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An Investigation of Comfort Level Trend Differences Between the Hands-On Patellar Tendon Bearing and Hands-Off Hydrocast Transtibial Prosthetic Sockets

Manucharian, Stephan R. MA, MSc, CP, BOCO

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JPO Journal of Prosthetics and Orthotics: July 2011 - Volume 23 - Issue 3 - p 124-140
doi: 10.1097/JPO.0b013e3182248bf2
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A prosthesis, as defined by Encyclopaedia Britannica, is an artificial substitute for a missing part of the body. This research focuses on a lower limb prosthesis, specifically on a transtibial prosthesis, with an attempt to compare two alternative methods of socket design and assess the trends in the perceived comfort levels associated with such designs. Structurally, a transtibial endoskeletal prosthesis consists of a socket with its interface and a method of suspension, and a foot with a pylon. All the components of the prosthesis and their respective alignment interact in a certain way and affect the outcome of the fitting. The center of this research, a prosthetic socket, has the following functions: a) link the prosthesis to the amputee so as to give comfortable transmission of support and control forces whether the amputee is walking, standing, or sitting; b) contain the residual limb tissues to allow optimal biological functions; c) provide sensory information; d) protect the residual limb from the environment; and e) suspend the prosthesis.1 A prosthesis, therefore, is interfaced to the amputee's residual limb through the socket. The fit of the socket has been shown to be of critical importance to prosthesis users and is influenced by various factors. There is little agreement in the literature regarding the most effective way of interfacing a prosthetic limb to an amputee's residual limb. The quality of study design is inconsistent, and thus making interstudy comparison difficult. This combined with the individual nature of residual limbs and the unique requirements of each amputee may explain the lack of agreement in the literature. Further research is required to improve the understanding of biomechanical variables at the residual limb/socket interface and the relationship with user comfort levels. Knowledge of how such variables influence user comfort may lead to improvements in quality of socket fit. Linde2 in “A Systematic Literature Review of the Effect of Different Prosthetic Components on Human Functioning with Lower Limb- Prosthesis” offers a reference to only one study relating to socket design. Linde made an assumption that a vacuum-controlled socket environment provides a better fit; however, he suggested that this study should be interpreted with caution due to the scarcity of quality studies pertaining to socket design. A goal of prosthetic rehabilitation would be the restoration of function and comfort. Prosthetic prescription has an enormous influence on prosthetic outcomes related to function and comfort. Being aware of the amputee's needs, when prescribing individual components, is essential.3 Previous authors have investigated the incidence of residual limb pain, documented prosthesis use, and satisfaction among amputee population.4–8 Residual limb pain caused by inadequate socket fit has been shown to be the primary reasons for dissatisfaction with artificial lower limbs. Dillingham showed in a study of 78 trauma-related amputees that, although 95% tended to wear their prostheses extensively (greater than 80 hrs per week), only 43% reported satisfaction with prosthesis comfort. Similarly, Nielsen8 found that of 109 amputees, 57% reported moderate-to-severe pain most of the time while wearing their prosthesis. The findings of Legro inferred that the comfort and fit of prosthesis were the most important functional characteristics of prosthesis. According to Postema,9 amputees rate “absence of pain in residual limb” and “no fatigue during walking” as the most important subjective aspects of prosthesis use. Pain has been a continual problem for amputees as reported in the study by Ehde.10 This study found that 74% experienced residual-limb pain with a mean intensity of 5.4 on a scale of 0 to 10. The cause of limb discomfort is multifactorial. The components that influence the outcome of a transtibial prosthesis, as noted earlier are as follows: a) a socket that normally includes an interface and has a means of suspension and b) a pylon and foot. These components must be properly aligned to accommodate the needs of each individual. The prosthetic socket essentially is the interface between the amputated limb and the ground. Weightbearing, for an individual with an intact limb, is transferred through the skeletal structures; whereas, in an amputee, it must be transferred to the skeletal structures through the soft tissues of the residual limb. Because the residual limb is not “designed” to withstand the force associated with weightbearing and ambulation of the individual, a prosthetist must design an interface that would “adapt” the residual limb for such a task. For the end user of the prosthesis, the socket must be comfortable, functional, and, above all, pain free.

The definition of pain according to the International Association for the Study of Pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage.”11 This definition may well be applicable to describing discomfort in the prosthetic socket because it is often associated with physical pain. Pain intensity, or in this case, discomfort level, like other sensations and perceptions, is a private experience that displays considerable variability. In this study, the choice of the measurement instrument and the statistical procedures was partly determined by the earlier association.

There are two main designs of transtibial sockets or interfaces available to modern prosthetics: a) patellar tendon bearing (PTB) socket and b) total surface bearing (TSB) socket. The hydrostatic or hydrocast socket is considered by some researchers a variation of the TSB design.12–14 The author of this study adapted the former viewpoint based on the belief that TSB socket and hydrocast socket fit are based on a similar weightbearing principle.

PRE-PATELLAR TENDON BEARING SOCKET OVERVIEW

Before the era of modern prosthetics, most of the transtibial socket designs were developed empirically and without clear understanding of the weightbearing principles. Early designs incorporated various degrees of weightbearing in the prosthetic socket whereby the weight was transferred past the knee and onto the thigh using side joints and a leather thigh lacer.15 Such design had inherent suspension problems which resulted in migration of the prosthesis downwards in swing phase resulting in skin irritation on the residual limb. The design of the socket usually was open-ended, which also presented problems of edema and verrucous hyperplasia. The weight and bulkiness of the prosthesis also did not contribute to its comfort.16 Based on practical results, many prosthetists and surgeons expressed strong opinions on the weightbearing characteristics and the design of the prosthetic socket; however, there was no consensus on their part as to the best method that should be used consistently. Some practitioners suggested the creation of relieves in the socket for the areas that were intolerant to pressure or weigh bearing, such as the tibial crest, fibular head, and the distal end of the residual limb. Others were convinced that the soft areas of the residual limb such as the patellar tendon, anterior compartment musculature, posterior aspect of the limb, and tibial flare could sustain more localized high pressure.13,17

PATELLAR TENDON BEARING SOCKET

The need for research projects focused on prosthetic socket design led to the Symposium on Below Knee Prosthetics at the University of California Berkeley Biomechanics Laboratory in 1957. Research objectives were developed at that symposium that eventually led to the PTB socket design formally introduced in 1959.18 It offered many revolutionary concepts for the time including the statement that the majority of the transtibial amputees fitted with a PTB socket did not require side joints and a thigh lacer.18 A new total contact theory also stated that distal contact was necessary and beneficial; whereby, weight tolerant and intolerant areas of the residual limb were identified and the socket biomechanics were defined for each of the progression phases of gait. Although currently the PTB socket design is still being used in practice by many practitioners, it is gradually being replaced with the more contemporary TSB or hydrostatic socket designs.

