AN ARTIFICIAL LIMB

Abstract: An artificial limb has an endoskeletal shin component (10A) which is of generally constant H-shaped cross section and is formed by injection moulding from thermoplastics material. In a preferred embodiment, the limb has a foot keel (10B) which is integrally moulded with the shin component (10A), the keel (10B) having a longitudinal web (20) which is coplanar with a central web (12) of the shin component (10A). The keel (10B) also has upper flanges (24, 26) which are contiguous with anterior and posterior flanges (14, 16) of the shin component (10A). Such a limb can be made light in weight yet strong in terms of resistance to transverse bending moments, and can be inexpensively produced. The constant cross section of the skin component allows it to be cut to a required length and clamped to an upper limb component (52, 60).

Description: AN ARTIFICIAL I .TMB This invention relates to an artificial limb and particularly to a lower limb prosthesis which is inexpensive to manufacture. Much ofthe development of artificial limbs has been to produce a prosthesis which is as light as possible yet is strong and functionally sophisticated. As a result, such prostheses tend to use expensive materials and manufacturing techniques. There is a need for a prosthesis which can be manufactured inexpensively and in large quantities, but which is still lightweight, robust, and comfortable to wear and use. According to a first aspect of this invention. there is provided an endoskeletal artificial limb comprising a load-bearing elongate structural member which is injection-moulded from a thermoplastics material. and has a longitudinal web and at least one integral longitudinal flange arranged transversely ofthe web. Preferably, at least a portion ofthe member is straight and of constant cross-section, with at least two integral longitudinal flanges located along opposite edges ofthe web, the cross-section being of H- or l-shape. Such a limb can be dimensioned so as to be lightweight, yet strong in terms of resistance to transverse bending moments. It has the additional advantage of having some torsional resilience which, in the case of a lower limb prosthesis, reduces shear forces acting between the amputee ' s stump and the stump socket. In a panicular embodiment ofthe invention the artificial limb is a lower limb prosthesis in which the structural member comprises at least a shin ponion of substantially constant cross-section. In this particular embodiment, the structural member includes a foot keel with anteriorly and posteriorly extending portions, integrally formed in one piece with the shin portion in a single injection-moulding operation. The keel may have a web extending in the anterior-posterior direction, co-planar and contiguous with the web of the shin portion. The keel may also have a flange extending lengthwise in the sole of the foot, integrally formed at the distal edge ofthe keel web. The flange extends transversely on both sides of the keel web. Preferably this sole flange is curved in the longitudinal direction ofthe foot so as to have a convex lower surface. The keel may extend both anteriorly and posteriorly relative to the shin portion, and may also have upper flanges which, in the case of the shin portion having two longitudinal flanges, are contiguous with those flanges, the upper flanges curving proximally from the foot to merge directly into the flanges ofthe shin portion. The portion of constant cross-section preferably extends to the proximal end of the elongate structural member, the limb further comprising a clamp fitted to the said end to enclose the longitudinal web and flange and for mounting to an upper limb component. The clamp is a thermoplastics component having a recess of a cross-section which corresponds to that of the structural member, the component thereby enclosing the proximal end ofthe member. The clamp may have cut-outs extending in the longitudinal direction ofthe structural member on opposite sides thereof, the cut-outs being spanned by respective clamping bolts extending between oppositely directed outer faces of the clamp whereby clamping forces can be exerted by tightening the bolts to pinch the or each flange ofthe structural member. The or each clamping bolt has the effect of distorting or deforming the material ofthe clamp to grip the structural member. Different upper limb components may be attached to the structural member by the clamp. In the case of a lower limb prosthesis, the clamp may be attached to or form a distal part of a knee assembly. Alternatively, it may connect the structural member to a stump socket, with or without an intervening alignment device. If the clamp is required to be detachable from an upper or proximal limb component, it may comprise a clamp housing for the structural member and a proximal plate which forms a bridge on the proximal side of the clamp housing, the bridge being integrally formed with the housing as a single