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I was reviewing the Valmassy text (Clinical Biomechanics of the Lower Extremities) where 9 foot types are described. I have a question regarding the compensation that is listed in the text (chapter 3). For each foot type with inverted forefoot (type 3 - inverted calcaneus, type 6- perpendicular rearfoot, type 9 - everted rearfoot), I am reading that the major compensation involves the foot abducting and the knee bending to get the forefoot down. I also read that the stj pronates to its fully pronated position. As most of what I have read emphasizes stj pronation as forefoot varus compensation, I am confused by the emphasis on foot abduction and bending of the knee. Is the major compensation at the stj, or its it more abduction and knee flexion? I haven't used much biomechanics in my training so far, so this is still a subject that I am still learning. Thanks for any replies.

 

The term compensation is somewhat of a problem. The idea of compensation is that a normal foot is in neutral position and foot deformities make it compensate out of neutral position. However, this way of looking at the foot does not really look at the foot where it eventually ends up. The forces acting on the foot when the foot is actually weight bearing are more important than the motions away from neutral position. The foot may never have been in neutral position to begin with.

I do like the idea of a partially compensated varus (forefoot or rearfoot). The foot that runs out of eversion before the first met reaches the ground. (The nine foot types don't ever tell you if have a partially compensated varus. Some types are more likely than others, but the foot types are non weight bearing measures.) Some of the partially compensated varus feet may exhibit frontal plane motion at the knee to get the medial forefoot down to the ground, but certainly not all of them. In the partially compensated varus foot, there will tend to be high lateral forefoot loads, and this combined with body weight will tend to put a valgus stress on the knee. So, this may be what their logic is, but it doesn't happen all of the time.

If you have a hard time understanding compensation, it's ok to let go of it. There are other ways of understanding the foot that don't use compensation to attempt to explain foot function.

Eric