In the previous post we discussed the variabilities of custom foot orthotic width and defined the four common width determinants. Now, a discussion of orthotic length determination would be logical. Three basic orthotic lengths are available, no extension, a sulcus extension, and a full extension. There is application for all three of these device types. Regardless of what extension is used, it is important to have proper frame length (the rigid or semi-rigid part of the device) to allow maximum benefit of the orthotic device. We will be discussing frame length evaluation below.
Generally speaking, the distal edge of the orthotic frame should be positioned just posterior (proximal) to the weight bearing surface of the metatarsal heads and should mirror the patient’s metatarsal parabola. This is particularly important in the 1st ray. Commonly, the orthotic frame can be manufactured slightly too long or too short. Neither miscalculation is good, a too short frame will lead to undercorrection in many cases, but a too long frame that isn't recognized and identified may lead to a therapeutic failure and potentially create unintended consequences. A frame that is too long for a patient’s foot may lead to an iatrogenic functional Hallux Limitus condition and create compensation mechanisms due to a lack of adequate propulsion through the great toe. It is easy to detect a too long orthotic frame with a simple examination technique.
This is usually performed during the orthotic dispense visit, but may be done at any time during the treatment course. With the patient sitting (or prone if you prefer) press the orthotic device against the patient’s foot. Palpate the metatarsal heads which should all lie just distal to the front edge of the orthotic frame. If no extension is present you can visualize the metatarsal heads. Next, with the back of the examiner's hand pressing the frame against the foot, the examiner’s thumb presses under the distal medial edge of the frame. With the other hand, move the great toe through a full range of motion in dorsiflexion and plantarflexion. If the device is too long, the plantar surface of the 1st metatarsal head will push the orthotic away, if it is the proper length the orthotic won’t move when you manipulate the patient’s 1st MTPJ. I use the same technique in evaluating the medial arch, the orthotic and the foot should maintain congruence throughout the 1st MTPJ range of motion. (Figure 1)
A similar examination can be performed with the patient standing on the orthotic device. (Figure 2)
I have found this to be a little less effective than the non weight bearing exam, however you can determine if the patient’s foot may or may not sit properly on the device. It is a common problem to see a gap in the posterior heel cup of the device and the patient’s foot, leading to a tendency for the patient’s foot to slide forward which will give the impression the device is too short. A simple adjustment can usually fix this problem. You can check the patient’s 1st MTPJ ROM when standing on the orthotic device versus when in a relaxed position without the orthotic, there should be improvement with the orthotic in place. This is a great demonstration to the patient that their orthotic is actually “doing something”.
Most orthotic problems can be avoided and optimum success attained, with proper evaluation and adjustment techniques. Please don’t hesitate to communicate with your team at KevinRoot Medical to reach for success in all your orthotic cases.
