Prosthetic sockets form the interface between the residual limb and the prosthesis and are important for the transmission of forces and distribution of pressure in persons with amputation.1 Combinations of prosthetic liners, socks, and/or the socket are worn over the residual limb. However, the insulative nature of prosthetic interface materials2,3 increases temperature of the residual limb causing sweating and moisture buildup.1,2,4 Socket wear, activity, and a hot climate increase residual limb temperature,5–7 with a 1°C to 2°C increase in residual limb skin temperature potentially causing discomfort.5 Increased humidity leads to dermatitis and infections.8 It also disrupts suspension forces,9 and skin with slight moisture is more susceptible to blisters than wet or dry skin.10 The most frequently reported problems that reduce quality of life for persons with amputation are heat and sweating in the socket (72%) and sores and skin irritation from the socket (62%).11 These type of residual limb skin problems impede daily prosthesis use, reduce mobility, and jeopardize the vocational activities of persons with amputation.8 When sweating becomes disruptive of socket suspension and/or causes discomfort, persons with amputation must stop their activity, remove the socket, and wipe down the residual limb and interface. Options available to persons with amputation to manage issues with sweating inside the liner or socket include antiperspirant sprays, botulinum toxin injections, medication, electrical stimulation, and surgery. However, these treatments are often not entirely successful. While a number of temperature regulation and sweat management methods have been explored,12–14 only recently have technologies such as the SmartTemp Liner from WillowWood (Mt Sterling, OH, USA) and the Silcare Breathe Liner from Endolite (Basingstoke, Hampshire, UK) become commercially available. The SmartTemp Liner is said to regulate heat by incorporating phase change material that responds to fluctuations in residual limb skin temperature, absorbing and storing heat as it builds up and delaying the onset of sweat. Furthermore, by releasing stored heat as the body cools, the liner is said to stabilize skin temperature to keep the person with amputation comfortable all day. A recent clinical trial indicated that the SmartTemp Liner resulted in significantly reduced mean skin temperature and perspiration during and after stationary cycling in persons with transtibial amputation compared with a placebo liner.14 The Silcare Breathe Liner features laser-drilled perforations to allow moisture to escape, presumably resulting in drier skin and a healthier environment for the residual limb (http://www.silcareliners.com/us/). The purpose of this technical note is to describe a simple, inexpensive technique for perforating any silicone prosthetic liner to expel sweat and enhance use of a lower-limb prosthesis.
MATERIALS AND METHODS
A liner holder was made to hold the liner during the perforation process (Figure 1A). The liner holder was made from a mandrel that was covered by a rolled towel and then a series of socks sufficient in number to form a cylindrical/cone shape, mimicking the distal shape of the liner to be perforated. The mandrel was approximately 2 cm in diameter and long enough to accommodate the liner to be perforated. The liner holder ensured that the liner did not move during the perforation process, allowing the perforation tool to be positioned reliably against the surface of the liner. The liners were simply held in place by the liner holder: the aim was to have total contact between the liner holder and liner without tension on the liner.
A silicone liner was placed over the liner holder with the external surface of the liner exposed (Figure 1B). A perforating roller typically used to perforate foam padding was then rolled over the distal end of the liner (e.g., PEL Perforating Tool, http://cascade-usadev.com/pelr-perforating-tool.html, Figures 1C, D). The perforating tool was rolled over the distal end of the liner in the pattern shown in Figure 1E. This particular perforating tool created consistently sized holes distributed approximately 1 cm apart. The distal portion of the liner was covered with holes without interrupting the sealing mechanism incorporated into the liner.
When the liner was inverted, the holes were visible all the way through to the inner surface of the liner (Figure 1F). Liner perforations were tested to determine permeability by pouring water into the liner. The proximal, open end of the liner was sealed by folding it upon itself, and forcing air/water through the perforations. Water droplets and air escaped through the small perforations with some resistance (Figures 1G, H).
RESULTS AND DISCUSSION
Initial clinical experience with this technique suggested that expulsion of sweat occurred and user feedback indicated improved prosthesis use as a result. Figure 2 demonstrates that sweat does indeed seep out of the perforations and can be seen as wet patches on the exterior fabric of the liner after active wear. One user with amputation described that liner perforations resulted “in whatever fluid exists to be pumped out [of the liner] into the socket and in some cases pumped out of the socket through the air relief valve [of] a dual chamber [vacuum] pump.” Another user with amputation stated, “I have had no damage to my leg from the holes or any marks either. I would NOT go back to wearing the liner without them [holes]; before the sweating was so bad I had to remove the liner and dry it out numerous times a day. Now I wear it all day with minimal slip, if any.” This technique appears to result in similar expulsion of sweat as is claimed of the Endolite Silcare Breathe Liner (http://www.silcareliners.com/us/).
An additional potential advantage of liner perforations is that they may help to reduce air pockets between the liner and skin when used with active vacuum pump systems. For example, in residual limbs that are oddly shaped and/or hairy, air might be trapped between the limb and liner when the liner is initially donned and the perforations may allow for that air to escape, improving the seal between liner and limb. The perforations may also help maintain contact between the limb and liner when the limb loses volume during the course of a day.
Although this technique has been used in clinical practice by the author (R.C.), experience is limited to an estimated 40 initial cases, approximately half transfemoral and the rest transtibial, wherein active vacuum pumps or suction were used. The long-term effects of perforations on liner durability or limb health are not yet known. Caution is required to ensure that one does not make too many holes and that the holes are not too large. If the holes are too large, use with active vacuum will likely result in water blisters. Using the perforating tool described will control the size and distribution of the holes and ensure that they are not too large. If there are too many holes, liner durability may be compromised leading to premature wear of the liner.
Although this technique has been successful with silicone liners, it is unclear if it would be equally successful with thermoplastic elastomer (TPE) or polyurethane liners given that they are generally less durable materials. Similarly, this technique has not been used with pin-locking liners, so it is unknown whether it would work well with that system. It is not typically recommended that patients wash the exterior textile of liners because it is not in contact with the skin. However, when the liner is perforated, washing both internal and external liner surfaces should be recommended given that any sweat expelled through the liner may lead to bacterial buildup on the external textile-covered surface. When cleaning the liner, patients should routinely push alcohol through the perforations to avoid bacteria buildup. This can be accomplished by pouring rubbing alcohol into the liner, folding the proximal edge to create a seal with the liner, and forcing air/alcohol out of the perforations.
This technical note describes a simple, inexpensive technique for perforating a silicone prosthetic liner to expel sweat and enhance use of a lower-limb prosthesis. Initial clinical experience with this technique suggested that expulsion of sweat occurred and user feedback indicated improved prosthesis use as a result.
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