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Physics of nail conditions: Why do ingrown nails always happen in the big toes?

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Although surgical treatment of nail conditions can be traced back centuries to the writings of Paul Aegineta (625-690 AC), little is known about the physical laws governing nail growth. Such a poor understanding together with the increasing number of nail salons in the high street should raise legitimate concerns regarding the different procedures applied to nails. An understanding of the physics of nail growth is therefore essential to engage with human medicine and to understand the aetiology of nail conditions. In this context, a theory of nail plate adhesion, including a physical description of nail growth can be used to determine the transverse and longitudinal curvatures of the nail plate that are so important in the physical diagnosis of some nail conditions. As a result physics sheds light on: (a) why/how nails/hooves adhere strongly, yet grow smoothly; (b) why hoof/claw/nail growth rates are similar across species; (c) potential nail damage incurred by poor trimming; (d) the connection between three previously unrelated nail conditions, i.e. spoon-shaped, pincer and ingrown nails and; last but not least, (e) why ingrown nails occur preferentially in the big toes.
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Physics of nail conditions: why do ingrown nails always happen in the big toes?
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2014 Phys. Biol. 11 066004
(http://iopscience.iop.org/1478-3975/11/6/066004)
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Physics of nail conditions: why do ingrown
nails always happen in the big toes?
Cyril Rauch and Mohammed Cherkaoui-Rbati
School of Veterinary Medicine and Science, University of Nottingham, College Road, Sutton Bonington,
LE12 5RD, UK
E-mail: Cyril.rauch@nottingham.ac.uk
Received 10 June 2014
Accepted for publication 12 August 2014
Published 16 October 2014
Abstract
Although surgical treatment of nail conditions can be traced back centuries to the writings of
Paul Aegineta (625690 AC), little is known about the physical laws governing nail growth.
Such a poor understanding together with the increasing number of nail salons in the high street
should raise legitimate concerns regarding the different procedures applied to nails. An
understanding of the physics of nail growth is therefore essential to engage with human medicine
and to understand the aetiology of nail conditions. In this context, a theory of nail plate adhesion,
including a physical description of nail growth can be used to determine the transverse and
longitudinal curvatures of the nail plate that are so important in the physical diagnosis of some
nail conditions. As a result physics sheds light on: (a) why/how nails/hooves adhere strongly, yet
grow smoothly; (b) why hoof/claw/nail growth rates are similar across species; (c) potential nail
damage incurred by poor trimming; (d) the connection between three previously unrelated nail
conditions, i.e. spoon-shaped, pincer and ingrown nails and; last but not least, (e) why ingrown
nails occur preferentially in the big toes.
Keywords: hard and growing tissues, biomechanics, dermatology, adhesion
Introduction
The human nail is a keratinized structure and window to the
nail bed, held in place by lateral nail folds (the cutaneous
folded structures providing the lateral borders of the nail). It is
made of dead cells that multiply from the proximal matrix. As
a result, the nail originates from this proximal matrix, grows
longitudinally, and ends at a free edge distally. Nail adhesion
to the nail bed involves a number of well characterised
microscopic adhesive units. These units are apposed in a
pattern along longitudinal epidermal ridges (or lamellae)
stretching to the lunula, the half moon, pale convex portion of
the matrix seen through the nail (gure 1(A)). On the
underside of the nail plate there is a complementary set of
ridges as if the nail plates were held to the nail beds via a set
of longitudinal rails. A similar anatomical structure exists
across all species. However, depending on the animal con-
sidered, the epidermal ridges can be more complex than in
man as they can display primary and secondary structures that
are thought to increase adhesiveness. For example, slow-
moving animals like humans and cattle have only primary
lamellae (Thoefner et al 2005) whereas fast-moving
animal like horses (Pollitt 1994) or heavy animals like ele-
phants (Benz et al 2009) have primary and secondary
lamellae (gures 1 (B), (C), (D) and (E) show the horse foot as
an example).
Even though there now exists an in depth and complex
cross-species description of macroscopic/microscopic anato-
mical and cellular/sub-cellular structures, how nail and hoof
growth inform their shape remains unclear. This apparently
simple question is in fact central to medicine as the rst
diagnosis of a nail/hoof condition by medics or vets is
necessarily a physical and visual appraisal of the shape or
form of the nail/hoof. In this context it is worth noting that
although nail cutting and hoof trimming have traditionally
been advocated to alleviate pain and reshape the nail/hoof
with time, there is little theory on which to ground these
Physical Biology
Phys. Biol. 11 (2014) 066004 (10pp) doi:10.1088/1478-3975/11/6/066004
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practices (Eliashar 2012). Furthermore, for each shape-related
condition, it is unclear whether another cutting/trimming
method exists that could be optimized. As a result, if a con-
nection exists between the zoology of nail shapes and the
zoology of nail conditions, it is paramount to describe how
these changes have been made possible and what physical
parameters are involved. These parameters should help to
dene the aetiology of nail/hoof conditions and give valuable
clues as to how they should be treated.
The present work considers the nail as an adhering solid
plate and will start by a brief hand-waiving introduction of
physical concepts used. The adhesion and growth stresses
present in nail will be modelled and incorporated into the
general balance of stresses to obtain unique solutions. The
optimization of the total energy of the nail including bending
and potential energies will be performed using the Euler
Lagrange method to determine the nail shape equation. The
nail shape equation will be tested against specic nail con-
ditions where changes in the shape of the affected nail occur.
We conclude that our model may provide a continuous rela-
tionship between three well known, but previously thought to
be unrelated, nail conditions namely ingrown, pincer and
spoon-shaped nails. Finally we shall also discuss the potential
importance of nail cutting in the aggravation of nail
conditions.
Model
Below we explain the d ifferent concepts that will be used.
As a nail is a growing solid that adheres to a substrate, the
adhesion of the nail plate on its bed is necessarily involved
in the way i t gr ows. Adh esion b etwee n cells and the
extracellular matrix is formed via specialized junctions
involving different sets of macro-molecules including more
complex ones such as focal adhesion or hemi-desmosomes
(Worth and Parsons 2008). Cellular adhesion has been
extensively modelled in different contexts. As a function of
the biology considered, the frameworks can differ, but
intermolecular bonds forming adhesions are usually treated
as Hookean springs that can either remain xed vertica lly
(Dembo et al 1988,DongandLei2000)and/ortiltfrom
their vertical position under stress (Reboux et al 2008). As a
nail adheres stron gly, but nee ds to grow smoothly (i.e.
without stick-slip), one possibility is that this adhesion
imposes a ratchet-like mechanism on the nail so that the
gr owth is es sentiall y confoun ded with diffusi on. This is
possible if the length of nail growth per unit of t ime has a
magnitude that is similar to the thermal tilting of an adhe-
sive unit. In these conditions the adhesive units should not
feel the nail to which they are bound, and a nail should
grow smoothly and adhere strongly. This ratchet-like model
Figure 1. Anatomy of nail and hoof adhesion. (A) Avulsion of the human nail showing the nail bed and in particular the epidermal ridges
interacting with the nail plate (gure reproduced from de Berker, Andre and Baran 2007). The anatomy of the epidermal structures is similar
across species. (B) Avulsion of the equine hoof capsule showing the bed and in particular the epidermal ridges interacting with the hoof
capsule. (The material was obtained from an ethically managed abattoir). (C) Internal view of epidermal ridges separated from foot (B). (D)
Internal view of dried epidermal ridges. (E) A microscopic section shows that in addition to the rst lamellae (pink colour) there is a second
one (dark blue/dark purple colour pointed by the black arrow) that is connected to the hoof capsule (red colour). The hoof-lamellar interface
increases the surface area for adhesion.
2
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
indicates a universal form of growth for hooves and nails in
non-pathological conditions but it needs to be amended
whenthegrowthrateofthekeratinizedplateistoofast.In
this case, the adhesive forces opposing the nail plate
movement and the mechanics of the plate need to b e con-
sidered together. To understand clearly how mechanical
stresses arise, it is essential to understand the mechanical
impact of the nail edge as a boundary condition.
