Lower-limb amputation is a challenging consequence of diabetes and dysvascular disease.1 The incidence of transtibial (TT) amputation has reduced in the United Kingdom; however, it remains the most common amputation level according to the latest statistics.1 After amputation, function and cosmesis are replaced by an unnatural biomechanical device: the prosthesis.2,3 TT prostheses consist of four main parts: the prosthetic socket and its interface, suspension mechanism, pylon, and foot.4
In bipedal gait, body weight is loaded axially through the musculoskeletal system. In a person with TT amputation, transmission of weight is facilitated through the residual limb soft tissue to the skeleton via the prosthetic socket’s interface.5
During stance phase, the user’s body weight is supported and comfortably distributed within the prosthetic socket by means of its design. By contrast, throughout swing phase, inertial forces (pressure and shear) exerted by the socket and its suspension mechanism onto the residuum suspend the prosthesis.6,7 Intolerable lengths of exposure to high levels of stress may cause skin irritation or breakdown. This may be further exacerbated by persistent perspiration that is associated with the use of silicone liners (SLs).8–10
Two overarching design concepts are known in TT socket design. The patellar tendon bearing (PTB) socket principles were introduced.3 This design was the first to facilitate “total contact” of the prosthetic socket by enclosing the residual limb as a whole. Total contact reduces the risk of edema and skin problems primarily by the “pumping effect” the socket creates during ambulation. This aids venous return, reducing the risk of edema while increasing the proprioceptive feedback and hence control of the prosthesis.5,6,9
Although the PTB socket is in total contact with the residuum, pressure throughout the socket is not evenly distributed. Weight is borne over anatomically pressure-tolerant areas and offloaded from pressure-intolerant/sensitive areas.6,9 Residuum shape can be captured by a variety of methods including a hands-on casting using plaster of Paris bandages as the prosthetist wraps around the residuum and applies pressure as required.11 Another “hands-off” method, computer-aided design/computer-aided manufacturing (CAD/CAM), is detailed in the article of Topper and Fernie.12
Traditionally, the prosthesis was suspended by either leather cuff straps or a thigh corset. Although these are still used, there have been several developments to the PTB socket. The supracondylar suspension patellar tendon bearing (SCPTB) socket completely incorporates the femoral condyles to suspend the prosthesis by virtue of their anatomical shape. The SCPTB aims to increase the contact area, especially for shorter residuums, to reduce pressure and provide mediolateral stability in cases of ligament laxity.3,6,13,14 Another variant is the suprapatellar supracondylar patellar tendon bearing (SP/SC/PTB) that extends proximally over the patella to aid with recurvatum control.6,13
The second socket design was introduced approximately three decades later as the total surface bearing (TSB) suction socket. As total contact sockets distribute weight transfer over the entire residual limb, this is considered to lower peak pressures due to the larger area (pressure [P] = force [F]/area [A]).5,6 It is reported that weight is more evenly distributed and borne over the whole residuum to be transmitted through a larger area.3 Moreover, pressure within the socket is reduced proximally and increased distally to allow for distribution of forces over a greater area, reducing pressure.5,6 The development of the Icelandic Roll On Silicone Sockets (ICEROSS) is an example of a TSB socket developed by Kristinsson.15 The residuum’s shape is captured by a hands-off casting technique via a pneumatic bladder, which distributes pressure evenly onto the residuum.11
There are various suction systems used in suspending TSB sockets including SL/suction suspension system (SSS/3S) or sleeve suspension.13,14 Both systems aim for air elimination from the socket through a one-way valve that is dependent on a seal created via the liner and the socket or alternatively via contact from a silicone or gel sleeve on the thigh makes contact with the skin on the thigh to ensure a good seal of negative pressure with a one-way valve (passive suction) by which air is not allowed inside the system.6,13,14 Its mechanism is reliant on friction and negative pressure. Other suction types are the hypobaric Iceross Seal-in (HIS) suspension and the vacuum-assisted socket suspension (VASS; active suction). With these systems, due to the enclosed environment from the liner, good hygiene is required to prevent skin irritation from sweat buildup and bacterial formation.13,16
Carl Caspers, CPO(E) introduced VASS technology in the late 1990s. Suction suspension is enhanced by a vacuum that actively elevates negative pressure and simultaneously controls forces by a mechanical or electrical pump to actively evacuate air from the socket.17
