Prosthetic Technology

Body-powered prostheses are useful tools that can restore the ability to pick up and grasp objects and assist the user&#;s sound hand. Body-powered partial hand devices can help restore function when the finger loss is as the PIP or MCP level. For people with higher amputation levels, movements of the upper arm, shoulder and chest are captured by the harness and cable system, and used to open and close the hook or hand, similar to how a bicycle handbrake system works.

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Movements of the upper arm, shoulder and chest are captured by the harness and cable system, and used to open and close the hook or hand, similar to how a bicycle handbrake system works. As users grow accustomed to the feeling of varying tension on the cable, they may experience an improved sense of the position of the limb and the degree of opening on the terminal device. Hooks can be made of aluminum, steel, or titanium and can be rubber lined for better gripping. The grip force of a voluntary opening hook is determined by the number of rubber bands holding the hook closed.

The components of a body-powered prosthesis include:

• A custom fit socket
• A terminal device such as a hook or hand
• A wrist unit
• A harness and cable system
• Above elbow prostheses will include an elbow unit
• Shoulder disarticulation prostheses will include an elbow and a shoulder

Many amputees like the durability and basic function of body-powered prostheses and find them particularly useful for working outdoors or in rugged or wet environments. A custom silicone interface can improve user comfort and is available in a wide range of colors.

The purpose of this study was to systematically review the therapeutic benefits of performing daily activities with passive, quasi-passive and active ankle&#;foot prostheses in people with a unilateral lower limb amputation. Remarkably, no studies investigated the long-term therapeutic benefits.

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Figure 4 captures the short-term therapeutic benefits of passive, quasi-passive and active prostheses. This figure shows the domains in which benefits were found. It was not possible to provide such an overview at the outcome measure level due to high heterogeneity. Overall, the numerous outcome measures per study yielded positive results on biomechanical, physiological, performance-related or subjective outcomes for the more advanced prostheses, implying therapeutic benefits for the individuals walking with them, though all studies also identified no or unfavourable effects. The technological innovations contribute to improving the quality of life in the short-term when people with lower limb amputation switch the conventional passive cushion foot for a more advanced prosthesis (i.e. the passive energy-storing release feet, the surface-adaptive quasi-passive feet, the active feet generating an external force through an actuator). However, comparisons between active prostheses and quasi-passive devices have not yet been conducted.

Short-term therapeutic benefits of passive, quasi-passive and active ankle&#;foot prostheses in people with a unilateral transtibial and transfemoral amputation. The arrows indicate the effect of switching from one type of prosthesis to another. For example, switching from passive non-ESR to quasi-passive prostheses entails positive effects on biomechanics, performance and RPE. ESR: energy-storing and release; RPE: rating of perceived exertion; ?: currently unknown, to be investigated; *effect based on studies only including people with a transtibial amputation

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Among the included studies, quality of life has been evaluated using biomechanical, physiological, performance-related or subjective measures. The biomechanical and physiological dimensions of quality of life have been assessed during level and slope walking in 94% of the included studies, while only 29% included the subjective dimension. In general, gait efficiency and efficacy improved in parallel with technological advances, though gait asymmetries remained [52,53,54,55,56,57,58,59,60,61,62, 64,65,66,67,68,69,70,71,72,73, 75,76,77, 79,80,81,82,83,84]. Further in-depth discussion of these parameters is not feasible due to the heterogeneity in outcome measure among the biomechanical and physiological parameters (Table 2). Nevertheless, it is the ultimate goal of prosthetic development to strive towards the most efficient gait patterns by seeking complete gait symmetry and matching the gait patterns as closely as possible to those of able-bodied individuals [37]. Furthermore, the limited data on the subjective dimension of quality of life revealed that the perceived effort and satisfaction increased in line with the advancement of the devices. The limited use of subjective measures can be attributed to the prohibitive cost of most active and quasi-passive devices for a subset of individuals. This factor might introduce a confounding variable in the data affecting subjective feedback. Conversely, these paywalls will not affect the biomechanical or physiological data. Nevertheless, subjective measures (e.g. perceived effort, satisfaction, feedback on the noise of motors in active prostheses) should be more prominent in prosthetic evaluations, as they are crucial to assessing the quality of life [87].