TOTAL SURFACE BEARING SOCKET

The TSB concept goes further than the PTB theory in that the pressure should be distributed even more equally across the entire surface of the transtibial residual limb. This theory, in contrast with the PTB concept, concentrates on the suggestion that even the previously accepted weight-sensitive areas now are able and should carry a portion of the patient's weight.20,21 Some earlier TSB techniques required an extremely accurate impression of the limb and meticulous rectification of the mold. Later on, with the development of advanced gel materials used as an interface between the limb and the rigid socket, the focus of the TSB theory shifted away from the labor-intensive rectification requirements as the physical characteristics of the gel interface allow for a larger margin of error in designing the socket. Several TSB rectification techniques still include certain elements of the PTB design, such as a patellar bar; however, the concept of creating an environment that applies pressure over all aspects of the limb is undoubtedly maintained. In modern prosthetics, this is most commonly achieved by applying a gel liner on the residual limb, taking an undisturbed plaster impression over the liner, then globally reducing the positive mold by a specific amount.

HYDROSTATIC SOCKET

The hydrostatic or hydrocast socket is based on a system originally designed by Murdoch22 in 1965 called the “Dundee” socket. In an attempt to eliminate in casting and rectification methods, all the factors relating to manual dexterity, Murdoch developed a no-hands technique using a hydrostatic tank for impression taking <50% weightbearing. This approach, further developed by Klasson, suggested creation of a transtibial socket with the environment designed so that the pressures are distributed equally to every point within a socket to minimize localized weightbearing areas.23 This concept is based on Pascal's principle of fluid dynamics. As described by Halliday and Resnick,24 this principle states that in a fluid at rest, the pressure on any surface exerts a force perpendicular to the surface and any additional pressure will be transmitted equally to every point in the fluid. Thus, the hydrostatic socket is designed without identifying any specific weightbearing areas. To obtain a socket fitting that supports the patient's weight in a hydrostatic manner, a pressure casting tank is used. The tank applies equal hydrostatic pressure on the limb as a negative mold is obtained. The positive mold normally does not require any rectification procedures other than light wire screen smoothening.

Although the methods used to achieve the appropriate fit differ between the TSB and hydrocast sockets, the concept of even (or almost even) distribution of pressure within the socket makes these two designs similar to each other and in contrast with the PTB concept. With the TSB socket, the rectification of the positive model is normally performed manually, which makes it more labor intensive and dependent on the hand dexterity of the practitioner or technician as compared with the hydrocast socket, the production of the positive model of which is virtually hands-off and with a high level of repeatability. In this study, for the purpose of clarity, the author uses the term “hydrocast TSB (HCTSB) socket.” The HCTSB socket allows the uniform pressure distribution to be perceived as more comfortable, as opposed to a PTB socket having selected areas of weight distribution. This study will attempt to investigate the trends in socket comfort perception within the variables of socket design.

LITERATURE REVIEW

Several attempts have been made to compare the fit of transtibial sockets of different designs. Convery and Buis25,26 in two consecutive studies analyzed dynamic residual limb/socket pressure distribution in PTB and hydrocast sockets. Force-sensing resistors were used to measure dynamic residual limb/socket interface pressures during the gait of a transtibial amputee. A total of 350 pressure sensor cells were attached to the inner wall of PTB and hydrocast sockets. Data were sampled at 150 Hz during approximately 0.8 sec of prosthetic stance of gait. The results showed that the pressure gradients within the hydrocast socket were less that those of the PTB socket. The proximal “ring” of high pressure in the PTB socket was replaced with a more distal pressure in the hydrocast socket. Engsberg et al.27 compared the fit of traditionally rectified PTB sockets and unrectified sockets, which were fabricated by retaining the shape of the residual limb; except for a distal end pad, an alginate gel process was used instead of casting. Forty-three adults with unilateral transtibial amputations were tested after randomly wearing both rectified and unrectified sockets for at least 4 weeks. Testing included a gait analysis, energy expenditure, and the Prosthesis Evaluation Questionnaire (PEQ). Results indicated no significant differences between sockets for gait speed and timing, gait kinematics and kinetics, and gait energy expenditure. There were also no differences in the PEQ, and 37% of subjects selected the rectified socket, 58% selected the unrectified socket, and 5% selected to use both sockets as their exit socket. The researchers concluded that there seemed to be more than one paradigm for shaping prosthetic sockets, which might be helpful in understanding the mechanisms of socket fit. The researchers, however, did not differentiate between PTB and TSB designs.

Goh et al.23 evaluated residual limb/socket interface pressure in amputees wearing a socket developed by a pressure casting system. The sockets were fabricated while the subjects placed their residual limbs in a hydrocast pressure chamber. Pressure was applied while they adopted normal standing positions. A specialty built pressure transducer was used for measuring pressure distribution in the socket while the subjects were standing and walking. Five unilateral transtibial amputees were involved in this study. The investigators expected that a hydrocast socket produced equally distributed pressure at the residual limb/socket interface, deviating from the conventional belief that pressure varies in proportion to the pain threshold of different tissues in the residual limb. Although the hydrocast technique was able to produce comfortable fitting sockets, no standard hydrostatic pressure profile for this type of socket was observed. Pressure profiles at three different moments of the gait cycle did not correlate with the expected pressure profiles.

In a different study, the same researchers compared pressure distribution between socket interfaces and residual limbs in PTB and hydrocast sockets.28 This was a pilot study involving four transtibial amputees who were fitted with both conventional PTB and hydrocast sockets. The same pressure transducer was used as in the previous study. Residual limb/socket interface pressure profiles were recorded for each subject wearing the two types of sockets during standing and walking. As some subjects exhibited similar anterior- posterior or medial-lateral pressure profiles for both prostheses, especially during push-off, other subjects exhibited high pressure distally in the hydrocast socket or higher pressure concentration at the proximal region in the PTB socket. The results were inconclusive due to the low number of subjects involved.

