A major component of any prosthesis is the suspension. Decreased amounts of vertical tibial translation have been directly correlated with successful, comfortable prosthetic fittings. 1 Of all types of suspensions, suction has been considered the “gold standard” due to increased proprioception, intimate fit, and decreased pistoning. Although less common in transtibial prosthetics, suction suspension was originally achieved using a semiflexible socket with a valve in the distal end. The flexible socket was then donned into the prosthesis. This means of suspension has been the subject of many studies comparing its efficacy with other methods. Grevsten and Eriksson 2 compared suction suspension with the supracondylar cuff by examining skeletal and soft-tissue movement in transtibial subjects. Radiographs were used to demonstrate that there was less skeletal movement in the suction socket (1.10 cm) than with the supracondylar strap (2.25 cm). They concluded this reduction was primarily due to less movement of soft tissue with the suction suspension, giving the amputee a better sense of stability and a smoother gait.
Suction suspension in transtibial applications presents its own challenges with difficult socket fittings because of the anatomy and the amount of soft tissue present. In 1986, Roberts 3 reported the results from a questionnaire sent to transtibial amputees who had worn sockets with different suspensions. She found that amputees preferred their suction sockets over previously worn prostheses due to diminished pain, improved skin condition, and increased activity levels. Roberts also sent a second survey to prosthetists and found that most are unfamiliar with transtibial suction suspension and attribute characteristics of the transtibial residuum as the chief deterrent to a successful fitting. Problems inherent with a bony limb and fluctuating volume created difficulties maintaining suspension. This led to the development of silicone suction socket (3-S) suspensions, which incorporate the suction concept yet allow for volume fluctuations.
Socket designs have also been studied to find their effect on suspension. Total surface bearing (TSB) sockets distribute weight equally within the socket. In contrast, the patellar tendon bearing (PTB) socket supports a major amount of weight on the patellar tendon. Using radiographs, Narita et al. 4 compared suspensions of TSB prostheses with PTB prostheses. The 3-S suspensions used with the TSB sockets were Icelandic Roll-On Silicone Sockets (ICEROSS). The PTB sockets used “knee” cuffs as their suspension mechanism. Narita and coworkers found that the suspension effects of the TSB prostheses were superior to the PTB prostheses. They attributed their findings to the large coefficient of friction between the silicone sleeve and the skin for the TSB prostheses.
Other suspensions have also been compared with one another. In 1990, Wirta et al. 5 compared several different suspensions and found that the rubber sleeve allowed the least amount of axial movement when monitoring soft tissue in the distal end of the socket.
In this case study, a 3-S suspension and a neoprene sleeve were compared because of their reported efficacy in previous studies.
The subject in this case study was a 37-year-old man who has been a transtibial amputee for approximately 19 years secondary to trauma. The subject has a short, conical residuum with moderate soft tissue distal to the tibia that becomes excessive when distal distraction is applied to the residuum. The subject has used both the neoprene sleeve and 3-S with lock mechanism as suspensions in the past. The prosthesis used in this study was fabricated and aligned by the authors. The subject was then allowed to wear the prosthesis for several months using the preferred 3-S system to ensure comfort before commencement of the study.
Six radiographs were obtained of the residuum within the prosthesis. Full weightbearing, partial weightbearing, and nonweightbearing views were taken in each suspension. Full weightbearing was defined in this study as single limb support on the residuum. Partial weightbearing involved dual-limb support with equal weight (as determined by the subject) on each lower extremity. Nonweightbearing was defined as the prosthetic foot being slightly off the ground.
The same prosthesis and liner were used for each radiograph to allow direct comparison of the two suspensions. For the neoprene sleeve studies, the sleeve was donned and the locking pin was removed from the liner. For the 3-S studies, the neoprene sleeve was then doffed and the pin was reattached to the liner.
