Usually, academic researchers are aware of the problem that them tagging their research subjects with tags entails: the tags would have to be correct. Of course we are all free to tag also researchers as, say, “healthy”, but without prior actual check, how can we be sure?
Now, everyone and their grandmother has arrived at realizing that “amputees” can be “healthy as an ox” – and not just that: they can be so fit as to fly an airplane, participate in sports and sports competitions, or do everyday tasks that are just as mundane as what you can read on this blog.
Worse – even Helsana (Swiss health insurance) correctly (as I must say) labelled me as “healthy”, and based on that, as “in no need for medical treatment” when I applied for a disability related surgery [link]. They were not inherently wrong.
In fact, the WHO also tries to distinguish between the adjectives healthy, ill, impaired, restricted, and limited, which is why they also discriminate between health on one hand (as feeling and being well), infirmity / impairment on the other hand, and disease on the third.
However, what always struck me as beautiful about the USA was their uncanny directness in verbalizing need, real need: and it seems as if there is a “no child left behind need” there. Here, we will talk about academic researchers that still believe in a “healthy” versus “amputee” dichotomy of this world.
So there are “healthy people” on one hand, and “arm amputees” on the other.
That is an odd contrast.
Because it expresses, states, reads, as “that is an arm amputee, therefore that person is sick“. But to call any healthy amputee sick seems clearly sick in its own way.
If you want to dispute this perception, take it to the authorities and instances that do treat amputees (with no actual illness in any narrow sense) as “healthy” – which, as far as I see it, is how it should be. Like, employers. As long as I am healthy, I will have to, want to, should go to work, and unless I have a doctor’s note that I am sick / ill (nothing to do with disability!), I cannot, will not stay at home. Of course there tends to be a certain higher prevalence of particular illnesses in the disabled community pending individual specifics, but as such, and for any individual, this is not a given. Or health insurances.
In other words, I may be healthy, and I may have a handicap, without contradiction, at the very same time.
Where does all that take us?
Treating amputees as lesser people by and large, and ignoring strict definitions of terms to guide the further examination generally, and to narrow down research problems specifically, poses a significant risk firstly for research and development and secondly for the amputee community.
It feels like these researchers employ the “healthy” adjective specifically to separate the world in more distinct groups than there really are. This then in my view indicates that they feel insecure, and the constant need to belittle arm amputees as “not healthy” cannot be healthy over time. As I believe such red flags to be just that, it is often interesting to dig deeper and I started looking into this years ago, and, how interesting.
This behaviour is a source of problems since a considerable time, as it has grown into a sort of culture.
Are arm amputees a punch and judy type group where researchers can “use” all “available” “subjects” (as in: king vs. subject, emperor vs. underling) as ever they please?
Can researchers throw around epithets such as “healthy” without having checked even frequent and prevalent conditions that appear relevant to the cause of the study?
Does this open up a glimpse into particular (so far hidden) vulnerability of researchers [link – I already have that stuff ready, just got to write that down]? I think it has at least the potential to do that.
There is another level of meaning here, as I also suggest that when I stated in 2008, that 10 years later, a body powered prosthetic hook will still by far be the best prosthetic device for real work, because social impediment and not technical obstacles would be the underlying real problem. And to find hooks to explain and demonstrate such always takes a bit of time. First to find the single bits and pieces. Then to see who governs, oversees, or maybe more often, does not oversee, an of that vast spending. Let us point to past relevance, with clearly present total lack of myoelectric error rate improvement over 40 years [link] after which, still, unabashed, undeterred, researchers, that I personally confronted with this, told me personally that myoelectric technology “was here to stay”, after which they only became a tiny bit more quiet when I started to post raw cost of wearing and utilizing a myoelectric arm as a user [link]. They want to reach error rates of below 0,03% since then! (Kidding). Myoelectric arms remain in fact a suffering and a struggle [link], as they are (in essence) junk technology [link]. Researchers nevertheless conspired to have arm amputees act out their suffering in a public circus setting under the umbrella of “Cybathlon”, where a prosthetic arm race is set up solely for staring and watching that struggle, and at the same time was at first explicitly intended to allow myoelectric arm technology to win such circus freak show competitions [link]. One interesting dead giveaway for their total failure to provide relevant ideas for any research into actually useful technology (e.g., how will I cut the hedges in summer? [link]) is the personal choice they made for their organizing body: zero own experience or skin in the game for the relevant technology [link]. All the while, the European Union seems to have thrown out over 50 million Euro for what I essentially regard as junk technology as it is not usable for real work, nor will it ever be, nor will it be comfortable and easy to put on and take off, nor will it be economic and efficient [link].
