Transcript STS vs. Plaster: A comparison

Foot Shapes Captured by Plaster
Casts vs. Resin-Impregnated
Slipper Socks:
A Qualitative Comparison
Kathleen M. Halat, DPM
San Francisco Bay Area
Foot & Ankle Residency Program
Kaiser Permanente - Oakland, CA
Description of the Slipper Sock
One-time use slipper sock
impregnated with an
extra-fast setting watercurable polyurethane
resin
New alternative to
plaster casting
Manufactured by STS of
Mill Valley, CA
Comes in 4 sizes
(S,M,L,XL)
Why use the Slipper Sock?
Clean
Easy to use
Quick drying
Light
Less likely to be
damaged during
shipping
Application of the Sock
Apply clear plastic bag to foot
Wet the sock
Apply the sock over the foot
Apply the plastic velcro strip
across the dorsum of foot at the
level of the arch
Hold foot in desired position
for casting
After cast dry, detach strip, slip
off sock
Purpose of this Study
Will a resin-impregnated
slipper sock capture the
same qualitative foot
shape as plaster casting
What is the time difference
in casting between the two
methods?
Patient Population
13 subjects, 26 feet
Subjects recruited from student volunteers
in the podiatry program at Samuel Merritt
College in Oakland, CA
Study Protocol - Casting
Each foot was casted with both
techniques and by the same person
All patients were casted supine with
the subtalar joint held in neutral
position
Prior to casting, heel bisection
drawn on patient’s posterior
heel/leg
After cast dried, the heel bisection
from the posterior leg was reflected
back onto the cast before removal
from the foot
Study Protocol - Timing
Time to dry:
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Time measured from when cast placed on
subject’s foot to when cast considered dry
enough to be removed without deforming the
cast
Average time to dry compared between
plaster and resin-impregnated socks
Study Protocol - Scanning
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Each cast was balanced to perpendicular using the
reflected heel bisection and then cut to a standard 2cm
height
The cast was then balanced and scanned using a 3D
CamCad system at Prolab-USA
From the scan, the following information was collected
and compared between the 2 techniques:
Forefoot width
Heel width
Arch height
Location of maximum arch height
Cast Evaluation
From the Lateral scan:
-Arch height
-Location maximum arch height
From the AP scan:
-Forefoot width
-Heel width
Results – Time for Casting
Average time for resin-impregnated sock:
1 minute, 50 seconds (range 75-155 seconds)
Average time for plaster cast:
2 minutes, 55 seconds (range 135-270 seconds)
STS cast 37% faster, difference statistically
significant (p<0.01)
Results – Cast shapes
Mean forefoot width:
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Sock: 3.38 cm, Plaster: 3.53 cm
Difference between Plaster – Sock for each foot:
Range (-0.04 to 0.39 cm), mean difference = 0.14cm
Statistically significant difference in average value?
NO (p=0.06)
Mean heel width
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Sock: 2.56 cm, Plaster: 2.49 cm
Difference between Plaster – Sock for each foot:
Range (-0.2 to 0.13 cm), mean difference = -0.15 cm
Statistically significant difference in average value?
NO (p=0.08)
Results – Cast shapes
Arch height
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Sock: 0.87 cm, Plaster: 0.98 cm
Difference between Plaster - Sock for each foot:
Range (-0.20 to 0.39 cm), mean difference = 0.08cm
Statistically significant difference in average value?
YES (p=0.03)
Location of maximum arch height
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STS: 3.74 cm, Plaster: 3.78 cm
Difference between Plaster - Sock for each foot:
Range (-0.50 to 0.70 cm), mean difference = 0.02cm
Statistically significant difference in average value?
NO (p=0.71)
Summary
Forefoot width, heel width and location of
maximum height are similar between the
two methods
Arch height is slightly lower when using
the sock, being on average 1mm less.
Casting with the resin-impregnated sock
is 37% faster than plaster
Troubleshooting the ResinImpregnated Socks
To get the best possible cast:
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Use the proper size sock
Apply the velcro strip correctly
Wet the sock completely and smooth
the resin over the entire sock before it dries
After applying sock, pull on posterior heel to
capture the heel contour
Use cold water the first few times you are
using the sock, allowing you to become
familiar with the technique/product
Do these differences really matter?
Average differences between the two
techniques for each measurement ranged
from 1-1.5mm
Is this going to make a difference in an
orthosis?
Additional research comparing orthoses
made from the two different techniques is
needed
Conclusions
Qualitative foot shapes captured by the two
methods are very similar
While arch height was lower with the resinimpregnated sock on average, it is not known
whether or not this difference is clinically
significant
In terms of time, resin-impregnated socks offer a
substantial benefit
Thank You!
To :
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ProLab-USA, in particular Ray Dixon
student volunteers at the San Francisco Veterans
Administration Health Center
STS of Mill Valley, CA