In the early days of my career, plastic braces were the wave of the future, and conventional metal orthoses were “old fashioned.” But over the years, I’ve managed to find a lot of value in the rugged simplicity of the conventional metal orthosis. I was lucky enough to have trained when almost every brace clinic had metalworking tools, and everyone knew how to use them. It is a skill and an art that has since been pushed nearly to extinction. Few technicians master metal orthoses, and few practitioners have ever made one.

Metal orthoses are simple to fabricate. I once visited a brace shop in Port Au Prince, Haiti, which was staffed entirely by people who were deaf mute. They made crude but very effective orthoses with little more than an anvil, a drill press, and a lot of files. They made their own rivets out of discarded nails, used cold-rolled steel for the bands and bars, and just filed the ends of the bars to create joints. It’s becoming less and less common to see even basic metalworking tools in most facilities these days, so a lot of technicians become frustrated by metal work. Though metal orthoses are simple to fabricate, some specialized tooling is needed to make the job easy and efficient. They also require practice. It’s hard to get really good at something you do twice a year with half the tools you need.

One of the primary reasons metal orthoses are used is that they’re really rugged. Even today, with modern thermoplastics and composites at our disposal, just the phrase “rugged orthosis” conjures images of Mel Gibson in the Mad Max movies wearing his old Pope Klenzack AFO with the joints on backward. This is one Hollywood image that is rooted in reality. These designs have long been favored by hard-working farmers, factory workers, and heavy-equipment operators. However, they can also be made to be quite light. Using lightweight aluminum and thin-gauge bands, you can produce devices whose weight, with the shoe factored in, compares to some thermoplastic designs.

Metal braces also offer a level of torsional rigidity that can’t be matched. When you’re trying to reduce genu varum or genu valgum, that rigidity allows the device to resist medial or lateral loads very well, even when there is a rotational element. If your primary pathological force is in the sagittal plane, such as a knee-flexion contracture or hyperextension, a conventional metal device is a great way to manage those forces. The inherent shape of the mechanical structure is normally a dual parallelogram. This shape allows the device to resist forces in every plane with a very small cross section. That means we get a lot of strength from a fairly small mass, and the patients get a lot of control without a lot of weight.

Metal orthoses usually offer a very small contact surface. This can be a disadvantage in cases with tissue damage or where tissue requires a broad, low-pressure contact force. A lot of people don’t need that, especially in warmer climates! If the patient has good tissue and the forces required for correction can be limited to a small area, then a metal orthosis can work well. Even in cases in which the contact patch has to be increased, this can often be done with a leather lacer. Less contact means less heat build up, less opportunity for impingement, and more comfort.

Metal orthoses are normally attached to a shoe, which presents its own set of pluses and minuses. Frequently, (especially with KAFO patients) the foot may not actually be involved in the pathology. If, for instance, the device is intended simply to correct genu varum, involving the foot could be counter-productive. When a thermoplastic foot cup is used, the patient will lose some ankle motion, inversion/eversion, and proprioception. These are all important mechanisms for normal locomotion. The attachment of the device to a shoe will maintain a lot of these factors as “normal.” Attaching the device to the shoe might limit footwear choices, even when a split stirrup is used, but the use of a plastic foot cup does not imply an unlimited choice of shoe options. Lastly, having a visible stirrup can be perceived as less cosmetically acceptable for some wearers, but for many the increased comfort and function are more than enough to offset this.

Of course, we get to use a lot of different materials in this industry, and just about all of them have a demographic to which they can be appropriately applied. Whether it is the comfort and control of thermoplastics, the low mass and high strength of composites, or the open, rugged designs of conventional metal, there is something for everyone.

Also published in the November 2009 issue of the O&P Edge. © 2009 O&P Edge