Researchers themselves seem to have a range of issues. They seem to not know what a simple muscle on a forearm does, with funny effects [link]. Katrin Grueber, former head of an institute they called Institut Menschen Ethik Wissenschaft, wrote what I felt was entire nonsensical garbage with relation to limb prosthetics, after which she refused to respond to my points of criticism twice (more details: see [link]). What is that, a new ethic? Et cetera.
This type of total ignorance defines a whole cohort, as I stated in 2008 already, that this is the type of people that will see to it (if they want it or not) that the body-powered prosthetic split hook will remain the thing to wear for any foreseeable future for anyone that wants to get things done, sweat or not sweat. They cannot even get the symbolic part of their arrogance right [link], nor does transhumanism help them as they cling to anachronistic conventionalism which defies their own claim to follow high-tech [link, link].
So, why?
With Sherlock Holmes, once the usual rational explanations are all off the table, with cold logic, only irrational explanations remain. I guess we are dealing with a range of people that for any reason keep their own personal inclinations hidden, not too well though, in a closet. As such inclinations are, they constitute a force of nature so they cannot be tamed. They will inundate, cry out for attention. Read the above again now, with that in mind. Makes the light go on?
We are just waiting for someone to call this by its name : )
Healthy subjects in research
A subject that is proposed to be healthy will have to be checked for that, unless the study explicitly states that health status is self-declared.
You cannot possibly suggest anyone to have a medically certified health status based on their simple assertion unless also the rest of the study is also faith based. Sure: we have been praying for better prostheses and treatments for phantom pain, but look where that got us!?
So we have divers, pilots, motor vehicle drivers, and so on, pass regular health checks – but you do not give a dime about arm amputees and their control groups as study subjects?
That, in my view, tells us a lot about the social standing of the arm amputee community. And more importantly, who cares. Certainly not some of these study authors.
Non-disabled people
The proper approach to people with upper limb difference as well as arm amputees is to acknowledge that they will have an impairment on one hand and that they may or may not have possibly health related issues on the other hand.
Let us approach the subject of allegedly non-disabled (“healthy”) people.
From [1]: in 2019, more than one half (53.8%) of adults aged 18–34 years, regardless of their development or full presence of limb parts, reported having at least one chronic condition, and nearly one quarter (22.3%) reported having more than one chronic condition. The most prevalent conditions were obesity (25.5%), depression (21.3%), and high blood pressure (10.7%). So if you select any convenience sample across that population and do not find some 50% having a chronic condition, then your sample will probably not be representative of the general population.
Differences in the prevalence of having a chronic condition were most noticeable between young adults with a disability (75.8%) and without a disability (48.3%) and those who were unemployed (62.3%) and students (45.8%). That still leaves about 25% of disabled people without a chronic condition.
From [2]: Drug overdoses were the leading cause of increased mortality in midlife in each population, but mortality also increased for alcohol related conditions, suicides, and organ diseases involving multiple body systems.
A general baseline to assert any adult person as “healthy” thus would be, based on above suggested health evidence, at least a blood pressure measurement, BMI, and a tox screen.
From [3], the health status of a subject in a clinical trial must be
assessed during the screening period to determine eligibility and during the course of the trial to determine maintenance of eligibility and potential adverse study / intervention effects. Screening assessments are usually based on medical history, physical examination, safety laboratory, vital signs, ECG, and check of inclusion and exclusion criteria.
I did not even make that up. It was here all along. Why is it always me that has to read things for you, anyway?
Health in arm amputees
An arm amputee that, on top of above mentioned general health issues, also does not suffer from skin related or musculoskeletal system related or other pain related issues, may be (then) considered healthy. Even if the pain is always there, I would call neuropathic deafferentiation type neuropathic phantom pain a part of my habitual constitution and not an illness or disease. Only that that type of cause makes for the smallest part of my phantom pains, which has peripheral causes that come and go, and that I can address. Read on though.
With regard to the skin, and particularly in the context of prosthetic arm use, we expect dermatitis (25/63), general rashes or other pre-existing diseases (14/63), friction rashes (5/63), epidermoid cysts (8/63), follicular hyperkeratoses (6/63), verrucous hyperplasia (3/63), calluses (1/63), traumatic ulcers (3/63) as well as infections (5/63) [4]; while that study emphasises problems of leg amputees, arm amputees will have somewhat similar issues, maybe not so many ulcers or extensive calluses. But even just half an hour or an hour of ballroom dancing, and my prosthetic liner will cause a friction/sweat skin rash that is so bad it makes my stump and phantom pains flare up. Personally, I wear a liner liner since years that does away with that [link]. Researchers, they ever check for that and report it? Nah, uninteresting ; ) better perform an fMRI, right.
