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The Incidence of Dermatological Problems in the Silicone Suspension Sleeve User

Christopher Lake, CP
Terry J. Supan, CPO

ABSTRACT

Since their introduction in the mid-1980s, roll-on silicone sleeves have evolved into a widely used method of prosthetic suspension. Through the course of clinical practice, certain recurring skin conditions have been associated with roll-on silicone sleeve use.

The purpose of this research project was to review pertinent literature and develop a survey to investigate the incidence of dermatological problems in silicone suspension sleeve users. Data were collected from patients as well as practitioners. Strong trends were noted indicating the incidence of dermatological problems in silicone suspension sleeve users is influenced by aging, activity level and use patterns. Observations made in clinical practice that currently have not been scientifically analyzed are noted separately.

Key words: Silicone; Prosthetics; Amputee; Dermatology; Skin; Suspension Sleeve.

Introduction

All amputees can experience dermatological problems secondary to socket fit, hygiene, existing pathology or excessive heat (1). While the history of this suspension method has been well-documented (2-4), the incidence of dermatological problems in roll-on silicone sleeve users has not been widely reported. The purpose of this research study was to establish an initial incidence of dermatological problems in the silicone sleeve user and provide the prosthetist with guidelines for the use of such a suspension system.

Review of Skin Physiology

Skin type and integrity are determined by ethnicity, genetics, and environmental and/or occupational variables. The skin represents the largest organ of the human body and is composed of the epidermis, dermis and hypodermis layers (see Figure 1) . The dermis contains an elastic matrix of collagen and elastin. Collagen provides the skin with its tensile strength; elastin provides the skin with elastic or recoil strength. The loss of elastin can be most apparent in the aged individual with saggy skin.

The outermost layer of the epidermis, the startum corneum, is comprised of cells containing a protein called keratin. This protein provides an impermeable barrier to, and restricts, the loss of water, maintaining critical hydration of the skin. Deeper within the dermis are the sweat glands and hair follicles. These structures receive their nutrients from capillary loops that course through the skin structure. When more closely analyzing the skin, ridges can be seen between the epidermis and dermis (see Figure 1) . These rete ridges actually are dermal papillae that extend like fingers from the dermis into the epidermis. The rete ridges provide a bond between the dermis and epidermis that prevents shearing of the epidermis from the dermis (5).

Literature Review

It has been reported the amputee can expect a period of excessive perspiration and irritation as an initial side effect of roll-on silicone sleeve use. These symptoms are said to subside with continued wear (2,6). It also has been noted that excessive perspiration can be treated using an antiperspirant lotion (7). Levy reported that in warm climates or during the summer months, increased warmth and moisture from perspiration promote maceration of the skin in the socket, which in turn favors invasion of hair follicles by bacteria (8). Since the residual limb has been found to present with more bacterial flora than the contralateral limb, the potential for bacterial infections and folliculitus exists (9). Previous articles on silicone suspension sleeves have concluded that perspiration has not proved to be an issue; subsides after continued use; appears in areas of nonfit and is more common in the geriatric population; and can be eliminated when the atmosphere is eliminated, as when the liner is rolled on (2,7,10,11).

Heat loss from normal skin takes place by radiation, convection, conduction and evaporation. All of these mechanisms of heat loss are interfered with, if not entirely abolished, when a tightly fitted socket is worn over the residual limb (12). Prolonged elevated temperatures could produce resultant heat rash.

As previously discussed, the rete ridges are directly responsible for the skin's resistance to shearing forces. The skin's ability to resist shearing is further compromised by the flattening of the rete ridges, which is a direct physiological consequence of aging. This decrease leaves the skin of an older individual at risk of injury under shear forces that would not pose a problem to a younger individual. This concept and the physiological consequence of aging are important since the majority of prosthetic patients are elderly individuals.

As the ridges flatten there is a decrease in surface area contact, which lowers the threshold shear force needed to cause shearing of the skin. This is most apparent clinically when an individual's skin tears upon removal of an adhesive bandage or when it blisters in a tight shoe. Katzberg first discussed this concept in 1958 (14). Clinically, the two most common areas where shearing is noticed when using silicone suspension sleeves are at the proximal liner trimline and posterior distal aspect of the residual limb. Shearing at the proximal trimline of the liner appears to occur in about a 2-cm area along the proximal edge.