To explain this let us isolate a thin longitudinal slab of
the nail plate, from the proximal matrix to the free end. As the
pink colour underneath the slab is proportional to the number
of adhesive units involved in the adhesion of the slab, the
longer the slab the higher the adhesion. As a result, with a
constant growth force emanating from the proximal matrix,
the longer the slab the harder it will be to make it move
forward or grow. Thus, given the parabola-like shape where
the adhesion of the nail terminates, the right and left extre-
mities of the nail of a thumb should grow faster than the
longitudinal slab positioned exactly in its center because the
latter would be longer than any other slab. Naturally, this is
never observed as the nail has solid properties. Nevertheless it
describes the set of residual longitudinal shear stresses
involved when the nail grows that result directly from the
boundary conditions. As a longitudinal shear stress promotes
a tendency toward rotation (i.e. to generate angular momen-
tums) but because nails do not rotate locally, another stress,
transverse this time, must balance the virtual rotation primed
by the shear stress. This transverse stress resulting from the
prole of the nail edge, is expected to have an impact on the
transverse curvature of the nails, which is important in the
diagnosis of nail conditions.
Thermal growth rate
To provide a model, let us rst focus on a single adhesive unit
that stands vertically without solicitation of any sort. Single
molecular adhesion can only last a time
k~1/
where,
k
,is
the unbinding kinetic (gure 2(A)). If, when the adhesive unit
has just bonded, a movement involving a constant velocity,
V
,
is now imposed on the unit and that the unit is fully compliant
mechanically, the unit will tilt up to a certain angle,
θ
, before
unbinding. This angle is expected to be,
θ
Vzk~/
0
(gure 2(B)). The thermal agitation of any free, i.e. unbound,
unit can also dene an angle proportional to the absolute
temperature,
θ
k
kT~
el B
2
, where
k
el
is the tilt modulus of
the unit,
k
B
the Boltzmanns constant and
T
, the absolute
temperature (gure 2(C)). Equating the two relations
allows one to dene a thermal velocity:
VzkkTk~/ (1)
th B el0
This velocity denes a limit below which adhesion/
binding is controlled by the thermal energy. This means that
the movement of a nail plate onto adhesive units is possible
without further damage of units other than those determined
thermally if the velocity is close to, or below, V
th
. Using
k
kT~10 10
el B
3
(Reboux, Richardson and Jensen 2008),
k
s~10
1
(Ra et al 1999) and
~10n
0
(Arnold
et al 2004, Cavalcanti-Adam et al 2006, Cavalcanti-Adam
et al 2007) one nds
V
da
y
~0.1 1mm/
th
at room tempera-
ture. The growth rate of nail/hoof/claw measured in a range of
species (table 1) falls within the range of thermal velocities
that can be predicted by this model. In addition, the very close
similarity between growth rates in-vivo suggests that physics
drives the process of growth. Indeed these in-vivo values are
not dependent on allometric properties and, as a result, do not
seem to involve the speciesspecies metabolic rates, at least
under normal conditions.
Binding probability of adhesive units
Above the thermal velocity the probability that a uni t
remains attached becomes a function of the stress imposed
on the unit. In this context, consider as above a single
adhesive unit that stands vertically without solicitation of
any sort. Once bound with a chemical energy,
Δ
E
0
,the
thermal escape rate from the bound state is
Δ
k
ef~
EkT/
0
B0
where,
f
0
, is a fundamental f requency. Upon movement of
the nail the unit tilts and the energy landscape changes. In
this context the unit has two possibilities, to remain bound
or to break and as a res ult the t ransi tion rate b etween the
bo und and unbound states is:
Δθ
−−
()
fe f~
Ek kT/2 /
0
el B0
2
.
Considering independent and identical adhesion units, a
kinetic model can be used to descr ibe t he p robab ility,
P
,
that a u nit is attache d over time:
=− × + ×
+
dP dt f P k P/(1)(2)
where
+
k
is the b inding rate. The last term on the right -
hand-side of equation (2) represents the probability that an
adhesive unit rebinds after unbind ing. In th is case, the
relaxation time relating to t he adhesive unit going from a
stretched state to its resting position before rebinding is
neglected. The later relation also assumes that there is no
competition between binding sit es and that a reservoir of
ligands exists so that the binding can be considered spatially
continuous. Consider ing a stea dy state re gime of g rowth,
i.e.
=
d
Pdt/0
,itfollows:
α=+
()
()
PV V1exp/2 (3)
2
1
where
=
V
VV/
t
h
and
α
=
−+
kk/
(gure 2(D)) . Equation (3)
shows the sensi tivity of
(
)
PV
with regard to the growth rate
of nails.
Adhesion force developed by adhesive units
Focusing on a single adhesion unit, the force that opposes the
growth can be determined trivially as:
×
(
)
k
Vzk VPV/
el th
0
2
.
Consider a small element of nail surface area, the adhesion
per unit of surface of nail is thus:
ρ
(
)
fV kVzk VPV() /
adh
el th
0
2
(gure 2(E)), where
ρ
is
the number of adhesive units per surface area of nail that will
3
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
be considered constant and
=
fkVzk pN/~10
adh
el th
0
0
2
. Note
that as the nail plate is a projection of the nail bed and that
avulsion of the nail plate reveals a pattern of longitudinal
epidermal ridges involved in adhesion ( gure 1), the true
total surface area available for adhesion is larger than the
visible surface of the nail plate and as a result a factor,
λ
,
needs to be introduced to determine the true number of
adhesive units per unit of surface area to draw comparisons
between species. In these conditions:
λρ=fV f VPV a()
¯
(
¯
)(3)
adh
adh
0
Balance of in-plane stresses
The adhesive stress being dened, plate mechanics theory can
now be used to start investigating the interaction between the
shape and adhesion of nails.
The nail is held in place by an adhesion stress and a
boundary stress generated by the skin folds. However, as the
change of nail shape is expected to be slow, the deformation
of the nail bed and related impact on the adhesion stress
normal to the nail bed is unlikely to intervene actively in the
process, suggesting that we can consider the adhesion stress
constant at least for moderate deformations. In addition, as the
full characterisation of the external stresses applied by the
skin folds on the boundary of nail are, for the moment,
unknown to us, we shall only focus on a nail plate that is free
from external stresses induced by skin folds.
Consider the in-plane description and a nail plate orien-
tated in such a way that the y-axis corresponds to the direction
of growth from the proximal to the distal parts and an x-axis
orthogonal to the y-axis along the proximal matrix
(gure 3(A)). Let us assume that the nail has a width,
l
,a
length,
hx()
, with a constant thickness,
e
. The initial 3D
stress tensor,
σ[
]
ij,
, can be reduced to a two dimensional stress
tensor:
=fxy
fxyfxy
fxyfxy
(, )
(, ) (, )
(, ) (, )
ij
xx xy
yx yy
,
,,
,,
with:
σ=
fdz
ij
e
e
ij
,
/2
/2
,
where
f
ij,
is dened as a force per unit of
length along the j-axis with direction along the i-axis
(gure 3(B)). Note that the terms on the diagonal dene
Figure 2. Adhesion and growth force. (A) Adhesive units bind and unbind to their ligand over time. In a steady state regime, with no
velocity involved, the bound and unbound states can be described by a basic 2 states model. (B) When the nail grows, the binding of the
adhesive units last until a certain value of the titling angle is reached, that is determined thermally or mechanically depending on the regime
considered. (C) When the adhesive unit is not bound, the tilt uctuates around the vertical position and the use of thermodynamics allows one
to determine the deviation from the average value. (D) Representation of the probability that a bond is not consumed as a function of the
growth rate and
α
. (E) Representation of the force generated by a bound adhesive unit as a function of the growth rate and
α
.
Table 1. Hoof/nail growth rates for different animal species.
