Buoyancy of Synthetic Casts

1
Buoyancy of Synthetic Casts Twee T. Do, MD Jose
Herrera-Soto, MD Alvin H. Crawford,
MD Cincinnati Childrens Hospital Medical
Center 3333 Burnet Avenue Cincinnati, Ohio 45229
Introduction The introduction of waterproof
lining has enhanced the quality of life for
those treated with casts. The synthetic
material contains billions of pores that repel
water and essentially enhances the bodys
natural buoyancy when in water. In the older
child or adult where the proportion of the leg
is relatively large compared to the rest of the
body, this enhanced buoyancy may be an
advantage. In the child with a smaller limb,
however, this enhanced buoyancy may have
potentially devastating risks in the pool. We
have had a near drowning complication in a
young child treated by a waterproof leg cast.
This led us to examine the buoyancy of
synthetic casts, and to determine its criteria
use in small children.
Conclusion
Methods
The cast of a 5 year old was used as a template.
A set of synthetic and regular casts were made.
All were weighed prior to testing. The casts
were then tested to failure (sinking) in the
Hubbard tank by sequential addition of lead
weights.
The results of this preliminary study show that
waterproof synthetic liners are very buoyant in
water. Although the amount of weight necessary
to sink the test casts in this study was small,
the weights consisted of solid lead pellets which
is not the case with a human limb. The enhanced
buoyancy of a synthetic-lined cast on the lower
extremity of a very young child less than 5 years
of age may pose a potential danger to that child
when immersed in a pool. The initial buoyant
force may be too startling and thus, prevent the
child from achieving a vertical position in the
water. This places them in a higher risk for
water intoxication and/or drowning, especially
when not properly supervised.
Results
The regular casts sank immediately after
immersion. Time from submersion to bottom ground
was less than 5 seconds. All waterproof casts
stayed afloat. With sequential addition of lead
weights, the casts finally sank at approximately
500 grams. The casts stayed afloat longer with
more weights in the supine position than the
standard upright position.
Figure 2. Standard fiberglass cast is then
wrapped around, allowing fracture control and
water-related activities
Table 1. Added lead weight comparisons Weight
added in grams
Case Report A fiberglass cast with waterproof
lining was placed on a 5 year old boy weighing
19.4 kg as postoperative immobilization for an
injury. Eleven days later, the patient was found
by his older sister floating face-down and
unresponsive in his backyard pool. At the time of
the incident, he had been left at the pool
unsupervised for about 5 minutes without a life
vest. By report, the patient was not a good
swimmer. In addition, his mother had noticed
seeing the child's casted Ieg floating in the
pool. His father (EMS-trained) resuscitated him
with CPR. Two weeks after discharge from the
hospital, the patient was re-evaluated in the
clinic and was doing well. The mother reported
that she had taken her son, this time wearing a
life jacket, back into the pool. She noted that
again the casted Ieg tended to float and that it
was impossible for the child to dip that leg into
the water.
Acknowledgments
The authors wish to thank Susan L. Foad, MPH for
poster preparation.
Reference
Herrera-Soto JA, Do TT, Crawford AH. Buoyancy of
synthetic cast and its implications to young
patients. J Pediatr Orthop. 200525366-368
Figure 1. Waterproof liners have grooves between
the bubbles of the liners to allow passage of
moisture through the cast. At least two layers
of liner should be placed.