Ryan Caldwell

Use of a partial foot prosthesis with vacuum-assisted suspension: A case study

Vacuum-assisted suspension uses the creation of a negative pressure differential to hold a gel liner securely to the walls of the prosthetic socket to reduce the migration of the residual limb within the prosthesis. The eliminated movement or pistoning of the residual limb within the socket is believed to contribute to increased comfort and function in persons with a transtibial amputation by reducing peak pressures during ambulation. A new socket system was developed with vacuum-assisted suspension for a person with partial foot amputation to take advantage of this better coupling. The purpose of this case study was to evaluate the use of a partial foot prosthesis with vacuum-assisted suspension in a 68-year-old man with a right transfemoral amputation and a left partial foot amputation, both of traumatic origin. A questionnaire was used to compare the subjects satisfaction and function between his previous and new prosthesis. Photographs of the residual limb were taken before initial fitting of the new prosthesis, 10 days after initial fitting, and at 2-month follow-up to document the appearance of the residual limb. The subject rated the prosthesis with vacuum-assisted suspension higher with regards to comfort during standing and walking (i.e., it was more comfortable) and lower for pain while wearing the prosthesis (i.e., it was less painful). Photographs at 2-month follow-up showed that the skin was healthier in overall appearance when compared with initial fitting. This case study suggests that the use of a prosthesis with vacuum-assisted suspension may be a viable design for improving comfort, function, and residual limb health for persons with partial foot amputation.

Northwestern University Flexible Subischial Vacuum Socket for persons with transfemoral amputation: Part 2 Description and Preliminary evaluation

Background: Current transfemoral prosthetic sockets are problematic as they restrict function, lack comfort, and cause residual limb problems. Development of a subischial socket with lower proximal trim lines is an appealing way to address this problem and may contribute to improving quality of life of persons with transfemoral amputation. Objectives: The purpose of this study was to illustrate the use of a new subischial socket in two subjects. Study design: Case series. Methods: Two unilateral transfemoral prosthesis users participated in preliminary socket evaluations comparing functional performance of the new subischial socket to ischial containment sockets. Testing included gait analysis, socket comfort score, and performance-based clinical outcome measures (Rapid-Sit-To-Stand, Four-Square-Step-Test, and Agility T-Test). Results: For both subjects, comfort was better in the subischial socket, while gait and clinical outcomes were generally comparable between sockets. Conclusion: While these evaluations are promising regarding the ability to function in this new socket design, more definitive evaluation is needed. Clinical relevance Using gait analysis, socket comfort score and performance-based outcome measures, use of the Northwestern University Flexible Subischial Vaccum Socket was evaluated in two transfemoral prosthesis users. Socket comfort improved for both subjects with comparable function compared to ischial containment sockets.

Northwestern University Flexible Subischial Vacuum Socket for persons with transfemoral amputation-Part 1: Description of technique:

Background: Current transfemoral prosthetic sockets restrict function, lack comfort, and cause residual limb problems. Lower proximal trim lines are an appealing way to address this problem. Development of a more comfortable and possibly functional subischial socket may contribute to improving quality of life of persons with transfemoral amputation. Objectives: The purpose of this study was to (1) describe the design and fabrication of a new subischial socket and (2) describe efforts to teach this technique. Study design: Development project. Methods: Socket development involved defining the following: subject and liner selection, residual limb evaluation, casting, positive mold rectification, check socket fitting, definitive socket fabrication, and troubleshooting of socket fit. Three hands-on workshops to teach the socket were piloted and attended by 30 certified prosthetists and their patient models. Results: Patient models responded positively to the comfort, range of motion, and stability of the new socket while prosthetists described the technique as “straight forward, reproducible.” Conclusion: To our knowledge, this is the first attempt to create a teachable subischial socket, and while it appears promising, more definitive evaluation is needed. Clinical relevance We developed the Northwestern University Flexible Subischial Vacuum (NU-FlexSIV) Socket as a more comfortable alternative to current transfemoral sockets and demonstrated that it could be taught successfully to prosthetists.

Quantification of rectifications for the Northwestern University Flexible Sub-Ischial Vacuum Socket:

