Academy Society Spotlight: Choosing a Gel Liner

Urethane, silicone, and thermoplastic elastomer (TPE) are materials that can be used to fabricate prosthetic liners. A liner can be uniform in thickness or taper from its distal to proximal ends. A common question among less experienced practitioners is, "What are the differences between liners?" It may not be immediately clear whether silicone, TPE, or a different material is warranted in a given situation. Without guidance, the wide variety of manufacturers, liner properties, and materials available, as well as patients' differing skin types and fitting concerns, can make choosing a liner difficult for a practitioner who is beginning in the profession.

Photograph courtesy of Össur.

INTRODUCTION The most common form of socket interface found in lowerlimb prosthetics is the gel liner; however, since many different styles exist, a new practitioner may need guidelines when trying to choose the correct option for a patient. For my prosthetic residency research project, I surveyed experienced prosthetic practitioners in order to assess aspects of gel liners. The survey asked practitioners to state the preferences they had developed through their years of experience. For the purpose of this study, an experienced practitioner is defined as someone with more than five years of experience in the O&P profession.

This study also examined the opinions of experienced practitioners and compared them to some of the industry's perceived patterns. These commonly held perceptions were determined by a consensus reached during this practitioner's discussions with approximately 20 other practitioners who had varying years of experience and worked in a variety of regions throughout the country. One of these patterns is, for example, that most patients with transtibial amputations use gel liners and pin lock systems. I also found common perceptions about how gel liner durability compares across the various manufacturers.

When it comes to understanding gel liner options, the first distinction is the different materials from which they are constructed: silicone, urethane, or TPE with mineral oil. Factors that differ between these materials include stiffness, durability, patient comfort, and cost. Gel material stiffness is defined as "the amount of deformation that occurs under axial load" (Liston and Stevens, 2012). Not only are there differences between gel liner material from style to style, but other differences persist, such as if a fabric cover is used and, if so, from what material it is fabricated.

Current literature includes information about various liners as they have been introduced to the market over the years. Descriptions of how gel liners can improve the interface with the user's skin and which gel liners are appropriate with different socket designs or vacuum systems are also available. Some literature includes scientific studies, such as Covey et al.'s "Flow Constraint and Loading Rate Effect on Prosthetic Liner Material and Human Tissue Mechanical Response," in which the compressive properties of four different gel liner materials were compared to human muscle as a function of geometric flow constraint and loading rate by examining the materials' stiffness, residual displacement, and energy absorption. Another example is the study by Coleman et al. that compared patient satisfaction with Pelite and Alpha® liners. Despite this research, a compilation of the gel liner combinations typically used by experienced practitioners is not yet available.

SURVEY DETAILS The survey was open to prosthetic practitioners in the United States. The survey, created in Google Docs, was made available on the OANDP-L listserv and distributed via e-mail to a preexisting list of prosthetic practitioners. Both the listserv post and the e-mail included a link to the survey, and once the respondent submitted the survey, the data was stored within Google Docs. The survey was open for three weeks; 118 responses were received.

The survey topics included the following: rate of gel liner use in patients with transtibial and transfemoral amputations; type of suspension used with transtibial and transfemoral prostheses; factors that affected the practitioner's liner selection; the variety of manufacturers whose products were chosen; problems with perspiration or allergic reactions; the level of patient satisfaction with the liner; durability; prefabricated versus custom liner usage; and preference of gel liner thickness. There were 18 questions, 14 of which were multiple choice. One question asked the respondent to rate several gel liner thicknesses in order of patient comfort. Others included Likert scales and open-ended questions for which the respondent could elaborate in as much detail as he or she chose.

The first question, used to determine inclusion criteria, asked how many years of prosthetics experience the respondent had. Because the goal of the survey was to establish the preferences of experienced practitioners, responses from practitioners with five or fewer years of experience were omitted, resulting in a final sample size of 92. The other questions gauged the respondents' insights regarding gel liner usage.

This survey only differentiated between patients with transtibial and transfemoral amputations with respect to the amount of gel liner usage and the prosthetic suspension system used. Otherwise, responses pertained to the respondents' overall lower-limb amputee patient population.

RESULTS Gel Liner Usage Of the 92 respondents, 72 percent recommend gel liners to at least 80 percent of their patients with transtibial amputations. However, only 35 percent of the respondents recommend gel liners to at least 80 percent of their patients with transfemoral amputations. Further, 98 percent of the practitioners who responded to the survey recommend gel liners to at least 40 percent of their patients with transtibial amputations, and 89 percent recommend gel liners to at least 40 percent of their patients with transfemoral amputations.

Suspension Systems When asked about the most common form of suspension for patients with transtibial prostheses, 58 percent of the respondents primarily provide their patients with pin lock systems. The complete breakdown of responses about suspension options used for this population is illustrated in Figure 1. Regarding suspension for those with transfemoral prostheses, there was a wider diversity of opinions, which are illustrated in Figure 2. In addition to the pin lock system, other transfemoral suspension systems reported include seal-in liners, suction, vacuum, or a combination of multiple suspension systems.