Due to its biomechanical focus, the prosthetic evaluation primarily targets aberrated movement patterns that can be remedied in the short term by a prosthesis [4, 6, 7]. However, movement patterns are orchestrated by the intertwining between biomechanical factors and the human brain [27, 88]. This entails that the brain plays a vital role in the organization and performance of human gait [88]. Magnetic resonance imaging revealed that amputation causes thinning of the premotor cortex and visual-motor area combined with a decrease in white matter integrity in the premotor area contralateral to the amputation and at a bilateral connection between both premotor cortices [27]. These changes interfere with movement planning or coordinating eye movements in relation to limbs and lead to decreased perception&#;action coupling [27]. Additionally, amputation causes changes in limb representation in the primary motor cortex and somatosensory cortex, and causes decreased connectivity between many brain areas, including the primary motor cortex, primary somatosensory cortex, basal ganglia, thalamus and cerebellum [27]. These changes in connectivity translate towards reduced motor control and balance and potentially lead to falls [9, 10, 27]. Remarkably, only a single study examining the effect on brain functioning across prosthetic ankle&#;foot prostheses has been included in this review [75]. De Pauw et al. [75] explored whether motor-related cortical potentials differed between passive and quasi-passive prostheses during daily activities using electro-encephalography but did not detect any difference between both devices. The absence of an effect is not unexpected, considering neuroplasticity is a time-consuming process, and sufficient familiarisation time was not provided [89,90,91,92,93,94]. Unravelling neuroplasticity in relation to the type of prosthesis may provide a new understanding of the effects of prostheses to improve the quality of life in people with a lower limb amputation.

A conceivable approach to account for the brain&#;s influence is through dual tasks, conditional on adequate familiarisation [95]. Dual tasks involve the concurrent performance of two tasks and are regarded as a measurement of cognitive-motor capacity as they require executive function and attentional demand [95]. Their performance usually results in decreased mobility and deteriorated gait patterns leading to increment falls [96, 97]. Out of the included articles in this review, only 1 investigated the difference between passive and quasi-passive prostheses during the performance of a dual-task during treadmill walking [75]. They found that only in individuals with a transfemoral amputation attention demands (reaction times and accuracy) increased during walking with the quasi-passive prosthesis compared to the current prosthesis and able-bodied individuals [75]. Lack of familiarization time to habituate to the new prosthetic device may have influenced these results. As discussed earlier, the negative implications of performing dual-tasks are attributable to cognitive demands associated with prosthetic use, balance and gait disturbances, and brain adaptations [9, 10, 27, 95]. Combined with the fact that dual-tasks represent daily activities, the recommendation is to include dual-task paradigms in the evaluation process of prostheses [95].

The design, development and evaluation of prosthetic devices is an iterative process requiring high cross-disciplinary collaboration between multiple research branches. This review reveals that the current emphasis in prosthetic evaluation has been placed on comparing ankle&#;foot prostheses without long-term evaluation. Since none of the included studies investigated the long-term benefits of comparing different ankle&#;foot prostheses, we, for example, cannot make any substantiated statements about the association between the onset of secondary injuries and the use of different types of prostheses solely based on studies conducted at a single point in time. Furthermore, it should be emphasized that the included studies mainly involved people with a transtibial amputation. In contrast, only six of the included studies included people with a transfemoral amputation, limiting the results&#; generalisability within the prosthetic population [59, 60, 73,74,75,76]. Also, the majority of the studies (94%) are based upon biomechanical and physiological findings during the performance of walking tasks, except for 2, which used performance and subjective measures [63, 86]. Another concern relates to the overall high risk of bias. The high risk of bias can be attributed to the lack of randomisation, the inability to blind participants to the prosthetic condition and the lack of reporting protocol deviations. Specifically, the lack of randomisation and inability to blind participants are essentially inherent to prosthetic research. Taken all of the aforementioned elements into account, heterogeneity of the outcome measures combined with small sample sizes, limited familiarisation time, and the high risk of bias of the included studies do not allow robust conclusions to be made. Therefore, the recommendation is to perform adequate sampled studies with a limited number of outcome measures and ample familiarisation time evaluating a prosthetic device during daily activities. Secondly, the recommendation is shifting the emphasis towards the psychosocial dimension of quality of life through questionnaires finding a suitable poise between objective and subjective measures to obtain a thorough insight into the benefits of prosthetic devices. A recent review provides an overview of psychometric properties of functional, ambulatory, and quality of life instruments to be used in people with a lower limb amputation [43]. At last, we advise conducting prospective studies assessing the benefits of passive, quasi-passive and active prostheses in the longer term similar to those already conducted comparing prosthetic knees or those investigating quality of life after an amputation without comparing prosthetic devices [14, 30, 98,99,100,101].

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