injection-moulded component. Another possibility, in the case of a prosthesis for an above-knee amputee, is to form the upper part ofthe shin as a knee housing which has an integral clamp housing for receiving the proximal end ofthe structural member. In another embodiment, the clamp is replaced by a housing having a recess with a cross- section corresponding to the cross-section ofthe structural member, the recess being so dimensioned that the structural member is an intimate fit within the recess. The member may be held in place simply by friction, or a latch feature or by an adhesive. In keeping with the concept of a prosthesis with the minimum number of components and with minimum cost, in the case of a lower limb prosthesis the foot is preferably a unitary foam structure moulded in situ over the foot keel referred to above. The central longitudinal axis of a straight shin portion may pass through the foot at a distance from the extreme posterior end of the foot which is equal to between 0.29 and 0.33 as a proportion of the total length of the foot. More particularly, the proportion is between 0.30 and 0.32. A toe-break strip made of. for instance, a resilient polyurethane material may be bonded to the distal face ofthe keel to extend anteriorly ofthe keel. With regard to the material of the structural member, this is preferably a fibre-loaded thermoplastics material such as nylon loaded with glass fibres (typically less than 10 mm in length). The proportion of fibres by weight is preferably between 35% and 60%. as a percentage of the total weight of the material. The above-described limb can be cheaply produced by injection-moulding a limited range of structural members with different keel sizes, and moulding a foam foot in situ over the keel of each member with the member held in a predetermined position relative to the mould for the foot, to form a unitary shin and foot assembly. At the fitting stage, a shin and foot assembly of the required size is selected, the shin portion is cut to a required length and joined at the proximal end to a stump socket or. in the case of a prosthesis for an above-knee amputee, to a knee joint which is. in turn, connected to a socket. An alignment device may be included between the socket and the shin portion. If required, a cosmetic flexible foam covering may be slid over the shin portion. The invention also includes. according to a second aspect thereof, a method of making an artificial limb comprising selecting a unitary shin and foot assembly having a shin portion comprising a structural member which is injection-moulded from a thermoplastics material and which, over at least a proximal end portion is of constant cross-section having a web and at least one transverse flange, cutting the shin portion to a required length, securing the cut end ofthe shin portion in a receptacle, and securing the receptacle to a stump socket. According to a third aspect of the invention. there is provided a shin component for an artificial limb comprising an injection-moulded thermoplastics structural member having a longitudinal web and at least one integral longitudinal flange extending transversely of the web. According to a fourth aspect ofthe invention. a component for an artificial limb comprises a shin portion having a longitudinal web and at least one integral longitudinal flange extending transversely of the web. and a foot keel, the shin portion and the keel being integrally formed as a single-piece injection-moulded structural member. The invention will now be described by way of example with reference to the drawings in which:- Figure 1 is a side elevation of a lower limb prosthesis for a below-knee amputee: Figure 2 is a plan view of the main structural member of the prosthesis of Figure 1, sectioned on the line 2-2 in Figure 1 ; Figure 3 is a cross-section ofthe foot keel sectioned on the line 3-3 in Figure 1; Figures 4 A, 4B and 4C are respectively side, underside and front elevations of a proximal clamp for the below-knee prosthesis of Figure 1 ; Figure 5 is a side elevation of a lower limb prosthesis for an above-knee amputee: and Figures 6A to 6C are side, front and plan views of a structural member for a lower limb prosthesis incorporating an ankle joint. Referring to Figure 1 of the drawings, a lower limb prosthesis in accordance with the invention for a below-knee amputee has an internal structural member 10 comprising a shin portion 10A and a foot keel 10B integrally formed with the shin portion 10A. The structural member 10 is a one piece injection-moulded component made of a glass fibre loaded nylon material available from LNP Engineering Plastics (U.K.) Limited under the name VERTON. The shin portion is straight and of constant cross-section over its entire length, the cross-section being of H-shape. having a central longitudinal web 12 lying in a plane extending substantially in the anterior-posterior direction, and anterior and posterior flanges 14. 