Background: The fit and function of a prosthetic socket depend on the prosthetist’s ability to design the socket’s shape to distribute load comfortably over the residual limb. We recently developed a sub-ischial socket for persons with transfemoral amputation: the Northwestern University Flexible Sub-Ischial Vacuum Socket. Objective: This study aimed to quantify the rectifications required to fit the Northwestern University Flexible Sub-Ischial Vacuum Socket to teach the technique to prosthetists as well as provide a computer-aided design–computer-aided manufacturing option. Study Design: Development project. Methods: A program was used to align scans of unrectified and rectified negative molds and calculate shape change as a result of rectification. Averaged rectifications were used to create a socket template, which was shared with a central fabrication facility engaged in provision of Northwestern University Flexible Sub-Ischial Vacuum Sockets to early clinical adopters. Feedback regarding quality of fitting was obtained. Results: Rectification maps created from 30 cast pairs of successfully fit Northwestern University Flexible Sub-Ischial Vacuum Sockets confirmed that material was primarily removed from the positive mold in the proximal-lateral and posterior regions. The template was used to fabricate check sockets for 15 persons with transfemoral amputation. Feedback suggested that the template provided a reasonable initial fit with only minor adjustments. Conclusion: Rectification maps and template were used to facilitate teaching and central fabrication of the Northwestern University Flexible Sub-Ischial Vacuum Socket. Minor issues with quality of initial fit achieved with the template may be due to inability to adjust the template to patient characteristics (e.g. tissue type, limb shape) and/or the degree to which it represented a fully mature version of the technique. Clinical relevance Rectification maps help communicate an important step in the fabrication of the Northwestern University Flexible Sub-Ischial Vacuum Socket facilitating dissemination of the technique, while the average template provides an alternative fabrication option via computer-aided design–computer-aided manufacturing and central fabrication.

Comparative effectiveness of electric vacuum pumps for creating suspension in transfemoral sockets

ABSTRACT Introduction: There is increasing evidence to support the benefits of vacuum-assisted suspension (VAS) as a means of securing lower-limb prosthetic sockets to the residual limb. As use of VAS increases, there is need to assess comparative effectiveness of different vacuum pumps. This study conducted in vivo tests to evaluate the effectiveness of two commercial electric pumps, the Ohio Willow Wood LimbLogic and Otto Bock Harmony e-pulse, in transfemoral sockets. Materials and Methods: Tests evaluated (1) the rate and time of evacuation for each pump to achieve a clinically recommended socket-liner interface pressure of 17 in-Hg below atmospheric pressure while 18 subjects stood quietly and (2) the number of times each pump reactivated during 10 minutes of treadmill walking by 9 subjects to reestablish 17 in-Hg below atmospheric pressure after initial evacuation. Results: During quiet standing, each pump displayed an S-shape temporal profile of vacuum pressure until 17 in-Hg below atmospheric pressure was achieved. Across participants, the LimbLogic pulled vacuum at a faster rate than the e-pulse (62 vs. 39 in-Hg/min) and required less time to achieve the desired pressure (22 vs. 27 seconds). However, the LimbLogic reactivated once during walking to account for vacuum leakage, whereas the e-pulse did not reactivate. Conclusions: The small differences in outcome metrics between pumps suggests that they were comparable in terms of effectiveness for creating and maintaining VAS of transfemoral sockets. This study describes simple methods that can be used in future studies when comparing electric vacuum pump performance.

Evaluation of a Prototype Hybrid Vacuum Pump to Provide Vacuum-Assisted Suspension for Above-Knee Prostheses.

Vacuum-assisted suspension (VAS) of prosthetic sockets utilizes a pump to evacuate air from between the prosthetic liner and socket, and are available as mechanical or electric systems. This technical note describes a hybrid pump that benefits from the advantages of mechanical and electric systems, and evaluates a prototype as proof-of-concept. Cyclical bench testing of the hybrid pump mechanical system was performed using a materials testing system to assess the relationship between compression cycles and vacuum pressure. Phase 1 in vivo testing of the hybrid pump was performed by an able-bodied individual using prosthesis simulator boots walking on a treadmill, and phase 2 involved an above-knee prosthesis user walking with the hybrid pump and a commercial electric pump for comparison. Bench testing of 300 compression cycles produced a maximum vacuum of 24 in-Hg. In vivo testing demonstrated that the hybrid pump continued to pull vacuum during walking, and as opposed to the commercial electric pump, did not require reactivation of the electric system during phase 2 testing. The novelty of the hybrid pump is that while the electric system provides rapid, initial vacuum suspension, the mechanical system provides continuous air evacuation while walking to maintain suspension without reactivation of the electric system, thereby allowing battery power to be reserved for monitoring vacuum levels.

Change in residual limb size over time in the NU-FlexSIV socket: A case study

Background: This case study represented a unique opportunity wherein a long-time user of sub-ischial sockets had kept nearly every socket he wore for a decade. This individual let us borrow these sockets so we could digitize them and indirectly assess change in residual limb size over time by calculating changes in socket volume and circumferences over time. Case Description and Methods: Over a decade, the subject maintained a relatively stable body weight of 84–88 kg and received nine sub-ischial sockets. The internal surface of each socket was scanned using a mechanical digitizer and volume and circumferences calculated. Findings and Outcomes: Socket volume increased 31.3%, from a low of 2659.2 cm3 for the oldest socket to a high of 3490.6 cm3 for the most recent socket. Proximal circumferences increased more than distal circumferences with a 15.9% total increase proximally versus 8.9% total increase distally. Discussion and Conclusion: The results suggest that this individual’s residual limb increased in size over time despite the compressive effect of the socket and liner. In addition, the increase in circumference was greater proximally than distally, which is where the remaining muscle bellies are located. Clinical relevance This case study provides insight into the long-term effect of the sub-ischial socket on residual limb volume given compression of the soft tissues by the socket system.

