2/18/2010 5:13 PM
I consulted with a client today who had a patient with peroneus brevis enthesiopathy.
The goal with orthotic therapy in these cases is to increase the force that the orthotic is exerting on the foot lateral to the subtalar joint axis. Since the peroneus brevis is acting to evert the foot, our orthoses should assist this action in order to reduce the need to fire this muscle. Not suprisingly, it is often patients who are laterally unstable who experience this problem.
Remove soft tissue varus (supinatus) when taking the negative cast. This is imperative as it results in greater forefoot valgus in the negative cast and ultimately in the orthosis. This results in an orthosis that will better support the lateral forefoot and thus reduce the need for the PB to fire. Watch our casting video
- Material: A semi-rigid polypropylene. Either direct-milled or vacuum formed.
- Heel cup height: A deep (18mm) heel cup will be used so that we can apply force on the lateral heel
- Width: Wide to spread force over a larger surface area and thus improve comfort.
- Cast Fill: Standard or minimum. We are not worried about collapse of the medial arch in this pathology so a standard fill should work well.
- Skive: A lateral heel skive can be used to increase the force applied on the lateral aspect of the subtalar joint and apply a pronatory torque. This is essentially the opposite of a medial heel skive.
- Cover: Cover to the toes or sulcus. Glue cover posterior only so adjustments can be made easily. I like EVA, but the choice of cover material is primarily personal preference.
- Rearpost: Prescribe a “no-bevel” lateral rearfoot post which is vertical (not beveled in) on the lateral aspect. This increases the lever arm applied lateral to the subtalar joint axis and again increases pronatory torque, which in turn will decrease tension on the peroneus brevis.
- Forefoot Extension: A valgus forefoot extension can be used to increase force under the lateral column during mid-stance and toe-off. A valgus extension is usually composed of Korex and will extend from the distal end of the orthosis to the sulcus of the toes.
IMPORTANT - CHECK YOUR LAB
It is very important that your laboratory not overfill the lateral column. This is a common problem, so evaluate this carefully. The best control, and clinical outcome, will occur when the lateral column of the positive cast is true to the shape of the foot.