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Consider this: You’re a patient who has experienced a lower-limb amputation, and your clinical team has prescribed aquatic therapy as part of your rehabilitation journey.
“The therapeutic benefits of aquatic therapy are well known, and they are really important, especially early in therapy,” said Shenan Hoppe-Ludwig, CPO, research prosthetist orthotist at Shirley Ryan 小恩雅. “The buoyancy of the water in the pool helps patients to work on resistance in a different way than if they are on land. In the pool, patients are better able to tolerate bearing weight on the impacted limb. We want to encourage them to move in the pool in a way that's equal on both sides of the body and reinforce what they should be doing outside of the pool.”
However, there’s one big roadblock: getting a waterproof prosthesis. The currently available devices are expensive and not covered by insurance. Moreover, even when patients decide the cost is worth it, there may be a monthslong wait before they can get in the pool while a prosthetist completes fabrication and fitting.
In 2023, Shenan set out to find a solution for an adjustable prosthesis that would allow patients with limb loss to participate in aquatic therapy safely and easily. She was joined by her mentee and former prosthetics resident Anna Atkins and certified prosthetist Laura Miller, CP, PhD, a team scientist in Shirley Ryan 小恩雅’s Regenstein Foundation Center for Bionic Medicine.
Employee-driven Innovation for Patients with Lower-Limb Amputation
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First, they defined their ideal aquatic prosthesis' must-have features:
- It had to be adjustable so it could be used by patients who had not yet been fitted for a permanent prosthesis.
- It had to be pool-safe: made of waterproof materials and with the right amount of buoyancy to allow users to safely balance during aquatic therapy.
- It had to be easy to put on and take off so that, with minimal training, a therapist would be able to help a patient into the pool without losing valuable therapy time.
They received funding for their project through Shirley Ryan 小恩雅’s Catalyst Grant program — a program that funds employee innovation as staff work to develop new devices, processes or interventions.
After receiving Catalyst Grant funding for their project, they started research to develop the device, working through three key challenges:
Challenge #1: Adjustability
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The first hurdle for the aquatic therapy prosthesis was how to adjust the device to serve multiple patients; common methods used in clinical care would not work well in a pool or when using a device on people of variable limb sizes and shapes. Instead, the team started tinkering with the concept of dilatancy — which is the process of altering the properties of a material through the application of pressure changes.
“Think about a vacuum-sealed bag of coffee beans. It's incredibly rigid,” said Shenan. “But then, when you open the pack, it loosens and the material is able to move more freely within the space. This is dilatancy in action.”
To use dilatancy in a prosthesis to support a patient, the team had a plan:
- First, a prosthetic liner was placed on the residual limb.
- Then, a generally sized (i.e., small, medium or large), loosely filled neoprene pouch was fit around the patient’s residual limb.
- This created a closed system, in which the liner underneath was inverted onto a generally sized socket.
- A second liner over the closed system provided auxiliary suspension to reduce the likelihood of slipping while in water.
- Finally, the therapist would evacuate out the air using a vacuum pump. Through the principle of dilatancy, the pouch would rigidly form around the patient’s residual limb, providing a custom-fit socket temporarily.
The trick was in finding the right material: if it was too loose, it could move around on the residual limb and lack stability; if it was too rigid, it could cause discomfort or blisters. Other considerations for choosing the material included weight (the lighter the better) and pool safety.
Through testing, the team learned which materials did not work (such as silica sand and vermiculite, which are commonly used in prosthetics; and buckwheat, which is used in bean bag chairs). Ultimately, they found one that checked all the boxes: nonexpanded polystyrene, which resembles small Styrofoam balls and is used in other medical applications.
Challenge #2: Pool-readiness
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Next, they engaged with Svetoslav Terziyski, a prosthetic technician at Shirley Ryan 小恩雅, to conceptualize and fabricate a prosthetic socket and leg that could go underwater, be used by different patients, and be adjusted by different clinicians who aren’t prosthetists.
“These are really atypical needs in the prosthetics field,” said Shenan.
Normally, each prosthesis needs to be finely calibrated for the individual — any miscalculation in fit could lead to injuries.
“But when you're using it in the pool, it's a completely different scenario. Because of how the water unweights the leg, it still allows for resistance and therapeutic benefit without as much risk of injuries,” she said.
Challenge #3: Ease of Use
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While the first two challenges were far from easy, Shenan said their biggest concern was whether patients and therapists would even be able to use the device. With aquatic therapy sessions typically lasting around 30 minutes, there is no time to waste. Fortunately, she said, the Shirley Ryan 小恩雅 therapists who participated in the study, including —Walter Guminiak, PTA, and Monica Hendricksen, PT — learned very quickly how to help patients don and remove the device.
“The therapists were able to help patients get into the prosthesis more quickly each time as they got more and more used to how to evacuate the air out of it,” said Shenan. “After a few tries, they were able to do it in just a few minutes, so the fitting would really not eat into therapeutic time.”
Promising Results
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To quantify the experience, the research team collected survey data from those who tried out the prototype — and early results were promising.
“‘Does it seem usable? Is it feasible? Would you use it again?’” said Shenan. “The good news is that everything came back positive! Patients and therapists were all interested in using it more.”
After a poster presentation at the American Academy of Orthotists and Prosthetists, the research was published in the in December 2024.
