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Should We Abandon The Concept Of The Subtalar Neutral Joint Position?
Yes. Providing insights from the literature as well as his clinical experience, this author says subtalar neutral joint position is an ill-defined, unreproducible concept, which has little relevance to understanding the dynamic forces of weightbearing.
By Eric Fuller, DPM
The concept of subtalar joint neutral position should be abandoned. I am not saying that people should abandon what has worked for them. What I am saying is that we need to critically evaluate whether the concept of neutral position is valid for explaining foot function and why orthotics work. The inventors of neutral position have made many very good observations about how feet work. I will discuss some of their observations and show how using neutral position overcomplicates the explanation and impedes understanding.
The continued use of neutral position is an impediment to the advancement of the understanding of foot function. To understand why this is so, one must explore the development of the concept and its many uses.
When asked how he came up with neutral position, Merton Root said, “One morning in 1954, just by luck I guess, I was standing in the shower without any thought about the foot and all of a sudden the concept of neutral subtalar joint position flashed into my mind.”1 Root described it is a position that is neither pronated nor supinated. Later, Bill Orien, DPM, said, “Neutral position is a figment of Mert Root’s imagination.”2
Recognizing The Problems With The Definition Of Subtalar Joint Neutral
This circular definition is the first problem with neutral positon. A position somewhere in the middle of the range of motion is picked and all points on one side of that range of motion are considered pronated and all points on the other side of that point are considered supinated. This will be true for any arbitrarily chosen location within the available motion of the subtalar joint.
To further compound the problem with the definition, the creators of the subtalar neutral joint position concept came up with more ways to find the point they thought was neutral. One description involves moving a non-weightbearing foot through subtalar joint motion and finding the dell in the arc of motion. Another definition of neutral positon is one-third of the total range of motion from the maximally pronated position. A third definition is when the tangents to the curvatures above and below the malleolus are parallel. There is no research examining whether all these definitions even describe the same position of the joint, let alone whether or not finding neutral position with these methods is reproducible. A single, repeatable definition of neutral position is necessary if research is to be conducted on other measurements related to neutral positon.
The inventors of neutral position felt that to compare feet, they needed to control for changes in foot shape that occur with subtalar joint motion.3 They are correct in pointing out that feet are different and there does need to be a way of describing why different feet function differently. The same treatment on different foot types will not yield the same result. Root wrote, “It was necessary to identify a standard position of the subtalar joint that could be used on all patients to eliminate structural deviations related to subtalar joint position. The standard could then be used to study variations among numerous feet.”3 There is an important point here that Root got right. The shape of the foot changes from one subtalar joint position to another.
However, this raises the question of whether the foot types that use neutral position in their definition (rearfoot varus and valgus and forefoot varus and valgus) are the best way to classify feet? Should one use a poorly defined, non-weightbearing position as a reference point for a weightbearing foot? If different feet sit in a position a different number of degrees away from neutral in stance, then there will not be a consistent change in foot shape from neutral position to the weightbearing position.
What Are The Best Positions From Which To Classify Feet?
Studies have demonstrated that neutral position measurements do not predict the motion that occurs in gait.4 In a relatively recent study, Jarvis and colleagues suggest there is no correlation between the measurements and foot motion.4 There may be some measurements that could be predictive of joint position in gait. Root wrote, “… uncompensated varus deformity, a condition generally caused by a combination of forefoot varus and rearfoot varus deformities. The patient with a significant rearfoot varus deformity has little to no available range of calcaneal eversion remaining after compensating for a rearfoot varus deformity.”3 This quote illustrates the brilliance and the deficiencies of using neutral position-based measurements.
There is a reason that surgeons say “thou shalt not varus.” The foot that stands at its end of range of pronation and has little force on the medial forefoot will tend to have certain problems. The use of neutral position measurements overcomplicates this relatively simple situation. If the clinician insisted on using leg and heel bisections, he or she could calculate whether the subtalar joint was at its end of range of motion without ever looking at neutral position. Only tibial varum, calcaneal eversion to leg and resting calcaneal stance position are necessary to calculate whether the subtalar joint is at its end of range of motion.
