Comparative assessments and device-based investigations

Historically, prosthesis assessments involving myoelectric prehensors have often been technically orientated. Newly-developed or re-designed myoelectric prehensors have often been compared with the body-powered split-hook type in studies when analysing simple and specific activities (6). Viewing the split-hook as the ‘gold standard’ in terms functional usability is questionable however, since this is not a modern device (it has been available for over a century) and can no way be considered to be as usable as the natural hand (57). In

67 similar assessments, using a split hook has been found to take twice as long as the same task undertaken with the natural hand (126). However, using a myoelectric prosthesis was said to take more than twice as long as the split-hook itself (126).

Most prehensor-based evaluations involve the use of only one subject (6). An early example of this form of study was carried out by Agnew (1981) who found the split-hook to be more functionally useful than a myoelectric hand (219). The assessment methods used at this time were based around simple timed tests, which although easy to measure, may not provide the most accurate levels of functionality measurement.

Another example of single-subject study was conducted by Meredith (1994), who compared the relative capabilities of a split-hook, a myoelectric prehensor and an electrically- powered hook using a single-subject prosthesis user (88). A series of ADLs and standardised measures were used in this investigation, although it was said that some familiarity with the equipment may have influenced the results. In this study, the results indicated that the electrically-powered hook was the most functional prehensor, although the user was said to be most familiar with this device, which possibly skewed the results (88).

Carey et al (2009) also used a single subject study to compare the functional usability of a body-powered split-hook to that of a modern myoelectric hand prehensor, again using ADLs based on common daily tasks (19). The body-powered prosthesis was employed for more common tasks but the prosthesis user was said to be reasonably proficient with both prosthesis types (19).

Investigations contrasting the available function from different methods of operation have also taken place, most notably those examining the respective function available from voluntary opening (VO) split hooks (the standard method) or voluntary closing (VC) split- hooks (6). Crandall and Tomhave (2002) found that the voluntary closing split-hook was the most functionally effective (20). This type of appliance is also used more extensively in upper limb sports prostheses, since the users can regulate the amount of grip strength and hence perform more accurate movements and tasks (220). In standard voluntary closing devices, the grip strength is pre-set, usually via the use of electric bands positioned around the proximal aspect of the hook (4).

68 The VC hook was found to require less activation force than the VC hand to achieve similar levels of grip strength by Smit and Plettenberg (2010) (138). The grasp dynamics of the split hook, rather than the addition of a cosmetic glove, was said to have been the cause for this significant (8 times larger) difference in required mechanical exertion (138).

A small number of studies have also compared myoelectric prehensors (6). Kyberd et al (2011) used the SHAP to assess the functionality of a range of myoelectric hands, with differing operating options (141). These options included different control methods, such as threshold and proportional, as well as different opening regimes, such as VO and VC, and differences in the degrees of freedom afforded by each hand. Of all these factors, it was the control method that proved to be the most influential, although the single subject was not a prosthesis user (the signal acquisition was attained from the author’s forearm for this paper) (141).

Van der Niet et al (2010) compared the respective functionality attained from the I- Limb (a multifunctional, multiple degree of freedom myoelectric hand) with a single degree of freedom, more standard myoelectric hand, the Otto Bock DMC (8). The assessment methodology again included the use of the SHAP, with the subject this time being a prosthesis user, at the wrist disarticulation level of limb absence. The i-limb proved to be no more functional overall then the Otto Bock DMC, and had an overall functionality index score (74/100) that was significantly higher than the I-Limb (52/100) (10). However, the prosthesis user stated that they preferred the I-Limb, despite the greater degree of functionality that was apparently available from the Otto Bock DMC (8).

These comparative studies offered an accurate representation of an individual’s distinct functional capabilities, and could be quantified and repeated consistently, but had a very narrow scope of application, and often did not relate to overall prosthesis functionality. The small numbers of subjects involved in these types of studies, who were not always prosthesis users, limits the effectiveness of the data in achieving overall prosthesis goals as defined by prosthesis users.

Larger scale studies of upper limb prosthesis usage patterns have been undertaken, and have normally employed the use of questionnaires. The following section outlines the results and implications of some of these studies.