Animal
Growth rate
(mm day
1
) References
Horse 0.20.3 (Butler and Hintz 1977)
Sheep 0.10.2 (Shelton et al 2012)
Deer 0.10.2 (Miller et al 1986)
Cow 0.10.3 (Harrison et al 2007, Telezhenko
et al 2009)
Elephant 0.10.3 (Benz, Zenker, Hildebrandt, Weis-
sengruber, Eulenberger and
Geyer 2009)
Pig 0.30.4 (Johnston and Penny 1989)
Rat 0.10.2 (Godwin 1959)
Human 0.10.2 (de Berker, Andre and Baran 2007)
4
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
the classical surface tension whereas the non diagonal
terms dene the shear stresses. Finally, the balance of
stresses on an element of surface
d
xd
y
of the nail can be
written as:
∂+=fxy fxy(, ) (, ) 0 (4)
x
xx
y
xy,,
∂+
−⋅=
fxy fxy
fVHyhx
(, ) (, )
()
(
()
)
0(5)
y
yy
x
yx
adh
,,
where
−=
H
yhx
(
()
)
1
if
yhx()
or zero otherwise and
where
hx(
)
denes the adhesion prole (see gure 3). As no
local rotation appears when nails grow, the conservation of
angular momentum imposes that:
=fxy fxy(, ) (, ) (6)
xy yx,,
Hence the 2D stress tensor is symmetrical. To fully
dene the problem, boundary conditions need to be added,
and two of those can be dened. We rst assume that the
growth stress
fx()
0
is only dened at the origin on the y-axis
(i.e. proximal side) and has direction along the y-axis. This
rst boundary condition leads to:
=−fx fx(,0) () (7)
yy,0
Furthermore, let us assume that no force is applied dis-
tally i.e. that the nail has a free distal edge. Therefore two
further conditions follow (see appendix 1):
′⋅= f xhx hx f xhx(, ()) () (, ()) (8)
xx
x
xy,,
′= f xhx hx f xhx(, ()) () (, ()) (9)
yy
x
xy,,
From the geometry of the nail (i.e. its symmetrical
shape), it is obvious that the stresses will have to follow some
important symmetry conditions. Figure 3(C) enounces all the
symmetries with regard to the stresses:
−=
−=
−=
∂=
fxyfxy
fxyfxy
fxyfxy
f
(,) (,)
(,) (,)
(,) (,)
0 (10)
xx xx
yy yy
yx yx
y
xy
,,
,,
,,
,
The set of equations (4)(10)denes the physical stresses
present in a growing nail.
Stress solutions
Let us consider a solid nail growing at a constant velocity,
V
.
Without further assumptions and using the set of
equations (4)(10) it is possible to determine the components
of the stress tensor analytically. To this end, let us consider
Figure 3. Nail characteristics. (A) The nail is described by a system of axes allowing a simple analytic representation.
hx()
is the adhesion
prole i.e. the upper boundary between the white and pink parts (i.e. delimiting the yellow region from the blue one), and
hx()
the
most distal part of the nail (i.e. delimiting the blue region from the outside). These proles are symmetrical and will be expressed by
polynomials involving even functions only. For a clearer representation, h
0
corresponds to the limit of the green area from the proximal
matrix. (B) Representation of the set of stresses applied to the element of surface dxdy. (C) Results concerning the symmetry analysis. The
stress tensor can be used on every side of the small square dxdy to determine the conditions of symmetry with regard to the set of forces
applied to the nail. Given the balance of angular momentums we will further assume that
y
f
x,y
is also equal to zero everywhere on the x-axis.
This is equivalent of considering that the shear stress along a longitudinal slab is constant (does not change much at the lowest order) along
the y-axis.
5
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
equations (5)&(7) and integrate equation (5) over the y
variable. By virtue of
∂=∂=ff0
y
xy
y
yx,,
(i.e.
f
yx,
is inde-
pendent of the y variablesee equation (10)). One obtains:
=− +
−∂ ×
fxy fx f V Huhxdu
fx y
(, ) () ( ) ( ())
( ) (11)
y y adh
y
x
yx
,0
0
,
Replacing equation (11) into the boundary condition
given by equation (9) leads to:
=
+
−+
fx f
hx
fu f Vhu du
() (0)
1
()
() ( ) () (12)
yx yx
x
adh
,,
0
0
Provided the adhesion prole of the nail and the prole
of the distal edge, equation (12) completely determines
fx()
xy,
and, by symmetry,
fx()
yx,
.As
fx()
yx,
is an odd
function (equation (10)), the shear stress in x = 0 has to be null
and as a result:
=f (0) 0
yx,
. Therefore,
fx()
xy,
and, by sym-
metry,
fx()
yx,
are now fully determined. Replacing
equation (12) into equation (11) allows us to complete the
determination of,
fxy(,
)
yy,
, as follow:
=−
+
+
∂′
×−+
fxy fx
y
hx
hxf V
Hu hx du
hx
y
hx
y
hx
hx
fu huf V du
(, ) ()1
()
() ( )
(())
() ()
()
()
() () ( ) (13)
yy
adh
y
x
x
adh
,0
0
0
0
Using equation (4) together with
∂=fx() 0
y
xy,
(equation (10)) allows one to determine that:
∂=f 0
x
xx,
,namely
that
f
xx,
is only dependent on the variable y,i.e.isconstant
along the x-axis for a given value on the y-axis. As
f
xx,
is only a
function of the variable y, it is convenient to introduce y
using the reciprocal function,
h
1
of the edge equation dened
as
′′ =
hhx x(())
1
. Therefore, using the boundary condition
given by equation (8) allows the full determination of,
f
xx,
:
=′
=
∂′
=∂ ×
−−
()
fxyhx
fx
hx
hy fhy
(, ())
()
()
() () (14)
xx
xy
x
y
xy
,
,
1
,
1
As a result, provided the shapes of the adhesion prole and
edge of a nail, with the set of equations that have been determined
so far, it is possible to determine the stress tensor components
without any ambiguity. It is worth noting here that it is only when
the growth and adhesion stresses do not compensate each other,
i.e.
−+ fu f Vhu() ( ) () 0
adh0
,that
f
yx,
and
f
xx,
differ from
zero. In turn this could lead to some pathological conditions
The normal case
Let us rst consider a nail that is trimmed in such a way that:
′=hx hx() ()
and which has a growth prole given by:
=fx f Vhx() ( ) ()
adh0
. In this case, one nds:
=
=
=−
ff
fxy fx
y
hx
0
(, ) ()1
()
(15)
xx xy
yy
,,
,0
Equation (15) shows that the only existing stress is linked
to the growth stress. Such a stress should dene the natural
longitudinal curvature, i.e. the claw shape, of any growing nail.
The pathological case
Let us now consider a nail that is trimmed in such a way that:
′=hx hx() ()
and that has an imbalanced growth prole such
that:
=− + Fx f x f Vhx() () ( ) () 0
adh0
. In this case,
one shall assume also that,
Fx()
, is small and is an even
function of the variable x to preserve the conditions
regarding the symmetry of the nail. As a result,
Fx()
can be developed using Taylor series as follow:
=+
=
=
Fx F F x i() (0) /2!
i
xx
i
1
0
2
i2
. Naturally, each term
in the later development is expected to be small compared to
the leading term. Applying the same operation to the equation
of the edge,
==+
=
=
hx hx h h x i() () (0) /2!
i
xx
i
1
0
2
i2
,
and replacing the Taylor series of
Fx()
and
′=hx hx() ()
into
equations (11), (12) and (13), leads to:
α
β
γ
=
=
=−
+
=
=
fx
Fx
h
x
fx
F
hh
x
fxy fx
y
hx
yx
hF
h
x
()
(0)
(0)
()
()
(0)
(0)
()
(, ) ()1
()
(0)
(0)
( ) (16)
yx
xx
xx
yy
xx
,
,
0
,0
2
0
2
2
where the expression of
α
x()
,
β
x(
)
and
γ
x()
are given in
appendix 2 and where
α
βγ===(0) (0) (0)
1
. We note here
that for nails having very at distal edges, i.e. when:
∂≪
=
h
1
xx0
2
, the stress component that will dominate over
all the others in the distal part of the nail (the yellow and
blue parts in gure 3(B)) is:
fx()
xx,
2
. This result suggests
that nails with a at prole such as those the big toe should be
more prone to distal transverse stresses, if the difference
between the growth and adhesion stresses is not properly
balanced.
2
As by denition:
=∂ffh/
xx xy
x
,,
(equation (14)), it follows that for at
proles the edge equation musty veries
∂≪h 1
x
and therefore,
ff
xx xy,,
.
From equation (13) and
∂≪h 1
x
, it follows that
−−ffxyhx~()
(
1/()
)
yy,0
.
As in the distal part of a at nail
y
hx~(
)
, one can assume
f ~0
yy,
or at least
very small. Note that these results do not hold when the nail has not a at
prole.
6
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
Application to ingrown nails: why the big toe?
The ingrowing nail or onychocryptosis is a condition
causing much discomfort and morbidity in school children/
adolescents/ young adults (Khunger and Kandhari 2009) and
is diagnosed in 15% of pregnant women (Ponnapula and
Boberg 2010). Though recognized for a long time, a satis-
factory treatment of onychocryptosis remains elusive, in part,
because the aetiology for ingrown nails is not understood.