If one does not want to use heel bisections, you could attempt to evert the foot and see if it everts. One way to do this is the Coleman block test. Another way to evaluate for partially compensated varus is a test described by Weed. He would have the patient stand and try and slide his fingers under the medial forefoot. With a partially compensated varus foot, one can easily slide his or her fingers under the medial forefoot because there is little force there. You do not need neutral position to see if you have a partially compensated varus foot.
Root described the partially compensated varus deformity as “a condition generally caused by a combination of forefoot varus and rearfoot varus deformities.”3 The division of the foot into forefoot and rearfoot obscures the situation. What if there was a forefoot valgus at the same time there was a rearfoot varus? The rearfoot varus foot is going to sit pronated from neutral position so the forefoot to rearfoot measurement will be more valgus than it was in neutral position. The forefoot to rearfoot measurement and the calculation of the location of neutral position add nothing to the ability to understand this situation.
The observation that the forefoot to rearfoot relationship changes when the subtalar joint is in a pronated position from neutral makes the use of the forefoot to rearfoot measurement for orthotic prescription writing problematic because the vast majority of patients do not stand in neutral position. The non-weightbearing measurement will not be the same as the weightbearing measurement.
That said, there is still usefulness of the invention of the intrinsic forefoot valgus post. Kogler and coworkers demonstrated that a forefoot valgus wedge can reduce the tension in the plantar fascia.5 In my opinion, however, the use of neutral position-based measurements is not the best way to choose the amount of forefoot valgus wedge to put in an orthotic.
Root wrote, “The neutral subtalar joint position of the rearfoot was selected as the best position in which to cast a foot to make a functional orthosis, and the midtarsal joint was placed in a fully pronated positon. These positions were selected by trial and error rather than as (a) result of any knowledge about normal function of the foot.”3 There are many studies that show orthotics work. This quote is why we should abandon neutral position as an explanation as to why orthotics work.
Final Thoughts
When navigating the questions of what prescription variables will be best for our patients, we can compare the foot in front of us to a hypothetical normal and try to make the foot more normal. Alternatively, we can treat the foot like an engineer would treat the foot. We can identify the injured part of the foot and model that part to determine how that part is overloaded enough to become painful. Then using that model, we can design an orthosis to reduce the loads on the injured structure.
Dr. Fuller taught biomechanics at the California College of Podiatric Medicine for 14 years. He is in private practice in Berkeley, Calif.
No. Emphasizing the key role of the subtalar joint neutral position as a starting position for accurate measurement in biomechanical assessment, this author argues that dissenters unduly dismiss the importance of this position in understanding normal and abnormal anatomy and foot function.
By Robert D. Phillips, DPM
Recently, researchers have been questioning and advocating to discard the measurement and utilization of the subtalar joint (STJ) neutral position in assessing and treating foot dysfunction.1 Unfortunately, these advocates fail to provide a good and reliable substitute, instead citing vague concepts such as “tissue stress theory” and semi-quantitative measures such as the “foot posture index.” Arguments against STJ neutral position promulgate much disinformation about its importance, measurement and use. One should not accept these arguments as legitimate.
The question at the heart of the controversy is: ‘Why do some feet hurt and develop deformities, and some do not?’ Whitman was an early inquisitor who discussed the origins of flatfoot symptoms, distinguishing normal from abnormal foot function, correcting the position of a foot prior to brace casting and proper positioning for casting itself.2 Unfortunately, no photographs or drawings of his process exist so there is ambiguity as to what he thought was the normal foot-leg relationship. Nevertheless, Whitman clearly felt that there was a position of the foot relative to the leg that he considered normal.
In another classic article, Lovett and Cotton added concepts about symptomatic feet, including that pronation can occur in a normal foot but past a certain point is pathologic and likely painful. They refer several times to a corrected foot position and advocated for measuring the degree of pronation.3 One must then consider the question: where is the zero point from which they are measuring this pronation? Failure to define such a point means no measurement is possible.
