SOFT-TISSUE INJURIES - Medicine for Mountaineering and Other Wilderness Activities - page 173

the thread, the ring is forced over the knuckle, the skin of which has been compressed by
the thread. If the ring is not freed, the procedure can be repeated.
Blisters
Traumatic blisters are caused by friction that pulls the skin back and forth over under-
lying tissues. Eventually a cleft or tear develops in the midportion of the epidermis—the
most superficial portion of the skin—and fluid collects in this cleft.
Figure 12-3. Technique for bandaging the hand in the “position of function”
For a blister to develop, the epidermis must be thick and tough enough to resist de-
struction by the friction, which otherwise would produce an abrasion. Also, the skin and
subcutaneous tissues must be bound to the underlying bone to some extent, or the friction
wouldjustmovetheskinandnoshearstresswoulddevelop.Finally,theskinmustbemoist
enough for the object producing the blister to adhere to the skin surface instead of sliding
back and forth. Only the last condition can be modified to prevent blisters, but the first two
conditions explain why blisters usually form at only a few specific sites, such as toes and
heels.
Themostcommoncauseofblistersisneworill-fittingboots.Bootsthatarelooseinthe
instep allow the foot to slide forward when going downhill, producing “downhill blisters,”
usually on the toes or front part of the foot. “Uphill blisters” are most common over the
heel or the Achilles tendon at the back of the ankle.
Bootsshouldfitproperlyandbe“brokenin”slowlyandthoroughly.(Onerecommended
method is to wet the boots and walk in them on a flat surface until they are dry.) Areas
prone to blister should be protected, preferably with one of the new blister coverings, but
adhesive tape, duct tape, or moleskin can be used. Duct tape has a smooth surface and
works well for covering blisters. Adherence between skin and boot should be minimized
by keeping the feet dry with powder, as well as by wearing a thick outer sock and a thin
inner sock that allow slippage between them. As soon as the pain or heat of an early
blister—a “hot spot”—has been detected, the area should be covered. (Well-fitting boots
do not provide enough space for thick coverings, such as rings of padded material.)
Healing is faster, pain is diminished, and the risk of infection is greatly reduced when
the blister roof is preserved. Blister fluid may have to be drained to allow the roof to be-