At any rate, in real life, the skin of the residual limb should be monitored closely by both the clinician and the patient, especially in the prosthetic training period, as excessive pressure or shear within the prosthetic socket can very quickly lead to skin breakdown [5]. If you want to perform a study, consider this.
Overuse of the intact limb in upper limb amputees is associated with a higher incidence of self-reported musculoskeletal pain in the upper limb amputee. This plays well into the pains related to the stump and phantom pain, as these tend to blur into each other.
Common areas of pain in the upper limb amputee are in the neck/upper back (57%) and shoulders (58.9%) [5]. Conversely, if your research sample at least initially does not at least contain 50% with such problems, then your sample risks to be skewed which tends to have an impact on the results interpretation.
The prevalence of pain in areas other than around the site of amputation is high, with chronic back pain being a complaint in 52% of upper limb amputees, neck pain in 43% of upper limb amputees, and contralateral limb pain present in 33% of unilateral upper limb amputees, respectively.
These are not percentages to ignore.
These secondary areas of pain are likely, in large part, attributable to overuse syndromes and compensatory strategies [5].
Not that real studies take that into account ; ) better head right over to the fMRI.
Examples: some papers
Phantom pain
Flor H, Elbert T, Mühlnickel W, Pantev C, Wienbruch C, Taub E. Cortical reorganization and phantom phenomena in congenital and traumatic upper-extremity amputees. Experimental brain research. 1998 Feb;119:205-12 [6]
This study of the Department of Psychology, Clinical Psychology and Behavioral Neuroscience, Humboldt-University, Berlin, Germany, Department of Psychology, University of Konstanz, Germany, Institute of Experimental Audiology, University of Münster, Germany and Department of Psychology, University of Alabama at Birmingham, USA describes “Five congenital and nine traumatic amputees, five without and four with phantom limb pain, participated in the study, as well as ten healthy controls. The traumatic group comprised a subsample of a large sample of 100 unilateral upper-extremity amputees, chosen according to availability for the investigation in the neuromagnetometer laboratory. All amputees volunteered for the project in response to inquiry by their prosthetist or physician. Table 1 shows age, gender, and time since amputation of the study sample. The congenital amputees were younger than the traumatic amputees. Time since amputation was not significantly different between the groups. The mean age at the time of the amputation was 22 years in the traumatic amputees (ranging from 12 to 52 years). The subjects underwent a comprehensive neurological and psychological investigation, which included detailed assessments of phantom pain and phantom sensations, stump pain and stump sensations, preamputation pain, telescoping, and mislocalization (Flor et al. 1995; Knecht et al. 1996). The comparison sample of ten healthy controls was matched with the congenital amputees for age (M=36.07 years, SD 12.05, range 23±51 years) and gender (six women, four men).” Their tables for sensibility of amputees does not contain “healthy” controls – why? Can healthy controls not be checked for two-point discrimination?
Firstly, the statement that “time since amputation was not significantly different between the groups” is strange as there exists no time since amputation for healthy controls; the inferred assumption that an amputation “actually occurred” for congenital amputees will have to be regarded as contentious.
While this study by Flor et al. apparently assumes a somewhat homogenous population among congenital limb difference by stating “(..) congenital amputees are not actually “amputees.” Rather their condition involves an aplasia of the limbs such as in phocomelia (a congenital deformity in which the limbs are extremely shortened) and peromelia (congenital malformation). (..) No nerves have been severed as in traumatic or surgical amputation”, they do not seem to provide any further distinction of mechanism for limb difference, in order to discern, for example, the slow process of limb loss caused by amniotic band syndrome [7] which has to be assumed to be physiologically different from limb agenesis.
At any rate, other authors were able to express such concerns, such as follows: “although the causes for the congenital limb atrophy were unknown for the subjects of the present study, it is very likely that their malformations could have occurred during very early developmental stages” [8].
Secondly, pain that is reported as phantom pain will first have to be examined from both a vascular / angiographic as well as from a musculoskeletal / orthopedic view. A neurologist and a psychological investigation do not appear as sufficient therefore [link].
Vascular aspects: There seems to be a high correlation between vascular abnormality and phantom pain [9], and with raised body temperature without treating or removing the vascular problems, phantom pains would rise [9].