Morton advocated for balance between the inner and outer forces on the foot.4 He identified a point of force neutrality where the forces pushing the foot in one direction balance the forces pushing in the opposite direction, placing ligaments and muscles at a point of least demand. In discussing foot muscle function, Creer also described a point from which there is a balance of inversion and eversion moments on the foot.5
What The Literature Reveals About Subtalar Joint NeutralAnd Challenges To Root Theory
Wright and colleagues published early kinematic data on STJ motion around a neutral position during gait. In doing so, they described this as the position of the ankle and STJ with the subject in relaxed stance, full knee extension, arms at sides, feet six inches apart and comfortable toeing out.6 While these authors used two subjects with no mention of foot abnormalities, their work still forms much of the dogma taught today about the normal motion of the STJ around a neutral position during gait.
“The subtalar joint is in the neutral position when the foot is neither supinated nor pronated.”7-9 I maintain Root’s definition is not a description of how to find STJ neutral position but is instead a statement of its existence. It likewise does not relate the STJ neutral position to any external conditions like Wright and colleagues did.
The beauty of the Root neutral position is that a person may stand with the heel vertical yet have symptoms attributed to abnormal pronation or abnormal supination.7-9 It means that a clinician cannot determine the presence of abnormal pronation of the STJ until one knows the location of STJ neutral position. If one utilizes Wright and colleagues’ definition of neutral, then we lose the ability to say that a person stands with the STJ abnormally pronated or supinated.
McPoil and Cornwall confirmed the findings of Wright and colleagues in 50 young, asymptomatic adults by noting that STJ motion is around the resting calcaneal stance position.10 They proposed that the Wright definition of neutral position was superior to Root’s definition. Many use this finding to support discarding Root’s concept but this argument is flawed. It assumes the asymptomatic subjects had normally functioning feet. Such an assumption is based on a belief that asymptomatic feet are normal and symptomatic feet are abnormal. These authors did not compare asymptomatic with symptomatic feet for differences in function.
They reported that the average subject stood with the STJ approximately five degrees pronated from neutral position.10 They do not indicate how far this is from maximal pronation or what the reserve of pronation was in stance. A “straw man” argument is also set up by assuming Root said that all pronated feet become symptomatic or that he advocated treating all pronated feet. It also assumes that none of these young people will become symptomatic in their life or how much pronation is tolerated for various activities.
Houck and team identified the value of using neutral position in analyzing normal and abnormal pronation.11 When comparing normal foot posture and abnormal pronatory foot posture, they found that the two groups did not vary in kinematic rearfoot and first metatarsal motion when researchers utilized the vertical as neutral position. However, when they utilized the Root concept of neutral position, the abnormal pronators had more pronation during gait than the normal group.
Root envisioned a taxonomy system for studying various foot types independently. The STJ neutral position was just one variable for establishing these foot types, specifically delineating rearfoot varus, rearfoot valgus and rearfoot normal. Unfortunately, most researchers fail to select one type to study and instead find young subjects who have not yet experienced foot injury or symptoms.
One such example is a recent challenge to the Root paradigm by Jarvis and coworkers.12 Their study concluded that all 140 subjects functioned similarly regardless of presenting forefoot deformity. However, methodologically, we find that almost every subject showed a neutral calcaneal position between eight and 12 degrees inverted to the leg. To deduce from their study that Root is wrong is an error in logic. As the subjects universally had rearfoot varus, the only conclusion to be drawn from the study by Jarvis and coworkers is that subjects with greater than five degrees of rearfoot varus function similarly and that further subcategorizing these subjects by the forefoot to rearfoot relationship does not change function. This is an example of drawing incorrect conclusions from good data. Regardless of the reputation of the study authors or the sophistication of their technology, readers must analyze the methodology of any study to ensure that the study’s conclusions are adequately supported by the results.
Recognizing The Importance Of STJ Neutral In Relationship To The Midtarsal Joint
The greatest importance of STJ neutral is the relationship between its position and the midtarsal joint. Elftman first discussed this relationship, noting when the STJ moved from fully supinated to fully pronated that the midtarsal joint became more mobile and the arch can flatten.13 Most Root critics fail to acknowledge the one truly innovative postulate: that the normal foot should stand with the midtarsal joint pronated to its end range of motion. In his paradigm then, a perfect foot is one in which the person stands with the STJ in neutral position and the midtarsal joint fully pronated.
