What Every Podiatrist Should Know About Blister

Transcription

CONTENTS
1…..
2…..
3…..
4…..
Acknowledgements
The Problem of Foot Blisters
What This Report Is and What It Isn’t
What Do You Think Causes Blisters?
Part One: Understanding Blisters
5.... Introduction
6.... Friction & Rubbing
7.... Shear
11.. Quotes From Researchers and Clinicians on Friction and Shear
12… Foot Blisters … Where Does Shear Come From?
12… How Much Shear Before Injury Occurs?
13… Skin Anatomy
14… Blisters vs Abrasions
Part Two: Blister Prevention Strategies
15… Factors Influencing Blister Formation
16… Blister Prevention Strategies
16… Alter Your Activity
17… Optimise Shoe Fit
18… Addressing Structural and Biomechanical Issues
22… Cushioning
25… Taping
28… Managing Skin Moisture
31… Double Sock Systems
33… ENGO Low Friction Patches
38… Summary of Blister Prevention Strategies: Pros & Cons
39… CONCLUSION
40… References & Recommended Reading
Cover photo from Getty Images
Acknowledgements
Many thanks to the following people for their advice and feedback in the final
stages of this Report:
Marty Carlson – Tamarack Habilitation Technologies Inc (US)
Jason Pawelsky – Tamarack Habilitation Technologies Inc (US)
Ian Griffiths – Ian Griffiths Sports Podiatry (UK)
Martin Fryer – Scientist and ultramarathon runner (AU)
Monica Rietveld – Myaree Podiatry (AU)
Jason Rzepecki – SportsPod by Jason Rzepecki (AU)
www.blisterprevention.com.au
Page 1
The Problem of Foot Blisters
Are you frustrated with your lack of success in dealing with you clients’ blisters?
Fed up with recommending blister prevention products you know are unlikely to
help?
Are you annoyed with the mess and the cost involved in trying to keep on top of
your own blister issue?
This is the problem of foot blisters. They’re common and they’re difficult to
manage. What’s more, it seems we’ve been mismanaging them for decades.
However, there are the beginnings of a change in the blister prevention
landscape.
Page 2
What This Report Is and What It Isn’t
This report is not the most academic article you’ll read about blisters and blister
management. But it may be one of the most easy to understand whilst being
extremely comprehensive. There is a substantial amount of referencing here but
this paper has not been researched systematically.
This is a gathering of my opinions on this topic which I feel I have a good
understanding of. I feel I can offer fresh insight and a new perspective to the
topic of blister causation and prevention techniques.
It stems from my personal struggles with foot blisters and my professional
special interest - I recently became the Australasian distributor of a blister
prevention product called ENGO Blister Prevention Patches which I have found to
be exceptional but a best-kept-secret for some reason. I only came across it by
chance in 2009.
In trying to understand why this product works so well and where it fits into the
established blister prevention landscape, I have come to realise that blister
causation is not well understood and this may be why blisters continue to be so
common and difficult to manage.
It does seem though that there are the beginnings of a shift in focus towards the
concept of shear. And this relates directly to blister formation and prevention
I believe there will be an increased level of
awareness and proactivity in regard to foot
blisters very soon. The landscape is changing
and as podiatrists, we need to be ahead of the
game.
Prepare yourself for
an increased level of
awareness and
proactivity in regard
to foot blisters
Page 3
What Do You Think Causes Blisters?
Friction? Rubbing? Sort of, but possibly not in the way you think – it depends
on your definition of friction and rubbing. Though these would have erroneously
been my answers until recently.
In fact, there are elements to blister causation that are quite counterintuitive –
and this is why blisters are so poorly understood and poorly managed.
Foot blisters are nothing new. The mainstream blister prevention strategies have
remained mainstream for decades. This is in spite of research showing that
many of them are not particularly helpful and in some cases, even
counterproductive (I’d like to draw attention these shortcomings as I don’t think
we fully comprehend these).
But year after year, the same advice and management techniques are
perpetuated by practitioners and the popular media. Blister treatment then
becomes the focus, rather than blister prevention.
I believe our lack of understanding is
responsible and this just isn’t good enough.
It’s time to stop giving poor blister
prevention advice and start being part of
the solution! To do this, we need to
understand what causes blisters – that is
Part One of this Report.
It’s time to stop giving
poor blister prevention
advice and start being a
part of the solution!
And Part Two is a reassessment of the various preventative strategies that exist.
If you’re serious about helping those in your care and who pay for your expertise,
this report will be of interest to you.
Page 4
PART ONE – Understanding Blisters
Introduction
Foot blisters are a common and deceptively debilitating ailment. Blister incidence
has been investigated in athletes, hikers and in military populations and ranges
from 33% to 50% (Brennan et al, 2012 and Richie, 2010). Blister management
has not progressed significantly in recent decades and blisters remain a familiar
injury requiring treatment. Richie (2010) sums up the state of blister
management today:
“Little insight or research into the prevention or
treatment of the most common foot injury in
sport has been produced in the past 30 years.
Physicians, coaches and athletic trainers continue
to advocate the use of petrolatum jelly and skin
powders to prevent blisters while the scientific
literature suggests these measures may actually
increase the chance of blistering on the feet.”
Richie, 2010
Page 5
Friction & Rubbing
Everybody knows that blisters are caused by friction; however, most people think
that friction is simply rubbing. Rubbing is a poor definition for friction and
rubbing doesn’t cause blisters, not strictly.
Definition
Friction is the force that resists the sliding of one surface across another. Two
surfaces either:
Glide easily against one another (low friction - slippery);
Or they tend to grip together (high friction - sticky).
The measurement of friction is the ‘coefficient of friction’. The
coefficient of friction (COF) is a number that represents this
‘slipperiness’ or ‘stickiness’ between two surfaces and is
generally below 1.0. Within the shoe, the COF between the foot,
sock and insole can range from 0.5 - 0.9. In contrast the COF
between a sock and a polished floor is around 0.2.
(Carlson, 2009)
Page 6
Shear
Understanding blisters is a bit more involved than simply talking about friction
and rubbing – there’s a bit of physics-speak involved. Don’t worry, physics is like
a foreign language to me, so I will keep this as simple as possible. There is,
however, one word that you need to get your head around – and that’s shear.
Definition
I think of shear as Distortion. Shear is the stretching and distortion that occurs
within the skin and soft tissue. Below is a picture explaining shear – or if you’re
viewing this online, take a look at this YouTube video.
Before a movement force
With a movement force
Diagram 1: Shear
Consider this wobbly box. There’s a movement force at the top of the box trying
to push it along. But it's not moving - it's stuck to the surface it's sitting on. The
reason the box is staying put is because of the force of friction - friction is the
stickiness or slipperiness between two surfaces. The friction here is high enough
to keep the box in place, in spite of the movement force that is trying to push the
box along.
But the box does change shape as a result of the movement force, it stretches
and distorts. This distortion is called shear. And it’s shear that is the damage that
causes blisters to form.
Page 7
Imagine this wobbly box was the foot: the movement force would be from the
bones at the top of the box, as they move back and forth with each step; the
skin is at the bottom of the box where friction is keeping it stuck to the sock /
shoe; and the wobbly middle section would be the layers of the skin and soft
tissues - tissues that are quite capable of stretching and distorting - to a point.
Let me give you four examples of shear.
Example 1
LEATHER CHAIR
Imagine you are sitting on a leather chair and you’re wearing shorts. You try to
slip down the seat, but your skin sticks to the leather and you can’t slide. The
high friction causes you to stick to the chair and try as you might, you can only