16 arranged along the edges ofthe web 12 and each extending in a medial-lateral direction. The cross-section ofthe shin portion 10A is more clearly visible in Figure 2. which clearly shows the H-shape. A shin portion having this configuration has high strength in the anterior-posterior and medial-lateral planes, yet is torsionally flexible to a limited degree, thereby allowing some rotation ofthe keel 10B about the central longitudinal axis 17 of the shin portion. The depth ofthe shin portion 10A in the anterior-posterior direction is within the range of from 25 to 35 mm, and is preferably less than 32 mm. In the preferred embodiment shown in the drawings, it is 30 mm. The width of the member in the medial-lateral direction preferably has the same dimensional limitations. The web and flange thickness is substantially uniform and within the range of from 2.5 mm to 5 mm. A uniform 4 mm thickness is preferred. As will be seen from Figures 1. 2. and 3 together, the keel 10B forms an anterior bridge portion 18 and a posterior heel portion 19 both integrally formed with the shin portion 10 A, the bridge portion extending into a metatarsal region of the foot, i.e. a region corresponding to the position ofthe metatarsal bones in the natural foot, and also has a central web 20 extending in the anterior-posterior direction, which is co-planar with the web 12 ofthe shin portion 10A and integrally formed with the latter. A sole flange 22 extends along the distal edge of the keel web 20 and transversely on both sides of the latter. Flange 22 is curved to form a lower surface which is convex in the anterior- posterior direction so that to the posterior of the shin axis 17, the flange 22 is inclined upwardly to the rear to a greater extent than to the anterior ofthe axis 17. The flange 22 is typically 40mm in width to provide a stable base for the prosthesis. Along the upper edge of the keel web 20 there is an upper anterior flange 24 which is contiguous with the anterior flange 14 of the shin portion and extends around an anterior end of the keel 10B to meet the lower flange 22. A similar flange 26 extends in the posterior direction contiguously from the flange 16 ofthe shin portion to meet the lower flange 22 in the heel region ofthe foot. The anterior end ofthe keel 10B lies behind the location corresponding to the ball ofthe foot in a natural foot, and a keel extension in the form of a resilient plastics strip 28, shown only in Figure 1. is attached to an anterior portion ofthe keel to extend into the toe region of the foot. Extension 28 is made of a thermoplastic elastomer available from Dupont under the Registered Trade Mark HYTREL, and is bonded to the lower or distal surface ofthe flange 22 ofthe keel 10B using double-sided adhesive tape. As shown in Figure 1. the keel 10B and a small part ofthe shin portion 10A is encased in a moulded foot 30. The material used for the foot moulding is a resilient foam material. The configuration of the keel, with the lower flange 22 inclined upwardly in the heel region ofthe foot results in a greater thickness of foam beneath the keel 10B in the heel region than in the instep region, the foot thereby corresponding to the conventional SACH foot configuration. The curved lower flange 22 provides for a continuous rolling movement ofthe keel 10B during the stance phase ofthe walking cycle, with the toe-break strip 28 providing resilient bracing for the forefoot at toe-off. In this embodiment, the distance between the posterior extremity 30P ofthe foot 30 and the axis 17 is about 0.305 times the overall length ofthe foot 30. Since the shin portion 10A is of constant cross-section, it can be sawn to a required length at the time of patient-fitting, and secured to a stump socket 52 by means of a clamp 32. as shown in Figure 1. Referring to Figures 4A - 4C. the clamp 32 is an injection-moulded component, preferably moulded from the same material as the shin and keel, and has two integrally formed parts. The first part is a clamp housing 32H having a distally open recess 34 of a cross-section corresponding to the cross-section ofthe shin portion 10 A. as will be seen by comparing Figure 4B with Figure 2. In this embodiment, the material of the housing 32H completely surrounds the recess 34 without a break. However, cut-outs 36 are formed on each side of the housing, on opposite sides of the central arm of the recess "H". these cut-outs 36 extending from the medial and lateral surfaces ofthe clamp housing 32H to within a short distance of the central part of the recess 34. Bores 38 penetrate the housing 32H on opposite sides ofthe recess 36 perpendicularly to the cut¬ outs 36 and, in this embodiment, in an anterior-posterior direction. When the shin portion 10A is fitted into the recess 34. bolts 40 (see Figures 1) received in the bores 38, are used to compress the sides of the housing 32H which, being flexible, deform and pinch the edges ofthe shin portion flanges 14, 16 to secure the shin portion 10A in the housing 