Posterio-lateral heel wear is normal and observed in just about every pair of shoes, boots, or other types of footwear one inspects.
I don't know what is meant by the term "foot progression angle"; however, the following is the reason why just about everybody wears the heels of their footgear on the posterio-lateral aspects:
There are no muscles on the anterior medial aspect of the tibia.
As a result, when the lower extremity is off weight-bearing and moving thru the swing phase of gait, the muscle groups on the lateral and posterior aspects of the lower legs (the calf muscles) contract slightly without any countering effects (due to the absence of musculature on the anterior medial aspects of the tibia) that would otherwise cause heel wear to be
located centrally on the posterior aspect of the heels of the footwear where most might like to believe would be "more normal" heel wear.
So when people see the heels of their shoes or boots wearing posterio-laterally, they think that this is "abnormal" wear; when it fact, it is perfectly normal as a result of the anatomy of the lower legs as previously described.
You're right in saying that "patients. parents, and shoe manufacturers ask about this 'phenomenon' all the time" and I hope that what I've posted here will bring some enlightenment to this "phenomenon".
It has EVERYTHING to do with our anatomy and little to do with biomechanics!
:)
Yours sincerely,
Dr. Louis C. Talarico, II, CEO & Director of Research
The Biomechanical Engineering & Shoe Research Laboratory
114 Hatch Road
New Gloucester, Maine 04260
Tel.: (207) 926-3488
E-mail: DrLCT2@BESRL.com
Dr LTC2: no disrespect, but surely this is not new? I was taught this as a student a million years ago. It was the shoe wear that was not posterio-lateral that was the issue. Rob