Leg Up

Project undertaken in course year 2022-23 with the Stanford School of Medicine

Project Goal

To develop a lower-leg prosthesis socket that tightens and loosens automatically to match loads required by the current stage of the walking cycle. The focus of this class project is to develop a mechanism to apply pressures needed to hold the prosthesis in place while staying below pressures that cause pain.

Project Motivation

Among over 2.1 million individuals in the US 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.  We aim to improve quality of life for lower-limb amputees by designing a socket that is simultaneously comfortable and safe. 


Current prostheses on the market often have issues with comfort and stability, which reduces the efficacy of the device.  A prosthesis socket that is too loose causes instability; one that is too tight causes skin irritation and pressure sores.  A socket that can adjust automatically would be the best of both worlds.

When walking, the need for the tightness of fit varies through the walking gait, with the tightest fit needed just before heel strike, and the loosest fit between heel off and toe off.

ME170 teams in previous years have developed a system that can determine the current phase of walking, which can be used in this project as input for when to tighten/loosen the prosthesis fit. 

The distal tip of the limb should not take on the load of the body weight, so pressures holding the prosthesis need to be sufficent to keep distal tip loads constant. 

Prosthesis, socket and residual limb.  The socket is the focus of this project.

High Priority Requirements

Ethical Considerations


A nylon socket with a tightening mechanism made of steel cable and four pulley hardpoints. Tightening mechanism is actuated by applying tension to the cable, which acts like a shoelace to tighten the socket. 

System hardware

Image on the left shows the CAD model of the socket with pulleys and attachments. Image on the right shows the final 3D printed design of the nylon socket with pulleys and cable. As tension is applied to the wire rope, the sides of the socket will be pulled together to apply pressure to the socket inside. 

Casting the limb model

To conduct testing, a model of the amputated limb is needed.  The team developed a 3D mold, and filled with concrete to prepare a model for the limb, and covered it with a layer of silicone gel to simulate muscle/skin.

Inside of socket

Placement of pressure sensors inside the socket.  The sensor in the center of the figure, at the bottom of the socket, measures pressure at the distal tip.  

Test setup

System used to apply tension in wire rope, tightening the socket around the concrete limb. A load is applied to the top of the limb - shown with brick under an Instron tester - to determine how pressure on the distal tip of the is affected by increasing load and pressure

Compressive pressure at popliteal muscle location

As the wire rope is tightened, the gap in the socket opening decreases, which is a measure of tightening the socket. 

At varying downward loads up to 1700N, the compressive pressure to keep the limb from slipping in the socket, is seen to level off at 0.35 MPa, which is below the max pain threshold of 0.44MPa.  

Test results for pressure on Distal Tip

As higher downward force is applied to the socket (up to 1700 N), the load on the distal tip *decreases* or stays constant. All values are below the max pain threshold of 0.45MPa

Test Observations

Some of the silicone from the limb can be seen to leak out of the socket during testing.  This may have skewed pressure reading results since some pressure was being relieved by the loss of silicone. 

Other testing conducted

Student team

Future Work