32H. The fact that the cut-outs 36 are blind means that continuous supporting blocks of material remain between the flanges 14 and 16 of the shin portion 10 A. The bolts 40 also act as tie bars to prevent failure of the housing 32H when subject to an anterior-posterior moment. The upper part ofthe clamp 32 in this embodiment is a mounting plate 42 formed as a bridge spaced proximally from the housing 32H and connected to the latter on the anterior and posterior sides. The top surface ofthe plate 42 is peφendicular with respect to the axis 17. and is penetrated by a central hole 44 for receiving a coupling bolt 46 (see Figure 1) for attaching the clamp 32 to upper parts ofthe prosthesis, in this case a conventional alignment device 48. Mounting of the stump socket 52 in the alignment device is effected by trapping the distal end ofthe socket between a socket plate 50 and a part-spherical cup 54 bearing against the proximal surface of the clamp plate 42. Bolt 42 is secured by means of a nut 56 distally ofthe bridge 42. The clamping load produced by the nut and bolt and is distributed across the plate 42 by a large washer 58. Using a plate 42 as described above, in combination with a spacer having a corresponding planar lower surface extending over the majority ofthe proximal surface ofthe plate, together with a large washer bearing against the distal surface ofthe plate 42 produces a connection able to withstand the bending moments applied to the prosthesis by the patient despite the use of a thermoplastics material for the clamp 32. Interposing an alignment device 48 between clamp 32 and the socket is not essential. In a simpler version ofthe prosthesis, the bridge plate 42 may be directly connected to the stump socket. A cosmetic foam covering 59 (shown in chain lines in Figure 1) is provided around the shin portion 1 OA, abutting the foot cosmesis 30. The limb described above is preferably manufactured and supplied in component form, i.e. as a shin and foot component, a clamp, an alignment device, and a stump socket. The shin and foot component is supplied as a single piece, i.e. with the foot 30 moulded in situ on the distal end ofthe structural member 10. At the fitting stage, the shin portion 10A is cut to a required length, clamp 32 is fitted and secured at the proximal end, the alignment device, if present, is fitted, together with a stump socket. In the preferred embodiment, the prosthesis has no mechanically moving parts, and no detachable fastening below the proximal end ofthe shin portion 10A. In addition, it has no metallic parts below the proximal end ofthe shin portion. The function ofthe bolts 40 in the clamp 32 is not only to secure the shin portion 10 A. but also to reinforce the clamp housing 32H to prevent splitting ofthe thermoplastics material from which it is made. However, the clamp 32H can, if required, be made of stronger material and the bolts 40 omitted, the shin portion 10A being secured in the housing 32H by other means, e.g. bonding. The shin and foot assembly ( 10. 30) described above can be used in a prosthesis for an above-knee amputee, as shown in Figure 5. In this case, shin portion 10A is secured by clamping or bonding in a knee cradle component 60. Cradle 60 rotates about a knee axis 62 with respect to a knee chassis 64 which has a bridge plate 66 similar to plate 42 ofthe clamp 32 described above. An alignment device and stump socket are secured to plate 66 in the same manner as described above for the below-knee prosthesis. Knee cradle 60 may include a clamp housing at its distal end like housing 32H described above with reference to Figures 1. 4A, 4B. and 4C. The housing may be rotatable with respect to the cradle 60 to adjust toe-in or toe-out ofthe foot. An ankle joint may be incorporated, as shown in Figures 6A to 6C which are views of an integral shin portion and ankle joint component 70 made ofthe glass-fibre loaded nylon material refeπed to above. In this case the lower end ofthe component 70 has flexible central hinge portion 72 which is of rectangular cross-section, being thinner in the anterior-posterior direction than in the medial-lateral direction to allow dorsi and plantar flexion. Anterior and posterior extensions 74. 76 ofthe shin portion 10A are in registry with and proximally spaced from stops 78. 80 adjacent the foot interface 82 to limit flexion in both directions as hinge portion 72 flexes under load. In this case the combined shin and ankle component 70 is shown as being demountable from a foot keel (not shown) by means of bolts (not shown) which are received in four bores 84 in the foot interface 82. It is perfectly possible for the foot keel to be integral with the component 70. In another embodiment of the invention, not shown in the drawings, the shin portion terminates at its distal end in a cylindrical boss integrally formed with the H-section, to allow clamping within a cylindrical sleeve forming part of an ankle joint, for example, or a SACH foot base.

