Foot orthoses

Details Foot orthoses Foot orthoses

1996-02-20

1998-09-01

Hindenburg, Max

Surgery

Diagnostic testing

Measuring anatomical characteristic or force applied to or...

600595, A61B 5103

Patent

active

058003649

DESCRIPTION:

BRIEF SUMMARY
This invention relates to apparatus and methods for use in the prescription, design and production of biomechanical functional foot orthoses.
Such orthoses can be used to compensate for, and to control, abnormal movement of, and within, a person's foot or feet. The orthosis is a customised insert which fits into the person's shoe or other footwear and is effective in exercising the desired control to the foot.
However, difficulties exist in the current techniques for determining the design of an appropriate orthosis to suit an individual foot. If the shape of the orthosis is inappropriate, the orthosis may not achieve the desired control over the person's foot, and it may even cause distress to the person using the orthoses.
Before an orthosis can be prescribed for a foot, it is necessary to measure the characteristics of the foot. This is usually done by a prescribing practitioner identifying predetermined reference points on the foot and marking these on the skin with a pen. Distances between certain points are then measured, and angles between lines joining the points are measured with a protractor or other instrument. A major problem with this technique is that it can be difficult to determine the exact positions of the reference points to mark on the foot. Further inaccuracies are caused by skin movement over the underlying bones of the foot, and difficulties in keeping the foot absolutely still in the appropriate position to take the measurements.
In view of the known difficulties in pin-pointing the reference points on the foot, a system of approximate points has been devised in which the points are, in general, easier to determine for each individual foot. It is then left to the fabrication laboratory at which the orthoses are manufactured to make estimate corrections to the measurements taken by the prescribing practitioner.
Although this simplifies the procedure for the practitioner, it represents a further source of inaccuracy.
When prescribing a design for an orthotic device, the prescription instruction usually comes from a standard neutral position cast (S.T.J.N.) with the forefoot maximally pronated on the rearfoot. The cast is usually plaster of paris bandage, and the final casting position is maintained by the prescribing practitioner physically holding the person's foot in a predetermined position. The neutral position has been defined as a standard reference position from which the deviation of the person's foot from "normal" can be quantified.
As an alternative to casting, another known technique involves the practitioner holding the person's foot in a predetermined stationary position while its profile is determined by a scanning laser beam.
Both of the above techniques suffer disadvantages in that they only study the foot in one stationary position. Kinetic measurements, for example, the range of available movement, cannot be made accurately, and consequently these have to be estimated by the prescribing practitioner. It can also be difficult, especially with children or with the elderly, to remain absolutely still for long enough to obtain an accurate cast or scan.
In the case of casts, it has been found that up to 75-80% of prescription casts are incorrect, and have to be corrected at the fabrication laboratories where the functional orthoses are made. Such a high rate of error is very unsatisfactory and can lead to further errors in an attempt to correct the original mistakes.
A further known technique for studying a person's foot is to place small adhesive pressure transducers on the foot, so as to monitor directly 3-dimensional forces with time, as the patient moves about. However, as well as being incapable of detecting rotational forces, this system is subject to movement of the skin on which the sensors are placed. The system also relies on significant assumptions being made regarding forces within the foot and regarding the position and orientation of the foot.
Established processes for the manufacture of the orthoses have often included many process stages, each requiring su

REFERENCES:
patent: 4267728 (1981-05-01), Manley et al.
patent: 4686993 (1987-08-01), Grumbine
patent: 4813436 (1989-03-01), Au
Begg et al. (1991) Clin. Biomechanics 6:168-72.

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