Short Saddle

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

Recent foot research has proven our experts to be correct, so we won’t be changing our insole profiles (because we know they are the best standard profiles on the market). However, we recognise that sometimes muscle dysfunction is such that a higher profile support is necessary. Commonly, this is just required temporarily, until rehabilitation can start to improve the situation.

Being made of TPU means the short saddle can both support and shock absorb under the more central foot vault. This addition adds an extra dimension to HealthyStep’s inbuilt comfort contouring profiles across its orthotic ranges. For a little extra vault support, use the short saddle. If vault and forefoot stability are more dramatically poor, use a long saddle instead. Effective foot orthosis provision is all about being customisable to changing situations, not setting treatment to one immovable custom prescription. Thus, a long saddle can be used first, then a short saddle as foot strength and stability improve. Finally, the basic orthosis shape may be sufficient, and if full function can be restored, an insole may no longer be necessary.

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 having a plantar vault, soft tissues can create profile changes that enhance these properties. Stiffening a structure actively is easier to achieve by decreasing the radius of 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 longitudinal ‘arches’. 

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 by offering compliance through muscle relaxation. This allows the vaulted profile of the foot to flatten, lengthen, and widen to act as a shock absorber. Thus, during the early stance phase, the foot should change shape more rapidly than at any other time, but in a controlled manner.  

The foot must start to stiffen once bodyweight has passed in front of the ankle. The foot now continues to flatten, lengthen, and widen, but at a much slower rate. This results from the foot’s connective tissue tension and increasing muscle activity. This mix of passive and active stiffening activity causes shape changes that increase the curvature of the forefoot vaulted profile in the transverse plane. This decreases the amount of muscle power required to sufficiently stiffen the foot to prevent midfoot buckling (known as midfoot break) at heel lift. Insufficient stiffness at heel lift can cause the metatarsal declination angles to be too low to permit important free digital extension as heel lift starts.

Damage to muscles or ligaments across the vault can disrupt foot compliance-stiffness levels. The short saddle is an addition that passively maintains the transverse plane contouring under the vault, even when the natural soft tissue mechanisms have significantly failed. This is extra distal arch support applied in a far more scientific manner than just adding material under the medial long arch.

Whether attached underneath a total-support contact device, such as an X-Line (as in the image above) or to the top of a Vectorthotic shell (as shown below) the effect of a saddle is to restrict how much curvature across the vault is lost, with support aimed at both the transverse and longitudinal profiles.