In an earlier study, Goh et al.29 evaluated the pressure distribution at the residual limb/socket interface in four transtibial amputees wearing the conventional PTB socket using the same pressure transducers. The goal of the study was to compare the obtained pressure profiles with the pressure profiles predicted by Radcliffe30 in 1961. Radcliffe assumed that a transtibial amputee is able to walk in a manner similar to a normal bodied person. During heel contact, the line of action of ground reaction force (GRF) acts anterior to the knee; causing the knee to extend. The hamstrings, acting to prevent knee hyperextension, would cause high pressure concentration at the patellar tendon and the posterior distal region. During mid-stance, the GRF would be acting posterior to the knee; causing the knee to buckle. This is resisted by the action of the quadriceps and forceful extension of the hip; and thus, high pressure concentration occurred at the patellar tendon, anterior distal area, and the popliteal region. During toe-off, where the line of action of the GRF remains posterior to the knee, the same three areas at the patellar tendon, anterior distal, and popliteal regions experienced high pressure concentration. Goh showed that none of the subjects demonstrated a pressure profile as anticipated by Radcliffe; Goh concluded that this was a result of the GRF and other factors affecting a pressure profile in a transtibial prosthetic socket. Kahle12 compared the fit of the PTB and ICEX® direct pressure casted molded sockets. Twenty-five subjects participated in this study; each subject was fitted with both types of sockets. Socket shapes were compared using physical measurements; tissue elongation and residual limb pistoning was analyzed by means of radiographs; and a verbal questionnaire was administered as well. The participants were asked to give their preference for either of the designs, based on comfort level. Most subjects (68%) preferred the ICEX pressure-formed socket design. Sellers et al.14 also compared the outcome of the PTB socket with the ICEX TSB socket. Twenty-six subjects participated in this study and were divided into two groups. One group received an ICEX direct molded TSB socket and the other group received a conventional PTB socket. Prosthetic Evaluation Questionnaire scores, mobility-related activities of daily life, and gait characteristics at base line and at 3 months after initial socket fitting were compared. Both sockets performed equally well in terms of patient satisfaction, mobility-related activities performed during daily life and gait performance.

Yigiter et al.31 investigated the effectiveness of PTB and TSB sockets on prosthetic fitting and rehabilitation. Twenty subjects were fitted with prostheses with both PTB and TSB sockets; prosthetic training was given for 10 days that included balancing activities, weight shifting, and gait exercises. Data analyses showed that prostheses with TSB sockets were perceived as lighter and having better suspension than the prostheses with PTB sockets. There was a statistically significant difference between the two socket types in walking and in other ambulation activities except in sitting and standing up from a chair, in favor of the TSB socket. Muller32 describes various transtibial TSB casting.

Klasson and Buis33 stated in their Manual that there are three distinct philosophic design methods for a prosthetic socket: a) the direct method, b) the iterative method, and c) choice from alternatives. The direct method is used when it is possible to go straight to a design which satisfies the expected specification, as all necessary information is available and the design and development process is under total control. If a direct method is available, it should be the best, the fastest and the cheapest. This fits in to the scheme of quality management concepts where it would be appropriate to “do it right from the start.” The iterative method involves trial and error processes of many current methods, such as hand casting. Hand casting has results that are excellent but very seldom similar and reproducible. Reproducibility would help prosthetists in recording measurable outcomes. Pressurized casting can offer surface matching and volume matching reproducibility, but only in static situations. The prosthesis must be used in a dynamic mode of operation and final matching should take place in both dynamic and static modes. The socket should respond to load application with some adaptation at constant volume. The socket design should use some type of measurable methodology.

Quality management techniques of the past were passed down from the master craftsman to the apprentice. One of the limitations of the craft approach was that relatively few goods could be produced accurately; thus, an advantage was that each socket produced could be individually shaped to suit the patient. It is extremely difficult for the craft approach to show reproducibility and consistency. Quality improvement standards may need to be implemented in the prosthetics profession. They are used for components of pylons and feet. Why not sockets? There is an abundance of literature on quality standards in manufacturing of mass-produced prosthetic components. Similar quality standards should be developed for production of prosthetic socket interfaces.

The concepts of surface matching and volume matching are used to provide rationally defined socket design goals. A summary of some recent attempts at using the direct method in socket manufacturing techniques is presented below. The newest generation of ICECAST® methodology uses the direct method of socket manufacturing, and thus eliminating the need for casting and rectification. Johannesson34 used the ICEX system in a Swedish hospital for 10 years and found that the ICEX facilitated rehabilitation. This was evident especially with delayed wound healing. Most of the sockets were directly formed and delivered, whereby 27% had their sockets changed within 6 months and 73% in 1 year. Fothergill35 reported on the newer ICECAST Anatomy that represents a further development of the original ICECAST pressure casting system.

Contour Cell™ shaping-chambers positioned over soft tissues areas can be inflated independently to achieve displacement of the tissue, creating a more nearly anatomically correct socket shape. The increased control over the socket shape enhances user comfort, stability, and rotation control. Because the residual limb is “loaded” by the pressure casting instrument during casting, it is possible to eliminate the need for rectification of the resultant socket shape. TSB sockets cast with ICECAST Anatomy represent an efficient and consistent tool for transtibial socket casting. Fabrication using the ICECAST and ICEX provide a technique using the direct method as mentioned in Klasson and Buis.33 Using the ICECAST as a standardized, easily documented procedure, sockets are produced with repeatable results. It is a method that is easily implemented; thus it is independent of a prosthetist's skill and experience and reduces manufacturing time. Volume matching and surface matching are theoretically possible with this system. With TSB socket designs, volume and surface matching are essential. For successful long-term use, the amputee must understand how to regulate volume throughout the day. This can be accomplished with socks and pads, as perfected volume adjustable sockets have yet to be designed. It would seem that The ICECAST-ICEX system may be a rational attempt at the direct method.

Another recent development in the direct method is presented by Chesapeake Medical Products, Inc., as the SocketCone™ technology.36 This technology in conjunction with ICECAST or hydrocast may be a positive application. SocketCones are made from a low temperature of 160° Fahrenheit thermoplastic reinforced with Kevlar® material. SocketCones are available in three sizes with two distal end adaptors to adapt to standard four-hole plates and shuttle locks. The system has the versatility of being used with definitive or preparatory prosthetic systems with an added benefit of never using plaster. This is another fine example of using the direct method.

Wu,37 at Centre for International Rehabilitation (CIR; Chicago, IL), developed one more example of the direct method - a transtibial socket fabrication system based on the dilatency process patented in the 1940s. The system uses sand to replace plaster of Paris for forming negative sand molds and positive sand models. Clinical trials suggest that fabrication times are approximately 60 minutes from patient evaluation and casting to dynamic alignment. The final sockets can be adapted to existing prosthetic components. The CIR casting system advantages are: (a) uses low-cost and low-maintenance equipment; (b) replaces plaster of Paris with sand, and (c) sockets are fabricated sockets using thermoplastic vacuum forming or resin lamination techniques. The CIR casting system is a technique that can assist in the rapid and inexpensive fabrication of transtibial sockets during a single clinic visit. Jensen et al.38 reported that sand casting resulted in satisfactory fittings compared with traditional prosthetist casting with plaster of Paris. Sand casting was tested because it represents a possible improvement in consistency of prosthetic fit of a transtibial prosthesis and reduces the influence of technical skill in relation to Plaster of Paris casting.