At first, Root accepted Elftman’s theory of how the midtarsal joint reached its end range of pronation. By experiment, however, Root and colleagues later rejected Elftman’s “osseous locking” mechanism and stated that the end range of motion was a function of the ligaments crossing the midtarsal joint.14 I had several personal orthotic casting technique sessions with Root and have subsequently analyzed how he clinically determined where the end range of motion of the midtarsal joint was since it is determined by ligaments. In a 1983 article, which discussed this analysis, I noted that Root determined that midtarsal joint end range of motion occurs when further pronation force against the forefoot produces no further midtarsal joint motion and instead starts producing STJ pronation.15
Given that the forefoot to rearfoot relationship changes with each position of the STJ, it is impossible to diagnose an abnormal forefoot to rearfoot relationship without having a neutral STJ position. With this standard position, we then make that forefoot to rearfoot relationship measurement with the STJ in that position. We can also prescribe treatment in which a plaster mold of the foot will match that actually measured. It creates a complete diagnostic and therapeutic theory.
What The Podiatrist Should Know About The Limitations Of Tissue Stress Theory
Unfortunately, those who promote discarding the STJ neutral position have not offered any unified replacement theory to dictate diverse treatment paradigms.16 An example is the “tissue stress theory,” in which, one waits for pathology to occur, identifies the painful structure, devises a theory for why the stress is present and subsequently pursues a stress-relieving strategy.17 This theory would purportedly replace the Root paradigm.
Kirby argues that “foot deformity” measurement “does not give us (nearly) enough information to predict the mechanical behavior of the foot and lower extremities during weightbearing activities and, therefore, is insufficient to prescribe the best orthoses for patients.”18,19
I agree that more information than frontal plane rearfoot and forefoot measurements is indeed necessary, but without the forefoot-to-rearfoot measurement, one does not know what the foot mold should look like with full midtarsal joint pronation. This requires placement of the STJ in a standardized position. In addition, while tissue stress theory can give us the direction in which one should push the foot, without a knowledge of the degree of subtalar pronation or supination, one does not know how much counter-torque is necessary to reverse the symptoms. In other words, tissue stress theory is only a qualitative tool as opposed to a quantitative tool.
The erroneous thinking is that if Root’s teachings aren’t enough to provide the best treatment, then none of Root’s concepts are needed. Notably, Root never said that one need not identify the stressed anatomical structures. Better clinical methods of identifying the STJ axis have added to but not replaced our abilities to identify etiologies of abnormal foot pronation.19 Subtalar joint axis theory does not tell us whether the STJ is actually abnormally pronated in stance or gait as there are many other etiologies of abnormal pronation.
Phillips and Lidtke showed that as the STJ pronates, its axis also moves into a more abnormal relationship to the foot.20 Addressing the etiology of abnormal pronation may indeed bring the subtalar joint axis back to its normal position to the foot. Using STJ neutral as the standard to identify an abnormal STJ axis allows one to distinguish if the abnormality is anatomic versus functional. If there is an anatomic abnormality, one may consider surgically addressing the primary etiology. However, if the STJ axis is only functioning incorrectly, one would want to avoid surgical correction of the axis. Root wrote that understanding symptom etiology and pathology allows us to choose proper treatment and avoid further disrupting function.21
A Closer Look At The Reliability Of STJ Measurements
Many argue STJ measurements are unreliable and thus should be discarded.22 Instead of dismissing the option, let us develop tools and techniques to improve reliability. A study by Diamond and colleagues showed that high inter-tester reliability was possible albeit with increased time and training.23 Unfortunately, the authors did not give a highly detailed description of their technique.
Ball and Johnson showed that the amount of torque applied to the rearfoot resulted in different rearfoot measurements.24 Most reliability studies identify examiners as being experienced or inexperienced, assuming all experienced examiners use the same technique. Therefore, future studies need to focus on how a technique can be fully identified and standardized.
