Skin Health and Stump Hygiene (part1)

Literally the word "hygiene" connotes a state or condition of health. But adequate hy¬giene, or good health, of the human skin pre¬sents a complex problem involving much more than a casual acquaintance with soap and water, the concept which usually comes to mind when hygiene is mentioned. The func¬tional state of our human integument is pretty much taken for granted by most of us. We know that this two-square-yard covering will, in most cases, repair itself in event of local injury, provided infection is avoided. Cheer¬fully we dissolve it in strong chemical solu¬tions. We broil it in the summer sun until it peels off like old birch bark. We allow it to be rubbed and blistered in tight shoes for vanity's sake. As a nation, we spend millions of dollars on elaborate sun-tan lotions guaranteed to produce in it the beautiful brown of the abo¬rigine and at the same time an equal fortune on lotions and creams which promise to bleach it out to the shade of a sheltered lily.
Even though the skin has remarkable powers of restoration, the conditions of use are occa¬sionally too damaging, or the opportunities for healing between periods of use are too brief for repair and maintenance. In such in¬stances, there may be an acute breakdown of the skin with a severe inflammatory reaction, or the process may be a gradual one, with a progressive deterioration of the skin and a loss of its protective properties. Among indi¬viduals in certain occupations, we frequently see both manifestations of such skin reaction. Housewives, mechanics, laboratory workers, and others whose work exposes certain areas of the body, particularly the hands and arms, to prolonged soaking in solutions and solvents, or even in plain water, are prone to recurrent skin irritation and breakdown. In such cases, the chemical and physiological properties of the skin are altered to such a degree that the skin's built-in protective functions are no longer effective. Even in the absence of pro¬longed soaking, the skin may be injured locally by contact with an irritant, such as a strong acid, or with a sensitizing agent, such as poison ivy.
All of these considerations similarly pertain to amputees who wear some type of prosthesis (Fig. 1), most of which are attached to the stump by means of a snugly fitted socket which excludes circulating air and traps the accumulated sweat against the skin. In the lower-extremity amputee, the effect is aggra¬vated by the added factor of weight-bearing and uneven loading on localized areas of the stump skin, especially in the adductor region of the stump and at other points of contact with the socket rim. Weight-bearing is at¬tended by other mechanical stresses, espe¬cially intermittent stretching of the skin and friction from rubbing against the socket edge and interior surface. The latter results in two important and harmful effects on the skin— heat, and abrasion of the skin surface, which in time can, by steady attrition, become highly destructive. Over a long period of time, heat alone may be capable of causing profound changes in the metabolism of living tissues. The stump skin of the amputee is especially vulnerable to the possible irritant or allergic
action of various materials that compose the socket of the artificial leg.
In this situation, then, the state of health of the stump skin is of the utmost importance in determin¬ing whether or not the prosthesis can be tolerated. If the skin can-not be maintained in a good func¬tional condition in spite of daily wear and tear, then the weight-bearing prosthesis cannot be worn, no matter how accurate the fit of the socket may be.
It is the purpose of this article to review some of the basic prin¬ciples of skin biochemistry and physiology concerned in the main¬tenance of good hygiene in the stump area. Included are some re¬marks relative to the use of certain disinfectant agents in skin cleans¬ing, and to some of the natural skin defenses against bacterial in-vasion, because these topics also are germane to the principal subject with which this article is concerned.