Practitioner Considerations Forty-two percent of respondents reported that the liner's material-silicone, urethane, or TPE-was the first factor they consider when choosing a gel liner for a patient, while 18 percent first consider ease of donning, 8 percent consider cost first, and 32 percent of respondents listed another factor as their primary consideration. The explanation provided for why respondents chose these answers ranged from their habits, to a liner's durability, to patient comfort, to the suspension system used by the patient. See Figure 3 for additional factors reported.

Liner Manufacturers Respondents were also asked about liner manufacturers and the variety of liners they offer their patients. When asked the number of manufacturers from which a practitioner typically ordered, 71 percent said they order from three to four different liner manufacturers, and 4 percent of practitioners reported ordering from five or more liner manufacturers. The remaining 25 percent said they order from two or fewer manufacturers. The practitioners were then asked if they preferred a specific manufacturer or model and to explain why. The three largest manufacturers each had over 20 percent of the respondents' support, as follows: ALPS, 30 percent; Össur, 24 percent; and WillowWood, 21 percent. Of the practitioners surveyed, 10 percent did not have a preference; 9 percent said their preference depended on the patient; and the remaining 6 percent reported that they preferred liners produced by other manufacturers.

Patient Issues with Allergic Reactions and Perspiration The survey then asked about the occurrence of allergic reactions to gel liners. Only three practitioners reported that 10 percent or more of their patients had encountered an allergic reaction to a gel liner.

Fourteen practitioners responded that over 10 percent of their patients use an interface, such as a liner-liner or sock, between the skin and the gel liner. The other 78 respondents use an interface in less than 10 percent of their patients.

Only 25 respondents reported that over 40 percent of their patients experience perspiration problems. Antiperspirant spray was listed as the first recommendation for treating perspiration problems by 28 practitioners, while 26 recommend a liner-liner, and 15 suggest antiperspirant wipes. The remaining 23 practitioners recommend other methods for dealing with perspiration including: using all three methods listed previously; an antiperspirant roll-on; deodorant; talcum powder; and removal or drying of the liner. A few said that they advise patients that there is a normal acclimation period and did not make a specific recommendation for treating the problem.

Patient Satisfaction Respondents were also asked if they received higher patient satisfaction with one style of liner over another. A majority of the practitioners, 58 percent, said they had not noticed higher patient satisfaction with a specific liner. Of the practitioners who did report a specific manufacturer that presented higher patient satisfaction, 14 percent listed Össur, 13 percent ALPS, 11 percent WillowWood, and the remaining 4 percent listed other manufacturers.

Durability Practitioners were then asked about liner durability and 23 respondents said they could not report a specific style with better durability. Of the remaining respondents, many listed durability by manufacturer, with Össur being the top choice and ALPS following as second (Figure 4). Other respondents listed durability based on the type of gel material utilized: 11 percent stated that silicone liners had better durability, 6 percent preferred urethane, and 1 percent said hybrid liners seem to have better durability.

Practitioners were also asked about liner replacement. When asked how long after delivery they typically returned liners for replacement, 12 respondents said they return liners within the first two months; 17 said within three to four months; 22 said within five to six months; 18 said within seven to eight months; and 23 respondents said it was nine months or more before they return liners.

Prefabricated versus Custom The last section of the survey discussed prefabricated versus custom gel liners. Only 8 percent of respondents use a custom gel liner for more than 25 percent of their patients, whereas 60 percent of respondents use a custom liner for 0-5 percent of their patients. Figure 5 represents the full range of results.

Liner Thickness Within the category of prefabricated gel liners, there is also a choice in the thickness of the gel used. Respondents were asked to rate the comfort level provided by four different thicknesses, as reported by their patients. The four thickness options provided in the survey were rated from most to least comfortable, as follows: 6mm, progressive, 3mm, and 9mm.

Discussion Throughout this study, practitioners were asked to comment on or rate a number of factors they take into consideration when determining what type of gel liner would best serve their patients with lower-limb amputations. To make this decision, practitioners said they must take into account the patient's residual limb in terms of skin condition, amount of soft tissue, and shape; their activity level and comfort; the flow of the material; ease of donning; and liner durability. Based on the 92 experienced practitioners surveyed, it appears that liner material is the primary factor in a practitioner's selection of a gel liner for a patient. Secondary factors include ease of donning and patient comfort.

This survey did confirm some of the commonly perceived patterns for prosthetic usage. The first confirmed pattern is that the most common system used for a patient with a transtibial amputation is a gel liner with pin lock suspension-over 70 percent of the respondents used gel liners with over 80 percent of their patients with transtibial amputations, and almost 60 percent of practitioners use a pin lock as the primary suspension system for this population. The systems commonly used among patients with transfemoral amputations appear to be more diverse; only 35 percent of practitioners were found to use gel liners on over 80 percent of their patients.