One study of 31 amputated limbs [9], excluding amputations for vascular disease, only containing tumor and trauma as indications for the amputation, reported a high correlation of vascular abnormality and phantom pain. When they then raised body temperature without treating or removing the vascular problems, as my own experience, phantom pains would rise. “The vascularization of the stumps was found to be profuse, sparse, or of an intermediate form. In some instances, the arteriographic appearances were probably pathologic, consisting of sinuous vessels and persisting venous networks. Pathologic vessels of this type were seen only in patients with pain. In those without any form of discomfort, the vascularization was as a rule sparse-unless skin infection was present or the stump had been treated with skin grafting. Skin temperature measurement showed the skin of the stump to rise in temperature when body temperature was raised in patients with phantom pain, while in those without current phantom pain the skin temperature usually did not rise” [9]. An interesting other paper to recommend is that of Reinhardt (1972) [10]. There, it appears that an overarching pathology seemingly is found in arteriovenous anastomoses. People with these in their stump, regardless of other vessel abnormalities, almost always had complaints of pain in their residual limb. That paper also summarizes that the majority of people without symptoms of phantom pain have normal vasculature in their stump, whereas the majority of people with phantom pains have pathological vasculature in their stump. The problem of such vascular abnormalities has been studied more extensively in lower leg varicosis [11]. There, congestion, and burning pain, are all there, described in detail. Activating the stump by using its muscles helps to reduce stasis as well [12, 13]. Also, it is known that with raised body temperature without treating or removing the vascular problems, phantom pains would rise [9], so documenting body temperature as such may be relevant.
This study by Flor et al. certainly does not document baseline stump / residual limb skin temperatures.
Musculoskeletal / orthopedic aspects: Asymmetry and related cervical spine issues are prevalent in unilateral arm arm amputees: “in upper limb amputees pain in the cervical spine was commoner than in the other groups” [14]. Muscle trigger points from overly tense muscle contractures are typical causes for referred pain [15, 16, 17]. A subset of that may be nerve compression, which is a typical source of neuropathic pain [18].
To consider these would constitute a bottom line for the assertion that an amputee is healthy. Peripheral phantom pain correlates were seemingly neither seriously considered, documented or excluded.
Such a study examining pain causes such as from phantom pain therefore should detail any typical prevalent concomitant pain causes before trying to evaluate what the amputee reports – maybe a visit to the sauna, a massage, a hot bath, and maybe just a week’s rest, and a bit of stump compression, and the reported phantom and other pain is almost gone? What then?1
Thirdly, the study does not examine two-point discrimination (2PD) of “healthy” controls. And yet, a simple check with normal two-point discrimination values for arms of “healthy” men and women [19] would have allowed Flor et al. to see that normal forearm 2-point discrimination is 14.1-18.6 mm, on the upper arm it is 14.4 to 22.0 mm. Conversely, this study by Flor et al. reports stump related 2-point discrimination of 61-85 mm, whereas the non-affected arm had a range of 72.8-75.2 mm. These are very high values!
We also wonder who reviewed this. This points to a possibly significant difference in sensory function, with the looming question what was really going on with these particular arm amputees.
A rather likely or plausible explanation seems to be that the test subjects were simply freezing at least a bit, as low temperatures are a cheap and effective method to lower the ability for a good two-point discrimination of the upper extremity [20, 21].
If we assume that Flor et al. had the amputees examined at least somewhat undressed if not in a cold room, which is not an unlikely scenario given these numbers, and given what appears to be the overall level of empathic care that seems to shine through between the lines, then that would shed a different light on the study conductors, that seemingly also may have protected “healthy” subjects from undergoing the same cold room treatment. Ambient temperatures aren’t listed in the study. But the 2PD distances look off.
So we do have a sociology study subject, and for a while already, it was not the arm amputees.
Back to the actual point though, no particular health checks seem to have been performed for the so-called healthy controls aged 23 to 51. It really looks as if they simply don’t now how healthy these people really are/were.