A further development of the original sand casting system was proposed by Reddy.39 Reddy redesigned the equipment that decreased the production time. This sand-casting procedure had a success rate of approximately 90% and was deemed to contribute to a higher consistency of good fits.

Goh40 of the National University of Singapore have collaborated on their version of a direct method using the direct pressure cast (DPCast) prosthetic socket with the hydrostatic pressure casting concept, using carbon fiber impregnated with resin. This seems to be similar to the ICEX methodology using direct lamination on the limb. The authors assumed that Pascal's principles of fluid dynamics are at work in their design and that pressure at one point will simply be transferred by the fluid principle to other accommodating soft tissues. The DPCast socket was successfully fit on 10 subjects. A new system added to the armamentarium of potential sand-casting equipment was developed in India by Mobility India.41 The complete system included vacuum forming, lamination station, and sand-casting capabilities. As stated by Convery et al.,42 “The consistency of production methods must be known before reliable comparison methods can be made. Without knowledge of intra-method consistency, it is impossible to draw any conclusions when comparing socket designs. Is it possible that we can arrive at consistency with computer applications? There is a question of how accurate are CAD measured prosthetic sockets.”

Geil43 stated that it is crucial that techniques used to produce limb sockets be accurate, repeatable, cost-effective, and have high patient utility. McGarry et al.44 from University of Strathclyde used a TracerCAD system to determine its accuracy when measuring a model of a transtibial limb of known dimensions and volume. Results showed that the TracerCAD measurement was not as consistent on a more complex transtibial model as for the original cylindrical model. Sanders45 reported that electronic shape files from 10 different manufacturers showed that quality varied considerably among the different manufacturers. This remains to be a challenge for central fabrication facilities. In contrast to the above, Oberg et al.46 stated in his study that the quality of computer assisted design (CAD)-controlled alignment method sockets was at least at the same level as conventionally made ones.

Jia et al.,46a from the Hong Kong Polytechnic University, concluded that dynamic finite-element (FE) models should be developed in association with kinematic information of the limb and prosthesis, material inertia, and variable GRF during walking. No technology currently exists to provide real-time continuous information on the internal distribution of mechanical stresses in the residual limb during fitting of the prosthesis or while using it, and this severely limits patient evaluations. In 2007, Portney48 stated that a clinically oriented patient-specific FE model of the residual limb was developed for real-time stress analysis. For this purpose, they used a custom-made FE code that continuously calculates internal stresses in the residual limb, based on boundary conditions acquired in real-time force sensors located at the limb-prosthesis interface. Validation of the modeling system was accomplished by means of a synthetic phantom of the residual limb, which allowed simultaneous measurements of interface pressures and internal stresses. Human studies were conducted in five transtibial patients. The dimensions of bones and soft tissues were obtained from x-rays of the residual limb of each patient. An indentation test was performed to obtain the effective elastic modulus of the soft tissues of the residual limb. Seven force sensors were placed between the residual limb and the prosthetic liner, and subjects walked on a treadmill during analysis. The authors concluded that real-time patient-specific FE analysis of internal stresses in deep soft tissues of the residual limb in transtibial amputation patients is feasible. This method is promising for improving the fitting of prostheses in the clinical setting and for protecting the residual limb from pressure problems and deep tissue injury. Portney49 continued these studies in 2008 to analyze the mechanical conditions in the muscle flap of transtibial amputation during load bearing using their patient-specific modeling approach which involves a magnetic resonance imaging scan, interface pressure measurements between the residual limb and socket and three-dimensional non-linear large deformation FE modeling to quantify internal soft tissue strains and stresses. The conclusion is that their patient-specific modeling method is an important tool in understanding the etiology of deep tissue injury in the residual limbs of transtibial patients. A new tool that could quantify the interface interactions would potentially be of great value, because it would reduce the chance of the prosthetist making an error at the fitting stage and could be used to validate finite element analysis models for investigations into understanding the residual limb/socket biomechanics. The main problem that needs to be addressed is the quantification/visualization of the residual limb/socket interface interactions and formulation of a relationship between the quantified values and the comfort of the prosthesis.50

Another technology that has the potential for integrating computer technology into prosthetic socket design is “rapid prototyping technology.”51 Rogers52 tested the feasibility of using selective laser sintering to fabricate a functional transtibial socket. The socket combined a rigid outer shell with a variably compliant inner shell and incorporated a fitting for a pylon directly into it. A comparison of socket performance suggested improved comfort, greater step symmetry, and similar lower-limb joint function. Herbert53 investigated the use of a rapid prototyping technology known as 3D printing. Although this system produced sockets that were lacking in strength and durability, this concept should still have merit with further research into better materials. Rovick54 at the Northwestern University used the fused deposition modeling approach called squirt shape, which integrates socket and pylon into a single structure. Hsu47 from Fooyin University integrated a CAD application programming interface of SolidWorks and Rapid Prototyping of fused deposition modeling to develop a rapid prototype system. This technology of rapid prototyping has the potential for using computers to measure and make a socket and possibly include a pylon. This may possibly be a great leap forward in having a computer-generated prosthetic socket using the direct method as proposed by Klasson and Buis.33

OUTCOME MEASUREMENT TOOLS OVERVIEW

Satisfaction With Prosthesis

Satisfaction With Prosthesis (SATPRO) is a self-report questionnaire consisting of 15 questions organized in a four-level Likert scale. It is designed to assess the satisfaction with the prosthesis and the services provided.55 Only 4 of 15 questions (27%) specifically address the comfort of the prosthetic device; the others cover physiological, utility, cosmetic, and satisfaction with practitioner services issues.

Prosthetic Profile of the Amputee

Prosthetic Profile of the Amputee (PPA) is a 45-question self-report questionnaire that measures the factors potentially related to prosthetic use and the actual use of the prosthesis by individuals with a lower limb amputation after discharge from rehabilitation.56 This tool provides a very broad assessment of the subject's physical condition, prosthesis, prosthetic use, environment, leisure activities, and general information.

