Abstract
For prosthesis users, knee units can range from simple devices costing $2000 up to $45,000 for high-end, microprocessor-controlled systems. These higher-end electronic knees provide significant advantages in stability, gait, and metabolic rate compared to their passive or mechanical counterparts. However, the high cost of such systems makes them inaccessible to most amputees. In this study, it was hypothesized that a microprocessor knee could be manufactured for less than $1000, with comparable stability and user experience to a high-end industry standard device. A prototype (E-Knee) was designed with a specific emphasis on stance stability, and was tested during patient gait trials. The gait trials used a repeated measures design to compare three knee devices (a simple passive knee, the prototype E-Knee, and a high-end knee). Ground reaction forces and a functionality questionnaire were used to compare devices. A microprocessor locking test was used to evaluate the prototype’s ability to prevent falls. Building on the LIMBS M3, a passive four-bar polycentric device, the E-Knee added sensing, computing, and controlling capabilities for a material cost of $507. Initial data from a two-subject trial served as proof-of-concept to validate the prototype and found that it improved gait by providing more stability than the M3 and had more gait-pattern similarities to the Ottobock C-Leg than to the M3. Patients reported no perceived differences in stability between the E-Knee and the C-Leg. Patient trials supported that the E-Knee prototype behaved more naturally than the low-end M3 device and had similar ground reaction forces to the C-Leg.
Highlights
185,000 lower-limb amputations are performed in the United States each year, with above-knee amputations (AK) making up 26% (48,100) [1,2]
The final prototype electronic knee (E-Knee) was composed of a modified LIMBS M3 (Figure 2A,B), a variable damper (Figure 2C), a magnetic sensor (Figure 2D), an Arduino microprocessor (Boarduino with ATmega 328; Figure 2E), a clamping mechanism (Figure 2F), and a power
According to the LEGS Functional Parameters Questionnaire (LFPQ), Subject 1 felt that the E-Knee was a considerable improvement over the M3
Summary
185,000 lower-limb amputations are performed in the United States each year, with above-knee amputations (AK) making up 26% (48,100) [1,2]. While there are many types of prosthetic knee devices on the market, microprocessor-controlled prosthetic knees (MPKs) have been touted as greatly beneficial to amputee stability. Gait symmetry in healthy subjects has been well defined by the literature [14,15], and microprocessor systems are designed to facilitate natural gait [16]. Ground reaction forces (GRFs) are commonly used to compare and evaluate both gait symmetry, asymmetry, and limb performance. Due to repeatability and relatively low variance among subjects in similar circumstances, GRFs can be used to quantitatively compare performance between knee systems. GRFs are used to study symmetry between intact and prosthetic limbs to determine gait normalcy [6]
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