Claims: CLAIMS 1. An endoskeletal artificial limb comprising a load-bearing elongate structural member which is injection-moulded from a thermoplastics material. and has a longitudinal web and at least one integral longitudinal flange extending transversely ofthe web. 2. An artificial limb according to claim 1 , wherein the web and flanges form at least a portion ofthe member, which portion is straight and of constant cross-section. 3. An artificial limb according to claim 2. wherein the shin portion has two integral longitudinal flanges which are located along opposite respective edges ofthe web. the cross-section being of H- or I- shape. 4. An artificial limb according to claim 1. wherein the structural member includes an integral anteriorly-extending foot portion. 5. An artificial limb according to claim 1. wherein the structural member includes an integral posteriorly-extending heel portion. 6. An artificial limb according to claim 1 , wherein the structural member is moulded from a fibre-loaded thermoplastics material. 7. An artificial limb according to claim 1, having a shin portion of substantially constant cross-section. 8. An artificial limb according to claim 7, wherein the structural member includes a foot keel integrally formed with the shin portion. 9. An artificial lir. iccor to claim 8. wherein the keel has a central web extending in the anterior-posterior direction which is coplanar with the longitudinal web ofthe shin portion. 5 10. An artificial limb according to claim 9. wherein the keel extends anteriorly and posteriorly with respect to the shin portion, has a longitudinally convexly curved lower flange and an upper flange, the upper flange being contiguous with the said longitudinal flange. 10 11. An artificial limb according to claim 10. wherein the shin portion has integral longitudinal flanges which are located along opposite respective edges ofthe web, and wherein the anteriorly and posteriorly extending portions of the keel have respective upper flanges which merge into respective ones ofthe said longitudinal flanges. 15 12. An artificial limb according to claim 7. further comprising a demountable clamp secured to the shin portion of constant cross-section. 13. An artificial limb according to claim 12, wherein the clamp has a clamp housing 20 including a distally opening recess of a cross-section coπesponding to the cross- section ofthe shin portion. 14. An artificial limb according to claim 12, wherein the clamp includes at least one tie bolt for tightening the clamp or the shin portion. 25 15. An artificial limb according to claim 7, including a unitary shin and foot assembly comprising εr- integrally moulded shin portion and keel, and a moulded foam foot encasing the keel. 30 16. A method of making an artificial limb comprising selecting a unitary shin and foot assembly having a shin portion comprising a structural member which is injection- moulded from a thermoplastics material and which, over at least a proximal end portion is of constant cross-section having a web and at least one transverse flange, cutting the shin portion to a required length, securing the cut end of the shin portion in a receptacle, and securing the receptacle to a stump socket. 17. A method according to claim 16. wherein the shin portion has at least two transverse flanges, the cross-section being H- or I- shaped. 18. A method according to claim 17, wherein the securing step comprises detachably clamping the shin portion in a clamp housing having a recess of a cross-section which coπesponds to the said constant cross-section. 19. A method according to claim 16, wherein the step of securing the receptacle to the sump socket includes coupling the receptacle to an alignment device with or without an intervening knee joint. 20. A shin component for an artificial limb comprising an injection-moulded thermoplastics structural member having a longitudinal web and at least one integral longitudinal flange extending transversely ofthe web. 21. A shin component according to claim 20, having at least two integral longitudinal flanges extending transversely ofthe web. 22. A shin component according to claim 20, wherein the web and the or each flange form at least a portion of the member, which portion is straight and of constant cross-section. 23. A shin component according to claim 20, wherein the structural member is formed of a fibre-loaded thermoplastics material. 24. A component for an artificial limb, comprising a shin portion having a longitudinal web and at least one integral longitudinal flange extending transversely of the web. and a foot keel, the shin portion and the keel being integrally formed as a single-piece injection-moulded structural member. 25. A component according to claim 24. wherein the shin portion has at least two integral longitudinal flanges extending transversely ofthe web. 26. A component according to claim 24, wherein the keel has a central web which is coplanar with the web of the shin portion and upper flanges which are contiguous with respective ones ofthe said longitudinal flanges. 27. A component according to claim 26. wherein at least an end part of the shin portion remote from the foot is straight and of constant cross-section. 28. A component according to claim 24. wherein the structural member is formed of a fibre-loaded thermoplastics material. 29. A component according to claim 28, wherein the length of the fibres in the structural member are mostly less than 10mm in length.

Inventors: HARRIS GRAHAM JAMES, SHORTER JOHN JEFFREY, WOOLNOUGH VICTOR JAMES, HARRIS, GRAHAM, JAMES, SHORTER, JOHN, JEFFREY, WOOLNOUGH, VICTOR, JAMES
Applicants: BLATCHFORD & SONS LTD, HARRIS GRAHAM JAMES, SHORTER JOHN JEFFREY, WOOLNOUGH VICTOR JAMES, CHAS. A. BLATCHFORD & SONS LIMITED, HARRIS, GRAHAM, JAMES, SHORTER, JOHN, JEFFREY, WOOLNOUGH, VICTOR, JAMES
Application year: 1996
Main classification: A61F2
IPC codes: A61F2