Controls Method And Predictive Algorithm - Active Volume Compensation

Prosthetic legs are used by lower limb amputees to walk.  A prosthetic leg is composed of a rigid socket with an artificial foot.  The socket is custom made to closely fit the residual limb. A close fit between the limb and socket is needed to allow force transfer during walking and provide sensory feedback to the amputee of where their limb is in space. 

Amputees have difficulty achieving optimal fit to allow them to walk comfortably.  The residual limb changes shape (volume) during the day and throughout the year.  Currently, to improve socket fit the amputee takes on or off sock liners to adjust for volume differences between their limb and the socket. Companies have tried to address patient fit using laces or ski boot buckles on the socket. This provides gross adjustment only and has not been shown to improve socket comfort or performance. 

Poor socket fit localizes pressure at a point 100mm below the patella (tibial crest, common “shin bone”).  This is undesirable. Skin ulcers form and walking is painful. Painful walking results in reduced socket performance, (EX: Rate your walking performance with a sprained ankle). Amputees frequently use a wheelchair until their leg heals. Re-amputation in diabetics is common from this condition. This cycle repeats over the lifetime of the patient. The patient is affected mentally and their well being suffers. 

Our solution uses active volume compensation to address the problem of prosthetic socket fit. Three shaped air bladders are positioned at the three loading areas of the socket. An air pump, pressure sensors and valves control bladder pressure independently.  A flexible piezoresistive pressure sensor is placed within the socket at the localized pressure point (tibial crest) to record pressure. A gyroscope is positioned within the socket to record motion for later analysis.  

A web based application has been developed. It allows the prosthetist clinician to control the input pressure within the bladders during device testing on a patient and records outputs from the tibial crest sensor and gyroscope. This web app use is limited to testing in clinic, and the graphic interface is usable only by a trained clinician. We have not developed algorithms or models to analyze data from air pressure sensors, piezoresistive pressure sensor, gyroscope or air pump/valves. 

The final embodiment of the device will provide comfortable motion by a patient for 12 hrs. The amount of volume compensation will be determined by limits of battery charge.  Most likely it will modify volume every 1-2 hours, however the ideal embodiment will shift bladder pressure constantly during the walking gait cycle. 

The project is to develop a mobile cell phone app that can be used by a patient and prosthetist to control the device optimizing patient comfort. Suggestions on achieving optimal comfort are expected. See below for input/outputs:

Inputs

• Piezoresistive pressure sensor (PPS) 
• Pump(s)
• Valves
• Battery
• Accelerometer/Gyroscope
• 3 air pressure sensors 

Outputs

• GUI
  • Simple control (patient)
  • Complex control (clinician)

Analysis

• Models to analyze gyroscope and PPS data linked to optimize clinical outcome are expected. 

NDA/IP Required