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Case Reports
. 2018 Jan 3;15(1):1.
doi: 10.1186/s12984-017-0340-0.

Case-study of a User-Driven Prosthetic Arm Design: Bionic Hand Versus Customized Body-Powered Technology in a Highly Demanding Work Environment

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Case Reports

Case-study of a User-Driven Prosthetic Arm Design: Bionic Hand Versus Customized Body-Powered Technology in a Highly Demanding Work Environment

Wolf Schweitzer et al. J Neuroeng Rehabil. .
Free PMC article

Abstract

Background: Prosthetic arm research predominantly focuses on "bionic" but not body-powered arms. However, any research orientation along user needs requires sufficiently precise workplace specifications and sufficiently hard testing. Forensic medicine is a demanding environment, also physically, also for non-disabled people, on several dimensions (e.g., distances, weights, size, temperature, time).

Methods: As unilateral below elbow amputee user, the first author is in a unique position to provide direct comparison of a "bionic" myoelectric iLimb Revolution (Touch Bionics) and a customized body-powered arm which contains a number of new developments initiated or developed by the user: (1) quick lock steel wrist unit; (2) cable mount modification; (3) cast shape modeled shoulder anchor; (4) suspension with a soft double layer liner (Ohio Willowwood) and tube gauze (Molnlycke) combination. The iLimb is mounted on an epoxy socket; a lanyard fixed liner (Ohio Willowwood) contains magnetic electrodes (Liberating Technologies). An on the job usage of five years was supplemented with dedicated and focused intensive two-week use tests at work for both systems.

Results: The side-by-side comparison showed that the customized body-powered arm provides reliable, comfortable, effective, powerful as well as subtle service with minimal maintenance; most notably, grip reliability, grip force regulation, grip performance, center of balance, component wear down, sweat/temperature independence and skin state are good whereas the iLimb system exhibited a number of relevant serious constraints.

Conclusions: Research and development of functional prostheses may want to focus on body-powered technology as it already performs on manually demanding and heavy jobs whereas eliminating myoelectric technology's constraints seems out of reach. Relevant testing could be developed to help expediting this. This is relevant as Swiss disability insurance specifically supports prostheses that enable actual work integration. Myoelectric and cosmetic arm improvement may benefit from a less forgiving focus on perfecting anthropomorphic appearance.

Keywords: Artificial arm; Artificial limbs; Body-powered prosthetic arm; Myoelectric prosthetic arm; Prosthesis design; User-driven design.

Conflict of interest statement

Ethics approval and consent to participate

The user featured in this retrospective publication of on the job prosthetic arm evaluation consented to the publication and happens to be the first author and corresponding author of this study. As this work details the results of direct prosthetic device evaluation and component development as a necessity of employed work, this does not conform to the structure of a trial but of hand(s) on real life rehabilitation. Any adverse or negative side effects of prosthetic use as well as time, cost and efforts for medical treatment or prosthetic part repairs are an integral part of life with using prosthetic arms for PDW, and this paper shows how some of the significant negative aspects were minimized through user driven efforts. Ethics approval for reporting health and prosthesis use based outcomes was applied for and granted. The name of the responsible ethics committee is the Cantontal Ethics Committee of the Canton of Zurich, Switzerland. The commitee’s reference number for this is BASEC-Nr. Req-2017-00088.

Consent for publication

The user featured in this study is the corresponding author and first author of this study. As he writes this line, he, again, consents to this publication.