THE SKIN AS A VITAL ORGAN

Man cannot live without his en¬velope of skin any more than he can exist without his heart or his liver. It might seem at first thought that the cutaneous covering of the body performs about the same function as the leather cover of a baseball —and very little more. Actually, the biochemical and physiological activities of the skin are every bit as complex as are those of the liver. The respiratory rate of the main cellular portion of the epidermis, based on oxygen-uptake studies and glycolysis measurements, has been computed to be from two to ten times as high as the rates of other body tissues.
The skin possesses many properties vital to health and life itself. Of particular interest to us from the standpoint of prosthetic design and use is the part it plays in mechanical sup¬port of the soft tissues of the stump. It pro¬vides a tough, elastic outer covering with a tensile strength of up to 2 kg. per sq. mm. Fur¬thermore,   this   covering  has   a   tremendous capacity for repairing itself after injury and for strengthening itself at points of mechanical stress, such as those occurring on the lower-extremity stump in association with the wear¬ing of an artificial limb. A familiar example of this is the "lichenification," or leatherlike thickening of the skin over the ischial tuber-osity and in the adductor region of the thigh. We know that "calluses," or localized thick¬enings of the horny outermost layer of the skin, will form at points of repeated pressure. Sometimes a BB-shotlike condensation of horny material will develop over a pressure point, producing the well-known "corn." All of these thickening processes illustrate the defensive reaction of the skin to abnormal mechanical stress by elaborating a natural cushion from its cellular elements.
Mechanical protection, however, is only one of many important services which the skin performs. Its function in the conservation of water and electrolytes, those ionized salts which constitute an essential part of the body fluids, is nearly as indispensable as is the func¬tion of the kidneys. The skin is extremely important in the regulation of the body tem¬perature within relatively narrow limits. It possesses certain important electrical and chemical properties. It is also the first barrier, and one of the chief defenses of the body, against infectious diseases.
Many other properties of the skin that are of less immediate importance to the problem of stump hygiene nevertheless have a bearing on human health and welfare. For example, we rely on the sensory organs of the skin for a good part of our information about the world around us. Through nerve endings at or near the surface, the body receives the outside en¬vironmental stimuli of heat, cold, pain, and touch. Also important to health is the role of the skin in maintaining a highly complex sys¬tem of pigment metabolism and in providing a source of vitamins important for growth and nutrition.
Although there are other vital functions of the skin, those cited serve to illustrate the im¬portance and variety of the services the normal skin performs. Some of these are described at greater length in the following portions of this paper.
THE ANATOMY OF THE SKIN
Plate I shows in semidiagrammatic form the principal structures of the skin concerned in stump hygiene. The skin is seen to consist of two distinct layers—the epidermis and the dermis, or true skin. These two layers are joined by a system of fingerlike projections, the rete pegs, which protrude down from the epidermis and interlock with the papillae, which project up from the dermis. This device furnishes a relatively large surface area at the dermal-epidermal junction, thus providing a strong bond between the two layers.
The most superficial layer of the epidermis is the so-called "horny layer," consisting of a material called "keratin," which is very simi¬lar to animal horn. Scattered over the surface of the skin are numerous deep pockets, called "follicles," into which sebaceous, or oil, glands discharge their contents. From the follicles protrude the hairs of the skin.
Two other types of glands in the skin have an important bearing on the subject of stump hygiene. They are the eccrine, or small sweat glands, which lie in coils near the base of the dermis, and the apocrine, or large sweat glands (not shown in Plate I), which are simi¬larly situated but are more localized in dis-tribution than are the eccrine glands. The watery sweat secretions pass to the surface of the skin by way of the sweat ducts, dis¬charging on the surface through the sweat-duct opening, or pore.
Deep to the dermis lies the subcutaneous zone. Here, cushioned in masses of fat cells, are the large blood vessels which serve the skin. From the arteries, smaller vessels rise, becom¬ing narrower as they branch, until they ter¬minate in fine capillary nets in the papillae of the dermis. Blood from the papillary nets returns again by a venous collecting system to the large veins in the subcutaneous tissue.

RELATION OF  SKIN STRUCTURES TO  DISEASE

All of these structures are vulnerable to damage from prolonged wear of a prosthesis. Injury to each different anatomical site results