Finally, HIS features a hypobaric seal attached to the liner that obviates the need for a sleeve to achieve suction and hence improves knee flexion range of motion (ROM) and user satisfaction.18,19
Locking liners (pin locks), in which a pin is attached to the distal end of the liner that connects to a shuttle lock incorporated within the prosthesis, have been used successfully with both PTB/TSB sockets.13 The “milking phenomenon” is associated with pin locking liners and is identified as a downward pull that is exerted on the residual skin by the umbrella-shaped distal end of the liner, at which the locking pin is attached. This creates peak pressures during swing phase and, when seated, results in discomfort, pain, and potentially skin problems such as blistering due to continuous cyclic shear.20–23
In 1965, Foort stated that up to 90% of persons with TT amputation may benefit from a PTB socket.3,24 In addition, Abu Osman et al.25 concluded that different depths of patellar tendon (PT) bar had an insignificant effect on the overall distribution of pressure within the socket and therefore speculated that it will be eliminated in the future. Overall, PTB socket remains the most frequent prescription.3 Furthermore, Kristinsson15 stated that numerous suspension mechanisms have been developed to reduce risk of suspension inadequacy within PTB sockets, yet none of these were considered effective before the introduction of suction suspension.15 However, Hall et al.26 reported that roughly 91% of all TT prosthetic users of TSB socket with SLs experienced a dermatological problem at least once on their residuum.
Optimum effectiveness of PTB socket cannot be achieved by sole loading of the PT bar. As most TT residuums tolerate minimal, if any, distal end bearing, additional pressure-tolerant areas must all be loaded.6 These are the medial tibial flare, fibular shaft, residual pretibial muscles, and popliteal area.3,5,6
In PTB socket, application of a vertical support force to the PT bar, according to Newton’s first law of motion, results in a downward and backward motion of the residual limb.5 Therefore, a counteracting anteriorly directed force is applied to the popliteal area by incorporating an adequately high, flattened posterior wall with an inward bulge to sufficiently compress soft tissue and eliminate motion.5,6 Pressure in TSB sockets is more equally distributed throughout the surface of the residuum. Increased pressure on tissues surrounding the weight-tolerant areas is believed to reduce pressure on intolerant areas. Weight distribution in TSB sockets is significantly reliant on the choice of interface.6
Hydrostatic shape capture techniques that originate from the TSB socket principle introduced by Kristinsson and developed by Klasson.2,14 They are based on Pascal’s principle, which states that external pressures are uniformly transmitted through a confined fluid in all directions perpendicularly to the surface of the container.4,5 Theoretically, the concept of hydrostatics presumes that the residual limb’s soft tissue behaves as fluid and abides by the fluid principle, whereas the hydrostatic system is replicated by the socket. Therefore, when the system is loaded, pressure is distributed equally and peak pressure areas are eliminated to enhance comfort.3,15,27
Murdoch28 was the first to use the hands-off principle when the Dundee socket was introduced. In an aim to eliminate positive cast modification and reduce manufacturing time, a fluid-filled tank in which the person with amputation placed his or her residuum in weight-bearing conditions28 was used and the PT bar was incorporated, resulting in a TSB socket. Klasson developed this approach by abiding by Pascal’s law of fluid dynamics, resulting in a TSB socket without the PT bar. Another hands-off shape capture technique29 uses a pneumatic bladder that encapsulates the residual limb with the subject seated. Hands-off techniques are believed to encourage consistency as hands-on techniques heavily rely on the prosthetist’s dexterity, knowledge, and skill.29
A literature review was conducted to investigate areas of discrepancy in the present knowledge with regards to available evidence in both TT socket design and suspension mechanisms to identify the most effective weight transfer mechanism and suspension techniques where possible. The article will report the most effective weight transfer mechanism as reported in comfort by both users and the prosthetist and that minimized pistoning to account for the most effective suspension. Nevertheless, all elements in the prosthesis are equally crucial for optimum function, prosthetic safety, and satisfaction, including choice of suitable socket design, suspension mechanism, prosthetic foot, alignment, and cosmesis.6
The review is composed of two parts: socket design and suspension. It is subdivided as to previous literature reviews, history, rationale, and advantages and disadvantages of each. Boolean searching and truncation were used in main keywords (Figure 1) in online search engines to obtain precise results.