Instrumentation can also be an important part of this unreliability. LaPointe and team showed that using a caliper to bisect the posterior heel was much more reliable than visually doing so.25 Freeman and colleagues showed that using a non-double arm goniometer resulted in very high inter-tester reliability for measuring STJ motion.26 Unreliability, therefore, could be due to standardization and/or instrumentation issues. Accordingly, we may need further research to improve both technique and instruments as opposed to rejecting the concept of measurement.
What Does The Foot Posture Index Say About The STJ Neutral Position?
Authors have also suggested use of the Foot Posture Index (FPI) to identify those who are at highest risk for injury.27 One of the problems with the Foot Posture Index is that it gives no treatment paradigm. How does the Foot Posture Index guide the practitioner in prescribing treatment or creating orthoses? When one looks at the philosophy behind the Foot Posture Index, there still has to be a “neutral” position from which to grade each of the six parameters from -2 to +2. For example, what constitutes the point at which a +1 medial bulge of the talar head becomes a +2 medial bulge for the Foot Posture Index if there isn’t a “zero” point?
Final Thoughts
Identifying and measuring pronation or supination in relationship to a neutral position is just one of many parts of the comprehensive biomechanical evaluation. Without it, one cannot really identify if rearfoot position or motion is normal or abnormal in stance and gait. Should practitioners rely only on the presence of symptoms to decide whether to treat? If so, preventative treatment will perish. While Root never taught that every pronated foot must be treated, he did advocate clinical quantification to identify the presence or absence of pronation, its severity and an ideal position to push the foot toward.
Science without measurement is philosophy. To measure anything, one must have a starting position. Without the STJ neutral position, foot treatment specialists of the world would take a step back from making clinical practice the science that it should be and decrease their ability to quantify normal and abnormal function.
Dr. Phillips is the Director of the Podiatric Medicine and Surgery Residency at the the Orlando Veterans Affairs Medical Center in Orlando, Florida. He is a Diplomate of the American Board of Foot and Ankle Surgery, and the American Board of Podiatric Medicine. Dr. Phillips is a clinical volunteer faculty Professor of Podiatric Medicine with the College of Medicine at the University of Central Florida. He is also a member of the American Society of Biomechanics.
Point
1. Lee WE. Podiatric biomechanics. An historical appraisal and discussion of the Root model as a clinical system of approach in the present contect of theoretical uncertainty. Clin Podiatr Med Surg. 2001;18(4):555-684.
2. Orien W. Lecture at Biomechanics Summer School; 2001; Oxford, England.
3. Root ML. Development of the functional orthosis. Clin Podiatr Med Surg. 1994;11(2):183-210.
4. Jarvis HL, Nester CJ, Bowden PD, Jones RK. Challenging the foundations of the clinical model of foot function: further evidence that the Root model assessments fail to appropriately classify foot function. J Foot Anke Res. 2017;10:7.
5. Kogler GF, Veer FB, Solomonidis SE, Paul JP. The influence of medial and lateral wedges on the loading of the plantar aponeurosis. J Bone Joint Surg Am. 1999;81(10):1403-1413.
Counterpoint
1. Harradine P, Gates L, Bowen C. If it doesn’t work, why do we still do it? The continuing use of subtalar joint neutral theory in the face of overpowering critical research. J Orthop Sports Phys Ther. 2018;48(3):130-132.
2. Whitman R. A study of the weak foot, with reference to its causes, its diagnosis, and its cure; with an analysis of a thousand cases of so-called flat-foot. J Bone Joint Surg. 1896;1(1):42-77.
3. Lovett RW, Cotton FJ. Some practical points in the anatomy of the foot. Boston Med Surg J. 1898;139(5):101-107.
4. Morton DJ. Mechanism of the normal foot and of flat foot: Part I. J Bone Joint Surg. 1924;6(2):368-386.
5. Creer WS. Some foot faults related to form and function. Br J Indust Med. 1944;1(1):54.
6. Wright DG, Desai SM, Henderson WH. Action of the subtalar and ankle-joint complex during the stance phase of walking. J Bone Joint Surg. 1964;46(2):361-464.