move as far as your skin can stretch - so you stay stuck to the chair. This
distortion and stretching within your skin and soft tissues is shear.
Example 2
AGED CARE RESIDENTS
I found this paper in a nursing journal (edited, Anderson et al, 2010) which,
although I have edited it slightly, explains it in a way that clicked for me - and it
might click for you too:
Friction and shear, seemingly innocuous properties of nature, can increase the
risks for injury to patients in the hospital setting during the positioning of
patients in the bed, during a transfer to another bed surface or wheelchair, and
when moving patients up in bed. The mechanism of injury is that the underlying
skin layers move with the patient, while the epidermal layers adhere to the bed
or chair surface because of friction, causing shearing of tissues under the skin.
Friction may induce the injury, but the resultant damage is shear to the
underlying tissue layers.
Page 8
Example 3
SHEAR ON THE FACE
Marty Carlson provides an even better insight into friction and shear, and shows
that just because one surface (the skin of Marty’s hand) isn’t moving against the
other (the skin of his face), doesn’t mean there is no potential for damage.
Here Marty is pressing against his face ie: he is
compressing the skin and soft tissue against his
cheek bone.
Marty has added some upward force to the
compression (he is still pressing). Notice there
has been some distortion … but his fingers have
not moved against the skin of his face.
This is because of the force of friction. It is not
slippery enough to allow the fingers to slide
against his face.
Now Marty increases the upwards force - there is
now even more distortion … yet his fingers and
face are still stuck together with no sliding of his
fingers. So what has moved?
The movement has occurred in the tissues
between his cheek bone and skin. This is shear
and repeated shear leads to tissue damage.
Diagram 2: A visual example of shear on the face
Page 9
Example 4
SHEAR AT THE BACK OF THE HEEL
Watch this video to appreciate shear as it pertains to blisters at the back of the
heel.
The purple area is a section of the soft tissue between the skin and the
calcaneus. It stretches as the bone moves upwards, even though the heel itself
has not lifted relative to the shoe. The heel is not rubbing up and down at the
back of the shoe, yet there is a lot of soft tissue shear. This is what causes
blisters!
Page 10
Quotes From Prominent Clinicians and Researchers
Here are some foot-related shear quotes from prominent clinicians and
researchers:
Paul W. Brand, MD
“There are two types of force which occur on the sole of the foot, one is
vertical force at right angles to the foot, which causes direct pressure on
the tissues. The other is horizontal force, or shear stress, which is parallel
to the surface of the foot and occurs in association with acceleration and
deceleration. Of the two forces shear stress is more damaging than
pressure.”
David Armstrong, DPM, PhD
“It’s the equivalent of podiatric dark matter: we believe it’s important but
we can’t measure it well. In fact, shear stress is probably more important
than vertical stress because it occurs twice per step instead of once.”
Cleveland Clinic researchers (Yavuz et al)
“Diabetic foot ulcers are known to have a biomechanical etiology. Among
the mechanical factors that cause foot lesions, shear stresses have been
either neglected or underestimated... Plantar shear is known to be a factor
in callus formation and has previously been associated with higher ulcer
incidence. During gait, shear stresses are induced with twice the frequency
of pressure.
J. Martin Carlson, CPO, MS (Engr.)
“The research literature clearly indicates that the shear (friction)
component of the contact loading is the direct culprit. Pressure is not the
direct cause of repetitive loading skin trauma (hot spots, blisters,
abrasions, and ulcers). Pressure is a factor that enables the friction / shear
to reach traumatic levels.”
Page 11
Foot Blisters – Where Does Shear Come From?
As we walk, run and play, the bones of our feet move relative to the skin. This is
an inevitable and normal consequence of transferring our weight and causes
stretching and distortion of the skin layers and soft tissues. Richie (2010)
describes it as “… the skeletal segments of the foot move out of synch with the
underlying soft tissue and components of the shoe.” This is shear and is the
cause of foot blisters.
Take a look at this ultra-slow-motion video of an athlete doing the ladder drill.
This shows a side to side activity and while it’s nothing close to the rigors of a
game of netball, basketball, tennis or football, you can clearly appreciate the fact
that the metatarsal heads are moving from side to side once the foot has
planted. This is shear.
The skin and soft tissue of the foot are capable of dealing with a lot of shear.
Remember, shear is a normal part of foot function. However, there will be a
point where shear becomes abnormal and damaging.
How Much Shear Before Injury Occurs?
Shear
How much shear can our feet handle before blister development begins? The
answer to that question depends on a range of determining factors including the
type, intensity and duration of the activity; in-shoe moisture conditions; material
properties; biomechanical function and structure; individual skin susceptibilities
and more.
It has been demonstrated there is a large individual variation in the propensity
for blister development (Sulzberger et al, 1966 and Yavuz and Davis, 2010). A
study performed on 54 American Army personnel found that 3 minutes of a
‘rubbing’ force produced blisters in some volunteers, whilst 50 minutes of the
same force failed to produce any blistering in others. This shows that some
people tend to be more ‘blister-prone’ than others.
At this point, it will be helpful to view this video showing how and why blisters
form at the ball of the foot.
Page 12
Skin Anatomy
Of all the soft tissues between the bone and skin surface - that is the layers of
skin, ligaments, the subcutaneous fatty tissue, muscle, fascia etc - the zone of
least resistance to shear is the stratum spinosum of the epidermis.
In areas where the stratum corneum and stratum granulosum are thick (palms
and soles) and the epidermis is firmly adhered to underlying tissue, shear tends
to cause a mechanical separation (micro-tears) within stratum spinosum, also
known as the prickle layer (Sulzberger et al 1966). Cells from the prickle layer
are found above and below the blister so it is within this layer that the failure
occurs. As the shear repetitions continue, microtears continue and begin to join
together (coalesce) and form a space (cleft) which then fills with fluid. This is a
blister.
Diagram3: The layers of the epidermis showing where blisters form
Page 13
Blisters vs Abrasions
What we have discussed so far is SHEAR. Shear is what happens in the skin and
soft tissue without there being any sliding movement of one surface against
another. Once one surface does slide over another (what most people call
rubbing), the whole situation changes.
We’ve established that blister formation occurs before anything moves over the
skin. But when an object is pushed or pulled hard enough to overcome the
friction keeping the object in place, the object actually moves. Think back to
Marty’s face experiment - if he was to push upward any further, his hand would
slide (rub) over his face.
When movement DOES occur against the skin, the skin is more likely to
be abraded. An abrasion is where the top layers of skin are rubbed right
off.
Neither situation (blisters nor abrasions) is much fun, but they are different.
Blisters and abrasions are separate entities with different mechanisms of injury
and affecting different layers of the epidermis. Watch this video for a thorough
understanding of the differences between blisters and abrasions. It’s quite an
important distinction to make if you really want to understand how and why
certain blister prevention strategies do and don’t work.
In reality, the two situations often coexist. Shear has already occurred to its
maximum before movement occurs – so a blister has often developed or is
developing by the time an abrasion occurs. Then, if the blister is subjected to an
abrasion, the roof of the blister will easily be rubbed off (de-roofed) leaving
behind a red raw sore.
For this reason, abrasion injuries will be included in this discussion as blisters and
abrasions are commonly lumped together and often occur concurrently.
Not all skin is predisposed to blister-formation. Where the