In each search engine, the search strategy was refined. A total of 135 articles were retrieved relating to inclusion/exclusion criteria (Table 1). The search strategy was further refined by checking title and abstract. Pubsage/ScienceDirect was used to retrieve literature from chosen studies. Included articles were appraised and graded using the Scottish Intercollegiate Guidelines Network (SIGN) checklists (https://www.sign.ac.uk). Details are provided in the review flowchart (Figure 2).
RESULTS AND DISCUSSION
Articles obtained were divided into three sections: reviews, socket design clinical studies, and studies investigating suspension techniques. Each table illustrates the main findings (PICO [Patient/Population, Intervention, Comparator, and Outcomes]), grade of evidence,30 and the presence of commercial bias.
After initial screening, four reviews were deemed suitable against the criteria. A recent and comprehensive systematic review on TT socket designed by Safari and Meier27,31 consists of two parts: measuring qualitative and quantitative outcomes. Gholizadeh et al.32 investigated TT suspension systems following a systematic approach. Richardson and Dillon33 reviewed literature investigating user experience of TT liners systematically, whereas Baars and Geertzen34 reviewed literature that investigates the possible advantages of SLs in TT prosthetics.
SOCKET DESIGN REVIEWS
Safari and Meier compared four TT socket designs including PTB/TSB. They listed hydrostatic and VASS as separate designs rather than a different shape capture mechanism in the former and socket suspension method in the latter.27 Hereafter, authors found that the misperception in socket design and suspension prevents drawing a solid conclusion on the suitability of socket design/suspension. Nevertheless, in part one, it was concluded that higher activity levels and increased satisfaction were achieved by TSB compared with PTB sockets (Table 2).
Further, ease of donning/doffing was correlated to suspension mechanisms, which significantly impacted patient satisfaction. Moreover, they found that perspiration, odor, and skin irritation were related to use of liners, but all these problems reduced over time. Although authors found evidence to support TSB sockets, socket satisfaction ratings were considered controversial as cause of amputation, activity level, age, and residuum characteristics were found to impact satisfaction and function.27
In part two of the review, authors reported that VASS surpassed other suspension techniques, followed by TSB/suction socket, TSB/sleeve suspension, and TSB/pin lock, respectively. PTB socket with either sleeve or SC suspension was least effective.31
Overall, it may be concluded that TSB/VASS are of utmost benefit to both user and clinician with regards to the reviewers’ thesis statement.
CLINICAL STUDIES ON SOCKET DESIGN
Yiğiter et al.8 reported that 75% of participants chose to keep the TSB prosthesis, indicating a high level of satisfaction. Also, it was noted that suspension effectiveness and patient balance were improved with the TSB socket. This could be related to different suspension mechanisms. Yet the authors also found that TSB sockets require higher accuracy in shape capture and are more difficult to manufacture. Furthermore, edematous and painful residuums were found to be unsuitable for TSB sockets.8 This is also mentioned in other literature,35,36 indicating that longer residuums with redundant soft tissue are contraindicated for TSB due to soft tissue bulging during knee flexion (Table 3).35,36
TSB/unknown suspension was reportedly found superior to PTB/unknown suspension.8 Due to the unidentified suspension methods, this finding is ambiguous to the reviewer; therefore, comparisons cannot be made. Yet the authors might have been referring to suspension provided by the design of socket, that is, SC/SCSP.
Conversely, Manucharian4 found that the PTB sockets scored higher comfort levels as reported by subjects. The author also found that comfortable socket fit is significantly reliant on individual factors, such as shape capture consistency.4 This parallels Safari and Meier’s findings.
