EXTRINSIC POSTING AND INTRINSIC GRIND DEFINITIONS
Intrinsic forefoot correction
In the cad software we change the angulation of the front portion of the device. In essence this will achieve one thing, a change in medial or lateral longitudinal arch shaping. i.e adding 4 degrees of varus correction to the forefoot in the software will create a heightening of the medial longitudinal arch in the distal portion of the device.
All forefoot modifications are intrinsic as standard unless otherwise prescribed.
Extrinsic Rearfoot Posting
The device is milled or printed as one piece with the rear foot post incorporated. The benefit is this post type will not compress over time, the disadvantage is it increases the weight of the device and bulk in the heel of the shoe. It also creates a very firm surface. If your patient has reduced fat tissue or calcaneal bursitis/bone marrow oedema we suggest using a cushioning layer on the dorsal surface of the heel cup (3mm poron) to improve comfort.
MD = Medium Density. Our lab standard EVA
HD = High Density. A shore 70 EVA. Very stiff and non compressive but long lasting.
Only half of the rear foot region is posted with EVA. i.e. For a prescription containing 4 degrees of rear foot varus correction only the medial half of the rearfoot will be posted.
This reduces bulk and weight to the device and applies forces only where required.
Intrinsic Rearfoot Grind
In the CAD software an angle is applied to the rear foot/heel portion of the device which in effect alters the shape of the heel cup. The plantar surface of the rear foot of the heel cup is then ground in the same plane as the forefoot to reduce rocking in the frontal plane.
We suggest that rear foot correction is kept to intrinsic when ordering dress orthoses, soccer orthoses and cycle orthoses. Please note intrinsic correction will deliver significantly less force than extrinsic posting.
Extrinsic Forefoot Posting
Medium Density EVA is added to the plantar aspect of the distal portion of the orthotic shell approximately 1.5 inches back from shell end. It acts to stiffen the device in the forefoot and thus apply greater force delivery/ modify ORF. We suggest applying no more than 6 degrees of extrinsic forefoot posting.
Extrinsic Forefoot Posting to Sulcus
Medium density EVA material is added to the plantar aspect of the orthotic shell approximately 1.5 inches from shell end terminating at the level of the sulcus.
Often used as a runners wedge (Varus forefoot post to sulcus) for MTSS. It is advised that no more than 6 degrees of forefoot extrinsic posting is requested and that the forefoot of the shoe is considerably deep enough to accommodate the added volume. Please consider the effect that forefoot varus posting to sulcus level can have on hallux function as it can restrict movement in the 1st MTPJ