Rearfoot Wedges

Most rearfoot posts used on foot orthoses are designed to only block frontal plane motions of rearfoot eversion or inversion, depending on whether they are applied to the medial or lateral sides of the heel cup respectively. 

Such rearfoot posts have been designed this way because eversion is frequently but erroneously, equated with subtalar and foot pronation while inversion is considered equivalent to subtalar and foot supination. Indeed, HeathlyStep’s rearfoot wedges do create such frontal plane resistance forces across the rearfoot, yet they are also designed to achieve so much. 

All HealthyStep’s orthoses have sagittal and transverse plane comfort contouring which slows the rate of lowering of the foot’s profile. The rearfoot wedges can enhance this action.

Because HealthyStep’s distinct comfort contouring profile is higher medially, HealthyStep insoles naturally direct the ground reaction forces through the orthosis (the orthosis reaction forces-ORF) towards the medial side of the rearfoot around the talocalcaneonavicular joint and the navicular bone itself. This blocks distal calcaneal plantarflexion, as well as navicular drop. During late midstance, the anterior part of the design limits medial cuneiform and 1st tarsomatarsal joint dorsiflexion. This interaction of body weight forces dorsiflexing the ankle and midfoot down is being resisted by the orthosis, as indicated by the grey arrows in the image below.

This clever HealthyStep design creates resistance to eversion moments occuring across the rearfoot in the frontal plane too. This is shown by the white arrow resisting the red eversion arrow within the heel cup in the top image below.  Comfort contouring sets up a resultant ORF (yellow arrow) directed posteriorly and superiorly against the body’s loading force vector directed anteriorly and inferiorly through the foot. However, through the utilisation of such contouring, more insole material is positioned on the medial side of the distal rearfoot and proximal medial arch. This means that the resultant ORF is directed slightly lateral to slow all the loading body weight forces driving the foot towards rearfoot eversion, abduction, and plantarflexion.

The addition of the 4º rearfoot wedge increases the medialisation of the ORF by bulking even more material strategically towards the area under the talocalcaneonavicular joint and navicular, increasing the lateral direction of the resultant ORF force. An 8º post being thicker, increases the resistive force, causing the result force vector to become even more laterally directed and better able to slow rearfoot eversion moments during loading and early midstance (see lower images above).

The most noticeable feature of HealthyStep rearfoot posts is that they are far longer than most others on the market, with the thickest and widest areas towards their anterior aspect.

The idea that the rearfoot only requires frontal plane control across the subtalar joint is erroneous for many reasons. This is not least because rearfoot motions arise from the ankle, subtalar (including the most anterior talocalcaneonavicular part), the distinct talonavicular joint, and the calcaneocuboid joint acting together. These joints work in unison, providing the rearfoot with the ability to move in all planes. The subtalar joint alone offers far more sagittal plane motion than was once thought (about 20% of that originally thought to come from the ankle during gait).

HealthyStep’s rearfoot posts are designed differently to reflect the multiplanar and multiarticular motions of the whole rearfoot that occur dynamically, rather than just frontal plane torques. In particular, they control that significant and recently confirmed, sagittal motion. They are therefore generating forces under the rearfoot in a more functional way. Their design reflects that the centre of ground reaction force (CoGRF) is moving anteriorly as increasing areas of the heel and then the forefoot, load. This process continues with the CoGRF moving towards the forefoot during early midstance, onto the forefoot during late midstance, and then into the forefoot alone once the heel lifts. 

Standard rearfoot posts only affect forces during loading response and very early midstance. But HealthyStep’s rearfoot posts are designed differently to prolong their influence by providing proximal vault forces (arch support) during all of the midstance. This is when most rearfoot posts have little or no influence because body weight has moved anterior to them. Thus, unlike most rearfoot posts, HealthyStep have designed a longer-lasting influence on the foot until the moment that the heel lifts.

By altering GRFs on the medial side of the rearfoot with HealthySteps’s rearfoot posts, clinicians can slow the rates of distal calcaneal plantarflexion, abduction, and eversion. They can also concurrently slow the rates of navicular drop, navicular adduction, and slow adduction and plantarflexion of the talus on the calcaneus. These are motions that promote flattening of the foot, commonly known as pronation. In excess, pronation (hyper-pronation) can be associated with too much foot flexibility when the foot should be stiffer. This has been linked to raised lower limb injury rates.

HealthyStep’s rearfoot wedges enhanced pronation-limiting effects resulting from the action of adding firm and angled material bulk (rather than worrying about actual degrees) being placed under the HealthyStep insoles’ unique profiles. Of course, HealthyStep insoles’ profiles are already designed to resist the rate of the foot’s motions associated with pronation but the rearfoot wedges can enhance this action when necessary.

Thus, the amount the foot pronates during loading response and midstance can be adjusted to the patient’s needs by selecting a specific HealthyStep insole profile and adding a rearfoot wedge as necessary. If the level of force from the unadjusted insole is sufficient, then no rearfoot wedge enhancement is required. However, if insufficient, a 4º or 8º wedge should solve most issues.

Reversing the Rearfoot Posts

If the left rearfoot wedge is added to the lateral side of the right insole (or vice versa), the wedges can be used to reduce rates of rearfoot inversion forces. This is achieved by increasing lateral forces under the calcaneocuboid and the lateral tarsometatarsal joints. 

Reversing the side that the rearfoot wedges are applied creates eversion and abduction force to resist the foot rotating into inversion and adduction. However, they still help in slowing proximal vault depression by resisting cuboid drop and lateral tarsometatarsal dorsiflexion. This is an ideal intervention for patients with cavoid feet and chronic lateral instability associated with ankle pains or chronic peroneal dysfunction. Apply as indicated below.

Using rearfoot wedges on the lateral rearfoot can also provide great benefits for those with early medial compartment degenerative joint disease of the knee, by reducing the adduction moment. This is achieved by redirecting the centre of ground reaction force (CoGRF) under the rearfoot during the contact phase and early midstance stage of gait. Osteoarthritis in the medial articulation of the tibiofemoral joint in those with a significant varus angulation to the knee, is extensively evidenced to benefit from a laterally posted insole containing foot vault support. This is especially so if the rearfoot also under-pronates (the heel appears inverted in the relaxed stance position).  

The effect on the knee is achieved by repositioning the CoGRF. On a varus knee, the GRF will be passing medial to it. It thus causes compression on the medial compartment by generating an adduction force or moment (see A below). When a lateral wedge is applied, the GRF can move closer to the knee, reducing the size of the adduction moment (see B). A medial rearfoot wedge in such knee alignment can be dangerous as the moment arm can be moved more medially, increasing the adduction compression (see C).

The contouring of the insole as present in all HealthyStep insoles, resists foot hyper-pronation risks that can result from adding a lateral rearfoot post. This makes a lateral rearfoot wedged HealthyStep insole an excellent option to assist patients with medial knee compartment degeneration.