From the literature, it appears that both socket designs may achieve satisfaction under different circumstances when compared with each other.
Selles et al.37 compared both PTB/TSB sockets with pin lock suspension. Authors reported that the PTB group spent a significantly higher percentage of time standing and ambulating, which might be affected by the initial volume fluctuation caused by new weight distribution. This is correlated with the increased number of visits postdelivery of TSB sockets.37 However, Prosthesis Evaluation Questionnaire (PEQ) scores were similar, which indicates that neither the socket design nor suspension affected satisfaction.37 Also, the economical aspect is the only difference between the designs, being significantly higher with TSB.37
Goh et al.38 reported that skill and upper-limb dexterity required for pressure cast are minimized, further decreasing casting time and subsequently cost, which contraindicates the findings of Selles et al. Yet, one subject in the study of Goh et al. reported continuous high pressures proximally in the PTB socket. This is possibly caused by the stretch effect over the soft tissues caused by localized pressure in weight-bearing areas as per socket design biomechanics.5,9 Although PTB sockets are designed to alleviate pressure from the distal end, another participant experienced distal pressure in the TSB socket due to fibular protrusion. Other participants reported similar pressure intervals during gait with both socket designs.38
It is therefore difficult to draw conclusions on optimum prescription of designs as each must be tailored to individual needs of the user.
Goh et al.,38 Manucharian,4 and Selles et al.37 all stated that TSB (hands-off) sockets required less manufacturing time as the requirement for positive cast modification is negated; thus less dexterity is required. Further, the studies, except Selles et al., noted that production expenses are reduced, henceforth decreasing error factors for users and facilitating shape capture consistency.37,38
However, Selles et al.37 reported higher visits with TSB sockets after fitting, which is a result of the reduction in volume due to a different pressure distribution. Manucharian4 also reported that discomfort with TSB/HC was attributed to volume fluctuations accompanied with TSB socket due to pressure redistribution, which is similar to the finding of Selles et al.4,37,39
Gholizadeh et al.32 found that the rate of pistoning within the socket is a good indicator of a suspension’s quality. Displacement of residuum within the socket was diminished with suction compared with other suspension mechanisms. However, suction systems were found to increase the difficulty of donning/doffing and are contraindicated in the presence of volume fluctuations, which again repeats the findings of previously mentioned literature.32 Pressure was found to be distributed more evenly with use of thicker liners; however, liners resulted in higher perspiration compared with a pelite interface (Table 4).32
Richardson and Dillon’s results were parallel to those of Safari and Meier (Table 4).27,31,33
Baars and Geertzen34 concluded that limited evidence significantly supports the advantages of SLs. their literature review showed a good indication of suspension improvement when aided by a liner. Furthermore, a positive impact on walking is noted: outdoor walking distances were increased and dependence on walking aids decreased.34
Henceforward, an SL/TSB may be preferred if perspiration was not reported as a source of hindrance by the user and if proven to reduce as mentioned in part one of Safari and Meier’s review.
CLINICAL STUDIES ON SUSPENSION
Narita et al.39 concluded that SL/TSB suspension is superior to PTB’s. The x-ray diagrams in the study display that TSB sockets were suspended by pin lock. Authors did not disclose the PTB socket suspension mechanism and referred to it as “conventional.” In the introduction, they discussed that PTB sockets were conventionally suspended by a thigh cuff; it is therefore assumed that experimenters used either a thigh cuff or an equivalent to suspend the prosthesis.39 Moreover, nine subjects were recruited, one of which was an individual with bilateral amputations; hence, 10 residual limbs were evaluated. Yet, only three cases were discussed in the assessment of suspension, with no justification provided. Ambiguity in the study methodology limits the reliability of the results (Table 5).
