The supination resistance test holds particular interest for me as I am currently doing some research into it myself for my Masters degree at Manchester University. To my knowledge it first appeared in the literature some 18 years ago (Kirby & Green, 1992). It is a very quick and simple test to perform, but like most clinical tests will need to be performed many times on many different feet before the clinician will feel comfortable with it. The main reason I feel it is so important is that it gives insight into the forces acting on the foot during weightbearing; something which we cannot physically see, and the importance of which are discussed in this blog.
Historically when examining the weightbearing foot all of our attention has been on its visual appearance (or posture). Indeed these visual observations and measurements still form the main portion of an objective clinical assessment, and for many will also dictate the prescription variables for foot orthoses. The potential problem with solely relying on visual alignment (or kinematics as they are referred to in biomechanics terminology) is that there is surprisingly little literature which shows that foot posture is actually predictive of injury. What this means is that the pronated foot type is not necessarily as evil as we had previously thought. Dr Christopher Nester of Salford University sums things up perfectly in his recent paper from the Journal of Foot & Ankle Research:
Rather than continue to apply a poorly founded model of foot type where the focus is to make all feet mechanically ‘normal’ we must embrace variation between feet and develop patient specific models of foot function.
In addition to this when we look at the research of how orthoses exert their effects (or ‘work’) it is clear that kinematic responses to orthoses are also variable and subject specific (Nigg et al, 2003; Huerta et al, 2009). This means that not all feet will respond the same if given the same orthotic prescription. And even if they did respond in a predictable way would this mean they would all get better? Sadly not, as Zammit and Payne discovered in 2007, when they investigated the relationship between kinematic response to an orthotic device (how much it ‘realigned’ the rearfoot) and the reduction in the individuals symptoms; and found that there was no correlation between the two.
Confused? So was I. I was taught that a pronated foot was a huge risk factor for injury. I was then taught to measure how much it was pronated, write a prescription based on this number and the orthotic device I issued would duly realign the foot into ‘neutral’ and the patients symptoms would of course disappear. It was a simpler time as you can imagine.
Not until I read an excellent research paper by Williams et al (2003) in the Medicine and Science in Sports and Exercise Journal did it start to make sense to me. This research took a group of individuals and made them run in 3 conditions: no orthoses, ‘standard’ orthoses and inverted orthoses (between 15-25 degrees inverted). It measured the kinematics (alignment) and the kinetics (the forces we can’t see). The results were astounding – there was no statistically significant difference in rearfoot alignment between the 3 conditions. However, when looking at the forces involved (particularly how hard Tibialis Posterior had to work) the more inverted an orthotic device was significantly reduced the demand on the soft tissues. The inverted orthoses reduced this demand almost 4-fold when compared to the no orthoses condition. Immediately we realised that our orthoses made people pain free by reducing damaging force, and not by ‘re-aligning’ them.
So what does all of this have to do with the supination resistance test? Well it is one of very few tests which give us insight into these forces (which may well be more predictive of injury risk and may better determine orthoses prescriptions than our visual assessment techniques do). If a foot requires a large force to supinate it then it is assumed that a greater contractile force from extrinsic supinators, such as Tibialis Posterior, may be required functionally (does this increase injury risk?) It may also dictate the sort of orthotic device which would be most appropriate. The harder it is to supinate a foot then the greater force an orthotic device would need to cause a supination moment, and conversely the easier it is to supinate a foot then the lower the force required from an orthotic device.
So how is the test performed?
- The patient is asked to stand in a relaxed position on two feet
- They are instructed to relax their feet during the test, and not help in any way
- The clinician places the tips of the index and middle fingers just beneath the navicular
- The clinician pulls directly upward (parallel to the tibia)
- The clinician notes the magnitude of force that is required to supinate the foot from its resting position
- The test is performed on the other foot
When done in this clinical setting the test is a little subjective, but with repetition gives the clinician a good idea of the forces involved (and despite its subjectivity may still offer more important information that visual assessment).
