Is Subtalar Joint Neutral A Scientific Measurement Or A Clinical Approximation?

Merton Root, DPM is credited by many for the invention of the concept of a neutral position of the subtalar joint (STJ). Dr. Root and colleagues defined the STJ neutral position as being “the point at which the foot is neither pronated nor supinated.” They also claimed that “from the neutral position, the calcaneus inverts with supination twice as many degrees as it everts with pronation.”¹ 

Ever since Dr. Root and coworkers popularized the concept, clinicians have used the neutral position as a reference for clinical measurements of the foot to determine whether the foot is “pronated or supinated,” and as an “ideal” STJ position for preoperative planning of reconstructive surgeries. In addition, most podiatrists still use the STJ neutral position for making negative casts or scans of the foot for custom orthoses. Numerous researchers have also used the STJ neutral position in their anatomic, radiographic, clinical or gait studies as a reference point for STJ rotational position and motion. 

However, there is a large elephant in the room when it comes to Root and colleagues’ definition for STJ neutral position, “the point at which the foot is neither pronated nor supinated.” Their definition of STJ neutral lacks scientific precision since it is a tautology. Tautology is defined as “saying the same thing twice over in different words.”² Accordingly, in regard to the definition of STJ neutral being “neither pronated nor supinated,” we must first determine the exact location of this neutral position before we can determine whether the foot is “pronated” or “supinated” However, we cannot determine the neutral position until we know whether the STJ is “pronated” or “supinated.” That is a problem if our goal, as a profession, is to be scientific in our approach to foot biomechanics. 

This lack of a precise, anatomically-based definition for STJ neutral position creates difficulties for scientific studies utilizing the STJ neutral position. A gold standard anatomical reference position of the articular facets of the talus and calcaneus relative to each other is required to identify the STJ neutral position. Without a method for consistent and reliably reproducible clinical examination for STJ neutral between different examiners with different training, there continues to be, and will always be, unacceptable inter-examiner errors in determining this position. For example, one examiner may determine STJ neutral position to be four degrees supinated away from another examiner with different training. Then another examiner may determine the STJ neutral position to be three degrees pronated from another examiner. Which, then, is the true STJ neutral position? 

To further illustrate the imprecision of clinical determination of STJ neutral, in podiatry school, I learned six totally different methods for determining the STJ neutral position. These methods included: 

• palpation of the talonavicular joint; 

• palpation of the talocalcaneal joint; 

• matching the curves superior and inferior to the lateral malleolus; 

• looking for relaxed skin lines in the sinus tarsi; 

• feeling for a “flat spot” within the STJ range of motion; and 

• the aforementioned 1/3rd - 2/3rd method.³ 

Unfortunately, without a gold standard scientific definition of STJ neutral and with so many different clinical methods to determine STJ neutral position, the relatively large errors that commonly occur between examiners with different training in the determination of STJ neutral position reduces the value of using STJ neutral position in scientific research. In fact, as a result of these large inter-examiner errors, any research study that measures STJ neutral position then becomes, at best, suspect or, at worst, meaningless. 

Certainly, having a rotational position within the STJ range of motion that could reliably act as a marker to determine when a foot is “pronated” or “supinated” would be useful clinically. It would also be helpful in the scientific study of foot biomechanics. However, until we can arrive at a consensus regarding what the precise talocalcaneal facet positions should be in STJ neutral, the neutral position of the STJ, as a measurement, must be considered scientifically invalid. 

In conclusion, “the” STJ neutral position that we determine in our daily practices approximates a midrange of motion measurement of the STJ that will vary from one clinician to another. It still may be useful for the individual clinician to compare one foot to another. However, due to its lack of scientific precision, that same STJ neutral position, when one uses it in any research on foot biomechanics, so weakens that research that it may be perceived as having little value for advancing the knowledge of foot biomechanics. 

Dr. Kirby is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is in private practice in Sacramento, Calif. 

1. Root ML, Orien WP, Weed JH, Hughes RJ. Biomechanical Examination of the Foot. Volume 1. Los Angeles: Clinical Biomechanics Corporation; 1971:54. 

2. Tautology. Lexico dictionary website. Available at: https://www.lexico.com/definition/ tautology . Accessed February 24, 2020. 

3. Root ML, Orien WP, Weed JH, Hughes RJ. Biomechanical Examination of the Foot. Volume 1. Los Angeles: Clinical Biomechanics Corporation; 1971:120-121.