Lower Limb Prosthesis

• US 20120130508A1
• Filed: 02/02/2012
• Published: 05/24/2012
• Est. Priority Date: 12/14/2007
• Status: Active Grant

• Current Assignee: Blatchford Products Limited (CBPE Capital LLP)
• Original Assignee: CHAS A Blatchford & Sons Limited
• Inventors: HARRIS, Graham, MOSER, David, ZAHEDI, Mir Saeed
• Granted Patent: US 8,628,585 B2
• Time in Patent Office: Days
• US Class Current: 623/50
• CPC Class Codes: A61F 2/6607 Ankle joints
• CPC Class Codes: A61F 2/68 Operating or control means
• CPC Class Codes: A61F 2/74 fluid , i.e. hydraulic or pneumatic
• CPC Class Codes: A61F 2/748 Valve systems
• CPC Class Codes: A61F 2002/5006 Dampers, e.g. hydraulic damper
• CPC Class Codes: A61F 2002/5033 for adjusting damping damping means A61F2002/5003
• CPC Class Codes: A61F 2002/6621 Toes
• CPC Class Codes: A61F 2002/6642 Heels
• CPC Class Codes: A61F 2002/6657 having a plate-like or strip-like spring element, e.g. an energy-storing cantilever spring keel
• CPC Class Codes: A61F 2002/6854 for locking or unlocking a joint
• CPC Class Codes: A61F 2002/705 Electromagnetic data transfer for implantable prostheses A61F2250/0002
• CPC Class Codes: A61F 2002/707 Remote control

Abstract

In a lower limb prosthesis an ankle unit has a combination of an hydraulic piston and cylinder assembly providing a continuously damped range of ankle flexion and a resilient telescopic shock absorber. The damping resistance of the piston and cylinder assembly is the predominant resistance to ankle flexion and is provided by a piston which is axially moveable in a cylinder centred on the shin axis. The wall of the cylinder has a cylindrical outer bearing surface for a sleeve which is translationally displaceable relative to the piston and cylinder assembly according to the axial load, the sleeve being resiliently mounted by a compression spring which extends axially within the sleeve and has an integral end portion forming an upper bulkhead of the cylinder. The sleeve is also rotatable on the cylinder wall, the spring providing torsional resistance.

Claims

1. A lower limb prosthesis comprising a shin component defining a shin component axis, a foot component, and an ankle joint mechanism coupling the shin component to the foot component, wherein the ankle joint mechanism provides a continuously hydraulically damped range of ankle flexion and is constructed and arranged such that, over at least part of the range, the damping resistance is the predominant resistance to flexion, and wherein the shin component has a superior part and an inferior part which are resiliently interconnected so as to be translationally displaceable relative to each other according to the axial load on the shin component, the direction of relative displacement being substantially vertical when the foot component is at rest in an unloaded state on a horizontal supporting surface.

2. A prosthesis according to claim 1, wherein the shin component is in the form of a telescopic unit in which the superior shin component part and the inferior shin component part respectively comprise an outer sleeve and a cylindrical housing slidably received in the sleeve, and wherein the ankle joint mechanism comprises a hydraulic piston and cylinder assembly incorporated in the cylindrical housing so as to lie within the cylindrical envelope defined by the cylindrical housing, thereby to allow the sleeve to overlap at least part of the piston and cylinder assembly when the telescopic unit is fully compressed.

3. A prosthesis according to claim 2, wherein the telescopic unit has a longitudinal axis and wherein the ankle joint mechanism comprises an hydraulic linear piston and cylinder assembly having a central axis substantially aligned with the longitudinal axis.

4. A prosthesis according to claim 3, wherein piston and cylinder assembly has a cylinder with an upper bulkhead and a lower bulkhead, and a cylinder wall joining the upper and lower bulkheads.

5. A prosthesis according to claim 4, wherein the cylinder has upper and lower variable-volume chamber parts separated by a piston and interconnected by at least one bypass passage incorporating a valve, wherein the or each valve is located in the lower bulkhead.

