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Oct 25

Written by: Larry Huppin, DPM
10/25/2010 2:13 PM

 A question from a client today:

Under what circumstances would you reduce manually a forefoot varus, 1st ray elevatus, or forefoot supinatus while performing a foot casting? 

The short answer to the question is: always. We recommend always applying a plantarflexion force to the first ray when casting. Our reasoning is noted below. Now, in the case of a true forefoot varus, applying this force won’t do anything. Forefoot varus is a rigid (skeletal) deformity.

In a 1986 study, Roukis and Scherer found that prevention of first ray plantarflexion resulted in decreased first MPJ dorsiflexion (hallux limitus). A subsequent study by Scherer, et al. looked at the effect in stance of a polypropylene orthosis made from a nonweightbearing negative cast taken with the first ray plantarflexed on patients with a functional hallux limitus. Results of this study were that mean dorsiflexion at the first MPJ increased 90%.

In a 2000 study, Harradine found that increasing eversion of the heel decreased available dorsiflexion at the first MPJ. According to Root, et al. “ground reaction against the first metatarsal head will force the first ray into a dorsiflexed position when the foot is everted by pronation”, and based on the study by Roukis, et al. it can be hypothesized that the decrease in hallux dorsiflexion is secondary to the dorsiflexion of the first ray.

These studies indicate that first ray dorsiflexion leads to decreased hallux dorsiflexion, resulting in functional hallux limitus. Casting the foot with the first ray dorsiflexed will result in an orthotic device that holds the first ray dorsiflexed. This may contribute to increased first MPJ symptoms as a result of joint jamming.

It turns out that casting with a plantarflexed first ray may have other benefits. A cadaveric study by Kogler in 1999 found that valgus forefoot wedging decreased strain on the plantar fascia under experimental weightbearing conditions, while varus wedging increased strain. This study showed unequivocally that the most effective way to decrease strain on the plantar fascia is to evert the forefoot.

To provide the force needed to evert the forefoot, a valgus wedge can be added to the orthosis, but valgus should also be captured within the orthotic plate itself. To do so, as much valgus as possible should be captured during the casting process. To accomplish this, the subtalar joint should be held in neutral, the midtarsal joint maximally pronated and the first ray should be plantarflexed during casting.

View our casting video for more details.


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