Competing interests

The authors declare that there is no competing or commercial interest and no conflict of interest.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
On location – Death scenes that warrant a board certified senior forensic pathologist to travel on location and perform a full body investigation with forensic scientists and photography usually are “extraordinarily extraordinary”. Indoors or outdoors work [a: simulated/staged teaching death scene mock-up showing protective gear (arrow) – the body will be fully undressed, without cutting clothes, and then turned over and back while obtaining a detailed body surface inspection; b: outdoors death scene with burn victim on passenger seat (arrow) in a -15 deg C winter night with ice and snow covered roads] usually is problematic on several levels; at this particular death scene with the burnt car, several specialists repeatedly fell to the ground due to extremely slippery and steep ground. Undressing and examining a body from all angles (c: deep hand / finger injury, details in D through F) requires careful preservation of losely attached evidence so that even an attacker’s hair remains in place (c, d: dressed body; e, f: undressed). Attacker was a cat in this instance
Fig. 2
Fig. 2
Occupational strains – a: Duration of deployment correlates with excessive sweat; myoelectric sensors start to usually fail due to sweat (purple line) after 10 min of bodily exertion, a third of a minimal duration of a death scene investigation; after 1 h working on scene, excessive sweating occurs in 50% of all cases and before 2 hours are reached in all cases; logistic regression (blue curve) indicates that excessive sweating occurs in over ∼ 85% of cases with duration of deployment over 1,5 hours; Chi-Square LR p < 0.001. b: Half of the non-remote but all of the remote locations generated excessive sweating (Chi Square LR p=0.0036). c: When undressing a body was a requirement, excessive sweating occurred in 60% of the cases but just in 25% when body was found naked (Fisher’s Exact Test: n.s
Fig. 3
Fig. 3
a: Manner of death (x-axis) correlates with required manual skill level (MSL) (y-axis; color code see right side of diagram) in that suspected homicide cases require a MSL of 8 to 10, whereas other manner of deaths range from 3 to 10; the differences between the manner of death categories with regard to MSL are statistically significant (Chi Square LR p=0.0013). b: Manner of death (x-axis) also significantly correlates with sweating being a significant workplace issue for suspected homicides (100%), accidents (80%) and others (about 50%). The differences between manner of death categories with regard to excessive sweating occurring are statistically significant (Chi Square LR p=0.005)
Fig. 4
Fig. 4
Principal Component Analysis (PCA) shows that the actual factors directly impacting excessive sweat causing soaked clothes are duration of deployment and manual skill level estimate. Ambient temperature correlates negatively with excessive sweating in that very cold death scenes are usually outside and do not always allow for an excessively differentiated clothing layer adaptation due to the nature of these scenes. Weight of body, and requirement to undress the body pale against these in comparison for the examiner in question
Fig. 5
Fig. 5
a: Conventional figure-nine harness (Otto Bock, Germany) compresses the brachial plexus (red star: compression point on brachial plexus, green star: humeral head and deltoid muscle for orientation; matching anatomy diagram in b) in what is a well known problem, also for backpacks. b: brachial plexus (nerve structures, highlighted red) with harness compression point (red star) in comparison with location of humeral head and compression point for shoulder anchor as shown in c. c, d: New development with a composite flexible thermoplastic EVA (ethyl-vinly acetate) and rigid carbon fiber shoulder anchor that effectively solves the problem by shifting the pressure point to the humeral head and deltoid muscle (green star) while relieving the brachial plexus (red star) by virtue of a rigid bridge
Fig. 6
Fig. 6
“PUPPCHEN” wrist – design details [106]: It contains one part, the wrist mount proper, that resides on the end of the prosthetic socket (#3) and a second part, an adaptor, that resides on the terminal device (#4). The design principle of the lock uses balls (#3, B). They hold the adaptor (#4) inside the socket-side wrist unit (#3) by residing in a circular groove of that adaptor (#4, H). The pressure on these balls force them inside that circular groove. That pressure can be released by turning the lock (#3, D) in such a way that a shoulder inside that lock (#3, A) is displaced so that the balls (#3, B) can slide back and release the adaptor (compare #1 and #2: black square). Rotation of the terminal device is prevented by interlocking the adaptor’s lower rim (#4, K) with a matching ring contained in the wrist (#3, C). The locking/unlocking switch (#3, D) is pushed up by virtue of springs at its base (#3, E). When unlocking the wrist (#2), these springs (#3, E) get squeezed
Fig. 7
Fig. 7
Opening the locked wrist lock. Left image: Grab wrist unit with a firm grip. Middle image: Pull wrist unit towards socket. Right image: Turn wrist unit to lock it in the ’open’ position
Fig. 8
Fig. 8
Changing terminal device position. Left image: pull out terminal device by a few millmeters. Turn it. Push it back in. – Closing the wrist lock. Middle image: Grab wrist unit. Turn it to allow it to slide back. Right image: Allow wrist unit to slide back. It is pushed into the ’locked’ position ny action of internal springs
Fig. 9
Fig. 9
a: Wrist unit (diagram see Fig. 6, usage Figs. 7- 8) with socket mounted side (1) and terminal device adapters (2: UNF 1/2-20 threading; 3,4: Otto Bock sub-16mm diameter). b, c: assembled CBPA with (1) terminal device, (2) wrist, (3) carbon fiber socket, (4) cable, (5) shoulder mount/brace
Fig. 10
Fig. 10
Bowden cable setup [105]: bendable but not stretchable element (6) on which two anchor points (4,5) are mounted between which the cable housing, sheath or conduit (3) for a cable (1,2) is placed so that any pull along the cable will forcedly press the endings of the sheath/conduit/housing (3) firmly into the anchor points (4,5) which as a design principle requires that the distance between the anchorpoints (4,5) is always smaller than the length of the conduit (3)
Fig. 11
Fig. 11
Socket mounted camera with video stills from workplace video documentation. CBPA (a-d) successfully grasps and holds on to plastic cover to pull body over from striker to CT table. TBI (e-h) can be seen to slip off not able to pull about 70 kg body weight by pulling plastic cover. Also, TBI fails to open jar with petrochemical substance (i-h) despite cleaning jar surface to make it less slippery

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