in a specific disease complex of the skin. For example, excessive heat and moisture may result in a local blocking of the sweat-duct pores. We are familiar with this condition in the form of what is known popularly as "prickly heat," a common malady in warm, humid climates; and the same disorder can occur over stump skin under similar environ¬mental conditions.
Prolonged use of negative-pressure sockets, and to a lesser degree of conventional sockets, may lead to engorgement of the small blood vessels of the skin, resulting in local areas of rupture and extravasation of blood into the surrounding tissues. The dark pigmentation often seen on the terminal end of the stump is the result of this bleeding under the skin. It is usually accompanied by some degree of edema, a state in which there is an abnormal collection of watery fluid in the soft tissues. Thus the skin disorder here is essentially focused in the circulatory system, whereas the previously cited condition of sweat-duct blockage affects primarily one of the glandular systems of the skin. It follows, then, that the over-all hygiene or good health of the stump skin reflects, among other things, the func¬tional state of each of the anatomical com¬ponents of the skin.
SKIN GLANDS AND  STUMP  HYGIENE
In the skin of the lower extremity, three different types of glands produce secretions that are discharged on the surface of the skin. These are the eccrine glands, the apocrine glands, and the sebaceous glands (Plate I). During daily use of a prosthesis, their secre¬tions accumulate inside the socket, where they may become a serious hazard to local stump hygiene.
The Eccrine Glands
The eccrine glands, or small sweat glands, are distributed over the entire surface of the body. They are accessory structures that develop from the epidermis. They are true secretory glands, producing a clear, aqueous fluid, and their functioning is vital to the heat regulation of the body, since these glands are the principal source of sweat. It has been esti¬mated that there are over two million of these glands in the skin of a normal adult and from
500 to 600 per sq. in. over the skin of the thigh and lower leg. It has been reported that the capacity for sweating is considerably less for females than for males. According to Weiner {23), roughly 50 percent of heat sweat comes from the trunk, 25 percent from the head and upper limbs, and 25 percent from the lower limbs.
Sweat Deposits. Eccrine sweat is a clear, watery solution containing 0.5 to 1.0 percent of solids. These solids play an important role in stump hygiene because, in the absence of adequate daily cleansing, their accumulation on the surface of the stump and in the socket interior may serve as a source of irritation and to some extent as a culture medium for the growth of harmful organisms. The eccrine sweat solids include urea (in at least twice the concentration found in blood plasma); creatine and creatinine in minute quantities; uric acid; a variety of different amino acids; ammonia; free choline; occasional traces of glucose; lactic acid and lactate (to the extent of more than 2 grams in 90 minutes of heavy physical labor); many of the water-soluble B-vitamins; traces of dehydroascorbic acid; and the minerals sodium, potassium, calcium, magnesium, sul-fates, phosphates, and iron. In addition to the sweat solids, there are the secretions of local oil or sebaceous glands, plus a quantity of nitrogenous material made up of keratin shreds and other cellular debris which has been des¬quamated from the surface of the skin.
This is the residue which collects on the skin and in the socket under normal conditions. If the skin has been damaged by abrasion against the socket wall, or if an eczematous skin con¬dition is present, there may be "weeping" or oozing of serum over the surface, where it mixes with the sweat, oil, and skin debris. This serous material is deposited on the inte¬rior wall of the socket, where it dries and sets almost like glue. Successive laminations are added from each day's accumulation, until a considerable thickness may be attained (Fig. 2). Constant wearing and rubbing against the skin may produce a polished, glassy finish on the surface. In the interests of good hygiene, this deposit should be cleaned out of the socket interior regularly.
The innervation  of eccrine  sweat glands,pharmacologically speaking, is parasympa-thetic or cholinergic. Dale and Feldberg (10) demonstrated that the postganglionic nerve fibers liberate acetylcholine at their endings on the receptor cells of the sweat glands. Where excessive perspiration, or hyperidrosis, has been a serious problem, clinical application of this finding has been made by treatment of the patient with an anticholinergic blocking agent to diminish sweating. Drugs like methantheline bromide (Banthine®) and diphemanil methyl sulfate (Prantal®), which are anticholinergic, have been tried.
Such treatment has proved sometimes very helpful, sometimes of slight benefit, and often discouraging. Even though excess perspiration may be reduced, there are not infrequently unpleasant side-effects, such as a sensation oi heat, dryness of the mouth and throat, head¬ache, and urinary retention. In the amputee, who often has an overheating problem in the first place, any further impairment of his cool¬ing mechanism may not be tolerated. In some cases, however, an effort to control excessive sweating may be worth a try; certainly any drying effect that such drug therapy may exer¬cise in the stump area will contribute to the hygienic state of the stump skin.