Fuchs, X., Diers, M., Trojan, J., Kirsch, P., Milde, C., Bekrater‐Bodmann, R., Rance, M., Foell, J., Andoh, J., Becker, S. and Flor, H., 2022. Phantom limb pain after unilateral arm amputation is associated with decreased heat pain thresholds in the face. European Journal of Pain, 26(1), pp.114-132. [22]
The study from the Institute of Cognitive and Clinical Neuroscience, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany, Biopsychology and Cognitive Neuroscience, Faculty of Psychology and Sports Science, Bielefeld University, Bielefeld, Germany, Department of Psychosomatic Medicine and Psychotherapy, LWL University Hospital, Ruhr University Bochum, Bochum, Germany, Department of Psychology, University of Koblenz-Landau, Landau, Germany, Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, Connecticut, USA, Department of Psychology, Florida State University, Tallahassee, Florida, USA, Department of Psychiatry and Psychotherapy, Medical Faculty Mannheim, Central Institute of Mental Health, University of Heidelberg, Heidelberg, Germany, Integrative Spinal Research, and Research Chiropractic, Balgrist University Hospital, University of Zurich, Zurich, Switzerland combines a lot of people to basically provide pain stimuli to 37 unilateral arm amputees and (only) 19 healthy amputees, as they write.
Method summary is “in this study, we applied QST in 37 unilateral upper- limb amputees (23 with and 14 without PLP) and 19 healthy controls. We assessed heat pain (HPT), pressure pain, warmth detection and two- point discrimination thresholds at the residual limb, a homologous point and the thenar of the intact limb as well as both corners of the mouth”. All that can be deduced about the proposed health status of the participants is that the people without upper limb difference apparently are “healthy” – so for all we know they could also be leg amputees or suffer from Parkinson’s disease, as research method does disclose any health check by a medical professional.
As in the other studies cited here, presence of neuroma, musculoskeletal or skin issues were seemingly neither considered nor examined 2.
The introduction of the study tries to propose that “both peripheral and central mechanisms are involved in chronic PLP (Flor & Fuchs, 2017; Flor et al., 2006; Ramachandran & Hirstein, 1998). However, their exact roles and impact are under debate”, but no attempts seem to be made to focus on peripheral causes for stump and phantom pains, specifically in this study.
The study even mentions neuroma 3 but no further work seemed to have gone towards actually identifying such in the 37 arm amputees that then were subjected to, well, extra pain.
Because a perfect excuse to get amputees to feel more pain than they already had, here, was by using heat, and justifying that in what seem to me to be obscure reasons. After all they did not appear to consider any actual therapy, so they seemed to just poke around, literally. Which is fine of course with willing subjects, at least from any legal view.
I just wonder, exactly why? Was this really necessary? Why is it left up to me to treat my phantom pain by compressing my stump, avoiding skin injury and massaging / heating my neck/shoulder/back muscles, why is it still and always left to me to build my own prosthetic arm parts so it actually serves as asymmetry relief, why do I have to do all of these myself?
Data showed two-point discrimination (2PD) on the forearm of amputees on the stump (4.95 cm), their non-amputated arm (5.42 cm) and non-limb-different “healthy” controls (5.31 cm) (supplementary materials in [22] and graphically shown in Fig. 2 “2PDT” of [22]). No ambient temperature was published so why not assume just for argument’s sake that they let the subjects shiver and freeze before providing heat pain stimuli. Again, a simple check with normal two-point discrimination values for arms of “healthy” men and women [19] would have allowed Fuchs et al. to see that normal forearm 2-point discrimination is 14.1-18.6 mm, on the upper arm it is 14.4 to 22.0 mm. Again, low temperatures are an established cheap and effective method to lower the ability for two-point discrimination of the upper extremity [20, 21].
Yeah, and no health check for the “healthy” ones as far as we can read.
EMG, electrodes
Leone F, Gentile C, Cordella F, Gruppioni E, Guglielmelli E, Zollo L. A parallel classification strategy to simultaneous control elbow, wrist, and hand movements. Journal of NeuroEngineering and Rehabilitation. 2022 Jan 28;19(1):10 [23]
The publication of the Unit of Advanced Robotics and Human-Centred Technologies, Università Campus Bio-Medico di Roma, Rome, Italy and of the INAIL Prosthetic Center, Vigorso di Budrio, Italy states “the parallel PR-based strategy was tested on 15 healthy subjects, by using only six surface EMG sensors”, “the reported results were obtained by considering the mean values on 15 healthy subjects”. It also states “Ethics approval and consent to participate: Not applicable”. This is interesting, as EMG sensors can cause skin problems [24, 25, 26], so informed consent should really be considered.
The research subjects and the claim that they are healthy also seem a terra incognita in this study.
At least, blood pressure, BMI, a tox screen, as well as a skin inspection by a dermatologist, before and after the study, would have been something that I consider appropriate.
But then, this also means, that quite possibly, and also in the eyes of the journal editors, who seemingly approved of this level of human research conduct, EMG sensors and myoelectric prosthetic arms do not constitute medical devices.