Folliculitis can result in patients who have an ill-fitting prosthesis as well as in those who have an optimally fitting one. The mechanism involved combines residual limbs that present as hairy and oil with the increased pressures in the prosthetic socket (8,14,15). Soreness of the residual limb might be caused by the pulling action of the liner on the residual limb during ambulation. It has been reported in the literature that the milking action of the liner can make a residual limb appear healthier due to increased circulation (1). Irritation in the back of the knee when sitting, usually seen in a high posterior wall, also can be caused by the bunching or wrinkling of the liner and socks upon knee flexion.

Allergic reactions in the form of a rash or dry, irritated skin (contact dermatitis) have been cited as being caused by the materials used in the fabrication of liners and sockets (16-22). Extensive research by Dow Corning in Midland, Mich., has provided several interesting findings, including the finding that silicones are among the safest biomaterials available for use in the medical and pharmaceutical industries (23). Silicone is known as the standard against which all other man-made, medical materials are compared since the body has no serious reaction to this natural material (24). However, the FDA has noted a lack of studies investigating silicone rubber, which is similar to the silicone used in prosthetics. (25)

It has been concluded that silicone used in items such as hearing aids, underwater masks and mouthpieces has resulted in little or no skin irritation. Silicone is considered to be a hypoallergenic material, and any allergic reactions are commonly noted to be secondary to rubber accelerators or antioxidants in the rubber [that] are not present in silicone rubber (26). One manufacturer of products used in prosthetics, Silipos, has performed studies that are available to the public. (This manufacturer does not fabricate silicone liners but uses a polymer material similar to silicone.) Independent testing has concluded Silipos' patented gel does not initiate an adverse reaction in a sample of 63 individuals (27).

In the silicone suspension sleeve prosthesis, the silicone liner is the only material in contact with the skin. As stated previously, silicone is considered to be hypoallergenic. With this in mind, one should begin to focus on other variables that could influence adverse reactions. Further investigation has revealed several contributing variables that could have direct influence over the incidence of dermatological problems.

Contributing Variables

Reason for Amputation

The reason for amputation has a great influence on the prosthetic prescription and management of a patient. Skin differences between burn patients, diabetics, amputees secondary to peripheral vascular disease (PVD) and traumatic amputees are well-known. Due to the incidence of amputation and clinical presentation, of particular interest are differences between diabetic/PVD and traumatic amputees. While traumatic amputees often have excessive scarring, in most cases their skin is well preserved and without compromise. Diabetic/PVD patients, on the other hand, present with a decrease in sweat gland function, are less tolerant to shear forces and have a decrease in the skin's structural stability secondary to a compromised microcirculation (8,28,29).

Gender

Two gender-related factors affect the skin: The skin of a female is more resistant to shearing and is thinner than the skin of a male, and the collagen content in a female's skin does not decrease at the same rate as in males. In fact, collagen levels remain consistent until menopause as opposed to a steady decrease by decade in males (30-34).

Age

With increasing age, the skin's moisture content, hair follicle and sweat gland function decrease. This physiological fact coupled with the flattening of the rete ridges and the decrease of elastic integrity (elastin) causes the skin to become fragile and easily injured by minor trauma (13,30-34).

Level of Amputation

When referring to the principles advanced by Radcliff, Foort and Long, it can be said there are significant differences in the biomechanical principles of sockets designed for certain levels of amputation. The only region of human skin inherently designed for weightbearing is the plantar surface of the foot. Due to the weightbearing and movement functions of the legs, skin problems are more common in lower-extremity amputees than in upper-extremity amputees (15). It also has been observed that levels of resistance to shear vary at different anatomical regions such as the thigh versus the lower leg (34,35).

Hair Type and Sun Sensitivity

The literature suggests fair skin, red or light hair color, light eye color, and freckles are phenotypic markers of increased susceptibility to sun-induced skin damage (36). Sun sensitivity is relevant because sun-damaged skin exhibits less sweat gland function and elasticity (37). These two variables usually are not considered during prosthetic management.

Activity

An individual's activity level is directly proportional to the amount of weightbearing and distraction forces placed on the residual limb. Some individuals report soreness from liner use; therefore, activity level is an important factor in regard to liner use.

Regional Humidity Level

Regional humidity level and resultant perspiration have long been believed to be contributing factors to amputee skin problems. In the literature (8) as well as in the authors' clinic, the incidence of skin problems increases dramatically during the humid summer months as opposed to winter months when humidity is lower; this occurrence appears unaffected by liner use or socket design. Proper documentation from the National Climatic Data Center allows for further investigation of this issue (38).

Sock Ply and Liner Color

Sock ply fit is directly related to socket fit. Individuals who wear an excessive amount of socks could be subject to an increased incidence of problems secondary to a prosthesis that is too large.