Eccrine Sweat Retention. In pro¬fuse sweating, the sweat is expelled from the eccrine glands onto the surface of the skin at intraductal pressures ranging as high as 250 mm. of mercury. If the outlet at the surface of the skin becomes blocked by masses of keratin, local inflammation, or other obstruction, this pressure may be sufficient to cause rupture of the duct (Fig. 3). If the rupture takes place near the surface at the level of the horny, or keratin layer, the sweat collects in this layer in a raindroplike configu¬ration of little blisters. If the rupture is deeper in the skin, there may be local inflammation, charac¬teristic of "prickly heat." Where the duct is ruptured still more deeply, symptoms are few or none, and the only surface sign consists of small, noninflammatory eleva-tions, or "papules." Sweat retention may involve most of the skin surface of the body and may be accom¬panied by pronounced generalized symptoms of fever, headache, and exhaustion, a con¬dition usually confined to tropical climates. More commonly it affects only a localized part of the body. It has been reported in many different types of eczema and in a variety of healing inflammatory lesions. Preliminary investigations of eczematous eruptions of the stump suggest that sweat retention occurs in this area also. The heat and humidity which prevail over the stump skin during use of a prosthesis are factors which encourage the development of sweat-duct blockage and local¬ized sweat retention.
The Apocrine Glands
The apocrine glands, unlike the eccrine glands, develop from the follicular epithelium of the hair, as do the sebaceous glands. Apo-crine glands are much larger than eccrine glands, and they are limited in their distribu¬tion to the underarm area, the breasts, the midline of the abdomen, and the anal and geni¬tal areas. Modified apocrine glands are also found in the external canal of the ear and in the vestibule of the nose.

The apocrine secretion is a turbid, whitish-to-yellowish fluid which dries like glue to form a light-colored plastic. The total number of apocrine glands is greater in women than in men, and axillary sweating starts earlier in adolescent girls than in adolescent boys.
The apocrine glands in the groin and axilla are occasionally the site of a chronic, extremely stubborn disease of the skin called "hidraden-itis suppurativa." This disease is characterized by large, burrowing, painful cysts which are filled with a foul discharge. These periodically break down and drain, then heal with scarring, and the process may be repeated indefinitely. Frequently the condition is so severe that sur¬gical extirpation, followed by skin-grafting, affords the only means of controlling it. Rarely, hidradenitis suppurativa is encountered in amputees. In such cases it can cause a really serious handicap, making the use of a pros¬thesis or crutches impossible.
Innervation of the apocrine glands is exclu¬sively adrenergic, as compared with the cho-linergic innervation of the eccrine glands. The apocrine system re¬sponds sluggishly or not at all to heat. How¬ever, it does respond promptly to emotional or painful stimuli. In the management of this aspect of the amputee's hygiene, therefore, it is important to bear in mind that pain or ten-derness in the stump, or an emotional disturb¬ance, may aggravate any existing skin disor¬ders in the groin or un¬derarm regions through stimulation of this spe¬cialized glandular sys¬tem.
Unfortunately, the apocrine glands occur in the areas upon which the amputee must depend for sup¬port in the use of a crutch   or   an   above¬knee prosthesis. The apocrine glands can be a source of considerable grief, if, through poor hygiene, infection, or other cause, these areas are allowed to become unserviceable for weight-bearing.

