The previous post in this series discussed the rearfoot considerations of building a custom foot orthotic, and continuing with the theme of breaking down and simplifying the process into three parts from posterior to anterior, this post will address the midfoot components of the custom Root type food orthotic. Once again I will stress the necessity of a good biomechanical exam and gait evaluation, along with other considerations of any given individual patients needs, such as intended shoe gear, activity, body morphology, gender, age and weight in help determining which orthotic corrections will prove to be the most beneficial to the patient.
Defining the midfoot portion of the orthotic device as from the just distal to the plantar fascia insertion point extending distally to the area of the tarso-metatarsal (Lisfranc’s) joint. It is also helpful to divide the central portion of the orthotic device into medial and lateral components. Generally speaking, the apex of the orthotic is most medial near the Talo-Navicular joint, curving downward laterally for approximately 2 ⁄ 3 the width of the device. The lateral 1 ⁄ 3 of the orthotic is generally (but not always) relatively flat compared to the medial portion.
Determining the medial arch height is the most critical decision regarding the midfoot portion of the orthotic. When the lab receives the scan or impression of the patient’s foot, if no preferred designation is given for arch height on the prescription, the default is to automatically lower the arch 3 mm. Lowering the arch often makes the orthotic more comfortable for the patient. Many exceptions to the 3 mm standard exist, and it behooves the practitioner to know when it might be best to have full arch support or conversely, a more flattened orthotic frame on the medial side. The relative rigidity or flexibility of the frame material should also be determined at this point, as well as the potential use of a frame filler, to help determine the level of arch support of the orthotic device. One “trick” I found helpful in my practice, to help tolerate medial arch support in certain cases, is to have the lab lower the medial arch of the frame a certain amount, and replace the lost support with a Scaphoid pad of equal height.
Additional corrections to the medial middle portion of the orthotic, besides the scaphoid pad are available. The modifications page of the KevinRoot Medical website is a valuable resource with a large menu to choose from. A wide arch profile or a medial flap are both capable of increasing the medial support in the hypermobile flat foot. A Navicular button out can be used to accommodate enlarged or accessory Navicular bones. A fascial groove is an underutilized modification, it can be used with or without the presence of plantar fibromatosis, when maintaining a tight medial arch support is important while simultaneously avoiding irritation of a bowstrung plantar fascia.
The lateral aspect of the midfoot portion of the orthotic device should conform to the anatomy of the patient’s foot. It is often a relatively flat surface but in many cases can be convex or concave. In the case of desired additional lateral support of the midfoot, one should consider using a lateral frame reinforcement, with or without additional corrections. The “Denton Modification” is described in detail by Dr Richard Blake on the webpage for the lateral frame reinforcement on the KRM website. Another unusual modification is the “Carlton Saddle” which is used to help offload the heel and metatarsal heads by elevating the midfoot. Cuboid offloading pads are available in various heights for cases of Cuboid subluxation. A cutout for a prominent 5th metatarsal base is also valuable in cases associated with metatarsus adductus or post 5th metatarsal fracture.
I cannot stress enough the value of marking your scan or impression appropriately when requesting specific modifications such as pads and cut outs. Accuracy and ultimately effectiveness is greatly reduced in the absence of accurate markings of the negative scan or impression. I would encourage all KRM clients to familiarize themselves with the custom modification page of the KRM website, it will enhance your ability to quickly and effectively prescribe the best orthotic device for all your patients.
