Alternative Techniques for the Clinical Assessment of Foot Pronation

To the Editor:

I am writing with regard to the article published in the March 1998 issue of the Journal entitled “Alternative Techniques for the Clinical Assessment of Foot Pronation” by Hylton B. Menz. The author presents two very useful stance measurements, navicular drop and navicular drift, which add greatly to the clinician’s ability to assess the foot, particularly the midtarsal joint. However, I have concerns regarding the philosophy presented in the article, namely, that “traditional measurements” should not be performed. I believe this philosophy to be based on flawed research and concepts.

In the article’s introduction, the author states, “Recent reports, however, have seriously questioned this paradigm.” The paradigm to which Menz refers, as stated in the previous paragraph, is that foot morphology influences foot function. Menz disagrees with this paradigm; he bases his opinion on studies that do not find a predictable correlation between measurement of foot morphology and gait observations in the same feet. This is despite one of his references (Song et al [1]), a study performed in a very scientific manner demonstrating that there are gait characteristics associated with foot morphology.

The author carries his argument that form does not influence function a bit further. Specifically, he criticizes the measurements presented by Root, Orien, Weed, and Hughes and singles out the frontal-plane measurements for criticism. The basis of his criticism is a long list of studies that do not follow the proper methodology for performing the very measurements he criticizes. Many of the studies cited by the author are based on podiatry “folklore.”

Part of the folklore to which I am referring is that talonavicular congruity is subtalar neutral position. The talonavicular joint is part of the midtarsal joint, and is not part of the subtalar joint. The talonavicular joint is no more a marker for subtalar position than ankle neutral position. The references presented by Menz support the lack of correlation between talonavicular congruity and calcaneal position. In the section entitled “The Subtalar Joint Neutral Reference Position” the author describes how to properly find subtalar neutral, then implies that there is some justification for using talonavicular congruity as subtalar neutral. The studies cited do not demonstrate that frontal-plane measurement of subtalar neutral position is unreliable or invalid, but merely that folklore-based methodology for performing the frontalplane rearfoot measurements is widespread, even among those who have the most interest in this area. The article also demonstrates how difficult it is for many of us to give up on folklore.

It is important to remember that the investigators in the research studies cited by Menz did not take the trouble to research the appropriate methodology for their studies and improperly placed the subtalar joint in its neutral position. What would make the reader think that any other part of the research project was performed in the appropriately disciplined manner, for example, properly performing a calcaneal bisection, measuring in the proper plane, and so on?

Also in the section entitled “The Subtalar Joint Neutral Reference Position,” after having defined subtalar neutral position, the author opens the following paragraph by stating that subtalar joint neutral position has “no clear anatomic definition.” As mentioned by the author, talocalcaneal congruity and one-third of the range of motion from the maximum pronated position define subtalar neutral position. I am not sure what the author means by “no clear anatomic position.” Subtalar neutral is no less clear than ankle or hip neutral positions.

Each of the measurements reviewed by Menz has a place in the complete evaluation of a patient. The valgus index reflects rearfoot alignment as a composite reaction of the subtalar, midtarsal, and various forefoot joints to ground reactive forces and a variety of other influences. Thus the valgus index expresses more about foot posture than any single joint measurement, such as relaxed calcaneal stance position. This does not mean that relaxed calcaneal stance position is of no value. Actually, the valgus index and relaxed calcaneal stance position together are of more value than either is separately. Discounting relaxed calcaneal stance position as useless is analogous to assessing visual acuity with an eye chart only, and not evaluating for astigmatism or retinal pathology. No one measurement will ever be able to perfectly classify feet or perfectly predict foot mechanics in gait.

I agree with Menz that too much attention has been given to frontal-plane assessment of the foot, when transverse- and sagittal-plane measurements provide useful information. Frontal-plane measurements have been popular because they are deceptively easy to perform. Performing the “traditional” measurements properly requires significant discipline, and the reason that much of the medical community fails in their performance is that very few people are familiar with the proper methodology or the need for discipline. The podiatric, physical therapy, and orthopedic communities received a wonderful gift in the publications of Root, Orien, Weed, and Hughes. A portion of the gift was standardized terminology, a systematic approach to evaluation that quantified foot morphology, and explanations as to how pathology might be linked to mechanics. It is my opinion that the medical community should question and add to the foundation created by Root et al, rather than disrespectfully performing folklore-based research. The navicular drift and navicular drop measurements presented by Menz are a good example of adding constructively to the foundation. Folklorebased research does nothing more than create confusion and misconceptions.

Many of the misconceptions are perpetuated by teaching variations from ideal foot morphology in isolation, and by trying to classify each foot on the basis of a single measurement. Foot mechanics are influenced by the direction of the foot’s many moving joint axes and ranges of motion in each plane, by the morphology of all parts of the body to varying degrees, by neuromuscular influences, and so on. Assessing each factor influencing foot mechanics gives the clinician more information that can be used to help understand and alter the patient’s pathomechanics. The gait patterns that we observe visually or with sophisticated devices are the sum total of all of these influences on the foot, resulting in each person’s unique gait pattern.

Navicular drift and navicular drop are two very interesting and useful measurements for evaluating our patients. These measurements provide insight as to how the midfoot moves when the foot is bearing weight, and are a composite of primarily subtalar, midtarsal, and forefoot joint motions, with the midtarsal presumably being the dominant joint contributing to the motion measured. There is nothing wrong with these measurements when talonavicular congruity is used as the reference position from which the motion is measured. Navicular drift and drop can be used equally well for prescribing foot orthoses to influence the undesirable talonavicular motion and for evaluating whether an opening Evans calcaneal osteotomy has successfully reduced midfoot motion. I applaud Menz for enlightening the podiatric community as to these relatively new measurements.

In sum, I wish to reiterate that the “new” measurements presented in this article were reviewed quite well by the author, and will be very helpful to those who add them to their armamentarium of tools for clinical evaluation. Yet I disagree with the author when he states that foot morphology does not influence foot function. In addition, I disagree with the use of poorly performed studies, rooted in podiatric folklore, as the basis of any kind of criticism. Although this article has considerable merit, it could have been a hallmark article if the studies cited had been used to discount folklore rather than perpetuate it.