Different theories were initially proposed and classied
according to whether the primary fault is based on the nail
plate or not (Haneke 2008). However a structural abnormality
of the nail plate has been ruled out (Pearson et al 1987), but it
was demonstrated instead, that a change in the transverse
curvature of the nail plate (i.e. curvature along the x-axis)
located distally promotes the condition (Pearson, Bury,
Wapples and Watkin 1987). As a transverse curvature of the
nail plate is involved, this suggests in turn, that some
mechanical consideration may be underlie the aetiology of
onychocryptosis.
It is well known that ingrown nail occurs predominantly
in the big toe. From a physical point of view one central
difference between the big toe and all other toes or ngers is
the fact that the adhesion prole of the nail plate is remark-
ably at (but not straightas otherwise the boundary
conditions dened by equation (8) and (9) would not apply).
As seen above, this means that the transverse stress
f
xx,
is the
leading stress in the distal part of the nail. If an exaggerated
distal curvature of the nail denes the ingrown nail, it is
central to determine how the curvature is related to the
transverse stress.
To determine how the shape of the nail is affected we
concentrate on the energies method.
As
f
xx,
is the leading stress in the distal part of the nail, the
potential energy of the nail can be simplied to
E
f~dS
xx
1
,
where the integration is performed over the nail surface area.
As the potential energy is transformed into a bending energy to
imposeanewconguration to the nail and that, ingrown nails
are diagnosed by a change in the transverse curvature (i.e.
along the x-axissee gure 4(B)) and not by longitudinal
curvature (i.e. not along the y-axis), it is legitimate to assume
that the only curvature involved is the one along the x-axis. In
these conditions, Kirchhoffs theory of plate bending allows us
to rewrite the bending energy under the form (Helfrich 1973,
Ventsel and Krauthammer 2001):
=−
()
E
CCdS
D
x2
2
0
2
,
where the integration is performed over the nail surface and
where,
υ=−
D
Ye /12 (1
)
3
,istheexural rigidity of the nail
plate (
Y
, is the Young modulus assumed to be isotropic across
the nail and;
υ
the Poissonscoefcient),
C
x
, the transverse
curvature of the nail surface along the x-axis and,
C
0
,the
spontaneous curvature of the nail that is identical to the cur-
vature of the nger
3
. For small deformations, it is convenient
to describe the nail using the Monge gauge, i.e. by its height
′=
z
wx y(, )
, with respect to a reference plane where x
and y are the Cartesian coordinates in the reference plane. As
′′=
d
xdy dS
and
d
S
are related together by:
= +∂∂ +∂∂
d
Swxwy1(/) 1
(
/
)
dS
22
,makinguseof
the small deformation hypotheses:
∂∂ww~~0
yy
2
and of
∂≪
w 1
x
and
∂≪
ew1
x
2
;itispossibletorewritethesum
of energies to the leading orders in the displacement along the
z-axis as follows:
⎜⎟
⎜⎟
+
∂′
+′+
∂′
+
∂′
∂′
EE
Dw
x
C
fy
w
x
o
w
x
w
x
~
2
()
1
1
2
dS
; dS (17)
xx
12
2
2
0
2
,
2
3
3
3
Finally, removing the superscript prime (i.e. “’”) as all
the physical variables are now expressed in the x Cartesian
referential, the EulerLagrange method determines the
equation of the nail shape (see appendix 3):
λ∂− ∂=wyw( ) 0 (18)
xx
42
where
λ
=yfy
D
() ()/
xx,
. Using Fourier series with the fol-
lowing initial conditions:
=
=
w
w
x 00
,
∂=
=
w 0
x
x 0
and
∂=
=
wC
x
x
2
0
0
leads to the ingrown nail equation:
λ
λ=+
()
wx y w
C
y
xy(, )
()
cosh ( ) 1 (19)
0
0
Figure 4. Nail shape and related conditions. (A) Transverse prole of the distal part of a nail for different sign of
λ
. (B) Photos of nail
conditions: pincer nail (left), ingrown nail (middle) and spoon-shaped nail (right); photos from Baran R et al (2014).
3
Nails are composed of dead cells that grow from soft tissues and therefore
it is legitimate to assume that any nail should take the shape of the nger in
normal conditions.
7
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
Let us assume that
λ yl() 1/
, where
l
is the width of
the nail, one nds:
++
λ
w
xy w x x(, )~ 1
C
y
0
2
2
()
12
2
0
. This
last relation shows that the sign of
λ
y()
(i.e. the sign of
fy()
xx,
) will inuence the sign of the curvature as seen in
gure 4(A). As
β=
=
fy hy() ( ())
xx
F
hh
,
(0)
(0)
1
x
x
2
0
, the leading
term of
fy()
xx,
, i.e.
=− +FffVh(0) (0) ( ) (0)
adh0
, can
change sign depending onto whether the growth stress is
larger or smaller than the adhesion stress.
Inuence of trimming on nail conditions
fy()
xx,
is dened by the boundary condition given by
equation (14) and, as a result, exists only when the distal edge
of the nail is slightly curved. Therefore, cutting the nail in a
straight way, i.e. removing the slight curvature, and main-
taining this prole over time should remove
fy()
xx,
and
therefore improve the ingrown nail condition.
Conversely, bad trimming of the distal part of the nail
may amplify the magnitude of,
fy()
xx,
. To demonstrate this
point, assume in this case that the distal part is trimmed such
that
′=′−hx h a xl() (0) (2/)
m2
.If
Fx() 0
, from
equation (14) the transverse stress can be rewritten as,
′−
fah y~
[
/
(
(0)
)
]
xx,
m
m
1
, showing that the magnitude of the
transverse stress can be very high. This suggests that careful
attention should be given to the different ways of trimming
nails to avoid the worsening of nail conditions involving the
transverse curvature.
Discussion
It has been known since the time of Hippocrates that a par-
ticular change in nail shapes can signify specic underlying
conditions (Myers and Farquhar 2001). From a physical point
of view, nail growth and shape are necessarily inter-related.
Therefore, it seemed important to investigate whether physics
could play a role in, and as a result explain, the aetiology of
some nail conditions.
As our daily experience of nail suggests that the nail plate
is hard and therefore should be considered as a solid we have
modelled both the adhesion and balance of stresses in this 2D
system. When diseased nails are surgically removed, their
shapes remain the same and as a result we made the implicit
assumption that the nail adapts the unbalanced stresses by
changing shape over time. To conclude, the model suggests
that the imbalance between the growth and adhesion stresses
is responsible for changing the distal transverse curvature of
nails, and con rms that it is the big toe that is predominantly
aficted by nail conditions of mechanical origin due to its at
prole.
This important result seems to agree relatively well with
observations in the eld of nail conditions. For example, in
man, the term pincer nails (gure 4(B) left) describes an
exaggerated transverse curvature of the nail plate along the
longitudinal axis (Baran et al 2001, Cornelius and
Shelley 1968). This condition is mostly acquired during
advanced age (Lee et al 2008). Although the aetiology is not
fully understood a change in nail growth related to a weaker
growth force with advanced age has been suggested (de Berker
et al 2007). The other well known condition, the ingrown nail
(gure 4(B) middle), is often diagnosed in school children/
adolescents/ young adults (Khunger and Kandhari 2009) and
pregnant women (Ponnapula and Boberg 2010). It is remark-
able that this condition occurs in patients where metabolic
growth is active. For example, in pregnancy, periods of high
sex hormone productions are well known to accelerate nail
growth (Hewitt and Hillman 1966, Ponnapula and
Boberg 2010). A last condition referred to as spoon-shaped
nails corresponds to an inverted curvature of the nail
(gure 4(B) right). This shape can be described by the model.
Indeed, such a condition, which occurs in newborns or in brittle
nails, is expected to appear when the growth stress is small
enough to allow the curvature inversion (so that
λ
<y() 0
) and/
or the nail is thin enough and thus brittle (Fawcett et al 2004)as
λ
ye() 1/
3
. This shape is also predicted if the adhesion of the
nail drops, possibly as a result of aging.
Each condition cited above is diagnosed based on the
shape of the nail. These shapes can be modelled by a set of
physical equations suggesting that pincer, ingrown and
spoon-shaped nails are interrelated conditions forming a
continuum. In this context, physics suggests that the imper-
fection in nail growth, possibly due to aging and/or metabolic
changes, can precisely dene the aetiology of some nail
conditions. Finally, although it seems that any condition
should recover with time, the trimming has great importance,
and should be carefully monitored, especially with the
increasing number of nail salons.
