Restoring function is the key purpose of non-cosmetic upper limb prostheses, and perceived functional gain has been recognised as a key determining factor for prosthetic acceptance and user satisfaction (100). Successful functional restoration relies upon two aspects:
1. The extent to which the technical features of the prosthesis support the intended functions, such as being of bearable weight, having a terminal device with sufficient aperture width, grip force, and DoFs to acquire objects. This can be referred to as “engineering evaluation” and is usually ensured by the manufacturer and assessed by standard technical tests;
2. The ability of the amputee to employ these features to perform functions. Functions in
this context refer precisely to the performance of manual tasks including ADLs, work- related and sport and recreational activities. This can be referred to as “functionality evaluation”.
Functionality (ability to perform manual tasks) (25) is the focus of ongoing research in the field of upper limb prosthesis evaluation. In the literature, many functionality-related terms are discussed, including “functional use”, “functional gain”, “functional value”, and “prosthetic efficiency”. Functionality evaluation also varies between studies: some authors report the number of tasks that can be performed with the prosthesis (101-103) while others infer functionality from describing the quality of the performance (104-106). Alternatively, “time to complete task” is used to indicate functionality (25, 107). Functionality has been estimated by two different approaches: using interviews/questionnaires and using observational tests.
2.8.1. Interviews/questionnaires based evaluation of the functionality
Interviews/questionnaires that aim to evaluate upper limb prostheses usually involve exploring qualitative aspects of the manual performance that are likely to be related to functionality. These include: “the ability to perform activities” (102), “the ease of performance with the prosthesis”, “the usefulness of the prosthesis for performance” (108) and “the restrictions that the prosthesis imposes on the ability to perform” (109).
A number of questionnaires have been validated for upper limb prosthesis evaluation, but only two of them are suitable for adults; namely the Orthotics and Prosthetics User Survey
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with its Upper Extremity Functional Status (UEFS) module (OPUS) (105, 110), and the Trinity Amputation and Prosthesis Experience Scales (TAPES) (109).
OPUS is a questionnaire designed for evaluation of upper limb and lower limb prosthetic and orthotic users (105). It is claimed to allow comprehensive assessment of the functional status, health-related quality of life and satisfaction of the users. Each of these aspects is addressed in a self-contained module. Functionality is estimated in the Upper Extremity Functional Status (UEFS) module based on the difficulty associated with performing 19 ADLs rated on a 4 point scale (0 = not able, 1 = difficult, 2 = easy, and 3 = very easy) (110). In addition, amputees are asked to state whether or not they perform each of the tasks using their prosthesis. The UEFS list and its scoring scale have recently been revised and validated (110).
TAPES, in its original form (111), is a 54-item self-administrated questionnaire that focuses on the adaptation of the amputee to their amputation, prosthesis use, satisfaction and the level of activity restrictions that the amputee experiences in everyday life. Additionally, the TAPES assesses phantom and residual limb pain, and other medical problems unrelated to the amputation. The TAPES was originally developed for lower limb amputees and subsequently the internal reliability of the TAPES modules for assessment of upper limb amputees was established (109). Insight into functionality can be provided from two main modules that assess the level of adaptation to the prosthesis (psychological adjustment module) and level of restriction imposed by the prosthesis (activity restriction module) in functional social and athletic activities.
2.8.2. Clinical observational tests
In addition to interviews/questionnaires, functionality can be assessed by evaluating the performance of the amputee in a number of manual tasks within a clinical or laboratory environment by means of observational tests. The evaluation mostly takes into consideration the time to complete the set of tasks (25) or quality of the performance based on the clinician/researcher’s judgement (108).
Several observational tests have been used to evaluate functionality of the upper limb in children and adults (see recent critical review (112)). However, only a few of them have been validated specifically for upper limb prosthetic evaluation. Of these, only the Southampton Hand Assessment Procedure (SHAP) (25) and the Assessment of the Capacity for
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Myoelectric Control (ACMC) (104, 113) are suitable for upper limb prosthetic evaluation in adults.