Trinity Amputation and Prosthetic Experience Scales

Trinity Amputation and Prosthetic Experience Scales (TAPES) consists of 54 items subdivided into four sections. Most of the items use a five-level Likert-type scale. Although this instrument addresses the issue of prosthetic comfort, it is primarily aimed at examination of the psychosocial processes involved in adjusting to a prosthesis, the specific demands of wearing a prosthesis and the potential sources of maladjustment.57

Prosthesis Evaluation Questionnaire

PEQ is a self-report instrument that contains 54 questions organized into nine functional domain scales and uses the Visual Analogue Scale (VAS). Each individual domain is validated separately and may be used independently. One of the nine domains covers the issue of the quality of the prosthetic fit. It consists of eight questions. Three of the eight questions investigate such sensations as phantom pain; two questions cover possible presence of pain in the contralateral limb; one question addresses inquires about the perceived weight of the prosthesis; and the remaining two questions (25%) specifically address the issue of socket comfort.

Socket Comfort Score

Socket Comfort Score (SCS) is a single-question self-reporting tool that uses an 11-point numerical rating scale (NRS) specifically validated for assessment of prosthetic socket fit comfort.58 The previously mentioned outcome measures, although comprehensive from the standpoint of the broadness of coverage that includes comorbidity, psychological, social, utilitarian, and other aspects of prosthetic wear, fail to address the specific area of socket comfort as a standalone parameter. Comfort, like pain, is a very subjective symptom and therefore it may be appropriate to adapt measurement methods established in pain clinics, such as the NRS for quantifying and communicating socket fit comfort. Participants were asked to rate the comfort of their socket on a 0 to 10 scale where 0 represented the most uncomfortable and 10 represent the most comfortable socket imaginable. Ratings of clinical evidence of poor fit were recorded independently. After the appropriate intervention, the patients gave the new numerical ratings of comfort. The analyses of the data showed repeatability, criterion-related validity, and sensitivity to change of SCS.

RESEARCH METHODOLOGY

ETHICAL APPROVAL

This study was approved by Fox Commercial Institutional Review Board, Springfield, IL on May 20, 2008, and was assigned number 080516-001.

HYPOTHESES

The key hypotheses of this study are as follows:

H10: Initial and final comfort levels of the PTB and HCTSB socket types will be identical.

H20: There will be no change between the initial and final comfort level measurement within each socket type.

Which will be tested against the alternative:

H1A: Initial and final comfort levels of the PTB and HCTSB socket types will be different.

H2A: There will be either improvement or decline of comfort level between the initial and final measurements within each socket type.

SUBJECTS

Two convenience samples of similar size of adult transtibial amputees were selected for this study from existing patients of Orthopedic Arts Laboratory, Inc, a prosthetic patient-care facility located at 141 Atlantic Avenue, Brooklyn, NY, who had been fitted with new prostheses. The following criteria were used in selecting appropriate candidates. The candidates are successful wearers of definitive prostheses before the last fitting. In addition, candidates with the following conditions were excluded: a) amputation of any level of the contralateral lower limb and b) open wounds of any size on the residual limb. The following subject background data were used in this study: a) age, b) gender, c) activity level, as defined by Medicare Functional Classification Levels (MFCL), d) cause of amputation, e) side of amputation, f) time after amputation, and g) previous socket type. Group 1 included 21 subjects who were fitted with transtibial prostheses with PTB type sockets and group 2 included 15 subjects who were fitted with transtibial prostheses with HCTSB type sockets.

MEASURES

There are numerous tools available for outcome measurement in lower-limb amputee rehabilitation as presented in the previous chapter; however, a limited number focuses on the specific issue of comfort of a prosthetic fitting. As the goal of this investigation was to analyze the perceived comfort of the prosthetic socket, the author was searching to find a validated outcome measurement tool that would specifically focus on that issue.

The SCS instrument was used by the author for the purposes of this research project. Below, the author will present the main reasons why the other outcome measurement tools were deemed less inadequate for this investigation. The SATPRO questionnaire uses a four-level Likert scale and therefore requires nonparametric tests for statistical analysis, which are not as powerful as parametric; only a quarter of the questions cover the specific issue of prosthetic socket comfort. The PPA tool, as it is designed for a much broader assessment of an amputee, dedicated very few questions that address socket comfort; it also uses a combination of different scale types that makes statistical analysis difficult. The TAPES instrument was not applicable to the investigated subject matter due to a different assessment goal—it focuses mainly on psychological issues. Although the PEQ tool is a well-regarded, validated comprehensive outcome measurement instrument, it aims to assess prosthesis-related quality of life and has very few items covering the socket comfort issue, which was the center of this investigation, and thus making it less appropriate for this project.

The SCS, used in this investigation, is a validated self-reporting tool that focuses specifically on the issue investigated in this research project. It is also very brief and easy to administer, making potential subjects agree to the participation in the study with more eagerness. The SCS is a verbally administered tool and consists of the following single question: “On a scale from zero to 10, if zero represents the most uncomfortable socket you can imagine and 10 represents the most comfortable socket you can imagine, how would you score the comfort of the socket of your artificial limb at the moment?” Using patient decision aids such as the SCS instrument can help promote evidence-based decision-making processes.59 Decision aids help patients to participate with their practitioners in making deliberative, personalized choices among healthcare options. The key elements of decision aids have been described by the Cochrane Collaboration.60 The use of decision aids is usually reserved for circumstances in which patients need to carefully deliberate about the personal value of the benefits. Evaluation studies from a Cochrane systematic overview have shown that decision aids improve decision making. A critical challenge during the next few years will be developing best practices for deploying those decision aids that have been validated in clinical practice so that they are used and promote evidence-based decision making that is consistent with patient values.

DESIGN AND PROCEDURE

A retrospective chart review was used to collect and analyze the data for this double post-test, two-independent-group design study. Each group received a different type of intervention.

Subjects of group 1 were fitted with prostheses with the PTB-type sockets. The casting and rectification procedure were performed according to the training manual of Northwestern University Prosthetic-Orthotic Center, Chicago, IL. Subjects of group 2 were fitted with prostheses with the HCTSB-type sockets using a weightbearing hydrocast technique. For this purpose, a pressure cast tank was constructed. It was made from a tough synthetic material, polyvinyl chloride (PVC), in a shape of a cylinder of 23 cm in diameter, 68-cm high, and 8 mm in the thickness of the wall. The bottom of the cylinder was sealed with a PVC cap and designed with a flat external surface by means of acrylic resin. Provisions were made for a water inlet and outlet by rubber water hoses in the lower portion of the tank. A layer of heavy-duty polyethylene bag was placed inside the tank, the upper portion of which was reflected over the top circular opening of the tank; heavy-duty pressure-sensitive adhesive tape was used to secure the polyethylene bag over the tank. A circular rubber gasket was placed over that seal and secured tightly by means of steel base clamps. An air valve was incorporated in the upper portion of the tank to initially evacuate air trapped between the tank wall and the plastic lining (Figure 1).

F1-4
Figure 1.:
Pressure tank construction.

