Long Saddle

Healthystep’s insoles offer superb 3-dimensional comfort contouring of the foot’s ‘arch’. Our clinical experts have always viewed the foot as possessing a complex, multi-tied viscoelastic asymmetrical conical vault. This structure enhances the foot’s ability to shock absorb and store energy. It does this through deformation and muscle-induced shape changes to alter stiffness and compliance properties across the foot in an adaptable manner.

Extensive new research evidence has proved our design team correct, so we won’t be changing our insole profiles (because we know they are the best profiles on the market already). However, we do recognise that sometimes foot muscle dysfunction is such that a higher-profile support is more desirable for a better outcome. Commonly, this is just required temporarily, until rehabilitation can improve the situation.

Experienced experts in foot orthosis prescription have long used bespoke saddle-profiled additions, but these are the first commercially produced standardised saddles. Being made of TPU means they can both support and shock absorb under the plantar foot when the natural ‘arch’ biomechanics are failing. This adds an extra dimension of customisation to HealthyStep’s inbuilt comfort contouring profiles across its orthotic ranges.

Engineering laws state that structures can stiffen by increasing their curve (by decreasing the radius of curvature) and by shortening the distance between supports, known as the span distance. By having an asymmetrical concave under-surface, the plantar foot can alter both curvatures and span distances longitudinally, transversely, and obliquely. This means the plantar foot creates a variable hemi-coned shape, narrower proximally (see figures A and B below). Increase the curves within the vaulted profile of the foot, and it will stiffen. Increase the length of the longitudinal arch, and it becomes more flexible. 

Muscle contractions and connective tissue tensions in ligaments and fascia also play an important part in creating greater compliance or stiffness. However, by possessing a plantar vault, soft tissues across the vault can create profile changes that adapt these properties. Stiffening a structure actively is easier to achieve by increasing curvatures across the shortest spans. Thus, stiffening the foot is easiest through the transverse plane, from medial to lateral, rather than trying to do so across longer longitudinal ‘arches’.

During a step, the foot increases its vaulted profile before forefoot loading by activating muscles that create extra elastic stiffness. Once the forefoot makes ground contact, this elasticity is used as a shock absorber as stiffness is reduced through muscle relaxation. This allows the vaulted profile to flatten rapidly to act as a shock absorber. Thus, during the early stance phase, the foot should lengthen and widen more rapidly than at any other time, but in a controlled manner.

Once bodyweight has passed in front of the ankle, the foot should start stiffening. The foot now continues to flatten, lengthen, and widen, yet at a much slower rate as the foot’s connective tissues tension and stiffen under rising stress, while muscles supporting the foot become increasingly active. This mix of passive and active stiffening activity causes shape changes that decrease the radius of curvature of the forefoot transverse plane vaulted profile. This decreases the amount of muscle power required to make sure the foot is stiff enough for the heel to lift without the midfoot buckling (known as midfoot break).

Damage or weakness to muscles or ligaments within the vault can change all this ability and sometimes dramatically so. The standard comfort-contoured profiles of Healthystep insoles reflect the far more common but less severe issues with vault biomechanical dysfunctions. The X-line TPD design particularly reflects the importance of tibialis posterior in foot vault mechanics.

An ability to influence the foot’s vaulted profile using orthoses that can be easily modified as necessary is important for dynamic modern foot care.

The Long Midfoot Saddle is an addition that passively maintains longitudinal and more importantly, transverse plane contouring under the vault even when the natural soft tissue mechanisms have significantly failed. This is extra ‘arch’ support, but applied in a far more scientific manner than just adding material under the medial long arch alone.

Whether attached to the underside of a total-support contact insole, like an X-Line (as pictured above) or added on top of a Vectorthotic shell (or bespoke hard shell…see image below), the effect of a saddle is to restrict how much the curvature across the vault is flattened. In each situation, when positioned correctly to the insole design, the saddle’s contour support is aimed at both the transverse and longitudinal profiles.