Mass-Customized Sole/Insole Design Process
The above processes can arrive at the inside dimensions of a particular shoe that best fits the user. However, the standard shoes may still need further customization to support the user's particular body dimensions such as arches. Thus, a mass-customized insole is detailed next.
One embodiment is a diagnosis and a system for design of patient-specific orthotics focused principally on dealing with the kinetics of pronation. In the functioning foot there are specific relationships between the anatomical structures commonly identified from both the frontal plane and the sagittal plane of reference. Instability can result from a misalignment between the forefoot and rear-foot which prevents the foot from functioning in a fully integrated manner. However such a simple structural (kinematic) classification as this overlooks the critical matter of how muscular energy is transmitted through anatomical structures in such a way as to confer normal motion (kinetic function) on the foot. For example, the pronation force about the sub-talor joint axis is known to increase as a result of structural misalignment. But an analysis in kinetic terms would account for the origin and magnitude of the pronation force and why this force affects the sub-talor joint. Once the problem is presented in kinetic terms, the anatomical structures are seen to play their part in the resolution and transmission of forces rather than suggesting their source.
The system also models kinetic processes in the foot using Kirby's dynamic equilibrium between the sum of pronation and supination forces occurring about the sub-talar joint axis. (“Rotational Equilibrium” theory (Kirby, K. A. 2001 “Sub-talar joint axis location and rotational equilibrium theory of foot function” JAPMA 91(9): 465-487)), the content of which is incorporated by reference. Assessed from the sagittal plane of reference, the foot has been described as a compound pivot made up of three key pivots. The three key sagittal plane pivots can be named the “Heel rocker” the “Ankle Rocker” and the “Forefoot Rocker”. Foot pronation results when a restriction occurs at either the ankle pivot or the forefoot pivot during gait. Restriction is revealed by the inability of the ankle or forefoot rocker to function normally. Restriction can be anatomical or physiological in origin and its extent can be influenced by footwear or orthotics or both. If restriction at a key pivot sites persists of foot becomes chronically unstable, pronation becomes endemic. This process can lead to deterioration in pivotal function and further instability.
The fabrication of an orthotic insert or shoe for a patient's foot can include providing shoe sensors with pressure sensors or accelerometers (as detailed in FIG. 1F which shows exemplary footwear with sensors and heater/cooler embedded therein) to the user to pace the foot to one or more of the following tests and ascribing a test value(s) within a predetermined set of relative values for each test which is indicative of one or more properties of the patient's foot:
(i) supination resistance test (as defined); and
(ii) Jack's test (as defined);
(b) recording each test value in a database;
(c) comparing the test values to control values indicative of one or more predetermined orthotic designs stored in the database; and
(d) selecting an orthotic design(s) from the predetermined orthotic designs dependent on that comparison.
The process may further include one or more of a skeletal integrity test, a fascial chord tension test, an ankle joint stiffness-lunge test, a principal activity velocity test, a sagittal plane morphology test, and a hamstring stiffness test. More explanation of the
various tests is as follows:
(a) Supination Resistance Test—This is the amount of force required to resupinate the foot. With the patient standing in a relaxed weight bearing position, the force is graded on various levels and recorded from very low to very high. This index reveals where the centre of pressure is to be applied to the foot by the orthotic device, whether towards the back or the front. Foot integrity is also estimated from the amount of change in arch amplitude observed when the foot goes from a non-weight bearing position to a weight bearing. The change in arch amplitude may be measured within a range of five increments categorized from very low to very high; if the amplitude changes by two increments, the foot is classified as a foot with poor integrity, whereas if the change is just one increment the foot would be classified as one with good integrity. If there is no change then the integrity measure is scored as excellent. These integrity measures give further information for application of the design parameters that relates to the amount of rear foot to fore foot support.
(b) Windlass mechanism test—Jack's Test and Fascial Chord Tension Test. The force required to lift the hallux when the patient's foot is in a full weight bearing position is determined by The Jacks Test. When the hallux is lifted, the foot automatically begins to resupinate. The force to initiate the foot resupination is graded on three levels form low to high. This index provides additional information as to the placement of the centre pressure in the orthotic design. Fascial Chord Tension Test is as follows. With the foot non-weight bearing, the first metatarsal is dorsi-flexed and the prominence of the fascial chord is recorded. The prominence of the fascial chord is graded from low to high. This parameter is important as this allows the design to be modified to accommodate the fascial chord by way of a fascial groove. It is important to be able to adjust the design this way to help protect and facilitate the windlass effect. The orthotic design may require further adjustment including wedging in the rear foot to help push the chord out of the way.
(c) Sagittal plane morphology test. This categorizes the foot in terms of the gradient, the anterior calcaneal surface and the foot apex position. The gradient is evaluated as low, medium, or high. The foot apex position when combined with the gradient is categorized as rear, central, or forward, providing key information on the amount of soft tissue that surrounds the anterior heel area and can affect the amount of rear foot orthotic contour applied in the design.
(d) Hamstrings tension test. This is a test indicating the amount of tension in the hamstrings so as to determine the possible compensatory impact on the ankle joint in the close kinetic chain. Hamstring tension is graded on three levels low, medium and high. When the tension is categorized as high changes are made to the design so as to facilitate sagittal plane function.
(e) Lunge test. Failure in this test implies that greater ankle joint facilitation must be provided for in the design. The design will reflect the increased force needed to establish foot resupination.
(f) Principal activity velocity test. The principle activity velocity is defined as the level of activity the device is being designed for whether that is predominantly standing or moderate walking or running. The activity is graded on three levels from low to high. This is recorded as an index. When applied to the design it influences whether there is a need to more closely contour to the foot type or wedge more the rear foot area of the orthotic. The greater the velocity the greater the force of correction required and the further back the device apex should be.
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