The Sebaceous Glands
The sebaceous glands occur wherever there are hair follicles. In addition, there are scat¬tered, free sebaceous glands which are inde¬pendent of the follicles. Their secretion is an oily liquid composed of fatty acids, alcohols, hydrocarbons, and certain vitamin precursors. This material, called "sebum," becomes solid at about 30°C (86°F), the prevailing skin-surface temperature.
A unique feature of sebaceous-gland secre¬tion is the capacity of the glands to secrete very rapidly onto a defatted skin surface, but at a rate which gradually declines until the new fat layer of the surface reaches a certain critical thickness. When this occurs, sebum production stops or falls to a minimum. If, however, the fat layer is removed, rapid secre¬tion starts again. The more viscous the sebum becomes, the earlier the sebum expulsion is stopped. As a result, more oil is secreted per unit time at a high environmental temperature than at a low temperature.
Presumably, the counterpressure of the oil film on the surface prevents further production by back-pressure in the gland. There is an interesting fact, however, which is not entirely explained by the back-pressure theory: if the duct of the gland is blocked by sebum only, no pathologic change takes place in the secre-tory cells of the sebaceous glands, but if the obstruction is caused by masses of keratin or other foreign matter, as in the case of come¬dones ("blackheads") and various types of follicular keratoses, degenerative changes in the gland set in relatively early.
This phenomenon of controlled oil produc¬tion is one in which a normal physiologic proc¬ess appears to work with the amputee rather than against him in the wearing of a pros¬thesis. Here, the accumulating lipid film under the socket will serve as its own shut-off valve for further secretion, without damage to the sebaceous glands in the stump skin.

HEAT   CONTROL   AND   THE    HEALTHY   SKIN
Healthy skin exercises a vital role in the thermoregulation of the body, a function in which the skin of the lower extremities nor-mally has an important share. This surface control supplements the central heat-regula-tory center in the hypothalamus of the brain. At basal conditions, the heat balance of the normal body is maintained by cutaneous vaso-motor adjustment through an environmental temperature range of 25° to 31°C (77° to 88°F), the  so-called   "zone  of vasomotor  control."
Above this range, at 31° to 32°C (88° to 90°F),
when cutaneous blood flow has reached its maximum, sweating sets in—the "zone of evaporative regulation." Between 31° and 36°C (88° and 97°F) and at low humidity, evaporative heat loss easily maintains normal temperature. Below the zone of vasomotor control, the skin temperature falls, and body temperature is maintained chiefly by chills (the "zone of cooling"). If environmental tem¬perature is maintained below a critical level of 31° to 32°C, there is generalized, but grossly invisible, periodic sweating known as "insen¬sible sweating." Consequently, although the principal thermoregulation in this temperature range is vasomotor, there is still an assist from the sweat glands in cooling the skin surface.
The values cited are those reported for the normal. In the amputee, significant areas of cooling surface, along with the component sweat glands, have been subtracted from the total reserve of functional skin surface. In addition, the complex and important system of vascular shunts and arterioles in the ampu¬tated limb or limbs has also been lost from the total heat-regulatory mechanism. As a result, a number of characteristic and troublesome disturbances of temperature and heat control are associated with amputation.
Among these is the phenomenon of the poikilothermic stump, which has been studied by staff members of the University of Cali¬fornia Medical School (22). In this condition, the surface temperature over the distal part of the stump, and over a considerable portion of the stump proximally as well, tends to be¬come stabilized at the temperature of the sur-rounding air, more or less independently of any vasomotor control. Thus it is seen that, in a lower-extremity amputation, not only is part of the original heat-control surface per-manently lost but the remaining stump surface is no longer normally effective as part of the heat-control mechanism. Nevertheless, it is important to maintain the hygiene, or good health, of this remaining skin area in order to preserve whatever function it may still possess for heat regulating, and particularly for cooling.

MECHANISMS of HEAT LOSS
Heat loss from the normal skin takes place by radiation, convection, conduction, and evaporation. All of these mechanisms are interfered with, if not entirely abolished, over the stump area when a tightly fitted socket is worn, Excessive local heating of the stump can result (Fig. 4), particularly during warm, humid weather, and a major hygienic problem can arise under such conditions.
Heat loss from the skin by radiation takes place in the form of infrared rays in the range of 5 to 20 m/u. Under normal conditions, radia¬tion accounts for about 60 percent of total heat lost from the body. In the amputee, it
seems probable that loss of heat from the stump area by this mechanism is greatly re-stricted by the socket of the prosthesis. We do not at present, however, have any data to con¬firm this supposition.
Convection depends upon the transfer of energy by means of moving air and thus is negligible as a means of heat loss from the stump when a prosthesis is worn.