The research team at La Trobe University in Melbourne took this one step further and built a machine which quantitatively measured this supination force in Newtons. They found some fascinating results:
- The manual version of the test (as described above) is reliable for experienced users
- The amount of force required to supinate a foot is only weakly related to how pronated it is
- The amount of force required to supinate a foot is highly correlated to the subtalar joint axis position (I won’t go into this now – it is worthy of its own blog entry and will get one in due course)
- Body weight explains about a third of the force required to supinate the foot
These findings are what we see clinically when performing the test – the force to supinate feet is variable, and does not seem to be hugely influenced by body weight (I have experienced a 13 year old girl who weighed 7 stone have a higher supination resistance than a 19 stone rugby prop forward).
The team at La Trobe have also done much research which has not been published yet (personal communication with Craig Payne) and one which interests me particularly. They took 28 individuals all who had problems with only one limb and all of which had been previously considered to be due to ‘excessive pronation’. They recorded the Foot Posture Index (a protocol which classifies feet into categories based on visual observations) on the injured side versus the uninjured side, and then measured the supination resistance on the injured side versus the uninjured side. They found that when looking at foot posture the injured side was more pronated in 15 out of the 28 subjects. However when looking at supination resistance it was higher on the injured side in 25 out of the 28 subjects. Does this tell us that supination resistance is more predictive of injury that foot posture? Well not quite as it was a cross-sectional design, but it certainly suggests this is worth investigating further in a prospective study.
The supination resistance test is probably now one of the key things from my assessment of patients which dictates my orthoses choices. I pay more attention to it than I do the foot posture. However further work is required to fully understand supination resistance and whether it is prospectively predictive of injury risk (or can validly be used to determine dynamic kinematic responses to different levels of force from foot orthoses).
Picture from: Kirby, K. A. (2002). Supination Resistance Test. Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002 (pp. 155). Payson, Arizona: Precision Intricast, Inc.
Huerta, J. P., Moreno, J. M. R., & Kirby, K. A. (2009). Static response of maximally pronated and nonmaximally pronated feet to frontal plane wedging of foot orthoses. Journal of the American Podiatric Medical Association, 99(1), 13-19.
Kirby, K. A., & Green, D. R. (1992). Evaluation and nonoperative management of pes valgus. In S. DeValentine (Ed.), Foot and Ankle Disorders in Children (pp. 295). New York: Churchill Livingstone.
Nester, C. J. (2009). Lessons from dynamic cadaver and invasive bone pin studies: do we know how the foot really moves during gait? Journal of Foot & Ankle Research, 2 (18)
Nigg, B. M., Stergiou, P., Cole, G., Stephanyshyn, D., Mundermann, A., & Humble, N. (2003). Effect of shoe inserts on kinematics, centre of pressure, and leg joint moments during running. Medicine & Science in Sports & Exercise,35, 314-319.
Noakes, H., & Payne, C. B. (2003). The reliability of the manual supination resistance test. Journal of the American Podiatric Medical Association, 93 (3), 185-189.
Payne, C. B., Munteanu, S., & Miller, K. (2003). Position of the subtalar joint axis and resistance of the rearfoot to supination. Journal of the American Podiatric Medical Association, 93 (2), 131-135.
Payne, C. B., Oates, M., & Noakes, H. (2003). Static stance response to different types of foot orthoses. Journal of the American Podiatric Medical Association, 93 (6), 492-498.
Williams, D. S., McClay Davis, I., & Baitch, S. P. (2003). Effect of inverted orthoses on lower-extremity mechanics in runners. Medicine & Science in Sports & Exercise, 35, 2060-2068.
Zammit, G. V., & Payne, C. B. (2007). Relationship between positive clinical outcomes of foot orthotic treatment and changes in rearfoot kinematics. Journal of the American Podiatric Medical Association, 97, 207-212.