I spoke to a ProLab client this morning who is considering getting a ProLab foot scanner in order to replace plaster casting in his office. He was concerned, however, because he sees a lot of diabetic patients and tends to do a lot of accommodative orthoses and he is wondering if the scanner was appropriate for that. Before we answer these questions, I think we have to first define accommodative and functional orthotics.
A functional orthotic is one where the forefoot has been balanced to the rearfoot. This is the most basic of definitions. In general, the cast that is used for this type of foot is nonweightbearing. Because it is non-weightbearing and there is no soft tissue splay that occurs during the casting process, we have to add soft tissue expansion to the positive cast so that the orthosis does not end up too narrow for the foot.
An accommodative device on the other hand, is one in which there is no balancing of the forefoot to the rearfoot. Traditionally, the cast that is used for accommodative orthosis is semi-weightbearing. Because it is semi-weightbearing, there is soft tissue splay that occurs with the weightbearing of the foot and so there is no additional expansion that is necessary to add to the positive cast in order to accommodate the soft tissue.
To get back to our original question, the scanner cannot do a semi-weightbearing or full-weightbearing cast. It has to be a non-weightbearing cast. However, 99% of the time an orthotic for diabetic patients can be made from a nonweightbearing cast and in most cases it is actually the preferred method.
Although traditionally soft accommodative orthoses are usually made off a semi-weightbearing cast, there is no reason at all why you could not make a soft accommodative device off a nonweightbearing cast. The lab simply has to do standard balancing in addition to adding lateral and heel expansion. I am of the opinion that this is a preferred method of taking a cast of diabetic patients because you do gain the additional support that comes from functional correction.
The only situation that I can think of wear a semi-weightbearing cast is going to be preferred is a patient with significantly deformed foot, such as might occur after Charcot arthropathy. In a foot like that that has a significant rockerbottom shape, for instance, I think semi-weightbearing cast would be beneficial.
In addition, there is more and more evidence that using more rigid and controlling orthosis are actually more effective orthotic devices for diabetic patients. This because diabetic patients have the most progressive ulceration under the metatarsal heads and more rigid devices are more effective in transferring pressure off of this area. Of course, you also want to use accommodative materials on top of these more rigid devices and make sure that the devices are the full width of the foot so the patient does not come down on the edge of the orthotic device.