Otherwise, this would have constituted a clinical trial with an obviously unapproved experimental medical device, which clearly will require registration and proper governance.
Politically, it may be necessary to remove any “medical device status” for external limb prosthetics in order to maintain consistency and legal correctness.
Even for a self-test of approved relevant prosthetic arm components (and some not registration relevant parts my own), I had obtained approval of ethics committee [27].
Chadwell A, Kenney L, Granat M, Thies S, Galpin A, Head J. Upper limb activity of twenty myoelectric prosthesis users and twenty healthy anatomically intact adults. Scientific data. 2019 Oct 10;6(1):199 [28]
This study of the University of Salford, Health Sciences Research Centre, Salford, United Kingdom proposes that “twenty participants (14 male, 6 female) with unilateral upper limb absence at a trans-radial level were recruited from six (4 NHS, 2 University) sites across the UK. All participants had a single degree of freedom myoelectric prosthesis (e.g. Steeper Select or Ottobock DMC Plus/VariPlus/Sensor Speed). Full metadata is provided with the dataset. The age of the prosthesis users ranged from 18 to 75 years (median age 54 years). Eleven people had congenital limb absence (6 Right/5 Left), and nine had an amputation (6 Right/3 Left); six of the amputations had occurred on the dominant side. Time since amputation ranged from 8–47 years (median 24 years). Time since prescription of a myoelectric prosthesis ranged from 1.5–39 years (median 20 years). A group of twenty anatomically intact participants (9 male, 11 female, age 23–61, median age 41, 3 left handed) with no upper limb impairments were also recruited through the University of Salford. Ethical approval for this study was granted by the University of Salford School of Health Sciences Research Ethics committee (REF: HSCR 16–25), by the University of Strathclyde Department of Biomedical Engineering Ethics Committee (DEC.BioMed.2017.220) and through the NHS IRAS system (IRAS Project ID: 193794). Informed consent was gained from all participants.”
The title of the study is “upper limb activity of twenty myoelectric prosthesis users and twenty healthy anatomically intact adults” whereas the term “healthy” is not used in the study text itself. The study does not detail how, in what medically documented way, the subjects were actually healthy, particularly with regard to the type of health concerns that seems to ail a group of people aged 18-75 years.
While this is a considerable amount of text, the control group was clearly termed “healthy” as per study title, but not the people with limb difference.
And yet, no dermatological results for health of skin, musculoskeletal system and so on, was reported here or in the metadata. With regard to the single relevant anatomical structure affected by EMG electrodes, which is the skin, and muscle status such as degree of atrophy, the authors did not explain or report any particular attention or care.
This can be handled differently: when I participated in one study, my suddenly exacerbated strong phantom and stump pains were immediately referred to study doctors that contained a neurologist and an orthopedic specialist.
The method section as well as the supplementary metadata other supplementary data also did not contain informed consent details. There one could see if that form was more informative with regard to at least self-declared health status.
Schone, H.R., Udeozor, M., Moninghoff, M. et al. Biomimetic versus arbitrary motor control strategies for bionic hand skill learning. Nat Hum Behav (2024) [29].
The study is of the Laboratory of Brain and Cognition, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA, from the Institute of Cognitive Neuroscience, University College London, London, UK, from the Rehab Neural Engineering Labs, University of Pittsburgh, Pittsburgh, PA, USA, the Department of Physical Medicine and Rehabilitation, University of Pittsburgh, Pittsburgh, PA, USA, the Medical Center Orthotics and Prosthetics, Silver Spring, MD, USA also the Coapt, Chicago, IL, USA. 7 Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, USA, the The Regenstein Foundation Center for Bionic Medicine, Shirley Ryan AbilityLab, Chicago, IL, USA and the MRC Cognition and Brain Sciences Unit, University of Cambridge, Cambridge, UK.
As far as the “healthy” volunteers are concerned: “sixty-one healthy volunteers (40 women; mean age, 24.8 ± 0.66 years; all right handed) were recruited from the NIH community and the Washington, DC metro area and were randomly assigned to 1 of the following study groups: biomimetic (n = 21; 14 women; mean age, 23.9 ± 0.57 years), arbitrary (n = 21; 12 women; mean age, 25.9 ± 1.28 years) or untrained (n = 19; 14 women; mean age, 24.6 ± 1.41 years). All participants were unaware of the other participant groups to minimize any potential biases on participant performance. All participants had no known motor disorders.” Interestingly, they did not describe any of the volunteers as “anatomically intact” or “nondisabled”, or “without upper limb deficiency”. So, how could we know what these people had that was relevant for the study?