The following casting technique was used for HCTSB socket:

  1. Apply tube gauze onto the residual limb; secure it around the subject's thigh with medical-grade adhesive paper tape.
  2. Mark mid-patellar tendon for reference purposes with an indelible pencil.
  3. Apply plaster wrap cast over the residual limb. Make sure the wrap is of uniform thickness (approximately five layers of plaster bandages).
  4. Ask the subject to stand up holding on to parallel bars or a handle bar; place his/her residual limb in the tank.
  5. Lower the water level in the tank before beginning the casting procedure. This creates a vacuum between the polyethylene bag and the inner surface of the tank tube, making the bag cling to the tank wall and thus creating an accessible space for insertion and positioning of the residual limb.
  6. Start pumping up water into the tank until the water level starts supporting the residual limb.
  7. Ask the subject to put his/her body weight onto the amputated side and raise his/her contralateral limb.
  8. Insert a weighing scale under the contralateral foot and ask the subject to stand in his/her normal standing position, with his/her hands on the parallel or handle bars only for balance support, but not for weightbearing.
  9. Monitor the reading on the weighing scale to insure that approximately one-half of his/her body weight is placed on the weighing scale.
  10. Monitor subject's right and left anterior-superior iliac spines to ensure level standing.
  11. Once the plaster wrap hardens, depressurize the pressure tank, and remove the residual limb from the tank.
  12. Remove the plaster wrap from the residual limb.

No positive model rectification was performed except for smoothening of minor irregularities.

Sockets for subjects in both groups were fabricated using 6-mm Pelite inner liner with a 12 mm Plastizote distal cushion and acrylic outer interface. A silicone airtight suspension sleeve was used as a suspension means. An automatic expulsion valve was fitted distally in the sockets to evacuate air trapped in the socket. Reasonable attempts were made to maintain the previous foot/ankle design.

The subjects underwent usual fitting and alignment procedures. On completion of this stage, the subjects were asked to assess the socket comfort using the self-report SCS instrument as described earlier. The subjects were then asked to take possession of the prostheses and start using them on a daily basis. The subjects were instructed to contact the researcher in case adjustments were required. The number of adjustments performed during this first month of use of the prostheses was noted. The subjects were reassessed 1 month later for socket comfort using the self-report SCS questionnaire.

The goal of the study was to compare the outcomes of each type of intervention. The outcome was measured immediately after the intervention and 1 month thereafter. The measuring instrument used was an 11-point single question NRS. This type of experimental design is generally strong in internal validity. The study was conducted by a single investigator.

The threshold for significance used in this study was p of 0.05 of the occurrence of type 1 error. The two hypotheses tested were expressed in two-tailed form, indicating that significant differences in either the positive or negative direction would be sufficient to reject the null hypotheses.

RESULTS

The full sample consisted of 36 subjects. These subjects were divided into two groups: those who were fitted with transtibial prostheses with PTB-type sockets (PTB group, N = 21) and those who were fitted with transtibial prostheses with HCTSB-type (HCTSB group, N = 15). Table 1 exhibits the category frequencies of the key variables that define the sample.

T1-4
Table 1:
Sample characteristics

Although the data produced by a Likert-type rating scale used in this study are of ordinal nature, the author of this study chose to use parametric statistical tests for their analyses. A review of the pertinent literature revealed that the quantitative ordinal data produced by such scales as the VAS and Likert scales generally may be treated as interval, provided the scale item has at least five and preferably seven categories. In this study, an 11-point Likert-type scale was used, which increased the appropriateness of the data to be analyzed by parametric procedures.61 The statistical literature supports the robustness of t tests of mean differences and correlations to violations of normality assumptions produced by the use of ordinal scales.62–66 Some researchers suggest that quantitative ordinal data should be analyzed using both parametric and non-parametric procedures.67 Some who conducted such comparison conclude that the tests yielded similar results.68 However, such precautions are generally not necessary except in cases of borderline significance.

Descriptive statistics on initial and final socket comfort levels for full sample and for each socket type group is presented in Table 2.

T2-4
Table 2:
Initial and final SCS levels

The initial and final socket comfort levels for the PTB and HCTSB groups were compared through the use of t tests for differences in independent groups. The results of these analyses are shown in Table 3. Levene's test for the homogeneity of variance indicated that the variances were not significantly different. The t tests for both measures were significant and indicated that the comfort levels in the PTB group were higher than in the HCTSB group.

T3-4
Table 3:
Differences between groups on socket comfort measures

The differences within groups between the initial and final socket comfort levels were assessed using paired t tests. The results of these tests are reported in Table 4. As can be seen there, the difference between comfort levels was only significant for the HCTSB group.

T4-4
Table 4:
Differences within groups on socket comfort measures

Analyses were conducted within each group and for the overall sample to determine whether there was any relationship between a variety of demographic and treatment condition variables and the measures of socket comfort. The results of these analyses are summarized in Table 5. Only two variables exhibited significant relationships with socket comfort. In the PTB group, Time since amputation exhibited a significant positive relationship with Initial Socket Comfort level. In both groups, socket comfort levels were significantly different between previous socket types.

T5-4
Table 5:
Relationships with socket comfort level measures for PTB group, HCTSB group and total sample

To further explore the latter, an analysis was conducted to compare the socket comfort levels of subjects whose socket design had changed from before the study. During this investigation, four subjects in the PTB group changed from TSB to PTB socket type; nine subjects in the TSB group changed from PTB to TSB socket type. This analysis was conducted within PTB and HCTSB groups, and for the overall sample. The results are presented in Table 6. In both the PTB and HCTSB groups, and in the total sample, the initial and final socket comfort levels were higher for subjects whose socket types had not changed. These differences reached statistical significance in all of the comparisons except for the final socket comfort level in the PTB group, where it barely missed significance as the result of adjustments necessitated by the finding of unequal variances between the two socket-changed groups.

T6-4
Table 6:
Effect of socket type change on socket comfort levels

Finally, the effect of the need for adjustments on ratings of socket comfort levels was analyzed. First, because the PTB group had only four adjustments among its 21 members, it was decided to recode the number of adjustments for all subjects into 0 (=no adjustments) and 1 (=1 or more adjustments). The change in initial and final socket comfort levels were computed as the arithmetic difference between the initial and final socket comfort levels. There was no need to residualize the initial level out of the difference because the initial level correlated at only −0.027 with the difference. The changes in comfort levels for the two adjustment subgroups were compared by t tests for the PTB and HCTSB groups and for the overall sample. The results of this analysis are presented in Table 7. The findings in that table reveal that adjustments were associated with significant decreases in the mean comfort levels of the PTB and HCTSB groups and in the sample as a whole. In all cases, over the course of the study the comfort levels of subjects with no adjustments improved and the comfort levels of subjects who received adjustments got worse.

