The medial heel skive is an effective technique for providing greater control in an orthoses. It incorporates an interior varus wedge into the medial aspect of the heel cup of the orthosis. In order for this to be effective, the heel cup must be high enough to apply force medial to the subtalar joint axis.
As this technique becomes more popular, it becomes increasingly important to understand how to prescribe properly. Keep in mind that medial heel skive can lead to heel irritation at the edge of the orthosis in two instances: when the heel cup is too narrow and when the heel cup is too shallow.
Since the medial heel skive puts greater pressure on the heel fat pad, it widens the heel fat pad. Using a deeper heel cup can help contain the heel fat pad and prevent lateral edge irritation. Also make sure you provide caliper measurements of the heel width on weightbearing to your lab in order to ensure proper width in the orthoses.
Since a medial skive shifts the foot laterally, the heel cup must be deep enough to contain the heel and provide control without causing edge irritation. The minimum heel cup depth when using a medial heel skive is 14 mm. The heel cup depth should increase as the amount of skive increases. Therefore, you cannot use a medial skive with a dress orthoses since the heel cup depth is generally less than 14 mm.
When you are combining a medial skive with inversion, the slope you create can cause the foot to slide into the upper lateral edge of the heel cup. Using a deeper heel cup will prevent this problem. To avoid lateral heel cup edge irritation, use a 20-mm or 22-mm heel cup when the amount of skive plus the amount of inversion is greater than 5. To give you an example, 4mm skive plus two degrees of inversion = 6. Therefore, you would prescribe a 22-mm heel cup.