Orthoses to fît shoes
R. G. S. Platts *
A. Field *
S. Knight *
Orthoses which fit inside shoes have, in many cases in the past, been fashioned to the shape of the patient's foot. It is suggested that improved stability and comfort is achieved if, instead, the outside shape of the foot-piece of the orthosis is fashioned to the inside shape of the footwear. A method for achieving this is described.
Thermoplastic polymers like polypropylene and high molecular weight polythylene and glass reinforced plastics have now an established place for use in lower extremity orthoses. Ankle-foot orthoses in polypropylene and knee-ankle-foot orthoses in polyethylene are common examples. Because the use of these materials enables an intimate fit with the leg and consequent improved cosmesis, it seems to have been the practice in many cases, to extend the intimate fit to include the ankle and foot and then to apply the footwear over the rounded, anatomically-shaped, but rigid, foot-piece.
This ensures a poor fit of the orthosis to the footwear which is not normally anatomically shaped and doubts on this point can be readily resolved by a look at the last of a normal shoe.
Lower extremity orthoses which extend into the footwear are invariably required to sustain either vertical loading or to confer horizontal stability in either sagittal or coronal planes—or both. These forces must be transferred from the orthosis as a whole, acting as an exo-skeletal shell, through the footwear to the ground. In this sense the footwear is also an exo-skeletal shell, which needs to be removable from the orthosis, but which is connected to it only by friction enhanced by straps or laces etc.
We thus have, for example, in the coronal plane (Fig. 1 , left) an orthosis with a rounded (anatomical) heel shape. On uneven ground there is a tendency for rotation of the shoe around the orthosis heel. Whereas, if the orthosis is shaped to fit the shoe exactly (Fig. 1 , right) it is not so free to rotate especially when there is any vertical loading in addition to that from footwear fastenings. The same kind of considerations apply to the shaping in the sagittal plane. It is clearly sensible to create an intimate fit between the exo-skeletal shells which are connected only by frictional forces.
An abnormal foot can be accommodated inside the shoe-shaped orthosis by modifications such as arch supports, metatarsal pads, blocks, etc. built into the inside.
A satisfactory method of achieving an intimate fit of orthosis to footwear is as follows:
The inside shape of the shoe is obtained from;
a commercial last of the standard footwear so that it fits easily into the shoe (usually one size smaller) or, the last/cast upon which special surgical footwear has been made or, a cast of the shoe (trimmed to make it an easy fit in the shoe).
A "last shell" is made from the last/cast (Fig. 2 , top). It is convenient to have the extension up the back of the heel to prevent deformation of tissues when taking the weight of a flail leg.
The last shell is taped to the patient's leg prior to casting (Fig. 2, bottom).
The cast is taken incorporating the last shell.
The positive mould has therefore imparted to it the profile of the last shape (as in a.) and therefore the inside shape of the shoe.
The plastic orthosis moulded on to this positive fits the shoe (Fig. 3 ). (The thickness of the material used is accounted for by the loose fit of the last and the slight shrinkage of thermoplastic materials on cooling).
A certain amount of difference in heel height may be accommodated in most orthoses by the flexibility of the base of the foot-piece. If patients need to use footwear with widely differing heel heights, the second orthosis may be made with a different pitch.
The above method has been employed in 54 knee-ankle-foot orthoses in ortholen and in 31 ankle-foot orthoses in polypropylene.
Patients have commented on the improved stability and comfort. The method requires that the orthotist has the intended footwear in advance of making the orthosis. This is an advantage because it emphasizes the need to co-ordinate the footwear with the orthosis—a process too frequently neglected. It also makes it easier to control and maintain the correct attitude of the foot at the time of casting—a vitally important feature for a satisfactory, close-fitting plastic orthosis.