69 3.2.2 Upper limb prosthesis usage patterns and survey results

Questionnaires have been widely used to acquire prosthesis functional usage rates from larger numbers of users and also have the advantage of being genuinely equitable in sourcing information (57, 80). In addition, they may be distributed to larger numbers of upper limb prosthesis users than would reasonably be expected to participate in other functionality assessments (80).

Surveys in various International countries, with different prescription availability for myoelectric prostheses, have generally demonstrated relatively low uptakes and usage rates for myoelectric prostheses, although the focus of these assessments has not specifically targeted functional capability or specific levels of myoelectric prosthesis usage (14-18, 20, 21, 49).

Body-powered prostheses have been shown to be worn for longer periods than myoelectric prostheses by the majority of upper limb prosthesis users for work-related activities (6). Stein and Whalley (1983) demonstrated that a prosthesis user took twice as long to undertake similar tasks with a body-powered prosthesis, and five times as long with a myoelectric prosthesis, when compared to a fully-functioning natural hand performing the same tasks in one study (126).

In 1989, Roeschlein and Domholdtz surveyed 86 prosthesis user subjects in Indianapolis, USA (221). Most of those surveyed wore body-powered hooks for functional purposes; these were deemed functionally useful by the majority (65%) of those surveyed. Very few users (only 3) used myoelectric prostheses, and only 1 of these users deemed their prosthesis functionally useful (221).

At around the same time, Balance and Wilson (1989) in Canada found that new sockets were being refitted to approximately 30% of the prostheses worn by children within their survey (51). Socket design and delayed response times were quoted as disadvantages with respect to the myoelectric prosthesis, which was only worn part of the time during the day by those supplied with it (51). Table 3.1 (below) provides an analysis of the studies published to date which have investigated upper limb prosthesis using case studies, functionality assessments or questionnaires.

70 Table 3.1: Surveys performed investigating upper limb prosthesis functionality. A review was an examination of records available within the clinic and not questionnaire-based.

In Slovenia, Burger and Marincek (1994) found that only 2% of users wore a myoelectric prosthesis, with 70% wearing cosmetic prostheses (16). Many amputees within this survey were found to compensate with the natural limb where possible, and most of the

Author Study type Ref

No. Sample Size (n) Level / Prostheses types studied Uptake % Stein & Walley (1983) Review (126) 20 All levels / All types - Van Lunteren et al (1983) Survey (18) 13 All levels / All types 61 Millstein et al (1986) Survey (147) 83 All levels / All types 33 Glynn & Hunter (1986) Survey (93) 78 All levels / All types 86 Datta & Ibbotson (1998) Review

Survey

(222) 29 All levels / All types -

Balance & Wilson (1989) Review (51) 17 All levels / All types - Roeschlein & Domholdt

(1989)

Survey (221) 86 Transradial/ All types 56

Jones & Davidson (1995) Survey (49) 76 All levels / All types 52 Atkins et al (1996) Survey (14) ~2,500 All levels / All types 32 Hubbard et al (1997) Survey (235) 142 All levels / All types 45 Kyberd et al (1998) Survey (17) 68 All levels / All types 79 Routhier et al (2001) Survey (223) 18 All levels / All types 56 Kuyper et al (2001) Review (13) 224 All levels / All types

(children)

-

Crandall & Tomhave (2002)

Survey (20) 24 All levels / All types 84

Burger & Marincek (1994)

Survey (16) 414 All levels / All types 63

Dudkiewicz et al (2004) Review (15) 45 All levels / All types - Pylatiuk et al (2007) Online (12) 54 All levels / Myoelectric - Biddiss & Chau (2007b) Survey (214) 242 All levels / All types -

71 subjects with transhumeral or more proximal levels of limb absence didn’t use functional prostheses, which were seen as unreliable. Around this time, in Australia, Jones and Davison (1995) found that no limb wearers were using a myoelectric prosthesis; the body-powered prostheses that were used instead were said to be useful for lifting and carrying activities (49).

The relatively low numbers of upper limb prosthesis users compared to those requiring lower limb prostheses has meant that large scale surveys have been rare. One of the few notable large-scale studies was performed by Atkins et al (1996) in the United States, where the survey sample comprised of approximately 2500 upper limb prosthesis users (14). This survey demonstrated that almost twice as many adult prosthesis users (63%) wore body- powered prostheses compared to myoelectric prostheses (37%) (14). The results demonstrated that multiple functional use was a key priority, as well as the need for enhanced finger movement and wrist function, with less dependence being needed on visual attention during the performance of everyday activities. Myoelectric users also identified electrode reliability in supplying the appropriate signal as being problematic in many cases, and questioned the reliability of both these and the subsequent response of the myoelectric hand (14).