When discussing color of the liner, many practitioners express concern regarding pigments used during the processing of the silicone liner. According to Dow Corning, medical grade silicone is considered hypoallergenic. The term medical grade denotes the silicone has undergone tests, including skin sensitization. These tests are in compliance with the Tripartite Guidance and ISO 10993-1:1992(E), which require medical products such as silicone to meet minimum standards under varying types and duration of exposure. To avoid compromising the hypoallergenic status of the material, any additives introduced into the liner, including pigments, must undergo the same tests as the raw silicone (39,40).

Use of Powders, Deodorants or Sheaths on the Residual Limb

Powders and deodorants often leave a residue on the skin that can become a skin irritant within the closed environment of the liner. When an individual uses a sheath between the skin and the liner, several significant changes in prosthetic fit are suspected. Shear forces at the proximal edge are thought to be reduced because the liner is no longer in direct contact with the skin, and a small amount of air is allowed to circulate around the residual limb. A sheath also serves to wick sweat away from the skin, possibly reducing the adverse effects of moist skin in the closed socket.

Personal Hygiene

Hygiene-related concerns revolve around when the residual limb is washed, frequency of washing the residual limb and liner, cleaning agents, and shaving the residual limb. Good residual-limb hygiene is essential for all amputees. Asking the question, Do you wash your liner and residual limb? is not sufficient in examining this variable. The following questions are relevant to this issue: How many times a week/day are the liner and residual limb washed? What is used to clean the liner and residual limb? Does the amputee shave the residual limb?

These questions have obvious implications on skin health. The ramifications of when the liner and residual limb are washed are not so easily understood. It has been reported that the skin must be dry before donning the prosthesis because of the dermatological consequence of maceration of skin in the closed, airtight environment of the prosthetic socket (8,14). It is suggested the patient wash both the residual limb and the liner at night to ensure a dry environment when donning the prosthesis the next day.

Overall Duration and Hours Per Day the Liner Is Worn

This variable investigates the dermatological problems with regard to how many years this suspension type has been worn and the number of hours per day the liner is worn. Of particular interest is the incidence of dermatological problems in individuals who switched to this suspension type from another suspension type versus individuals who began their initial prosthetic management in a silicone suspension sleeve. Previous study has found individuals who switched from another type of suspension complained more of perspiration, itching and soreness (7).

Methodology

Surveys (see Appendix I) were collected from 56 amputees using the silicone suspension sleeve system, of which 33 were under the direct care of siu School of Medicine, and 23 were from different states. The survey responses of the local and out-of-state users were compared, and responses were found to be consistent; this finding allowed a combination of the two groups. There were 44 males and 12 females. Mean age was 52.9 years with a range from 15 to 85.

A chi-square test of independence, or Fisher's exact test as appropriate, was used to compare the various proportions. Paired t-tests and Pearson correlation coefficients were used as further investigation deemed appropriate. A p value of .05 or less was regarded as statistically significant. In several cases where the p value did not indicate significance, percentages still were reported because the authors feel the percentages, though not statistically significant, are clinically relevant and, in many incidences, are supported by the literature.

Results

Gender differences were not evident within the sample. Investigation of aging revealed the following findings: As age increased (by decade), there were significant decreases in the reported incidence of perspiration (p=.002), residual-limb soreness (p=.002), folliculitis (p=.003) and heat rash (p=.003).

Level of amputation did not show statistical significance, but percentages do warrant further investigation (see Figure 2) . There was an overall trend toward transfemoral amputees having less incidence of dermatological problems than transtibial amputees.

Cause for amputation offered several interesting observations. The data showed that, in respect to perspiration, contact dermatitis, folliculitis, heat rash and residual-limb soreness, traumatic amputees (n=24) presented with higher incidences of problems than vascular amputees (n=25) (see Figure 3) . Traumatic amputees tended to be significantly younger (p=.0001) with an average age of 44 years versus 62 years for the vascular group. The traumatic amputees had been amputees for an average of 10 years versus a vascular amputee average of three years. This, too, is a significant observation (p=.0038). When examining the activity level, the traumatic amputee population was more active (p=.0002). Traumatic amputees exhibited a 62-percent reported incidence of active to athletic activity as opposed to a 12-percent incidence among the vascular group.

Hair color analysis offered no significant findings; only one noticeable difference was found. In accordance with the literature, those individuals who sunburn easily (n=19) presented with a 37-percent reported incidence of perspiration as opposed to a 67-percent reported incidence among the group that did not sunburn easily (n=36). Regional humidity level analysis did not offer definitive conclusions secondary to sample size although increases in reported perspiration were noted in higher humidity levels.

