Most prosthesis users—especially lower-limb amputees—complain that the volume of their residual limb diminishes throughout the day. In fact, by the time lunch rolls around, adding another prosthetic sock is common. Ottobock offers a solution to this problem by creating a system that actively manages residual limb volume.
Ottobock designed the Harmony System for transtibial as well as transfemoral prostheses users. The system features five components: PUR (Polyurethane) liner, sheath, Harmony socket, sleeve, and Harmony pump.
Researchers at St. Cloud State University in Minnesota found that using all five components together effectively prevents volume loss and minimizes residual limb volume fluctuations throughout the day. Furthermore, studies also found that using the Harmony System promotes better blood circulation in your residual limb.
Residual limb fluctuation
As the day goes on, the residual limb loses its volume while wearing a prosthesis. This phenomenon is attributed to traditional weight-bearing sockets that squeeze fluid out of your residual limb. These conventional sockets “press” tissue fluid out of the residual limb during the phase of walking wherein the foot remains in contact with the ground.
Although the fluctuation of residual limb volume is expected, the extent of these fluctuations depends on various factors, including vascular diseases, the condition of the connective tissue, age of the prosthetic user, and the type and fit of the socket.
To address volume loss, most lower-limb amputees will add a gel sock or a knitted prosthetic sock in the afternoon, which provides short-term relief.
Conventional sockets that use either a one-way valve and pin liner system can not prevent volume fluctuations. Users of both systems often report movement between their residual limbs and the socket, which often leads to painful skin irritations. To counteract these effects, lower-limb prosthetic users need to implement effective volume management.
An active volume management system
Credit: Ottobock US
Ottobock designed the Harmony System to prevent volume fluctuations in the residual limb. The Harmony system prevents pressure peaks in load-bearing areas of your socket, which makes maintaining a full connection between the prosthesis and residual limb effortless.
During the stance phase of walking, instead of squeezing tissue fluid out of your residual limb, the Harmony System distributes pressure over the entire surface of your limb evenly. This mechanism reduces the total load on your limb and stabilizes the amount of fluid in your residual limb. This stabilization and negative vacuum pressure created by the Harmony pump prevents your prosthesis from squeezing fluid out of your limb and requiring additional sock ply.
Optimum socket fit
It is widely known that prosthetic users can only make the most out of their prostheses if their socket fit is optimal. To date, existing prosthetic technology forces the natural contour of your residual limb to adapt to the walls of your prosthetic socket. The more the contours of your limb differed from the socket shape, the greater the compromise between comfort.
It’s a good thing that along with the Harmony System comes a new plaster cast and modeling technique that makes representing individual limb contours possible within a prosthetic socket. This new technique, performed by your prosthetist, optimizes socket fit and simplifies the modeling process. Coupled with a custom prosthetic liner that is formulated to change shape when pressure is applied, equals increased comfort.
To be able to fit the Harmony System, prosthetists are required to learn this new plaster cast and modeling technique. This makes wearing leg prostheses more comfortable than before.Do you use the Harmony System? Have you worn other systems? Please share your experiences in the comments section below.