Secondly, pattern recognition control depends on many more than “just” two electrodes. To explain this to people that have little or no idea about these prostheses and their control: to get a good signal one needs good muscle. Not atrophied fatty muscle. Arm amputees like me with a below elbow amputation have a forearm stump. With absence of hand comes absence of forearm muscle training so muscles are atrophied, mostly. Because most muscles on a forearm stump are atrophied it is already problematic to use two electrodes, one for open and one for close. The one muscle most of us have that gives a good signal tends to be the extensor carpi radialis and brachioradialis; both tend to be strong and not atrophied despite absence of wrist and hand, but, because they also help to flex the elbow. So for prosthetic technicians, muscles with good signals are used with preference. This includes extensor carpi radialis and brachioradial muscles; then everyone acts surprised when the user flexes the elbow and unintendedly activates the prosthetic hand. To add complexity of control past simple open and close function as enacted by two electrodes, one on the biggest extensor side muscle and one over the biggest flexor side muscle, more electrodes are placed on the arm stump. As most of my arm stump muscles are entirely atrophied, any myoelectrode signal there risks to be very noisy, garbage really. Correctly, this study text goes “Today’s technology is far from Skywalker’s—even the most advanced bionic limbs are slow and operated using just a few degrees of freedom” – yes! That has clear technological reasons! Number one is that for any other type of control I don’t have the necessary muscles, nor do most other arm amputees. A software that wants to convert multi-electrode signals with garbage signals to meaningful hand gestures or motion has to overcome basically the impossible. Without surprise, we therefore find that many studies in the field of myoelectric control test their devices only on what they call “healthy” study subjects, by which they also imply that:
1) healthy means non amputated, not much else; if we are lucky they may add that they also do not have a motor disorder; they usually do not add that the health they mean covers the presence of full upper extremities in the average anatomy book sense;
2) with that, they then imply, as any one can “see” who is or is not an arm amputee, that “healthy” can be “seen”, adding to the chagrin to anyone with an “invisible” illness or disability, as well as coming across as arrogantly ableist, whereas I am now to be blamed with not offering the ruling non-disabled class my total unreserved submission (which was something a friend of mine who now oversees a whole university once told me that he clearly expected from me – seeing as if I was an amputee – and rather seriously, not in a joking manner; seems they still try to put that puppy on the road, too).
3) healthy is an adjective that can be used without checklist or medical documentation, which is interesting considering the above insights about health in adults generally.
4) the paper leaves no notes with regard to the skin of the participants after the study. This seems relevant because myoelectric electrodes can cause skin issues such as superficial burns (references: see elsewhere).
Even with obesity, electrodes may be more difficult to use when fat is more [30]. The absence of a proper check for fat thickness at myoelectrode sites easily may distort the research findings.
At least, not a single concise compact explicit sentence in this study claims or proposes that their forays into having “healthy” participants “play” with expensive technology at any point in time is actually intended to be successfully used by actual amputees. The claims are all embellished and indirectly pushed – but nowhere does it say that actual amputees with atrophied muscles can expect a similar result. To be fair, that is a reasonable way to motor around the big elephant in the room, which is, that this (also?) is research by researchers for other researchers that aims for one goal only: academic citations, from people that think the same.
If ever anyone of these academic “performers” wanted to improve real life for real people providing real work, I guess we’d know by now.
What is phantom pain as it emerges from these studies?
Phantom pain, as it emerges from these studies and as used in that context there, may well just be an undifferentiated unidentifiable unassignable conglomerate of pain perceptions.
That is because no attempts at searching for frequent typical other causes for pain, such as peripheral causes, were made, in any of these studies, at least not as far as the method description goes.
This becomes obvious when one follows down the rabbit hole of the tag “healthy” that was assigned without proper checks to a control group that appeared to lack an upper limb difference.
Prosthetic technology researchers may want to work towards political lobbying to get external prosthetic components unlisted as medical devices.
Otherwise we expect their research to be submitted to extensive experimental device test review beforehand.
Checklist
- Healthy and disabled / impaired are distinctly not the same. We can not presume a health status for a person with, or, without disability, without having checked. The same goes for disability. A base line for all adults may cover psychiatric health, tox screen, BMI, blood pressure and, as soon as prosthesis or pain related aspects are relevant, skin and musculoskeletal issues.
- For myoelectric studies, a thorough ultrasound or MRI examination to document the degree of muscle atrophy and the presence of neuroma seems relevant. There are a number of signal problem and nerve issue causes and so why not check for the obvious.
