Analyzing Pressure Distributions of Mid-Gait Tightening Mechanism in Below-the-Knee Prosthesis Socket

There are approximately 2.1 million people currently living with limb loss in the US. This number is projected to double by 2050 due to the prevalence of cardiovascular diseases and diabetes. Among the individuals who have undergone amputation, 80-90% are lower leg amputees. For many of them, prostheses are crucial in enabling them to carry out regular activities and perform their jobs. However, current prostheses on the market often have issues with comfort and stability, which reduces the efficacy of the device.

A socket that is too loose causes instability; one that is too tight causes skin irritation and pressure sores. Our project sought to address this issue by validating the feasibility of a socket design that can adjust its fit to match the load required at each stage of the walking gait cycle. To do this, we designed a custom socket that can tighten and loosen via a lacing mechanism on two sides of the socket. The lacing mechanism uses steel cable and four wheel bearing hardpoints. When tension is applied to the cable, the walls of the socket tighten. We then tested the effect of this socket on the user’s residual limb. The objective was to produce pressure map that showed how forces on the residual limb varied over various socket tensions and residual limb axial loads.

Results showed that as the cable tension increased, the pressure in different locations on the socket walls increased similarly and without respect to axial load applied to the residual limb. The pressure at the distal tip of the residual limb also decreased as cable tension increased, but it increased with increasing axial load. We concluded that the relatively even wall pressure distribution created by the lacing tightening mechanism makes it a promising choice for further work, because evenly distributed pressure helps to prevent pressure points that can cause skin breakdown, sores, and discomfort. Future work would center around integrating a motor to create a socket that senses the gait cycle and adjusts the fit automatically.

Our project highlights the potential of a lacing tightening mechanism to address the issues of socket comfort and stability faced by lower-limb amputees with prostheses. As further research is conducted, this design could lead to more effective and efficient prosthetic devices for lower limb amputees, ultimately improving their quality of life.