Mechanisms and component design of prosthetic knees: A review from a biomechanical function perspective

Abstract

Prosthetic knees are state-of-the-art medical devices that use mechanical mechanisms and components to simulate the normal biological knee function for individuals with transfemoral amputation. A large variety of complicated mechanical mechanisms and components have been employed; however, they lack clear relevance to the walking biomechanics of users in the design process. This article aims to bridge this knowledge gap by providing a review of prosthetic knees from a biomechanical perspective and includes stance stability, early-stance flexion and swing resistance, which directly relate the mechanical mechanisms to the perceived walking performance, i.e., fall avoidance, shock absorption, and gait symmetry. The prescription criteria and selection of prosthetic knees depend on the interaction between the user and prosthesis, which includes five functional levels from K0 to K4. Misunderstood functions and the improper adjustment of knee prostheses may lead to reduced stability, restricted stance flexion, and unnatural gait for users. Our review identifies current commercial and recent studied prosthetic knees to provide a new paradigm for prosthetic knee analysis and facilitates the standardization and optimization of prosthetic knee design. This may also enable the design of functional mechanisms and components tailored to regaining lost functions of a specific person, hence providing individualized product design.

Can a powered knee-ankle prosthesis improve weight-bearing symmetry during stand-to-sit transitions in individuals with above-knee amputations?

“…Microprocessor-controlled prostheses can support amputee users during net-negative energy tasks like stand-to-sit transitions by providing resistive torque at the joint level [12], [15], [18], [23], [26], [46]. However, the damping systems implemented in these microprocessor-controlled prostheses are limited in their ability to accurately control the resistive joint torque and to dissipate large amounts of energy, especially at large exion angles [6]-[8], [47]. Using their embedded actuators, powered prostheses can more precisely control the joint torque while dissipating large amounts of energy, even at large knee exion angles [33].…”

“…Nonamputees stand with slight exion of the hip and knee, and initiate sit-down by relaxing their hip extensors, contracting their knee exors slightly (~10 Nm) to bend the knee, and moving their center of gravity posterior to produce exion torque at the knees [52]. In comparison, above-knee amputees normally stand with a more extended hip, which locks the prosthetic knee in extension as the prosthesis is aligned to be mechanically stable [47]. Thus, the residual hip exors need to contract not only to ex the hip joint, but also to ex the prosthetic knee and dorsi ex the prosthetic ankle.…”

“…Prosthetic alignment introduces additional asymmetries. Prosthetists usually align above-knee prostheses so that the user is stable during quiet standing without expending excessive energy [47]. They do this by changing the angles and offsets of the knee and ankle interfaces until the ground reaction force vector passes through the center of the foot and anterior to the prosthesis knee joint during quiet standing.…”

Prosthetic Knee Mechanism Using a Double Locking System as a Safety Measure

“…The most commonly used manual knee-locking system consists of a lever or latch that is activated by pushing a button or pulling a cord. Liang et al (2022) describe that this type of system is recommended for patients with low mobility (K1) or for geriatric patients. Another is geometry locking, which is a passive method that uses the shape and position of the prosthesis mechanism to prevent knee movement in positions such as hyperextension.…”

“…When the user applies weight to the prosthesis, the hydraulic mechanism compresses and the locking system is activated, reducing the torque at the Knee prostheses can be monocentric or polycentric and use mechanisms configured according to prescription as well as selection criteria to generate basic flexion and extension movements. Liang et al (2022) describe that these criteria depend on the interaction between the user and the prosthesis, which includes five functional levels ranging from K0 (the patient is unable to move safely and without assistance) to K4 (can move without restriction and tolerate high levels of impact, stress and energy). One of the aims of the design and selection of mechanisms is to avoid joint hyperextension and unwanted movements that could lead to the user becoming unbalanced or falling.…”