T7-4
Table 7:
Effects of adjustments on socket comfort levels

The finding that socket comfort levels tended to decrease as the number of adjustments increased for subjects who required adjustments of their prostheses, seemed counter-intuitive and prompted further exploration of the data. It was conjectured that such decreases in comfort accompanying adjustment were more likely associated more recent amputations. For this analysis, due to small sample size, it was decided to recode time since amputation into the following: 0 (=<36 months), 1 (=>36 months). However, it was found that among those who had changed socket types, recency of amputation was not associated with differences in socket comfort levels (t = 0.066, p = 0.948). Among both more recent (36 months or less) and less recent (more than 36 months) amputees, those whose socket design had changed had significantly more adjustments than those who had no such change (t = −2.283, p = 0.036, 16 df and t = −4.949, p < 0.001, 16 df, respectively). Finally, among both more recent (36 months or less) and less recent (more than 36 months) amputees, those whose socket design had changed reported significantly lower socket comfort levels than those who had no such change (t = 0.251, p = 0.005, 16 df and t = 5.517, p < 0.001, 16 df, respectively).

It was also conjectured that the HCTSB socket design works less well for subjects whose amputations were caused by peripheral vascular disease (PVD) conditions as compared with those whose amputations were traumatically caused. This was thought to result in more adjustments being required and in lower socket comfort levels. However, these expectations were not borne out by the data. Subjects with traumatically caused amputations who changed to the HCTSB socket design actually required more adjustments than those with PVD-caused amputations (means = 2.67 vs. 1.60, although this difference failed to reach significance due to the small sample size). In addition, subjects with traumatically caused amputations had lower SCS (means = 4.0 vs. 5.9, which just barely failed to reach significance: t = −2.310, p = 0.056).

DISCUSSION OF RESULTS

The following limitations were observed in relationship to the results yielded by this study.

  1. No randomization of subjects: the study analyzed convenience samples of subjects who had been already fitted with new prostheses in an existing clinical setting. Convenience sampling is a type of nonprobability sampling that involves the sample being drawn from that part of the population which is close at hand. Therefore, the researcher using such a sample cannot scientifically make generalizations about the total population from this sample because it would not be representative enough. However, convenience sampling is acceptable and very useful for pilot studies or trend analyses like this one.
  2. Unequal group sizes: N1 = 21, N2 = 15. However, the different group sizes did not affect the statistical results. In the case of the t tests for differences between the groups, the standard error of the difference is the pooled standard error, computed by using the group sizes as weights for each group's contribution to the pooled estimate. Thus, the difference in group sizes did not exert any effect on the test for the difference between the groups. For the within group tests (between occasions), there was actually lower power to detect a significant difference for the smaller group, and yet it was this group for which a significant difference was detected.
  3. The majority of subjects had long-term clinical relationships with the investigator and the author's opinion is that this fact might have influenced the subjects' acceptance or non-acceptance of the alternate socket designs for their prostheses.
  4. Both PTB and HCTSB sockets were fabricated using Pelite inserts to reduce the variables of different material properties. Although PTB-type sockets are routinely fabricated with this type of inserts in modern practice, they are not as commonly used for TSB sockets, for which gel inserts are more popular.

The study yielded statistically significant results, showing that the comfort levels experienced by subjects fitted with PTB sockets were higher than those of the subjects fitted with HCTSB sockets both initially and 1 month later. Between the initial and the final comfort level assessments, comfort levels increased for the PTB group and decreased for the HCTSB group. The fact that most subjects favored the PTB design may mean for the clinician that a) PTB-type designs, with all their shortcomings, should not be discarded as outdated yet; b) although theoretically the hydrocast socket design ensures better surface and volume matching in a static situation, the dynamic nature of prosthetic fittings may interfere with “the ideal fit.” Subjects' age, activity level, cause of amputation, and gender did not exhibit any significant relationship with the outcome measurements. The only variable that did exhibit a significant positive relationship with the initial socket comfort level was time since amputation in the PTB group only. In both the PTB and HCTSB groups, and in the total sample, the initial and final socket comfort levels were higher for subjects whose socket types had not changed. Although it is true that socket type changed for more subjects in the HCTSB group than in the PTB group, 40% versus 19%, a significant difference in initial comfort levels between the socket-changed and socket-not-changed groups was evident for both socket type groups. This difference was found consistently on the initial and final comfort measures for the PTB and HCTSB groups and for the sample as a whole. It reached significance in all cases except for that of the final comfort measure in the PTB group. In the latter case, the difference between the socket-changed and socket-not-changed groups was actually even greater on the final comfort level measure than on the initial comfort level measure. However, this difference failed to reach significance as the result of the reduction in degrees of freedom of the t test, necessitated by the adjustment for variance inequality between the socket-changed and socket-not-changed groups. This adjustment compensates for the higher likelihood of type 1 error when the variances between the groups being compared differ significantly.

Any change in socket design was not tolerated well, which was intuitively expected. Therefore, clinicians should use caution when suggesting an alternate design of prosthetic sockets to their patients. Adjustments performed to the prosthetic sockets were associated with significant decreases in the mean comfort levels in both groups, which seemed to be illogical; however, review of the clinical notes suggested that in many cases, especially those in which the socket type had been changed, the subjects did not like their new sockets in the beginning and all attempts of the prosthetist to improve the comfort of the socket and promote acceptance of the socket were unsuccessful. In most cases of decreased SCS level, the subjects insisted on being refitted with an alternative socket design. In contrast, the subjects who were initially happy with the fit did not return to the facility for adjustments, and as they got accustomed to the new socket, the SCS level increased.

During the process of this study, the reviewed clinical notes produced information that suggested that HCTSB sockets were tolerated significantly better by subjects with longer and volumetrically stable residual limbs. The author attempted to statistically analyze the potential correlation of the limb volumetric stability and the outcome by comparing the SCS score between the subjects whose amputations were caused by PVD and those whose amputations were of traumatic nature. In this analysis, the author assumed that the residual limbs of the subjects of the former group were subject to larger volumetric fluctuations. The statistical results were counter-intuitive and failed to reach significance due to small sample size.

