Foot Posture and Foot Orthoses -- The Lost Connection? Part I of II.

Dr. Ed Glaser, DPM

Dr. Glaser is the President and developer of Sole Supports orthotics.

INTRODUCTION

            Chiropractors rely on the study of human form and posture to determine deviations from normal and apply appropriate corrections to the underlying structure.  It is commonly accepted that departures from correct form, posture or structure, either through acute trauma or insidious degradation, affect function.  Muscles exert their pull and force more efficiently across joints and the human body is better able to counteract the effects of gravity and the ergonomics of our sedentary lifestyles, when the ideal postural balances are maintained.  This concept is illustrated by studies of the cervical spine which have demonstrated that changes in joint position and moment arms affects the moment generating capacities of muscles (1), and that posture has an effect of motion coupling(2).  There is a conservation of energy and an efficiency of function essential to the biomechanical workings of the human body. 

            When considering these concepts within the scope of current popular foot orthosis intervention strategies, the question arises as to why these concepts have not been applied to the foot to any significant degree.  Although clinicians may consider these concepts in their clinical evaluation, it seems that these ideas have lost traction when it comes to foot orthosis design and correctional model.  In many common models, emphasis is less on correcting foot posture that may have deteriorated and more about shifting tissue stresses and forces.  Although shifting tissue stresses may provide pain relief, it may be too narrowly focused and not provide the most complete preventative solution to the problem. 

 

DISCUSSION

            The Podiatric concept of basing a foot orthosis around the tenet of subtalar neutral has been called into question.  Investigations have demonstrated the lack of correlation of rear foot motion during gait to a valid measure of subtalar joint neutral position during weight bearing (3;4).  This underscores the fact that when considering orthotic intervention to affect dynamic function, the subtalar joint neutral position cannot be relied on to predict the corrected position.  In addition, the ability and degree to which a custom orthosis can even control rearfoot motion is debatable.  Davis et al showed that there are few differences between a custom and a semi-custom device in the ability to control the rearfoot (5) and that foot orthotic devices do not produce significant change in rearfoot-tibial coupling (6). 

            Measurements of the rearfoot to forefoot relationships in the static position have been the foundation for a clinical rationale.  Investigations into the assumptions behind these measurements have shown that the goniometric measurement of the forefoot to rearfoot relationship is unreliable regardless of clinical experience (7).  In addition, one study revealed that when comparing groups of doctors casting for foot orthotics  (inexperienced, experienced and “expert”) there is a 16.5 degree variation in the measurement of frontal plane forefoot to rearfoot angulation across the groups(8).  This relationship is the major determinant of arch height. When considering the degrees involved in the strategy of posting the rearfoot (i.e 4-10 degrees) this variability casts doubt on the practicality of rearfoot control with a posted orthosis.  Foot type analyses that involve primarily frontal plane static measures may have less to offer than more dynamic and robust analyses.  Clinical measures of static foot structure that have included subtalar range of motion and calcaneal eversion and inversion, have been shown to have poor interrater reliability(9) .  Moreover, these rearfoot measurements are poor predictors of dynamic rearfoot motion (10). 

            To review, if these static measurements are unreliable, and unrelated to the function of the patient’s foot in motion, then any skepticism on the part of the clinician regarding these types of foot posture measurements, is warranted.  However, abandoning the concept of foot posture altogether because the rearfoot measurements don’t correlate, does not help with the great incongruity that exists - we generally accept the concept of an ideal architecture to the rest of the human body, so why should this not apply to the foot?

SUMMARY

            In contrast to the clinical murkiness of the measurements discussed above, we do know that there are statistical differences in the biomechanical function between the planus and rectus foot. (11;11).  It is thought that changes in foot structure affect dynamic function (12) and foot morphology has been implicated in a variety of lower extremity overuse injuries (13;14).  A pronated foot posture is thought to be a factor in various pathologic conditions of the foot; for example the excessively pronated foot has been cited as a cause of limited dorsiflexion at the first metatarsophalangeal joint during gait (15;16).  Munteanu et al also postulated that people with pronated feet are more likely to exhibit limitation of dorsiflexion at the first MPJ during gait, and found that orthoses focusing on the forefoot to rearfoot relationship (Blake-style inverted) did not significantly change the range of motion (17). Could this be due to the focus of this type of intervention on subtalar rotation, rather than on restoring proper orientation or posture to the entire foot?

            Since the days of Merton Root, single axis position (subtalar “neutral position”) has been the goal of orthotic intervention.  It is clear the relationship of these measurements to the improvement of the human gait cycle is questionable. Part II of this article (January 2013, AJCC) will advance these topics presented herein.

Reference

10.  McPoil TG, Cornwall MW. The relationship between static lower extremity measurements and rearfoot motion during walking. J Orthop Sports Phys Ther 1996; 24(5):309-314.

11.  Song J, Hillstrom HJ, Secord D, Levitt J. Foot type biomechanics. comparison of planus and rectus foot types. J Am Podiatr Med Assoc 1996; 86(1):16-23.

12.  Cavanagh PR, Morag E, Boulton AJ, Young MJ, Deffner KT, Pammer SE. The relationship of static foot structure to dynamic foot function. J Biomech 1997; 30(3):243-250.

13.  Krivickas LS. Anatomical factors associated with overuse sports injuries. Sports Med 1997; 24(2):132-146.

14.  Yates B, White S. The incidence and risk factors in the development of medial tibial stress syndrome among naval recruits. Am J Sports Med 2004; 32(3):772-780.

15.  Roukis TS, Scherer PR, Anderson CF. Position of the first ray and motion of the first metatarsophalangeal joint. J Am Podiatr Med Assoc 1996; 86(11):538-546.

16.  Harradine PD, Bevan LS. The effect of rearfoot eversion on maximal hallux dorsiflexion. A preliminary study. J Am Podiatr Med Assoc 2000; 90(8):390-393.

17.  Munteanu SE, Bassed AD. Effect of foot posture and inverted foot orthoses on hallux dorsiflexion. J Am Podiatr Med Assoc 2006; 96(1):32-37.