While many of the comments received with the survey suggested that practitioners should not limit their choices to only a few liner styles or manufacturers, this was not exemplified in the survey results, as only 4 percent of the responding practitioners regularly order from more than four gel liner manufacturers. In fact, 25 percent of the practitioners regularly order from only one or two manufacturers. It would appear that most practitioners focus on a few styles that they believe work for most, thus ordering from only two or three different manufacturers on a regular basis. The three manufacturers most commonly cited were Össur, ALPS, and WillowWood.

In terms of liner durability, Össur was rated highest as the liner manufacturer of choice and silicone was rated highest as the material choice. This confirms a common perception that I have discovered within the industry that Össur is accepted as a manufacturer of extremely durable liners. An aspect to consider alongside liner durability is how much time passes after delivery of a liner before it is returned for replacement. Surprisingly, over 30 percent of practitioners surveyed are returning liners within the first four months. Only 25 percent of practitioners surveyed are using liners that last longer than nine months after delivery.

Survey Limitations Several limitations to the survey were identified that could be improved upon to increase data reliability in future surveys. It may be beneficial to sort respondents by geographic location in order to determine if there were regional differences. The survey only differentiated between patient populations as either having a transtibial or transfemoral amputation in the first four questions and did not allow respondents to specify a liner preference for each patient group. The survey also did not ask specifically about the difference in materials used-silicone, urethane, or TPE. This forced some practitioners to add them as optional answers. Many comments at the end of the survey included an explanation for one or more of the respondents' answers in that they were not allowed to leave any question blank even if they would have preferred to mark the question as not applicable. This may have skewed the results by including responses that were not valid. Finally, three of the questions were purely open-ended and another four questions, while multiple choice, provided the respondents with the opportunity to create their own alternative answer; this variance in responses required subjectivity to quantify answers for those questions. Further research is also needed to determine which liners are most durable and which ones are most comfortable for patients.

Conclusion The results of this survey will be beneficial for new practitioners as they build their knowledge about gel liners. Many elements factor into the decision of which liner might best suit a patient. In addition to manufacturer and material, practitioners must consider patient comfort, preference, suspension system, activity level, and liner durability. After years of experience it may be easy for a practitioner to develop habits that may not be in the best interest of every patient; as such, it is crucial to maintain an open mind when selecting what best meets each patient's needs. With such an individualized issue, it seems that further research would be beneficial to fully understand the impact that different gel liners have on patients.

Amy Watts, CPO, is a member of the American Academy of Orthotists and Prosthetists Lower Limb Prosthetics Society. She completed her O&P education at Century College, White Bear Lake, Minnesota. Watts has been in the profession for more than four years and earned her prosthetics certification in January 2013. She enjoys the variety in O&P, as well as the team approach to patient care that is practiced while helping patients regain their independence.

Academy Society Spotlight is a presentation of clinical content by the Societies of the American Academy of Orthotists and Prosthetists in partnership with The O&P EDGE.

References ALPS South. 2011. Retrieved from ALPS Prosthetic Products: www.easyliner.com/prosthetics.php Liston, J., and P. Stevens. 2012. Liner Selection: Diminishing the impact of impact . The Academy Today 8 (1): A-7-A-8. Covey, S. J., J. Muonio, and G. M. Street. 2000. Flow constraint and loading rate effects on prosthetic liner material and human tissue mechanical response . Journal of Prosthetics and Orthotics 12 (1):15-41. Coleman,. K. L., D. A. Boone, L. S. Laing, D. E. Mathews, and D. G. Smith. 2004. Quantification of prosthetic outcomes: Elastomeric gel liner with locking pin suspension versus polyethylene foam liner with neoprene sleeve suspension. Journal of Rehabilitation Research & Development 41 (4):591-602. Denune, J. 2005. Ready, set, relax . The Academy TODAY 1 (1):A-8. Fergason, J., R. Hayda, and D. G. Smith. 2006. Use of silicone gel liners for skin traction and preservation of limb length . Journal of Proceedings of the 2006 American Academy of Orthotists and Prosthetists Annual Meeting & Scientific Symposium : 36. Field, M. 1985. The development of a new interface . Orthotics and Prosthetics 39 (1):70-3. Francis, R. 2002. Use of the alpha liner to improve skin conditions . Journal of Proceedings of the 2002 American Academy of Orthotists and Prosthetists Annual Meeting & Scientific Symposium : 17. Francis, R. 2003. An improved socket system for transfemoral amputees . Journal of Proceedings of the 2003 American Academy of Orthotists and Prosthetists Annual Meeting & Scientific Symposium 26. Koepke, G. H., J. P. Giacinto, and R. A. McUmber. 1971. Silicone gel below-knee amputation prostheses. Inter-Clinic Information Bulletin 10 (12):13-5. Lehneis, H. R., D. Sung Chu, and H. Adelglass. 1984. Flexible prosthetic socket techniques . Clinical Prosthetics and Orthotics 8 (1):6-8. Swanson, A. B. 1972. Silicone-gel pads to improve end-bearing tolerance in lower-extremity amputees. Inter-Clinic Information Bulletin 11(9):13-7. The Ohio Willow Wood Company. 2011-2012. Products & Services, Liners. Retrieved from www.willowwoodco.com/products-and-services/liners

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