Veterans Affairs

Prosthetic socket fit sensor

Fully integrated device to assess socket fit for increased comfort and performance

Medical & Biotechnology

Maintaining good socket fit can be an ongoing struggle. A new sensor system, integrated into the socket, helps amputees identify fit changes in real-time. Image: Health.mil

Scientists at the U.S. Department of Veterans Affairs (VA) have recently invented a socket fit sensor that can be used to identify pressure points in lower limb prostheses. The patented technology is available via patent license agreement to companies that would make, use, or sell it commercially.

Prosthetists build residual limb sockets to safely and comfortably distribute weight within the socket. But, limbs change shape and volume over time, which can lead to improper socket fit and potentially injurious interface pressures and shear stresses. Individuals with lower-limb amputations and their clinicians have identified poor socket fit as one of the most significant problems and unmet needs. In a six-year retrospective chart review, skin problems were found in 40.7% of lower-limb prosthesis users, and problems with the fit of the prosthesis and socks contributed to over 90% of these cases.

To maintain proper socket fit, most individuals with lower-limb amputations are instructed to compensate for changes in limb volume by using prosthetic socks. Socks are the most common method of adjusting socket fit because they are inexpensive and effective when used properly.

While some prosthesis users are able to successfully manage their prosthetic socks or have minimal volume changes and thus do not require daily socket fit adjustments, many have difficulty with sock management. This is true for new amputees, those with significant daily limb volume changes, individuals with cognitive impairment, and those simply too busy to go through the routine of donning and doffing socks throughout the day.

Addressing this issue of continual socket fit in an effective and inexpensive manner, VA researchers have developed a socket fit detection device incorporating a self-contained sensor assembly. The device is designed to fit in the distal end of a socket and can replace the existing limb attachment mechanism. The sensor produces a signal in response to changes in pressure within a gas or fluid chamber. Based upon the outputs received from the sensor, electronics signal a quality of fit between the residual limb and socket.

Besides a pressure sensor, the device includes an accelerometer to produce an output indicative of a type of movement of the patient and provide context to the recorded pressure data.  For example, the acceleration data can provide information concerning the type of movement of the patient (sitting, standing, swaying, and the like) while also allowing for extrapolation of usage information and gait information.

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