SHAP is a universal observational test (for prosthetic or anatomical assessment) that addresses the functionality of unilateral hand in its performance (25). The SHAP comprises completion of 26 timed tasks: 12 abstract object tasks and 14 activities of daily living (ADLs). These tasks were identified in previous studies and include the natural contribution of all six prehensile patterns. When performing SHAP, subjects are instructed to use their prosthetic hand as long as the task can be achieved unilaterally, and as a main manipulator when the task is bimanual. Subjects are encouraged to use the previously mentioned 6 gripping patterns while grasping the objects. The scoring of tasks is proportional to the time needed to complete the task. Aspects of the SHAP psychometric properties have been established on normal subjects (25). The SHAP procedure is available at http://www.shap.ecs.soton.ac.uk/about- pubs.php.
SHAP has recently been used to compare the functionality of different prosthetic terminal devices (114-116). When used to compare the performance of different commercial 1 DoF myoelectric hands, SHAP also highlighted the determinant influence of the hand shape and control strategy on the overall functionality (115). For instance, the smallest hand tested (OttoBock Transcarpal hand) had a restricted gape which presented the user with difficulties in picking up large objects, and scored significantly lower on SHAP than the other hands. Interestingly, opening speed was reported to have only a limited effect on the hand’s functionality (115).
In addition to providing interesting comparative data between different devices, SHAP more importantly shows how far devices are from the anatomical hand with regard to their functionality. SHAP score (usually referred to as functionality index) was found to be above 95 out of 100 when the test is completed using the dominant anatomical hand in young adults (25). In comparison, using the prosthetic hand, functionality index values range from 17 out of 100 (117) to 80 out of 100 (118).
While SHAP is a useful measure, it is based on measures of number of tasks performed and time taken to perform them (115), and hence provides no indication of how a subject performed the tasks. The ACMC was specifically developed to evaluate the ability to control the myoelectric prosthesis (108). For prosthetic evaluation it is assumed in the ACMC that the
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ability to control the prosthesis would be demonstrated differently while grasping, holding, releasing and co-ordinating objects and hence the ACMC focuses its evaluation on each of these phases of the task. The ACMC involves scoring of 30 items covering aspects related to the performance of any bimanual ADL including: gripping, holding, releasing, and coordinating between two hands. These items are scored based on a 4 -point ordinal scale (0 = not capable, 1 = sometimes capable, capacity is not established, 2 = capable on request, and 3 = spontaneously capable). The items’ scores are then converted into linear measures by using Rasch measurement models. Since these items can be observed in any bimanual ADL, any purposeful bimanual activity that is deemed meaningful to the prosthesis user can be used for this assessment. The ACMC is suitable for prosthetic evaluation in adults and children. Certain psychometric aspects have been demonstrated, including acceptable validity and good sensitivity to change (104). Recently, further work on ACMC validity has been conducted in which discriminant validity and unidimensionality of the ACMC was established (119).
ACMC has also been used in a comparative case study (114). ACMC results showed the different abilities of the user to control the i-Limb plus and DCM Otto bock hand with the superiority of the i-Limb plus. As part of the reliability investigation of the ACMC, the ACMC was also used to infer the improvement resulting from learning to control the prosthesis over a period of time (120). The investigation involved assessment of two groups of users (established users and new users) at least 6 times over a period of 18 months. The ACMC indicated high capability to use the prosthesis in established users whereas in new users a trend of improvement was demonstrated (120).
The major limitation of the ACMC is its inter-rater reliability, that is, the results of this test are strongly influenced by the experience of the scorers (113). ACMC is also limited in its myoelectric prosthesis control evaluation; therefore it is not suitable to compare different control systems or to compare prosthetic performance to anatomical hand performance. ACMC scoring may need revision (119), additionally, criteria for manual task selection are required to address the influence of task difficulty on ACMC scoring (119).