- An arm amputee can have pain such as phantom pain, also because of neuroma, muscle trigger points / myofascial problems, nerve irritation or compression particularly in context of musculoskeletal or spine problems, skin issues also in context of prosthesis use, because of deep tissue injury such as bruised neuroma or nerves, as well as vascular or circulation pathology or problems. But unless we actually check these all by specialist medical doctors, and ancillary tests such as angiography, there is a good chance we will be sailing in the pitch dark with our phantom pain assumptions.
- Medical devices require proper handling formally and practically. Prosthetic devices can and will cause skin problems (such as inflammation, mechanical and sweat rashes, allergic reaction) including burns (skin electrodes). We thus will have to register our trial as medical device trial, and depending on whether it is research with approved or non-approved parts, the application will differ. Unless these are not considered medical devices at all. Which could be considered, because whether I burn my skin on an oven, stove, grill or with a myoelectric electrode does not seem to constitute such a big difference in terms of burn injury trying to heal afterwards. Particularly if no one cares anyway.
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Footnotes
- Then, the world will be a whole lot better, and if only for a day.
- From [22] “Method – Participants: Thirty- seven unilateral upper- limb amputees and 19 healthy controls (HCs) took part in this study. We employed QST and the assessment of phantom phenomena and chronic pain. The sample was recruited from a nation- wide database on which we had previously reported (Bekrater- Bodmann, Schredl, et al., 2015). The participants were selected from the data-base and contacted directly. The criteria for selection were unilateral arm amputation and eligibility for magnetic reso-nance imaging testing (used in another study). We recruited amputees with and without PLP and attempted to achieve comparable distributions of age, sex and side of amputation between the groups. The study was approved by the Ethics Commission II of the Medical Faculty Mannheim, Heidelberg University. The amputees were divided into two groups— one with PLP (PLP; N = 23) and one without PLP (non- PLP; N = 14). Grouping was based on the Phantom Pain Severity subscale of the German version of the West Haven- Yale Multidimensional Pain Inventory (MPI; Flor et al., ,1990, 1995; Kerns et al., 1985) adapted for separate assessments of PLP and RLP. The MPI is a 22- item questionnaire that uses a 7- point numeric rating scale for each item ranging from 0 to 6. The Pain Severity subscale is calculated as the average value of three items assessing (a) the intensity of momentary pain, (b) the average pain during the last week and (c) the inten-sity of pain- related suffering. Amputees with a Pain Severity score of 0 were assigned to the non- PLP group and all other amputees to the PLP group. The HC were matched for age, sex and stimulation sites with amputees from both groups. Sample and demographic details are provided in Table 1.There were no statistically significant differences between the three groups (PLP, non- PLP and HC) in the distribution of sex [ratio male/female: PLP, 20/3; non- PLP, 12/2; HC, 16/3; χ2(2, N = 56) = 0.06, p = 0.97] and age (mean ± standard devi-ation [SD, years]: PLP, 51.3 ± 12.3; non- PLP, 53.1 ± 10.6; HC, 51.6 ± 11.7; F(2, 53) = 0.10, p = 0.90). The PLP group and the non- PLP group did not significantly differ in their level of amputation (mean ± SD [% arm length]: PLP, 32.0 ± 18.8; non- PLP, 40.2 ± 23.9; t(22.7) = −1.10, p = 0.28) or side of amputation [χ2(1, N = 37) = 0.53, p = 0.47]. None of the ampu-tees was amputated at an age below 5 years and the groups did not differ significantly with respect to age of amputation (mean ± SD, range [years]: PLP, 27.1 ± 12.5, 13– 55; non- PLP, 19.8 ± 11.5, 5– 45; t(29.5) = 1.80, p = 0.08). All amputees were in a later stage after amputation with at minimum 3 years pass-ing between amputation and sensory testing and the groups did not differ significantly with respect to that (mean ± SD, range [years]: PLP, 24.1 ± 11.4, 9– 58; non- PLP, 33.3 ± 15.6, 3– 55; t(29.5) = 1.84, p = 0.08). All amputees were right- handed before amputation and so were all of the HC, according to the Edinburgh Handedness Inventory (Oldfield, 1971”
- From [22]: “Peripheral factors relate to nociceptive input stemming from the residual limb and can in-volve peripheral sensitization, spontaneous discharges from the residual limb due to involuntary movement or physiolog-ical arousal (Sherman et al., 1989), neuromas (Devor, 1991; Fried et al., 1991; Wiffen et al., 2006), or activity generated in dorsal root ganglia (Vaso et al., 2014).”