Eric,

>When the STJ supinates the center of pressure will be more lateral.  If there 
is enough eversion available at the subtalar joint, when the STJ pronates the 
center of pressure will be more medial.  It seems to me that high and low 
gear push-off complicates the above simple understanding of center of 
pressure.  Can you explain to me what the high and low gear adds to the above?<

NO! I wish I could! The difficulty is identifying when the need to compensate by utilizing a more lateral loading or more medial loading of the forefoot during propulsion affects or is affected by STJ position. Not so simple either way!

Ray,

>I have not uncommonly seen patients with a
markedly supinated foot - often termed a high degree of partially
compensated rearfoot varus - and utilizing what BM would call their low gear
axis) with a marked medial shift of the COP (using in-shoe F-Scan) that
seemed to be the result of extremely high pressures under the first MTPJ and
hallux.<

Me too. Ultimately it is probably timing that counts. We need to be able to transfer weight from the weight bearing limb to the swing limb just prior to heel strike. If we are unable to pivot over the first MTPJ we may utilize a "low gear" type axis for too long but will still eventually have to transfer the weight medially to the other leg. We'd fall over if we didn't! Therefore it is not uncommon to see loading of the medial column. But at what time? 

I think we are again taking BMs work too literally.  We also seem to concentrate on absolutes. Look at the axis of propulsion in the shoe uppers of patients. Invariably a Hallux rigidus will demonstrate an oblique axis from Distal medially to proximal lateraly. This is what I see as a Low gear. A crease directly across the met heads to me indicates a relatively "normal" propulsion line. Perhaps High gear. Some people with FHL will do one or the other depending on the nature of their compensation.  High and low gear is merely a way  of visualizing  gross compensatory mechanisms clinically. Most people will utilize both a lateral and medial transfer of weight as the step progresses. I believe it is the manner and timing of this weight transfer which results in pathology. But I could be wrong!

Graham



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