A New Concept in the Fabrication of Double Upright Orthoses
Karl W. Bremer, Jr., C.O. *
INTRODUCTION
The concept of having the uprights for a double upright knee ankle foot orthosis (K.A.F.O.) formed using templates and a pneumatic pressure system has intrigued the author for a number of years. Many ideas have been pursued in an attempt to develop a system that was economical, efficient, easy to use, in need of little maintenance, took up a relatively small amount of space, and could be set up on a standard work bench.
Using the pneumatic forming system in conjunction with carbon fiber composite material, which is used for the bands of ankle foot orthoses (A.F.O.) and K.A.F.O.'s, has made it possible to achieve substantial savings in time. A single K.A.F.O. can be produced in two to 2 1/2 hours time, which is approximately one-third the time otherwise necessary. The orthotist or orthotic technician, requiring less skill, is capable of producing three or four double upright K.A.F.O.'s a day.
THE PNEUMATIC PRESS
The Press* consists of an air bag mounted in a steel support frame. The bag (a section of fire hose) is six inches in diameter and 36 inches long, sealed at both ends, and connected to the shop air system by a nozzle in the middle. At 100 p.s.i. (pounds per square inch), 4,320 pounds of pressure is exerted in the expanded state. This is sufficient for bending stainless steel uprights up to 3/16" by 3/4" in size. Aluminum uprights are annealed for ease of forming and to lessen the chance of breakage. For annealing, the uprights are heated with a torch and the temperature checked, using white soap, which turns a dark brown, or wood, which skates across the surface like soap, and then quenched in cold water for faster cooling. Air cooling also works, and of course 2024T3 grade aluminum alloy regains most of its hardened properties in 24 hours.
A series of ten templates ranging from infant to adult sizes are used to form the uprights (Step 1 ). In 80 percent of the cases, the one standard adult template is used. Use of a template not only speeds the process, but also diminishes marring of the surface and rotation about the long axis of the upright. For any given patient, 90 percent of the required bends can be formed using a standard template. The remaining ten percent of the contouring is done by hand (Step 2, Step 3, Step 4, Step 5, Step 6, and Step 7).
The benefits of using the pneumatic press become evident when forming bilateral K.A.F.O.'s with double uprights, providing the lower extremity tracings have a standard non-atrophied shape. In conjunction with the use of the carbon fiber material, a substantial time savings is achieved. This reduces the time required for completing the orthosis to a total of approximately four and one half to five hours. The four uprights are pressed and shaped within a 20 to 25 minute period.
SUBSTITUTION OF CARBON FIBER COMPOSITE BANDS FOR ALUMINUM BANDS
The use of carbon fiber composite is the result of several years of experience looking for a substitute for aluminum bands. Initially, 1/8" nyloplex was used. Nyloplex is easy to shape, and has beneficial rigidity and memory properties. However, we found that it tended to crack when riveted with metal rivets and when subjected to prolonged stress. As a substitute we tried 1/8" and 3/16" polyvinyl chloride. It is not brittle like nyloplex and otherwise is easy to shape and has good memory. However, its lack of rigidity rendered it unacceptable.
Experience with carbon fiber composite inserts, to reinforce the ankle sections of L.S.U. Reciprocating Gait Orthoses, led us to use carbon fiber composite material+ in sheet form (Step 8 ). To date, this has proven to be the material of choice. Bands ranging in width from l 1/4-l 1/2, depending upon patient size, are laid out on a sheet of the composite material, so as to minimize waste. The bands are cut out using a bandsaw with a skip tooth blade. The two-ply carbon sheet is adequate for small to medium size orthoses on children up to age 12. On larger patients the three-ply sheet is recommended. To minimize the possibility of wrinkles developing when the bands are formed, the bands should be cut out on a bias so the fibers are at a 45° angle relative to the direction of bend. This will also cause the edges to radiate outward from the patient and appreciably increase the resistance to torque. So far, only one instance of breakage has occurred amongst 150 bands. In this instance, the two, two-ply bands on a K.A.F.O. failed. These were changed to a pair of three-ply bands without further incident.
To form the bands, a special device is used. The properly contoured uprights are attached to the extensions and stirrup. They are then mounted in the knee joint alignment fixture which has been set to the proper medial-lateral diameter as dictated by the patient's measurements (Step 9, Step 10, and Step 11 ). The depth and tilt of the thigh and calf bands are established by setting the two horizontal tables. The bands are heated, secured in place with spring loaded clamps, and allowed to cool for 2 1/2 minutes (Step 12 , Step 13 ).
COST AND TIME COMPARISONS
A carbon fiber band costs about $7.50. Five minutes or less is needed to put the three bands in place, ten minutes is needed to finish and attach the bands, for a total of 15 minutes.
An aluminum band costs about $2.50 per band. It takes about 15 to 20 minutes to put each band in place or about one hour to position and attach all three.
It takes approximately two to two and one half hours to fabricate a K.A.F.O. using the pneumatic press and carbon fiber composite bands, versus six hours to fabricate a K.A.F.O. using the conventional technique and materials.
Step 14. Step 15, Step 16, Step 17, Step 18
*Available from Bremer Brace Company, Inc., 1724 South Orange Avenue, Orlando, Florida 32806.
+Available from Durr-Fillauer Medical, Inc., Orthopedic Division, 2710 Amnicola Highway, Chattanooga, Tennessee 37406.
|