CONCLUSIONS AND FUTURE DEVELOPMENTS

Hands-on and hands-off methods of socket design reproducibility issues were investigated by Buis et al.69 and Convery et al.42 The studies concluded that a hands-off casting technique produced much more consistent results and that there is considerable inter- and intrarater variability in hands-on methods. These issues of consistency and repeatability are even more relevant for many developing countries, which lack the opportunity and means to educate prosthetists and lack modern prosthetic facilities and resources to acquire materials of high technology.70,71 In this light, hands-on prosthetic socket design may be viewed an art; and an individual prosthetist may have the knowledge, technique, skill, and experience to make some styles work better than the others. Therefore, the success of a comfortable prosthetic socket fit is heavily dependent upon subjective factors. For that reason, the interrater and possibly intrarater repeatability of a socket design cannot be high for hands-on systems. It would be of a great benefit to such countries to have a prosthetic socket system developed that would drastically decrease the user error factors. Consistency of results of a successful “hands-off” method will provide for improved quality control, reduced production time and lower production expense as certain tasks may be delegated to lesser skilled employees. Although the results of this study clearly favored the PTB design, the HCTSB sockets produced by the hands-off method were quite satisfactory. It was conjectured that volumetric fluctuations of the residual limb had a negative effect on the comfort of and the satisfaction with the hydrocast socket fit. It was beyond the scope of this study to attempt to measure this relationship, which should be a topic of future research. It was also conjectured that there was a negative relationship between the length of the residual limb and the success of the hydrocast socket fit. Although the same relationship may exist in fitting of other types of prosthetic sockets, it may be more pronounced with the HCTSB design, and this could become a subject for further studies.

The past has shown there to be a reliance on hands-on techniques in the field of prosthetics. Because the optimal method has yet to be discovered, the patient must rely on the prosthetist's clinical judgment to make and fit a transtibial prosthesis. Though a prosthetist can modify a socket successfully, many are unable to define exactly what was done to the positive model. During the rectification process, the original shape is lost as material is added and removed. Because modifications are made over the entire shape and not as a series of individual changes, picking out exactly how the residual limb shape was modified is difficult. Both hands-on and hands-off techniques sometimes require more than one test socket to be fabricated before a successful fit is achieved. An average of more than one iteration is currently the acceptable clinical range for fitting a limb prosthesis; and a direct method with no iterations may be a beneficial practice.

The Report on the State-of-the-Science Meeting in Prosthetics and Orthotics, published in February 200672 provided an overview of current research needs in socket design. The report states that the prosthetic fit SCS by Hanspal would be a good survey instrument for use in the clinic to allow an objective assessment of prosthetic socket fit. The dilemma of good socket fit becomes apparent when trying to determine what may be the best prosthetic components for each individual amputee. Matching functional ability with the proper components is a solution for optimizing physical performance. Indices of functional ability are increasingly used to rate the status of patients studied in clinical research or treated in clinical practice.

It may be better suited to select patients for outcome studies based on the same functional level as delineated in the MFCLs. There are five levels within the MFCL and these were created to describe levels of functional ability and in turn designate the appropriate prosthetic components for each class level. The Amputee Mobility Predictor (AMP)73 was designed to determine the amputee's readiness for ambulation. The AMP is the first clinically applicable measurement tool for amputees with the efficiency, reliability, validity, and predictive potential necessary to possibly differentiate among functional classes as per the MFCL. The AMP can be used either without or with the use of a prosthesis, providing objective information that may furnish the clinician with greater insight into the amputee's readiness to ambulate and the selection of prosthetic components to permit the amputee to achieve an optimal gait. The AMP offers clinicians a valuable tool for the justification and prescription of prosthetic care for the amputee.

The methods provided by Neumann74,75 on measurement of socket discomfort provide conclusions which indicate that psychophysical methods for measuring sensations of pressure, discomfort, and pain are feasible. They may hold promise as tools to help with the fitting of sockets and for research conducted on liner and socket designs and materials. The methods provide patients with a means for expressing and communicating the sensations and discomfort problems associated with socket fit. Although the research was carried out on patients using PTB sockets that feature non-uniform pressures, an experiment featuring uniform pressure also was conducted. The data suggested that psychophysical response functions for pressure sensation may change with experience and exposure to the forces encountered inside a socket. The data of the experiment indicated distinctive pressure sensation responses among the three subjects, which could reflect different amounts of experience with the fitting and wearing of a prosthesis, different residual limb tissue characteristics, or different response functions. The inexperienced patient might present a fitting challenge different from the experienced user, who may be able to more quickly identify problem areas. The methods could provide helpful information for the fitting of many other socket types including TSB sockets. Psychophysical methods could be used to increase knowledge on the sensations of deep pressure that are experienced by individuals—a subject for which virtually no information exists.

Signal detection theory76 entails a number of concepts that are relevant to understanding discomfort perceptions and socket fitting. One of its most significant contributions is the insight that the socket discomfort judgments made by patients may not always be a simple response to perceived sensations. They may be complex decisions that are influenced by the relative costs and benefits of hits, correct rejections, false alarms and misses. The attitudes and interpersonal skills of the prosthetist could influence some of these perceived benefits and costs.

Dycor77 is developing a practical biomedical device designed to assist users to imagine what they would like to feel, and at the same time, feel what they try to imagine. The device is called B3P which is designed to facilitate exteriorized psychogenic proprioception (EPsP) in both neuropathic and transected lower limb. Similar to proprioceptive neuromuscular facilitation, EPsP appears to enhance a more natural body image and normal phantom sensation. Adding the element of B3P, sensory input has the most unexpected engaging and animating effect on the user. There appears to be a relationship between B3P proficiency and the maintenance or attainment of a more natural feeling phantom limb. This more natural feeling closely coincides with simultaneous prosthetic function. It has been discovered that there is an inverse relationship between B3P proficiency and the presence of phantom pain, limb pain or both.

The American Academy of Orthotists and Prosthetists has established a Master Agenda76,78,79 methodology for establishing guidelines for developing a consistent process of evidence reports. The evidence reports are used to expand into state-of-the-science conferences. The Academy's guidelines can help to educate researchers and practitioners. The Certificate Program for Professional Development called “Evidence Based Practice” and the State of the Science Conference course titled “Outcomes Measures in Lower Limb Prosthetics”80 can provide cohesive guidelines to help improve and justify the clinical care for patients and design better experiments. In 1896, Marks81 wrote: “Ease and comfort in wearing an artificial leg can only be obtained by means of proper fittings—no matter how well the limb may be constructed, or with what nicety all the parts operate, the limb is worthless if it causes pain to the wearer, chafes the residual limb or excites irritation. The artificial limb is something that cannot be obtained by mechanical methods.” The author is confident that it can be ultimately said that someday that very elusive comfortable prosthetic fit by mechanical methods will be obtained using the direct method.

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    FU2-4
    Figure
    Keywords:

    prosthetics; socket comfort; patellar tendon bearing; hydrocast

    © 2011 American Academy of Orthotists & Prosthetists