Sutton et al. stated that increased stability is achieved in a shorter time with TSB/VASS compared with PTB with weight-bearing thigh cuff. Significant improvement in skin condition was also found. Further, balance improvement, gait symmetry, and variant cadence were observed within only a year of TSB/VASS use.40
In addition, Klute et al.41 reported improved socket fit with TSB/VASS in regard to reduced pistoning. Satisfactory fit was achieved in a shorter time and with fewer check sockets for PTB/pin suspension.41 Consequently, this could confirm the finding of Selles et al. that TSB sockets could be more costly when more diagnostic sockets are required to optimize fit. Fewer steps were taken when VASS sockets were assessed; if combined with PEQ results, preference in favor of PTB/pin suspension is suggested.41
TSB/VASS maintained constant limb volume after treadmill walk, whereas slight reduction in volume after the walk was scored with PTB/pin lock.41 The superior suspension from VASS was thought to be the main factor in the prevention of volume loss41 and improved stability.34
Board et al.23 reported improved suspension, gait symmetry, stance duration, and step length with TSB/VASS. Pistoning is also reduced with VASS; therefore, a better fit is obtained from VASS over suction, resulting in reduced skin problems and improved gait symmetry.23
Moreover, all significance reached was in favor of TSB/VASS23. Optimal socket fit of TSB/VASS would normally maintain volume or minimally increase the volume of the residuum. The gain in volume reported was thought to be attributable to other variables including participants experiencing gain in water mass or wearing a prosthetic sock for 2 hours before donning TSB/VASS.23,42 Contrariwise, the suction group scored loss in volume, suggesting that fluid had been drawn out of residuum due to proximal negative pressures.23
However, it cannot be said that TSB/VASS would serve the user better with PEQ’s41 results considered.
Nevertheless, residuum health scored higher with PTB/pin lock regarding rash formation, sores or blisters, ingrown hairs, swelling affecting socket fit, sweat, and odor.41 Moreover, approximately double the activity levels were reported with PTB/pin lock than with TSB/VASS by Klute et al.,41 which could be related to donning inconsistencies. Improved skin condition was recurrently reported with TSB/VASS. Evidence showed that TSB/VASS not only prevents skin problems but also encourages healing.41 This statement is supported by the finding of Traballesi et al.42 that TSB/VASS negates the requirement for early ambulation such as Pneumatic Post-Amputation Mobility (PPAM) Aid before the primary prosthesis. Furthermore, VASS subjects were able to walk within days from protocol initiation. Traballesi et al.42 stated that wound healing is achieved with TSB/VASS.
It was also reported that suction can be difficult to maintain, particularly at TT level as bony prominences are more evident than with an individual with transfemoral (TF) amputation where soft tissue coverage is more manifested. In addition, presence of pain or edema is another contraindication of the TSB/suction socket.14,27,31 This parallels Safari and Meier’s27,31 statement that the suspension mechanism has an effect on satisfaction and function of socket.
Two studies investigated TSB/HIS, in which results are similar with regards to reduction in pistoning, improved suspension, and difficulty of donning/doffing. Although Gholizadeh et al.19 and Brunelli et al.18 agreed on superiority of HIS over pin lock and suction suspension, Gholizadeh et al.19 reported that as multiple factors affect patient satisfaction, pistoning is not a determinant of socket satisfaction levels from the user perspective. Brunelli et al. stated that feeling increased stability within the prosthesis as a result of reduced pistoning could primarily determine user satisfaction.18 However, the comparator was different in both studies and subjects preferred pin suspension over TSB/HIS in a study by Gholizadeh et al.19 Subjects in the study of Brunelli et al.18 reported improvement in some aspects with TSB/HIS: cosmesis, rate of ambulation, hours of use, and general well-being.32 Although pistoning was significantly reduced, motor capability of energy cost of walking (ECW) figures were not improved. This is probably due to the high activity level of subjects recruited. This could be related to either subject fitness or the insensitivity of outcome measures used. Significant improvement in suspension was reported in both systems after 7 weeks; therefore, authors speculate that it requires 7 weeks to acclimate to the HIS system. However, no other studies confirmed this statement.18
The study of Coleman et al.20 concluded that participants significantly preferred PTB/passive suction for ambulatory activities over TSB/pin lock. PEQ results revealed equal satisfaction levels and intensity of ambulation for both systems. This is related to higher comfort consistency over long periods with PTB/passive suction. TSB/pin lock scored well for socket comfort over short periods, but this decreased over longer periods. Reduction in comfort over time could be attributable to increased perspiration and the “milking phenomenon.” Furthermore, skin irritation proximally and elsewhere was evident. In addition, elastomeric liner durability and economical aspects were of concern while neoprene liner durability was questioned, yet affordable. This could indicate that satisfaction is more reliant on the suspension mechanism in relation to donning/doffing rather than socket design, echoing the findings of Klute et al.