Conclusion
We suggest that some nail conditions affecting the nail shape
can be explained by rst principles. These are thus not dis-
parate conditions but form a continuum of natural conditions.
Acknowledgements
The research was funded by the University of Nottingham
and Vertex Pharmaceuticals. The authors declare no conict
of interests and would like to thank Professor Oliver E Jensen
for fruitful discussions; Florence Hillen and Emily Paul for
proof reading the manuscript; and Ramzi Al-Agele for pro-
viding horse materials.
Appendix A. balance of stresses and boundary
conditions
We consider the square a given by gure 3 (B.1) to
determine the balance of stresses and focus on the y-axis. The
balance of stresses gives
∂+fxy fxy f V(, ) (, ) ( )
y
yy
x
y x adh,,
8
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
−=
H
yhx
(
()
)
0
, where
−=
H
yhx
(
()
)
1
if
yhx()
or
zero otherwise. Integrating this equation over the y-axis gives:
=
−∂
−⋅
fxy fx
fxy
fVHyhx
(, ) (,0)
(, )
()
(
()
)
dy (A1.a)
yy yy
y
x
yx
adh
,,
0
,
Where
=−fx f x() (,0)
yy0,
as dened in the text.
Assuming further that no force is applied on the distal edge of
the nail, one nds:
=′+
=
{}
fxhx n e
fxhxn fxhxn
(, ())
(, ()) (, ())
0(A1.b)
ij
y
yx
x
yy
y
,
,,
where
+∂ =− +
n
hx hxe e1() ()
xxxy
2
. The balance of
stresses along the x-axis can be determined similarly:
∂+=fxy fxy(, ) (, ) 0 (A1.c)
x
xx
y
xy,,
As one assumes that no stress is applied over the x-axis
the only relation regarding the boundary condition of the
distal edge, is:
=′+ =
{}
fxhx n e
fxhxn fxhxn
(, ())
(, ()) (, ()) 0 (A1.d)
ij
x
xx
x
xy
y
,
,,
as seen in the text.
Appendix B
α =
+∂ +
+∂
=
=
=
=
x
FxF i
hxhi
()
1 / (0)(2 1)!
1/(0)2!
i
xx
i
i
xx
i
1
0
2
1
0
2
i
i
2
2
β
γ
=
+∂ +
∂∂
=
∂∂
×+ +
+∂
=
=
=
=
=
=
=
=
=
=
=
=
x
FxF i
hx h i
x
hx h i
FxF i
hxhi
()
1 / (0)(2 1)!
/(21)!
()
/(21)!
1 / (0)(2 1)!
1/(0)2!
i
xx
i
i
xx
i
xx
i
xx
i
xx
i
xx
i
i
xx
i
1
0
2
1
0
2( 1)
0
1
0
2( 1)
0
1
0
2
1
0
2
i
i
i
i
i
2
22
22
2
2
Appendix C. Energy optimisation using the Euler
Lagrange method
Consider the free energy:
⎜⎟
++
Ew
Dw
x
C
fy
w
x
()~
2
() 1
1
2
dS (A3.a)
tot
xx
2
2
0
2
,
2
One needs to nd the function,
w
, that minimizes the free
energy above. Let us perform a small variation of
δ→+
w
ww
. The concomitant change in the free energy is
then:
⎜⎟
⎜⎟
δ
δ
δ
+
++
+
−+ +
E
Dw
x
w
x
C
fy
w
x
w
x
Dw
x
Cfy
w
x
~
2
() 1
1
2
dS
2
() 1
1
2
dS (A3.b)
tot
xx
xx
2
2
2
2
0
2
,
2
2
2
0
2
,
2
Where
δ
δ=+EEwwEw()()
tot tot tot
. Working the
energy difference to the rst order of the small quantity
δ
w
one nds:
⎜⎟
δ
δ
δ
+
ED
w
x
C
w
x
fy
w
x
w
x
~
( ) dS (A3.c)
tot
xx
2
2
0
2
2
,
Splitting equation (A3.c) into two different integrals, i.e.
over the curvature and the gradient of
w
one nds:
δ
δ
δ
δ
=
+
D
w
x
C
w
x
x
w
x
C
w
x
xx
w
x
Cw
w
x
w
dS
dy
dy
dS (A3.d)
x
x
x
x
2
2
0
2
2
2
2
0
2
2
0
4
4
0
0
0
0
And
δ
δ
δ
=
fy
w
x
w
x
S
fy
x
w
x
wy
fy
w
x
wS
() d
() d
() d (A3.e)
xx
xx
x
x
xx
,
,
,
2
2
0
0
9
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
Where the interval
xx[,
]
o0
is the interval of integration over
the x-axis, i.e. the extend of the projection of the nail surface
area over the x-axis contained in the Cartesian reference
plane. Using the conditions of symmetry, namely that
δ
w
and
w
are even function of the variable x, from equations (A3.e)
&(A3.d) it follows that
δ
E
to
t
can be reduced to zero if:
=
w
x
fy
w
x
() 0 (A3.f)
xx
4
4
,
2
2
References
Arnold M, Cavalcanti-Adam E A, Glass R, Blummel J, Eck W,
Kantlehner M, Kessler H and Spatz J P 200 4 Activation of
integrin function by nanopatterned adhesive interfaces
Chemphyschem. 5 3838
Baran R, Dawber R, Haneke E, Tosti A and Bristow I 2014 Informa
Health Care (Abingdon, Oxford: Taylor & Francis)
Baran R, Haneke E and Richert B 2001 Pincer nails: denition and
surgical treatment Dermatol. Surg. 27 2616
Benz A, Zenker W, Hildebrandt T B, Weissengruber G,
Eulenberger K and Geyer H 2009 Microscopic morphology of
the elephant's hoof J. Zoo Wildl Med. 40 71125
Butler K D Jr and Hintz H F 1977 Effect of level of feed intake and
gelatin supplementation on growth and quality of hoofs of
ponies J. Anim. Sci. 44 25761
Cavalcanti-Adam E A, Micoulet A, Blummel J, Auernheimer J,
Kessler H and Spatz J P 2006 Lateral spacing of integrin
ligands inuences cell spreading and focal adhesion assembly
Eur. J. Cell Biol. 85 21924
Cavalcanti-Adam E A, Volberg T, Micoulet A, Kessler H,
Geiger B and Spatz J P 2007 Cell spreading and focal adhesion
dynamics are regulated by spacing of integrin ligands Biophys.
J. 92 296474
Cornelius C E III and Shelley W B 1968 Pincer nail syndrome Arch.
Surg. 96 3212
de Berker D A, Andre J and Baran R 2007 Nail biology and nail
science Int. J. Cosmet. Sci. 29 24175
Dembo M, Torney D C, Saxman K and Hammer D 1988 The
reaction-limited kinetics of membrane-to-surface adhesion and
detachment Proc. of the Royal Society of London Series B-
Biological Sciences vol 234, pp 5583
Dong C and Lei X X 2000 Biomechanics of cell rolling: shear ow,
cell-surface adhesion, and cell deformability J. Biomech. 33
3543
Eliashar E 2012 The biomechanics of the equine foot as it pertains to
farriery Veterinary Clinics of North America-Equine Practice
28 283
Fawcett R S, Linford S and Stulberg D L 2004 Nail abnormalities:
clues to systemic disease Am. Fam. Physician 69 141724
Godwin K O 1959 An experimental study of nail growth Journal of
Nutrition 69
1217
Haneke E 2008 Controversies in the treatment of ingrown nails
Dermatol. Res. Pract. 783924
Harrison S M, Monahan F J, Zazzo A, Bahar B, Moloney A P,
Scrimgeour C M and Schmidt O 2007 Three-dimensional
growth of bovine hoof as recorded by carbon stable isotope
ratios Rapid Commun. Mass Spectrom. 21 39716
Helfrich W 1973 Elastic properties of lipid bilayerstheory and
possible experiments Zeitschrift Fur Naturforschung C-A
Journal of Biosciences C28 693703
Hewitt D and Hillman R W 1966 Relation between rate of nail
growth in pregnant women and estimated previous general
growth rate Am. J. Clin. Nutr. 19 4369
Johnston A M and Penny R H C 1989 Rate of claw horn growth and
wear in biotin-supplemented and non-supplemented pigs
Veterinary Record 125 1302
Khunger N and Kandhari R 2009 Ingrown toenails Indian J.
