Inverted Polycentric Linkage Prosthetic Joint
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Solution Overview
Problem
Existing prosthetic knee joints have limited range of motion due to interference between components at large angles of flexion, leading to difficulties in activities like kneeling and squatting, and result in thigh lengthening and poor device fitting.
Innovation Solution
A prosthetic joint with an inverted polycentric linkage mechanism, allowing greater angles of flexion by enabling the first linkage to pass through the space between the pair of linkages, and an adjustable distal prosthetic limb part for customizable length and rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional polycentric linkage mechanism is used with a single posterior linkage and pair of anterior linkages, then the joint provides structural stability, but the range of motion is limited due to interference between components at large angles of flexion
Solution Approach 1:
The patent inverts the traditional linkage arrangement by positioning the first linkage (anterior in knee, posterior in elbow) closer to the mid-plane and the second pair of linkages (posterior in knee, anterior in elbow) farther from the mid-plane. This inversion allows the first linkage to pass through the space created between the second pair of linkages during deep flexion, enabling greater range of motion comparable to anatomical joints while maintaining structural stability
2Adaptability or versatility
If traditional linkage arrangements are used to provide polycentric joint, then the joint mechanism functions reliably, but interference occurs between components at large angles of flexion preventing kneeling and squatting activities
Solution Approach 1:
By inverting the linkage arrangement and spacing the connection points appropriately, the first linkage can pass through the space between the second pair of linkages during deep flexion, eliminating component interference and enabling activities like kneeling and squatting that were previously impossible
Solution Approach 2:
The patent utilizes the spatial dimension created by the inverted linkage arrangement, allowing the first linkage to move through the three-dimensional space between the second pair of linkages during flexion, thereby achieving greater angular displacement without physical interference
3Strength
If socket and connections are incorporated to connect prosthetic components, then the prosthetic joint is securely assembled, but the thigh length is extended creating limb length discrepancy
Solution Approach 1:
The patent integrates the connection functions directly into the proximal and distal parts of the joint mechanism, merging the socket and connection elements with the structural components. This eliminates the need for separate extended socket sections, thereby maintaining secure assembly while reducing the overall thigh length and minimizing limb length discrepancy
4Manufacturing precision
If specialist tools and trained technicians are required for servicing, then the prosthetic device can be precisely maintained, but the user cannot adjust the device themselves requiring considerable travel
Solution Approach 1:
The patent incorporates adjustment mechanisms that allow the user to service and adjust the prosthetic device themselves without requiring specialist tools or trained technicians. This empowers the user to perform maintenance and adjustments at home, eliminating the need for considerable travel to professional services while maintaining adequate service precision
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The prosthetic joint achieves a range of motion comparable to anatomical joints, enabling greater activity participation and reducing thigh length discrepancies, while allowing users to adjust their prosthetic without specialist tools.
Implementation Method 1
a resiliently deformable element arranged to deform as the distal part rotates from the extended position to the flexed position so as to exert the torque
Data Source
AI summary
A prosthetic joint comprising: a proximal part having a proximal side, a distal side opposed to the proximal side, and a mounting point on the proximal side configured to connect to a proximal prosthetic limb part, a distal part configured to connect to a distal prosthetic limb part, a polycentric linkage mechanism connected to the proximal and distal parts and arranged to rotate the distal part from an extended position, where the distal part is disposed on the distal side of the proximal part, to a flexed position, where at least a portion of the distal part is disposed on the proximal side of the proximal part. The distal part is arranged to rotate relative to the proximal part about an instantaneous axis of rotation, the axis of rotation defining a medial-lateral axis of the proximal part. The linkage mechanism comprises a first linkage and a further pair of linkages, each of which are pivotally connected to the proximal and distal parts via respective connection points. The position of the instantaneous axis of rotation is determined by the location of the connection points of the first linkage and the further pair of linkages. The connection points of the first linkage are spaced from a mid-plane of the proximal part by a smaller distance along the medial-lateral axis than the connection points of the pair of linkages. The distal part is spaced from the proximal part in the direction of flexion as the distal part is rotated between the extended position and the flexed position. In the extended position, the connection points of the first linkage are spaced from the mounting point by a smaller distance in the direction of flexion than the connection points of the pair of linkages.