Did You Know? stratum corneum and granulosum are relatively thin and
the epidermis is not adhered firmly to underlying
structures, like the skin on the forearms, thighs, back and buttocks, an abrasion
is more likely to occur when subjected to shear. Frictional forces tend to quickly
and easily wear away these outer layers as they are thin and not very resistant
to such forces. This type of skin trauma is an abrasion and is commonly referred
to as chafing. Chafing is a common complaint of cyclists as their inner thighs rub
up and down against the bike seat. And male distance runners can suffer with
chafing of their shirts against their nipples and often tape them to prevent this.
Page 14
PART TWO – Blister Prevention Strategies
Factors Influencing Blister Formation
Looking at blister prevention simply and logically:
Blisters are a shear injury
To prevent blisters you must reduce shear
There are 4 ways to do this
BLISTER
PREVENTION
STRATEGY
REDUCE
SHEAR CYCLE
REPETITIONS
REDUCE
MOVEMENT OF
BONES
REDUCE
PEAK
PRESSURE
✔
✔
✔
Optimise Shoe Fit
✔
✔
Address Structure &
Biomechanics
✔
✔
Alter Your Activity
✔
Cushioning
Taping
REDUCE
COEFFICIENT
OF FRICTION
Not applicable
Manage Skin
Moisture
Double Sock Systems
✔
✔
✔
Low Friction Patches:
ENGO
Let’s
-
✔
look at each blister prevention strategy individually and discuss:
how they work
the pros and cons of each
what the research says
Page 15
Blister Prevention Strategy – Alter Your Activity
If activity is modified so that the number of shear cycle repetitions
is reduced, bone movement is minimised and/or peak pressures
are reduced, blisters can be avoided. Here are a few examples of how
to achieve this (imagine this is the advice you’re giving your client):
1) Reduce the intensity of your activity – reduce your running speed;
avoid hills; play a less active position on the field
2) Reduce the duration of your activity – cut back your running
distance; choose a shorter hiking trail; only play ¾ of a game.
3) Reduce the frequency of your activity – cross-train with less weightbearing activity; no multi-day events; skip training
Or … you could get serious and get to the bottom of the blister problem!
Page 16
Blister Prevention Strategy – Optimise Shoe Fit
One of the easiest ways to reduce the magnitude of shear is to optimise
shoe fit. By doing so, bony excursions are minimised and peak
pressure can be reduced.
-
Shoes that are too small and tight increase the pressure on the
skin and underlying soft tissue at bony prominences. This causes
shear to become excessive with less cycles and causes blisters to
develop quicker.
-
Shoes that are too big and loose allow larger bony excursions and
therefore more shear leading to blisters, or cause the skin to move against
the shoe or sock leading to a skin abrasions.
So shoe length and width are very important. But so is adjustability. Foot
swelling will occur when activities are prolonged, even in elite athletes.
Optimising shoe fit is the whole reason we as podiatrists like lace-up shoes (as
opposed to a slip-on / pull-on shoe) – they ensure a snug fit and the support the
shoe can provide is maximised. Below are two examples of how firm lacing can
prevent blisters and abrasions.
Example
HEEL BLISTERS
For posterior heel blisters or abrasions, using the very last eyelet can make all
the difference – the heel is held down better in the shoe, minimising heel
slippage.
Example
BLISTERS UNDER THE METATARSAL HEADS
For blisters under the metatarsal heads or abrasions at the dorsum of the toes,
ensure laces around the midfoot are firm to minimise the foot sliding forward
with each step, something that is particularly important on downhill terrain.
Other than this, there are many lacing techniques that may help, depending on
the blister location http://www.fieggen.com/shoelace/).
Although this seems intuitively correct, Richie (2010) cites three studies that
have not confirmed optimal shoe fit as an effective blister prevention strategy
and suggests factors other than shoe fit must be implicated.
Page 17
Blister Prevention Strategy – Addressing Structural &
Biomechanical Issues
There are several structural and biomechanical issues that may lead to
an increased magnitude of shear distortions predisposing to blisters.
This is where our expertise as podiatrists comes to the fore – in
minimising relevant biomechanical issues via stretches, mobilisations,
paddings, orthoses or other appropriate means. These interventions aim
to reduce shear by either reducing the movement of the bones or by
reducing peak pressure.
Example
REDUCING BONE MOVEMENT
One example of a relevant biomechanical issue where the movement of the
bones is the cause of high shear would be blisters at the back of the heel.
Diagram 4 is the sequence we saw earlier in video form. Before the heel lifts at
the end of midstance, tension in the Achilles tendon increases. Before the heel is
deemed to lift, the calcaneus moves upwards (relative to the skin) causing shear.
This happens with each step and is normal and not blister-causing; however, if
the calf muscle complex is tight, this can occur to excess. Tension develops
sooner and leads to an increased magnitude of shear, causing a blister.
Notice the heel itself has not lifted in the shoe but the calcaneus has, creating
high soft tissue (represented in purple) shear. It may even make the heel lift
relative to the shoe, causing an abrasion. When blister-causing and abrasioncausing forces coexist, the blister is quickly de-roofed.
No Shear
Moderate Shear
High Shear
Diagram 4: Shear at the back of the heel
Page 18
Example
REDUCING PEAK PRESSURE
Pressure is a factor that enables shear to reach blister-causing levels. Therefore,
reducing pressure can reduce shear (Yavuz & Davis, 2010). If you think back to
Marty’s face experiment, if he was pressing only lightly against his cheek bone,
Marty’s hand would have slid upwards without as much stretching and distortion
of his face ie: less shear.
Podiatrists are specialists in selectively reducing pressure on the feet where
required. We achieve this through various means including:
1) Stretching and manual therapies – For example, calf stretches and/or
lower tibiofibular joint mobilisations can favourably alter the timing and
magnitude of force across the metatarsal heads.
2) Pressure deflection and redistribution - In the form of paddings that apply
to the foot or insole, such as the often-mentioned Moleskin. Here’s a great
demonstration video by Podiatrist Emily Smith for Oxfam Trailwalker.
3) Foot orthotics – by altering the magnitude and timing of forces, both
vertical (pressure) and parallel (shear) on the plantar surface of the foot in
a way to allow more normal function and to decrease pathologic loading
forces. – adapted from Kevin Kirby’s definition of a foot orthosis from a
Precision Intricast Newsletter.
Just a word on paddings which is probably obvious: The tricky thing when using
thicker materials is that shoe-fit may be compromised and may predispose to
additional problems such as blisters elsewhere or even musculoskeletal injury if
gait is adversely affected. This may be a small issue for your average client but
for a runner or hiker or someone taking part in an endurance or multi-day event,
small changes like this can detrimental. For this reason, it is advised to keep the
bulk to a minimum when used as a preventative strategy.
I wish to make one point very clear here. It is important to not implicate
pressure as THE cause of blisters. Pressure is a contributing factor to shear, but
not the primary factor. Blaming shear-related injuries on pressure is a common
theme, in podiatry particularly, and Carlson accurately states:
Page 19
“With only a few recent exceptions, researchers typically mention
that shear forces are an important factor in skin breakdown but
then proceed to measure and relate to peak pressure values and
factors”
Carlson (2006)
“Shear sensor technology is still far from miniaturisation to the
point where it could accurately map shear load distribution. This
fact seems to have acted as an almost complete barrier to
practical, useful research relating to peak friction loads”
Carlson (2006)
PRACTITIONER GUIDE
On the following page is a summary of some of the structural and biomechanical
factors that could be implicated in blister causation and potential treatment
interventions to consider, for common blister locations.
There are links to threads in Podiatry Arena that help explain terminology or
concepts some practitioners might not be familiar with.
This list is by no means exhaustive or comprehensive. In a real-life situation,