Perspiration increased with TSB as reported; however, this did not affect patient satisfaction. Yet, ease of donning/doffing was directly correlated with patient satisfaction.24,30 These findings concur with Baars and Geertzen.34 However, Safari and Meier27,31 reported that skin problems are reduced with TSB/SL compared with PTB due to even pressure distribution. Nevertheless, skin problems were not resolved by using an SL but may be aggravated by the buildup of high levels of perspiration.34 This is related to sweat buildup due to the confined environment an SL creates.
As concluded from the studies examined, weight bearing is achieved with TSB more evenly in combination with suction suspension. Among suction mechanisms examined, VASS has proven superior to other types with regards to equal weight-bearing between limbs. This parallels Safari and Meier’s27,31 findings.
Gholizadeh et al.19 reported that TSB achieve increased weight bearing through the prosthesis compared with PTB, improving balance. Authors attributed this to total contact, which further improves proprioceptive feedback and pressure distribution.19 Similar results were found by Sutton et al.,40 demonstrating that more equal weight distribution is likely to be attributable to the change in socket type.
Difficulty of donning/doffing increased with suction,40 and improper donning can result in either loss of suction—and failure of the system—or blistering as reported by Sutton et al.40 and Klute et al.41 Pistoning with TSB/VASS was significantly reduced versus PTB/pin. Although authors stated that TSB/VASS may be easier to don as there is no pin to align, subjects reported lower frustration levels with PTB/pin. A more optimal fit and reduced pistoning was obtained with TSB/VASS, yet subjects favored PTB/pin over VASS, which was related to lower frustration levels with donning. This supports the statement of Gholizadeh et al., Safari and Meier, and Baars and Geertzen that patient satisfaction is not affected by the rate of pistoning.
Improved skin health was reported with TSB/VASS, around the fibula head, midpatella tendon, and proximal brim, by Sutton et al. However, these areas were identified as problematic by one subject in the study of Goh et al. Therefore, due to the contradictory findings, it is difficult to draw a comparison about the effect of TSB on skin health.
Board et al.23 also reported that volume loss was prevented in TSB/VASS. These diurnal fluctuations are important as they contribute to ill-fitting sockets and consequent loss of suspension resulting in skin problems, gait deviations, and system failure.23 If pistoning is minimized, skin breakdown is reduced or expectantly eliminated.7,8
TSB/VASS is superior to PTB/pin in terms of socket fit due to reduced pistoning, hence improved suspension.41 Yet subjects favored PTB/pin. However, Coleman et al.20 compared PTB/passive suction with TSB/pin lock and found that 10 of 13 subjects chose PTB/passive suction socket when asked to choose a sole prosthesis. This was thought to be due to inconvenient donning/doffing of TSB/pin lock, perspiration of gel liner, and discomfort due to pin.12
Superior suspension of TSB/pin lock sockets are also reported by Narita et al.39 and Yiğiter et al.8 over TSB/unknown suspension. In TSB, the difficulty of maintaining a good fit/suspension is related to the requirement for adequate pressure levels, which can subsequently result in volume reduction. This may compromise the socket fit, which is proven problematic to the skin and may lead to ulceration.39 Board et al.23 found that TSB/passive suction contributes to initial loss in volume, due to the new weight distribution. This was supported by Manucharian,4 who found that TSB/passive suction might have caused volume fluctuations resulting in reduced satisfaction and comfort levels.23
Klute et al.41 found that although pin lock provides security, the presence of the “milking phenomenon” is challenging. Yet, subjects favored pin suspension over VASS. This is attributed to lower frustration levels with donning, although pistoning is reduced with VASS thereafter, supporting the statement of Gholizadeh et al. and Safari and Meier that patient satisfaction is not affected by the reduction of pistoning.27 Furthermore, skin irritation at the proximal end and elsewhere is probably due to “milking phenomenon” that was reported with TSB/pin lock.12 Finally, with TSB/HIS, Gholizadeh et al.19 reported that subjects stated that the HIS felt like a part of their body due to the firm attachment of the liner with the socket wall. HIS resulted in significantly less pistoning, resolving the “milking phenomena.” Yet they were more satisfied with the pin lock.31 This emphasizes the survey finding of Gholizadeh et al.32 that the majority of users prefer TSB/pin lock. Again, this reinforces the fact that pistoning is not a determinant of satisfaction.
