Forefoot Wedges

Controlling levels of compliance across the foot during a step is a fundamental principle of foot function. Many foot and lower limb pathologies link to dysfunction in the adaptive capabilities of the foot to achieve cycles of increasing or decreasing compliance. This
capacity of the foot is fundamental to locomotive health.

After forefoot contact, the foot should initially provide higher levels of shock-absorbing compliance. However, after this, the foot starts a stiffening process that reaches its highest level of stiffness around the heel lift boundary and into the early part of acceleration. This is because the forefoot is required to push against the ground to generate stability and assist forward momentum as the heel lifts, passing body weight onto the next step. Tibialis posterior and peroneus longus working in cooperation, play a pivotal role in making sure foot stiffness can be appropriate before heel lift, while also shifting body weight momentum to align to the line of progression through the medial metatarsophalangeal (MTP) joints. This is easiest to appreciate by looking at the effects of tibialis posterior and peroneus longus across the distal midfoot bones (the 3 cuneiforms and the cuboid) and considering these motions in relation to those of the metatarsals (see image below).

To achieve this weight-bearing shift to the medial metatarsals, the forefoot should adduct and evert as the midfoot plantarflexes as the heel lifts into acceleration, as shown in the image below.

The resultant forces created by forefoot adduction and eversion, off-loads and then lifts the lateral MTP joints off the ground. Pressures increase under the medial MTP joints, ideally mostly under the 1 st and 2 nd , as the medial forefoot drives into the ground as the heel continues to lift upwards.

Elastic energy released from the Achilles tendon powers heel lift. However, the stiffening that permits this power to be transferred across the midfoot and applied to the forefoot to drive off the ground, depends on other extrinsic and intrinsic muscles stiffening the midfoot and reposition the forefoot. Tibialis posterior and peroneus longus are key elements in achieving this, assisted by the long digital flexors and multiple plantar intrinsic muscles. Their combined action compresses the midfoot articulations together in such a way, that the metatarsal shafts, tarsometatarsal joints, and the midfoot increase their transverse plane curvature across the foot’s vault (or arch). The passively more mobile 1st tarsometatarsal joint, should now dramatically increase its stability for the application of acceleration power to the medial forefoot. These multiple motions of stability move pressures and forces under the foot towards the medial MTP joints. The 1 st and 2 nd MTP joints are the most mechanically suitable joints to rotate the foot around at heel lift, as the ankle and midfoot start to plantarflex. This is because in most patients, they align to the lower limb and foot’s line of progression.

All HealthyStep insoles are intrinsically designed and fabricated to help facilitate these motions. However, sometimes foot and ankle muscles are so weak that they do not have enough power to create the stable medial forefoot platform necessary for acceleration by use of the standard insole profile alone. HealthyStep’s forefoot wedges aid motions that create forefoot stability while concurrently assisting in positioning of the medial MTP joints to improve their freedom of extension, in those who require extra help (see image below).

HealthyStep’s forefoot wedges enhance forefoot adduction and eversion. They also resist motions of forefoot inversion that can link to lateral ankle instability.

This is particularly so in cavoid feet with a valgus orientation to their forefoot. Cavoid feet subject to ankle osteoarthritis are particularly prone to inversion moments across the forefoot. Combining HealthyStep’s insoles with a Rearfoot Rocker addition and a forefoot wedge can prove an excellent combination where ankle motion is reduced in laterally unstable cases of ankle degeneration.

Reversing the Forefoot Posts

By adding left forefoot wedges to right insoles and vice versa, HealthyStep’s forefoot post can reduce rates of forefoot inversion instability that can cause the rearfoot to evert and the midfoot to excessively dorsiflex. Excessive forefoot inversion, abduction, and dorsiflexion occur in more severe forms of foot mobility, such as higher levels of tibialis posterior dysfunction. However, please be very careful to assess the benefits to gait after placing the post in this position before the patient leaves the clinic.