It is my opinion that a foot that maintains a “mobile adapter" posture during the late stance phase of gait when forward propulsion should be occurring is the most common problem we see when treating the lower extremity biomechanically. A stable medial column in which the 1st metatarsal sesamoid complex can remain resistant to ground reactive force and thus allow a full range of motion of the 1st metatarsal phalangeal joint resulting in a powerful forward push off during walking, running and jumping is what is needed for efficient bipedal machines. Of course this does not happen in isolation of other factors, but it is what we have the most control over with the use of custom foot orthotic devices. Here are some tips in optimizing your orthotics ability to control your patient’s forefeet.
The essential component of the orthotic forefoot is the post. It can either be “intrinsic” or built into the shape of the frame of the orthotic, or “extrinsic” or added as a flat, solid addition to the plantar surface of the frame. Combinations also exist primarily in cases of high degree deformities. Posts can be either varus or valgus. Intrinsic posting is generally more easily tolerated and fits well in shoes. The amount of correction built into the orthotic depends on the deformity measured during the biomechanical examination, the range of motion of the first ray and any variations in the metatarsal parabola. The default correction when no measurement is indicated on the prescription, is to “balance” the forefoot correction to perpendicular to the vertical bisection of the heel within the intrinsics of the frame.
The next decision to be made in the forefoot construction of the orthotic device is the use of an extension. Extensions are either sulcus length or full length. Extensions are helpful for a variety of reasons. They provide extra cushioning to the plantar metatarsal head areas, and provide for placement of pads and accommodations of the forefoot. One added advantage to extensions, in my opinion, is they help keep the orthotic in proper placement within the shoe, particularly in athletic or other large volume shoes that are manufactured with a removable insole. The rigidity or flexibility of the orthotic frame is also a factor in determining the corrective ability of the orthotic device. My general rule of thumb was to typically use a more rigid orthotic for a flexible foot, conversely a more forgiving orthotic device in a more rigid foot type.
Various accommodations are available to enhance the functionality of the orthotic device. Two popular modifications are the Morton’s extension, and reverse Morton's extension. The Morton’s extension is additional padding under the 1st metatarsal head and hallux to elevate it and protect a damaged or arthritic 1st MTPJ. The reverse Morton’s extension is the opposite, with removal of some of the cushioning under the 1st ray to allow the 1st metatarsal head to plantarflex and enhance the range of motion of the 1st MTPJ. Caution should be exercised in using Morton’s extension when adequate 1st MTPJ range of motion is available. A further modification of the reverse Morton’s is the “dynamic wedge” modification which adds an upward ramp (Cluffy wedge) under the Hallux to promote its dorsiflexion. Similar to the reverse Morton’s is the dancer’s pad, which will also allow more plantarflexion of the 1st metatarsal, but is more appropriately used to accommodate an already plantarflexed 1st ray or prominent sesamoid bone.
Some practitioners prefer to use 1st ray cutouts which remove the medial portion of the distal edge of the orthotic frame to allow more plantarflexion of the 1st metatarsal. This modification can be useful when dealing with a hypermobile plantarflexed 1st ray. I would advise using a tip post in conjunction with the 1st ray cutout to prevent weakening of the medial arch of the orthotic device.
A myriad of modifications and accommodations are available for a variety of forefoot conditions related to the over-pronated forefoot. I would direct the reader to study the modifications page of the Kevin Root Medical Website, or spend time looking over all the options available on the Foot ID Pro app.
