EVIDENCE INFORMED PRACTICE
Problems with ‘normal’ – the subtalar joint Studies have shown that the structural anatomy of the human subtalar joint varies from person to person, with some exhibiting two facet joints between the talus and calcaneus, and others having three (4). Furthermore, it has been shown that the spatial location of the subtalar joint axis can – and – does vary from person to person, and this will directly influence the magnitude of pronation and supination noted in a given person/ foot (5). In light of this sort of evidence it seems odd that there would be an expectation that all individuals could, or should, function similarly or identically. Additionally, a fairly recent study from China rather controversially concluded that the subtalar joint was not in its ‘neutral’ position when the foot was placed in the traditional concept of ‘neutral; instead finding that in 12 cadaveric specimens the most common approximate subtalar joint neutral position was when the foot was in 10° of abduction, 20° of dorsiflexion, and 10° of eversion (6).
Further problems with ‘normal’ Across many studies, all of the data collected from pain-free and injury- free subjects and athletes shows that very few individuals meet the historical definition of ‘normal’. One study that investigated the frontal plane relationship of the forefoot with the rearfoot in 234 healthy feet showed that less than 5% had a neutral relationship between the two (7). Another examined 120 healthy individuals both non-weight-bearing and weight-bearing, and not one subject conformed to the criteria of a ‘normal’ foot (3). Further searching through the literature shows that the majority of data collected from sampled populations suggests that the normal (average) foot position at rest is actually mildly to moderately pronated (8, 9). It has therefore been quite rightly concluded that the incidence of ‘normal’ foot alignment as historically described is in fact extremely small (10). Rather than continuing to apply a poorly founded model of foot type (whose basis is to make all feet meet criteria
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for the mechanical ‘ideal’ or ‘normal’ foot), we should embrace variation between feet, and identify it as an opportunity to develop patient-specific clinical models of foot function (11).
MEASURING PRONATION Considering the many different ways to quantify foot level pronation, there is no agreement on the best method for examining static subtalar joint pronation, as clinical measurement of foot position is inherently challenging due to the complex interactions of the pedal joints (12). What is clear is that, irrespective of the measurement method chosen, the reliability of such measurements (particularly the inter-rater reliability) is found to be poor to moderate at best (13). This has raised questions as to whether such measurements are of any value clinically (14). With respect to finding the subtalar joint neutral position, even experienced podiatrists are only within 3 degrees of subtalar joint neutral 90% of the time as shown by a Canadian study (15). Another issue to consider with static measurements of pronation is that there is some disagreement as to whether they are relevant to dynamic foot function, with growing evidence that there is little to no relationship between the two
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BOX 1: ‘NORMAL’ ALIGNMENT (WITH THE SUBTALAR JOINT IN ITS NEUTRAL POSITION) AS NOTED BY ROOT ET AL.
n Calcaneal bisection in line with the lower third of the leg n Calcaneal bisection perpendicular to the ground n Plane of the metatarsal heads should be perpendicular to calcaneal bisection
(16, 17). Indeed many podiatrists have ceased clinically quantifying these measurements for all of these reasons.
PRONATION AND ITS CORRELATION WITH INJURY
It is a commonly held belief that pronation will increase the risk of lower extremity injury. However (perhaps surprisingly) this is not particularly well supported by the literature, with very few studies actually showing that pronation increases injury risk. Instead, there are numerous pieces of work that have shown there is no association with foot type and injury (18, 19), with some research even suggesting that a pronated foot type is actually protective against injury (20). This is not to say that some individuals will not suffer pain or discomfort that may be associated with their foot motions or pronation patterns, but what
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