there will of course be unique structural and biomechanical combinations and this
guide takes no account of the activities undertaken or footwear used.
Page 20
LOCATION OF BLISTERS
EXAMPLE OF STRUCTURAL /
BIOMECHANICAL ISSUE
CONSEQUENCE
INTERVENTION
Tight gastrocnemius-soleus muscle complex
(increased ankle joint dorsiflexion stiffness)
Increased tension in Achilles causes the
calcaneus to lift (not the heel) causing increased
shear
» Calf stretches
Plantar 1st metatarsal head
Compliant (flexible) plantarflexed first ray /
forefoot valgus
Larger anteroposterior first metatarsal head
movement
Medioplantar
1st MPJ
» Hallux abductovalgus
» Excess STJ pronation / medial loading
Poor footwear fit with first metatarsal head
bulging over sole of shoe
» 2nd to 5th metatarsal forefoot extension padding and
other interventions to reduce medial forefoot
dorsiflexion forces (moments)
» Improved footwear fit (sole width)
» Minimise subtalar joint pronation forces (moments)
Under hallux interphalangeal
joint
Inadequate windlass mechanism function
Higher pressure under hallux interphalangeal
joint
Plantar 5th metatarsal head
Stiff (rigid) anterior cavus
Higher lateral arch flattening forces – increased
plantar 5th metatarsal head peak pressure
Plantar Metatarsal Heads 2-4
Increased peak pressure plus forward / backward
movement of 2nd-4th metatarsal heads
Dorsum of toes
Compliant (stiff) anterior cavus forefoot
equinus with high 1st and 5th ray flexibility
compared to 2nd-4th
» Straight toes nonweightbearing
» Ligamentous laxity with pronated / flat foot
posture
Fixed digital clawing
Higher pressure at dorsum of toes due to toe box
too shallow
» Footwear with adequate depth in toebox
» Adjustability (laces/velcro) to enable firm fitting
around midfoot / prevent forward slide
» Silicone toe sleeves
Between toes
Adductovarus digital deformity of lesser toes
Under medial longitudinal
arch with orthosis
» Medially deviated STJ axis
» Excess interdigital pressure due to lesser toe
deformity
» Digital movement during gait
Soft tissue of plantar first ray are subjected to
high compression and shear between bones and
orthosis
» Interdigital wedging to reduce peak pressure
» Interdigital cushioning to absorb shear and reduce
peak pressure
» Modify orthosis prescription variables to push on
medial side of STJ axis
» Facilitate windlass mechanism
Back of Heels
Toe apices
» Orthotic pushing lateral to STJ axis
Toes claw during gait
» Heel lifts / heel height differential
» Lower tibiofibular joint mobilisation
» Orthoses with prescription variables to improve
windlass mechanism: first ray wipe, forefoot valgus
extension, Cluffy wedge, reduce ankle joint stiffness
» Reduce ankle joint dorsiflexion stiffness
» Increase orthosis contouring of lateral arch
Improve windlass mechanism, increase medial and
lateral arch contour, reduce ankle joint dorsiflexion
stiffness
» Orthoses with appropriate prescription variables to
reduce excessive joint excursions
» Toeprops.
Page 21
Blister Prevention Strategy – Cushioning
Cushioning, when used in the right way, increases surface area and
therefore reduces peak pressure. The diagram below shows this
clearly. Notice the curve of graphs A and B. The pressure peak is
lowered in case B when cushioning is used as the load is spread over a larger area.
Diagram 5: Cushioning spreads load over a larger area thereby reducing the
peak of pressure – from Carlson 2006
Because pressure is a factor that enables shear to reach blister-causing levels, as
we discussed in the last section, reducing pressure can reduce shear.
Page 22
www.blis
terpreve
ntion.co
Example
SPENCO® & PORON®
Spenco and Poron are cushioning materials commonly used in Podiatry. Studies
have shown a Spenco insole to reduce the incidence of blisters compared to
wearing no insole, and compared to wearing two socks. Another study found
Spenco and Poron to perform similarly (Knapik et al, 1995).
Example
GELS
Gels can reduce shear even better than foams. Below is the rest of the picture
from the previous page. “Gel materials have a constant volume, so they cushion in
a more efficient manner. As compression occurs at the apex of a bony prominence,
some gel material moves toward the periphery, creating a bulge. This enlarges the
supportive contact area, forming a "cradle" under the bony prominence” (Carlson
2006). Unfortunately, gels tend to degrade relatively quickly.
As well as increasing surface area, cushioning materials can also absorb some shear
due to their material properties. By absorbing some shear, living tissue undergoes
less shear; making it less likely that blisters will develop.
Diagram 6: Fixed volume gels can further reduce peak pressure
– from Carlson 2006
Page 23
Again, it is important to not implicate pressure as THE cause of blisters. Pressure is
a contributing factor to shear, but not the primary factor. When used intelligently,
cushioning materials can be very helpful. But practitioners and athletes alike will
be well aware that cushioning alone is not the holy grail of blister prevention.
For cushioning to be effective, its properties must be a good match to the job at
hand. If it’s too soft, the cushioning material will simply flatten and will not reduce
the peak pressure at all. Cushioning should also not be used to excess:
“Cushioning degrades control and energy efficiency. Ideally, cushioning
should be used sparingly ...”
(Carlson, 2006)
And again, adding more bulk means less room for the foot, potentially increasing
pressure elsewhere, particularly around the toes and forefoot.
Page 24
Blister Prevention Strategy – Taping
You will likely be very surprised when I tell you that I don’t think tape applied to
the skin prevents blisters at all. This is in spite of taping being one of the most
popular blister prevention strategies that exists.
Looking back at the 4 ways to reduce shear, taping doesn’t actually achieve any of
these:
1)
2)
3)
4)
Reduce
Reduce
Reduce
Reduce
the number of shear cycle repetitions
bone movement
peak pressure
the coefficient of friction (COF)
So why did Elastoplast and Leukoplast sports tape help reduce my heel blister
problem?
Sports tape works not as a blister prevention strategy but as an abrasion
prevention strategy, in my opinion. By providing an adhered protective layer - a
physical barrier to the effects of rubbing (sliding) on the outermost layers of the
epidermis - the skin is protected from being rubbed right through. But remember
this is an abrasion, not a blister.
This may be why many athletes realise that “taping can only do so much” for
blisters. Taping doesn’t reduce shear.
This was certainly my
experience. I would
tape my heels before
exercise - and it would
help a lot. I wouldn’t
end up with red raw
sores at the back of my
heels. But I’d still notice
a blister had formed.
So it hasn’t stopped the
blister, but it had
stopped it from deroofing (ie: the
abrasion) and that was
a big help, there’s no
doubt.
Do you disagree with this? If so, by
what mechanism does taping
prevent blisters? Is there an
additional mechanism that I
haven’t thought of? Or does it fit
one of the four I have mentioned?
I welcome your thoughts.
Page 25
Have you wondered why tennis players often have to get on-court medical attention
because of a blister - yet they already have their feet taped? Same with distance
and endurance runners - even though they have taped their feet, they finish the
race with blisters. It doesn’t reduce shear.
This remains one of the most common misconceptions today in my opinion - that
taping is an effective blister prevention strategy. It will reduce the likelihood of a
blister de-roofing, but it won’t prevent the blister.
Diagram 7: Rafael Nadal having his forefoot blisters retaped
during the US Open 2011
Is taping useless? No, not useless! For one, tape will help keep the blister roof
intact, preventing it from being abraded (rubbed off) ... although it can be difficult
to remove the tape without compromising the intact blister. And I’m sure
circumferential taping can provide some support to the skin, preventing some
shear. But circumferential taping is often avoided so as not to become constrictive
with increased foot volume from swelling. So although tape is not useless, in my
opinion, it is not a great blister prevention strategy. But it can work very well as an
abrasion prevention strategy.
Instead of ignoring taping, I would like to provide some practical advice to
practitioners who are educating their clients on self-taping as an abrasion
prevention strategy, as there are some potential difficulties. I sincerely don’t wish
to insult anyone’s intelligence, this is simply in the interests of being thorough.
Page 26