Dermatol. Venereol. Leprol. 78 27989
Lee J I, Lee Y B, Oh S T, Park H J and Cho B K 2008 A clinical
study of 35 cases of pincer nails Ann. Dermatol. 23 41723
Miller K V, Marchinton R L and Nettles V F 1986 The growth rate
of hooves of white-tailed deer J. Wildl Dis. 22 12931
Myers K A and Farquhar D R 2001 The rational clinical examination.
Does this patient have clubbing? JAMA 286 3417
Pearson H J, Bury R N, Wapples J and Watkin D F 1987 Ingrowing
toenails: is there a nail abnormality? A prospective study
J. Bone Joint Surg Br. 69 8402
Pollitt C C 1994 The basement-membrane at the equine hoof dermal-
epidermal junction Equine Veterinary Journal 26 399407
Ponnapula P and Boberg J S 2010 Lower extremity changes
experienced during pregnancy J. Foot Ankle Surg. 49
4528
Ra H J, Picart C, Feng H S, Sweeney H L and Discher D E 1999
Muscle cell peeling from micropatterned collagen: direct
probing of focal and molecular properties of matrix adhesion
Journal of Cell Science 112 142536
Reboux S, Richardson G and Jensen O E 2008 Bond tilting and
sliding friction in a model of cell adhesion Proc. of the Royal
Society a-Mathematical Physical and Eng. Sciences vol 464,
pp 44767
Shelton J, Usherwood N M, Wapenaar W, Brennan M L and
Green L E 2012 Measurement and error of hoof horn growth
rate in sheep Journal of Agricultural Science 150 3738
Telezhenko E, Bergsten C, Magnusson M and Nilsson C 2009 Effect
of different ooring systems on claw conformation of dairy
cows J. Dairy Sci. 92 262533
Thoefner M B, Wattle O, Pollitt C C, French K R and Nielsen S S
2005 Histopathology of oligofructose-induced acute laminitis
in heifers J. of Dairy Science 88 277482
Ventsel E and Krauthammer T 2001 Thin Plates and Shells: Theory,
Analysis and Applications (Boca Raton, FL: CRC Press)
Worth D C and Parsons M 2008 Adhesion dynamics:
mechanisms and measurements Int. J. Biochem. Cell Biol.
40 2397409
10
Phys. Biol. 11 (2014) 066004 C Rauch and M Cherkaoui-Rbati
... Ingrown nail may occur more easily in pregnant women in association with increasing edema. 17,18 Ingrown nail commenced after pregnancy in 23.8% of female patients in this study. ...
... 2,8 Lateral deviation of the nail plate can lead to ingrown nail by compromising the relation between the nail plate and the nail bed and by exacerbating irritation between these structures. 2,18,27 Lateral deviation in the nail plate was determined in 9.9% of the present patients. Excessive angulation of the nail plate can also lead to a disposition to ingrown nail 18 and was observed in 35.8% of the present patients. ...
... 2,18,27 Lateral deviation in the nail plate was determined in 9.9% of the present patients. Excessive angulation of the nail plate can also lead to a disposition to ingrown nail 18 and was observed in 35.8% of the present patients. ...
Article
Background: Ingrown nail is a condition frequently seen in children and adolescents, the pain from which can affect their daily living activities and school performances. The purpose of this study was to determine the clinical and sociodemographic characteristics of ingrown nails in children. Methods: The clinical and sociodemographic characteristics of patients aged 0 to 18 years presenting with ingrown nail were evaluated retrospectively from clinic records. Results: Sixty-two patients aged 3 to 18 years (mean age, 15 years; male to female ratio, 1.06) were enrolled. A total of 175 ingrown nails were evaluated (all of them were in the halluces, 54.3% of them were on the lateral margin). A positive family history of ingrown nail was present in 15.7%. High prevalences of incorrect nail cutting (72.1%), trauma (36.1%), poorly fitting shoes (29%), hyperhidrosis (12.9%), obesity (9.7%), and accompanying nail disorders (9.7%) were determined among the patients. Conclusions: This study revealed the clinical and sociodemographic characteristics of ingrown nails in children. These data will be useful in preventing the occurrence of ingrown nail by revealing and then eliminating predisposing factors.
... Ingrown nail may occur more easily in pregnant women in association with increasing edema. 17,18 Ingrown nail commenced after pregnancy in 23.8% of female patients in this study. ...
... 2,8 Lateral deviation of the nail plate can lead to ingrown nail by compromising the relation between the nail plate and the nail bed and by exacerbating irritation between these structures. 2,18,27 Lateral deviation in the nail plate was determined in 9.9% of the present patients. Excessive angulation of the nail plate can also lead to a disposition to ingrown nail 18 and was observed in 35.8% of the present patients. ...
... 2,18,27 Lateral deviation in the nail plate was determined in 9.9% of the present patients. Excessive angulation of the nail plate can also lead to a disposition to ingrown nail 18 and was observed in 35.8% of the present patients. ...
Article
Background: Ingrown nail is a common health problem that significantly affects daily life due to its painful nature. The purpose of this study was to reveal the clinical and sociodemographic characteristics of ingrown nails. Methods: The clinical and sociodemographic characteristics of patients older than 18 years presenting with ingrown nail were investigated. Results: Two hundred six patients aged 18 to 77 years (mean age, 39 years; female to male ratio, 1.45) were included in the study. A total of 729 lesions were evaluated (718 ingrown nails were on the feet and 11 were on the fingers). A family history of ingrown nail was present in 7.6% of the participants. Of the 206 patients, 26.7% were treated with surgical methods for ingrown nails previously and experienced recurrence. Ingrown toenails were in the hallux in 81.3% of patients, and 52% were on the lateral margin. Incorrect nail-cutting habits (73.5%), poorly fitting shoes (46.2%), excessive angulation of the nail plate (35.8%), obesity (34.1%), trauma to the feet (24.3%), pregnancy (23.8% of women), hyperhidrosis (16.8%), and lateral deviation of the nail plate (9.9%) were closely associated with ingrown nails. Conclusions: This study revealed the clinical and sociodemographic characteristics of ingrown nails. The study data will be useful in preventing the development of ingrown nail and recurrences after treatment by identifying and then eliminating conditions establishing a predisposition to it.
... Cho et al reported a peak in young people and adults aged above 50 years. The ingrown toenail often affects the big toe because it is generally caused by repeated mechanical trauma exerted on the flat surface of the nail by shoes, especially tight-fitting ones [5]. Ingrown toenails can be classified into into four types namely the childhood type, the lateral and distal hypertrophy of the fold of the nail, pincer nails, and the juvenile ingrown toenail [6]. ...
... Ropivacaine appears to be the local anesthetic drug preferred by surgeons and anaesthetists for peripheral nerve block [3] in nail surgery because of its rapid onset of action and long duration of action of analgesic effects of up to 9 hours. However, because lidocaine is cheaper and readily available in low-resource setting, it is more used combined with epinephrine as adjuvant for the anesthesia of this surgery [5]. It is worth to mention that adrenaline as an adjuvant to local anesthesia also potentiates the local anesthetic effects. ...
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Background: Currently, the management of ingrown toenail (onychocryptosis) ranges from conservative medical management to surgical treatment. Surgical management is typically performed as an outpatient procedure due to it numerous advantages such as the simplicity of the technique and the low incidence of postoperative complications. The most common postoperative complications are recurrences and surgical site infections, whereas gangrene complicating a surgical site infection has been scarcely reported. We are reporting a rare complication following ambulatory surgery untimely requiring amputation. Case presentation: A twelve-year-old boy was referred to our orthopedic surgical department for a surgical site infection complicating an initial surgical management of a left ingrown big toenail leading to a dry gangrene of the affected toe. The gangrene toe was amputated under peripheral nerve block and the patient was discharged home the same day on antibiotics, analgesics and with sessions of rehabilitation and psychological support planned. The postoperative course was uneventful at 6 months of follow-up. Conclusion: The authors report this case to draw clinicians' attention, especially wound care specialists, orthopedists and podiatrists to this rare but potentially debilitating disease.
... In subgroup analysis, an increase in the HIA was associated with the lateral nail fold involvement. Rauch et al. reported that transverse stress is the leading stress in the distal part of the nail, and the hallux is prone to ingrown toenails due to its flat shape [30]. We suspect that patients with a laterally deviated distal phalanx may be exposed to superimposed pressure onto the second toe, thereby contributing to the development of an ingrown toenail. ...