Poor function was quoted as reason for non-usage by Gaine and Smart (1997). Of the 55 users within this survey, the male-female ratio was 8-1 (44). Although daily usage rates were still high, it was said that this is not always a good guide with regard to satisfaction, since there are other reasons (apart for functional employment) for prosthesis usage (44).

Lack of function was found to be the largest problematic factor for prosthesis users who were surveyed in 1998 by Kyberd et al in Oxford, United Kingdom; with almost one third of prosthesis users stating that this was the greatest limitation in the usefulness of their prosthesis (17). Their conclusion was that future functional prostheses should offer more function than current variants, which were also described as being too heavy by many prosthesis users. Cosmetic prostheses could be used for passive functions, but users complained that the wire fingers within the foam hands, which were not devised for functional usage, broke frequently when moved into different positions.

72 Dudkiewicz et al (2004) surveyed 45 upper limb prosthesis wearers in Israel, but only three of these had previously used a myoelectric prosthesis; all of which were subsequently replaced with a cosmetic prosthesis (15). The cosmetic prosthesis was again the most used of all the prosthesis types. Dissatisfaction issues reported with myoelectric prostheses included increased weight compared with other prostheses, plus the sweating which resulted from an intimately fitting socket and a lack of cosmesis. The average myoelectric limb user was found to be considerably younger than the respective body-powered user. Younger users were said to be more conscious of cosmesis, and favoured a compromise in function for an improvement in prosthetic appearance. At more proximal levels of limb absence, usage of myoelectric prostheses was said to be particularly low.

Pezzin et al (2004) found that upper limb prosthesis users are less satisfied with their prostheses than lower limb users (102). A well-fitting, easy to use prosthesis that enabled the user to undertake ADLs was said to be of paramount importance to the prosthesis user. Datta et al (2004) found that almost 34% rejected their upper limb prosthesis and stated that ‘we have no evidence to suggest that the provision of externally powered prostheses for proximal upper limb deficiency are likely to be any more successful in terms of function or lower rejection rates’ than other prostheses (21).

However, an internet survey by Pylatiuk et al (2007) demonstrated that a high degree of satisfaction was felt by myoelectric prosthesis users (n=54) of all age ranges with respect to the cosmesis afforded by them (12). Conversely, most myoelectric prosthesis users wanted a higher degree of proprioceptive feedback, which could be more readily accomplished when using a body-powered prosthesis via a harness. Many users complained about the increased weight of the myoelectric prosthesis and the relatively slow grasp speed. This may have been related to electrode sensitivity, because 20% of users also stated that electrode contact and interference issues were a significant problem with respect to the control of the prosthesis (12).

Biddiss and Chau (2007b) found that 20% of those surveyed didn’t employ their prosthesis (n=242) (214). Those with acquired limb absence were less likely to reject their prostheses than those with a congenital absence, and more proximal levels were also more likely to reject the prosthesis. Females too were more likely to reject the prosthesis. A large proportion of non-users, 88%, stated that the limb was too tiring and too difficult to use.

73 These authors stated that ‘future research should focus on more comfortable, functional technology’ (214).

Most surveys conducted between the inception of myoelectric prostheses and the present day still state that body-powered prostheses still have significant appeal, despite the fact that body-powered prostheses do not provide any level of cosmetic appeal, and the harness associated with them is seen as a significant disadvantage for prostheses of this type (4). The performance of finite tasks using all types of prostheses is still found to be problematic, and often leads to rejection (6). Nevertheless, most authors have still concluded that the body-powered prosthesis with a VC split-hook was the most functional type of prosthesis (6).

Of all the user categories, children are the ones most predominantly prescribed myoelectric prostheses (73). The appeal of a ‘bionic limb’, particularly for parents, is hard to resist (6). However, a static socket and a growing residual limb do not appear to be compatible in terms of functional usefulness and are clearly of interest to this thesis. The following section examines those surveys that have been undertaken with children as the prosthesis user subjects.