5/20/2010 9:05 AM
Prescribing rearfoot post motion is one of the more confusing issues on orthotic prescriptions.
Traditionally, the post motion is prescribed as 4/4, 0/0, or some other similar combination. It is important to understand what each of these numbers mean.
The first number is the amount of lateral grind on the post that holds the front edge inverted before forefoot loading. This is most often 4 degrees to accommodate the inverted position of the heel at heel contact.
The second number is the amount of motion the orthotic has during forefoot loading when the front edge comes down to the ground.
A 0/0 post is ground parallel to the front edge of the orthotic and is intended to keep the front edge flat in the shoe regardless of foot movement.
A 4/4 post is one in which the lateral aspect of the post is inverted 4 degrees to the front edge of the orthosis and there is 4 degrees of motion (eversion) allowed to bring the medial half of the post parallel to the front edge of the orthosis.
A 4/0 post is a varus post that holds the front edge of the orthotic inverted and should only be used with an accompanying forefoot varus post for patients with an uncompensated rearfoot varus. This technique holds the orthotic inverted during the entire stance phase of the gait cycle and has no motion.
Given all this, the rearfoot post is in most cases simply a stabilizer of the orthosis inside the shoe. It is difficult to predict how much frontal plane motion of the orthosis there will be inside the shoe. Thus, in most cases you will prescribe 0/0 or 4/4 but it probably does not make that much difference clinically which one you prescribe.
If you want extra control, don’t invert the post but rather ask us to invert the cast. This is a more effective technique and makes the orthotic much more stable in the shoe then inverting the orthotic by inverting the rear post.