Activity level differences were noted only in perspiration, folliculitis and heat rash (see Figure 4) . The sample was divided into a low/moderate activity group (n=35) and an active/athletic group (n=21). The lower activity group reported a 49-percent incidence of increased perspiration, and the higher activity group reported a 67-percent increase. Incidence of heat rash was 20 percent in the lower activity group versus 48 percent in the higher activity group. There was a significant (p=.03) difference between the groups for increase of folliculitis, with the lower and higher activity groups reporting a 17-percent and 48-percent incidence, respectively.

As sock-ply fit increased (grouped in three-ply intervals), minute differences were noticed indicating increase in sock ply could result in increase of dermatological problems. No statistical significance was noted.

Investigation of liner color exhibited some interesting results. There was no evidence that color has any impact on contact dermatitis though it was found 73 percent of the pink liner users (n=11) reported excessive perspiration as opposed to 59 percent of the white liner users (n=29) and 40 percent of the clear liner users (n=15).

Individuals who used a sheath (n=10) between the liner and their skin reported a 10-percent incidence of contact dermatitis as opposed to an 18-percent incidence in individuals who used nothing (n=33). Individuals who used powder between the liner and skin (n=5) reported a 50-percent incidence of contact dermatitis. In addition, there was less reported incidence of folliculitis in the sheath users (10 percent) as opposed to individuals who used nothing between the liner and skin (30 percent).

It was found that within the sample there was strict adherence to good hygiene, making statistical evaluation impossible. Folliculitis was seen in 57 percent of amputees who shaved their residual limbs (n=6) versus 24 percent of the amputees who did not shave their residual limbs (n=49). This is relevant but not statistically significant (p=.09).

Respondents then were divided into three groups related to number of years of use with a silicone liner: one year or less (n=20), one to three years (n=20) and three years or more (n=16). As indicated in the years of wear graph (see Figure 5) , there were increases in the reported incidence of contact dermatitis, folliculitis and residual-limb soreness with increased years of use. No statistically significant results were found relating to length of time the liner is worn per day.

An important finding resulted from the investigation of whether the silicone liner was the only suspension ever used or if the individual had switched from another type of suspension. The incidence of contact dermatitis in first-time users (n=31) was 10 percent as compared to 36 percent in individuals who were switched (n=25) from another suspension system. This finding is statistically significant with a p value of .04.

Discussion

With an increase in age there is a decrease in the incidence of perspiration and folliculitis secondary to the decrease in sweat gland and hair follicle activity. The concurrent decrease in heat rash and residual-limb soreness can be explained with further observation of age and activity level. These findings are in agreement with the literature.

Level of amputation also yielded results that are in agreement with the literature. Transfemoral amputees presented with a lesser incidence of folliculitis than transtibial amputees. This finding suggests socket design and soft-tissue-to-bone ratios play a role in increased incidence of folliculitis. It can be speculated that the weightbearing forces are more concentrated and higher in transtibial amputees, causing the higher incidence of folliculitis in this population.

Etiology of amputation results indicated diabetic/vascular amputees were less likely to suffer from excessive perspiration, contact dermatitis, folliculitis, heat rash and residual-limb soreness than traumatic amputees. The decrease most likely is due to the pathological effect of diabetes/PVD on sweat gland function as well as the finding that diabetic/vascular amputees were an average of 18 years older, were less active and had worn a prosthesis for a shorter period of time than traumatic amputees. The higher activity level individuals generally reported a higher incidence of folliculitis. This trend may be due to the increase of weightbearing forces on the residual limb with higher activity.

The lack of differences when examining hygiene data is, in fact, an important result in itself. Even though nearly all of the subjects demonstrated good hygeine, dermatological problems existed. Furthermore, although inconclusive in this analysis, poor hygiene can only lead to future problems and cannot be overlooked.

Individuals who switched from another system to the silicone liner reported an increased incidence of contact dermatitis. Based on this finding it might be appropriate to recommend that amputees wear silicone liners for several weeks before fabrication of the prosthesis. What is not clearly understood is why individuals who have worn the liner longer report higher occurrences of contact dermatitis, folliculitis and residual soreness. This type of result has been noted clinically and has been commented on by several consulting prosthetists.