Technique modifications for a suction suspension version of the Northwestern University Flexible Sub-Ischial Vacuum socket: The Northwestern University Flexible Sub-Ischial Suction socket

Background and Aim: Development of a passive suction version of the Northwestern University Flexible Sub-Ischial Vacuum socket would expand application of sub-ischial sockets to a larger proportion of persons with transfemoral amputation. While active vacuum suspension provides more positive coupling of the residual limb to the prosthetic socket, there are circumstances when use of active vacuum is not appropriate or feasible. Therefore, this technical note describes the technique modifications required to cast, fabricate, and fit a passive suction version of the Northwestern University Flexible Sub-Ischial Vacuum socket (i.e. the Northwestern University Flexible Sub-Ischial Suction socket). Technique: Most technique modifications stem from the use of an internal seal with the Northwestern University Flexible Sub-Ischial Suction socket and the need to account for the greater relative motion occurring between the residual limb and socket with passive suction compared to active vacuum suspension. Discussion: Between January 2015 and March 2018, 266 Northwestern University Flexible Sub-Ischial Suction sockets were fit successfully using the described technique modifications. Clinical relevance A passive suction version of the Northwestern University Flexible Sub-Ischial Vacuum socket—the Northwestern University Flexible Sub-Ischial Suction socket—broadens the application of sub-ischial sockets to a larger proportion of the population with transfemoral amputation.

Stakeholder perspectives for possible residual limb monitoring system for persons with lower-limb amputation

Abstract Purpose: To gather ideas from lower-limb prosthesis users and certified prosthetists regarding possible residual limb monitoring system features and data presentation. We also gathered information on the type of residual limb problems typically encountered, how they currently manage those problems, and their ideas for methods to better manage them. Materials and methods: Two focus groups were held; one with certified prosthetists and another with lower-limb prosthesis users. Open-ended questions were used in a moderated discussion that was audio recorded, transcribed, and assessed using applied thematic analysis. Results and conclusions: Seven individuals participated in each focus group. Prosthetists came from a mix of practice settings, while prosthesis users were diverse in level of amputation, aetiology, and years of experience using lower-limb prostheses. Residual limb problems reported by participants were consistent with those in the literature. Participants suggested better managing residual limb problems through improved education, better detection of residual limb problems, and using sensor-based information to improve prosthetic technology. Participants favoured short-term use of a possible residual limb monitoring systems to troubleshoot residual limb problems, with temperature and pressure the most frequently mentioned measurements. Participants described that an ideal residual limb monitoring system would be lightweight, not interfere with prosthesis function, and result in benefits with regard to prosthetic care and socket function that outweighed inconveniences or concerns regarding system use. A potential positive of system use included having objective data for reimbursement justification, although it was pointed out that the residual limb monitoring system itself also needed to be reimbursable. Implications for Rehabilitation Stakeholders suggested better managing residual limb problems through improved education, better detection of residual limb problems, and using sensor-based information to improve prosthetic technology. Stakeholders favored short-term use of a possible system to troubleshoot residual limb problems, with temperature and pressure the most frequently mentioned measurements. Stakeholders described that an ideal residual limb monitoring system would be lightweight, not interfere with prosthesis function, and result in benefits with regard to prosthetic care and socket function that outweighs any inconveniences or concerns regarding system use. Stakeholders indicated that a potential positive of system use included having objective data for reimbursement justification, although it was pointed out that the residual limb monitoring system itself also needed to be reimbursable.

Technique for Perforating a Prosthetic Liner to Expel Sweat

Introduction Sweating and moisture buildup are caused by the insulative nature of prosthetic interface materials increasing the temperature of the residual limb. Hence, heat and sweating in the socket are among the most frequently reported problems that reduce quality of life for persons with amputation. The purpose of this technical note was to describe a simple, inexpensive technique for perforating a silicone prosthetic liner to expel sweat and enhance use of a lower-limb prosthesis. Materials and Methods A liner holder consisting of a towel and socks layered over a mandrel to mimic the distal liner shape was made to stabilize the liner during the perforation process. With the liner placed over the holder such that the exterior surface was exposed, a perforating roller was used to perforate the distal end of the liner. When the liner was inverted, the holes were visible all the way through to the inner surface of the liner. Results Expulsion of sweat through the perforations was demonstrated by pouring water into the liner, folding the proximal, open end of the liner to create a seal, and forcing water droplets to escape the perforations with some resistance. Additional evidence that water escaped was seen by the wet patches that formed on the exterior fabric of the perforated liner after active wear. One user with amputation described sweat being pumped out of the perforated liner into the socket and in some cases out of the socket through the air relief valve of the vacuum pump. Another user with amputation indicated that the perforations did not damage the skin and reduced slippage of the liner with respect to the limb. Conclusions Initial clinical experience with this technique suggested that expulsion of sweat occurred and user feedback indicated improved prosthesis use as a result. Current experience using this technique in clinical practice has been limited to silicone liners. The long-term effects of perforations on liner durability or limb health are not yet known.