Literature included was from 12 different countries and included different states/regions from within. This may have affected the consistency of the results obtained due to varying fabrication methods conducted in various regions.
Baars and Geertzen34 reported heterogeneity in etiology, participant selection criteria, age, and acclimatization of prosthesis use (Table 5). A decade later, Safari and Meier27,31 reported very similar limitations, indicating that development of research methods in prosthetics is very slow. Similar limitations were found in included studies limiting comparisons made due to the aforementioned vast heterogeneity in design, intervention, and comparators.
Yiğiter et al.8 compared TSB with PTB; however, suspension and shape capture mechanisms were not mentioned. The term “soft liner” was stated as an interface material for both sockets. Moreover, TSB was referred to as “total contact,” obviating the fact that PTB sockets are also total contact. Advantageous results reported in favor of TSB were attributed to “total contact.” Outcomes that favored TSB included higher weight-bearing acceptance along with improved balance and ambulation activities. All of outcomes were related to total contact and good pressure distribution and thus to increased proprioception and control of the prosthesis.13,34
Selles et al.37 reported that standard deviation discrepancies were high within both groups, indicating that some subjects extremely favored the new prosthesis or older prosthesis, which could be attributable to familiarity or raised expectations of a new socket.13,14,27,31 Still, only one participant did not keep the new prosthesis at the end of trial (PTB or TSB), according to the authors, indicating that most subjects contradicted themselves. Reviewer anticipates that PEQ was not well explained or due to insensitivity of the PEQ or due to acclimation periods.
Manucharian4 reported a significant decrease in comfort correlated to the increase in the number of adjustments made to the hydrocast total surface bearing sockets. This could be related to the experimenter’s choice of interface (pelite) to minimize variables. Reviewers indicate that the accuracy and legitimacy of the results could have been affected, as SLs were considered a prime discriminant between the two socket designs due to the material characteristics detailed previously. Although most patients did change the design of socket from their original prosthesis, a significant discrepancy was noted in comfort scores between the changed and nonchanged groups in favor of the changed group. Comfort and satisfaction were negatively affected by limb volume fluctuations in the hydrocast total surface bearing socket. Fluctuations could have occurred as a result of gapping within the socket or an undersized socket, with volume increasing to accommodate the additional space.4
Details on whether or not the terminated subjects from the study of Klute et al.41 were included in the analysis are not mentioned.
Despite the methodological errors noted in the studies and the commercial bias that may have impacted the accuracy of results, findings of this review are partially consistent with Safari and Meier’s27,31 review with regards to suspension superiority. Effectiveness of socket design was not clear due to the significant heterogeneity as mentioned by previous authors; therefore, comparisons cannot be effectively made, and in some cases, the results are unreliable. However, biomechanically, TSB sockets allow for a more even weight distribution when combined with suction, particularly VASS. In addition, minor yet promising evidence is provided on TSB/VASS regarding wound healing and early ambulation. However, PTB sockets are still successfully used and in some studies preferred over TSB. A conclusion on whether preference is due to suspension mechanism or design itself cannot be drawn. Therefore, systematic reviews must be conducted to normalize acclimation periods for socket design and suspension along with crossover randomized controlled trials (RCTs) with larger sample sizes for effective clinical basis to be made for improved clinical practice with minimal commercial bias.
The authors would like to thank Mr. Stephanos Solomindis for the time he devoted and his appreciated input and advice.
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