Application to Clinical Practice

The ABC-certified practitioners involved in the data collection also were surveyed (see Appendix II) concerning their professional experience. Through their suggestions as well as the research findings, the following list of fitting rationale has been developed. The advantages for use are:

• Superior form of suspension with minimal pistoning.
• Management of unstable limb volume in the transfemoral patient who desires the benefits of a suction suspension. Volume fluctuation can be managed through proper sock management.
• Secure feeling of suspension.
• A decrease in the perceived weight of the prosthesis through minimal pistoning and elimination of a hanging weight.
• Flexible and accommodative interface that intimately follows skin contours and transfers shear forces that were traditionally noted between the skin and socket to the outer liner surface and skin. Though it has yet to be scientifically proven, strong clinical observations support the theory that shear forces are nearly eliminated in the silicone liner environment.
• Improved cosmesis through the elimination of belts, straps, neoprene sleeves and proximal trimlines found in supracondylar suspensions.

Silicone suspension sleeve use may not be advantageous if any of the following are present and cannot be alleviated through modification of the component or fit of the prosthesis:

• Known skin sensitivity to silicone. In addition, consultation with a dermatologist is helpful. This issue may be alleviated by using a sheath between the skin and liner.
• Poor cognitive capacity, which would inhibit proper use of the suspension system, resulting in possible residual-limb harm due to improper donning, hygiene, shuttle lock use, etc.
• Residual limb that presents with invaginations or a shape that interferes with total contact of the liner that cannot be alleviated through the use of auxiliary products such as distal end caps.
• Adherent distal scar tissue or hypersensitive distal ends that cannot tolerate the distraction forces created by ambulation in a prosthesis using a silicone suspension sleeve system. Improper donning or an excessively large liner causes distal gapping, which, in turn, can cause irritation at the distal end. This issue would present with the same complaint of sensitivity by the patient. To determine if there is distal gapping, pull on the locking pin and note the distal shape. If the liner puckers or develops concavities, then the liner either was donned improperly or is too large for the patient. Redon the liner, determine the cause and address accordingly.
• Compromised hand function that interferes with independent donning of the liner. Sometimes this issue can be resolved by rolling the liner off so it is rolled and not simply inverted (see Figure 6) . This offers the patient an increased area of liner to manipulate for donning the liner. Though this helps the individual in donning and doffing, issues regarding independence in hygienic practices still need to be addressed.

Conclusion

The preliminary data suggest the elderly diabetic/PVD amputee would benefit most from silicone suspension due to the transfer of shear forces from between the skin and socket to between liner and socket. The elderly diabetic amputee is at increased risk of skin breakdown secondary to dermal-epidermal shearing. Issues of proximal shearing can be addressed through the use of a sheath to break the area of liner contact with the skin. Special attention should be taken to ensure the liner is neither too tight, causing increased pressure over the patella upon knee flexion (2), nor too loose, causing areas that lack contact or exhibit excessive wrinkling of the liner upon knee flexion, resulting in hamstring tendon irritation.

When initially formulating the methods for this research project, a goal of providing objective, scientifically based information was set. The authors believe this goal has been partially met. The base of knowledge regarding silicone suspension sleeves in prosthetics must be expanded.

After reading this article, multiple studies in continuation of this topic should come to mind. The responsibility of providing answers to the many questions weighs on both manufacturers and prosthetists.

In summary, the existence of dermatological problems in amputees using silicone suspension sleeves may be secondary to physiological changes in aging and pathology. Activity level, socket fit and biomechanics, and wearing patterns are significant factors influencing the occurrence of such problems.

The existing literature in prosthetics has not expanded into the dermatological literature when drawing conclusions regarding skin-related problems in silicone suspension sleeve users. Further studies with expanded patient populations must be conducted before any conclusions may be drawn. 5

Acknowledgements

The authors would like to thank the following individuals, listed alphabetically, for their assistance with this project: Michael Allen, CPO; Wade Bader, CPO; Daryl Barth, CPO; William Beiswenger, CPO; David Boone, CP; Thomas Current, prosthetic resident; Greg Gruman, CPO; Chris Hovorka, CPO; Joel Kemper, CP; John Mooney, CPO, OTR; David Procter, CPO; Paul Prusakowski, CPO; and Dale Spraque of Cascade Orthopedic Supply.

Special thanks to David Burk Jr. for illustration work; Stephen Markwell for his assistance with the statistical analysis and editing of the manuscript; Dr. Stephen Stone, MD, dermatology, and Gary Berke, MS, CP, for their critical review of the manuscript; and Pat Sriner, Douglas Cantrall, RTO, and Thomas Current, prosthetic resident, for their editorial assistance.

Technical support for the gait study was provided by Peak Performance Technologies in Englewood, Colo., and Reebok International Ltd. in Stoughton, Mass.

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