The Research

Research indicates orthotic insoles produce only small, unpredictable, and subject-specific changes in foot posture and joint motion ^[1,2], and that the height of the medial longitudinal arch is a poor indicator of how the foot functions, i.e. how it reacts to vertical ground reaction forces (GRF) and is probably a pathomechanically insignificant metric. ^[3-7]

A number of recent studies suggest the symptom-relieving benefits of orthotic insoles may be primarily due to kinetic rather than kinematic changes in lower-limb function ^[8-10], i.e., orthotic insoles alter the magnitude, direction, and temporal patterns of GRF (external moments) on the plantar surface of the foot, which in turn alters the tensile and compressive forces acting upon the osseous and soft-tissue structures of the musculoskeletal system ^[8-10], and modulates the temporal activity of major muscle groups.

Ground Reaction Force (GRF)

GRF is a vector composed of vertical force, anterior-posterior shear, and medial and lateral shear. It has been postulated that only three orthotic design variables can alter the components of GRF:

1. The top-surface geometry,
2. The load-deformation or stiffness of the shell, and
3. The frictional characteristics of the top surface of the device. ^[12]

The Spenco Medics™ Paradigm

While all orthotic insoles with a heel cup and a degree of arch support will produce small and unpredictable kinematic changes in some wearers some of the time, they are likely to produce a greater kinetic effect in all wearers all of the time. When prescribing orthotic insoles as part of a comprehensive treatment program for lower-limb pathology, perhaps more than motion control, clinicians should consider how changing the magnitude and direction of GRF at the foot-orthosis interface may modulate the tensile and/or compressive forces acting upon the injured structure. For example, if an excessive pronation force is causing the tibialis posterior tendon to function outside its zone of optimal stress (ZOOS) as the etiology of tendinitis, and orthotic insole designed to increase the supination moments (reduce the pronation moments) should be dispensed without too much emphasis being placed on achieving a change in foot posture. This orthotic prescription method has been called the Tissue Stress Theory or Paradigm. ^[13]

Spenco Medics™ Preformed Professional Orthotics are available in four configurations: "Sport" with a blue, high-performance technical top cover and "Dress" with a leather-style brown top cover to complement most dress shoes. Both Sport and Dress are available in Full-Length and 3/4-Length for low-volume or tighter-fitting shoes. Spenco Medics™ Diabetic + Insoles come in Full-length only with non-replaceable heel and forefoot cushioning zones. Spenco Medics™ Diabetic+ Insole features a Plastazote® top cover to reduce friction and cushion the sensitive diabetic foot.

The anatomy of a Spenco Medics™
Orthotic Insole

1. 
   3-POD™ GRF MODULATION SYSTEM

   Interchangeable pods of different densities piston through the semi-flexible cradle to modulate ground reaction forces. Select a firm medial and soft lateral heel pod to reduce excessive pronation forces around the tarsus.

2. DEEP HEEL CUP

   Helps to stabilize the rearfoot.

3. TOTAL SUPPORT^® TECHNOLOGY

   Semi-flexible Cradle redistributes GRF across the whole plantar surface.

4. ADDITIONAL PODS FOR CUSTOMIZATION

   Varying density heel and mid-foot pods allow for in-office prescription modifications.

5. FIRST METATARSAL HEAD CUT OUT

   Promotes improved first-ray function.

1. 
   3-POD™ GRF MODULATION SYSTEM

   Interchangeable pods of different densities piston through the semi-flexible cradle to modulate ground reaction forces. Select a firm medial and soft lateral heel pod to reduce excessive pronation forces around the tarsus.

2. DEEP HEEL CUP

   Helps to stabilize the rearfoot.

3. TOTAL SUPPORT^® TECHNOLOGY

   Semi-flexible Cradle redistributes GRF across the whole plantar surface.

4. ADDITIONAL PODS FOR CUSTOMIZATION

   Varying density heel and mid-foot pods allow for in-office prescription modifications.

5. FIRST METATARSAL HEAD CUT OUT

   Promotes improved first-ray function.

Spenco Medics™ Sample Prescriptions

LOW PRONATION FORCES

Use to the lower-density pod set as shown.

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MODERATE PRONATION FORCES

Use the higher-density pod set as shown.

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HIGH PRONATION FORCES

Use the lower-density pods on the
lateral heel and mid-foot, and the
highest density pod on the medial heel.

---

NEUTRAL BALANCE:
EQUAL DUROMETER TO ALL THREE AREAS

Use the higher-density pod set as shown.