Vertical tibial translation, the change in distance from distal tibia to the top of the lock mechanism, was then measured directly on each radiograph. Additionally, soft-tissue translation was noted on the radiographs and measured from the visible distal soft tissue of the residuum to the top of the lock mechanism for both suspension types.
The amount of vertical tibial displacement is recorded in Figure 1. The distance between the distal end of the tibia and the superior end of the lock mechanism while using the neoprene sleeve was 6.3 cm in the weightbearing position, 6.5 cm in the partial weightbearing position, and 9.9 cm in the nonweightbearing position. The distance between the distal end of the tibia and the superior end of the lock mechanism while using the shuttle lock was 6.4 cm in weightbearing position, 6.7 cm during partial weightbearing, and 9.5 cm while nonweightbearing. The difference in vertical displacement of the tibia between full weightbearing and nonweightbearing within the prosthesis was 3.3 cm for the neoprene sleeve and 3.1 cm for the shuttle lock.
In Figure 2, the vertical displacement of the residuum’s distal soft tissue is recorded. The distance between the distal end of the residuum and the superior end of the lock mechanism while using the neoprene sleeve was 2.4 cm in the weightbearing position, 2.4 cm in the partial weightbearing position, and 4.4 cm in the nonweightbearing position. The distance between the distal end of the residuum and the superior end of the lock mechanism while using the shuttle lock was 2.4 cm in weightbearing position, 2.4 cm during partial weightbearing, and 2.6 cm while nonweightbearing. The amount of vertical distal soft-tissue movement between full weightbearing and nonweightbearing within the prosthesis was 2.0 cm for the neoprene sleeve and 0.2 cm for the shuttle lock.
There was little difference in vertical tibial translation when using the neoprene sleeve and shuttle lock suspensions. The overall vertical tibial movement was greater than averages previously reported by Grevsten and Eriksson. 2 These differences may be due to the short tibia and the amount of distal soft tissue in this case.
The movement of distal residual limb tissue differed for each type of suspension, with less movement noted in the shuttle lock suspension. This difference may be attributed to the adhesion of the skin to the 3-S liner and its direct attachment to the shuttle lock/prosthesis, preloading the distal tissue with distraction when donning, and/or the type and condition of the residuum.
No large differences were seen between full weightbearing and partial weightbearing for both tibial displacement and soft-tissue displacement.
An afterthought of this study was that the distal end of the socket was not sealed for the neoprene sleeve suspension radiographs. Because negative pressure has been reported as a major component of the neoprene’s ability to suspend the prosthesis, it may have affected the distal soft-tissue movement. 6 To validate whether negative pressure was a suspension component that altered the results for the neoprene sleeve studies, another set of radiographs should have been taken using the neoprene sleeve suspension with the distal end of the socket sealed. It must be noted, though, that not all knee sleeves work on this principle. Many knee sleeves available are composed of materials that allow air to pass through the walls.
The subject did report a perceived difference between suspensions with the neoprene sleeve allowing more vertical movement and a preference for the shuttle lock suspension. However, he was comfortable in both suspensions. This leads to the question: “Is a patient’s perception of suspension influenced more by skeletal or soft-tissue movement?” In this study, the patient’s perception was more influenced by soft-tissue displacement, which coincides with the results of Grevsten and Eriksson. 2
Two types of suspensions, the neoprene sleeve and the silicone suction socket suspension with lock, were compared to find the reported efficacy of each. This case study used radiographic measurements to quantify vertical tibial displacement and vertical soft-tissue displacement for a single subject using both suspensions.
There was similar tibial translation between the two types of suspensions examined. The shuttle lock suspension produced less distal soft-tissue movement than the neoprene sleeve in this case. This could be related to the lack of negative pressure within the prosthesis while using the neoprene sleeve and/or the direct attachment of the 3-S system to the prosthesis.
Although there are advantages/disadvantages and indications/contraindications for each type of suspension, there still needs to be further investigation into the efficacy of each and the benefits related to the patient’s perception. Further study in this area with various limb shapes and liners should continue to be pursued.
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