Background

Venous stasis leg ulcers are the most common type of ulcers on the lower extremities. They most often occur on the medial aspect of the ankle and can be either partial or full thickness. Their shape is usually irregular and there is often associated edema, skin hyperpigmentation, induration, and thickening of the dermis and epidermis. Plaquelike lesions, called lipodermatosclerosis, are frequently observed. Erythema may be present, especially when the feet are dependent. This remarkable redness can frequently cause the clinician to suspect the presence of cellulitis. These ulcers are often painful and are accompanied by a significant amount of exudative drainage, again suggesting cellulitis.

Leg ulcers affect an estimated 500,000 to 1 million people in the United States. One percent of people in industrialized countries will suffer from a leg ulcer at some point in their lives and the vast majority of these are secondary to venous problems. Venous leg ulcers are the end result of chronic venous insufficiency (CVI), which leads to venous hypertension, inadequate venous blood return, and increased capillary pressure in the lower extremities. Chronic and recurrent venous obstruction, progressive valvular damage, and impairment of the calf muscle pump are the root causes of CVI.

A variety of hypotheses have been proposed to explain the pathophysiology of venous ulceration. One theory is that sluggish venous flow leads to the adherence of leukocytes to the capillary walls, resulting in obstruction of the local capillaries and the migration of additional leukocytes into the surrounding subcutaneous tissue. Proteolytic enzymes and toxic metabolites are released, increasing capillary permeability and destruction. Local ischemia, tissue necrosis, and ulceration are the final result. The fibrin cuff theory suggests that increasing venous hypertension causes fibrinogen molecules to leak out of the damaged capillary endothelial cells, polymerizing to fibrin and forming thick deposits around the remaining capillaries. Thus, “fibrin cuffs” form, posing a barrier to diffusion of oxygen and nutrients throughout the tissues of the lower extremities and leading to fibrosis, necrosis, and ulceration.

The trap hypothesis incorporates the theories described previously and further suggests the extravasation of erythrocytes from the capillary bed. These “trapped” red blood cells are broken down in the tissues and release hemoglobin, which is metabolized to hemosiderin. This hemosiderin is responsible for the brown hyperpigmentation, often referred to as brawny edema, characteristic of the advanced stages of CVI. The associated thin, glistening skin and induration of brawny edema result from the associated fibrin cuffs and fibrosis. Already prone to ischemia and tissue necrosis, the involved areas develop venous stasis dermatitis and attendant intense pruritus, resulting in scratching, skin breakdown, and ulceration.

Introduction

Surgical repair is not the standard or first-line treatment for venous stasis ulcers. The application of a firm compression garment to the involved lower leg has been used for thousands of years, and for more than 300 years, compression in one form or another has been the mainstay of treatment for venous stasis leg ulcers and CVI. As early as the 1600s, a rigid lace-up stocking was used, but it was not until the mid-1800s that elastic bandages were invented and used for treating this condition. Multiple forms of compression therapy are available today, including hosiery, bandages, boot systems, orthotics, pneumatic pumps, and various combinations of these.

The exact mode of action of compression is not fully understood, but the theory is that pressure applied to the calf muscle raises interstitial pressure, reduces venous insufficiency, lowers superficial venous hypertension, and facilitates venous return by supporting the calf muscle pump. Additional proposed benefits associated with compression therapy include the softening of lipodermatosclerosis, reduction of venous reflux, increase of arterial flow to the ulcer site, improvement in the microcirculation, increased oxygenation to the wound site, and stimulation of fibrinolysis. In short, continuous compression decreases venous congestion, lowering retained volume in the lower extremities and facilitating a favorable wound healing environment.

This chapter considers only one frequently used type of compression therapy, the Unna boot. It is important to understand that other compression systems are commercially available and effective for the treatment of venous stasis ulcers. Although the Unna boot is favored in the United States, the multilayered elastic compression bandage or wrap is more popular in the United Kingdom. Short stretch bandages are widely used throughout the remainder of Europe, as well as Australia. Which type of compression is the most effective remains unclear from a review of the most current evidence-based literature (see Bibliography). What is clear is that compression is more effective than no compression, high compression is more effective than low compression, and multilayered systems are more effective than single-layer systems.

The Unna paste boot is used primarily when a semi-immobilizing, soft-pressure or gradient-pressure dressing over a joint, extremity, or even the scalp is needed. It is commonly available in a 3- or 4-inch roll or bandage that is impregnated with a calamine–gelatin–zinc oxide compound (Fig. 41-1). Unna paste dressings are soothing and antipruritic and require less frequent dressing changes than conventional dressings. When dressing changes can be scheduled from 3 to 11 days, instead of one to three times per day, savings in health care cost and patient convenience can be realized.

Figure 41-1 Examples of commercial Unna paste boot materials.

(Courtesy of Dynarex Corporation, Orangeburg, NY.)

Indications

Use of the Unna paste dressing has varied over the years. With the advent of air cushion or foam splints, its use for ankle sprains has diminished. Unna paste dressings continue as a therapeutic mainstay for chronic venous disease with or without venous stasis ulcers. Without some type of dressing, healing-associated pruritus can lead to scratching and subsequent enlargement of the ulcers. The Unna boot can be used as a symmetric gradient-pressure dressing for venous stasis ulcers to help reduce venous hypertension, control edema, and counteract delayed venous return. As such, the Unna boot is a proven, effective part of overall therapy. Débridement should be carried out before application, if indicated, and then the ulcer should be covered with a permeable dressing, such as Tegaderm (pouched or regular).

Recent studies have advocated Unna paste dressings over split- or full-thickness skin grafting of burns on extremities. The advantages of using the Unna paste dressing compared with conventional dressing changes two to three times per day include earlier hospital discharge, patient comfort (because of fewer painful dressing changes), and higher graft acceptance rate (nearly 100% in some studies, probably because of less graft disturbance during critical microcirculation formation).

Unna paste dressings have been used over skin graft donor sites on the scalp. Use on scalp donor sites led to a significant reduction in a complication called concrete scalp (thick exudative crusting over the hair-bearing scalp, which tends to scar).

When pediatric patients excoriated their lower extremity skin grafts because of pruritus, the Unna paste dressings allowed healing and higher percentage skin graft acceptance. Parents spent less time changing the dressings (15 minutes vs. 3.5 hours per week), and the children had fewer play- and sleep-time disturbances compared with conventional three-times-per-day dressing changes and use of antihistamines.

When Unna paste dressings were used over skin-grafted, molten metal burns of the lower extremity, the benefits included early ambulation and earlier hospital discharge and return to work (44 vs. 84 days).

In acute and chronic tendonitis, the Unna boot acts as a soft immobilizer.