Article
Background This case-control study aimed to explore an association between foot alignment and development and presentation of the ingrown toenail. Methods Radiographs were evaluated for hallux interphalangeal angle (HIA), hallux valgus angle (HVA), talonavicular coverage angle (TNC), talo-first metatarsal (Meary’s) angle, and calcaneal pitch angle (CP), as well as medial sesamoid position in a cohort of 103 young and healthy patients (mean age of 20.5 years) with ingrown toenails. A control group of 63 patients was included, and the radiographic parameters were compared. Subgroup analysis was performed in patients with lateral (n = 65) or medial (n = 38) nail fold involvement. Results The overall study group demonstrated a larger TNC and Meary’s angle and smaller CP than the control group, while no significant difference was found regarding the HIA and HVA. The lateral nail fold group had a larger HIA when compared to the medial nail fold group. Multiple regression analysis revealed that for ingrown toenail development, the only risk factor was a decrease in the CP. In the case of lateral nail fold involvement, an increase in the HIA found to be the only factor. Conclusion A lower medial longitudinal arch seems to be a predisposing factor in developing an ingrown toenail. The lateral nail fold involvement was associated with lateral deviation of the distal phalanx. The result of this study could provide information on prevention, treatment, recurrence, and patient counseling of an ingrown toenail in otherwise young and healthy individuals.
... Dadurch wird bei der Großzehe die laterale Nagelplatte gegen den lateralen Nagelwall gedrückt, was wiederrum zu einer lokalen Irritation führen kann. Weitere Ursachen sind mangelnde Nagelpflege/Hygiene, wiederholte Traumata am Nagelorgan, Hyperhidrose, Nagelpilzbefall, Diabetes mellitus, Immunsuppression, Schwangerschaft, die Einnahme von EGF-Rezeptor-Inhibitoren oder mechanische Ursachen durch Fußfehlstellungen [7,[10][11][12][13]. Auch Hyperostosen bzw. ...
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Zusammenfassung Der Unguis incarnatus ist ein häufiges Krankheitsbild, mit dem sich Patienten in der Hausarztpraxis, der dermatologischen Klinik oder der chirurgischen Notaufnahme vorstellen. Häufig führt die inkonsequente konservative Therapie oder die falsch-indizierte operative Intervention zu langwierigen und komplikationsreichen Verläufen, inklusive Rezidiven. Die Patienten sollten über die Komplexität des Nagelorgans aufgeklärt werden, um der Banalisierung der Erkrankung vorzubeugen, und eine entsprechende Compliance in der Therapie zu erreichen. In diesem Manuskript wird die sachgerechte Versorgung des Unguis incarnatus im Sinne eines praktischen Behandlungsalgorithmus dargestellt. Die konsequente konservative Therapie ist bei akutem Unguis incarnatus mit milder Ausprägung die Therapie der ersten Wahl mit guten Behandlungsergebnissen. Nagelerhaltende operative Eingriffe kommen bei moderaten/schweren akuten Formen zum Einsatz. Der chronische Unguis incarnatus , ohne floride Infektion, stellt eine elektive Operationsindikation dar. Sowohl bei den nagelerhaltenden Eingriffen als auch bei erweiterten operativen Maßnahmen ist eine chirurgische Operationsaufklärung obligat.
... In the r.h.s., the first term is the adhesion stress that is proportional to the angular growth rate of the hoof (v u ) c and the constant f 0 adh that characterizes the adhesion of the hoof [44]; and the second term is the component of the ground [39,40] royalsocietypublishing.org/journal/rsif J. R. Soc. Interface 16: 20190214 reaction to the weight applied on the surface of the hoof capsule (in-plane description). ...
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Global inequalities in economic access and agriculture productivity imply that a large number of developing countries rely on working equids for transport/agriculture/mining. Therefore, the understanding of hoof conditions/shape variations affecting equids' ability to work is still a persistent concern. To bridge this gap, using a multi-scale interdisciplinary approach, we provide a bio-physical model predicting the shape of equids' hooves as a function of physical and biological parameters. In particular, we show (i) where the hoof growth stress originates from, (ii) why the hoof growth rate is one order of magnitude higher than the proliferation rate of epithelial cells and (iii) how the soft-to-hard transformation of the epithelium is possible allowing the hoof to fulfil its function as a weight-bearing element. Finally (iv), we demonstrate that the reason for hoof misshaping is linked to the asymmetrical design of equids' feet (shorter quarters/long toe) together with the inability of the biological growth stress to compensate for such an asymmetry. Consequently, the hoof can adopt a dorsal curvature and become 'dished' overtime, which is a function of the animal's mass and the hoof growth rate. This approach allows us to discuss the potential occurrence of this multifaceted pathology in equids.
... La adherencia de la lámina al lecho está dada por la complementariedad existente entre las crestas epidérmicas del lecho ungular y las de la porción ventral o inferior de la lámina. 10 Un cambio en este patrón microscópico de adhesión en carriles longitudinales por la presencia de una lesión en el espacio subungular puede alterar la forma y configuración de la lámina, haciéndola más susceptible a la fragmentación. ...
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Nail plate destruction is not an exclusive sign of malignant pathologies, even though they should be included as a differential diagnosis when found. We discuss three cases of benign tumors that presented with important nail plate destruction, breaking the paradigm that just malignant tumors debut with it. We also elaborate two hypotheses about the mechanism of this clinical sign, whether or not nail matrix compromise is found. © 2018 Catedra Universitario, Facultad de Medicina. All rights reserved.
Article
Background: Orthonyxia is an effective, noninvasive treatment for transverse nail curvature deformity. Objective: To discover the factors influencing treatment results of superelastic wire orthonyxia (SEWO). Material and methods: A retrospective study was conducted using clinical records of patients treated with SEWO. A multiple linear regression model was used to explain the correlation between correction pace (% per week) and the other collected variables (patient age, sex, position of treated toe, wire diameter [WD, mm], wire residence time [WRT, weeks], nail plate thickness [PT, mm], baseline nail curvature index [NCI], number of previous treatments, and the correction pace of previous treatments [CPT, % per week]). A logistic regression model was used to identify risk factors for adverse effects. Results: A total of 475 cases were collected from 197 patients. The correction pace was positively related to baseline NCI, WD, and correction pace in previous treatment. Also, it was negatively related to WRT and nail PT. No clinical factor was correlated with the occurrence of side effects. Conclusion: The correction pace of SEWO is affected by the baseline NCI, the diameter of the wire, nail PT, the CPT, and the WRT.
Chapter
This chapter provides the scientific backdrop to the interpretation and understanding of many diseases of the nails and their management. Embryogenesis represents the original growth of the nail, which is continued throughout life and reiterated when there is nail loss or recovery from surgery. An understanding of the regional anatomy and the physiology of the components enables analysis of clinical signs according to their biological origins. Addressing a presenting problem from first principles based upon the science of the nail unit will help clinicians to make a precise and accurate diagnosis. Scientists designing medication and physical mechanisms of engaging or interpreting nail disease will require the story of nail biology to be laid out for them in the language of anatomy and science. They will in turn be able to add to this story as much of the literature in nail biology comes from scientists addressing fundamental problems, using techniques found in other areas of medicine.
Article
Although ingrown nail (IN) is common, there is no large‐scale study regarding its epidemiology and risk factors, such as foot deformity. The purpose of this study is to determine the demographics of IN and clarify its association with bone‐related comorbidities of the ankle, foot and toe. Patients in a representative sample cohort of the National Health Information Database of South Korea from 2004 to 2013 who had IN were compared with a control group without IN. Ten‐year overall incidence was 307.5/100 000 person‐years (95% confidence interval, 304.1–310.9). IN incidence and prevalence showed an increasing trend, and IN was more common in women than in men. Incidence showed bimodal peaks, among teenagers and among participants in their 50s. The IN group showed more common valgus deformity (64.3%) than did the control group (61.6%), and flat foot was also a significant risk factor of IN. There were increasing tendencies of IN incidence and prevalence among females. Confirmed bone deformity, especially acquired valgus or varus deformity, and flat foot were associated with IN.