Firstly, as the skin perspires, the tape’s adhesiveness becomes less effective.
Therefore the tape may become unstuck (fully or partially), thus potentially
becoming ineffective at best and at worst, a blister-causing irritant.

Due to the tape losing its adhesiveness, depending on the duration of the
event, tapes often have to be reapplied.

Thirdly, it takes skill and practice to tape properly (Vonhof, 2011). It is
paramount that the edges of the tape are smooth and in an appropriate
location and creases are avoided.
John Vonhof discusses foot taping of the various blister-prone areas of the feet in
good detail in his book Fixing Your Feet – Injury Prevention and Treatment For
Athletes (5th edition). It is an excellent reference for any of your clients who
require detailed information on self-taping. Podiatrist Trent Salkavich also provides
this helpful video on how to tape the foot.
The fact is that topical applications on the skin tend not to be hard-wearing and
require constant replacement or reapplication during longer duration activities,
which can prove prohibitive. Richie’s 2010 friction blister literature review states of
topical applications:
“Few things applied to the feet will
stay intact for more than one hour
of vigorous activity. Therefore,
measures that focus on footwear
may be more efficacious.”
Richie, 2010
Page 27
Blister Prevention Strategy – Managing Skin Moisture
Skin drying strategies and skin lubricating strategies, although at
opposite ends of the skin moisture spectrum, are well-known blister
prevention methods. These strategies are based on the fact that moist
skin produces higher friction than very dry or very wet skin (Akers and Sulzberger,
1972, Naylor, 1955 and Sulzberg et al 1966). In other words, you can reduce the
incidence of blisters by keeping the skin either very dry or very wet.
The very low or very high skin moisture strategies aim to reduce the coefficient
of friction value between the sock and the skin to below blister-causing levels.
Remember that the coefficient of friction is a number that represents this
‘slipperiness’ or ‘stickiness’ between two surfaces and is generally below 1.0.
Within the shoe, the COF between the foot, sock and insole can range from 0.5 0.9. In contrast the COF between a sock and a polished floor is around 0.2
(Carlson, 2009)
As a hypothetical example, let’s say a runner is getting blisters. Because his feet
sweat a lot, his socks end up quite damp – this is a moist environment. If we could
measure the COF between the foot and the sock, we might get a value of 0.7. If
this runner could make his skin either much drier or much wetter, the COF value
might reduce to 0.5. Let’s say the blister-causing COF threshold for this runner is
0.6. At this level, either of these methods will theoretically be successful blister
prevention strategies. But how do we accomplish this?
Example
VERY DRY SKIN
Drying the skin by reducing the effects of perspiration with powders, antiperspirants
and drying compounds is a method used by many (Vonhof, 2011). Examples
include 2Toms Blistershield Powder, Neat Feet Roll-on, Compound Benzoin Tincture,
alcohol wipes and more. The effect of these products is variable which is
understandable as sweating is impossible to eliminate altogether, particularly with
exercise, long duration events and in hot or humid conditions. Repeated application
will help but this is not always possible (you don’t often see runners stop mid-race
to swap socks, dry their feet or dust them with powder!).
Additionally, skin irritation is not uncommon with some of the more effective
products (Knapik et al, 1995 and Knapik et al, 1998) and in regard to powders,
your clients should of course be advised to not apply excessive amounts,
particularly between the toes, as powder plus moisture will create a caked mass
that may become a blister-causing irritant itself.
Page 28
Socks can also play a role in reducing moisture and it has been shown repeatedly
that synthetic socks perform better than cotton and wool socks (Herring and Richie,
1990; Sanders et al, 1998; and Wong et al, 1998). Synthetic socks that are made
of a moisture-wicking material such as Coolmax will move moisture away from the
skin into the outer sock layer, allowing for more effective evaporation through the
shoe upper.
For moisture-wicking socks to be a truly effective blister prevention strategy, the
shoes must have significant ventilation to allow for the moisture to be evaporated
through the shoe (hiking boots are much less ventilated than mesh-top sport
shoes). To maximise the chance of moisture-wicking socks maintaining a low
enough coefficient of friction when activity is prolonged or over several days, it’s
obvious that taking shoes and socks off at breaks to allow them and the skin to dry,
and if possible, having another pair of socks handy, will help.
It seems that moisture-wicking socks could bring about a reduction in friction and
shear that could make all the difference, more than likely with short duration
exercise. However, it seems unlikely that the skin can be kept dry enough to be
effective in longer duration activities or in hot and humid conditions.
Example
VERY LUBRICATED SKIN
At the other extreme, increasing skin moisture to achieve very wet, lubricated skin
will also reduce the skin’s coefficient of friction. Examples of lubricating products
include Vaseline and BodyGlide. Unfortunately, reducing friction over the whole
foot is not a good thing. You can imagine as the foot slides around excessively, the
foot is at risk of other problems such as nail trauma and even musculoskeletal
injury caused by the overall lack of traction of the foot in the shoe.
At this point it is important to point out that friction is not
all bad everywhere. In preventing blisters, it is not the
aim to reduce friction everywhere. When it comes to
feet in shoes, friction is necessary to stop the foot
moving around excessively. Without it, gait would be
adversely affected, potentially predisposing to other
injuries.
Page 29
Skin lubricating strategies are quite popular with athletes. This is in spite of
research showing that friction increases above baseline measures between one
and three hours of applying lubricants (Nacht et al 1981). This is understandable
as the preparation will absorb and dissipate into the sock over time. For these
reasons, depending on the duration of the event, ongoing reapplication is required.
Also, increasing epidermal hydration
causes the skin to become weaker and
less able to resist trauma. It’s like how
your skin goes when you’re in the bath
for too long (but to a lesser extent).
Imagine then having to run, accelerate,
decelerate, change direction etc. on this
weak wrinkly skin!
For these reasons, increasing skin
hydration as a means of blister
prevention is possibly not the most ideal
option.
NOTE: The common
lubricant Vaseline
(petrolatum jelly) can
be extremely counterproductive to blister
prevention,
particularly on offroad surfaces, for the
reasons already
mentioned but also
due to a tendency to
attract grit, which
increases the
likelihood of blisters or
other skin trauma.
Page 30