6. A prosthesis according to claim 2, wherein the piston and cylinder assembly has a cylinder with first and second variable-volume chamber parts separated by a piston, and interconnected by at least one bypass passage, the or each bypass passage being confined within the said cylindrical envelope.

7. A prosthesis according to claim 4, wherein the telescopic unit includes an axial coil spring arranged to be compressed when the unit is subject to an axial load, the coil spring and the piston and cylinder assembly being arranged in a superior-inferior relationship.

8. A prosthesis according to claim 7, wherein the coil spring and the upper bulkhead of the cylinder are constituted by a monolithic element received in the said cylindrical housing.

9. A prosthesis according to claim 7, wherein the coil spring has first and second ends secured against rotation in the superior and inferior shin component parts respectively, and is configured to act both as a compression spring resisting translational relative displacement of the shin component parts and as a torsion spring resisting relative rotation of the shin component parts.

10. A prosthesis according to claim 1, wherein the ankle joint mechanism defines a medial-lateral ankle joint flexion axis and the shin component comprises a telescopic unit in which the shin component parts are slidable relative to each other in the direction of a telescopic unit centre line, which centre line passes within 30 mm of the ankle joint flexion axis.

11. A prosthesis according to claim 10, wherein the telescopic unit centre line is to the posterior of the ankle joint flexion axis.

12. A prosthesis according to claim 10, wherein the telescopic unit centre line passes through the foot component at a distance of between 0.2 L and 0.4 L to the anterior of the posterior extremity of the foot component, where L is the overall length of the foot component between its anterior and posterior extremities.

13. A prosthesis according to claim 1, wherein the ankle joint mechanism defines an ankle joint flexion range extending from a dorsi-flexion limit of between 2°

and 5°

with respect to a mid-stance condition and a plantar-flexion limit of between 5° and

8°

with respect to the mid-stance condition.

14. A prosthesis according to claim 1, wherein the cylindrical housing of the shin component is pivotally connected to the foot component for pivoting about an ankle joint flexion axis.

15. A prosthesis according to claim 14, wherein the piston and cylinder assembly has a piston with a piston rod pivotally coupled to the foot component to define a piston rod pivot axis spaced from the ankle joint flexion axis.

16. A prosthesis according to claim 1, wherein the foot component comprises an energy-storing fibre-reinforced plastics leaf spring extending from the ankle joint mechanism to a toe section of the foot component.

17. A prosthetic ankle unit comprising the combination of:

an hydraulic linear piston and cylinder assembly providing a continuously damped range of ankle flexion and defining a central axis, the assembly including a cylinder wall centred on the axis and enclosing a fluid-filled chamber the volume of which varies with movement of a piston therein, and

a telescopic shock absorber which is coaxial with the piston and cylinder assembly and comprises an outer sleeve which is slidably received on the outside of the cylinder wall and resiliently connected thereto so as to be translationally displaceable relative to the cylinder wall according to the axial load applied to the sleeve, the sleeve overlapping at least part of the fluid-filled chamber when the shock absorber is fully compressed.

18. A prosthetic ankle unit according to claim 17, wherein the shock absorber includes a compression spring coaxially mounted in the sleeve and resiliently interconnecting the sleeve and the cylinder wall of the piston and cylinder assembly.

19. A prosthetic ankle unit according to claim 17, wherein the sleeve is rotatable relative to the piston and cylinder assembly about the central axis.

20. A prosthetic ankle unit according to claim 19, wherein the resilient connection between the sleeve and the cylinder wall comprises a resilient element which biases the sleeve both translationally and rotationally.

21. A prosthetic ankle unit according to claim 18, wherein the fluid-filled chamber is bounded by a transverse bulkhead and wherein the compression spring is a coil spring which is integrally formed with the said bulkhead.

22. A prosthetic ankle unit according to claim 17 including a foot element and a shin element and wherein the piston and the cylinder wall are each pivotally mounted to the foot element, and the shock absorber sleeve forms part of the shin element.