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A theory of the elasticity of lipid bilayers is proposed. Three types of strain, i. e. stretching, tilt and curvature, are distinguished and the associated stresses are identified. It is argued that in the case of vesicles (= closed bilayer films) the only elasticity controlling nonspherical shapes is that of curvature. Euler-Lagrange equations are derived for the shape in magnetic fields and under excess outside pressure. It is shown that magnetic fields can deform spherical vesicles into ellipsoids of revolution. Under excess outside pressure the spherical shape becomes unstable at a certain threshold pressure. Both effects can be influenced by a spontaneous curvature of the bilayer. Some possible experiments to determine the elastic properties are also discussed.
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As a simple theoretical model of a cell adhering to a biological interface, we consider a rigid sphere moving in a viscous shear flow near a wall. Adhesion forces arise through intermolecular bonds between receptors on the cell and their ligands on the wall, which form flexible tethers that can stretch and tilt as the base of the cell moves past the wall; binding kinetics is assumed to follow a standard model for slip bonds. Our model reveals three distinct types of motion: either bonds accumulate at the peeling edge and slow down the cell almost to a halt; or bonds adhere strongly, but without creating any significant torque, and the cell tank-treads over the wall without slipping; or the cell moves near its free-stream speed with bonds providing weak frictional resistance to sliding. Under realistic conditions, the model predicts bistability among these three states, implying that at critical shear rates the system can switch abruptly between firm adhesion, tank-treading and free sliding. The model suggests that sliding friction arising through bond tilting may play a significant dynamical role in cell--adhesion applications such as neutrophil rolling and bacterial colonization under flow.
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Ingrown toenails are one of the most frequent nail disorders of young persons. They may negatively influence daily activities, cause discomfort and pain. Since more than 1000 years, many different treatments have been proposed. Today, conservative and surgical methods are available, which, when carried out with expertise, are able to cure the disease. Packing, taping, gutter treatment, and nail braces are options for relatively mild cases whereas surgery is exclusively done by physicians. Phenolisation of the lateral matrix horn is now the safest, simplest, and most commonly performed method with the lowest recurrence rate. Wedge excisions can no longer be recommended.
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Onychocryptosis or ingrown toenail is a very common pathology of the toenail unit, chiefly affecting adolescents and young adults. The ingrown toenail is responsible for disabling complaints like pain and difficulty in walking. It is associated with significant morbidity, hampering the quality of life as it interferes with sporting activities, school, or work. It principally occurs in the hallux. It is ascribed to poor trimming of the nails in combination with local pressure due to ill-fitting footwear, hyperhidrosis, poor foot hygiene and nail abnormalities. Pain, swelling and discharge are the main clinical features. Four stages of the condition have been described. Diagnosis is usually evident, but it should be differentiated from subungual exostosis and tumors of the nail bed. The current standard of care focuses on conservative treatment like the gutter splint technique in the initial stages, and in cases that are resistant to medical management or recurrent, surgical correction is the treatment of choice. There are various surgical techniques that are described in literature. Although there is no ideal technique, lateral nail plate avulsion with lateral matricectomy by phenol is commonly used and reported to be more effective in reducing recurrences. The aim of this review article is to focus on this common pathology of the nail, the various techniques employed in management and aid in the selection of treatment according to the stage and severity of the disease.
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Pincer nail is a nail deformity characterized by transverse overcurvature of the nail plate. Pincer nail can affect a patient's quality of life due to its chronic, recurrent course; however, there have been no clinical studies on the pincer nail condition in Korean patients. The purpose of this study was to characterize the clinical findings and treatment of pincer nail. In addition, possible etiological factors were considered, and treatment efficacy was evaluated. The medical records and clinical photographs of 35 patients (12 males, 23 females) who were diagnosed with pincer nail between August 1, 2005 and July 31, 2009 were studied. Patient age ranged from 10 to 77 (52.09±17.26) years, and there was a predominance of female (23 out of 35 patients, F:M=2:1). The mean duration of the disorder was 7.45 years (range 0.25~40); 85% had pincer nail for at least 1 year. In addition, 40% had a history of previous treatment and recurrence. There were 82.8% patients with the common type of pincer nails. The most commonly involved nails were both great toenails. Among 35 patients, nail grinding was started in 30 patients, and 25 patients showed clinical improvement with nail grinding. The width index increased and the height index decreased after treatment. The mean follow up period was 8.42 months (range 1~27), and 7 patients showed recurrence after 8.8 months (range 2~20). Among 35 patients, 5 patients were treated with nail extraction with matricectomy, and the symptoms resolved immediately. The mean follow up period was 7.6 months (range 0~19), and recurrence was not observed. Onychomycosis was also present in 37.1% of patients, and itraconazole pulse therapy for 3 months was added. The results of this study demonstrate the clinical features of pincer nail in Korean patients. The findings show that the common type of pincer nail was most common, and nail grinding as a conservative treatment greatly improved pincer nails despite a risk of recurrence. When onychomycosis was also present, oral antifungal therapy added to nail grinding resulted in a more rapid change in nail thickness and clinical improvement.
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WE HAVE recently observed three cases of a unique idiopathic distortion in the shape of the nails in which there appears to be an excessive transverse curvature of the nail plate, thus producing a pinching and loss of soft tissue of the involved fingers. This nail dystrophy may produce severe pain in the involved digit and relief can be achieved by removal of the plate.Report of Cases Case 1. —In August 1959, a 54-year-old white woman was seen as an outpatient at the Hospital of the University of Pennsylvania for pain of one month's duration in the distal portion of the right thumb. The patient stated that there had been a gradual onset of pain without apparent cause. There had been no unusual trauma and the patient knew of no foreign body entering the skin. On examination, all nails of both hands and feet showed an unusual degree of
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Determining the rate of hoof horn growth in sheep is important for understanding the physiology and pathology of the foot and the impact of the environment and the treatment of diseased feet on foot health. It could lead to improved understanding of the interaction between hoof horn and pasture/barn floor characteristics and in methods for prevention and treatment of ovine foot diseases. In the current study, the hoof horn was measured using a previously tested protocol on all eight digits of 21 healthy yearling mule ewes on a farm in North Wales on four occasions over a period of 53 days. The mean hoof horn growth rate was 0·11 mm (s.e.m. 0·02) per day; the residual error variance was 0·024 and the R2 was 0·245. There were no significant differences between hoof horn growth rates in front and hind feet or between medial and lateral claws or over time.
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Shoes were originally applied to horses' feet to protect against excessive wear. Over the years, countless types of shoes and farriery techniques have been developed not only as a therapeutic aid to treat lameness but also to maintain or enhance functionality. The past 3 decades have provided equine veterinarians and farriers with new information relating to limb biomechanics and the effects of various farriery methods. This article describes the principles of foot biomechanics and how they are affected by some of the more common farriery and shoeing techniques.
Article
Context The association between digital clubbing and a host of diseases has been recognized since the time of Hippocrates. Although the features of advanced clubbing are familiar to most clinicians, the presence of early clubbing is often a source of debate. Objective To perform a systematic review of the literature for information on the precision and accuracy of clinical examination for clubbing. Data Sources The MEDLINE database from January 1966 to April 1999 was searched for English-language articles related to clubbing. Bibliographies of all retrieved articles and of standard textbooks of physical diagnosis were also searched. Study Selection Studies selected for data extraction were those in which quantitative or qualitative assessment for clubbing was described in a series of patients. Sixteen studies met these criteria and were included in the final analysis. Data Extraction Data were extracted by both authors, who independently reviewed and appraised the quality of each article. Data extracted included quantitative indices for distinguishing clubbed from normal digits, precision of clinical examination for clubbing, and accuracy of clubbing as a marker of selected diseases. Data Synthesis The profile angle, hyponychial angle, and phalangeal depth ratio can be used as quantitative indices to assist in identifying clubbing. In individuals without clubbing, values for these indices do not exceed 176°, 192°, and 1.0, respectively. When clinicians make a global assessment of clubbing at the bedside, interobserver agreement is variable, with κ values ranging between 0.39 and 0.90. Because of the lack of an objective diagnostic criterion standard, accuracy of physical examination for clubbing is difficult to determine. The accuracy of clubbing as a marker of specific underlying disease has been determined for lung cancer (likelihood ratio, 3.9 with phalangeal depth ratio in excess of 1.0) and for inflammatory bowel disease (likelihood ratio, 2.8 and 3.7 for active Crohn disease and ulcerative colitis, respectively, if clubbing is present). Conclusions We recommend use of the profile angle and phalangeal depth ratio as quantitative indices in identifying clubbing. Clinical judgment must be exercised in determining the extent of further evaluation for underlying disease when these values exceed 180° and 1.0, respectively.