7. Lee WE. Podiatric biomechanics. An historical appraisal and discussion of the Root model as a clinical system of approach in the present context of theoretical uncertainty. Clin Pod Med Surg. 2001;18(4):555-684.
8. Root ML, Orien WP, Weed JH, Hughes RJ. Biomechanical Examination of the Foot. Los Angeles:Clinical Biomechanics Corporation;1971:116-121.
9. Root ML. Biomechanical examination of the foot. (Letter to the Editor) J Am Podiatr Assoc. 1973;63(1):28-29.
10. McPoil T, Cornwall MW. Relationship between neutral subtalar joint position and pattern of rearfoot motion during walking. Foot Ankle Int. 1994;15(3):141-145.
11. Houck JR, Tome JM, Nawoczenski D. Subtalar neutral position as an offset for a kinematic model of the foot during walking. Gait Posture. 2008;28(1):29-37.
12. Jarvis HL, Nester CJ, Bowden PD, Jones RK. Challenging the foundations of the clinical model of foot function: further evidence that the Root model assessments fail to appropriately classify foot function. J Foot Ankle Res. 2017;10(1):7.
13. Elftman H. The transverse tarsal joint and its control. Clin Orthop Rel Res. 1960;16:41-46.
14. Root ML, Orien WP, Weed JH. Normal and Abnormal Function of the Foot. Los Angeles: Clinical Biomechanics Corp;1977
15. Phillips RD, Phillips RL. Quantitative analysis of the locking position of the midtarsal joint. J Am Podiatr Assoc. 1983;73(10):518-522.
16. McPoil TG, Hunt GC. Evaluation and management of foot and ankle disorders: present problems and future directions. J Orthop Sports Phys Ther. 1995;21(6):381-388.
17. Fuller EA, Kirby KA. Subtalar joint equilibrium and tissue stress approach to biomechanical therapy of the foot and lower extremity. In: Biomechanics of the Lower Extremity: Theory and Practice. Denver:Bipedmed;2007:205-264.
18. Kirby KA. Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters. Payson, AZ:Precision Intricast;1997:267-268.
19. Kirby KA. Methods for determination of positional variations in the subtalar joint axis. J Am Podiatr Med Assoc. 1987;77(5):228-234.
20. Phillips RD, Lidtke R. Clinical determination of the linear equation for the subtalar joint axis. J Am Podiatr Med Assoc. 1992;82(1):1-20.
21. Root ML. An approach to foot orthopedic. J Am Podiatr Assoc. 1964;54(2):115-118.
22. Jarvis HL, Nester CJ, Jones RK, Williams A, Bowden PD. Inter-assessor reliability of practice based biomechanical assessment of the foot and ankle. J Foot Ankle Res. 2012;5(1):14.
23. Diamond JE, Mueller MJ, Delitto A, Sinacore DR. Reliability of a diabetic foot evaluation. Phys Ther. 1989;69(10):797-802.
24. Ball P, Johnson GR. Technique for the measurement of hindfoot inversion and eversion and its use to study a normal population. Clin Biomech. 1996;11(3):165-169.
25. LaPointe SJ, Peebles C, Nakra A, Hillstrom H. The reliability of clinical and caliper-based calcaneal bisection measurements. J Am Podiatr Med Assoc. 2001;91(3):121-126.
26. Freeman D, Jaeger A, Johnson R, Geletta S, Cooper K, Toney P. Reliability study of the Phillips BiometerTM for the measurement of subtalar joint range of motion. Foot. 2007;17(2):102-110.
27. Redmond AC, Crosbie J, Ouvrier RA. Development and validation of a novel rating system for scoring standing foot posture: the Foot Posture Index. Clin Biomech. 2006;21(1):89-98.
Additional References
28. Elveru RA, Rothstein JM, Lamb RL. Goniometric reliability in a clinical setting: subtalar and ankle joint measurements. Phys Ther. 1988;68(5):672-677.
29. Van Gheluwe B, Kirby KA, Roosen P, Phillips RD. Reliability and accuracy of biomechanical measurements of the lower extremities. J Am Podiatr Med Assoc. 2002;92(6):317-326.
