FWT Pressure Sensing System

Recently we were asked to fit a patient with an off-loading AFO for a crushed ankle. The orthosis of choice was a PTB double upright with a solid stirrup attached to a shoe with a steel shank. The orthosis was fabricated, fitted and the patient left the office. I am sure quite a number of you have had this same scenario in your office, but the question remains, did you really off-load the patient's ankle? How do you know?

The same situation is especially true with the diabetic or insensate patient when fitting foot orthoses. It does not require a PhD to look at a callus or bunion to know that pressure exists. The question is, how much pressure is there, and if you have made a modification to an orthotic device, what did you accomplish?

For the past thirty years, our facility has been seeing all types of foot problems both with and without sensation. With the insensate foot, there has always been the additional problem of pressure as sensation is not readily apparent. Available to us today are a number of diagnostic computer-driven systems for the evaluation of pressure problems. These systems are accurate, and very comprehensive in their information. The problem is they are also very expensive and not always available, and they are difficult to transport to an outside clinic.

Whenever you see a patient in your office with a plantar callus, heel spur, collapsed arch or bunion, you don't need a computer to tell you what needs to be done. The problem is, did you accomplish your treatment goal? For years our foot orthotics program was: take an impression of the foot, fabricate the orthotic device of choice and then fit the patient. After fitting, the patient was then sent home to "see how this works." In a week or two, if the problem has not been corrected, we would make some changes and the patient is once again sent on his way to "see if this solved the problem."

The same scenario occurs with an off-loading AFO. How do you know that you have really unloaded a patient in an AFO if you cannot measure pressure in the shoe? Our goal at Felix Brace and Limb Co.. whether with the aid of computer or manual dexterity, is pressure relief with documentation.

In 1992, our facility began working on a pressure-sensing device for the prosthetic foot so an amputee could determine when the foot touched the ground. This was accomplished by placing a pressure-sensing device in the prosthetic foot and attaching electrodes to a stimulating medium. With our system, an EKG pad was placed on a site with normal sensation. Unfortunately, after application on a number of amputees, the system proved to be essentially useless as all of the amputees evaluated were able to tell immediately when the foot touched the ground through pressure in the socket, and the project was abandoned.

The use of electronic pressure evaluation did, however, become quite useful when pressure over the fibular head of an amputee needed to be evaluated inside the socket. The unit was redesigned and the FWT (Felix, Wilkins, & Trott) Pressure Sensing System was developed for spot pressure-sensing. Since that time, the FWT Pressure Sensing system has become an invaluable tool in the diagnosis, evaluation and treatment of diabetic foot care, in socket pressure evaluation, and orthotic pressure problems.

The basic unit for the FWT pressure system is an Ohmmeter meter similar to ones available at Wal-Mart or Radio Shack. The meter is modified to mate with a pressure sensor disk. The modifications include optional resistors, selector switch, and external wiring to both the meter and to the sensors. The time required to finish modifications to the meter is approximately 6 to 8 hours. (The finished meter can be seen on the Internet at www.arkemall.com/fwt.)

The finished unit is connected to two sensors by a single wire, allowing for two evaluation sites. Each evaluation site may be monitored by adjusting the meter from S-1 to S-2. The primary benefit of the system is to establish a pressure reference before and then again after intervention whether it be an adjustment to an orthosis or a prosthesis. This evaluation or measurement can then be entered in the patient record for future reference.

The pressure sensing disks we use are commercially available and relatively inexpensive. The sensors, however, must be modified to unite with the meter. The sensors are 7 to 8 microns thick. They are flexible, reusable and replaceable. The sensors are placed directly on the skin using scotch tape, Micro Pore, or paper tape. (Place the tape on the back of your hand first to help reduce the "stickiness" of the tape. This prevents damage to the sensors when the tape is removed.)

With the sensor in place, your patient can now don a shoe, prosthesis, or orthosis and ambulate with pressure being indicated during each phase of gait. There is no computer, tether cable, or force plate required. You and your patient can now view exactly what is happening before and after modification to the orthosis or prosthesis. This documentation has been a great advantage to both my patients and me as we can both see the results of the treatment.

Portability, availability and simplicity of operation make the unit ideal for diabetic clinics. Placement of the sensor requires only seconds and immediate information about pressure is available.

A significant beneficial aspect of the system is the ability to accurately document your findings and results in the patient's chart.

At the 1997 AOPA Assembly in Charlotte, North Carolina, a number of units were available for a hands-on evaluation by the attendees. They were able to place sensors in their shoes and evaluate the placement of a metabar using a pencil under the sole of the shoe. Also if they happened to have an orthosis in the shoe, they could see what pressure relief they actually had— for the first time!

For more information on the FWT Pressure Sensor system and its use, look on the internet at www.arkemall.corn/fwt or contact Leland Felix at FWT Pressure Sensors 310 Higdon, Hot Springs, Arkansas 71913.

Addendum:
Since this presentation, the sensors used in this system are no longer available from the manufacturer. A replacement is currently under evaluation, and hopefully will be on the market soon.

Once the system is up I will be available for presentations if you have any inquiries.