of each other. They can also rotate, preferably by about ±10° with respect to each other because the slots 22 are made wider than the stems of the screws 30. Retightening the screws urges the plates 10, 12 together so that the friction of their abutting surfaces prevents further movement. It will be noted that the plates 10, 12 are identical except for the mounting hole details described below and all the slots 20, 22 and slideway 16 are straight and parallel. During setting up of the limb it is desirable to provide a fine adjustment for use by the prosthetist. For this purpose a jack plate 35 is attached to either end of a plate 10 or 12 by insertion of bolts 37 through plain holes 39 into the bores 24. A further threaded hole 41 in the plate 35 is aligned with the slideway 16 so that a jacking screw 43 may be brought into contact with an end of the guide bar 26 and thereafter tightened to displace the guide bar 26 as required. Although a single jacking assembly is sufficient to displace one guide bar 26 in one direction at a time, they are conveniently used in pairs with one jacking screw 43 being loosened while the other one is tightened. Furthermore, a pair of jacking devices fitted to adjacent ends of the plates 10, 12 preserves a predetermined X and Y dimension if the shift device is subsequently freed or disassembled, although rotational position is not preserved. The structure of the first plate 10 is further shown in Figures 3 and 4. Each region 14a of the means 14 is formed with a pair of clearance holes 45 from its visible face to accept threaded shanks of clamping screws whose heads are inserted from the blind face into relatively large diameter counterbores 47. Figures 5 and 6 show the structure of the second plate 12 which is formed in its regions 14a with two pairs of threaded bores 49. Midway between the holes 49 of each pair a through-hole 51 is formed in the region 14a, the diameter of the hole 51 (Figure 5) being equal to that of the counterbore 47. In the assembed shift device the plates 10, 12 can be slid so that the holes 51 register with each pair of counterbores 47 in turn, permitting a screw to be inserted via a hole 51 into the counterbore 47 and clearance hole 45. There is then screwdriver or key access through the hole 51 to the head of the screw which may be engaged in and tightened into a threaded bore of an adjacent limb component. This arrangement permits the shift device to be fitted to a component such as a knee prosthesis where restricted screwdriver access does not permit screws to be inserted through the component into threaded bores like the bores 49 of plate 12. As shown in Figure 7, the shift device of the invention generally indicated by the reference numeral 55 may advantageously be used between a socket attachment cup 57 and the top member of a prosthetic knee 59 to permit the axis of the socket to be shifted in an anterior/posterior plane and/or in a medial lateral plane and/or to be rotated relative to the knee. Such a knee may be a uniaxial knee as described in Specifications EP-A-0243081 and EP-A-0219335 or it may be a 4-bar knee as described in specification EP-A-0243081. It has the advantage of occupying a short axial length along the leg which means that it can be used for many patients of differing stump length without undue displacement of the prosthetic knee centre from its height in the natural leg. The underside of the knee unit may be provided with an alignment device 60, conveniently a ball and socket device as described in Specification EP-A-0224373 the female part of the device being attached to the knee and the male part of the device having a socket that fits onto a shin tube. The shift device may also be used between a socket and a shin part of an artificial leg for a below-knee amputee. It will be appreciated that modifications may be made to the embodiment described above without departing from the invention, the scope of which is defined in the appended claims. For example, a second form of the shift device is shown in Figure 8. It may be noted in Figure 3 that the pattern of clearance holes 45 and counterbores 47 defining an attachment position for upper or lower limb components is positioned at the centre of plate 10, 12 and is symmetrically located with reference to the slots 20, 22. The position where the holes 45 of one plate are disposed coaxially with the holes of the other plate is seen in Figure 2 and it may be seen that displacement of plate 10 or 12 in either direction from that position is catered for. It has been found that the provision of such bidirectional adjustment is unnecessary and that a more compact form of the plates 10a, 12a (Figure 8) may be made in which the slots 20a, 22a are half the length shown in Figures 3 and 5 and the pattern of fixing holes 45a, 49a is offset so that its centre line 61 coincides with one end of the oval slots 22a. With this arrangement, displacing the plates 10a, 12a so that the clamping screws 30 (Figure 1) from one end of the oval slots 22a to another moves the counterbore 47a of plate 10a and bore 49a of plate 12a from an aligned condition to a displaced position. For a maximum displacement in X and Y directions of x and y, the plates establish a displacement vector between (0, 0) and (x, y). Displacement vectors in the other three quadrants (x, -y); (-x, y); and (-x, -y) can be obtained by removing the alignment device from the upper and lower limb components and re-fastening it in a new one of the four possible angular positions defined by fixing holes or bores 47a, 49a.

Claims: 1. A shift device for a prosthetic limb comprising: first and second plates (10, 12) having adjoining flat faces in sliding contact; means (14) on an outer face of each plate (10, 12) defining a slideway (16); means guiding the slideways (16) of the first and second plates (10, 12) for movement generally at right angles to one another; said means including first and second guide bars (26) slideably received in each slideway (16); means in each slideway (16) defining one or more longitudinal slots (20) whose length permits limited relative translational movement of the plates (10, 12): and clamping screw means (30) passed through each slot (20) of each of the first and second plates (10, 12) into the guide bar (26) in the slideway of the other plate (12, 10), said clamping screw means (30) being releasable to allow relative movement of the plates and on re-tightening immobilising the plates. 2. A device according to Claim 1, wherein there are two slots (20) in each slideway (16) extending from its ends partway therealong and each guide bar (26) receives a pair of clamping screws (30) passed through the slots. 3. A device according to Claim 2, wherein each plate (10, 12) is flanged to either side of the slideway (16) and elongate closed slots (22) through which the clamping screws (30) pass are formed in each flange, the clamping screws (30) being a clearance fit in the elongate closed slots (22) to permit limited relative rotational movement of the plates (10, 12). 4. A device according to any preceding claim, wherein each plate (10, 12) is formed with through-hole (45, 47, 49) for attachment of adjacent limb parts, the holes (45) in the first plate (10) being plain and having larger diameter counterbores (47) from the blind face of the plate for receiving a head of an eventual clamping screw, and the second plate having at least one relatively large diameter through-hole (51) movable into register with the counterbores (47) to permit clamping screw insertion and to give key or screwdriver access to the head. 5. A device according to Claim 3, wherein each plate (10a, 12a) is formed with four through holes (45a, 47a; 49a) disposed in a pattern that is offset (61) relative to a pattern of slots (20a, 22a) in the plate (10a, 12a) so that the plates are movable between one extremity of their relative travel where the through holes (47a, 49a) are aligned and other positions within the range of travel where the fixing holes (47a, 49a) are offset. 6. A device according to any preceding claim, further comprising jacking means (35) attached to one of the plates (10) at an end of a slideway (16) and including a jacking screw (43) registering with the guide bar (26) therein for effecting controlled translational movement of the other plate (12). 7. A device according to Claim 6, comprising a pair of jacking means (35) attached to opposed ends of the slideway (16). 8. A prosthetic leg including a knee joint, and a shift device according to any of Claims 1 to 7, attached between the knee joint (59) and upper parts (57) of the leg. 9. A leg according to Claim 8, wherein an alignment device (61) is attached between the knee joint (59) and lower parts of the leg, said alignment device (61) permitting adjustment of the angle between the knee (59) and lower parts of the leg in an anterior-posterior and in a medial-lateral plane.

Inventors: COOPER, JOHN EDWIN
Applicants: J.E. HANGER & COMPANY LIMITED
Application year: 1987
Main classification: A61F2
IPC codes: A61F2