The previous forum post on this subject discussed the basic concepts of pronation and supination of the foot. Now, it would be helpful to break it down further, to simplify the process to three components; rearfoot, midfoot and forefoot, each component with corresponding significant findings of the biomechanical exam and gait analysis leading to accurate foot orthotic construction within the confines of a busy clinic practice, with limited time and resources. We will start with the first portion of the stance phase of the gait cycle, the rearfoot.
The foot strike of the human foot can vary depending on cadence, stride length, shoe type versus barefoot, as well as many other factors. For simplicity sake we will be discussing an average walking gait visualized without shoes. Typically heel strike occurs on the lateral, posterior, plantar of the heel, with normal shoe wear occurring approximately at the 5 o’clock and 7 o’clock positions of the rounded portion of the heels. As the body moves forward over the foot, the heel tends to evert (pronate). The purpose of this motion is to absorb shock and adapt to an uneven weight bearing surface. Over pronation or under pronation may occur during this time, leading to either instability or lack of shock absorption. Heel contact may be affected by structural components above the foot such as the tibia, knees and hips. Also lack of ankle dorsiflexion may lead to absence or diminution of the heel strike. Asymmetry of the heel strike may be an indicator of limb length discrepancy.
The major components of a custom orthotic to treat rearfoot issues are the heel cup and the rearfoot post. The heel cup is the concave surface of the orthotic in which the patient’s heel will sit. The heel cup can vary by depth, deeper for additional motion control of inversion or eversion of the calcaneus, shallower to allow better fit within low volume shoes. The shape of the heel cup can be altered by the addition of a heel skive, which is a flattening of the dorsal concave surface of the heel cup either medially or laterally. Generally used to provide additional motion control of excessive heel inversion or eversion without changing the actual angular correction of the orthotic device. The amount of heel skive can vary depending upon the prescriber's preference and the patient’s needs.
The rearfoot post can be either extrinsic (a flat surface added to the plantar aspect of the heel cup), or intrinsic (built into the heel cup of the orthotic frame by removing frame material from the plantar surface of the orthotic frame at the desired angle. Extrinsic posts are generally more controlling than intrinsic posts, but intrinsic posts are preferred when space within the shoe is at a premium, providing a lowered seating of the foot within the shoe. Corrections of zero to 8 degrees in either varus or valgus direction can be incorporated into most orthotic devices. Posts can sometimes incorporate a rocking motion, such as a 4 degree varus post with four degrees of motion to allow the heel to become vertical. Extrinsic rearfoot posts can also be undercut, so as to be narrower at the shoe/orthotic interface than the width of the heel cup.
Additional corrections can be incorporated into most orthotics depending on the individual clinical need. Lateral flanges are available for cases of excessive heel inversion leading to lateral instability, or medial flanges for excessive heel eversion in cases of flexible pronation deformities. Full heel cushions, horseshoe pads, heel apertures with and without filler can be made on a case by case basis. Heel lifts can be added to the posts as desired, up to 6mm in height. A heel elevator may be used in certain cases particularly when the orthotic needs to be paired with a shoe or boot with a higher than average heel elevation such as a western boot.
A minimum evaluation of the patient’s rearfoot should include a non weight bearing measurement of the heel position with the foot in subtalar neutral position (patient prone) amount of heel inversion and eversion, heel position during relaxed stance and subtalar-neutral stance, as well as during gait analysis including heel strike and heel raise.
This summary of rearfoot evaluation is not intended to be totally comprehensive, I would encourage practitioners to master these concepts in order to better serve their patient’s biomechanical needs in an effective and efficient manner.