Blister Prevention Strategy – Double Sock Systems
Double sock systems come in two forms:
1) Literally wearing 2 pairs of socks
2) Socks that have two layers at certain locations within the sock
Double sock systems are an example of a blister prevention strategy
which aims to reduce the COF between the various interfaces to
reduce shear distortions within the skin.
An interface is where two surfaces meet. When we wear shoes and socks there are
two interfaces:
1) The skin-sock interface
2) The sock-shoe interface
Diagram 8: There are two material interfaces when wearing a shoe and sock
Blister-causing in-shoe conditions sees high friction levels between both of these
interfaces at such a level that the skin, sock and shoe are all in fixed (stationary)
contact, while the bones move relative to them – causing shear.
When wearing a double sock system, we add an additional interface, the sock-sock
interface.
Page 31
The idea is that the COF between the two sock layers is lower than that on either
side of the socks. If this can be kept low enough, the two socks will glide against
one another easily and this will reduce soft tissue shear.
Wearing two pairs of socks has been shown to somewhat reduce blister incidence in
a military population when compared to the standard-issue military sock (Knapik et
al, 1996). This consisted of a synthetic polyester or nylon inner sock combined
with a padded wool outer sock. Essentially, a tight very thin inner sock with a low
coefficient of friction with a thick outer sock that maintains its bulk in spite of
moisture is the desired arrangement.
In spite of this, there is little information about specific successful two-sock
combinations available. Also, double-sock systems don’t seem to be commonly
commercially available or used extensively.
Toe-socks such as Injinji are popular and can be thought of as a form of two-sock
system for interdigital areas and may theoretically reduce the incidence of
interdigital blisters. That is assuming the COF remains sufficiently low. This socksock interface is actually the same material, whereas the principal of double sock
systems is to use the effect of different sock materials for friction reducing
properties. However, blister incidence may be reduced as a result of the increased
bulk between the toes acting as cushioning to reduce pressure peaks. If so, this
mechanism of action would fit better under ‘cushioning’. Of course, if there is
digital deformity such that the toes cannot accommodate this extra interdigital bulk,
albeit minimal, or if the toebox of the shoe does not accommodate this extra bulk,
pressure will increase.
Page 32
Blister Prevention Strategy – ENGO Low Friction Patches
ENGO Blister Prevention Patches have been incredibly helpful to me on a
personal and professional level. Following is a discussion of this strategy
as a way to introduce you to ENGO, as I know most podiatrists have not
heard of it.
Polytetrafluoroethylene (PTFE) is a low friction film which is used extensively in the
manufacturing sector to reduce mechanical wear and energy consumption. It has
exceptional non-stick, water-repelling, ultra-low friction properties as it has the
third lowest coefficient of friction of all known materials. Here’s the Wikipedia link
to PTFE.
PTFE is also used on self-adhesive stickers called ‘patches’ which apply to internal
shoe surfaces (inner shoe lining, insole, orthotics) to reduce friction and prevent
skin trauma. There are two brands of PTFE patch available, both made by
Tamarack Habilitation Technologies Inc. One is called ShearBan®, a practitioner
product used predominately in the orthopaedic and prosthetic industry on
prostheses at amputation stump sites to reduce the incidence of skin breakdown.
The other is ENGO®, a retail blister
prevention product used mainly by
athletes and active people whose
activities and occupations predispose
them to foot blisters. Both products
consist of the same PTFE film and the
same adhesive but the backing of
ShearBan is slightly thicker and allows
for some conforming around curved
shapes, vital in prosthetic limb
applications. ENGO is thinner which suits
Diagram 9: ENGO Blister
in-shoe applications so as not to
Prevention Patch
compromise shoe-fit.
ENGO Blister Prevention Patches may be the type of solution that Richie (2010)
alludes to when he suggests:
“Few things applied to the feet will stay intact for
more than one hour of vigorous activity. Therefore,
measures that focus on footwear may be more
efficacious.”
Richie (2010)
Page 33
Patches are applied to the device (shoe / insole / orthotic) rather than the skin. By
doing this, unlike other blister prevention strategies, the COF at the sock-shoe
interface is reduced.
Diagram 10: The blue ENGO Blister Prevention Patch reduces the
COF of the shoe – sock interface
PTFE reduces the ‘stickiness’ between the shoe and sock so that they can glide over
one another at an earlier point in time. This enables the sock to be ‘released’ from
the shoe’s grip to slide with the bone. Take a look at this video to see what I
mean. By allowing the skin to slide with the bone at an earlier point, when the
shear distortion is still quite small, blisters can be averted, in spite of very high
pressure.
By allowing the sock to easily perform this small early glide against the shoe, PTFE
reduces the shear that causes the microtears within the epidermis. The glide is just
a small one, but that is all it takes to negate blister-causing shear (and ulcercausing shear - Scherer, 2012).
Tests have shown PTFE Patches to reduce the coefficient of friction (COF) in the inshoe environment by up to 80% - as seen in diagram 11 on the next page. This is
measured against a cotton sock: the standardised measurement protocol, however,
measurements have also been taken using a moisture wicking synthetic sock
(diagram 12).
(Take a look at the COF of Moleskin and Spenco!)
Page 34
PTFE’s COF is in the vicinity of 0.16 which is significantly lower than all other inshoe materials. And this very low COF is maintained even in moist conditions,
making it just as successful for endurance applications where perspiration is
significant, in wet outdoor environments and in hot and humid climates.
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
Moleskin (J & J)
Plastazote 1/8"
PPT-Poron
Coefficient of Friction - Dry Cotton Sock
ENGO
Russette Leather
Coefficient of Friction - Wet Cotton Sock
Diagram 11: The coefficient of friction of several materials against a cotton sock
in dry and moist conditions (modified from Carlson, 2001)
1
0.9
Dry Polyester Diabetic
Sock (Coolmax)
0.8
0.7
Moist (30% Water by
Weight) Polyester
Diabetic Sock
(Coolmax)
Dry Cotton Stockinette
0.6
0.5
0.4
0.3
Moist (30% Water by
Weight) Cotton
Stockinette
0.2
0.1
0
ENGO Russette Leather Poron
Spenco
Plasterzote
Diagram 12: The coefficient of friction of 5 materials against 2 sock type in dry
and moist conditions (from Payette, 2010)
Page 35
Not only that, ENGO prevents abrasions too, as the video on the previous page
shows.
ENGO Patches have been used in various athletic groups with favourable results. A
summary of these anecdotal results include:




42 of 42 volleyball, soccer and American football players who applied ENGO to
their shoes/insoles at the stage of hotspot development successfully avoided
blister development.
Of 10 volleyball, soccer and American football players who applied ENGO once a
blister was already formed, 6 required no further skin treatment.
4 soccer players with bilateral posterior heel blisters compared the effect of
ENGO Patches on one shoe and standard management techniques on the other
foot. At day 4, the heels with ENGO received no further treatment. At day 10,
all non-ENGO heels were still requiring further skin treatment.
Callus development across the ball of the feet in basketball players before
ENGO required weekly debridement. After the application of ENGO Patches to
the shoe innersole, after 3 months, callus debridement was only required 4weekly.
Scherer (2012) cites a blinded and randomized trial of 299 subjects by Lavery et al
entitled ‘Shear reducing insole prevents foot ulceration in high risk diabetics’ which
is yet to be published. The trial uses ShearBan on an orthotic at the forefoot in
neuropathic diabetics and has found a 70% reduced incidence of foot ulcers.
PTFE Patches have also been the subject of several single subject case studies
(Carlson, 2001; Carlson, 2006, Carlson, 2009; Kuffel, 2009; Stevens, 2009).
ENGO patches meet certain criteria that make it a legitimate and successful longterm blister prevention strategy:
1) PTFE eliminates up to 80% of friction making it all but impossible for blisters
to form
2) Patches are extremely durable, providing 500km blister protection
3) Patches are self-adhesive, utilising a pressure-sensitive adhesive which
enables them to stay in place in spite of the challenging in-shoe conditions
4) ENGO’s COF does not increase with moisture
5) At only 0.38 mm thick, shoe fit is unchanged
Page 36
6) Patches come in several shapes and sizes and can be cut to size and applied
to any internal shoe surface - including to insoles and orthotics
7) ENGO allows the targeted management of friction so that normal foot and
lower limb function is unaltered and unimpeded
8) ENGO comes with an unconditional money-back blister-free guarantee
One of the significant benefits of ENGO Patches is that it addresses friction only
where needed. The advantage of a targeted management of friction the way that
ENGO allows is that by targeting only high friction areas, normal in-shoe friction is
maintained, leaving foot and lower limb function unaltered and unimpeded. This is
in contrast to the indiscriminate friction reduction provided by lubricants.
Remember, not all friction is bad. And in fact, some friction is required.
These properties make ENGO Blister Prevention Patches stand out from other
preventative strategies, in my opinion.
There is one notable shortcoming of ENGO patches.
Interdigital blisters cannot benefit from PTFE as there is no inshoe surface to adhere it to. Some users apply ENGO to the
outer interdigital area of toe-socks to achieve the desired
result, but this application will not last the rigours of a soapy
washing machine cycle!
If you haven’t considered ENGO before, I suggest you do. It’s a blister prevention
strategy that you can recommend to your clients with 100% confidence - that it will
prevent blisters and not cause other problems. In my experience, you can’t get
that from any other strategy.
Page 37
Summary of Strategies: Pros & Cons
BLISTER
/ ABRASION
PREVENTION STRATEGY
PROS
CONS

