Polycentric Thigh Prosthetic Knee with Articulated Arms
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Solution Overview
Problem
Patients with thigh prostheses face challenges in achieving a natural gait pattern due to the need for a stronger equinus position during the swing phase, leading to increased energy exertion and potential stumbling, as conventional prostheses require compensatory movements to prevent ground contact and counteract perceived leg shortening.
Innovation Solution
A thigh prosthetic component featuring a polycentric knee joint with ventral and dorsal articulated arms, allowing the pivot point to be adapted during the gait phase, and a lower leg unit with both ventral and dorsal connecting elements that facilitate dorsal extension during toe-off, enabling a more natural gait and reducing energy expenditure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional prosthesis design is used, then the structure is simple, but the patient must assume a stronger equinus position during swing phase leading to increased energy expenditure and unphysiological movement
Solution Approach 1:
The patent implements a polycentric knee joint mechanism where the effective pivot point dynamically shifts during the gait cycle. The ventral and dorsal articulated arms create a movement trajectory that automatically adjusts the knee joint's center of rotation, enabling natural knee flexion during swing phase without requiring compensatory equinus positioning. This dynamic geometric transformation resolves the contradiction by providing energy-efficient movement through increased mechanism complexity.
Solution Approach 2:
The invention changes the geometric parameters of the knee joint mechanism by introducing ventral and dorsal articulated arms with specific axis configurations. This parameter change transforms the single-axis rotation into a polycentric mechanism, altering the movement trajectory to achieve natural gait patterns. The parameter modification enables the knee joint to flex appropriately during swing phase, reducing energy expenditure while maintaining structural integrity.
2Ease of operation
If the prosthesis is designed shorter to facilitate swinging through, then swing phase movement is improved, but the patient experiences a limp and perceived leg length discrepancy
Solution Approach 1:
The polycentric knee joint mechanism dynamically adjusts the effective leg length during the gait cycle. During swing phase, the geometric configuration of the ventral and dorsal articulated arms enables natural knee flexion that increases ground clearance, facilitating smooth swing through. During stance phase, the mechanism stabilizes to maintain proper leg length and alignment. This dynamic adaptation resolves the contradiction by providing ease of operation during swing while maintaining gait stability during stance.
Solution Approach 2:
The mechanism prepares the knee joint for swing phase movement during the transition from stance to swing. The ventral and dorsal articulated arms are configured to automatically initiate knee flexion as the heel rises, preemptively positioning the prosthetic limb for smooth swing through. This preliminary action eliminates the need for compensatory movements and maintains natural gait stability throughout the cycle.
3Reliability
If the patient assumes compensatory equinus position to prevent ground contact during swing, then stumbling is prevented, but the movement becomes unphysiological and loads the spinal column
Solution Approach 1:
The polycentric knee joint mechanism dynamically generates appropriate knee flexion during swing phase, which naturally lifts the prosthetic foot clear of the ground. This dynamic ground clearance mechanism eliminates the need for compensatory equinus positioning at the ankle. By transferring the ground clearance function to the knee joint through geometric transformation, the invention prevents stumbling while maintaining physiological alignment and reducing spinal column loading.
Solution Approach 2:
The ventral and dorsal articulated arms act as intermediary elements that mediate between the thigh shaft and the lower leg unit. These articulated arms create a mechanical linkage that transforms hip movement into natural knee flexion during swing phase. This intermediary mechanism provides the necessary ground clearance without requiring compensatory movements at the ankle or excessive spinal flexion, thereby preventing stumbling while reducing harmful loads on the spinal column.
Data Source
AI summary
A thigh prosthetic component for connecting to a thigh shaft. The component includes a pivotable knee joint and an upper part and a lower part connected by ventral and dorsal arms. The ventral arm is articulated to the upper part and to the lower part via distinct axes. The dorsal arm is articulated to the upper part and to the lower part via distinct axes. The component further includes an ankle pivotably connecting a foot part to a lower leg unit connected to the knee joint. The lower leg unit has ventral and dorsal connecting elements transmitting thrust and traction. The ventral connecting element is pivoted to the foot part and to the lower part. The dorsal connecting element is articulated to the foot part and to the upper part and the dorsal articulated arm such that an adjustment of the knee joint from stance to swing positions causes a dorsal extension of the foot part.