13/02/2018
Inaccuracies in Root et al Theory: Is Subtalar Joint Neutral Position a Scientifically Valid Measure?
What is the subtalar joint (STJ) “neutral position”? Merton Root, DPM, and his colleagues, John W**d, DPM and William Orien, DPM, popularized the concept of the STJ “neutral position” as a midrange position within the range of motion of the STJ that they felt was the optimal position for the foot to function in. Unfortunately, the STJ neutral position itself is a rotational position of the STJ that has never been adequately defined in a scientific manner. A precise anatomical definition of the STJ neutral position (i.e. knowing exactly where the articular facets of the talus and calcaneus articular facets are in relation to each other) is necessary for researchers to determine whether Dr. Root’s theories are reliable and accurate. Currently, the STJ neutral position is not a scientifically valid measure of rotational position of the STJ.
The definition for STJ neutral position used by Root and co-workers is “that position of the subtalar joint in which the foot is neither pronated or supinated.” Root et al's definition of the STJ neutral position as being “neither pronated or supinated,” is a big problem. It is likely the best example of a tautology or "circular reasoning" within podiatric biomechanics (Root ML, Orien WP, W**d JH. Normal and Abnormal Function of the Foot. Clinical Biomechanics Corp., Los Angeles, CA, 1977). How do you scientifically test for something that can't be defined? Answer: you can't!
Tautology is defined as “the saying of the same thing twice in different words, generally considered to be a fault of style”. The tautology of Root et al’s definition of STJ neutral position is very easy to see. When I first heard this definition of STJ neutral position as a 1st or 2nd year podiatry student at the California College of Podiatric Medicine over 35 years ago, I remember a very uncomfortable feeling that something just wasn't right about the terms "pronated" or "supinated" being used within the definition of the neutral position of the STJ.
Using Root et al’s definition of STJ neutral position we must first be able to determine whether the foot is “pronated” or “supinated”. Said another way, we must first determine where within the STJ range of motion STJ neutral is in order to determine whether the foot is “pronated from neutral” or “supinated from neutral”. However, since Root et al defined STJ neutral position as being “that position of the subtalar joint in which the foot is neither pronated or supinated”, then their definition of STJ neutral is a circular, or a tautological definition. In other words, until the clinician decides where “neutral position” is within the STJ range of motion, they can’t decide whether a certain STJ rotational position is either "pronated" or "supinated" from “neutral”.
This lack of a anatomically-based and non-tautological definition for STJ neutral position creates great difficulty for scientific study of the STJ neutral position. In fact, without a proper anatomical definition for STJ neutral, our current concept of STJ neutral has no scientific validity. It is non-testable for scientific purposes.
In other words, without the definition of "STJ neutral" having assigned to it precise reference to the three-dimensional relationship of the articular facets of the talus relative to the articular facets of the calcaneus, we have no testable definition for STJ neutral. In addition, we don't have a single method for clinical examination for STJ neutral position that can be reproduced reliably by different examiners. As a result, there are large inter-examiner errors in determining “the” STJ neutral position. The result of this large inter-examiner error is that one examiner may determine the STJ neutral position as being possibly 2-3 degrees pronated or supinated away from another examiner’s determination of STJ neutral, both of them saying that they have found “the” STJ neutral position, and both of them also thinking the other examiner is wrong.
I learned six techniques for determining STJ neutral position during my student years and during my year of Biomechanics Fellowship at the California College of Podiatric Medicine (CCPM) from 1984-1985. These are as follows:
1) Palpation of the talo-navicular joint for “congruency”. This method is popular, and seems to have been mostly promoted initially on the east coast of the United States during the 1970s. However, the talo-navicular joint is not the STJ and, for that reason, both Drs. Root and W**d condemned the talo-navicular palpation method of determining STJ neutral as being inaccurate in the lectures I heard them give and my conversations with them.
2) Palpation of the talo-calcaneal joint for “congruency”. I heard Dr. Root lecture on this subject many times but never saw anyone demonstrate it or reproduce it in all my years of working with Dr. W**d, Dr. Ron Valmassy, Dr. Chris Smith, Dr. Richard Blake, Dr. John Marczalec, Dr. William Sanner and Dr. Lester Jones, all of whom were Dr. Root’s students and taught biomechanics at CCPM during my student years and my year as Biomechanics Fellow. In all my studies of the STJ, I have never been able to reliably palpate the margins of the STJ clinically, even in the most thin patients. I don't believe it can be done reliably on a large range of patients.
3) Curves superior and inferior to the lateral malleolus. This method is described in Root et al’s first book (Root ML, Orien WP, W**d JH, RJ Hughes: Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971, pp. 118-121). However, this method was considered to be a secondary method and not overly reliable or accurate by the professors of biomechanics at CCPM probably due to its range of error and the large variability in shape of the lateral malleolus.
4) Skin lines in sinus tarsi. This was a favorite method of Dr. Chris Smith, one of my biomechanics professors at CCPM, and involved pronating then supinating the STJ until the skin lines within the sinus tarsi of the STJ were “relaxed” or visible but not stretched. Again, there is likely a fairly large range of error in this method from one examiner to another and I saw no other professors at CCPM use Dr. Smith's technique.
5) Feeling for “flat spot” within range of motion of the STJ. This was the technique for determining STJ neutral position which was most heavily favored by the biomechanics professors at CCPM and is the technique which I still use to determine the "STJ neutral position". Unfortunately, there has been no research on using this method to see how accurate and reproducible it is. My educated guess is that the "flat spot" within the range of motion of the STJ represents the point of maximum congruency between the posterior articulating facets of the talus and calcaneus within the range of motion of the STJ.
6) 1/3rd-2/3rd method. Root et al taught that the STJ neutral position is that position where the supination range of motion is twice that of the pronation range of motion. "From the neutral position of the subtalar joint, two-thirds of the total prange of frontal plane motion is inversion (with supination) , and one-third is eversion (with pronation: giving a ration of 2:1 ((Root ML, Orien WP, W**d JH, RJ Hughes: Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971, pp. 38). None of the biomechanics professors at CCPM used this method when teaching in the biomechanics clinic at CCPM. However, Dr. W**d taught us this method during our second year of podiatry school at CCPM, that we were tested on.
In conclusion, there are significant problems with scientifically attempting to study the "STJ neutral position" due to the lack of a firm scientific definition for neutral position in the STJ. As such, the concept of a "STJ neutral position" is likely not scientifically valid. Large inter-examiner errors occur when determining STJ neutral position which make all such studies which use STJ neutral position as part of their research potentially meaningless or suspect.
That is not to say that the STJ neutral position concept is not a useful clinical and theoretical concept. It would be helpful to know, both clinically and for scientific research, exactly when a STJ is "pronated" and when a STJ is "supinated". However, until we can scientifically validate where exactly the talar articular facets should be relative to the calcaneal articular facets of the talo-calcaneal joint, the "STJ neutral position” must be treated as an unreliable clinical measurement. In other words, "the STJ neutral position" that we determine clinically is currently, at best, simply an approximation of a mid-range of motion measurement of the STJ that will vary significantly from one clinician to another. As a result, when "STJ neutral position" is seen in any research on foot biomechanics, the research must be viewed with a very critical eye and assumed to be of little value scientifically.