Modify Activity

???

A good idea for more
than just blister
prevention

Shoe Fit
Addressing Structural &
Biomechanical Issues
Cushioning
Taping




Blisters are common in spite
of good shoe fit
Possible long-term
blister prevention

Not applicable to all blisters
Widely available




Won’t prevent all blisters
Changes shoe fit
More is not necessarily best
Some degrade quickly

Doesn’t prevent blisters,
abrasions only
Difficult to apply
Loosens easily
Requires ongoing
reapplication
Widely available





Managing Skin Moisture

Widely available


Double Sock Systems

Use combinations of
socks you already have

Eliminates up to 80% of
friction
Durable and costeffective
Doesn’t change shoe fit
Unaffected by moisture
Apply to shoe/insole/
orthotic, not skin
Targeted friction
management
Money-back guarantee

Low Friction Patches ENGO





An unacceptable blister
prevention strategy
Just not practical or possible
for everyone
Difficult to achieve
Can increase blister
development
Requires ongoing
reapplication
Negative effects of all over
friction reduction

Not widely used or available

Can’t apply to interdigital
areas unless wearing toesocks
Page 38
CONCLUSION
Blisters remain a common, potentially debilitating and relatively ignored injury.
Their importance is downplayed by many, possibly because they continue to prove
difficult to manage with mainstream preventative methods.
Serious athletes and those in active occupations know just how important blister
prevention is and consider it an essential part of their preparation. At best, blisters
will reduce performance and take the enjoyment out of a healthy pastime. At
worst, they can cause serious ill-health if improperly managed and can preclude
people from continuing with physical activity they would otherwise enjoy, or
occupational activities they are required to perform.
I feel our understanding of foot blisters is lacking, particularly in regard to:
-
the definition of friction and rubbing and how this pertains to blisters
the importance of the concept of shear
the differentiation between blisters and abrasions
the shortcomings of mainstream blister prevention strategies
is taping a blister prevention strategy or not and if so, how?
the features of PTFE Patches
Although friction blisters require more research, current research should be heeded
and the causative mechanisms, individual susceptibilities and treatment options be
fully understood by all those involved in first aid, foot health, sports medicine, retail
footwear, sports participation, and other relevant industries.
I sincerely hope this discussion has helped you become more informed about
blisters and your management options, and has provided fresh insight into this
most common yet difficult problem.
I welcome any questions you may have and would sincerely appreciate your
feedback: be it good, bad or indifferent! Please feel free to get in touch.
Thanks for reading.
Rebecca Rushton BSc (Pod)
Esperance Podiatry & ENGO Blister Prevention
[email protected]
January 2013
Page 39
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Management
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What Every Podiatrist Should Know About Blister

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