The hominid thumb and its influence on the employment during evolution

Full text

Reumatismo 1/2019 51
COMMENTS
Reumatismo, 2019; 71 (1): 51-52
n SHORT REPORT
The ability of modern humans to manip-
ulate, modify, and utilize their physi-
cal environment is unparalleled amongst
primates. The sh Rhipidistia, our earliest
known ancestor, had pectoral ns that phy-
logenetically preceded the arm, which then
developed from the high cervical segments.
Fish have no neck and the bones of their
pectoral ns are articulated with the skull.
Opposed to this, the intrinsic muscles of
the hand in the human are innervated by the
two lower branches of the brachial plexus
(1). Hands perform a vital role in most dai-
ly human activities (2).
The hominids living at the end of the Mio-
cene about 15 million years ago began to
develop bipedal locomotion, liberating
their hands for independent use. From an
evolutionary stand point, the nger bones
straightened the curvature that was used to
grasp tree branches, and the thumb, formed
last, receded in length, and diverged from
the adjacent digits (3).
This could be the rst succession of mus-
culoskeletal adaptations for improved func-
tion and survival to have been described in
the course of their evolution. The evolu-
tion of musculoskeletal adaptations into
activity-related wear of the hand joints can
be demonstrated nowadays with activity-
related hand pathologies. Furthermore, in
this age of handheld electronic gadgets, for
many individuals the thumb is repeatedly
used to text on smartphones countless times
per day. Adults using mobile phones punch
out numbers with their thumbs and develop
synovitis in their carpometacarpal joints.
The inuence of activity-related wear on
the development of pathologies might have
already been present in the early stages of
the evolution of the hand, such as those
that occurred to primates when they began
to develop bipedal locomotion, liberating
their hands for independent use (4).
That the evolution of the human hand
has given our species the opportunity to
evolve into more complex activities and
societies is a fact, and this could have in-
uenced the development of our species’
brain. But, on an individual scale, does the
hand shape our brain activity? Is there a
correlation between hand wear and brain
activity as shown by brain mapping? We
already know that orthopaedic disorders
of the hand that reduce the patients’ motor
repertoire induce neurofunctional chang-
es in the cortical representation of hand
movements. Thus, hand wear inuences
cortical motor mapping (5). Widespread
hyperalgesia is a feature of OA. OA is a
chronic disease in which mechanisms of
pain are not fully understood (6). Asso-
ciation between clinical and neurophysi-
ological outcomes is highly important to
improve therapeutic approaches for hand
OA. Villafañe et al., reported that radial
nerve mobilisation on the affected side
induced bilateral hypoalgesic effects in
people with carpometacarpal osteoarthri-
tis (7). We already know that, although
the perceptual implications of the ana-
tomical changes and the rules that facili-
tate transfer of learning to other tactile
abilities remain unclear, repetitive tactile
stimulation on the hand modies neural
representations in primary somatosensory
cortex (SI) of non-human primates (8). It
is likely that the development of new tech-
Corresponding author:
Jorge H. Villafañe
IRCCS Fondazione Don Carlo Gnocchi,
Milan, Italy
E-mail: mail@villafane.it
The hominid thumb and its influence
on the employment during evolution
J.H. Villafañe1, R. Cantero-Tellez2, P. Berjano3
1IRCCS Fondazione Don Carlo Gnocchi, Milan, Italy; 2Physical Therapist University of Malaga, Spain;
3IRCCS Istituto Ortopedico Galeazzi, Milan, Italy
Non-commercial use only

COMMENTS
52 Reumatismo 1/2019
J.H. Villafañe, R. Cantero-Tellez, P. Berjano
COMMENTS
nology brings an opportunity to reduce
hand wear. Dictation software can make it
unnecessary to use pencils, keyboards or
tactile screens of smartphones, robots will
clean our pavements without any involve-
ment of our hands, self-driving cars will
free our hands from steering wheels, iris
or face recognition will make unnecessary
the use of ngerprints (though it is argu-
able whether this is a signicant source
of wear), surgical robots will amplify our
hand strength and preserve surgeons from
trapeziometacarpal arthritis. One question
still remains open: just as hand wear can
induce brain plasticity into less functional
neuronal circuits, will hand underuse car-
ry as a consequence an underdevelopment
of our brain? In other words, by freeing
us from hand use, is technology going to
reduce our brain functions? Only time and
science will answer this question.
Contributions: JHV, design of the study
and interpretation of the results; write, sub-
mit and tracking of manuscript; RC, inter-
pretation of the results; write, submit and
tracking a manuscripts; PB, write, submit
and tracking of manuscript.
Conict of interest: the authors declare no
conict of interest.
n REFERENCES
1. Diogo R, Wood B. Soft-tissue anatomy of the
primates: phylogenetic analyses based on the
muscles of the head, neck, pectoral region and
upper limb, with notes on the evolution of
these muscles. J Anat. 2011; 219: 273-359.
2. Marzke MW, Toth N, Schick K, et al. EMG
study of hand muscle recruitment during hard
hammer percussion manufacture of Oldowan
tools. Am J Phys Anthropol. 1998; 105: 315-32.
3. Ladd AL. Editorial comment: Symposium:
Thumb carpometacarpal arthritis. Clin Orthop
Relat Res. 2014; 472: 1093-4.
4. Bertozzi L, Valdes K, Vanti C, et al. Investi-
gation of the effect of conservative interven-
tions in thumb carpometacarpal osteoarthritis:
systematic review and meta-analysis. Disabil
Rehabil. 2015; 37: 2025-43.
5. Gandola M, Bruno M, Zapparoli L, et al. Func-
tional brain effects of hand disuse in patients
with trapeziometacarpal joint osteoarthritis:
executed and imagined movements. Exp Brain
Res. 2017; 235: 3227-41.
6. Villafane JH. Does “time heal all wounds” still
have a future in osteoarthritis? Clin Exp Rheu-
matol. 2018; 36: 513.
7. Villafane JH, Bishop MD, Fernandez-de-Las-
Penas C, Langford D. Radial nerve mobilisa-
tion had bilateral sensory effects in people with
thumb carpometacarpal osteoarthritis: a ran-
domised trial. J Physiother. 2013; 59: 25-30.
8. Trzcinski NK, Gomez-Ramirez M, Hsiao SS.
Functional consequences of experience-de-
pendent plasticity on tactile perception follow-
ing perceptual learning. Eur J Neurosci. 2016;
44: 2375-86.
Non-commercial use only